BeagleBone Robotic Arm Controller
Contents
1. Servo motion control Local closed loop Accuracy of motion per axis Servo controller Adds open 0 75 dependant SSC 32 09 Adds closed 1 25 Figure 1 Breakdown of Arm Assembly Lynxmotion which is the company that created the Arm Controller supports the baud rate measurements with RIOS the default program for configuring the SSC 32 controller 11 Each component can be configured for position in degrees as well as maximum grip The gravity can also be compensated for to allow for fine tuned control when moving to specific angle degrees Figure displays an older version of the arm which allows the rotation of components with regards to 180 degrees per axis 2 Definition of the Problem t wN 1 AR USB to Serial a z f gt y or BeagleBone Robotic Arm Webcam Figure 2 Physical Diagram of the System The Physical Diagram of the system is shown in Figure 2 The Client sends the input command to the Beaglebone which will then signal that a command was received It will then send the signal of that command out to the Robotic Arm This method does not involve error handling or any dangerous tasks that are carried out but instead the commands received are completely carried out by the Robotic Arm The Client is able to see the results via a Webcam that is connected to the Beaglebone The Client machine communicates with the Beaglebone via a Web Interface and the Beagle Bone co2. position within the given time In the current placement example the servo can take longer than one second but it will attempt not to Commands can also be grouped for the servo motor and by arranging the time values for each input the largest time constraint will win but each motor can operate at different speeds To execute the servo commands outside of the environment the echo command must be used preferably from a bash shell as echo e 1 P2500 3 P750 r gt dev ttyUSBO This ensures the command can go through for the serial port to interpret To check the baud rate the command Stty f dev ttyUSBO Will list all available options for the serial device If any options are lacking screen can reset the option by specifying it as a parameter 11 5 Conclusion For this project communication between the BBS and the Arm Controller were completed as well as connection to the Web Camera viewable through a Web Interface The BBS was able to open a file descriptor to the Serial Communications port in order to control the Arm and any commands received from the Web Interface from a Client would carry out the command to the Arm For challenges in this project the most major is lack of documentation and support for microcontrollers and the SSC 32 board in particular Because the Arm Controller was purchased through a proprietary company the only sure way to interface with it was through RIOS which is the company software d
3. BeagleBone Robotic Arm Controller Dominic Latassa Thomas Turney Draft 4 12 1 2014 CEN 4065 Software Architecture amp Design Instructor Dr Janusz Zalewski Software Engineering Program Florida Gulf Coast University Ft Myers FL 33965 1 Introduction The Robotic Arm known as the ALSA Robotic Arm features base rotation single plane shoulder elbow wrist motion a functional gripper and optional wrist rotate 1 There have been several previous projects done with it some with control via Windows Embedded 2 3 and one with Linux 4 5 The current project aims to interface it through a Beaglebone board 6 The Beaglebone is a low cost development board that is able to boot off of a popular operating system such as Linux and features network connectivity and serial interfacing It is intended to restore the state of the ALSA Arm to a point where one can control it remotely through the Beaglebone on an Internet connection Monitoring the Arm through a Webcam is also within the scope of the project The ALSA Arm is operated via a series of Servo motors The motors connect through the SSC 32 Servo controller featuring MiniSSC II emulation which utilizes an Atmega 186 processor 7 Servos are placed in ports 1 5 on the board which communicates off of a RS 232 serial interface The effective Baud rate is either 2400 or 9600 with 115200 for PC communication Baud rate is defined as the oscillation of bits per second which c
