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Senior Design 1 Final Project Documentation

1. Table 4 7 2 1 Battery specifications from some available lawnmowers In addition to running the blade motor the autonomous lawnmower design needs to supply power to the drive motor system As described in the drive subsystem section the DC brush motor powering the rear wheel drive have power requirement of 24 volts and approximately 50 amperes The project also has a number of sensors and a microprocessor which have power requirements of about 5 volts and current draw on the order of milliamperes Since the typical cordless electric mower uses about 40 minutes to cut the average lawn the drive subsystem and other subsystem also need to be powered for 40 to 50 minutes From this information it can be calculated that the battery capacity required for this project is approximately 26 ampere hours This capacity is in addition to the capacity required for the cutting motor To power the system one large battery could be used to power everything The project may also be powered using the factory supplied battery for the cutting mower and another battery for the rest of the system Since budget is an issue for this project it was advisable to go the multiple battery route using the factory supplied battery to power the blade motor An important decision to make when choosing a battery is the battery type From table 4 7 2 1 it can be seen that most batteries used for cordless electric lawnmowers in the market are lead acid Th
2. SUBMIT gt 130 RE Inquiry from Think RC inbox x A Support lt support thinkrc com gt 5 39 PM 21 hours ago A Y to me Hello Andrew It is okay that you use this image Please let us know if you have any further questions or concerns S Thank you Susannah i p 818 787 1188 www ThinkRC com Become a fan on facebook for special coupon codes news updates and free giveaways http www facebook com thinkre Original Message From Andrew Cochrum mailto drewman2000 amail_com Sent Tuesday April 23 2013 11 06 AM To Think RC Subject Inquiry from Think RC would like to request permission to use the image of a brushed vs brush less motor that you have in the FAQ section This image will be used in a design paper for a senior design project at the University of Central Florida Thank you Andrew Cochrum WinstTRUMENTS W Cart Help Search 2 Improve your ni com experience Login or Create a user profile Contact NI y indicates required information Customer Service Information First Name y Andrew National Instruments Corporation 11500 N Mopac Expwy Last Name Y Cochrum Austin TX 78759 3504 Tel 800 531 5066 E mail v andrewc knights uct edu Pacote GUFE Subject x Shaft encoder image permissions Message yY i would like to re quest permission to use the images that appear on the
3. ss ssssesessseseseeessseesseessersseessseeesseessrese 101 5 1 Design Summary Computational Subsystem s sesssesessseesseesseessesseressseesseso 101 5 2 Design Summary Navigation Subsystem essssssesssesssssersseessersseesseressseessees 103 5 3 Design Summary Obstacle Avoidance Subsystem ceceeeeeeeseeeeceeeeeeeneeeees 106 5 4 Design Summary Drive Subsystem e cc ceesceceescecesececeseeeceeeeecseeeecseeeeeeeeeees 108 5 5 Design Summary Power Subsystem c j 5 g2seesnchpedicdeeesb gel auwas 110 5 6 Printed Circuit Board PCB DGSieins foc5csicsaa en vecsuatacedvaceetisesesyestea eel aeweae 114 6 Project Prototype Construction and Coding eee eseeeseceseeeseeeeseeceaeceeeeeeeeeaeesaeen 115 6 1 Interfacing Subsystems with Mower Chassis cescesecsseeeerceceeeceneeeeeeeeaeeeaeens 115 G2 Docking Statio No ei ied aaa a A E A A EE A ER 115 T ProjectPrototype hE SUIS soo ah t argos oseae eaen a T R O eens 116 7 1 Maintaining Straight Path and Executing 180 Turn c cccccscssssssessesestesseeeseseene 116 7 2 Avoid Randomly Placed Obstacles eecceescecsseceessececseccecseececeeececseeeecsneeeenaeees 119 Administrative Content inr eet nde hee naan aus ta dia gate AS 121 8 1 Milestone DISCUSSION sinss ires Geegoetiseesiadaudecs ai oea ide beis eissa ETE eased bees 121 8 2 Budget and Finance Discussion esseseseseesesstseresresseseresressteeresreeseestesreesees
4. Lawn Mower Wireless Transceiver Laptop Left Whee Encoder AK SimpleCV Microcontroller Program USB HO Webcam Ullrasonic Distance Sensor Figure 4 4 1 A Navigation subsystem general topology Note dotted arrow signifies a wireless connection To summarize the Webcam established the perimeter of the lawn in addition to any obstacles to the best of its abilities and the data collected by the other sensors digital compass and ultrasonic distance sensor were used to further increase the resolution of the position calculations What follows is an in depth discussion of each individual sensor and its intended use within the overall navigation subsystem 4 4 2 Magnetic Compass CMPS03 by Devantech Limited 49 Two digital compass modules were cosidered both manufactured by Devantech Limited the CMPS03 and the CMPS10 Both offer Inter Integrated Circuit I2C and Pulse Width Modulated PWM output modes In order to avoid excessive tilt errors caused by measuring the z or vertical component of the Earth s magnetic field both modules must be kept horizontal to the plane of movement The CMPS10 seeks to rectify this by including a 3 axis accelerometer and 16 bit processor along with the 3 axis magnetometer This onboard accelerometer would sense any deviations from a completely horizontal orientation and using this information the processor would attempt to filter out the measured vertical com
5. Pa curved path curvature strongly exaggerated Desired straight line path Figure 2 3 1 C Geometric relations for finding the radius of curvature Reprinted with permission from Dr Johann Borenstein 3 3 1 2 Inertial Navigation Using an inertial measurement unit IMU for calculating the position of a mobile platform over an extended period of time is generally unsuitable In the case of accelerometers measurements are integrated twice to yield position causing any small error to increase without bound with the passage of time Thus during the automated lawnmower s hour or so of operation its position calculations would become increasingly inaccurate Also accelerometers in general are highly sensitive to changes in horizontal orientation Components of gravitational acceleration would be detected when the autonomous lawn mower traverses uneven terrain skewing the lateral acceleration measurement and in turn reducing the accuracy of the calculated position Therefore an IMU could only be used as a supplement to an existing navigation system if at all One such scenario would be to use the IMU s gyroscope component in conjunction with an odometry based navigation system In odometric systems any momentary orientation error would lead to a constantly growing lateral position error Thus the gyroscope would allow for the correction of these errors before any relevant calculations are performed decreasing the overall system s s
6. Using Quadrature Encoders with E Series DAQ Boards page The images will be used in a design paper for a senior design project at University of Central Florida _ 131 a e Untitled i https bl2prd0711 outlook com owa ae Item amp a New amp t IPM Note amp cc MT QuMTYuMzAlLjEsZW4tVVMsZGFOYWNibnRicixd Send H 0 GB amp amp B Options e To honasis gmail com Cc Subject IMU Gimbal Assembly Image Permission Tahoma glo 8 I y 15 B A I would like to request permission to use the image of an IMU Gimbal Assembly that you have at http www hg nasa gov alsj gimbals html This image will be used in a design paper for a senior design project at the University of Central Florida Thank you Andrew Cochrum Reply Reply All Forward Chat wr E amp amp amp X Wr e gt e Re Sabertooth 2x25 Image Permissions Dimension Support support dimensionendgi Monday April 22 2013 236 PM support dimensionengineering com andrewc andrewc knights ucf edu You can use the images within the Sabertooth 2X25 PDF for the purpose of your senior design project paper at the University of Florida Dimension Engineering Support 1 330 634 1430 www dimensionengineering com From andrewc Sent Monday April 22 2013 2 27 PM To support dimensionengineering com Subject Sabertooth 2x25 Image Permissions
7. 1 000 2 000 fascias te em wom aa aw Ham Moderate Low Low Cannot tolerate trickle charge tolerance Self discharge 20 5 30 5 lt 10 5 month room temp Cell voltage 2V 1 2V7 1 2V7 3 6V8 3 8V8 3 3V nominal 2 40 Full charge detection voltage V cell Float 2 25 by voltage signature Discharge cutoff aD 1 00 2 80 voltage V cell 1C Peak load current 5c 20C gt 3C gt 30C gt 30C Best result 0 2C 1C lt 1C lt 10C lt 10C Charge temperature 20 to 50 C 0 to 45 C 0 to 45 C 4 to 122 F 32 to 113 F 32 to 113 F Discharge 20 to 50 C 20 to 65 C 20 to 60 C temperature 4 to F 4 to 49 F 4 to 140 F Maintenance 3 6 months 30 60 days 60 90 days Not required requirement topping chg discharge discharge Safety requirements Thermally Thermally stable fuse Protection circuit mandatory stable protection common Figure 4 8 2 1 A Specifications of various batteries Reprinted with permission from BatteryUniversity com oO 218 oO CN g 9 Foa Q oO Charge cutoff 92 4 7 2 2 Voltage Regulator Circuit Voltage regulation for this design is pretty simplistic The electric design for the blade motor is already taken care of in using a factory designed lawnmower as a base By using a 24 volt battery in powering the drive system there needs to be no regulation of voltage for the motor controller and DC drive motors The only voltage regulation is needed to power the elect
8. aligning the robot for docking procedure and the second part is the actual physical design of the docking station For the docking procedure Silverman used a combination of robot vision and IR sensors to find and align with the docking station On their docking station an orange square was created and placed at the back center of the actual docking platform The robot was equipped with cameras that used a robot vision algorithm to detect the orange square Once detected the robot had detected the station and could approach it for docking procedures Figure 4 7 1 A Docking station using robot vision and IR Reprinted with permission from Silverman et al On the left side of the figure above shows their basic docking station with the orange square mounted on the wall behind the system Once within range the docking station is also equipped with an infrared LED which is detected by an infrared sensor on the robot Using the information from the robot vision in combination with the data from the IR sensor the robot is able to align itself to complete the docking process As small amounts of error can be expected in the docking process Silverman s physical design included a conic receptacle for the final docking This ensured that a good electrical connection could be made as the cone shape essentially funneled the robot into the appropriate final docking position Multiple views of the conic docking station can be seen below 85 Fi
9. label it n where n is an integer b Otherwise label it 0 2 Go to the next pixel a If itis also a blob color and is adjacent to blob 1 label it 1 b Otherwise label it n 1 3 Repeat until all pixels have been analyzed Figure 4 4 5 C compares the input and output image after running the blob detection algorithm The benefit of this algorithm is that it can identify multiple instances of an object and keep track of the number of occurrences of said object pertaining to the target blob color To further refine the accuracy of this algorithm it can be coupled with a shape detection pattern recognition algorithm For example suppose the number of plastic 63 cones within the webcam s field of vision is desired However unrelated objects that share the same color as the plastic cones are present within the image in question To eliminate these false positives from the analysis the following shape detection algorithm is implemented Palmisano 1 Run edge detection algorithm to find the border line of each shape 2 Count the number of continuous edges a A sharp change in line direction signifies a different line can be accomplished by determining the average vector between adjacent pixels b If three lines detected shape is a triangle c If four line detected shape is a square d If one line detected shape is a circle 3 Optional By measuring the angles between lines the type
10. the RN XV WiFly module wire antenna manufactured by Roving Networks was chosen This module supports a variety of communication protocols The Wi Fi connection between the laptop and the microcontroller would utilize serial communication which would be more than 66 sufficient for transmitting the absolute xy coordinates of the lawn mower but xy coordinate tracking became complicated for the system and resulted in the risk of inaccuracies This module uses very little current when active 38 mA when receiving and about 180 mA when transmitting data at 10dBm and would only consume about 4 uA when in sleep mode However since it is constantly communicating more specifically receiving data with the laptop at the base station it rarely enters a state in which the sleep mode can be activated XBee or XBee Pro ZIGTX ZIGRESET ZIGRX GND 5V 78L33 Figure 4 4 6 A Logic converter for interfacing a 5 VDC microcontroller with the 3 3 VDC Wi Fi module Reprinted with permission from KronosRobotics com The RN XV interfaces with hardware using TTL transistor transistor logic UART and a supply voltage of 3 3 VDC However the ATMega328 microcontroller was operating on a 5 VDC voltage supply and thus a logic converting circuit was necessary between the WiFly module and the microcontroller to prevent damage to the former Figure 4 4 6 A shows a schematic diagram for interfacing a microcontroller operating at a 5 VDC supply with an X
11. w counter sevenseg display w sloop 82232283 2 44 chk_encoder mov new encoder and new 0000001 1b mov temp new xor temp old jz return cic ri old xor old new jb old 1 up down dec counter skip up inc counter and mov old new return ret sevenseg jmp pc w retw Get latest state of input bits Strip off all but the encoder bits Is new old If so return without changing counter Clear carry in preparation for rotate left instruction Move old to the left to align old 0 with new 1 If the XOR resut is 1 increment counter otherwise decrement counter 00001111b display lookup table 126 48 109 121 51 91 95 112 127 115 119 31 78 61 79 71 Figure 4 3 4 3 A Assembly language code to interpret wheel encoder data 4 3 4 4 Connecting Ultrasonic PING The ultrasonic PING was used as a means to detect obstacles that are nearby the mower The sensor detects the obstacle and originally designed to deliver a chirping sound that would be returned back to the sensor Once the sensor receives the response the time taken to receive the signal would be used to determine the distance of the obstacle The following diagram illustrates how the sensor is interfaced to a microcontroller An I O pin is used to send and receive data and two pins are used to supply power The following pseudocode is an example of how the microcontroller can be programmed to
12. 3 3 Shaft Wheel Encoder cisco tien acti ceaesistees ede elk iiin n ni 18 3 3 4 Inertial Measurement Unit IMU cccccccccccccessessnseceeececeeeesenseaececeeeeseneens 19 3 3 5 Methods of DC Motor Control essesssseeseseeeseeresseseresressersresrersereresressreseeseessee 21 3 30 Voltage RE OUI ALO RSS a a a A E 23 3 3 6 1 Linear Voltage Regulators sssnssessseseseseesseesseesseesseessseessseesseesseesseessees 23 3 3 6 2 Switching Voltage Regulators 32 0 ean oie enue 24 4 Project Hardware and Software Design Details eee ceeeceeeeceecesececeeeeeceeeeeeneeeeenaeees 25 4 1 Overall System Block Dia start yi acicenaeeeeevee ideas oe lees eee dle eee ates 25 4 2 Electric Lawnmower Selection sesssseesssessesssesseressetesseesstsseesseeesseeesseesseesseesset 25 4 3 Computational Subsystem sesissy cssisasegsreceenncadsascsvedoadeonadeassnseuensoaceatibgesndeassaceanstoaoec 27 4 3 1 Microcontroller Selection esseeseseeseeseeereseesseesresrrestesstseresresstssrestessessessressesee 27 4 3 2 Interfacing with Other Subsystems sssesesssesesssessseesssessessseresseesssressresseessee 28 4 3 3 S0ttWare Implementation renaire a E wes EE R 30 4 3 3 1 Reference point calculation sesesseessessseesseeessstessessessseessseessseessresseessee 30 4 3 3 2 Thresholding for Locations ceisecscsssusescacdasensuatasecsadsasvnccane tedestatuavactesnseces 32 43 3 3 Obstacle Detecti n moscserii iesean a E a hee Eaa 33
13. 4 3 3 4 Thresholding and Computer Vision for Obstacle Detection 34 4 339 LN WoL SS LETS hig ties Dhawan E de was EEE 35 4 3 3 6 Motor Controller Output from Microcontroller cceeeeceeeeceeeeeeeeeeeees 37 4 3 4 Microcontroller Analysis and Implementation 0 0 0 0 ecceeececeseeeeeeeeeeeteeeeeaes 38 4 3 4 1 Creating Available Ports 2 0 0 0 ceeeccsssecssececssccecssccecssccecssccecsscceescesenseens 39 43 AD Connecting Compas Sisner n recat aas R Garten ees 42 4 3 4 3 Connecting Rotary Encoder iascscees sauce ted toeeacgeaseaesi seeded ge etnta ds cenkanmaeninse 43 4 3 4 4 Connecting Ultrasonic PING 0 0 eee eeescecesececseeeecseeeeceeeeecseeeeseeeeeeaeees 45 4 3 4 5 Connecting Antenna Wireless Card eeeeeecceseececseececeeececeeeeeesteeeenaeees 46 4 3 4 6 Connecting Motor Controller ceeceeescecseceeceeeeeceeneecseeeecseeeeenneeeenaeees 47 4 3 3 FLOW Os he 6 Reem pe ere oe Dae eR yee Ore Morr treet MeaML T nore ener 47 4 4 Navigation SUSY SUCH 25 cct iat oc ceaseaavedeces se ccancecuretsct anseaceaameaegas Gaacaneneaseashee eater Reoeiees 47 AAEM OW CLV NCW di Lat A Rie asic Beale cl TD OT Sn ake ee aati Bil ae n 47 4 4 2 Magntetic Compass CMPS03 by Devantech Limited 00 ee eeeeeeeeeeeeees 49 4 4 3 Rotary Encoders 1024 Pulse Revolution Quadrature Rotary Encoder Model Number A6BZ CWZ3E 1024 by YUMO 1 eeeeccesecsteeneeeeeeseeeseenaeeneeens 54 4 4 4 Ultrasonic Distance Sensor PING
14. Borenstein J H R Everett L Feng and D Wehe Mobile Robot Positioning Sensors and Techniques 1997 n pag Web Borenstein J and Feng L 1996 Measurement and Correction of Systematic Odometry Errors in Mobile Robots IEEE Journal of Robotics and Automation Vol 12 No 5 October Bumper Switch VEX Wiki RSS N p 4 May 2012 Web lt http www vexforum com wiki index php Bumper_Switch gt CAP 4453 Robot Vision Spring 2013 Home Page EECS Dvision of Computer Science N p n d Web 23 Apr 2013 Cassinis Riccardo Docking and Charging System for Autonomous Mobile Robots University of Brescia n d Web CMPS10 Tilt Compensated Compass Module Robot Electronics N p n d Web 22 Apr 2013 lt http www robot electronics co uk htm cmps 10doc htm gt CMPS03 Compass Module Robot Electronics N p n d Web 22 Apr 2013 lt http www robot electronics co uk htm cmps3tech htm gt 125 Computer Science and Engineering University of Washington N p n d Web lt http www cs washington edu education courses cse466 10au pdfs lectures 04 interfacing pdf gt Cortex Microcontroller VEX Robotics Cortex Microcontroller VEX Robotics N p n d Web 23 Apr 2013 lt http www vexrobotics com 276 2194 htmI gt CSM 12C32 Development Module for Freescale MC9S12C32 N p n d Web lt http www0 egr uh edu courses ece ece4437 support laboratory CSM12C32 CS M12C32_UG pdf gt DC
15. Ideapad Z560 laptop Lenovo 1 597 00 0 00 used DC brush motor with X 2 181 64 0 00 donated gearbox and wheel ATmega328 with Atmel 4 29 99 119 96 development board for testing PING Ultrasonic Parallax Inc 1 29 99 29 99 Distance Sensor Sabertooth 2x25 V2 Sabertooth 1 124 99 124 99 motor controller HMC5883L Triple Sparkfun 1 14 95 14 95 Axis Magnetometer Lifecam HD 5000 Microsoft 1 34 99 34 99 Webcam and USB extension 12V Sealed Lead Acid Batteries com 2 59 99 119 98 Battery 33 35 Ah LM2825 5 0 fixed Texas 1 Free sample 0 00 output switching Instruments regulator LM2825 3 3 fixed Texas 1 Free sample 0 00 output switching Instruments regulator Breakout board for Sparkfun 1 2 95 2 95 XBee module RN XV WiFly Module Roving Networks 1 34 95 34 95 Wiring Antenna PCB 2 Layer Full Spec Advanced 1 77 00 77 00 Circuits Various PCB x x 60 00 60 00 components DIR 655 Wireless D Link 1 94 99 0 00 donated N Router 25 A Solid State Relay Shenlan 1 25 00 25 00 Drive subsystem Home Depot X 30 00 30 00 fabrication supplies Webcam telescopic Home Depot X 100 00 100 00 platform building supplies Estimated Total 924 76 Table 8 2 Parts list with prices for budget Since this project is not sponsored the cost was of great concern All financing was provided by the project team members with no outside help Any cost cutting measures that present themselves was taken to keep down
16. In other words the microcontroller would seek to 59 increase this measured distance by continually rotating the autonomous lawn mower platform allowing it to safely pass the object 4 4 5 HD Webcam LifeCam HD 500 by Microsoft Several options were evaluated for computing the absolute position of the autonomous lawn mower Initially ultrasonic beacons were to be placed along the perimeter of the lawn and trilateration would be used to determine the xy coordinates of the lawn mower within the confines of the area enclosed by the beacons Unfortunately the accuracy of this system quickly deteriorated as the lawn mower approached the boundaries of the lawn a problem that could be rectified by the addition of more beacons However since these beacons would each require a seperate custom PCB printed circuit board a ultrasonic transmitter and an independant power system the cost of developement was quickly driven to an unacceptable price especially since this project is not sponsored and thus was funded completely by its members Also the time required to troubleshoot and successfully implement such a system would consume much of the fabrication and testing period leaving little time to employ the other features The second method involved using a GPS based system However the accuracy was not sufficient for this application The commercially available differential GPS products that could have supplied a satisfactory degree of resolution
17. Motor Interfacing with Microcontrollers Tutorial L293D H Bridge Interfacing with Microcontroller Rickey s World of Microcontrollers amp Microprocessors DC Motor Interfacing with Microcontrollers Tutorial L293D H Bridge Interfacing with Microcontroller Rickey s World of Microcontrollers amp Microprocessors N p n d Web 23 Apr 2013 lt http www 805 1projects net dc motor interfacing 1293d interfacing with microcontroller php gt Devantech SRF04 Ultra Sonic Ranger Finder N p Cornerstone Electronics Technology and Robotics II n d PDF Dixon Jonathan and Oliver Henlich Mobile Robot Navigation N p 10 Jun 1997 Web 22 Apr 2013 Embedded Lab N p nd Web 23 Apr 2013 lt http embedded lab com blog page_id 7124 gt Encoders Automation Direct N p Web 22 Apr 2013 lt http www automationdirect com static specs encoderfaq pdf gt Gerkey B Vaughan R and Howard A 2003 The player stage project Tools for multi robot and distributed sensor systems Proceedings of the International Conference on Advanced Robotics pages 317 323 Guthrie Andrea Daniel Bender Anthony Thomas Paul Lozovyy Masato Hayashi Jason Goode and George Thomas Robotic Lawnmower Design N p n p n d PDF Hereford J M Siebold M and Nichols S 2007 Using the particle swarm optimization algorithm for robotic search applications Proceedings of the 2007 IEEE Swarm Intelligence Symposium SIS 2007 pag
18. Phase Ais 1 4 T 1 8 T faster Note Phase Ais 1 4 T 1 8 T slower than phase B than phase B Figure 4 4 3 A Output timing diagram from the A6B2 CWZ3E 1024 encoder datasheet Reprinted with permission from Yueqing Ying s Import amp Export Co Ltd The output channels A and B would be viewed by the microcontroller as a two bit Gray code ensuring accurate readings even at high rotational speeds An incremental encoder would lose its position data when power is removed from the circuit which is a likely 55 scenario for a battery powered system A reference point must be established to resume encoder measurements once power is restored to the autonomous lawn mower The third output channel Z zero index in Figure 4 4 3 A would be used as this reference point This signal only goes high once for each complete revolution of the encoder The microcontroller can therefore keep track of how many revolutions of the wheel have occured and from this data extrapolate the distance travelled by the autonomous lawn mower This would also serve as a reference starting point after the aforementioned power failure scenario The addition of this zero index would also serve as a reset condition in which after a pre defined number of revolutions has occured the distance travelled as computed by the microcontroller from the encoder output speeds would be cleared to avoid the accumulation of errors due to the integration required Therefore th
19. S1 control motor 1 and any signals received on S2 control motor 2 This method is one of the preferred methods due to the ease in which a pulse can be generated by the microcontroller Since the microcontroller would be getting a constant feed from the navigation system it can correct the automated lawn mower s direction and speed on the fly by shortening or lengthening the pulses Below is an example of the command flow while the vehicle is in operation Current Heading Information Read In Desired Heading Calculated from Stored Data Course Course Correct Right Correct Left 1 Shorten Pulse i Lengthen Pulse 2 Lengthen Pulse 2 Shorten Pulse Figure 4 6 3 2 A Example heading correction flow chart when using pulses to control motor controller The fourth method for controlling the motor controller is through simplified serial commands Serial data is sent to input S1 sending a value of 1 127 would command motor 1 Sending a value of 128 255 would command motor 2 Sending a value of 0 would shut down both motors This is the preferred method for control due to its simplicity and accuracy The last method for controlling the motor controller is through packetized serial commands Packetized serial uses TTL level serial commands to set motor speed and direction Unfortunately packetized serial is only a single direction interface and therefore cannot provide feedback to the microcontroller The transmit line from the
20. The error would be railed to a pre determined range i e floor and ceiling values would be set any calculated results below or above these values respectively would be limited to these minima maxima to avoid driving the motor controller actuators to saturation conserving power and preventing any possible damage that might occur to the motors themselves The optimal values for the floor ceiling and gain parameters were determined through trial and error once it is implemented in the field This implementation allowed the autonomous lawn mower to maintain its orientation along a specified heading for the most part however lateral drift may occur over time The other sensors within the navigation subsystem compensated for this deviation or else a more robust control system would have to be devised and implemented 53 M PE Desired Heading Min Max Gain K Plant includes motor controller and icrocontroller Correction ain K compass module Current Heading Figure 4 4 2 C Proportional gain controller for following a digital compass heading 4 4 3 Rotary Encoders 1024 Pulse Revolution Quadrature Rotary Encoder Model Number A6BZ CWZ3E 1024 by YUMO The selection of rotary encoders proved the most difficult in terms of weighing the potential advantages disadvantages of a potential product solely based on the component specifications provided by the manufacturer and before implementing them within the complete lawn mower s
21. The number of rotations would be used to determine relative distance In one example digital input signals can be used by the 43 rotary encoder to allow the microcontroller to determine the speed and direction of a shaft s rotation This particular rotary uses a particular method for determining the direction of the shaft whether it is clockwise or counterclockwise When the encoder shaft is turning clockwise the signal returns a particular sequence of binary numbers than when it is turning counterclockwise If phase 1 is high and phase 2 is rising the direction is clockwise If phase 1 is low and phase 2 is rising the direction is counterclockwise In general the rotaries generally uses light sensors that detects the amount of light blocked and the offset determined Voltage signals are needed as well as input pins The following assembly language code illustrates how the microcontroller can accept an input from the rotary encoder as illustrated by pins RAO and RAI in the above image and determines the direction and uses a counter according to the above direction images device pic16c54 rc_osc wdt_off protect_off reset start encoder ra display rb Variable storage above special purpose registers org 8 temp ds 1 counter ds 1 old ds 1 new ds 1 Set starting point in program ROM to zero 0 start Irb 0 Set rb to output Ira 255 Set ra to input counter old encoder old 0000001 1b chk_encoder
22. Ultrasonic Distance Sensor by Parallax DG E sted leche t eet Se Gia Sed Sie MS sei als Satta ots atc a cada 57 4 4 5 HD Webcam Lifecam HD 500 by Microsoft cceeecceeeeceeeeeeeeceeeeeesteeeesaes 60 4 4 6 Wireless Communication RN XV WiFly Module Wire Antenna by Roving IM CE WOLD eases Sajak a eaten Jat a ial and Ohi et A ace lde teeter lee ates 66 4 5 Obstacle Avoidance Subs yStemi ix sccscsiss seascesvacdsel ecncaces sucess ofeaccaatacasteesheeestat peanceaians 67 4 5 1 Distance Proximity SemSOr 3i2c sieass0 sedasasagsacssevsdenca stead ea cegedaesongeedeecnedaatanastass 68 4 5 2 Collision SOUS OF 35 seeds essen ccesesoceyecaneky ha E EEE EEI Sao EEE E SEEE ASE EE 69 4 5 2 1 Collision Sensor Selection y 2 03 oii tet dha ance 69 4 5 2 2 Mechanical Design Bumper System eeceeeececesceeceeececeeeeeeeneeeesaeees 70 4 5 5 PLECIPILALOM SENSO sisena ea E E aaed ona eae aco teenies 71 4 5 4 Software Implementation 3 545 405 cashesa ce aise isan cs ah eg ena nce fp aes vasncees Sorvino ees 72 4 5 4 1 Overall Program Flow CUArtsictcccses doses ganas iaealedahes iecsanasseereecebinehocdageosbesean 72 4 5 4 2 Calculating Obstacle Avoidance Route eceeeceeeesneeeseececeeeeeeeteeeenaeees 73 4 6 Driv Subsystem isesi Aa sde s cenG cae e e a E a E a E 76 4 6 1 Motor Controller Selection sessssseeseseseseessessseseresressrserssresstseresressessresressesee 76 4 6 2 Right Left DC Wheel Motors sssssseesss
23. a precipitation sensor to avoid being in use while it is raining The reasoning for this function is three fold First it is advisable to avoid having the mower outside in inclement weather as to avoid damaging any of the electronic equipment mounted on the lawnmower Second mowing grass that is wet is not optimal for the health of the lawn Mowing wet grass should be avoided as it can spread lawn disease and also result in a bad cut due to the wet grass clogging the lawnmower LawnCare net Finally the accuracy of the project may be compromised under wet conditions If the mower wheels slip this could decrease the accuracy of the wheel encoding resulting in inaccurate measurements of the device s position Repeated slipping in the rain would just increase the error over time resulting in larger inaccuracies To combat these issues the project would contain a rain sensor that can alert the device when it is operating in inclement weather conditions so that the device may return to its docking station and avoid the described problems Most current designs for rain sensors are built for irrigation or sprinkler systems The majority of these devices are custom designed to only work with specific irrigation systems In addition to these devices there have also been advances in rain sensors for automated wiper systems for vehicles Rain sensors typically work by collecting small amounts of rain which when it hits a certain level closes a contact there
24. and easy to implement on a printed circuit board Linear regulators are available for positive and negative output voltages They are available in fixed voltages such as the 78xx series of linear regulators or adjustable voltages like that provided from the LM317 Readily available linear regulators provide output voltages on the range from 1 to 40 volts with current from the load at less than 1 to 1 5 amperes The input voltage requirements for linear voltage regulators have minimum and maximum limitations The minimum voltage requirement is determined by the dropout voltage as determined from the datasheet of the linear regulator This dropout voltage is typical 2 3 volts so for a 5 volt regulator a minimum input voltage of 7 8 volts would be required The maximum input voltage is dependent on the part selected and typically goes to about 40 volts Linear voltage regulators were sufficient for this project The required voltage is well within the range of a readily available linear regulator The current requirements for the microprocessor and sensors are of the magnitude of milliamperes which is also easily met through the use of a linear regulator The dropout voltage requirement was also met as the battery provided input voltages of much higher a level than the desired regulator output For this project linear regulators met the minimum requirements and could therefore be used for all voltage regulation needs The benefit of using a linear voltag
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26. as an output and driving the pin low high then low again to generate the required 5 us input trigger pulse tour Figure 4 4 4 A to wake up the distance sensor The pin is then configured as a digital input in preparation to receive the return echo pulse tm The pin is then passed to the pulseIn function included in the standard Arduino library which outputs the duration of the pulse on the pin passed as an argument and returns the duration in micro seconds of said pulse as a floating point number This number is then converted to the distance of the object in inches using the aforementioned method To demonstrate functionality this distance value was then transmitted via serial connection to the computer where it was printed to the console Also pins 8 9 and 10 of the microcontroller were connected to a red LED light emitting diode a green LED and a simple piezoelectric buzzer respectively 58 PinMode pingPin OUTPUT digitalWrite pingPin LOW delayMicroseconds 2 digitalWrite pingPin HIGH delayMicroseconds 5 digitalWrite pingPin LOW PinMode pingPin INPUT duration pulseIn pingPin HIGH inches duration 0 01356 2 Figure 4 4 4 B Part of the code used to test the PING ultrasonic distance sensor This code snippet controls the direction of the pin 7 on the microcontroller used to interface with the distance sensor The program would turn on the green LED when the distance of
27. com Bumper Switch Image Permission Lindsey Carlin lindsey_carlin innovationfirst com Monday April 22 2013 1 15 PM Jason You have our permission to use the requested image in your design paper Thank you for checking Regards Lindsey Lindsey Carlin Director of Corporate Communications Innovation First International lindsey _carlin innovationfirstcom 903 453 0858 office 512 663 6844 cell Joppel April 21 20 To news vexrobotics com I would like to request permission to use an image of the bumper switch application that appears on your website A A A adio at http www vexforum com wiki index php Bumper_Switch If permission is granted this image will be used in a design paper for a senior design project at University of Central Florida If you could respond to this request it would be greatly appreciated Thank you Jason Oppel Student UCF 136 Robot Docking Station Image Permission MAILER DAEMON MAILER DAEMON gt Monday April 22 2013 3 36 PM Delivery is delayed to these recipients or groups gaurav robotics usc edu milo robotics usc edu dnies robotics usc edu Subject Robot Docking Station Image Permission This message hasn t been delivered yet Delivery will continue to be attempted gt joppel Mon 11 17 AM gt MAILER DAE Delivery is delayed to these recipients or groups milo robotics usc edu Subject Robot Docking Station Image Permission This me
28. curved path taken by the mower due to the left and right wheels having unequal diameters Using simple geometric relations the radius of 118 curvature R is calculated and along with the wheelbase b the unequal wheel diameter error of the mobile robot Ez is found These two correction constants C and Cp are then used in the well established odometry algorithm for differential drive mobile platforms AU L Ri CLIR CmN1 R i Where AU z is the incremental distance traveled for the left and right wheels Cm is the conversion factor that translates encoder pulses into linear wheel displacement and Nz is the encoder pulse increment for the left and right wheels The UMBmark provides an excellent tool for analyzing and comparing the performance of the navigation system across a spectrum of different hardware arrangements involving encoders Since the drive subsystem of the autonomous lawn mower would consist of pre fabricated components connected together in a manner that may not be optimal due to budget restrictions time constraints component level operational restrictions etc an accumulation of errors may render the encoder based navigation system ineffective For example the intended wheel diameter as defined in software may not accurately represent the effective wheel diameter which may become affected by modifications to the acquired mower chassis to accommodate the drive system Using this benchmark these physical imperfe
29. detect an obstacle using this sensor 45 Make the I O pin an Output Bring LOW the pin that the PING rangefinder is connected Bring the pin HIGH for 5 microseconds Bring the pin LOW Make the I O pin an Input Wait until the pin goes HIGH Use a timer to see how much longer it takes for the pin to become LOW The time it took to become low is now our raw distance in microseconds Divide Raw Distance by two since it includes the time for a return trip of the sonar Raw distance 2257 is our distance in cm Raw distance 889 is our distance in inches Figure 4 3 4 4 A Pseudocode for obstacle detection The above pseudocode is used to detect the distance of an obstacle According to the code the pin is waited to become low and high The amount of time it takes to receive the pulse of sound would be multiplied by the speed of sound to determine the raw distance The distance would be divided by two to compensate for roundtrip and that value would be returned to the microcontroller input The microcontroller would compare that value to a certain threshold value to determine whether the mower is close enough and is ready to be maneuvered accordingly 4 3 4 5 Connecting Antenna wireless card Antennas were initially considered for our original design for absolute positioning and camera processing The camera would be connected to a laptop which would need to wirelessly send information to the microcontroller The first step is to interfa
30. drawback in which the end user must carefully place the beacons in the initial setup of the perimeter To compute the area of the triangle enclosed by the beacons at points 1 and 2 and ultimately the current location of the mower Figure 3 3 2 A Heron s formula is used Area S x Sp S X Sp d1 X Sp d2 S d1 d2 2 S distance between beacons Where Sp semi perimeter 15 dl distance between mower and beacon 1 d2 distance between mower and beacon 2 From the area of the triangle its height h can be calculated h 2 x Area S Referring to Figure 3 3 2 A it can be seen that if the two beacons are placed on the line passing through x 0 the height of the triangle would become the horizontal position x coordinate of the mower The vertical position y coordinate of the mower can be calculated using the Pythagorean Theorem and the values d and h y yd h As noted in the application report the value of the x coordinate can either take on a positive or negative value without the utilization of a third beacon This can be rectified by setting the fixed points at the outer edge of the enclosed area in which the mower s location is sought Another drawback of utilizing only two beacons to determine the mower s position is that the error increases as the distance from the mower to the line S Figure 3 3 2 A note that this distance is represented by h decreases According to the r
31. driving the blade and the two wheels in the propolsion subsystem to avoid any magnetic fields generated by the motors This elevation distance would be fine tuned upon fabrication and testing in the field Before use in the overall system the CMPS10 compass module must be calibrated with the proper inclination associated with Orlando FL The onboard EEPROM Electrically Erasable Programmable Read Only Memory is pre loaded with the inclination associated with Norfolk England the location of the Devantech Limited manufacturing plant The procedure is outlined in its entirety in the technical documentation The factory settings can be restored in case the user calibration causes errors 50 o o o o o o o o CMPS03 Arduino Figure 4 4 2 A CMPS03 Compass Module interfaced with an Arduino Uno development board utilizing the I2C bus Note green wire is SCL line and blue wire is SDA line Reprinted with permission from Devantech Limited An Arduino Uno development board equipped with an ATmega328 microcontroller was used to test the functionality of the CMPS03 compass module The compass module was interfaced with the microcontroller using the I2C bus at a baud rate of 9600 bits per second see Figure 4 4 2 A above Pins 2 and 3 of the CMPSO3 are the SCL clock and SDA data lines respectively They are connected to the analog pins A4 and A5 which correspond to the SCL and SDA lines on the microcontroller respectively Since bo
32. integrating a small voltage between SRP and SRN where SRN is nearest to the PACK connection P6 TS 11 Pack thermistor voltage sense use 103AT type thermistor P5 HDQ 12 Open drain HDQ Serial communication line slave P4ISCL 13 Slave I7C serial communication clock input Use with a 10 K pull up resistor typical Also used for LED 4 in the four LED mode P3 SDA 14 Open drain slave I C serial communication data line Use with a 10 kO pull up resistor typical Also used for LED 3 in the four LED mode 1 1 Input O Output P Power I O Digital input output Figure 4 7 2 3 A Pin out descriptions for bq34z110 Reprinted with permission from Texas Instruments From the bq34z110 datasheet a typical implementation for the part is shown in the figure below This part would form the backbone of the battery charge monitoring system The data collected and measured from this device would enable the monitoring of the battery while in use as well as while it is recharging PACK O Figure 4 8 2 3 B Circuit diagram showing the battery charge monitor Reprinted with permission from Texas Instruments 95 4 7 3 Software Implementation Most of the power subsystem for this project lies in the choice and design of the battery and voltage regulation which require no software design There is software design necessary for the docking and recharging of the lawnmower Using robot vision procedures the lawnmower would be abl
33. of shape can be determined e g rhomboid equilateral triangle etc The two dimensional projection of a cone is a triangle thus by including this additional shape requirement to the color parameter any extraneous objects that are not the plastic cones can be filtered out from the final calculation The edge detection algorithm mentioned in step one of the above procedure is relatively simple to implement Again each pixel of the image is gone through For each pixel the surrounding eight pixels are analyzed From this set the values of the darkest and lightest pixels are recorded The difference between the darkest and lightest pixel is compared to the threshold value This threshold value is usually computed be running a heuristics program on the image in question Essentially a heuristics program generates a histogram of the pixel intensities within an image and the average of this distribution is often used as the threshold If the aforementioned difference between the darkest and lightest pixel values is greater than this threshold the pixel is rewritten as 1 otherwise it is rewritten as 0 Figure 4 4 5 D shows the result of running an edge detection algorithm and illustrates the importance of selecting an appropriate threshold value 64 Figure 4 4 5 D Results from running an edge detection algorithm Starting from top left going clockwise original image good threshold value threshold value too low and threshold
34. on the docking frame Once either or both of the markers have been located the docking procedure moves onto the next step 96 of aligning with the docking station A flow chart of the docking procedure is shown in the figure below Figure 4 7 3 2 A Flow chart for docking procedure The alignment process is the most complex and most important part of the docking procedure Without accurate alignment the lawnmower would not enter the docking station properly This could cause the electrical contacts with the charging station to not be made causing the lawnmower to never be able to charge suitably or even not at all To ensure proper alignment the lawnmower uses a pair of markers located on the docking station Two markers at different location are required so that an appropriate position can be determined The markers are placed in a manner that is shown in the figure below H Front View Side View Figure 4 7 3 2 B Alignment markers on docking station As seen in the figure the markers are aligned in a directly vertical position only when viewed from the front Note that from the rear of the docking station that only the top 97 marker is visible Given that the markers are located in the center of the docking station once the vertical alignment is made the lawnmower can pull directly into the charging area If the markers are not aligned correctly a signal is sent to the drive subsystem to move to a new location where the
35. rotary encoders measure the relative movement of the shaft This type of shaft encoder uses only two optical or mechanical sensors to detect shaft rotation from one angle to the next To keep track of the shaft s current position external circuitry can be used to count the movements of the shaft from a particular reference point In mechanical encoders cams on the shaft make rotate to make contact with mechanical sensors that are then used to determine the shaft s position 18 Optical encoders can determine movement by reading two light and dark coded tracks using photodiodes Channel B Code Track on Disk Channel A Channel B 90 Figure 3 3 3 B Example of a quadrature encoder output Reprinted with permission from ni com Above is an example of an incremental encoder that uses two output channels to determine the position of the shaft Channel s A and B are coded on the disc to be 90 degrees out of phase and alter between light and dark The two output channels can then indicate the position and the direction of rotation If the sensor detects that A is leading B by 90 degrees then the shaft is rotating clockwise If the sensor detects that B is leading A by 90 degrees then the shaft is rotating counter clockwise The position of the shaft can then be derived by the constant monitoring of the number of pulses and the relative phase between A and B An optical shaft encoder can usually be used at high speeds and still be a
36. software calculates that the alignment would be correct Upon arriving at that position the marker alignment is evaluated again This evaluation and correction is repeated until proper alignment is established For software purposes the alignment is broken down into several functions The first function is called locatemarkers This function finds the markers and notes their two dimensional vertical and horizontal positions These positions are stored in variables and continuously updated as the lawnmower moves during the docking procedure Once the locations are know that information is sent to another procedure called checkalign to determine is the vehicle is in proper alignment This is simply done by checking the horizontal values of each marker position to see if they are equal If they are equal then the lawnmower is aligned This procedure has a simple output of if the lawnmower is aligned and 0 otherwise It should be noted that the docking procedure has the lawnmower backing into the docking station This means that the cameras for detecting the lawnmower are mounted on the rear of the lawnmower assembly The reason for the rear position of this procedure is twofold The charging plates for the lawnmower batteries are mounted to the rear of the lawnmower chassis It also needs to avoid the front of the vehicle to avoid contact with the collision sensor or falsely flagging the ultrasonic obstacle sensors All movements of the lawnmowe
37. starting area measure the absolute position and optionally orientation of the vehicle 4 Compare the absolute position to the robot s calculated position based on odometry and using the following equations a Ey Xabs Xca c where position error is equal to the absolute position of the robot Xaps minus the position of the robot computed from odometry X qic b y Yaps Ycaic Same conventions apply for the y component of position c Oqns Ocaic where orientation error g is equal to the absolute orientation of the robot Oaps minus the orientation of the robot computed from odometry O qic 5 Repeat steps 1 4 for four more times total of five runs 6 Repeat steps 1 5 in the counter clockwise direction The results of the procedure are represented as the measure of the odometric accuracy for systematic errors Emax syst Which is calculated from the following equations Emax syst Maxey Tee To g cw 7 c g cw Oe g cw To g cew c g ccow Weg cew n 1 Xc g cw ccw y EXi CW CCW i 1 n 1 Yc g cw ccw y EYicw ccw i 1 Where Thus Xeg cw ccw and Yeg cw ccw are the horizontal and vertical components respectively for the average of the errors computed for both the clockwise and counter clockwise iterations of the benchmark over a period of n trials Refer to Figure 7 1 A for a graphical representation of the above equations and Figure 7 1 B for a
38. system utilizing odometry it is clear that these aforementioned errors must be as well defined as possible allowing for corrective techniques to be employed within the system The University of Michigan Benchmark UMBmark provides a quantitative measurement of systematic odometry errors and to a limited degree non systematic errors The benchmark yields a single numeric value that represents the odometric accuracy of the system in question Emax syst With respect to systematic errors The inclusion of the two produced error constants wheel diameter error Eg and wheelbase error E in software has yielded a 10 to 20 fold reduction in systematic errors when applied to several differential drive platforms according to the authors of the benchmark What follows is an overview of the testing procedure established by the UMBmark 1 At the beginning of the run measure the absolute position and optionally orientation of the vehicle and initialize the onboard odometric starting position to that position 2 Run the vehicle through a 4x4 meter square path in the clockwise direction making sure to a Stop after each 4 meter straight leg b Make a total of four 90 degree turns on the spot c Run the vehicle slowly to avoid slippage 3 Upon return to the starting area measure the absolute position and optionally orientation of the vehicle 4 Compare the absolute position to the robot s calculated position based on odometry and
39. that were threaded through the telescopic structure denoted by the circles on the tube body in Figure 4 4 5 A This provides the required elevation for the webcam while maintaining portability since it can be collapsed to a manageable length Figure 4 4 5 B Computer vision system CAD software Google SketchUp Black box represents the lawn mower roughly to scale Beige cylinders along the perimeter of the lawn represent landmarks e g small brightly colored plastic cones or some other visually unique structure The webcam support structure was then placed at a suitable distance from the perimeter of the area to be traversed by the lawn mower At the top of the support beam the camera was mounted with a downward inclination e g the camera would be pointing below the horizontal plane intersecting the top of the support beam This ensured that the landmark structures closest to the support beam are included within the webcam s field of vision The type of landmarks utilized is irrelevant what is important is that the object be easily discernible from the background of the image the reasons for which will be discussed later which for this application was the grass lawn Figure 4 4 5 B illustrates the general setup necessary in order to use camera vision for static obstacle and boundary detection 62 and for establishing a Cartesian coordinate system that would be used for the absolute position measurements in the navigation subsy
40. the mobile platform Thus other techniques must be implemented to assist in filtering out the errors introduced into the system during normal operation The simple linear equations utilized by the odometer hold true if and only if the wheel revolutions measured by the encoder directly translate to the actual linear displacement experienced by the mobile platform Non systematic errors would result from unintended interactions between the surface the robot is traversing and the wheel In the case of the autonomous lawn mower non systematic errors would be introduced into the system due to wheel slippages on a wet lawn Thus the equations no longer represent the actual distance travelled since the encoder may not have the means to filter out these errors Systematic errors also must be considered and attenuated which result from an inaccurate representation of the system in software i e physical imperfections of the robot unequal wheel diameters uncertainty about exact wheelbase etc These types of errors can be minimized using odometry and a landmark navigation system in conjunction with one another this is but one of many possible solutions The number density of the landmarks placed in the area of operation is determined empirically using the worst case systematic error magnitude as a reference However inaccurate measurements can still occur if the non systematic errors are left uncompensated To successfully implement a navigation
41. to determine whether an area to the right or left has already been mowed and if the area to the right or left is an obstacle If absx 10 alreadymowed true amp amp absy 10 alreadymowed true If absx 5 edge false amp amp abs 5 edge false Signal 01 signal to turn left since right area is already mowed and the area to the left both vertically and horizontally are safe Else The above code is a sample of the kind of implementation that can be used in the microcontroller to send signals to the motor controller With testing and design the code was more conditional to allow movement in various directions depending on whether there is an obstacle along the path or to the left or right Signal 00 stops the mower 4 3 4 Microcontroller Analysis and Implementation The microcontroller being used had various pins and ports that were used for inputs and outputs In this design various components were needed to be connected and programmed as inputs or outputs in an appropriate way to operate properly Components 38 such as the wheel encoder and the compass would have served as inputs The motor controller was most an output but could also be an input The wireless card that was originally considered would transfer data to and from the microcontroller so would need to be both input and output 4 3 4 1 Creating Available Ports For this design there was need for many input output ports However there
42. to determine the battery s state of charge Texas Instruments has developed a battery monitor that can determine the battery capacity at any given moment to within 95 accuracy The bq34z110 supports many lead acid battery configurations from 4 to 64 volts This part has a number of output interfacing capabilities to allow for monitoring of the battery in a variety of ways This part was capable of handling all of the projects battery monitoring needs Voltage regulation was required to provide a 3 3 to 5 volt input power from the 24 volt batteries Due to the large difference in input and output voltages a switching regulator was advisable for the voltage regulation needs for the project A buck converter that can handle 24 volt input and provide about 1 amp output was required for this project s voltage regulation needs The LM22670 buck converter could handle an input voltage range from 4 5 to 42 volts It can provide an adjustable output voltage as low as 1 285 volts and an output load current of up to 3 amperes This information shows that this part meets the voltage regulation needs for this project In addition to providing an adjustable output voltage Texas Instruments provides a LM22670 that gives a fixed 5 volt output voltage For the 5 volt regulation needs of this project this fixed output LM22670 5 0 was used Using the fixed voltage part simplifies the overall design of the voltage regulator circuit and lowers the part requirement on t
43. to the device The slow charge time of lead acid batteries is not a hindrance to the function of this project Assuming the battery allows the lawnmower to fully cut the entire lawn the lawnmower did not need to be ready for a time period of almost a week This allowed plenty of time for the battery to charge Multiple batteries were used in the final design due to the high power requirements each by the blade motor and drive system The factory supplied battery was used for the cutting mower and another battery for the rest of the system The power for the remaining electronics was supplied by using one of these batteries A table presenting the power requirements of the subcomponent is listed below Note that a 26Ah battery should provide enough power for the lawnmower to run for approximately 30 minutes Component Current draw Supply Number of Net Current per component Voltage components draw Encoders 100 mA 5 VDC 2 200 mA Ultrasonic 30 mA typ 5 VDC 1 35 mA distance sensor 35 mA max Microcontroller 40mA per I O pin 5 VDC 11 pins 440 mA Digital 25 mA nominal 5 VDC 1 25 mA compass module Motor Negligible 24 VDC 1 Negligible controller Wheelchair 25A 24 VDC 2 50 A motors Wireless 38 mA active 3 3 VDC 1 38mA Interface Total current SLIA draw nominal Table 5 5 Chart showing power consumption by part One importance that was originally intended to be implemented to a
44. use the rain gauge from Argent 71 Data Systems The lower price would fit better in the overall budget and the high voltage requirements for the optical IR sensor precludes it from use in this design 4 5 4 Software Implementation The heart of the obstacle avoidance system lies in the software implementation The navigation subsystem of software establishes the boundaries and current location of the lawnmower It also keeps track of the sections of lawn that have already been mowed Using this information the current path of the lawnmower is established While traversing this path the obstacle avoidance module could be called upon should the obstacle sensors detect an object in the current path that needs to be avoided Using a similar procedure to the navigation subsystem that maps the mowed sections any obstacles are marked on the internal path area as something to avoid and a new path is calculated The obstacle avoidance subsystem was programmed and handled by the microprocessor on the project s printed circuit board 4 5 4 1 Overall Program Flow Chart The overall program flow for the obstacle avoidance route calculation subsystem is fairly straightforward It is initiated upon the detection of an obstacle by either the proximity or collision sensor This interrupts the current path and the program recalculates a new route 12 Travel currently calculated path Obstacle detected from sensor Stop vehicle Ma
45. value too high Reprinted with permission from John Palmisano www societyofrobots com Figure 4 4 5 E shows how the blob detection algorithm can be used to monitor the position of the lawn mower relative to the webcam The point of view is from atop the webcam support structure within the virtual environment By defining the position of the webcam in three dimensional space relative to the plane of interest i e the lawn in software it is possible to calculate the absolute distance from any point within the enclosed space to the webcam itself Motion in the direction perpendicular to the camera FOV can be easily determined by watching the blob move horizontally across the image through each frame of the live feed Watching the blob move up and down in the vertical direction of the image suggests that the lawnmower is traversing a two dimensional distance essentially flying from a point on the ground to some arbitrary distance above it according to the program processing the image data This would produce an incorrect measurement of the distance travelled since only two components of a three dimensional movement are considered Notice that in Figure 4 4 5 E the lawn mower position that is further away from the webcam would be represented as a smaller blob compared to the lawn mower position that is physically closer By measuring the ratio between blob sizes the distance travelled in the direction of the webcam s FOV is accurately calcula
46. various applications where a shaft or wheel rotation needs to be accurately measured This information is then used along with various other inputs i e IMU GPS ect to accurately track the motion and position of an autonomous vehicle An absolute shaft encoder can determine the position of its encoder shaft from the moment that the encoder is powered Unlike an incremental encoder it tracks the absolute shaft position relative to where it started An absolute encoder may use magnetic mechanical or optical sensors with a rotating disc to determine the current position of the shaft Mechanical encoders use contacts that slide and a disc with metal patterns designed to encode specific shaft positions Magnetic encoders sense the position of magnetized strips on a disc while optical disc devices detect specifically coded light and dark areas on the disc The position data from an absolute shaft encoder is outputted in either digital or analog forms Digital data is often represented in binary gray code or binary coded decimal Gray code is a modified form of binary coding in which adjacent pattern codes differ by one bit reducing errors in positional data The digital data can usually be outputted in parallel or serial formats such as RS 422 SSI or CAN Light Sensor s Light Source Rotating Disk Figure 3 3 3 A Example of an optical shaft encoder Reprinted with permission from ni com Quadrature encoders also known as incremental
47. were well outside the price range for this project It can be seen that the leading disadvantage of the aforementioned systems was high cost By using landmark navigation through computer vision most of the developement cycle would be centered around software developement which allows for low cost fast prototyping cycles and flexibility in terms of feature sets If written correctly the computer vision software could produce accurate results at a fraction of the cost neccessary for implementing one of the previously mentioned techniques Several options are available for computer vision software MATLAB offers a Computer Vision Toolbox that includes a suite of image processing algorithms and various functions that inferface with input and output devices However the MATLAB liscense is expensive and the program itself requires a large install and consumes a lot of system resources on the host PC SimpleCV is an open source framework for building computer vision applications using the Python programming language It is built open the OpenCV library that apart from being open source was created specifically for users that require the power of MATLAB at no additional cost SimpleCV is dependant upon several Python packages such as NumPy used for matrix manipulation SciPy includes a multitude of functions necessary for executing complex mathematic operations such as integration and matplotlib used for generating various plots all of which a
48. would be depressed enough to engage a lever limit switch thus notifying the microcontroller that a collision has taken place and to initialize corrective procedures i e disable the motor driving the wheels and or blades An alternative method would involve suspending a heavy duty string around the mower chassis One end of the string would be anchored to a fixed point on the mower body while the other end would attach to a sensor which monitors the tension in the wire To further increase safety an easily accessible kill switch was mounted on the mower itself If time permitted sensors to detect the mowers horizontal orientation would have been implemented to disable the cutting blades should the mower accidentally tip over One final major consideration for the design of this project was to create this project in as low cost a way as possible As of this writing no funding and or sponsorships were expected to help reduce the direct financial obligations for this project from the group members Because of this the total projects costs needed to be kept as low as possible resulting in a reduced cost final design 2 3 Project Requirements and Specifications The design project is for an autonomous lawn mower In our original attempt the lawn mower would have initially go through a mapping mode to create a grid of the yard to be cut This cutting map would have been stored in memory to be repeated thereafter by the lawn mower on future
49. 0lbs This means that the motors that are selected to drive the automated lawn mower should be able to handle this weight with ease driving on off road terrain Since the average consumer s lawn is not perfectly flat the automated lawn mower s motors also need to be able to handle a maximum of a 30 degree incline or decline This means that the DC motors would need to be able to handle a chassis that would weigh about 200lbs 77 Brushed DC Motor Brushless DC motor SC Battery Comunutator Field Magnet Figure 4 6 2 4 An example of a brushed and a brushless motor Reprinted with permission from thinkrc com Another topic for consideration is whether to purchase brushless or brushed motors A brushless motor uses a permanent magnet external rotor driving coils set up in three phases several Hall effect devices to sense rotor position and other various drive components Each coil is activated one phase after another by the drive components which are controlled by signals from the Hall effect sensors The coils act as three phase synchronous motors containing their own variable frequency drive electronics Several advantages of brushless motors include low noise reduced size due to thermal characteristics high efficiency and low maintenance due to no internal brushes Some of the disadvantages of using a brushless motor include complex controls for the motor which are expensive higher cost of construction and an electric cont
50. 1024 AtMega328 Microcontroller 1 Rotary Encoder 1024 2 Figure 5 1 A Inputting 2 Rotary Encoder to Port D of Microcontroller The navigation subsystem contains the PING Ultrasonic Distance Sensor and the Collision Sensor Both require 1 digital sensor each and the CMPS03 compass requires 2 analog channels Port B contains timer features which are needed for the distance sensor and the collision sensor Both inputs can be connected to port B Since the CMPSO3 requires 2 analog channels an A D converter would have possibly been needed The AVcc would be needed as a supply voltage to the A D converter The AREF pins may also need to be used as an analog reference pin for the A D converter The converted digital signal can then be inputted to 2 additional bits of port B 101 PB 7 0 PING Ultrasonic AtMega328 Microcontroller Distance Sensor Collision Sensor Figure 5 1 B Inputting Ultrasonic Sensor and Collision Sensor to Port B of Microcontroller PB 7 0 AtMega328 Microcontroller Figure 5 1 C Inputting CMPS03 to Microcontroller using A D converter to port B Finally the Drive Subsystem is Bidirectional which is primarily an output The motor controller used is the Sabertooth 2x25 Motor controller which requires 1 serial port Port C contains 7 bits that can possibly be used for this subsystem Additionally the reset pin PC6 can be used as long as the RSTDISBL fuse is programmed The reset