4. avior of the BBS with respect to connected components When a command is sent to the BBS from the Web Interface it is verified and then send to the Robotic Arm If executed the BBS will send a confirmation to the Web Interface The BBS will also take the stream of images offered by the webcam for the Client to view While the BBS only sends command to the Arm internally the BBS can monitor the state of the Arm and from there be able to communicate to the user if the Arm is offline 1 Connect 2 Start 3 4 7 Send Images i lt Er TEPPER 2RN 5 Begin Image Streaming 9 Recieve 12 Move Arm 13 Confirm Figure 4 Sequence Diagram Figure 4 describes behavior of the system at startup time The Client connects to the Web Interface which begins allowing the BBS to initialize any components that have not yet started Before the Client sends a request they already have an image feed from the Webcam Once a request is sent the BBS will be able to process internally and deliver any errors that might occur such as the Robotic Arm being offline One finished with processing and checking for errors the BBS will move the ARM and the Web Interface will be able to send the confirmation message to the Client Enter code here as Arm Position S separated by newlines 5 peed sep y Execute Slide Controls Position between 500 2500 speed in milliseconds e g 1 1500 1000 Execute Code Figure 5 Web Interfac
5. build136 htm ssc32feat 8 Baud TechTerms Inc March 29 2013 URL http www techterms com definition baud 13 9 Matej Connect to a Serial USB on Ubuntu 10 10 July 16 2011 URL http stackoverflow com questions 5347962 how to connect to a terminal to serial usb device on ubuntu 10 10 10 Roth T AVR Libc Documentation September 3 2012 URL www nongnu org avr libc 11 Gay L Lynxmotion RIOS SSC 32 V1 06 Lynxmotion July 30 2009 URL http www lynxmotion com images data rios 106h pdf 12 LynxMotion Inc SSC 32 Ver 2 0 Firmware Manual 2005 URL http www robotshop com media files pdf users guide ssc 32 pdf
6. e Figure 5 shows the Web Interface the user would face when operating the arm Each of the sliders represent individual positions the arm can move in The status on the left side will notify the user of any connection or parsing errors of the controller and if it is currently in operation At the bottom custom code can be put in for the controller to follow Each line contains the arm the position of the arm and the speed that the arm moves Selecting Execute Slide Controls will allow the arm to move according to the sliders but will ignore the code Selecting Execute Code will only execute the code that is in input and ignore slider controls First the user code will be parsed and if any errors are encountered the Status window will display the issue 4 Implementation Initial implementation of the Robotic Arm involves communication with the standard for SSC 32 servo controller The BBS is running Ubuntu 10 10 and the first activity was upgrading this to the latest version for ARM The commands to update are as follows sudo apt get install update sudo apt get install upgrade Because of the nature of the lab it is necessary to activate the Ethernet port on the BBS which is performed by sudo ifconfig ethO up sudo reboot Since the SSC 32 operates with RS 232 communication standards Ubuntu needs to recognize the connection interface of USB to Serial The tools for this can b
7. e obtained through apt get as sudo apt get install stty termios gcc avr libc Once these components are installed active development can begin Rebooting the system allows youto dmesg grep tail to view the recent component connections made Stty automatically assigns the USB to serial port as dev tt yUSBO This will be the basis of the connection To open the connection to serial the command will have to be used screen dev ttyS0O 115200 Which will open a blank screen with a single 1 Any characters entered are a direct feed to the serial port To end the session you type Ctrl A Shift K and say yes to kill the session Each time a carriage return is preformed r or enter on the keyboard the SC 332 interprets the command Commands can be formatted according to the firmware documentation from lynx motion 12 An example command is 0 P1500 S1000 r 10 Where is followed directly by the servo motor you wish to control P denotes the position of the motor that it is intended to be P can be between 500 and 2500 where 1500 is considered centered for the servo Inputting commands greater or less than the limits will only push the servo to the limit value The S stands for speed in milliseconds to reach the intended point Therefore the position the servo will move to is 1500 and it will move for an entire second If you place the S before the P this acts as a timer where the servo will attempt to move to the correct