51. 5 3 3 in which an output voltage of 3 3 volts is provided If other voltage requirements are needed the circuit below can be easily modified to change the output voltage VIN 4 5V to 42V 9762 FB LM22670 ADJ EN BOOT 22 a i D VOUT 3 3v Figure 4 7 2 2 A Buck converter voltage regulator circuit with output of 3 3v Reprinted with permission from Texas Instruments 93 4 7 2 3 Battery Charge Monitor Monitoring the charge of the battery is an important design feature for this project It is necessary to monitor the battery charge during its use as well as when it is being charged During the use of the lawnmower while it is functioning the battery charge needs to be continually monitored so that its levels never get too low Once it reaches a certain threshold the lawnmower would be programmed to detect this state quit mowing and return to the docking station By doing this the lawnmower avoids running out of power before reaching the charging area and thereby getting stuck and in need of user assistance In addition to monitoring the charge state while functioning the battery charge needs to be monitored while recharging This is important so that the charging procedure can end once the battery is fully charged Charge monitoring in this case is vital as excessive overcharging of the battery can damage the battery and cause it to lessen its ability to hold a full charge For this project lead acid batteries appeared to be the ba
52. I would like to request permission to use the images within the Sabertooth 2x25 PDF Theses images will be used in a design paper for a senior design project at the University of Central Florida Thank you Andrew Cochrum 132 SoR Requesting permission to reprint images Inbox x Joseph Corteo lt josephcorteo gmail com gt 9 44 AM 12 hours ago to robots Hello First of all great site have learned quite a bit love the added humor as well am an Electrical Engineering student at the University of Central Florida am currently working on my senior design documentation we are building an autonomous lawn mower am using computer vision in the navigation subsystem am requesting permission to include images as examples from your Programming Computer Vision Tutorial series Thank you A John Palmisano lt palmisano gmail com gt 1 59 PM 8 hours ago A to me Documentation just for a school report and not to be published online correct If that s the case you are granted permission Joseph Corteo lt josephcorteo gmail com gt 2 07 PM 8 hours ago ew gt to John Correct All images will be referenced in the bibliography Thank you Joseph Corteo lt josephcorteo gmail com gt 1 49 AM 20 hours ago to sales support Hello lHello am an Electrical Engineering student at the University of Central Florida USA working on my senior design documentation Our proje
53. IMUs respectively are susceptible to high steady state error due to the presence of unbounded error due to the integration performed by such instruments These long term errors can be filtered out by correlating the relative positioning data produced by these sensors with the data obtained from reference based systems such as magnetic compasses active beacons global positioning systems GPS landmark navigation model matching etc Thus the system would benefit from minimal error in both its short term and long term position calculations For the aforementioned reasons the navigation subsystem of the lawn mower would consist of the following sensors and their implementation would be outlined in the following discussion Magnetic Compass Two wheel shaft encoders One ultrasonic distance sensor One HD Webcam The above sensors would allow the microcontroller to ascertain the lawn mowers current position within the area of operation From this information the microcontroller can than record and plan the movement of the lawn mower until the goal has been completed Referring to the image below Figure 4 4 1 A the general overview of the navigation subsystem is as follows the stationary USB HD Webcam was connected to a laptop loaded with computer vision software SimpleCV that employed various image processing techniques to translate the image of the lawn and the lawn mower moving 48 about the confines of the lawn into three pieces
54. John PROGRAMMING COMPUTER VISION TUTORIAL Part 3 Computer Vision Algorithms Society of Robots N p Web 23 Apr 2013 lt http www societyofrobots com programming_computer_vision_tutorial _pt3 shtml gt Parallex Digital Compass N p n d Web lt http www unf edu cchoi Sensors PDF Digital 20Compass pdf gt PING Ultrasonic Distance Sensor 28015 Parallex N p n d Web lt http www parallax com dl docs prod acc 28015 PING v1 3 pdf gt Product Description Sabertooth 2X25 V2 Regenerative Dual Motor Driver Dimension Engineering LLC n d Web 24 Apr 2013 lt http www dimensionengineering com products sabertooth2x25 gt 127 Product User s Manual HC SR04 Ultrasonic Sensor N p Cytron Technologies n d PDF PROGRAMMING COMPUTER VISION TUTORIAL Part 2 Computer Image Processing Society of Robots N p Web 23 Apr 2013 lt http www societyofrobots com programming_computer_vision_tutorial _pt2 shtml gt Reading Rotary Encoders N p n d Web lt http www tufts edu programs mma emid RotaryEncoder pdf gt Silverman Milo C Dan Nies Boyoon Jung and Gaurav S Sukhatme Staying Alive A Docking Station for Autonomous Robot Recharging The 2002 IEEE International Conference on Robotics and Automation 2012 1050 055 Web Simpson Chester Linear and Switching Voltage Regulator Fundamentals National Semiconductor n d n pag Web lt sva ti com assets en appn
55. Permission granted Good luck with your project Best Regards Gerry From Joseph Corteo Sent Friday April 19 2013 8 57 PM To sales robot electronics co uk accounts devantech co uk robot electroni Subject Permission to Reprint Diagrams in Senior Design Documentation Requesting Permission to reprint images Joseph Corteo lt josephcortea gmail com gt Apr 22 1 day ago A r to sales benjamin Hello am an Electrical Engineering student at the University of Central Florida USA working on my senior design documentation Our project consists of an automated lawn mower am using the A6B2 CW2Z3E rotary encoder datasheet to keep track of the distance traveled am requesting permission to reprint the Output wave and Model Output diagrams from the datasheet listed above in our senior design documentation Thank you Click here to Reply Reply to all or Forward CSE466 Software for Embedded Systems Catalog Description Software issues in the design of embedded systems Microcontroller architectures and peripherals embedded operating systems and device drivers compilers and debuggers timer and interrupt systems interfacing of devices communications and networking Emphasis on practical application of development platforms Prerequisites either CSE 352 or CSE 378 either CSE 303 or CSE 333 Credits 4 Portions of the CSE 466 Web may be reprinted or adapted for academic nonprofit purposes providin
56. Senior Design 2 Final Project Documentation The Manscaper Autonomous Lawn Mower Senior Design Project AS UCF Group 2 Andrew Cochrum Joseph Corteo Jason Oppel Matthew Seth Table of Contents Ih Ex cutive Summary oeste s Fahey r e raa aha taes a es use aaea aa tnae TaSi 1 2e Project Descripti On ceii E E E A E E E eh Ria ea ia a a th 1 Zk Project Movatn 25200 lt a crashes n e a tages are eiues ote T aah actus eae eos 1 2 2 Proj ct Goals AM OE COU VES sash cindy an eiecaulivains ouside antag Cotte cena ees deena aw e a oa oa es 2 2 3 Project Requirements and Specifications sssesssesssssseeeseeessseessressersseeeseressseessreso 4 3 Research Related to Project Definition eesssssesssssseessesesseesssettsseesseessesseresseessseessrese 5 SL Existing Similar Projects e ea a ace fences EE E e aia 5 3 2 Existing Commercially Available Products s sssessensseeeseeessseessressersseesssessseessrese 6 3 3 R levant Technolo tiesi oo rna a a EE E a 7 3 3 1 Techniques and Sensors Used in Mobile Robot Positioning Systems 7 Fle ed Wy IE Odo meyan sere aa E T A L a E 7 3 3 1 2 Inertial Navigation xe en e E R A A R RG 12 33l Magnetic Compasses a nen lot a eter e etie 12 33 LAActive Beacons misnieccyiise mei E S 13 3 3 2 Using a System of Low Cost Transmitters to Calculate the Position of a Mobile Platform via Trilateration s seeeesseesseesseesseeesseessseessrrsseesseresseressresseesseessee 14 3
57. The next procedure involves the proximity sensor input this procedure shall be called findobstacle The ultrasonic proximity sensor is continually sending out and receiving signals to detect obstacles This information is returned as a pulse of a width that is proportional to the distance from the sensor of the obstacle that is detected To avoid stopping only when it is truly necessary an obstacle needs to be within a certain close range to be considered something that should trigger an avoidance procedure This distance needs to be one that is not so close that it causes a collision It also should not be too far away so parts of the lawn are not avoided carelessly This distance is best estimated at 14 inches If the ultrasonic sensor returns a value that is less than or equal to 14 inches the avoidance procedure should be called Similar to the collision detection procedure this should also send a signal to the drive subsystem to stop the mower and then recalculate a new route Stepping back from some software procedure specifics for a bit some general information regarding the obstacle avoidance route calculation needs to be addressed There are countless search algorithms that have been developed that are useful for path finding applications One popular algorithm is the A or A star search algorithm The A algorithm starts by defining the area as a grid or matrix of points called nodes by the algorithm At any given time there is a startin
58. Wheel Motor Control Method s The Sabertooth 2x25 motor controller has five different input methods that can be used to control the motor controller The first is an analog control that accepts a OV to 5V analog input connected to terminals S1 and S2 of the motor controller The voltage read on S1 controls motor 1 and the voltage read on S2 controls motor 2 OV is full reverse 5V is full forward and 2 5V is stop This method can be problematic because the microcontroller would need to hold the voltages on S1 and S2 perfectly in order that the same amount of power is given to both wheels Any variation in the voltages and one wheel would rotate faster than the other and the automated lawn mower would be sent off course which would then require correction from the navigation system Due to these complications the analog voltage is not the preferred method of control The second method for communication with the motor controller is through an R C input mode This 82 allows the motor controller to be used with a standard hobby radio control transmitter and receiver Since the primary goal is automation there would be no user controlling the automated lawn mower externally and therefore this method of control is not ideal The third method for controlling the motor controller is through pulses transmitted to terminals S1 and S2 A 1000us 2000us pulse controls speed and direction 1500us is stop Similar to the analog method any signals received on
59. after making contact with the wall Finally various obstructions of varying sizes should be placed in the path of the moving vehicle If all tests are passed the collision detection system is ready for a live environment The proximity sensor is tested in a similar manner as the collision sensor Initially the device can be tested and adjusted by aiming the lawnmower towards a solid wall A measuring tape should be placed against the wall along the path of the vehicle Once the lawnmower is within the designed limits of distance from the wall determined by the design specifications the lawnmower should stop The detection distance combine with the stopping distance should place the stopped lawnmower far enough away from the wall so the there is still enough room to turn away If the distance is too small software adjustments should be made to increase the obstacle detection distance so that the avoidance distance is suitable After this test has been passed the proximity sensor should be tested using obstacles of increasingly smaller size Once the obstacle avoidance tests have passed such that the lawnmower stops the next phase in testing can commence The A avoidance route calculation needed to be tested The lawnmower route should be setup so that it traverses in a straight line for approximately 5 meters This was similar to the straight line test that has already been completed This time an obstacle to be avoided should be placed along the s
60. an be used to create more available ports is to use decoders and multiplexers This is effective is more bits are needed for signaling One way is to use the enabled decoder approach 39 bits n signals uC enable Enabled Decoder Figure 4 3 4 1 B Enabled Decoder Schematic Reprinted with permission from Department of Computer Science and Engineering University of Washington In Figure 4 3 4 1 B the microcontroller is providing log n bits The result is n available signals that become available in which one of those signals is used as a hot signal This is used for input only devices This could be necessary for input signals such as the wheel encoder and compass which would act as input only devices The need of this technique is necessary since multiple pins could be needed for each device This may not work if the multiple pins are not input only Figure 4 3 4 1 C illustrates the registered decoder approach n signals select lines Registered Decoder Figure 4 3 4 1 C Registered Decoder Schematic Reprinted with permission from Department of Computer Science and Engineering University of Washington In the registered decoder approach no signal is needed as a hot signal More pins are required from the microcontroller to the multiplexer and the decoder The initial log n bits would become n signals Similarly to the enabled decoder approach this only applies to input only signals If a hot signal is
61. and multiply this difference in time travel to by the speed of sound to ultimately produce the current straight path distance between the mower and the beacon that sourced the signal lengths d1 and d2 from Figure 3 3 2 A If the lawn to be mowed spans a large area the air temperature gradient across the lawn can become quite large and thus affect the speed of sound resulting in a percent error in distance calculations as significant as 11 to 12 percent for some ultrasonic units To minimize this error a temperature sensor may be interfaced with the microcontroller in order to update the stored speed of sound constant Cair before each distance calculation in accordance with the following equation Cair 331 5 0 6 XT m s Where T is the measured air temperature in degrees Celsius Base station radio Robot radio Beacon 1 M Beacon 2 ML Beacon 3 Beacon 4 mm Beacon 5 mu Beacon 6 wm Beacon 7 _ _ S Beacon 8 mu Figure 3 3 2 B Time line for a single positioning sequence Reprinted with permission from Bristol Robotics Laboratories To use this method of trilateration employed by the Bristol Robotics Laboratories the distance between the beacons involved must be somehow passed to the microcontroller during the mower s navigation of the lawn or pre programmed into its memory banks before program execution as will become apparent shortly This creates a substantial
62. are typically not always enough available ports For this reason it might have been necessary to use a microcontroller that has expansion capabilities in which we can have more ports available One technique to create more ports is to use port sharing methods with simple glue logic However if ports being shared have signals that are going in the same direction then glue logic would not be needed For example multiple LED displays can be connected to the microcontroller and operated independently by sharing connections to RS RW and DB but not E In our design we can use a similar method for sharing the various input signals If we were to share a port for the antenna and the motor controller for example simple glue logic would be used if we use this technique Figure 4 3 4 1 A Port Sharing Schematic Reprinted with permission from Department of Computer Science and Engineering University of Washington The above diagram illustrates 5 LEDs that are connected to the same port Since LEDs are typically outputs this is closely related to the application needed for the motor controller The motor controller would probably be both input and output but mostly output depending on the binary sequence received For testing purposes depending on the number of bits needed the above LED sharing technique can be used as output signals from the same port to verify the correct signal is being sent to the motor controller Another technique that c
63. ation in reverse or if the motor is to be used as a brake switches 1 and 2 in Figure 3 3 5 A are closed The second method for controlling DC motors is through a motor controller This is the more expensive way to control DC motors as most high current motor controllers start at about 100 and go up from there however the use of a motor controller allows for more precise control of the current that is supplied to the motors which translates to accurate speed control Using a motor controller is ideal for use with automated vehicles since the vehicle does not operate at high speeds and the vehicle needs to stop for objects and smoothly start up again If the automated vehicle can slowly speed up from a stopped position then the sensors and digital compass would be able to function more accurately and keep the vehicle on a preset track For these reasons a motor controller is worth the extra cost in building an automated vehicle to ensure navigational accuracy The lawn mower chassis was driven by two wheelchair motors that operate at 24 volts These motors require between 20 and 25 amps of continuous current to run at full speed A motor controller that can interpret commands given from a microcontroller is ideal so that steering and navigation of the automated vehicle are achieved with ease Although the DC motors does not continually consume 25 amps due to the motors being operated at lower RPMs a motor controller that can sustain these high curren
64. bee wireless module This circuit can be applied to the RN XV with no alterations since they are virtually identical in terms of pin configurations and electrical characteristics 4 5 Obstacle Avoidance Subsystem A primary objective of this project is realized by the obstacle avoidance subsystem The lawnmower needs to detect obstructions in the cutting path and steer clear of running into or over them which could damage the mower and or the obstacle The primary approach of avoiding obstacles was with the implementation of an ultrasonic distance proximity sensor For redundancy a collision sensor was also added to the design in case the mower 67 actually hits an object Finally the initial intent for the addition of a precipitation sensor would keep the mower from running in the rain which could damage the device 4 5 1 Distance Proximity Sensor A distance proximity sensor was the primary device used to avoid obstacles Using an ultrasonic sensor objects in the path of the moving lawnmower can be detected and the distance to the object can be determined To accommodate an appropriate stopping and turning distance the ultrasonic sensor was able to detect objects directly in front of the lawnmower 0 0 inches up to a distance of about 24 inches The sensor was able to detect objects with a width of approximately 2 inches or greater There are many ultrasonic sensors available that are usable for this project The sensor choices for this p
65. bile Platform via Trilateration The position of the mower throughout the yard could be discerned through trilateration To utilize trilateration two pieces of information must be known the distances from the object of interest to at least three different known points and the co ordinates position of these points Consider the figure 3 3 2 A 2 S om L T sf Pa 2 1 a Figure 3 3 2 A Given the measured distances d1 and d2 value of h x coordinated and y can be calculated Reprinted with permission from Bristol Robotics Laboratories The blocks 1 and 2 are ultrasonic transmitters positioned at the perimeter of the enclosure yard These transmitters would then pulse at predetermined intervals and fixed order see Figure 3 3 2 B This would accomplish two things the microcontroller would be able to distinguish which particular beacon transmitted the signal and secondly a reference point in time to where the time of flight of the signals would be calculated from is established This ultrasonic pulse train is then synchronized with a clock on the 14 microcontroller via radio transmission Thus the predetermined intervals between pulses would be held constant throughout the mower s operation to insure the highest accuracy is achieved Since the time at which the pulse from the beacon is transmitted is known the microcontroller would measure the amount of time it takes for the signal to reach the onboard receiver trave
66. by tripping a switch There are also optical devices that sense rain using infrared light as well a newer capacitive touch rain sensors that are being used for automated vehicle windshield wipers After some research the choice of rain sensor to implement was originally narrowed to two designs The first sensor is an optical IR rain sensor from Agrowtek This sensor is customizable using a DIP switch on the sensor Setting the DIP switches all the sensor sensitivity to be adjusted to detect varying levels of rainfall rates It has a digital output and operates on 24 Vdc It also includes a built in heater should temperatures drop below 32 degrees Celsius The second sensor is part of a weather assembly kit that is available from Sparkfun electronics This rain sensor is a self emptying rain gauge that closes a switch when filled with approximately one hundredth of an inch of rain This sensor acts as a simple switch with the contacts of the switch located on a RJ11 cable from the sensor Device Type Optical IR Rain Sensor Rain Gauge Switch Manufacturer Agrowtech Argent Data Systems Voltage 24 Vdc 0 Vdc Sensitivity Adjustable single drop to 1 per hour Detects every 0 011 Output Digital Switch on RJ11 cable Price 219 00 69 95 Table 4 5 3 Rain sensor specifications Although the optical IR sensor from Agrowtech is the better device due to its variable sensitivity setting this project would be better suited to
67. ccurate Some units can rotate up to 30 000 RPM and remain accurate However most mechanical encoders are much more limited in speed due to the moving mechanical parts For this particular application the autonomous vehicle was powered by two wheelchair motors and achieves a maximum speed of about 5 miles per hour Due to the low speed application either mechanical or optical sensors could be used without fear of failure However due to the accuracy needed to correctly navigate across a yard a mechanical encoder would not provide the same level of precision needed for the autonomous vehicle application This leaves either optical or magnetic shaft encoders For the sake of simplicity although optical shaft encoders were chosen for this particular application it was not used in the final design 3 3 4 Inertial Measurement Unit IMU An inertial measurement unit IMU is a staple component of navigational equipment used in everything from boats to aircraft and spacecraft Using a combination of accelerometers gyroscopes and other electrical sensors inertial measurement units can measure orientation acceleration rates and rotational changes The inertial measurement unit usually shares space with three accelerometers and three gyroscopes Manufactures often produce these measurement units in different shapes and styles with differing levels 19 of accuracy to meet the needs of various applications The inertial measurement unit can also be u
68. ce a wireless card to the microcontroller One example of a wireless card that can be used is the KST TX0O1 and the KST RX806 RF modules that are transmitter and receiver pairs that can transfer data Typically the microcontroller would receive data and the laptop would send data However the microcontroller would also need to send data to the laptop If these modules are used then there might be need for two pairs so that both the laptop and the microcontroller would be receivers and transmitters The transmitter and receiver modules can be connected to microcontrollers However one would be connected to a laptop In this design the transmitter would mostly be needed to send data from the laptop instead of a microcontroller As a result USB adapters may be necessary for connecting to the laptop If the microcontroller does not need to send data then only one pair of wireless cards would be needed This module would receive data such as absolute current location or possible obstacles that might be detected by the camera vision In our final design instead of using wireless cards a WiFly module was used with a router 46 4 3 4 6 Connecting Motor Controller The motor controller mostly served as an output that receives data from the microcontroller to move the mower in a certain direction Typically two bits can be used for four simple movements The motor controller is connected to two output ports on the microcontroller The signals ca
69. ce at all times during the lawn mowers operation to ensure accurate readings 52 include lt Wire h gt define ADDRESS 0x60 defines address of compass void setup Wire begin conects I2C Serial begin 9600 void loop byte highByte byte lowByte Wire beginTransmission ADDRESS starts communication with cmps03 Wire write 2 Sends the register we wish to read Wire endTransmission Wire requestFrom ADDRESS 2 requests high byte while Wire available lt 2 while there is a byte to receive highByte Wire read f reads the byte as an integer lowByte Wire read int bearing highByte lt lt 8 lowByte 10 Serial printin bearing delay 100 Figure 4 4 2 B Code loaded onto ATmega328 microcontroller to test functionality accuracy of the CMPS03 digital compass module Reprinted with permission from Devantech Limited Using the heading calculations from the CMPS03 compass module a simple proportional control loop see Figure 4 4 2 C can be implemented in the microcontroller software to direct the autonomous lawn mower in a direction determined by the user or other sensor inputs from within the navigation subsystem During the lawn mowers operation the subroutine would continually calculate a steering correction based on the heading error The heading error would be the difference between the intended direction of travel and the current directional orientation of the mower
70. comparison of the performance of a system before and after the inclusion of the correction constants via software 117 _ of cw runs Y T cluster Center of gravity Center of gravity cew Q a cluster Pi gay ere NTO lt lt Figure 7 3 A Typical results from running UMBmark for a total of five trials with an uncalibrated TRC LabMate Robot Reprinted with permission from Dr Johann Borenstein Y mm Center of gravity of cw runs _B after correction X mm 10 Before correction cw Before correction ccw m After correction cw 15 m After correction ccw 20 8 251 eemenmtien antenna Figure 7 1 B Position errors after completion of the bi directional square path experiment 4 x 4 m Reprinted with permission from Dr Johann Borenstein From the centers of gravity computed above X g cw ccw and Yeg cw ccw the aforementioned correction constants expressed as Cy and Cr for the left and right wheels respectively can be calculated According to the designers of the UMBmark the two prevalent causes for systematic error are unequal wheel diameters and the uncertainty about the effective wheelbase In most cases the error introduced by unequal wheel diameters is far greater than that of the effective wheel base thus the latter is considered negligible and is not included in the calculation of Cy and Cp as will be seen shortly Referring to Figure 7 1 C c is the
71. ct consists of an automated lawn mower am using the PING Ultrasonic Distance sensor datasheet for the obstacle avoidance subsystem am requesting permission to reprint the timing diagram under the Communication Protocol section and the Test 1 and 2 diagrams under the Test Data section from the datasheet listed above Thank you Support 11 04 AM 11 hours ago Hello Joe Permission granted Have fun Kevin Cook www_Parallax com 916 624 Joseph Corteo 11 19 AM 11 hours ago Thank you will do Lauren Davis lt Idavis parallax com gt 1 52 PM 8 hours ago ea to me Hi Joseph You are welcome to reprint these images for educational purposes Feel free to email me with any other questions Sincerely Lauren Lauren Davis Marketing amp Education Manager Parallax Inc Idavis parallax com www parallax com 133 Permission to Reprint Diagrams in Senior Design Documentation inbox x Image Permissions x El Joseph Corteo lt josephcorteo gmail com gt Apr 19 4 days ago ea to sales accounts support11 Hello am an Electrical Engineering senior at the University of Central Florida currently enrolled in senior design our project is a completely autonomous lawn mower am requesting permission to reprint the CMPS03 Magnetic Compass diagram http www robot electronics co uk htm arduino_examples htm Thank you Support Apr 22 1 day ago lv to me Hi Joe
72. ctions of the autonomous lawn mower can be easily compensated for at a minimum of cost we curved path curvature strongly exaggerated Desired straight line path Figure 7 1 C Geometric relations for finding the radius of curvature Reprinted with permission from Dr Johann Borenstein 7 2 Avoid Randomly Placed Obstacles Once the drive subsystem was tested with straight line and turn testing the obstacle avoidance system was tested For this testing the proximity sensor and the collision sensor were independently tested For this point in testing the avoidance route does not need to be calculated To be a successful test the obstacle avoidance sensor data is read If an obstacle has been detected a signal is sent to the drive system to brake and stop the wheels 119 The first test was for the collision sensor For this testing interference from the proximity sensor was avoided To avoid have the proximity sensor from detecting an object that sensor was temporarily angled away The initial test should have the user manually depress the bumper switch while the lawnmower is moving forward A successful test is determined if the lawnmower stops moving after the switch is depressed Once that test has passed more complex testing can be performed A good test was to have the lawnmower move towards a wall This provides a good platform in which a collision is assured For a successful test the lawnmower should stop immediately
73. cuts The lawn mower would have included on board obstacle detection to avoid cutting any unexpected impediments in its path Upon completion of cutting the lawn the mower would then return to its charging station and notify the user that it is done This entire process with the exception of the learning mode would be completed without any required user interaction Project Specifications e Mower size o 26 x 35 x 12 5 Wx Lx H e Mower location accuracy o Accurate to within 12 e Forward speed o 1 2 mph e Obstacle detection distance o 2cmto3m e Average lawn size o 0 33 acre 14374 80 square feet e Time to cut test area o Preferably lt 30 minutes o Realistically actual time to complete is low priority However mower should cut entire area on one charge and have enough power to return to its charging station e Battery life o gt 30 min o Would sustain cutting blades wheel motors and all other subsystems until the entire area has been cut and if the mower were to return to a docking station e Battery charge time o Roughly 3 hours o Since grass is mowed usually on a weekly basis the charge time is of low priority 3 Research Related to Project Definition 3 1 Existing Similar Projects Initial research for the project involved looking at similarly designed and completed projects An autonomous lawn mower design has been completed various times using varying methods The documentation for these projects was e
74. cutting session and maneuver around these areas possibly disabling the motor driving the cutting blades to conserve power if these previously cut areas need to be traversed The aforementioned straight path navigation implemented by the commercially available mowers could still be implemented in this iteration however using an improved sweeping method To reduce this straight path distance especially in very long and or wide lawns the mower could divide through software the area to be mowed into sections This could be implemented by temporary boundaries established by the microcontroller on the fly Thus the mower would sweep between the boundaries of this virtual section and proceed to each adjacent section once its current section has been fully mowed This would in theory greatly reduce power consumption by minimizing unnecessary redundancy associated with the straight path navigation method In our final design although there were difficulties in keeping track of previous locations we were able to improve the efficiency of commercial products by using computer vision to determine boundaries and rotate the mower in an appropriate direction depending on the boundary or obstacle encountered By implementing a computer vision setup the lawn mower is able to be tracked as target where it is A high mounted camera was able to track the location of not only the lawnmower but also the boundary markers By matching its location to the yard locati
75. d an imbalance with weight of the batteries and the chassis was easy to tip In our second chassis the wheels were positioned a little further back and eliminated the center of gravity issue A shaft encoder was originally to be used to keep track of each rotation made by the wheels The encoders were to be mounted to the frame and attached to the drive shafts via a timing belt An optical shaft encoder could determine movement by reading two light and dark coded tracks using photodiodes Two channels are coded on a disc 90 degrees out of phase and alter between light and dark The two output channels could then indicate the position and the direction of rotation If the sensor detects that one is leading the other by 90 degrees then the shaft is rotating clockwise If the sensor detects that the second is leading the first by 90 degrees then the shaft is rotating counter clockwise The position of the shaft could then be derived by constantly monitoring of the number of pulses and the relative phase between the two channels 5 5 Design Summary Power Subsystem 110 For this project the power subsystem design is broken into two main subsections the battery required to run the project and keeping that battery charged and the voltage regulation circuit required to supply the required power needed by each electronic device Since this project is a prototype with budget limitations a lead acid battery is the most feasible options to supply power
76. d y coordinates using the aforementioned process The distance from the beacon situated at point 3 is then measured and the xy coordinates are now calculated using beacons 2 and 3 This process continues around the perimeter utilizing each successive pair of transmitters resulting in 8 xy coordinate pairs However note that when the robot calculates the xy coordinates from beacons 2 and 3 the result obtained would correspond to a coordinate system that is rotated by 45 degrees clockwise from that of the original xy coordinate pair This can also be said for the beacon pairs 4 and 5 6 and 7 and 8 and 1 with varying degrees of rotation of course Thus all successive measurements must be rotated back to the frame of the first measurement to ensure consistency This can be implemented using the standard rotational matrix operation R R Where R p sin sin cos v column vector contaning coordinates of point Thus column vector R contains the original xy coordinates Y rotated counter clockwise through an angle about the origin of the coordinate system This transformation can only be used to describe rotations about the origin of the coordinate system a limitation that does not hinder its application since as mentioned previously the straight line containing both beacons being referenced is considered to pass through the origin for each set of calculations 17 3 3 3 Shaft Wheel Encoder A shaft or wheel encoder is used in
77. ditional layer of redundancy To integrate the motor platform onto an existing electric lawn mower chassis the existing rear wheels are removed and an extra 1 5ft section was attached to the back of the mower The section was be made out of steel and was attached via elbow brackets This extra platform would not only hold the two DC motors via custom brackets but would also hold the two batteries that would be used to drive the DC motors and the enclosure for all the automated mower s electronics Each motor s manual clutch would need to be easily accessed so that the motors can be freely rotated for easy movement by the user Since the clutch levers may not be easily accessible after the motors have been mounted it may be necessary to add custom brackets to be able to engage and disengage the clutches easily The automated lawn mower would have a differential steering system so it is necessary for the front of the chassis to be able to move in any direction unhindered This means the wheels at the front of the existing chassis needed to be removed After removal of the front two wheels a bracket was attached to the front of the automated lawn mower for two free castoring wheels The two free castoring wheels was then attached to the bracket and allowed the automated mower to be turned exclusively using the rear wheel drive system 4 6 3 Software Implementation Software implementation is extremely simple due to the Sabertooth 2x25 motor con
78. e R is calculated and along with the wheelbase b the unequal wheel diameter error of the mobile robot E4 is found R PO pe By R h Therefore fees 2 bEq 1 2 Cp Ea These two correction constants are then used in the well established odometry algorithm for differential drive mobile platforms AU Jri Cir CmNL Ri Where AU z is the incremental distance traveled for the left and right wheels Cm is the conversion factor that translates encoder pulses into linear wheel displacement and N_ is the encoder pulse increment for the left and right wheels The UMBmark provides an excellent tool for analyzing and comparing the performance of the navigation system across a spectrum of different hardware arrangements involving encoders Since the drive subsystem of the autonomous lawn mower consists of pre fabricated components connected together in a manner that may not be optimal due to budget restrictions time constraints component level operational restrictions etc an accumulation of errors may render the encoder based navigation system ineffective For example the intended wheel diameter as defined in software may not accurately represent the effective wheel diameter which may become affected by modifications to the acquired mower chassis to accommodate the drive system Using this benchmark these physical imperfections of the autonomous lawn mower can be easily compensated for at a minimum of cost 11
79. e current position of the lawn mower would become the new reference point from which all new distances are calculated until the reset condition is encountered thus repeating the process for the duration of the current lawn mowing session As previously mentioned the resolution of this encoder can be scaled according to the damands and or limitations of the completed system This particular encoder has a base resolution of 1024 PPR puleses per revolution If both channels A and B are read by the microcontroller known as X2 logic then the resolution is effectively doubled since the controller would now count 2048 pulses per revolution across both channels If an even greater degree of accuracy is required the microcontroller can also count the rising and falling edges of the signal on both channels effectively quadrupling the base resolution to 4096 PPR X4 logic The resolution can also be fined tuned mechanically by affixing a seperate pulley to both the wheel and encoder shafts and then coupling together via a timing belt For example if the wheel shaft pulley is n inches in diameter and the encoder shaft pulley is m inches in diameter where n gt m then the encoder shaft would rotate n m times for every true wheel revolution increasing the effective resolution n m fold e g for a wheel shaft to encoder shaft ratio of 4 1 the resolution would be increased 4 fold This timing belt implementation would also prevent any sli
80. e from the north then that value should be converted to 0 degrees and the actual North direction would be 360 292 5 67 5 Moreover the initial angle value should be determined and saved and then calibrated to 0 Reference_angle 0 Compass_angle function to input angle If Compass_angle reference angle Difference Compass_angle Reference_angle any other returned value will be recalcutated by difference While true 42 Compass_angle function to input angle Reference_angle compass_angle difference The above code recalculates the angle each time an angle is read This particular compass contains 6 pins in which two are for power and ground The four pins are connected to the microcontroller This is one reason why additional ports might be necessary in the design to accommodate for the amount of pins and ports each device would need The compass needs both input and an output pins on the microcontroller in which the output is needed to send an enable signal to the compass and a signal are needed to send to the compass to tell it whether to measure an angle or reset One of the first steps to obtaining an accurate angle is the reset the compass The compass is reset by first setting the enable signal to low This signal comes from the microcontroller indicating that the compass is being used And the signal 0000 is sent to the compass As long as the compass receives a signal that begi
81. e lawn mower was originally designed to continuously receiving the xy coordinates from the laptop located at the base station rarely needing to send any data back to it and its low cost 104 Figure 5 2 B Webcam support structure Figure 5 2 B illustrates the support structure that was used to elevate the webcam above the ground so that it can completely survey the lawn and the lawn mower navigating through it Figure 5 2 C Overall setup for using computer vision Figure 5 2 C shows how the webcam support structure was placed in relation to the lawn The beige cylinders along the perimeter represent brightly colored plastic cones that were used by the SimpleCV computer vision program to establish the boundaries of the lawn Using various image processing techniques and algorithms available within the SimpleCV library e g blob detection object detection shape detection etc a coordinate system would have been created in software to assist in the calculations of the absolute location of the lawn mower throughout its navigation of the lawn 105 Figure 5 2 D FOV of the webcam from the top of the support structure Figure 5 2 D shows an example of how the computer vision program was able to calculate the distance to the lawn mower black box and from this infer the absolute location of the lawn mower within the yard Using blob detection the SimpleCV software compares the size of the blob created by the lawn mower throug
82. e lawnmower and electronics design procedures are required for monitoring and charging the battery as well as the overall design of the docking station used to recharge the device 4 7 1 Mechanical Design Docking Station Primary importance to a project of this type is the ability to recharge the battery used to power the device The simplest procedure in terms of design for completing this task would be to handle it manually That is have the user physically return the lawnmower to an appropriate area and plug it into a wall outlet for charging This method is feasible as the lawnmower would be equipped with the ability to push it around like a standard 84 lawnmower for learning mode operations This method also has the added benefit of adding a minimal cost to the project s overall budget However by making the charging procedure a manual one it cuts at the projects overall goal of being simple and easy to use with little interaction required from the end user To accomplish this goal a docking station was initially to be added to the project to handle all of the charging requirements For reference some previous designs would be observed to extract any details and design features that can be used for this project The first project to look at comes from a docking station designed by Silverman Nies Jung and Sukhatme Their docking station was designed in two parts The first being the design of locating the docking station and
83. e regulator circuit needed to be designed to provide the correct voltage for each of the devices Finally to properly charge the battery and keep an eye on the battery power a battery charge monitor needed to be designed for the project 4 7 2 1 Battery As a cordless electric lawnmower the major electrical concern for this project lies in the selection of the battery that was used to power the overall device A battery needs to be 89 chosen such that it can power then entire mower system for a long enough time to mow the lawn of the user The battery needs to also be rechargeable so that the lawnmower can be used week after week during the mowing season Before choosing the specific battery the capacity requirements need to be calculated Battery capacity is typically measured in ampere hours Ah Provided an Ah rating the time in use can easily be calculated based on the power draw from the battery Typical cordless electric lawnmowers in the market have batteries ranging from 24 to 48 Volts with capacities of 2 to 4 ampere hours The table below shows some specifications from some of the top cordless electric mowers available today Black amp Cub Cadet Ryobi Recharge Earthwise Mower Decker CC 500 RY14110 Ultralite 60120 SPCM1936 BAT Battery Type Lead acid Lead acid Lead acid Lithium Lead acid ion Run Time mins 45 60 40 50 35 45 40 50 40 50 Charge Time hrs 12 12 10 2 15 Volts 36 48 48 36 24
84. e regulator is its simplicity of design There are no additional parts necessary as the voltage regulation is completely handled in the integrated circuit The simplicity of design also avails itself to easy integration into a circuit as the regulator is small and typically only has 3 pins The main disadvantage of using a linear regulator lies in its efficiency or lack thereof For cases in which the input voltage is much higher than the regulated output voltage the linear regulator is not efficient expelling the excess power as heat For this project the input voltage was 23 typically much higher than the output voltage This made a linear regulator very inefficient and also required heatsinks to handle the heat put out by the regulator 3 3 6 2 Switching Voltage Regulators Switching voltage regulators use a combination of transistors acting as switches and inductors and or capacitors acting as storage devices to provide a constant output voltage Switching regulators can further be divided into categories such as buck boost and buck boost regulators A buck regulator takes a higher input voltage and steps it down to a constant lower output voltage For this project a buck type regulator was required Switching regulators are available as complete integrated circuits just like linear regulators Typically used parts handle supply voltages of up to 40 volts or higher and can handle currents up to about 3 amperes Switching regulators do not co
85. e table does show one mower that uses a lithium ion type of battery Choosing the appropriate battery type requires the weighing of each types advantages and disadvantages According to information gathered from BatteryUniversity com there are some clear differences which are summed up here Lead acid batteries have been the most popular type of rechargeable battery for the longest 90 time period Lead acid batteries are the cheapest of all of the currently available rechargeable battery types They also have the benefit of being able to handle large currents Their disadvantages lie in their low capacity to weight ratio long time to charge and relatively quick breakdown after repeated charging Nickel based batteries are another type that are broken down into Nickel Cadmium or NiCd and Nickel metal hydride or NiMH batteries Nickel based batteries have some advantages over lead acid batteries They have a moderate capacity to weight ratio faster charge time and are still relatively low in cost Their disadvantages lie in their issues in self discharging over time The final major battery type is Lithium based batteries Lithium based batteries have the best energy capacity per weight of all of the battery types They also have a very short charge time and do not self discharge in a high manner like nickel based batteries Lithium based batteries main disadvantage lie in their high cost compared to the other battery types A comparison overview o
86. e to successfully docks into the charging area once the issues of tracking didn t affect the system Once that is complete the charging procedure begins using software that reads the battery monitor to recharge the battery 4 7 3 1 Overall Program Flow Chart To better envision the software implementation for the power subsystem a program flow chart is presented here The overall procedure is divided into two main sections The first handles the docking procedure which gets the lawnmower into proper position allowing for it to recharge Once the lawnmower has docked and the electrical connections have been made with the docking station the charging procedure can begin SSS Charging Procedure Docked Yes Monitor charge state Terminate charging i i i i i i i i i i i i i i i Start charging i i i i i i i i i i i i i i i Figure 4 7 3 1 A Overall flow chart for docking and recharging 4 7 3 2 Executing Docking Procedure The docking procedure involves a few steps including location alignment and docking To first dock with the station the docking area needs to be located Much like the boundaries and current location or the mower are mapped in the lawnmower s memory the location of the docking station is likewise mapped This provides the first step in location of the docking station As the lawnmower approaches the docking station the cameras begin to look for the orange markers located
87. eceive data from the navigation subsystem and the obstacle detection subsystem and the information was be used to signal how the mower should be maneuvered Output digital value Microcontroller Calculated results from nav subsystem and obstacle avoidance subsystem Motor controller Figure 4 3 3 6 A General Interfacing of Motor Controller The motor controller was programmed with digital values that were used for various movements Such movements could include forward movement which would move both wheels left turn which would likely stop the left wheel and allow the right wheel to move rotating it left right turn which would likely stop the right wheel and allow the left wheel to move rotating it right reverse or stop Binary bit values could be used to program the motor controller to respond accordingly If reverse were not an option a 4 bit system and be used but if reverse or any additional options were included 8 bits would be needed 37 Bit Value Operation 00 Stop 01 Left 10 Right 11 Forward Table 4 3 3 6 Motor Controller Truth table Accordingly the microcontroller needed to be programmed to send such signals to the motor controller The microcontroller needed to know whether there is an obstacle or a boundary and in the initial design its current location so that it can move forward right left or stop Below is a short pseudocode that could be used One way is
88. ect the distance of the obstacle Depending on the size of the mower position and orientation digital signals are sent to the drive subsystem to turn the mower accordingly 4 3 3 1 Reference point calculation In our initial design the two inputs for reference positioning would have consisted of the 2 wheel encoders and the compass The wheel encoder would provide the number of rotations of the tires The data recovered from the encoder can then be multiplied by the circumference 2 z This would provide a distance traveled value The compass would 30 provide a directional value From these two values a reference point can be established Below is a short starting code that can be used for calculating a reference coordinate Int tirediameter CONSTANT Numrotations input value from encoder DistanceTraveled tirediameter pi numrotations Direction input value from compass converted to an angle New_Position_x start_x DistanceTraveled cos Direction New_Position_y start_y DistanceTraveled sin Direction start_x New_Position_x start_y New _Position_y The above pseudocode would be looped continuously as long as the mower is active Most likely this code would be placed in a function that would be a part of a while loop The while loop would run as long as the mower is active and it would continuously replace starting position coordinates with the new position coordinates And the value of the starti
89. ed so low that it impacts the ground The only additional specification of the bumper design is that it needs to be secure enough to handle direct impact from a collision An example of the bumper mount is shown below a b Figure 5 3 A Design sample showing bumper sensor Reprinted with permission from Vex Robotics The project was originally designed to be equipped with a precipitation sensor to avoid being in use while it is raining The precipitation sensor that was to be used for this project is part of a weather assembly kit that is available from Sparkfun electronics This rain sensor is from Argent Data Systems and is a self emptying rain gauge that closes a switch when filled with approximately one hundredth of an inch of rain This sensor acts as a simple switch with the contacts of the switch located on a RJ11 cable from the sensor The software application for this subsystem reads all of the data from the above mentioned sensors Using this information it is determined if an obstacle is detected Once an obstacle is detected the software stops the mower in conjunction with the drive subsystem and calculates a new route The A search algorithm would serve as the defining procedure for calculating the obstacle avoidance route In software a procedure would be implemented called a 107 void a inputs start position and goal position of the mower location of obstacle output new route direction This proced
90. ed with a standard hobby radio control transmitter and receiver The third method for controlling the motor controller is through microcontroller pulses connected to terminals S1 and S2 A 1000us 2000us pulse controls speed and direction 1500us is stop The fourth method for controlling the motor controller is through simplified serial commands Serial data is sent to input S1 sending a value of 1 127 would command motor 1 Sending a value of 128 255 would command motor 2 Sending a value of 0 would shut down both motors The last method for controlling the motor controller is through packetized serial commands Packetized serial uses TTL level serial commands to set the motor speed and direction Packetized serial is only a single direction interface The transmit line from the microcontroller is connected to S1 The microcontroller s receive line is not connected to the Sabertooth 2x25 Because of this more than one Sabertooth 2x25 can be connected to the same serial transmitter This is because packetized serial uses an address byte to select the target device This large variety of control methods makes the Sabertooth 2x25 motor controller easy to integrate into any automated vehicle design and allows for simple programming to control the differential drive motors of the vehicle 4 6 2 Right Left DC Wheel Motors For this particular application of an automated lawn mower the completed vehicle should weigh somewhere between 100lbs and 15
91. eeseresee 123 Appendice Ssnan e E E ee 125 Bibliography eaen Aa eo aan e E aaah T ques nceducoonace wees 125 Copyriht Permissions meenen r e E E NESSE 129 iii 1 Executive Summary The Manscaper is an autonomous lawn mower that takes care of all of a user s grass cutting needs with very little contact from the end operator By handling this task autonomously the user is free to relax and be worry free about their lawn This project improved upon existing designs using advanced technologies to efficiently perform its dedicated task To accomplish its task this project had a specific set of goals which were to be easy to use accurate and efficient This project uses a variety of features to undertake its job The primary duty necessary for automation is to track the location of the mower as well as its environment Tracking and mapping are performed using a combination of computer vision and compass bearing detection An outside high mounted camera views the area which is interpreted using computer vision This method allows a precise location of the lawnmower to be determined at any given time In addition the computer vision function maps the lawn while marking the boundaries Compass measurements are read to keep a relative location The combination of all of this data provides the precise measurements required to navigate the lawnmower In addition to location mapping an obstacle avoidance system was integrated into the project Using u
92. engaged from the wheel This was so the automated lawn mower was able to have the motors disengaged from the wheels so that the mower can be pushed for operation in learning mode by the user for the initial design Since the clutch levers may not have been easily accessible after the motors have been mounted it was necessary to add custom brackets to be able to engage and disengage the clutches easily 109 Figure 5 4 B Example of mounted motors behind the main chassis upside down Reprinted with Masato Hayashi s permission Both motors drive solid rubber wheelchair tires due to the tire s need for traction on off road surfaces The DC motors were rated to push up to 300 pounds under normal operating conditions so with the total mower weight coming to under 150 pounds the motors should be able to handle the load and maneuver with ease Due to automated lawn mower s differential steering system it was necessary for the front of the chassis to be able to move in any direction unhindered This means the wheels at the front of the existing chassis needed to be removed A bracket was attached to the front of the automated lawn mower for two free castoring wheels The two free castoring wheels was then attach to the bracket and allow the automated mower to be turned by using the rear wheel drive system Although the original chassis had of the wheels directed to closer to the center for feasible turning center of gravity issues cause
93. ensitivity to non systematic errors i e wheel slippages 3 3 1 3 Magnetic Compasses As mentioned in the previous sections the orientation or heading of the robot is an important factor in influencing the magnitude of the accumulated error in positional measurements As opposed to a gyroscope a magnetic compass is intolerant to cumulative errors which plague navigational components that utilize dead reckoning However steps must be taken to shield the compass properly from noise such as the magnetic field permeating from the motors driving the wheels of the lawn mower In the case of the autonomous lawn mower interference from power lines surrounding the yard could provide noticeable interference 12 There are several types of sensor systems available however the most suitable for mobile applications is the fluxgate variant This type of magnetic compass offers low power consumption intolerance to shock or vibration a rapid start up has no moving parts and is relatively low cost However when used in applications that involve navigating across an uneven terrain the fluxgate compass must be gimbal mounted and mechanically dampened a fluid suspension system may also be used in order to prevent the compass from measuring the vertical component of the magnetic field and thus distorting the measurements taken Another advantage is the ease of integration into the overall autonomous lawn mower control system The measurements are alread
94. ent from or beyond the parameters stated by TI for that component or service voids all express and any implied warranties for the associated TI component or service and is an unfair and deceptive business practice TI is not responsible or liable for any such statements Buyer acknowledges and agrees that it is solely responsible for compliance with all legal regulatory and safety related requirements concerning its products and any use of TI components in its applications notwithstanding any applications related information or support that may be provided by TI Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards which anticipate dangerous consequences of failures monitor failures and their consequences lessen the likelihood of failures that might cause harm and take appropriate remedial actions Buyer will fully indemnify TI and its representatives against any damages arising out of the use of any TI components in safety critical applications In some cases TI components may be promoted specifically to facilitate safety related applications With such components TI s goal is to help enable customers to design and create their own end product solutions that meet applicable functional safety standards and requirements Nonetheless such components are subject to these terms No TI components are authorized for use in FDA Class III or similar life critical medical equipment unless authorized off
95. ent value which utilizes convolution and gradient calculation to compute a threshold value The edge detected image in the above image is the resulting output of this approach The mathematical approach is described as 2 al S Ox Oy Depending on the amount of differences in color that needs to be detected a lower or a higher threshold value can be used 4 3 3 5 Low thresholding By using a low thresholding approach the resulting image would be outputted 35 Figure 4 3 3 5 A Low thresholding edge detection Low thresholding produces an image that would detect edges very easily In the case of the chess pieces it detects multiple areas as edges Using a low threshold for obstacle detection with the lawn mower would allow the mower to easily avoid obstacles but a threshold that is too low may result in missed areas that should be mowed Accordingly a high threshold can also be used which sets pixels above the threshold the edges as white and black otherwise By using a high threshold the following image is outputted Figure 4 3 3 5 B High Thresholding Edge Detection The advantage of using a high threshold approach is that it would eliminate missed areas for the lawn to be mowed However the image above illustrates that the knight s head in the lower right corner is not detected as an edge Nevertheless it can be a potential obstacle The gradient approach could moreover be the best algorithm to
96. eport when the robot was 37 49 cm from the line connecting the beacons the error was more than 17 cm However this error quickly attenuates with the error being reduced to 4 cm at h 1 m If more than two beacons are implemented during the distance calculation this error is even further reduced to negligible levels As is apparent thus far by increasing the number of beacons involved in demarcating the perimeter the accuracy of the system increases as well The team at the Bristol Robotics Laboratories used a total of 8 beacons This allowed the microcontroller to estimate the position of the robot based upon several different time of flight measurement so that any outliers were filtered out of the final calculation According to the report repeated tests utilizing 8 beacons showed a variation of less than 1 cm for both the x and y coordinates Also if some of the beacons ultrasonic chirps were prevented from being heard by the onboard receiver due to some obstruction the position of the robot could still be calculated based on the remaining unobstructed signals from the other transmitters 16 8 7 Figure 3 3 2 C 2D arena layout used by the Bristol Robotics Laboratories Reprinted with permission from Bristol Robotics Laboratories As seen in Figure 3 the beacons are located at the vertices of the enclosed area The robot first measures the distances of beacons 1 and 2 from its current location and calculates its x an
97. epresentation of the battery charge state This representation can be done as 0 lights means 0 charge 1 light 98 is 25 2 lights is 50 3 lights is 75 and all 4 lights lit means that the battery is 100 charged The design of this feature is easy as the TI part bq34z110 provides output pins for these four LEDs No extra circuit design is necessary for this setup This application may also be designed to give a five LED output as shown in the figure below SOA SCL or ALERT GNO HOQ or ALERT Optimize for required voltage and current Figure 4 7 3 3 A Circuit showing 5 LED output for battery charge state Reprinted with permission from Texas Instruments For terminating the charge the software implementation would be similar to the initializing procedure When the battery monitor reads a full charge a flag is set that charging is now complete A simple function call termcharge can be used that read the flag for a successful charge completion If the flag is valid and the system is done with its recharge this function would send an output signal to open the switch that was closed when charging began Opening this switch stops the current flow into the battery thereby terminating the recharge This function is imperative to the overall battery health and life as overcharging the battery can have harmful effects on these 4 8 Printed Circuit Board PCB Design Interfacing all
98. er and the programming implemented 4 3 3 Software Implementation According to the block diagram of the overall design the microcontroller takes input values from the navigation subsystem and the obstacle avoidance subsystem The drive subsystem was both inputs and outputs For the navigation subsystem in order to ensure accuracy of the position of the mower both absolute and reference positioning were considered Reference positioning would have come from two wheel encoders and a compass for distance and direction computations respectively A camera was suspended at about 3 meters and was connected to a laptop to provide absolute positioning In our initial design a WiFly Module a router and the microcontroller were originally going to be used to transfer the absolute coordinate values of the current position Because reference value change as the mower is farther away there is more error so the absolute value from the camera would ensure accuracy The image from the camera would go to the laptop for processing the coordinate position values and transferred wirelessly to the microcontroller Periodically the reference point would be reset if the difference in absolute and reference values exceed a certain threshold The obstacle avoidance subsystem consisted of the ultrasonic PING sensor which was used to generate a chirp as it approaches an obstacle The speed of sound and the amount of time for the sound to bounce back would be used to det
99. es 53 59 Horswill Ian Simple Control Loops Northwestern Engineering Department of Electrical Engineering and Computer Science N p n d Web 23 Apr 2013 lt http www cs northwestern edu academics courses special_topics 395 robotics simple control loops pdf gt 126 Kramig Kenneth Robert Armstrong Eric Niehauser and Brian Laiveling Bearcat Sredder N p n p n d PDF Lester Patrick A Pathfinding for Beginners A Pathfinding for Beginners N p 18 July 2005 Web lt http www policyalmanac org games aStarTutorial htm gt Linear amp Switching Voltage Regulator Handbook ON Semiconductor Feb 2002 Web lt www onsemi com pub Collateral HB206 D PDF gt LM22670 LM22670Q 42V 3A SIMPLE SWITCHER Step Down Voltage Regulator with Features Dallas Texas Instruments 2013 PDF LPRS 2003 Lprs datasheet easy radio ER400TRS Transceiver www l prs co uk LV MaxSonar EZI High Performance Sonar Range Finder N p MaxBotix Inc 2012 PDF Microchip 2006 dsPIC30F401 1 4012 datasheet www microchip com Microcontroller Interfacing Techniques N p 3 Apr 2005 Web lt http www bipom com applications micro_interfacing pdf gt Mowing Wet Grass LawnCare net N p n d Web lt http www lawncare net mowing wet grass gt Murata 2007 Murata MA40S4 datasheet search murata co jp Optical IR Rain Sensor Operation amp Installation Manual N p Agrowtek Inc n d PDF Palmisano