8. esigned to work specifically on Windows operating systems Since the BBS can only utilize Linux due to the ARM architecture commands had to be highly customized for the SSC 32 to accept them Another major challenge is the age of the software stack The most recent update to this system was in 2005 which was almost 10 years ago However within this time span support for even the Lynxmotion RIOS system was difficult Whether it is due to lack of interest of the product or the rapid ageing of technology supporting the Robotic Arm controller proved to be difficult Suggestions for future development would be automatic Arm movement Because the Arm is able to respond to the BBS over the Web Interface it would be trivial to include scripts onto the BBS itself that could control the Arm in unique ways This could involve simple waves at a certain time or a series of movements that can be extended to the Web Interface as a clickable button On a more challenging note the Web Camera on the BBS can be read from the image stream Utilizing this stream it may be possible to notice the position of the Arm and a program could be developed for the Arm to interact with the environment For instance if a new object were placed within the vicinity of the Arm and the Web Camera were able to detect the foreign object the Arm could be manipulated to pick up the object and toss it i e the servos would be prompted in an erratic manner to apply force and po
9. mmunicates with the Robotic Arm via USB to serial interface The Webcam sends its images to the Beagle Bone for transmission to the Client Based on the functional description of the Beaglebone System BBS the software requirements can be formulated as follows 1 The BBS shall accept button input via the Web Interface which will set a component of the arm to move 2 The BBS shall accept input for each component of the arm via Web Interface which is set as Arm Controller number Position and Speed 3 The BBS shall accept text input via the Web Interface specifying one or multiple Arm components and their degrees of placement The BBS shall output an error message via the Web Interface if input components are formatted incorrectly The BBS shall output a status request via the Web Interface which will show the status of each Arm component by degrees The BBS shall output a display of the Robotic Arm s requested position via the Web Interface through a Web Camera stream The BBS shall output an error message via the Web Interface if the Arm is powered off The BBS shall output an error message via the Web Interface if the Arm is unable to move a component to a proposed position 3 Design Description From the software requirements the two interacting pieces of software are the Web Interface and the BBS Client Web Interface Robotic Arm Figure 3 Architectural Design Figure 3 displays the system beh
10. ontrols how often electronic pulses are received 8 Under Linux the serial inputs are seen as tt ySO or ttyS1 Searching with dmesg and using grep can help find the serial input From there the minicom utility can be used to interact with a serial interface even if this interface is operated on USB protocol 9 Since control of the SSC 32 chip is based on Atmel AVR libc is a library toolset to interact on a serial interface This utility allows debugging as well as systems level programming in C the intended language of use for this project 10 Light Weight Wrist Rotate HS 85BB ya AL5B Breakdown anos wii HS 645MG HUB 08 HS 485HB ASB 06 7 ASB 04 S ARS ASB 09 ia A LGA KT i oni Medium Duty Wrist Rotate LG NS ty Mn HS 225MG MA Heavy Duty Wrist Rotate HS 422 HS 485HB er HS 755HB a BR NS HS 485HB Vacuum Gripper Dimensions and Specs SSC 32 Servo Connections With Medium Duty Wrist Rotate Shoulder to elbow 4 757 Channel 0 Base Elbow to wrist 5 00 Channel 1 Shoulder Wrist to tip of gripper 3 375 Channel 2 Elbow Height arm parked approx 6 375 Channet 3 Wrist Height reaching up approx 15 75 Channel 4 Gripper open close Median forward reach approx 7 50 Channel 5 Wrist rotate optional Gripper opening 1 25 Alternate gripper opening 1 875 Lift weight arm extended approx 5 oz Weight 23 oz Range of motion per axis 180
11. wer along with a released grip This would be recommended as a senior level project and in some cases even a graduate level research subject 12 6 References 1 RobotShop Distributions About the Robot Arm Lynxmotion ALSA URL http www lynxmotion com c 124 al5a aspx 2 Fernandez A amp Fernandez V Robotic Arm Remote Control Robotic Arm Remote Control Florida Gulf Coast University November 29 2013 URL http itech fgcu edu faculty zalewski projects files Robotic_Arm_ Redesign Final2012 p df 3 Fernandez A amp Fernandez V Maintenance User Manual Robotic Arm Remote Control Florida Gulf Coast University April 18 2013 URL http itech fgcu edu faculty zalewski projects files Robotic_Arm_Remote_Control_User Manual_V4 pdf 4 Carroll J amp Thomas T Exclusive Online Robotics Robotic Arm Implementation and Testing Florida Gulf Coast University June 2 2014 URL http itech fgcu edu faculty zalewski projects files XRA ImplementationAndtesting pdf 5 Carroll J amp Thomas T Exclusive Online Robotics Robotic Arm Software Design Description Florida Gulf Coast University April 18 2014 URL http itech fgcu edu faculty zalewski projects files XOR S OftwareDesignDocument pdf 6 What is BeagleBone BeagleBone Foundation Junes 26 2014 URL http beagleboard org bone 7 Frye J SSC 32 Manual LynxMotion June 16 2010 URL http www lynxmotion com images html
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