100. esign The CSM 12C32 is a microcontroller that contains SCI and SPI communication ports and 31 W O lines It also contains Analog Comparator and includes other features such as jumpers and button switches One drawback that may affect the design is the time delay for input values For example processing data from a compass would take 30 40ms which could cause inaccuracies in current locations Also since the microcontroller includes many additional features which are not necessary there is more of likelihood that there would be malfunction The ATMega 328 is the best microcontroller choice for this design because it contains an appropriate balance of features that is necessary for the design This microcontroller has a reasonable amount of I O lines and serial ports that were needed Most of the inputs are digital but it also contains A D converter pins that may be necessary Below is a table 27 comparing the VEX Cortex the MINI MAX 51 C2 the CSM 12C32 and the ATMega 328 microcontrollers VEX Cortex MINI MAX 51 C2 CSM 12C32 ATMega 328 e Wireless with e 64K Flash Memory e 32K Byte Flash e Advanced built in 2K RAM 2K internal EEPROM RISC VEXnet EEPROM e 2K Bytes RAM Architecture technology e Programmable e 311 O lines e High e 8 Standard 3 Enhanced UART Serial Timer PWM Endurance wire Motor Channel RS232 Serial e SCI and SPI Non volatile ports Bott Communication Memory e 2 2 wire e Hardware SPI Serial Po
101. essesssesesssessseessresserssereseeessressresseessee 71 4 6 2 1 Mechanical Design Interfacing Motors with Existing Lawn Mower CHASSIS tx an A eE EERE ae og an 80 4 6 3 Software Implementation ss seseesseesseesseesseeesseessseesstessesseeesseesssressresseessee 81 4 6 3 1 Overall Program Flow Char t S ceesscessceceseececseececeeeeecseeeesteeeenaeees 82 ii 4 6 3 2 Wheel Motor Control Method s ccccccccccccesssssssecececececeesersseeeeeeeens 82 4 7 Power Subsystem srpna t aao quad yen tE an E a E ESA 84 4 7 1 Mechanical Design Docking Station sssssesesseessseesseesseesseesseessseesseesseessee 84 4 72 Electrical DES IM t a ead A RE E E E E EN 89 4 J2 Battery ale E E E E EN E 89 AT 22 Voltage Reg lator Circuiten e vos a E E eee ER 93 4 7 2 3 Battery Charge Monito an ire nta ea a a ta eSa 94 4 1 3 Software Implementations sss ccisescecisneavedsasegesccgssasedve sesvennasvssacduedgen den snevaaveluanaes 96 4 1 3 1 Overall Program Plow Chart ss s9sce 5 ccc a0sacsgenc suds faces teessans sass ittenndeoesenbegeeende 96 4 1 3 2 Executing Docking Procedure 5 25 lt sc0s34 sacascesaraceuadsaceantassetasionseateatqeuaiees 96 4 1 3 3 Initializing Terminating Charging sesssesesessssseessesssersseresseeesseessresseessee 98 4 8 Printed Circuit Board PCB Design sssessesseesssesssseeesseessresseesseessseerssressresseessee 99 5 Design Summary of Hardware and Software
102. f the different types of rechargeable batteries is shown in the figure below For this project a lithium based battery appears to be optimal due to its high energy capacity density It also is beneficial for the overall project due to its ability to handle a large amount of recharging over its lifetime Since a lawnmower would be recharged each and every week sometimes more during peak grass growing months a high recharge lifetime prevents the user from having to replace the battery very often However since this project is a prototype with budget limitations a lead acid battery is much more feasible The slow charge time of lead acid batteries is not a hindrance to the function of this project Assuming the battery allows the lawnmower to fully cut the entire lawn the lawnmower would not need to be ready for a time period of almost a week This allows plenty of time for the battery to charge There could be some issues given a large mowing area These issues could be offset in a production environment where decreased costs could allow for the use of a higher capacity battery or a lithium ion battery with a faster recharge rate 91 Specifications Lead Acid NiCd Li ion Cobalt Manganese Phosphate Specific energy 45 80 60 120 150 190 100 135 90 120 density Wh kg Internal resistance lt 100 100 200 200 300 150 300 25 752 25 502 12V pack 6V pack 6V pack 7 2V per cell per cell i 200 300 300 500 500 500 1 000 1 000 80 discharge
103. g node and a finish or goal node For the automated lawn mower project the start node would be defined as the current location on the area grid of the lawn mower The goal node is the straight line current path end point of the mower The grid matrix would also contain nodes that are considered closed or impassable These closed points can be boundaries of the lawn or already detected obstacles The A algorithm uses these points of reference to determine an optimal path Checking the straightest path first and then branching out from there adjacent nodes are checked until the path is reached The algorithm would ultimately choose the path of the shortest distance To help explain the algorithm take an example grid of nodes 0 1 2 3 0 Not mowed Start Boundary Boundary Not mowed End 1 Not mowed Boundary Not mowed Not mowed 2 Not mowed Not mowed Obstacle Not mowed 3 Not mowed Not mowed Not mowed Not mowed Table 4 5 4 2 Example grid showing node characterizations From this example the lawn mower starts at node 0 0 and needs to travel to node 0 3 The A algorithm determines the path as shown in the next figure 74 Figure 4 5 4 2 A A path search example Note that in the A node example above that there are multiple paths that are searched The shortest route is shown by the red arrow paths It is important to note that there are two possible quickest routes in this example The algorithm w
104. g the source is accurately quoted and duly credited The CSE 466 Web 1993 2012 Department of Computer Science and Engineering University of Washington Administrative information on CSE466 authentication required 134 qi B Requesting permission to reprint images Joseph Corteo lt josephcortea gmail com gt Apr 22 1 day ago ies to jan dyre bjerk Hello I am an Electrical Engineering student at the University of Central Florida am researching various techniques for navigating mobile robotic platforms am requesting permission to reprint Figures 1 4 and 6 from your paper Low Cost Ultrasonic Positioning System for Mobile Robots Thank you Click here to Reply or Forward amp Ashford edu Build your future today Ads Why this ad Earn your Bachelor s or Master s degree online from Ashford University Learn more Requesting permission to reprint images Inbox x image Permissions x Joseph Corteo lt josephcorteo gmail com gt Apr 22 1 day ago to johannb Hello I am an Elecrical Engineering Student at the University of Central Florida am researching navigation techniques for mobile robotic platforms am requesting permission to reprint ps aug A from oe paper ee ane Poning and Sensors and Techniques soruce http oai_ ai oa b ge adataPrefix html amp identifier ADA422844 Thank you Johann Borenstein Apr 22 1 day ago ea to me Joe grant you permission to reprint these
105. gn For prototyping a standard laptop was used by the computer vision camera to simplify the overall design Additional ideas that were not implemented in the final design included the mower executing its cutting routine in accordance with this schedule and returning to its charging station upon completion of its task or when the onboard batteries have reached critically low levels In addition a precipitation sensor would be implemented to monitor the amount of precipitation in the area If the threshold values are exceeded the mower would return to its sheltered charging station to protect its electrical components from water damage In addition to ease of use through automation the goal of this project was to create an autonomous lawnmower that is both accurate and efficient A majority of current commercial products sweep the area enclosed by the buried perimeter wire in a random 2 fashion Once the mower reaches the perimeter of the yard it rotates at a set angle and proceeds in a straight path until it encounters a boundary location once more at which point the process repeats itself It is apparent that such a method could become quite inefficient due to a variety of factors For instance unnecessary redundancy would most likely occur in which the mower continually passes over a previously cut section of the lawn To eliminate this problem the initial design was that mower would keep track of its previous positions during the current
106. gulator HMC5883L Digital Compass 12V 33 35Ah 12V 33 35Ah Sealed Lead Sealed Lead Acid Battery Acid Battery Figure 5 6 A Final Schematic of overall system 114 6 Project Prototype Construction and Coding 6 1 Interfacing Subsystems with Mower Chassis To integrate the automated lawn mower s subsystems into the current chassis only a few steps needed to be taken First the existing push bar and safety lever needed to be removed The leads going to the safety lever can then be cut and wired to a relay The microcontroller controls the relay allowing the cutting blade motor to be turned on and off independent of the rest of the automated mower s systems The battery for the cutting blade motor remains intact exactly like it came from the factory Figure 6 1 A Example of chassis extension Reprinted with Masato Hayashi s permission To integrate the motor platform onto the existing electric lawn mower chassis the original rear wheels are removed and an extra 1 5ft section was attached to the back of the chassis The section was made out of steel and was attached via elbow brackets This extra platform not only holds the two DC motors via custom brackets but also holds the two batteries that were used to drive the DC motors The enclosure for all the automated mower s electronics was also mounted onto this platform and all the electronics were powered by the two 24 volt batteries 6 2 Docking Station The dock
107. gure 4 7 1 B Conic docking station Reprinted with permission from Silverman et al A second docking station reference design comes from Cassinis Tampalini Bartolini and Fedrigotti from the University of Brescia in Italy For their design robot vision was also used as the primary method in completing the docking procedure On the docking station they mounted two lights along the center line of the docking area These two lights were mounted in a manner that had one light higher than the other A camera on the robot is used to detect the docking station lights using techniques from robot vision to accomplish the docking procedure The docking station used in this reference project is shown below Figure 4 7 1 C Docking station using two lights Reprinted with permission from Cassinis et al 86 By using a two light system the robot is able to align itself properly before entering the actual docking area If the robot is pointed straight on at the docking station and aligned so that the center of the robot is aligned with the center of the docking area then the cameras would locate the two lights one directly above the other Should the robot be misaligned in any way the two lights would veer from this alignment thereby alerting the system that it is not properly aligned A robot vision and alignment algorithm is programmed into the device to handle this docking procedure For this design the physical design of the docking station wo
108. h each frame of the live feed If the blob is becoming smaller and is moving across the screen in the vertical direction it can deduce that the lawn mower is moving away from the camera in the direction of the camera s field of vision Using this information and comparing this to the data from the encoders an absolute position can be determined 5 3 Design Summary Obstacle Avoidance Subsystem The obstacle avoidance subsystem for this project takes inputs from various sensors which are interpreted by the software The three sensors used in this subsystem are the proximity sensor the collision sensor and the precipitation sensor Used in conjunction these three sensors provide that data required for the lawnmower to avoid any hazards while performing its functions A proximity sensor was the primary device used in the obstacles detection and avoidance subsystem For this project an ultrasonic sensor was used to detect impeding objects This sensor was mounted onto the front of the lawnmower so that it can detect the obstacles while the mower is moving forward To accommodate an appropriate stopping and turning distance the ultrasonic sensor should be able to detect objects directly in front of the lawnmower 0 0 inches up to a distance of about 24 inches In addition the sensor should be able to detect objects with a width of approximately 2 inches or greater For this project the Maxbotix LV EZ1 was determined to be the best ultrasonic
109. he final docking station design has the added benefit of simplicity low cost and light weight The frame of the docking station would be made with wood with the electrical contacts mounted onto the back panel Simple orange balls such as a ping pong ball can be used for the orange alignment spheres This design would not weigh a considerable amount making the docking station easy to place in any position that the end user desires This could enable the design to achieve the goal of being easy to use with little work involved At the same time the docking station design would be durable enough to withstand repeated charging Unfortunately the docking station was not used since it would require tracking the coordinates of the mower which became an issue because of various inaccuracies 4 7 2 Electrical Design The overall electrical design for this project has most of the design considerations in concerning the battery to power the device and its subsystems The mower system includes two main components in the blade motor and drive motors that each requires a large amount of power to run In addition to these main components the autonomous lawnmower consists of further electronics in sensors and microprocessors that would also consume power Appropriate design considerations had to be made to account for the power needs such that the lawnmower can complete mowing the lawn before the battery power empties Once the battery has been selected a voltag
110. he final printed circuit board design The recharging of the batteries involved a few steps that were handled in the software application Before charging the lawnmower needs to successfully connect with the charging station This is accomplished by locating and then docking with the station under proper alignment The overall program flow for the docking procedure is shown in the figure below 112 Figure 5 5 A Software flow chart for docking procedure The docking procedure is broken down into several functions The first function is called locatemarkers This function finds the marker and notes their two dimensional vertical and horizontal positions These positions are stored in variables and continuously updated as the lawnmower moves during the docking procedure This information is then sent to another procedure called checkalign to determine is the vehicle is in proper alignment This is simply done by checking the horizontal values of each marker position to see if they are equal If they are equal then the lawnmower is aligned This procedure has a simple output of 1 if the lawnmower is aligned and 0 otherwise These functions are summarized below void locatemarkers inputs rear camera information outputs two dimensional positions of alignment marker 1 and 2 void checkalign inputs two dimensional positions of alignment marker and 2 output is_aligned flag Upon successful completion of the docking
111. he mower accordingly Thresholding could be used for the overall image as a whole to detect obstacles The algorithm for detected edges scans each pixel and when there is a change in color intensity above a certain threshold it is marked as an edge The resulting image on the right is printed The coordinate values of those obstacles could be saved Once the mower is moving its position could continuously be compared to the coordinate values of the detected obstacles A threshold could be set for the comparison of the mower s value and the edge value to begin getting ready to move after it has approached the obstacle close enough to a minimum value This flow chart illustrates the Edge Detection algorithm which can be used to detect obstacles and edges in the lawn 34 Read in input image Set threshold values Prepare output images Scan and scale each pixel Perform edge detection Figure 4 3 3 4 B Edge detection flowchart In this diagram it considers three cases of edge detection a low threshold value a high threshold value and a gradient or sobel threshold value This code sets high and low threshold values and prepares output images This segment verifies the image is able to be opened and scans each pixel of the image assuming it is 255X255 pixels and scales each pixel for pixel intensity values After scaling the code sets a double array for output images The first thresholding approach uses a gradi
112. he recharging can be done properly By creating a slotted connection on the charge plate connectors the metal bars on the lawnmower should fit snugly into the docking station This should ensure proper charging conditions Coding for the docking station should be done to control the docking and charging procedures The software should read data from the camera and use this information to interpret the location of the markers Alignment algorithms should be coded into the processor to allow for proper docking Once the lawnmower is docked appropriate programs would need to be written to allow for charging initializing and then termination when complete 7 Project Prototype Testing 7 1 Maintaining Straight Path and Executing 180 Turn To test the drive system the lawnmower first needed some basic tests Testing the mower s ability to maintain a straight path and execute a 180 degree turn is beneficial to prove the functionality of the drive system To accomplish this a testing procedure is provided 1 At the beginning of the run measure the absolute position and optionally orientation of the vehicle and initialize the onboard odometric starting position to that position 2 Run the vehicle through a 4x4 meter square path in the clockwise direction making sure to a Stop after each 4 meter straight leg b Make a total of four 90 degree turns on the spot c Run the vehicle slowly to avoid slippage 116 3 Upon return to the
113. icers of the parties have executed a special agreement specifically governing such use Only those TI components which TI has specifically designated as military grade or enhanced plastic are designed and intended for use in military aerospace applications or environments Buyer acknowledges and agrees that any military or aerospace use of TI components which have not been so designated is solely at the Buyer s risk and that Buyer is solely responsible for compliance with all legal and regulatory requirements in connection with such use TI has specifically designated certain components as meeting ISO TS16949 requirements mainly for automotive use In any case of use of non designated products TI will not be responsible for any failure to meet ISO TS 16949 139
114. images Johann Dr Johann Borenstein Research Professor The University of Michigan 3765 Bob amp Betty Beyster Building 2260 Hayward Street Ann Arbor MI 48109 2121 Ph 734 763 1560 Fax 206 203 1445 Internet eMail johannb umich edu Homepage www umich edu johannb 135 MB1010 LV MaxSonar EZ1 Image Permission 4 Tom Bonar thomas maxbotix com p 4 Monday April 22 2013 3 16 PM To joppel foppel knights ucf edu ca info maxbotix com Attachments LV MaxSonar EZ 3d jpg 997 KB Jason Thanks for the email am glad to assist you with your questions Please see my remarks below in black text 0 A B ations You state I would like to request permission to use an image of the MB1010 L V MaxSonar EZ1 that appears in the datasheet for said iter You are given permission to use the image on a paper for your senior design project If you would like have attached a high resolution photo of the LV MaxSonar EZ sensor If you need any other images on the bottom of the MB1010 product page there is a download link for all the LV MaxSonar EZ photos The download is entitled High Resolution Pictures zip We thank you for taking the time to request permission to use the sensor s photos for your project Please let me know if you have any questions Best regards Tom Bonar Technical Support of MaxBotix Inc Phone 218 454 0766 Fax 218 454 0768 Email thomas maxbotix com Web www maxbotix
115. ing station from the initial design was to be designed such that its construction is simplistic The main section of the docking station was three wooden boards that surround the lawnmower On the back board an electrical contact plate would mounted for charging This plate is wired to the charger such that it can be plugged into a wall 115 outlet The sides of the docking station should be angled away from center to allow for slight errors during docking The angle should be no more than 10 degrees away from a right angle No other construction modifications would be necessary as the docking station only needed to provide a platform for the recharging process The docking station should be built securely enough to withstand direct impact from the lawnmower while moving at drive speed Directly aligned with the center of the back board of the docking station an extension needs to be placed that rises vertically This extension should rise approximately 2 feet above the docking station Half up that extension a small platform should come out a few inches On this platform and at the top of the extension are the areas where the alignment markers are to be placed The alignment markers can be orange ping pong balls secured to these areas This extension with markers can be shown in figure 4 7 3 2 B earlier in this document The charge plate should be aligned to match the contact bars on the rear of the lawnmower This connection needs to be secure so t
116. ison of different motor controllers that are capable of sustaining at least 20 amps of continuous current to a DC motor Sabertooth 2x25 SyRen 25A Driver SyRen 20A Driver Base Price 124 99 74 99 74 99 Number of Channels 2 Continuous Current at 24V DA RA S Peak Current 50A 45A 30A Regenerative Drive Yes Yes Yes Thermal Protection Yes Yes Yes Overcur rent Yes Yes Yes Protection Lithium Protection Mode Yes Yes Yes Analog Input Yes Yes Yes Serial Input Yes Yes Yes Weight Rating of 300lbs 180lbs 180lbs Robot Table 4 6 1 Spec Comparison of Different DC Motor Controllers 76 The Sabertooth 2x25 is the obvious choice after looking at the table above Both of the other motor controllers required the purchase of 2 in order to control both motors since they are only design to handle one motor each In addition to the price difference having two separate motor controllers would occupy more space within the electronics housing and produce more heat which would affect other electrical components negatively With the feature set on the Sabertooth 2x25 motor controller there are five different methods used to control the motors The first is analog control a OV to 5V analog input is connected to terminals S1 and S2 OV is full reverse 5V is full forward and 2 5V is stop The second method for controlling the motors is through an R C input mode This allows the motor controller to be us
117. l Sunday April 21 2013 1108 PM To isidor buchmann cadex com I would like to request permission to use an image of the comparison table of secondary batteries that appears on the batteryuniversity com website at http batteryuniversity com learn article secondary batteries If permission is granted this image and table data will be used in a design paper for a senior design project at University of Central Florida If you could respond to this request it would be greatly appreciated Thank you Jason Oppel Student UCF Texas Instruments Incorporated and its subsidiaries TI reserve the right to make corrections enhancements improvements and other changes to its semiconductor products and services per JESD46 latest issue and to discontinue any product or service per JESD48 latest issue Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete All semiconductor products also referred to herein as components are sold subject to TI s terms and conditions of sale supplied at the time of order acknowledgment TI warrants performance of its components to the specifications applicable at the time of sale in accordance with the warranty in TI s terms and conditions of sale of semiconductor products Testing and 138 other quality control techniques are used to the extent TI deems necessary to support this warranty Except where mandated by
118. locate these boundaries and keep the vehicle in range The iMow also used a digital compass to control its route bearings as well as ultrasonic sensors to detect and avoid obstacles The drive system was powered by two independent rear wheels with one freely rotating castor on the front The autonomous lawn mower design from TUPU Fort Wayne was developed by a combination of electrical and mechanical engineers Their design documentation had a lot of project fabrication details and images that should prove helpful during the building stage For obstacle detection the IUPU design used a combination of an ultrasonic sensor and collision bumper sensor to detect obstructions The location and route detection was solely based on the use of wheel shaft encoders in conjunction with a digital compass to measure and track relative distance and direction Their conclusions from the design were that encoders and a compass alone are not effective enough to track the autonomous vehicle Small errors in drift can accumulate over time resulting in an ineffective method for tracking the device Ideas can be used from this design but improvements in location tracking are necessary to develop the design The drive system for their design was powered by two independent rear wheels with two freely rotating castors on the front The last similar design that was evaluated was from CSU as a design project that was entered into an autonomous lawn mower competition Their desig
119. lthough many methods exist for controlling 24VDC motors the two most simplistic ways for controlling a motor are through the use of an H bridge or by using a manufactured motor controller The first method for controlling DC motors is through the use of an H bridge This is the cheapest way to control a DC motor since a set of high current switches may only cost about 50 but it has its disadvantages An H bridge is built with four solid state or mechanical switches By only closing switches 1 and 4 see illustration a positive voltage is achieved across the DC motor If switches 1 and 4 are opened and switches 2 and 3 are closed the voltage across the motor is reversed which allows for operation of the DC motor in reverse Positive Voltage Switch 1 Switch 2 Motor Switch 3 Switch 4 Negative Voltage Figure 3 3 5 A Example of an H Bridge circuit 21 The disadvantage of using an H bridge is that the amount of current that flows through the switches is all or none This means that the motor is full on when the switches are enabled This makes for less precise control of the DC motor s speed and can be problematic if the motor runs at too high a RPM for the desired application when powered on The switches can be controlled with a simple truth table programmed into a microcontroller that enables and disables the switches depending on whether the motor voltage is to be forward biased forward operation reverse biased oper
120. ltrasonic proximity sensors the autonomous lawnmower can easily detect obstacles preventing any number of unfortunate mishaps The data collected from the navigation and obstacle avoidance systems is evaluated by an embedded microcontroller Using established path algorithms an efficient route for mowing the lawn while avoiding obstructions is mapped A feedback loop design is used to continuously monitor and adjust this path This data is fed to the drive system of the lawnmower through the drive motor controller The data passed to the motor controller enables forward and reverse motion braking and steering used to maneuver the autonomous lawnmower The power system of the project is designed to allow the lawnmower to execute long enough to complete its function The final design of the project was done in a manner to keep the final cost of the project as low as possible The group members were fully responsible for the financial responsibilities of the project design due to an inability to secure outside funding or sponsors for the project A budget for all the parts used was created to help keep the costs manageable 2 Project Description 2 1 Project Motivation The primary motivation for this project is to remove the chore of mowing your lawn By creating a lawn mower that handles this task autonomously the user is freed from this physically demanding and time consuming task The projected design helps those with physical limitations who c
121. mbal Assembly Reprinted with permission from Eric Jones The disadvantage of using an inertial measurement unit instead of a global positioning system to track the location of a vehicle is that inertial measurement units are prone to positional drift This is due to small errors in the inertial measurement unit s measurements Since the position is always derived from previous data the longer the inertial measurement unit is used to calculate position the more errors are accumulated 20 This is why most navigational systems have additional sensor and components to correct for this error including global positioning satellites and magnetic compasses The automated vehicle would use a combination of an inertial measurement unit along with various other inputs including triangulation data wheel shaft encoders and possibly even a webcam tracking system The inertial measurement unit would supplicate the other sensors and be used primarily as a redundancy This would be another layer of navigational data that the automated vehicle would have access to in order to ensure that the navigational information and position of the automated vehicle is as accurate as possible Since the degree of precision is quite high a deviation of a few inches would result in strips of grass not being mowed or mowing in unwanted locations such as plants and flower beds so the inertial measurement unit is crucial as a redundancy 3 3 5 Methods of DC Motor Control A
122. me Corteo E Mail fjosephcorteo gmailcom Hello I am an Electrical Engineering student at the University of Central Florida I am requesting to reprint the schematic diagram from the Create a MaxStream Zigbee 5v Interface Using a SParkFun MaxStream Breakout board Type 3 PDF in Message my senior design documentation Thank you PDF link http dilnmhSip6v2uc cloudfront net datasheets Wireless Zigbee maxstreaminterface3 pdf 129 Send 0 kw amp amp 4 B Options Draft autosaved at 4 31 PM To masato2525 facebook com Co Subject ION Robotic Lawnmower Image Permission Tahoma 10 B Ful Ft A I would like to request permission to use the CAD drawings of the back of your mower chassis that you have in the ION Robotic Lawnmower Competition PDF The images will be used in a design paper for a senior design project at University of Central Florida Thank you Andrew Cochrum E mail Us First Name Andrew Last Name Cochrum Email andrewc knights ucf edu Order No Phone State Florida Question Other would like to ask your permission to use the product images of the a Toro 20360 the Recharge Mower PMLI 14 and the GreenWorks Your Message 25312 The images will be used in a design paper of a senior design project at the University of Central Florida bs Receive Weekly How To Tips amp Specials o
123. me as possible For most mobile robot positioning applications two techniques are utilized one from each of the following groups e Group l Relative Position Measurements Dead Reckoning o Odometry o Inertial Navigation e Group 2 Absolute Position Measurements Reference Based Systems o Magnetic Compasses Active Beacons GPS Landmark Navigation Model Matching O O0Oo0o The remainder of this document will go through each of these techniques and discuss the strengths and weaknesses associated with each method when applied to the positioning of a mobile platform 3 3 1 1 Odometry Odometry provides good short term accuracy is relatively inexpensive and usually has very high sampling rates Keeping the budget for the autonomous lawn mower to a minimum is paramount making the low price point of this technique a very attractive feature Since integration of incremental motion information over time is implemented to calculate the distance travelled by the unit an accumulation of errors would be present in the measurements produced which would be exacerbated by the odometer s intrinsic high sampling rate This error becomes greater as the distance travelled by the mower increases which results in a proportionally reduced accuracy by the end of the mower s session of operation This also applies to orientation errors which causes large lateral position errors and would increase proportionally with the distance travelled by
124. microcontroller is connected to S1 and the microcontroller s receive line is not connected to the Sabertooth 2x25 More than one Sabertooth 2x25 can be connected to 83 the same serial transmitter because packetized serial uses an address byte to select the target device void DriveForward char address char speed Putc address Putc 0 Putc speed Putc address 0 speed amp 127 Microcontroller Figure 4 6 3 2 B Example of multiple motor controllers connected to a microcontroller using packetized serial commands Reprinted with permission from Dimension Engineering So in the above function if the address is 130 the command is 0 for driving in a forward direction and the speed is 64 the checksum should be calculated as the following 130 0 64 194 194 in binary is then 0b11000010 0b11000010 amp 0b01111111 0b01000010 Once all the data is sent this would result in the motor controller with address 130 driving forward at about half speed 4 7 Power Subsystem As with any product with electrical components the power subsystem is in control of making this project go For this project the power subsystem design is broken into two main subsections the battery required to run the project and keeping that battery charged and the voltage regulation circuit required to supply the required power needed by each electronic device Since this project uses a rechargeable battery to power th
125. motors simple brushed DC motors would do the job Availability and cost tend to limit the 78 choices when it comes to selecting a type of brushed DC motor for this reason wheelchair motors are the most practical In this design two 24 volt DC wheelchair motors are ideal in order to provide plenty of power to get through tall grass with no problems as well as steer the automated lawn mower The automated lawn mower is steered by operating the motors in opposite directions this is also known as differential steering and can be easily done with DC motors and a motor controller Below is a comparison between several different motors AmpFlow E30 Mars Brushless NPC T64 NPC 150 G PMAC Motor 41250 Base Price 249 00 450 00 330 93 181 64 fae ake 1 0 15 0 0 7 0 25 Motor Type Brushed Brushless Brushed Brushed Motor Diameter 3 1 in 8 in NA NA Geared Yes No Yes Yes Reduction Ratio 8 3 1 NA 20 1 34 1 Peak Torque 360 in lbs ka ae per 300 in Ibs 100 in Ibs Nominal Voltage 24V 24 48V 24 36V 12 24V No Load RPM 670 3500 230 174 Weight 7 1 Ibs 22 Ibs 13 Ibs 7 5 lbs Table 4 6 2 Spec chart for brushed and brushless motors 79 Table 4 6 2 shows a wide variety of brushed and brushless motors however most of these motors are quite overpowered for driving a 100 to 150 lb automated lawn mower This is why the NPC 41250 was chosen to drive the chassis Low RPM makes the motor easier to control and all
126. mount of control The datasheet and documentation provided by the manufacturer is detailed and informative 68 The SREFO04 ultrasonic sensor consists of 4 pins like the HC SR04 5V Ground Trigger Signal Echo Signal It has very similar specification to the Parallax PING ultrasonic sensor Compared to the PING sensor the extra pin does allow for easier communication as there is no bi directional pin It is also slightly cheaper than the PING sensor However the PING sensor is easily available without shipping costs and has a vast amount of technical documentation available Figure 4 5 1 4 Maxbotix LV EZ1 ultrasonic sensor Reprinted with permission from Maxbotix Based on gathered information the Maxbotix LV EZ1 was used for the obstacle avoidance subsystem This sensor is desirable due to a variety of factors It has a wide input voltage range low current draw a considerable amount of user control and a price in line with other sensors The HC SR04 is considered due to its low cost but its inadequate documentation makes it less attractive 4 5 2 Collision Sensor The main method for avoiding collisions was provided by the ultrasonic proximity sensor design as described in the previous section As an added bit of redundancy an extra collision sensor was added to the project design This adds an extra safety feature to the lawnmower to help prevent the mower from running over an object in case it is missed by the proximit
127. mower is capable of sensing this buried wire so that it knows when it hits the boundary While cutting the lawn the mower travels in a straight path until a boundary is reached Once that happens the mower stops and rotates at some specified angle back towards the unmowed lawn This process repeats where the mower reaches a boundary turns and cuts some more It is easily recognized that this cutting procedure is purely random and fundamentally inefficient The similar commercial products show that there is room for a better and more efficient autonomous lawn mower Existing products can be greatly improved upon by improving the cutting route algorithm By creating a process that plans the mowing path in a better 6 manner the lawn can be cut much faster therefore using less power In addition an improved design can be created to avoid having to bury the boundary wires Burying wires should be avoided to minimize work by the end user and eliminate the frustration of measuring and placing the cables A better location tracking method can be implemented using any number of relevant technologies that are available 3 3 Relevant Technologies 3 3 1 Techniques and Sensors Used in Mobile Robot Positioning Systems To calculate and monitor the position of a mobile platform a combination of methods and sensors should be implemented in conjunction with one another to insure accuracy whilst providing fast computation rates i e as close to real ti
128. n Bumper System To handle the bump detection a mounting addition is necessary for the lawnmower design This mount would hold the switch for collision detection and act as a bumper for the system This bumper needed to extend past the front of the lawnmower wheels so that the bumper switches are the first point of impact should the lawnmower make an impact with the obstacle The bumper should be low enough to make an impact with short obstructions but not mounted so low that it impacts the ground should the terrain undulate The only additional specification of the bumper design is that it needs to be secure enough to handle direct impact from a collision A simple metal bar provided the foundation of the bumper system The switch is mounted to the front of the bumper bar to process the initial point of impact The bumper bar was then bolted to the front of the lawnmower frame providing a secure connection to manage impact A design prototype of the bumper system can be viewed in the image below Figure 4 5 2 2 A Bumper switch mount Reprinted with permission from Vex Robotics To facilitate impact from more than one location two bumper switches were used and mounted to the bumper bar one on the left side and one on the right side This enables the lawnmower to more accurately detect a collision while still keeping with the same simple design 70 4 5 3 Precipitation Sensor The project was initially designed to be equipped with
129. n be programmed to perform simple movements such as turning right left stopping or reversing 4 3 5 Flow Chart The flow chart in Figure 4 3 5 A shows the general program flow for the project Input data is sent to the microcontroller from the wireless receiver compass ultrasonic sensor and rotary encoder This information is processed by the microcontroller to determine the path to be traveled by the mower After calculation the microcontroller sends signals to the motor controller to move the wheels Wireless receiver Positioning from computer vision Input angle Microcontroller Binary signal sent Input distance of obstacle to motor controller Uses input angle obstacle avoidance and relative distance Uses threshold to compare absolute values from wireless receiver Output digital signal to motor controller to move mower in appropriate direction Motor controller Ultrasonic sensor Input number of rotations Rotary encoder Figure 4 3 5 A Overall flow chart showing sensor inputs to microcontroller 4 4 Navigation Subsystem 4 4 1 Overview There is no single commercially available component digital or otherwise that can accurately deduce the location of a mobile platform in real time that is within the budget or scope of the project Most autonomous robotic platforms employ a navigation 47 subsystem that consists of a collection
130. n was different from the other three in that it used computer vision techniques in edge detection to locate the boundaries of the mowing area In addition wheel shaft encoders were used to improve the location tracking system For obstacle avoidance this group used infrared range finders instead of ultrasonic sensors to detect obstacles in the mower s path The same drive system as the other similar designs was used in this model After reviewing the similar designs a wide range of useable technologies are discovered which can be researched further By reading the conclusions and results of these projects information has been gleaned on areas that can be improved or modified This information helps in to move the research forward in a productive fashion 3 2 Existing Commercially Available Products There are some limited options available in the market today for consumers that wish to purchase a fully functional autonomous lawn mower These commercial applications are relatively expensive but promise to fully automate the yard cutting process Some of the products available at this time are e Tango E5 by John Deere e RL555 RL855 RL2000 by Robomow e Robotic Lawnmower by LawnBott All of these commercially available lawnmowers function in the same manner Using a buried cable system in which the lawnmower user buries wire delineating the lawn boundaries the lawn is inherently mapped so that the mower can stay within its confines The lawn
131. ng belt This would increase the resolution of the encoders by a factor that is dependent upon the pulley diameter ratio between the wheel and encoder shafts The resolution can be increased even further through the use of X2 double n base resolution and X4 quadruple logic via the software running on the ATmega328 This is the main reason why this particular model was chosen since the resolution can in theory be increased to that of more expensive options on the market through some mechanical and digital manipulation The ultrasonic distance sensor was used to detect obstacles in the path of the autonomous lawn mower during its operation This is an added safety measure to ensure that any obstructions that were not detected by the computer vision software would be successfully avoided It was chosen for its low price point and impressive sensitivity The compass module was chosen over its more advanced counterpart HMC5883L since the latter included a built in 3 axis accelerometer to compensate for measuring the vertical component of the Earth s magnetic field when the module is not parallel to the ground Normally this would be desired however since this compass was mounted on the lawn mower chassis it was subjected to high levels of vibration causing the CMPS10 model to experience excessive noise regardless of horizontal orientation The Wi Fly module was chosen over its competitors for its low current consumption when receiving data th
132. ng position coordinates would be used to calculate the new values as the mower moves The following block diagram illustrates the hardware of the encoders and compass that were initially going to be used to calculate these values Two Wheel Input value num_rotations Input value Encoder direction Microcontroller Figure 4 3 3 1 A General Interfacing of Wheel Encoder The microcontroller could then have a calculated value for a reference point However this point may not always be accurate In order to verify accuracy of a current position of the mower absolute positioning was also necessary Absolute positioning was done using a camera suspended on a pole and connected to a laptop with a WiFly module on the microcontroller and a router The following block diagram illustrates the original absolute positioning implementation in this design before the use of WiFly was considered 31 Microcontroller input absolute position value Camera on pole Figure 4 3 3 1 B General Interfacing of Wireless Communication 4 3 3 2 Thresholding for Location According to the above block diagrams there are two methods for detecting a point for the mower The absolute positioning used by the camera is used to verify accuracy For the most part the reference value could have been the value that is referred to in order to detect a point Moreover thresholding could be very necessary between the two values the absolute and the refe
133. ng selected would be low power but no lower than 5V to be reasonable for the power needed Also we wanted to select a microcontroller that could be programmed in an understandable language such as C so debugging would be easier Implementing functions is also simple with C programming which would be necessary for this design The VEX Cortex microcontroller is designed for robotic applications which is related to this design It has wireless capabilities which would facilitate the navigation subsystem and enable wireless debugging wireless downloading and wireless driving Motor parts could be connected to the available ports for the drive subsystem And the smart sensor port can be used for the obstacle avoidance subsystem for the various sensors needed It is also easily programmable with C Although the VEX Cortex Microcontroller is user friendly and capable for the design the cost is 250 00 which is above our original budget So we could explore another option The MINI MAX 51 C2 is a popular microcontroller subsystem This microcontroller is very scalable for programming and able to be programmed in C It also includes software options such as the Micro C compiler The DC regulators can also be used to power the sensors in the obstacle avoidance subsystem Although RF is not built in it can be connected and programmed with the available ports This microcontroller also contains numerous serial features However only few are needed in this d
134. not needed this approach can be possible to create more ports Finally Figure 4 3 4 1 D shows a diagram of the multiplexor approach This is used for output only signals 40 n signals select bits Multiplexor Figure 4 3 4 1 D Multplexing log n select bits Schematic Reprinted with permission from Department of Computer Science and Engineering University of Washington This approach creates n output signals from log n select bits This could be very necessary for signals for the motor controller if extra signals are needed In our design we have basic movements that would be signaled according to different binary signals However the design might need to enable the motor controller to do additional turns and movements which would require additional signals to accommodate a larger bit sequence For example a 4 bit sequence would enable 16 signals as opposed to 2 bit sequence that would only enable 4 signals An easier approach to create more ports is the use port expansion units port expansion Figure 4 3 4 1 E Port Expansion Schematic Reprinted with permission from Department of Computer Science and Engineering University of Washington Port expansion units would simplify the design since it can create multiple ports with a simple connection For this design multiple port expansion units could be used if needed to accommodate inputs and outputs The only drawback of port expansion units is that it may not support in
135. ns with 00 it knows that it is either in the middle of computing a value or is being reset Sending this signal would ensure that the microcontroller doesn t receive redundant compass reading that would cause the inaccurate results When the microcontroller is ready for the compass to read a value it sends a signal data 1000 to the compass As long as the microcontroller sends a signal that begins with 10 the compass is signaled to start a measurement After the compass receives the signal to begin measuring it takes about 30 to 40 ms to actually compute the value This would need to be considered if a consistent measurement is needed Too much delay may cause the current angle value to be inaccurate As long as enable is low the compass is in operation After the compass has completed its measurement it sends it back to the microcontroller The compass would send a reply 1100 to indicate that the measurement is complete and there were no errors 00xx if the compass is still in process and xx01 is the enable did not receive a signal Simple programming code from can be used to measure an accurate angle and to implement the software for reading compass angle values The pseudocode above would be used to convert the angle to the relative calibrated direction being considered 4 3 4 3 Connecting Rotary Encoder In addition to the compass readings the rotary encoder is an input device to the microcontroller to determine speed and direction
136. nvert the difference in power to heat like linear regulators and therefore have power efficiencies of up to 95 Like linear regulators the requirements of this project would also be met using switching regulators The input power supply and output power requirements fit into the specifications of readily available switching regulator parts Many current electronic devices using microprocessors use switching regulators so existing circuit designs could easily be manipulated for use in this project The benefits of using switching regulators lie mainly in their power efficiency Switching regulators are also readily available as complete ICs and would therefore be easy to integrate and implement into a circuit design The main disadvantage of switching regulators is that they can produce electric interference due to their utilization of inductors and can have a ripple voltage These can easily be compensated for using proper shielding and filtering For this project switching regulators provided the most benefit and was therefore used in the design Because the lawnmower was powered by a rechargeable battery power consumption needed to be held accountable and excess power loss should be limited For this reason the inefficiency of linear voltage regulators was not desirable for this project 24 4 Project Hardware and Software Design Details For this project there were many options and choices that were made to choose particular parts and
137. o to propagate returning a pulse that has a width equal to the time it took for the ultrasonic chirp to travel to the target and bounce back to distance sensor see Figure 4 4 4 A Thus to determine the distance from the front of the mower where the sensor was mounted to the obstacle is simply a matter of measuring the length of time the return pulse remains high multiplying by the speed of sound the constant can be adjusted with the addition of a simple digital thermometer input further increasing the accuracy of the calculations and then dividing this product by two 57 mt tout gt E iN MiN t thotvorr Lal tin max gt gt Sv SIG pin Ov Sonar TX gt tgurst Figure 4 4 4 4 Timing diagram of the PING ultrasonic distance sensor input output signal Reprinted with permission from Parallax Inc Similar to the CMPS03 compass module the PING ultrasonic distance sensor was tested using an Arduino Uno development board equipped with an ATMega328P microcontroller The code established a serial connection with the host computer polling the keyboard for a lowercase p input Once it received this character it would execute the ping subroutine until it encountered this letter again breaking from the subroutine and returning to its idle state The ping subroutine handles the pin used to interface with the distance sensor It initially configures digital pin 7 connected to the SIG pin on the sensor
138. of gravity Center of gravity cow T e cluster Pi 250 onamo a ma maas YW Figure 3 3 1 A Typical results from running UMBmark for a total of five trials with an uncalibrated TRC LabMate Robot Reprinted with permission from Dr Johann Borenstein Y mm m Center of gravity of cw runs B after correction 100 150 X mm 200 250 enter of gravity of ccw runs after correction Before correction cw Before correction ccw After correction cw m After correction ccw Figure 3 3 1 B Position errors after completion of the bi directional square path experiment 4 x 4 m Reprinted with permission from Dr Johann Borenstein From the centers of gravity computed above Xcg cw ccw and Yeg cw ccw the aforementioned correction constants expressed as Cy and Cr for the left and right wheels respectively can be calculated According to the designers of the UMBmark the two prevalent causes for systematic error are unequal wheel diameters and the uncertainty about the effective wheelbase In most cases the error introduced by unequal wheel diameters is far greater than that of the effective wheel base thus the latter is considered negligible and is not included in the calculation of C and Cr as will be seen shortly 10 Referring to Figure 3 3 1 C c is the curved path taken by the mower due to the left and right wheels having unequal diameters Using simple geometric relations the radius of curvatur
139. of information the absolute xy coordinates of the lawn mower itself the boundaries of the lawn and any static obstacles within the perimeter of the lawn This was then transmitted wirelessly to the WiFly module aboard the lawn mower chassis From the original design these xy coordinates perimeter demarcations and static obstacle locations would then be passed to the microcontroller to establish an overall layout of the area to be traversed The absolute position as seen by the USB HD Webcam would then be compared to the linear distance travelled between any two points as measured by the rotary encoders affixed to the two drive wheels As previously mentioned the odometry data dead reckoning combined with a fixed xy coordinate system absolute positioning would minimize the error between the calculated and actual position distances travelled of by the lawn mower The magnetic compass would provide the microcontroller with a sense of direction possibly reducing the complexity of the code implemented for certain maneuvers such as a 180 degree turn The ultrasonic distance sensor provided the microcontroller with real time awareness of obstacles that are present in the path of the lawn mowers intended route This provided an extra layer of protection against collisions with obstructions especially with obstacles that for whatever reason the USB HD Webcam has failed to see and pass on to the microcontroller in the initial viewing of the landscape
140. of sensors that compensate for each other s weaknesses This approach provides e redundancy If a particular sensor is experiencing an excessive amount of noise at any point during the lawn mowers operation the other sensors would be referenced with greater emphasis during this period until the noise has fallen below a pre determined threshold e scalability If the lawn mowers navigation about the terrain is not satisfactory additional sensory input can be implemented or removed if one proves problematic e accuracy As opposed to taking navigational data from a single source the microcontroller driving the wheels would be able to correlate data from multiple sensors ensuring any errors are minimized before computing the movement path of the lawn mower e reduced cost The group of sensors employed usually have a cumulative price tag that is lower than that of a pre built out of the box component It is common practice to implement a navigation system that utilizes two forms of positional data acquisition relative position measurement otherwise known as dead reckoning and absolute position measurement involving referenced based calculations As mentioned above the goal of this multi faceted system is to develop a noise insensitive environment for performing navigational calculations which can be achieved using this approach Components that utilize odometry and or inertial navigation such as encoders and inertial measurement units
141. of the components of the subsystems leads to the printed circuit board design The schematic of the overall system is shown below which was overall used in designing the PCB with the exception of the unused devices such as the encoders 99 1 2 3 4 5 7 8 9 Hp NHO RN XV Figure 4 8 A Schematic of overall system 100 5 Design Summary of Hardware and Software 5 1 Design Summary Computational Subsystem The selected microcontroller AtMega328 was able to interface with the subsystems of the design The navigation subsystem consisted of the compass and the wireless card for absolute positioning with the camera connected to the laptop The obstacle avoidance subsystem consists of the ultrasonic ping and the collision sensor The drive subsystem is the motor controller The motor controller with be a bi directional connection and the others are predominantly inputs The incremental encoder is the Rotary Encoder 1024 P R Quadrature which would have needed 3 channel inputs Two would be needed for this design with a total of 6 channels In the AtMega 328 the ports B and D act as 8 bit bidirectional I O ports Since 6 channels are needed one of the ports can be used Port B is related to port D except it has the addition of timer features which is not necessary for the rotary encoder but can be used for the other subsystems Moreover both wheel encoders can be connected to port D PD 7 0 Rotary Encoder
142. on determined from the learning mode this lawn mower design would give the same accurate cut each and every time This was partially implemented because although the camera was able to track the mower current location values were difficult to store Nevertheless this is a great improvement in efficiency over available consumer devices which cut in a random pattern until the entire area has been covered Safety is another factor that was considered for this project Implementation of obstacle avoidance is a primary objective for the safety of the project vehicle Through the use of ultrasonic sensors the mower discerns the location of obstacles present within the cutting area delimited by the border established during the mapping phase from computer vision Once an object is detected in its current path of motion the mower changes its directional orientation until the object is no longer in its field of view and proceeds around the obstruction If the mower fails to navigate around the obstacle an onboard collision detection system would cause the mower to reverse its direction of motion or in a worst case scenario disable the mower completely In the latter scenario the mower would have to be manually restarted by the user The collision detection system could be implemented through a variety of methods A bumper could be affixed to the front and sides of the mower This bumper would rest on springs and in the presence of a suitable force
143. oning form of navigation in which unbounded errors accumulate over time if they are not corrected by the inclusion of a reference point or some sort of filter This is a consequence of the fact that such an encoder outputs the motion of the shaft as opposed to the angle and from this the relative position is processed elsewhere Since the encoders are merely a part of the navigation subsystem its computations would be correlated with the absolute position calculated by the computer vision software this unbounded error would be minimized to an acceptable level once the output data has been filtered accordingly The encoder originally chosen for this project is the A6B2 CWZ3E 1024 incremental encoder by YUMO This encoder provides a flexible solution to the odometry problem in that the resolution of the output can be determined via the microcontroller increasing or decreasing it depending on the limitations of the fully implemented system This encoder offers quadrature output in which two output channels separated by a 90 degree phase shift are utilized This allows the microcontroller to determine the direction that the encoder is spinning depending on which channel is leading or lagging Figure 4 4 3 A Direction of rotation CW Direction of rotation CCW CW ccw T 360 T 360 ee il E ate o oe l OT p 14s eT 1 4 l 1 8T H m z z L L oD Note
144. orange spheres at two different heights along the center of the docking area The docking algorithm would use the position of the two orange spheres to align the mower for docking The use of orange spheres in place of lights or infrared LEDs reduces the requirement to either power the lights or add an IR sensor to the device On the rear of the lawnmower metal bars would be mounted to the lawnmower This setup is similar to the design shown in figure 4 7 1 D As the lawnmower makes appropriate contact to the docking station the 87 charging procedure commences A prototype design of the docking station to be used in this project is shown below Figure 4 7 1 E Lawnmower docking station design Note that in the design the sides are angled out from the back charging board By slightly angling the sides the docking station allows for small alignment errors in a similar fashion to the conic docking station shown in figure 4 7 1 B Should the lawnmower approach the docking area slightly off line the angled sides of the docking station would feed the lawnmower into the docking area In this manner suitable connections can be made with the charging contacts so that proper charging may commence A simplified prototype design of the charging bars mounted on the back of the lawnmower similar to figure 4 7 1 D is shown in the figure below 88 Figure 4 7 1 F Simplified design showing charging bars on rear of mower The physical design of t
145. otes f4 pdf gt Sommer Jason Saw Kapaw Sushant Basnet Thomas Snyder Josh Jackson and Maria Juarez Autonomous Lawn Mower N p n p n d PDF Spears W M Hamann J C Maxim P M Kunkel T Heil R Zarzhitsky D Spears D F and Karlsson C 2006 Where are you In Sahin E Spears W M and Winfield A F T Eds Second International Workshop on Swarm Robotics at SAB 2006 volume 4433 pages 129 143 Berlin Germany Springer Verlag Weather Sensor Assembly P n 80422 N p Argent Data Systems n d PDF Wide Range Fuel Gauge with Impedance Track for Lead Acid Batteries Dallas Texas Instruments Dec 2012 PDF Winfield A and Holland O 2000 The application of wireless local area network technology to the control of mobile robots Journal of Microprocessors and Microsystems 23 10 pages 597 607 128 Copyright Permissions Requesting permission to reprint image Joseph Corteo lt josephcorteo gmail com gt 12 33 AM 16 hours ago ste EN to kat Hello am an Electrical Engineering student at the University of Central Florida am currently working on my senior design documentation and am using SimpleCV to program the computer vision software that will assist in the navigation of our autonomous lawn mower am requesting permission to reprint the images from slide 92 of the PYCON 2013 slide show source Thank you Click here to Reply or Forward First Name Pesser Last Na
146. ould not otherwise mow their own lawn Even without a physical limitation the autonomous lawn mower provides the user with more free time This freedom is provided in a worry free platform in which little user interaction is required The project idea was introduced by group member Andrew Cochrum His initial design idea was to create a fully autonomous lawn mower that maps the target yard and lawn mower locations using triangulation methods from RF receivers transmitters The design is similar to the previous senior design project called iMow It is also an improvement on existing consumer autonomous lawn mowers including the John Deere Tango E5 The available commercial autonomous lawnmowers only cut in a random pattern with buried cables used as boundaries By implementing computer vision this project can mow the lawn much more efficiently than the commercial products by pre setting boundaries with a camera vision A variety of location methods were researched to determine the most effective method for the project 2 2 Project Goals and Objectives In keeping with the motivation behind the project the goal of this project was to reduce end user work through the utilization of an easy to use device The autonomous design eliminates the need to go outside and mow your lawn every week The project was initially designed to learn your yard in one initial session and then repeat the process indefinitely as needed This project improves on existing con
147. ould simply choose one of these routes as the new path for the mower The A search algorithm would therefore serve as the defining procedure for calculating the obstacle avoidance route In software a procedure would be implemented called a This procedure performs the path search by looping over the nodes as described earlier This procedure takes in inputs of the start node and goal node to determine the path The procedure results would be used to steer to mower passing appropriate results to the drive subsystem 75 4 6 Drive Subsystem 4 6 1 Motor Controller Selection After looking at many designs of H bridges and motor controllers the Sabertooth 2x25 regenerative dual motor driver was the most practical for this particular application According to the specs for the controller it can supply two DC brushed motors with up to 25 amps of continuous current each with a peak current of 50 amps to each motor The Sabertooth 2x25 also accepts various control inputs such as analog voltage radio control serial and packetized serial Independent control of speed and direction of each motor make the controller ideal for differential drive applications Being a regenerative motor driver means that the batteries get recharged when the controller receives a command to slow down or reverse a motor This would help with extending the battery life so that as much of the target area as possible gets mowed on a single charge Below is a compar
148. ower chassis and at least three beacons must be visible at all times during its operation Trees and other obstructions present within the area of operation could potentially block the signals broadcasted by certain transmitters as the autonomous lawn mower navigates its way through the yard Therefore as is the case with trilateration increasing the number of transmitters would create redundancy and insure that the mobile platform is always within line of sight of at least three beacons What follows is a brief analysis of several three point triangulation algorithms e Geometric Triangulation o Effective only when the mobile platform is within the triangle enclosed by the three beacons o Becomes highly unreliable outside this area e Geometric Circle Intersection 13 o Large errors occur when the three beacons and the mobile platform all lie on or close to the same circle e Newton Raphson o Fails when the initial guess of the robot s position and orientation exceeds a certain bound Regardless of the algorithm utilized the heading of at least two beacons must be greater than 90 degrees and the angular separation between any two beacons must be greater than 45 degrees In general none of the above methods provide an adequate solution when implemented on its own A combination of two or more methods tends to provide a more accurate measurement overall 3 3 2 Using a System of Low Cost Transmitters to Calculate the Position of a Mo
149. ows the automated lawn mower to slowly accelerate so that the electronics used for navigation have time to keep the mower heading in the correct direction The maximum amperage of the NPC 41250 at 24 volts is about 19 amps Since this is well below the motor controller s 25 amp continuous rating it should work very nicely with the motor controller 4 6 2 1 Mechanical Design Interfacing Motors with Existing Lawn Mower Chassis Both motors were mounted onto an extension of the main chassis with custom brackets and would drive the wheels directly Since the motors are already geared no additional gear reduction for power was necessary Each motor would need to either have a manual clutch integrated into the motor itself or be attached to the wheel via a gear so that the motor can be disengaged from the wheel This is because from the original design the automated lawn mower needed to be able to have the motors disengaged from the wheels so that the automated lawn mower can be pushed for operation in learning mode by the user Both motors would drive solid rubber wheelchair tires due to the tire s need for traction on off road surfaces The original lawn mower wheels could be used however most mowers are not self propelled which means the wheels are plastic and are designed to be easy to push The DC motors was rated to push 300 pounds under normal operating conditions so with the total mower weight coming to under 150 pounds the motors
150. pin is necessary for reprogramming and fixing errors since the drive subsystem is the final output 102 Serial Sabertooth AtMega328 Port 2x25 Motor Microcontroller Controller Port C Figure 5 1 D Sabertooth 2x25 Motor Controller to Microcontroller with Port C as serial port 5 2 Design Summary Navigation Subsystem The navigation subsystem of the project is a combination of a wide variety of components The inputs from these peripherals are inputted into the microcontroller which then is used to determine the path of the mower The block diagram of the navigation subsystem showing the various inputs is shown in Figure 5 2 A Lawn Mower akii Wireless Magnesc Transceiver Compass Io I o Laptop Y s sssssssssssssssssssssssssos n i Left Whee e Encode Wireless Card lt 1 oe oe oe oe J Microcontroller Right Whee Encoder USB HO Webcam Utrasonic Figure 5 2 A General overview of the navigation subsystem Distance Sensor 103 The navigation subsystem consists of the following hardware and software components e Lifecam HD 500 Webcam by Microsoft e PING Ultrasonic Distance Sensor by Parallax Inc e HMC5883L Compass e RN XV WiFly Module Wire Antenna by Roving Networks e Ideapad Z560 Laptop e SimpleCV open source framework by Sight Machine The two incremental quadrature encoders were to be coupled to the wheel shaft of the rear drive wheels via a timi
151. ponent of the magnetic field However according to the technical documentation there is no direct access to the processor embedded within the module thus any modifications to the algorithm s implemented to filter the measured data in case they prove ineffectual are not possible Another drawback involves the inherent limitation of accelerometers they are very sensitive to vibrations Since this module would be affixed to the lawn mower chassis the vibrations produced by the rotating mower blade would most likely cause extremely high noise levels in the bearing calculations which would further be exascerbated once the lawn mower traverses uneven terrian during its operation Since this added feature set serves as a detriment to the overall performance of the CMPS10 model in the scope of the automated lawn mower project the CMPS03 seems to be the better choice It provides the same heading resolution of 0 1 degrees as the CMPS10 except it does not include the accelerometer or the imbedded processor The CMPS10 can be kept horizontal throughout the operation of the mower by mounting it upon a two axis gimbal This provides a cost effective and simple solution that would rectify any minor deviations the flat topology of Florida ensures small variations in elevation from the horizontal and would be insensitive to the vibrations generated by the lawn mower blades The gimbal would then be elevated atop a beam a minimum of 24 inches from the motors
152. ppages of the encoder during the operation of the lawn mower preventing innaccurate measurements from taking place Despite the various techniques available to increase the resolution of this encoder it is limited by the maximum imput frequency of the microcontroller The propolsion system driving the lawn mower was powered by common wheelchair motors which can achieve speeds of about 6 mph with a 300 Ib load under ideal conditions The typical rear wheel diameter of a push lawn mower is about 8 inches which equates to about 128 15 revolutions per minute RPM or 2 14 revolutions per second RPS Even with a relatively low max input frequency of 10 kHz a maximum resolution of 4673 PPR can still be achieved which can safely accommodate the implementation of X4 logic on this encoder 4096 PPR It can be seen that the microcontroller only becomes a limiting factor when the rotational speed and or resolution are relatively high or alternatively the input frequency is exceptionally low This incremental encoder also accepts a wide range of input voltages anywhere from 5 to 12 VDC Since the output channels A B and Z are voltage levels to interface with a 56 microcontroller is simply a matter of supplying the same voltage to the encoder to ensure that the high and low output signals are correctly interpreted by the microcontroller Finally the encoder comes wired with a braided shield lead that might aid in noise isolation However ca
153. project of this type is the ability to recharge the battery used to power the device To accomplish this a docking station was to be added to the project to handle all of the charging requirements For the design of the autonomous lawnmower project the docking station should be built to satisfy two needs location and ease of alignment To avoid tripping the collision sensor the charging and docking equipment were to be mounted on the rear of the lawnmower chassis Since the collision sensor is mounted on the front of the lawnmower chassis only the lawnmower would not detect a collision as it makes contact with the docking station For guidance and alignment the lawnmower would have a rear facing camera mounted on the back of the project This camera would send information to the microprocessor which would in turn use the information to detect the docking station Mounted on the 111 docking station would be two orange spheres at two different heights along the center of the docking area The docking algorithm would use the position of the two orange spheres to align the mower for docking On the rear of the lawnmower metal bars would be mounted to the lawnmower to serve as a contact point with the charging station As the lawnmower makes appropriate contact to the docking station the charging procedure commences To monitor the battery charge state an impedance spectroscopy method was used This method uses impedance measurements on the battery
154. proportional commands to move in that direction For example if the motor controller were to receive the command 95 it would move forward at half speed This is because 95 is halfway between 64 full stop and 127 full forward For motor 2 128 is full reverse 192 is stop and 255 is full forward Intermediate values work the exact same way for motor 2 as they do for previously described motor 1 The design incorporated differential steering that is operating the motors in opposite directions to turn the chassis much like a tank 108 To integrate the motor platform onto an existing electric lawn mower chassis the existing rear wheels are removed and an extra 1 5ft section was attached to the back of the mower The section was made out of steel and was attached via elbow brackets This extra platform holds the two DC motors via custom brackets but also holds the two batteries that were used to drive the DC motors and the enclosure for all the automated lawn mower s electronics Both motors were mounted onto the extension of the main chassis and drives the wheels directly ta Figure 5 4 A Example of chassis extension with motors mounted Reprinted with Masato Hayashi s permission Since the motors are already geared no additional gear reduction for power was necessary Each motor needed to either have a manual clutch integrated into the motor itself or be attached to the wheel via an intermediary gear so that the motor can be dis
155. r it is the lowest cost The limitations of this method are that it is only based on on off control and monitoring There are many sub applications of the digital method that can be used in the design The navigation subsystem is based on receivers and digital compasses as shown in the block diagram For devices such as a compass a good level of accuracy and preciseness 29 is needed The receivers would probably provide a better accuracy with analog interfacing to ensure accuracy in the location of the mower Digital interfacing with this part would most likely affect an accurate location The obstacle avoidance uses many sensors for detecting obstacles and programming to mower to reroute accordingly These obstacles would need to be detected at a precise location which could be distorted with digital interfacing Depending on the ultrasonic sensor used in this design it may even have digital outputs which would eliminate the need for an analog to digital converter Since the drive subsystem is more of a response from the microcontroller as to where to go this would work well using digital interfacing According to the above flow chart a subcomponent of the digital method is the parallel method which consists of 4 bit 8 bit 16 bit or 32 bit interfaces Logic designs and truth tables would be used to control the drive subsystem and would tell the mower to move in a certain direction depending on the responses received by the microcontroll
156. r GreenWorks Style Electric Push Electric Push Electric Push Battery Type Lead Acid Lithium Ion Lithium Ion Battery Voltage 36V 36V 40V Cutting Width 20 in 14 in 19 in Side Discharge No No Yes Material Steel NA Steel Cutting Height 1 4 inches 1 3 inches 1 25 3 5 inches Weight 77 lbs 35 Ibs 49 Ibs Warranty 2 Years 1 Year 4 Years Base Price 369 99 449 99 469 99 Table 4 2 Electric Lawnmower specifications Images reprinted with permission from MowersDirect com From the electric lawn mowers shown above the GreenWorks 24 Volts 3 in 1 cordless mower was selected due to its price and features The steel deck is a sturdy platform to build upon and the mower is rated to cut 7 000 to 10 000 square feet on a single charge 26 4 3 Computational Subsystem 4 3 1 Microcontroller Selection For this design we needed to select an appropriate microcontroller that would be connected and programmed for the navigation subsystem the obstacle avoidance subsystem and the drive subsystem The navigation subsystem consists of a digital compass and a WiFly module to communicate with the laptop As a result it may be necessary to explore a microcontroller with RF capabilities Also floating point values are necessary as a part of the microcontroller s features in order to ensure an accurate value of the detected location The drive subsystem consists of the motor controller which connects to DC motors The microcontroller bei
157. r during the docking procedure are in reverse and easily handled by the drive subsystem 4 7 3 3 Initializing Terminating Charging The backbone of the charging procedure is provided by input from the battery charge monitor As discussed in a previous section TI part bq34z110 handles the calculation of the charge state of the battery Using the data discovered from the battery monitor the charge state can be determined at any given time The charging can only begin once the lawnmower has been successfully docked in the charging area Upon successful completion of the docking procedure as described in the previous section the software would flag the system to initialize charging procedures A simple function call initcharge can be used that reads the flag for a successful dock with the charging station If the flag is valid and the system is ready to charge this function would send an output signal to close a switch This switch would allow for current flow into the battery thereby initializing the recharge As the battery is charging the battery monitor would keep track of the current state of charge of the battery pack While charging it is good to know how far along in the charge procedure that the process is in This is typically done for say a smartphone using an animation to show the current battery capacity state For this project a simple LED system can be used Four small LEDs mounted on the lawnmower can be used to give a quick visual r
158. racy Computer vision setup Fabricate webcam support structure Test computer vision e Boundary demarcations e Absolute position coordinate calculation e Detection of static obstacles Obstacle avoidance setup Mount bumper switch assembly to chassis Install ultrasonic ping sensor Interface sensors with power system and microcontroller Test for functionality and accuracy Wireless communication setup Test transmission of data eg x y coordinates Test transmission speed 121 o Compass module setup Fabricate and install gimbal for compass mounting Interface compass with power system and microcontroller Test for functionality and accuracy o Overall route algorithm software implementation Combine all subsystems Perform real time testing o PCB Design Design PCB schematic and order PCB Install PCB into system Test project o Additional features Build docking station Test docking procedures Test recharge functionality Fine tune computer vision for better accuracy and improved features o Finish final documentation 4 24 2013 5 5 2013 5 15 2013 6 2 2013 6 16 2013 7 7 2013 7 21 2013 7 28 2013 Deadlines Figure 8 1 A Project Milestones with Deadlines 122 8 2 Budget and Finance Discussion Part Manufacturer Quantity Unit Price Net Price 25222 20 inch 24 volt Greenworks 1 369 00 retail 150 00 used Cordless Lawn Mower
159. re must be taken to mount the encoder as far away from other electronic devices to minimize noise The table provides specifications of interest taken from the A6B2 CWZ3E 1024 datasheet Parameter Value Unit Electrical Specifications Resolution 1024 PPR Pulses Per Revolution Input Voltage 5 5 12 10 VDC Current Consumption 100 mA Output voltage output Max Response Frequency 100 kHz Output Capacity Output resistance 2 KQ Sink current 35 max mA Residual voltage 0 4 max V Mechanical Specifications Station Torque 0 98 mN meter Allowable shaft load Radial 5 N Axial 3 N Maximum Rotating Speed 6000 RPM Weight 100 g Table 4 4 3 A6B2 CWZ3E 1024 incremental encoder device specifications from manufacturer datasheet 4 4 4 Ultrasonic Distance Sensor PING Ultrasonic Distance Sensor by Parallax Inc To supplement the navigational information provided by the SimpleCV computer vision program the PING Ultrasonic Distance Sensor by Parallax Inc was implemented within the navigation subsystem This module consisted of three pins supply 5 VDC ground and a bi directional TTL transistor transistor logic input output pin Thus in order to interface with the microcontroller only one pin is necessary The sensor emits a short ultrasonic burst when it receives an input trigger pulse 5 us typical pulse width from the controller It then waits for about 750 us allowing the ech
160. re open source and completely free Another added bonus of open source software is the robust user base which serves as an invaluable supply of pre written code that can be implemented and modified without any form of legal recourse This further shortened the time of developement since computer 60 vision is a relatively mature technology and thus many of the problems associated with it can be solved by finding the appropriate function and implementing it within the framework of an existing program The input to the SimpleCV program was the live video feed from the LifeCam HD 5000 Webcam manufactured by Microsoft which was connected to the host laptop via a USB cable Since the SimpleCV program was running on a laptop seperate from the lawn mower chassis the computation of the xy coordinates of the lawn mower did not impact the performance of the microcontroller The microcontroller would have initially simply received the coordinates wirelessly via the connected onboard reciever and use them in conjunction with the outputs from the magnetic compass module and the ultrasonic distance sensor Figure 4 4 5 4 Google SketchUp model of the webcam support structure Webcam was mounted to the top of the pole facing the lawn to be traversed Originally the laptop loaded with the SimpleCV computer vision software was to be mounted directly onto the automated lawn mower chassis along with the webcam This would simplify the communication be
161. rence value so that an accurate final value can be used by the microcontroller The coordinate points would have had two values x and y so two comparisons would be needed Ref_x new_position_X Ref_y new_position_y Diffx abs absx Ref_y Diffy abs absy Ref_y If diffx gt 32hresh diffy gt thresh Ref_x absx Ref_y absy The above pseudocode would be a function that takes the parameter of the reference coordinate points from the previous pseudocode the absolute coordinates from the camera and a threshold value If the values exceed a certain threshold the absolute coordinates would replace the reference coordinates A challenge in this design was calculating an accurate absolute coordinate point since the camera views the lawn from an angular perspective As a result a few conversions would be necessary to accurately 32 scale the coordinate values of the camera s perspective to the coordinate values of the flat surface of the mower Camera perspective Floor coordinates Figure 4 3 3 2 B Perspective of floor coordinates 4 3 3 3 Obstacle Detection S i Obstacle Detection Signal input Microcontroller Ping Sensor Obstacle Figure 4 3 3 3 A General Interfacing of PING Sensor For this design the mower had the ability to detect obstacles using the Ultrasonic PING that delivered a digital signal to the microcontroller The microcontroller was programmed to maneuver the mower
162. rk detected node on grid as obstacle Calculate new route Figure 4 5 4 1 A Overall Obstacle Avoidance Program Flow Chart 4 5 4 2 Calculating Obstacle Avoidance Route The software implementation of the obstacle avoidance subsystem may be divided into two main sections The first is the detection of an obstacle from the sensor data inputs The second section is the bulk of the software implementation and involves calculating the obstacle avoidance route Each time that an obstacle is detected this procedure needs to be called so that a new route can be calculated and the obstacle can be avoided To simplify the design of the obstacle avoidance software design each routine or decision in the obstacle avoidance system were represented by its own procedure The first and simplest procedure comes from the collision sensor input This procedure would be called detectcollision As stated earlier the collision sensor provides a digital input with a signal that is either HI if the collision sensor has been tripped or LO otherwise In the condition where the sensor is LO the collision sensor has not detected an obstacle so nothing needs to be done and the current path should continue to be traveled When the 73 sensor goes HI the procedure begins It should start by immediately sending a brake signal to the drive subsystem to stop the mower The next step is to mark the detected location as having an obstacle and then recalculating a new route
163. roject have been narrowed down to a few choices These sensors which are individually evaluated below are the Parallax PING HC SR04 Maxbotix LV EZ1 and SRFO4 A summary of their important product specifications are shown in the table below Sensor Parallax PING HC SR04 Maxbotix LV EZ1 SRFO4 Ultrasonic Sensor Supply 5 5 2 5 5 5 Voltage Vdc Supply 30 lt 2 3 30 Current mA Range 2cm 3m 2cm 0 5m Ocm 6 45m 3cm 3m Frequency 40 40 42 40 kHz Size mm 22x46x16 20x43x15 20x22x16 20x43x17 Price 32 99 5 99 29 95 29 50 Table 4 5 1 Research ultrasonic sensor specifications The Parallax PING sensor is readily available at retail stores like RadioShack It has 3 pins 5V Ground Signal The signal pin is bi directional and requires an input signal which triggers the ultrasonic burst The echoed signal is then returned via the signal line This sensor is widely used by hobbyists and an ample amount of documentation is available for support The HC SR04 has a very low cost and is available through many online retailers It consists of 4 pins Vcc Ground Trigger Signal Echo Signal The resources available for this product are limited in comparison with other products In addition the datasheet does not provide much information in terms of its overall capabilities The Maxbotix LV EZ1 is one sensor in the Maxbotix line of ultrasonic sensors This sensor has 7 pins to provide an ample a
164. roller is required to run the motor A brushed motor has a rotating set of coils that are wound with wire called an armature This acts like an electromagnet with two poles A mechanical rotary switch called a commutator reverses the direction of the electric current twice per cycle This reverses the flow of current through the armature so that the poles of the electromagnet push and pull against the permanent magnets located on the outside of the motor As the poles of the armature electromagnet pass the poles of the permanent magnets the commutator reverses the polarity of the armature electromagnet During the instant of switching polarity inertia keeps the motor going in the proper direction Several advantages to using brushed motors include simple two wire control low cost of construction simple and inexpensive control no controller required for fixed speeds and the motor can operate in extreme environments due to the lack of complex electronics Disadvantages to brushed motors are that they require periodic maintenance due to the brushes wearing speed and torque are moderately low at high speeds brush friction increases and reduces useful torque poor heat dissipation due to internal rotor construction and brush arcing generates noise causing electromagnetic interference The automated lawn mower would operate at low speeds and not require tremendous amounts of torque For these reasons along with the high cost and complexity of brushless
165. rom 1 to n in which n is the total number of pulses generated within one revolution of the encoder these types of absolute encoders also measure the number of revolutions which can then be used in the calculations executed by the microcontroller software in order to determine the total distance travelled by the automated lawn mower as opposed to including an additional subroutine in software to keep track of each revolution Absolute encoders generally use parallel data output which consists of a unique code pattern usually a Gray code for each quantized shaft position which usually involves a more complex interface with a system due to the large number of electrical leads required to carry the signal Since the microcontroller is now dealing with a data word as opposed to a pulse train the processing of such a signal could 54 take longer negatively impacting the execution speed of the microcontroller program For this reason absolute encoders are more suited for applications involving slow and or infrequent rotations which would be unsuitable for the autonomous lawn mower since it is in perpetual motion throughout its operation Another drawback is the cost of such an encoder which on average is more expensive than its incremental counterpart Incremental encoders apart from being cheaper than absolute encoders are also more flexible in terms of interfacing with an existing system This is offset by the fact that they are a dead reck
166. ronics which have requirements of 3 3 to 5 volts As described in the research section of this document a switching regulator is advisable for the voltage regulation needs for the project In choosing a switching regulator a few specifications are required to be met For this project the voltage is required to be stepped down from 24 volts to 3 3 or 5 volts The output current is less than 1 ampere These requirements provide us with the need for a buck converter that meets those voltage and amperage values In choosing a part to handle these requirements one particular device is a LM22670 step down switching voltage regulator from Texas Instruments The LM22670 handle an input voltage range from 4 5 to 42 volts It can provide an adjustable output voltage as low as 1 285 volts and an output load current of up to 3 amperes This information shows that this part meets the voltage regulation needs for this project In addition to providing an adjustable output voltage Texas Instruments provides a LM22670 that gives a fixed 5 volt output voltage For the 5 volt regulation needs of this project this fixed output LM2825 5 0 was used Using the fixed voltage part simplifies the overall design of the voltage regulator circuit and lowers the part requirement on the final printed circuit board design For voltages below 5 volts the adjustable output switching regulator LM2825 3 3 was used The figure below shows the voltage regulator circuit using the LM282
167. rts Segments Motor ports Interface e Key Wake up e 23 e 2C smart e 32 general purpose I O Port Progr ammable sensor port pins e BDMDEBUG VO Lines e UART Serial e In circuit Programming Port 8 channel 10 Ports Debugging of the e CAN20 bit ADC in e 8 Hi res 12 micro controller Mo dule TQFP and bit Analog through the serial port Anal coe ie ackage Inputs _ 5 channel 10 bit Comparatoi i 8 e 12 Fast digital Analog Digital S S Mhe nemal emperature T O ports which Converter ADC with Bac Orei Measurement can be used as 4 096V internal or an De ak e 6 channel 10 interrupts external voltage s iri bit ADC in 7 Programmable reference source Operon nie PDIP Package with easyC v4 e 6 Volts DC Adapter internal PLL e Temperature for Cortex or serial cable serial re Measurement ROBOTC for downloader online oe o e Programmable Cortex amp PIC technical manual and HYDE Serial UART schematics operation Table 4 3 1 Microcontroller Specifications 4 3 2 Interfacing with Other Subsystems This design contains three major subsystems The major input subsystems to the microcontroller are the obstacle avoidance subsystem and the navigation subsystem The image below is a block diagram of the microcontroller and the initial original design of how it would be interfaced with other subsystems in the design 28 Obstacle Avoidance Subsystem Drive Subsystem l Proximity Sensor A mee Lef
168. sed to measure gravitational forces which are commonly called g forces By measuring the various forces and keeping track of them the inertial measurement unit is able to produce a linear record of these measurements These values are then passed to some sort of processor that calculates the inertial measurement unit s position based on reported velocity direction and time elapsed This data can be directly overlaid onto an electronic mapping system that can tell the inertial measurement unit its geographical location Although this method of navigation is similar to a global positioning system or GPS it removes the need for contact with external sensors or satellites This is what gives this type of navigation the name of dead reckoning TORQUE MOTOR M DUPLEX BALL BEARING x axis SLIPRING 50 CONTACT GYRO ERROR RESOLVER 1X DUPLEX BALL BEARING SLIPRING 40 CONTACT MULTISPEED RESOLVER 1X AND 16X TORQUE MOTOR DUPLEX BALL BEARING Z SLIPRING 40 CONTACT te LM Z Axis MG AXIS Note MIDDLE X Xg X IRIG Xa X PIP GIMBAL 4 STABLE Yg Y IRIG Ya Y PIP MEMBER Zg ZIRIG Za Z PIP IMU CASE LM CUTAWAY Y axis TORQUE MOTOR DUPLEX BALL BEARING SLIPRING 40 CONTACT DUPLEX BALL BEARING DUPLEX BALL BEARING SLIPRING 40 CONTACT SLIPRING 50 CONTACT MULTISPEED RESOLVER 1X AND 16X MULTISPEED RESOLVER 1X AND 16X 300LM4 152 Figure 2 1 24 IMU Gimbal Assembly Figure 3 3 4 A Example of an IMU Gi
169. sensor to be used for the obstacle avoidance subsystem This sensor is desirable due to a variety of factors It has a wide input voltage range low current draw a considerable amount of user control and a price in line with other sensors of its type 106 For redundancy a collision sensor was added to the project design The addition of a collision sensor adds an extra safety feature to the lawnmower to help prevent the mower from running over an object in case the obstacle is missed by the proximity sensor For collision detection a simple bumper sensor or bumper switch is an easy and effective way to detect an impact A bumper sensor is handled by using a simple switch that is connected when depressed This switch is closed upon impact from a collision which alerts the software that a collision has been detected Any simple single pole single throw push button style switch can be used for bumper switch The switch needs to be rated at 5 volts and be durable enough to handle a direct impact with an obstacle To handle the bump detection a mounting addition was necessary for the lawnmower design This mount would hold the switch for collision detection and act as a bumper for the system This bumper needed to extend past the front of the lawnmower wheels so that the bumper switches are the first point of impact should the lawnmower make impact with an obstacle The bumper should be low enough to make impact with short obstructions but not mount
170. should be able to handle the load and maneuver with ease A shaft encoder was initially to be used to keep track of each rotation made by the wheels The encoders would be mounted to the frame and attached to the drive shafts via a timing belt An optical shaft encoder can determine movement by reading two light and dark coded tracks using photodiodes Channel B Code Track on Disk Channel A Channel B 90 Figure 4 6 2 1 A Example of a quadrature encoder output Reprinted with permission from ni com 80 Above is an example of an incremental encoder that uses two output channels to determine the position of the shaft Channel s A and B are coded on the disc to be 90 degrees out of phase and alter between light and dark The two output channels can then indicate the position and the direction of rotation If the sensor detects that A is leading B by 90 degrees then the shaft is rotating clockwise If the sensor detects that B is leading A by 90 degrees then the shaft is rotating counter clockwise The position of the shaft can then be derived by constantly monitoring of the number of pulses and the relative phase between A and B While the encoder could be used to keep track of position and heading this method tends to produce errors in the calculated values over time due to wheel slippage For this reason our automated lawn mower would track its position through the methods discussed in section 4 6 1 with the shaft encoder as an ad
171. software This section will break down the project into subsections to discuss the details in design selection 4 1 Overall System Block Diagram The overall system block diagram is shown in Figure 4 1 A which shows the connections of each of the parts used in the project design This block diagram will be broken into its various subsections and discussed further RN XV WiFly Distance to obstacle in path P Antenna Module PING LifeCam HD 5000 Webcam Image of lawn Simple CV xy coordinate of lawnmower Orientation CMPS03 Compass Module Dell Inspiron Laptop ATMega328 1024 PPR 1024 PPR Quadrature Quadrature Encoder Encoder Speed of rotation RIGHT LEFT Speed of rotation Motor speed and direction Sabertooth 2x25 Motor Controller Left DC Motor Figure 4 1 A Functional Overview of the project 4 2 Electric Lawnmower Selection An existing product on the market was used for the main chassis of the mower and cutting platform The platform must be electric with a removable rechargeable battery Ideally the mower would have a side discharge cutting deck and the main deck was made out of steel Adjustable ride height was not absolutely necessary but is always a plus Table 4 2 shows several electric mowers that were considered 25 Model 20360 PMLI 14 25312 Manufacturer Toro Recharge Mowe
172. ssage h Mon 3 15 AM 4 oppel A RM adios We To milo robotics usc edu You replied on 4 22 2013 11 17 AM I would like to request permission to use an image from your journal paper Staying Alive A Docking Station for Autonomous Robot Recharging appearing in the 2002 IEEE International Conference on Robotics and Automation The images in question are figures 2 and 5 from that paper If permission is granted this image will be used in a design paper for a senior design project at University of Central Florida If you could respond to this request it would be greatly appreciated Thank you Jason Oppel Student UCF 137 Docking Station Image Permission Riccardo Cassinis riccardo cassinis ing unibs it A B A Actions Monday April 22 2013 1 36 AM To joppel joppel knights ucf edu Please feel free to use them with the usual citation of the source Regards R Cassinis jopp el Sunday April 21 2013 11 04 PM I would like to request permission to use an image from your paper Docking and Charging System for Autonomous Mobile Robots from University of Brescia The images in question are figures 2 4 and 5 from that paper If permission is granted this image will be used in a design paper for a senior design project at University of Central Florida If you could respond to this request it would be greatly appreciated Thank you Jason Oppel Student UCF Table Data Image Permission joppe
173. stem Figure 4 4 5 C Left input image Right output from blob detection algorithm Reprinted with permission from John Palmisano www societyofrobots com The autonomous lawn mower and the landmarks for the purpose of this discussion the landmarks are assumed to be small brightly colored plastic cones would be coated with bright paint that is easily distinguished from the green earthy color of the lawn e g such as bright red for the autonomous lawn mower and bright yellow for the plastic cones The SimpleCV software can easily locate both the lawn mower and the yellow cones within the captured image by implementing a pixel classification algorithm By assigning each pixel to an object class based upon its RGB value color entities within an image can be quickly classified Defining the RGB value that matches the red color of the autonomous lawn mower and defining any pixels with a color equal in value to that of the plastic cones the algorithm would go through the entire image pixel by pixel and make the appropriate classifications of the objects within the current image frame based upon the pre defined color to object association declarations An alternative method to object identification within a given image is using the blob detection algorithm which performs the following operations on the pixels within the image 1 Go through each pixel in the current image a If the pixel is a blob color defined by the programmer
174. sumer products by removing the need to bury insulated wires to identify the boundaries of the lawn This complies with the stated motivation to reduce work by eliminating this tedious initial setup The project design was very easy to use with no user interaction required after the initial learning of the yard layout Our initial design was that this learning would consist of the user pushing the mower along the entire perimeter of the lawn during which the mower would map the yard and save its two dimensional coordinates in its internal memory The boundaries would be setup using easy to place markers In our final design we utilized computer vision as the learning in which the user set boundaries on the camera view before running the mower By using a computer vision process the location of the lawnmower can be maintained and the autonomous vehicle can stay within its boundaries Upon execution of its weekly cutting routines the autonomous lawnmower was able to reference these values to restrict its location to the area enclosed by the user s path during the learning phase In our initial design once the boundaries have been established the user simply needs to program the mowing schedule via a control panel on the mower chassis itself or wirelessly through some other interactive platform i e smart phone PC etc However the mowing scheduling was not implemented because of limited time and it would complicate the desi
175. t DC Motor Collision Sensor Microcontroller Motor Controller Precipitation Sensor Right DC Motor Joseph Navigation Subsystem Matthew Figure 4 3 2 A Block Diagram Showing Microcontroller Interface The drive subsystem would communicate with the microcontroller as an input as well as an output From this design since most of the interfacing elements are inputs the appropriate methods should be used Two main interfacing methods are analog or digital For this design it could have necessary to mix multiple methods for different subsystems depending on the requirements of each system There are two methods for interfacing the microcontroller The digital method is based on on off control and monitoring and the analog method is based on voltage based control and monitoring Both methods contain advantages and disadvantages Some advantages of the analog method are that it is fast has a simple interface and low programming However a few drawbacks that might impact this design might be an increase in cost if a higher resolution is desired and a more complicated circuit design if external digital to analog or analog to digital converters are needed Additionally the selected microcontroller needed to have built in analog inputs and outputs Some advantages of the digital method are that it is the simplest interface and since it is usually built into the microcontrolle
176. ted by the computer vision software This essentially allows the program to distinguish the bounds of three dimensional space that the lawn mower adheres to i e it can only travel along the ground 65 Figure 4 4 5 E Webcam POV from the top of the supporting structure illustrated in Figure 9 The two black boxes representing the lawn mower are of equal dimensions CAD software Google SketchUp To create the virtual grid lines necessary to establish a reliable coordinate system SimpleCV offers several line finding functions and approximations Using a combination of the previously mentioned algorithms the computer vision program can define pairs of plastic cones that are directly across the area of operation i e they lie on the opposite edge of the perimeter and lie on the same line that is orthogonal to both sides A virtual grid line can then be drawn through each pair of plastic cones using a line find algorithm similar to that shown in Figure 4 4 5 F The blob representing the lawn mower can be assigned an absolute xy coordinate using this virtual grid as reference 7 o y 7 Figure 4 4 5 F Line find algorithm implementation algorithm finds straight continuous edges within the image Reprinted with permission from Katherine Scott Eea P from the SimpleCV library The 4 4 6 Wireless Communication RN XV WiFly Module Wire Antenna by Roving Networks To communicate with the laptop near the webcam support structure
177. terrupts and the timing on the ports may be slightly different By creating extra ports for the microcontroller it would allow the design to be more feasible to connect different devices and subsystems Each subsystem requires various devices For the devices to work correctly out design might need additional devices to help ensure accuracy For that reason extra ports would be necessary 41 4 3 4 2 Connecting Compass The compass was an input connection to the microcontroller in which the microcontroller would read the data from the compass and compute an angle value For example a digital compass such as the Hitachi HM55B could be connected to the microcontroller as an input and programmed to return an angle value At a certain position the compass would most likely need to be calibrated to reset the angle value The Hitachi HM55B is a digital compass that is a dual axis magnetic field sensor with 6 bit resolution This device would be able to provide considerable accurate angle results because it can compute 64 directions 2 6 From the North angle the compass measures the angle clockwise W270 deg 180 deg Figure 4 3 4 2 A Compass and angle layout In our consideration the angle value computed by the compass would most likely not match the angle value needed based on the direction of the mower Hence calibration would be necessary For example if the lawn is being mowed in a consistent NW direction such as 292 5 degre
178. th lines are open drain each line is connected to the 5 voltage supply red line in Figure 4 4 2 A via a 1 8 kQ pull up resistor The value of the pull up resistors is dependent upon the clock frequency being supplied to the slave device 1 8 KQ is recommended for up to 400kHz which is sufficient for this testing application since the microcontroller code sets the baud rate at 9600 bits s as will be shown later Figure 4 4 2 B shows the Arduino code based on the open source programming language for microcontrollers Wiring that was used to test the compass module The Wire library includes functions necessary for establishing I2C communication with peripheral devices The CMPSO3 stores the measured bearing as a 16 bit unsigned integer in the range of 0 to 3599 This 16 bit word is stored as two bytes in registers two and three most significant byte is located in register two of the compass module and when requested would transmit the most significant byte upper eight bits to the master device The beginTransmission function begins communication with the I2C slave device at the address passed to it the subsequent write function queues the number of bytes to be transmitted and the endTransmission function transmits these bytes The received bytes are then stored in two separate variables the first one being shifted to the left by eight bits and added to the unaltered second byte the sum of which is divided b
179. the object in question was greater than 5 inches if it fell below 5 inches it would drive the pins connected to the red LED and the buzzer to a logical high and driving the green LED pin low producing a visual and audible notification see Figure 4 4 4 C It can be seen from the image that this particular sensor is quite sensitive since it was able to detect the small wire placed within its FOV field of view Figure 4 4 4 C PING ultrasonic distance sensor test Left image Green LED is driven high when object greater than 5 inches away Right image Red LED and buzzer are driven high when object is less than 5 inches away In the actual implementation of the completed system the distance sensor would be used to trigger an interrupt within the microcontroller environment allowing for the bulk of the code to be executed without interruption until an obstacle is detected within the lawn mowers intended path of travel The ISR interrupt service routine would then take over and calculate an avoidance path using a similar proportional control loop as in Figure 4 4 2 C in which a steering correction is produced based upon the error between the desired parameter in this case a distance greater than 3 meters e g a distance greater than 3 meters implies no object is present since this is the max range at which the sensor can detect an object and the current reading of a distance less than 3 meters implying the presence of an obstruction
180. the overall financial responsibility The overall cost was helped by choosing a used lawnmower as the base of the system High 123 quality cordless electric lawnmowers were available used in good condition from resources such as eBay and craigslist The DC motors used for the drive system were being donated by Brandon Parameter from the robotics club Additional donations or help with funding was continually being sought to help lower the financial obligations by the group members In case of no further assistance the group s members were prepared to cover the costs of the project to finish the prototype build 124 Appendices Bibliography AmpFlow Wheels amp Gearmotors Robot MarketPlace The Robot MarketPlace n d Web 24 Apr 2013 lt http www robotmarketplace com products ampflow_wheelmotors html gt Anderson Jeff Matthew Lippiatte and Darrell Murphy JMow Autonomous Lawnmower N p n p n d PDF Atmel N p n d Web lt http www atmel com Images doc8 161 pdf gt Battery University Basic to Advanced Battery Information from Battery University N p n d Web lt http batteryuniversity com gt BiPom Electronics N p n d Web lt http www bipom com products us 318646 html gt Borenstein J and Feng L 1994 UMBmark amp A Method for Measuring Comparing and Correcting Dead reckoning Errors in Mobile Robots Technical Report The University of Michigan UM MEAM 94 22 December
181. the software would flag the system to initialize charging procedures A simple function call initcharge can be used that read the flag for a successful dock with the charging station If the flag is valid and the system is ready to charge this function would send an output signal to close a switch This 113 switch would allow for current flow into the battery thereby initializing the recharge As the battery is charging the battery monitor would keep track of the current state of charge of the battery pack For terminating the charge the software implementation would be similar to the initializing procedure When the battery monitor reads a full charge a flag is set that charging is now complete A simple function call termcharge could be used that read the flag for a successful charge completion These functions are summarized below void initcharge inputs is_docked flag output signal to close charging switch void termcharge inputs fully_charged flag output signal to open charging switch 5 6 Printed Circuit Board PCB Design Using the schematic of the overall system the PCB can be designed for the project Final PCB design was accomplished using CadSoft EAGLE PCB design software WiFly PING SimpleCVv RN XV Ultrasonic Program Wireless Distance Module Sensor ATMega328P Microcontroller f LM2825 5 0 LM2825 3 3 Sabertooth 2x25 Switching Switching Motor Controller Regulator Re
182. thin 95 accuracy The bq34z110 supports many lead acid battery configurations from 4 to 64 volts This part has a number of output interfacing capabilities to allow for monitoring of the battery in a variety of ways A listing of the pin out functions of the chip are shown in the figure below and display the variety of ways that this part can be implemented 94 Table 1 bq34z110 External Pin Functions PINNAME yunneR TYPE DESCRIPTION P2 1 oO LED 2 or Not Used connect to Vss VEN 2 Active High Voltage Translation Enable This signal is optionally used to switch the input voltage divider on off to reduce the power consumption typ 45 pA of the divider network P1 3 LED 1 or Not Used connect to Vss This pin is also used to drive an LED for single LED mode Use a small signal N FET Q1 in series with the LED as shown on Figure 9 BAT 4 Translated Battery Voltage Input CE 5 Chip Enable Internal LDO is disconnected from REGIN when driven low REGIN 6 Internal integrated LDO input Decouple with a 0 1 yF ceramic capacitor to Vss REG25 7 2 5 V Output voltage of the internal integrated LDO Decouple with 1 yF ceramic capacitor to Vss VSS 8 Device ground SRP 9 Analog input pin connected to the internal coulomb counter peripheral for integrating a small voltage between SRP and SRN where SRP is nearest to the BAT connection SRN 10 Analog input pin connected to the internal coulomb counter peripheral for
183. to a new location As long as the microcontroller does not receive a signal from the sensor the mower continues to move in a consistent motion The following block diagram illustrates the implementation of the ultrasonic PING and how it served as an input to the microcontroller 33 4 3 3 4 Thresholding and Computer Vision for Obstacle Detection According to the above pseudocode thresholding is used to determine replace two simple coordinate values The concept of double thresholding in computer vision plays a major role in edge detection In the double thresholding edge detection algorithm an image is scanned pixel by pixel to detect an edge in the image against a background Original Image Edge Detected image Figure 4 3 3 4 A Edge Detection Images A similar concept could be used for edge detection of the lawn being mowed as well as obstacles The advantage is the consistency of a green color lawn that is to be mowed The green color would act as the background similar to the black background in the chess pieces above Any other color would become a different object This can include obstacles as well as out of bound values Ensuring accuracy for this component is very necessary since the Ultrasonic PING may or may not be 100 accurate Any inaccuracy can result in a collision The camera in this case could be used to detect obstacles as well This might also serve as an advantage to use the absolute positioning values to maneuver t
184. traight line path For a successful test result the lawnmower should detect the obstacle and stop like the previous test The A algorithm programmed into the software should quickly calculate a new route causing the mower to divert around the obstacle This new route should have the lawnmower finishing in the same position as if the obstacle was not there Once these tests have all passed the obstacle avoidance system is fully ready to be used in live situations 120 8 Administrative Content 8 1 Milestone Discussion Due to time constraints presented by the semester dates the project needed to be broken done into a set of milestones The milestones for this project were as follows e Spring 2013 O O Design Paper Research existing designs similar to our project Finalize project outline Research parts to be used Finalize parts list with suppliers and pricing Complete design paper Begin obtaining parts necessary for design e Summer 2013 O O Obtain required parts Propulsion system setup Mount wheel motors to wheel shaft Fabricate and install battery support Install front castor wheels Connect and test power system e Check blade functionality e Check wheel motor functionality Wheel encoder setup Mount wheel encoders to chassis Install pulleys on encoder shaft and wheel shaft Connect pulleys with timing belt Interface encoders with power system and microcontroller Test functionality and accu
185. troller s features Of the variety of different inputs the Sabertooth 2x25 motor controller accepts the simplest method of control for this particular application is serial commands By setting the dip switches on the motor controller it can accept simplified serial commands at 38400 baud Each motor is controlled independently based upon the serial command the Sabertooth 2x25 motor controller receives For motor 1 1 is full reverse 64 is stop and 127 is full forward All numbers that fall within these values are proportional commands to move in that direction For example if the motor controller were to receive the command 95 it would move forward at half speed This is because 95 is halfway between 64 which is full stop and 127 which is full forward For motor 2 128 is full reverse 192 is stop and 255 is full forward Intermediate values work the exact same way for motor 2 as they do for previously described motor 1 All these serial 81 commands can be easily programmed into the main microcontroller and incorporated into a control program for navigation 4 6 3 1 Overall Program Flow Chart s Below is a program flow chart that shows what an example navigation program may look like when implemented Navigation Instruction Sla Motor 1 CW Motor 1 CCW Motor 1 OFF Motor 1 CCW Motor 2 CW Motor 2 CCW Motor 2 OFF Motor 2 CW Figure 4 6 3 2 A Example Navigation Program Motor 1 CW Motor 2 CCW 4 6 3 2
186. ts is ideal as to not cook the circuitry if such high currents are needed Microcontroller CALCELT EI ELETTA Motor 1 Motor 2 Figure 3 3 5 B Example of a motor controller connected to a microcontroller Reprinted with permission from Dimension Engineering 22 3 3 6 Voltage Regulators The various sensors that are part of this project were powered by a rechargeable battery As this battery was required to supply power to various components with different voltage and current requirements voltage regulators were needed Cordless electric lawnmowers which provided the foundation of the project were typically powered by a battery of 24 36 or 48 volts The base lawnmower motor and blade system is already designed to use that voltage The system specifications required the sensors and microprocessor to require a consistent voltage of the order of 5 volts and current in the order of milliamperes Therefore voltage regulators were required that handled an input voltage of 24 48 volts and output a consistent voltage and current requirement for the electronics to be used Linear voltage regulators and switching voltage regulators were both evaluated to determine their effectiveness and possible use in the design of this project 3 3 6 1 Linear Voltage Regulators Linear voltage regulators use a transistor design to take an input voltage and provide a constant set output voltage They are available as integrated circuits that are small
187. tteries that would be used To properly charge a lead acid battery the charging needs to be done in three phases The initial phase provides the battery with a constant current and is used to get the battery cells to about 70 charge At this point the battery charge monitor needs to alert and switch to phase 2 of the charging At this point the current should be gradually decreased until the battery is fully charged Once the battery charge monitor recognizes 100 charge phase 3 is started which provides only a small current to maintain a full charge on the battery There are a few methods available to measure the charge state of the battery One popular method for charge state monitoring is called coulomb counting In this method the current supplied to the battery is measured and monitored along with the current that flows out of the battery Using these measurements an approximate value for the power remaining in the battery can be determined Since these measurements only represent the battery charge state under an ideal case this method can be inaccurate although useful for lithium ion batteries One good method for monitoring lead acid batteries is the impedance spectroscopy method This method uses impedance measurements on the battery to determine the battery s state of charge Using advances in the impedance tracking method Texas Instruments has developed a battery monitor that can determine the battery capacity at any given moment to wi
188. tween the laptop and microcontroller since wireless protocols would not be applicable Also this is usually the method employed by many mobile robotic platforms and thus a large amount of reference material is readily available online However mounting the camera in such a way would not be suitable for the purpose of absolute position measurements Also the excessive vibrations caused by the rotating mower blade would require further image processing to filter out the noise in 61 the image Therefore the webcam and laptop were relocated from their original mobile positions to a static base station The webcam must be elevated to a height of about nine feet in order to accurately survey the entire lawn example lawn dimensions 33 ft x 36 ft approximately This can be done easily using the structure shown in Figure 4 4 5 A The base of the structure is a cinder block within one of the holes a hollow aluminum rod was threaded through and secured by pouring cement within the hole the other hole may be filled as well to increase the weight of the base and thus improve the stability of the entire structure Two more hollow aluminum rods would be placed within the first rod each having a smaller diameter than the rod supporting it i e bottom rod diameter gt middle rod diameter gt top rod diameter Each rod measured roughly 3 feet in length for a combined length of 9 feet when fully extended It was held in this position by two metal pins
189. uld have just been a simple box shape On the terminating end of the docking station are metal contacts which supply the power to the device when properly docked On the robot are matching metal contacts that are designed to make contact with the charging end contacts of the docking station The contacts on the robot are long metal bars which increase the actual charging area should the robot dock in a way such that it is slightly misaligned The charging contacts on the robot in this design are shown in the figure below Figure 4 7 1 D Charging contacts for robot and docking station Reprinted with permission from Cassinis et al For the design of the autonomous lawnmower project the docking station should be built to satisfy two needs location and ease of alignment The initial chosen design would rely heavily on the second reference design from the University of Brescia To avoid tripping the collision sensor the charging and docking equipment would be mounted on the rear of the lawnmower chassis Since the collision sensor is mounted on the front of the lawnmower chassis only the lawnmower would not detect a collision as it makes contact with the docking station For guidance and alignment the lawnmower would have a rear facing camera mounted on the back of the project This camera would send information to the microprocessor which would in turn use the information to detect the docking station Mounted on the docking station would be two
190. ure performs the path search by looping over the nodes as described earlier It takes in inputs of the start node and goal node to determine the path The procedure results would be used to steer to mower be passing appropriate results to the drive subsystem Some software functions were also used to detect obstacles from the information provided by the proximity and collision sensors These two functions are summarized below void detectcollision input bumper switch input outputs brake signal to drive subsystem obstacle location for mapping and new route calculation void findobstacle inputs object distance from proximity sensor output brake signal to drive subsystem obstacle location for mapping and new route calculation 5 4 Design Summary Drive Subsystem In summary the drive system design used two NPC 41250 24 volt DC wheelchair motors that draw 19 amps each This provided plenty of power to navigate terrain as well as steer the automated lawn mower Both motors were controlled by the Sabertooth 2x25 motor controller which is capable of providing up to 25 amps of continuous current to each motor By setting the dip switches on the motor controller it can accept serial commands at 38400 baud Each motor is controlled independently based upon the serial command the Sabertooth 2x25 motor controller receives For motor 1 is full reverse 64 is stop and 127 is full forward All numbers that fall within these values are
191. use in this design because it does not cause the edge to be neither thin nor thick and there could be an appropriate balance of detecting obstacles and avoiding missed areas In this design 36 however since time did not permit and various complications in the design were considered we did not proceed with thresholding but instead used the preset boundaries from computer vision and SimpleCV techniques to maneuver the lawn as close to a boundary as possible without passing it The ultrasonic PING sensor was able to detect objects by delivering a pulse of sound and calculating the amount of time it takes for it to bounce back hence determining the distance of the obstacle The computer vision approach was initially designed to utilize color detection to detect an obstacle The advantage would be that it would not only be able to detect objects of volume but also be able to detect areas that might be too flat for the ultrasonic ping to detect These might include low flower beds mulch areas or electric or water compartments that might be within the grass area It is likely that such areas are a different color from green and would easily be detected as an edge This approach became difficult due to hues and color differences in lighting and hence was not implemented in the final design 4 3 3 6 Motor Controller Output from Microcontroller The motor controller was connected to the microcontroller as a digital output The microcontroller would r
192. using the following equations a Ey Xabs Xca c where position error is equal to the absolute position of the robot Xaps minus the position of the robot computed from odometry X qic b y Yaps Yca c Same conventions apply for the y component of position c E Oqns Ocaic where orientation error g is equal to the absolute orientation of the robot Oaps minus the orientation of the robot computed from odometry O qic 5 Repeat steps 1 4 for four more times total of five runs 6 Repeat steps 1 5 in the counter clockwise direction The results of the procedure are represented as the measure of the odometric accuracy for systematic errors Emax syst Which is calculated from the following equations Emax syst max r g cw TETTA To g cw Xc g ew Weg cw To g cew c g ccow Veg cew n 1 Xc g cw Ccw y EXi cw CCW i 1 n 1 Ve g cw ccw 7 y EYi cw ccw i 1 Where Thus Xeg cw ccw and Yeg cw ccw are the horizontal and vertical components respectively for the average of the errors computed for both the clockwise and counter clockwise iterations of the benchmark over a period of n trials Refer to Figure 3 3 1 A for a graphical representation of the above equations and Figure 3 3 1 B for a comparison of the performance of a system before and after the inclusion of the correction constants via software _ of cw runs Y ae cluster Center
193. valuated to determine which features could be added removed or modified from this design The specific projects evaluated were as follows e Bearcat Shredder from the University of Cincinnati e iMow Autonomous Lawnmower from the University of Central Florida e Autonomous Lawn Mower from Indiana University Perdue University Fort Wayne e Robotic Lawnmower Design from CSU These four projects were from engineering students for design projects at different universities All four had design documentation available online to research and evaluate For the Bearcat Shredder the design documentation did not provide much in the way of design details The automation for the project was handled by a laptop mounted onto the lawnmower Location detection was handled by receiving data from a GPS data mounted to the lawnmower This design was deemed inappropriate for the needs of this project GPS tracking is not accurate enough to handle location tracking which should be on the range of a few centimeters The drive system was powered by two independent rear wheels with one freely rotating castor on the front The iMow autonomous lawnmower was a senior design project completed by fellow University of Central Florida undergraduates in 2006 Due to the age of the design full design documentation was not available For perimeter detection the iMow used a set of lasers to demark the boundaries of the lawn to be cut Sensors on the lawnmower were used to
194. y in a digital form requiring no analog to digital conversion between the component and the microcontroller The optimal orientation subsystem setup would involve coupling the gyroscope from an IMU with a fluxgate compass The gyroscope is accurate over the short term but becomes less accurate with the progression of time The compass provides reliable long term measurements and would be aided by the gyroscope in calculations until the system has achieved steady state conditions 3 3 1 4 Active Beacons Active beacons are commonly used in navigation systems involving mobile platforms They provide accurate positioning information high sampling rates and are reliable However cost becomes an issue since multiple transmitters usually upwards of three units and receivers must be deployed in order for the measurements to be accurate The placement of the beacons is an important factor in determining the effectiveness of this type of system Thus the initial installation could be problematic The position of a mobile unit can be determined using trilateration triangulation or an amalgam of both methods Refer to the section 3 3 1 titled Using a System of Low Cost Ultrasonic Transmitters to Calculate the Position of a Mobile Platform via Trilateration for an in depth discussion on a possible implementation of a trilateration based navigation system To implement triangulation an omni directional receiver would need to be mounted onto the lawn m
195. y sensor 4 5 2 1 Collision Sensor Selection For collision detection a simple bumper sensor or bumper switch is an easy and effective way to detect an impact A bumper sensor is nothing more than a simple switch that is connected when depressed The switch is closed upon impact from a collision Using this information it can be determined whether or not a collision has happened If the bumper sensor is HIGH it means that the switch is closed and a collision has happened In this case the drive motors should stop and brake immediately and a new 69 path needs to be calculated On the other hand if the bumper sensor is LO the switch is open and the lawnmower can continue on its path since no collision has happened Any simple single pole single throw push button style switch can be used for the bumper switch The switch needs to be rated at 5 volts and be durable enough to handle a direct impact with an obstacle The basic circuit design is easily implemented for this sensor A 5 Vdc voltage is sourced into the bumper switch which goes back to the collision detection input line If the collision happened the switch closes sending the input high This notifies the software that a collision has happened A single pole single throw push button switch can be purchased from any electronics supplier There are many styles and designs that are appropriate for the lawnmower project which cost less than 4 per switch 4 5 2 2 Mechanical Desig
196. y ten and converted to an integer The final output is an angle reading from 0 to 359 9 degrees 51 Trial Angle between CMPS03 Actual angle of Percent error table surface output deviation from and CMPS03 degrees true north circuit board CCW from degrees degrees true north CCW from true north 1 0 0 46 9 45 0 4 2 2 0 0 62 6 60 0 4 3 3 0 0 93 8 90 0 4 2 4 0 0 187 9 180 0 4 4 5 0 0 282 4 270 0 4 6 6 20 0 51 9 45 0 15 3 7 20 0 69 4 60 0 15 7 8 20 0 104 5 90 0 16 1 9 20 0 243 7 180 0 35 4 10 20 0 7 5 270 0 36 1 Table 4 4 2 Accuracy test of CMPS03 compass module After calibration the compass module was placed on a flat surface parallel to the ground away from any sources of interference such as speaker systems facing true north using a cheap magnetic compass as reference The CMPS03 module was then rotated counter clockwise from the true north orientation comparing the actual measured angle deviation with that calculated by the compass module The percent error of the calculations was on average about 5 across all five trial runs see Table 4 4 2 However when the compass module was tilted to about 10 or 20 degrees from the horizontal the readings became extremely unreliable An angle of 115 degrees would result in readings anywhere between 80 and 140 degrees a max percent error of about 30 Thus it is paramount to keep the CMPS03 module parallel to Earth s surfa
197. ystem However estimates were made based upon the datasheet specifications of each individual component to narrow down the list of potential products to be considered What follows is a discussion detailing the decision making process for the selection of the shaft encoders to be used in the navigation subsystem The propulsion system of the automated lawn mower utilizes differential drive in which each of the rear drive wheels has its own motor and thus the speed of the two wheels are independently adjusted to steer the lawn mower in the desired direction Therefore two rotary encoders one for each wheel are required in order to properly control the drive system via a feedback loop Two types of rotary encoders where considered for this application absolute and incremental Absolute encoders are essentially angle transducers since the output is the current position of the shaft in question This shaft angle is maintained even when power is removed from the system and is available immediately when power is restored making it a desirable option for a battery powered robotic platform In addition such an encoder does not need to return to a calibration point in order to maintain accuracy since the angular position is directly calculated i e it is not inferred from the angular velocity as is the case with incremental encoders Absolute rotary encoders are also available in the multi turn variant In addition to measuring the absolute position f

Senior Design 1 Final Project Documentation

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