BALL BALANCING - TUM Neuroscientific System Theory (NST)
Contents
1. 8 2 Anaysing Components and Methods 9 2 1 eDVS Data Processing 9 2 1 1 Background 9 2 1 2 Data Format 9 2 1 3 Tracking Algorithm 10 2 14 N oise 10 2 2 Controlling MX28 11 2 2 1 Driving of Motor directly by PC 11 2 2 2 Connection of Motor with LPC1769 11 2 3 PID Control Algorithm 16 2 3 1 Background of PID Controller 16 2 3 2 Implementation in Project PID 17 3 Results 1111M 18 3 1 Connecting the System 18 3 2 Results of the Project 18 3 2 1 Component Level 18 3 2 22. 2 2 1 1 Basic Information The servo is the Dynamixel MX 28 which is provided by Korean company Robotis which has 360 turning ability and a resolution of 0 088 It uses a half duplex communication protocol to communicate other devices More specifically in this project the TTL protocol is used The servo also needs an adapter USB2Dynamixel which could convert the data form Uart form to the USB form setting the bridge between the computer and the servo Other than that the power supply of the servo is provided by an extra cable directly connected to the socket 2 2 1 2 Communication The communication is realized by a Matlab based interface Matlab 2013a and Visual Studio 2010 Ultimate are used to call the function from the dll file named dynamixel dll which is provided by Robotis A short source code is written using Matlab with simple command to set the ID of the two servos and simple command aiming at controlling the turning degree and the angular velocity is written 2 2 1 3 Motor Driving Two servos are series connected with each other with ID of 1 and 2 separately As a separation the servo with ID 1 is labeled with a white dot and the servo with ID 2 is labeled with a red dot All the command that could be sent to the servo are stored in the dll file and there is an control table provided by the Robotis with API references which give guidance for user to control the Servo Because of the limitation from the mechanical structure
3. UART FIFO Use bit FIFO enable bit 0 in register U0 2 3FCR Table 278 to enable FIFO 5 Pins Select UART pins through the PINSEL registers and pin modes through the PINMODE registers Section 8 5 Remark UART receive pins should not have pull down resistors enabled 6 Interrupts To enable UART interrupts set bit DLAB 0 in register U0 2 3LCR Table 279 This enables access to U0 2 3IER Table 275 Interrupts are enabled in the NVIC using the appropriate Interrupt Set Enable register 7 DMA UARTO 2 3 transmit and receive functions can operate with the GPDMA controller see Table 543 Figure 13 Basic Configuration Set MX28 Define motor Initialize active variables parameters set 1 Position of LPC_UART3 speed and MX28 Update new Sent Loop check data every requests for new data 1 5 or 20s get requests on uart3 16 BIBLIOGRAPHY Figure 14 Scheme of a simple operation on MX28 through LPC1769 In order to check if UART3 works well MX28 should be connected to LPC1769 not only physically but also in IDE In the same project we establish MX28 h and MX28 c to control the motor direct by the microcontroller Here I list some very important functions that must be defined and adopted to control the motor Among these to receive the data from motor is very slow After giving a request acquiring data we must wait for a long time The configuration of MX28 must be corresponding to which of UART3 That
4. TO APPEAR HERE 2 2 2 El This data format has all the properties described above besides that it contains byte that describe the time stamp of the event Time stamp is the time point which the event occurs 2 1 3 Tracking Algorithm The eDVS is used to track the ball In this project the shape of the ball is totally ignored only the mass point of the ball is taken into consideration The algorithm calculated the mean value of all the on events and off events the average value of coordinate of both on events and off events is considered to be the center of mass of the ball 92s 1ts 4265 Figure 8 Ball Tracking 2 1 4 Noise Noise is one of the biggest problems concerning the ball tracking the reflection from the ball or the reflection from the plate or the thermo noise of the sensor itself contributes to the most of the noise source A Butterworth Filter could be used as a physical filter to eliminate noise However in this project a so called position filter is used In which the continuous movement is assumed for the moving of the ball it distribute different weight to different position difference The new position which is further away from the old position is considered less likely to be true as a matter of fact with a less weighting factor The new position which is nearer to the old position is assumed be more likely which is given a higher weight 11 2 2 Controlling MX28 2 2 1 Driving of Motor directly by PC
5. chip evaluation boards and supporting development on external target boards 2 Anaysing Components and Methods 2 1 eDVS Data Processing 2 1 1 Background eDVS sensor could detect the movement of the ball by sense the change of light intensity The change of light intensity is converted to electrical signal and after the processing of the microcontroller the data would be synchronized and sent to the computer with a time stamp Depends on whether the light intensity is getting smaller or bigger it could be divided into two categories on event which the light intensity goes high from low and the off even in which the light intensity goes low from high 2 1 2 Data Format There are several typical formats of data from eDVS sensors In principle the eDVS sensor divides the detected space as a 128 by 128 matrix It sends two bytes of information one byte represent the x coordinate and the other byte represent the y coordinate there is also one bit represent the polarity of the events whether on event or off event which is included in the x coordinate 2 1 2 1 E This is the default data form The eDVS continuously send two bytes of data for each on or off events Oyyyyyyy pxxxxxxx the first byte contains information about y coordinate of the matrix the p in this case is a bit which determine the polarity of the event and the other x represents the x coordinate 10 ERROR USE THE HOME TAB TO APPLY UBERSCHRIFT 1 TO THE TEXT THAT YOU WANT
6. means the communication interface must be seamless abutted For example LPC _PINCON gt PINSELO 0x0000000A in MX28 c is to enable TxD3 RxD3 output pins Similarly LCR DIM DLL FDR IER FCR etc must also correspond to UART3 Figure 14 shows the basic scheme of controlling MX28 through LPC1769 According to that a main function has been composed to call the related functions 2 3 PID Control Algorithm 2 3 1 Background of PID Controller PID controller is one of the widely used and classic controllers in industry One of the major merits of this controller is its application for unknown system At the lack of precise understanding of the system itself certain control could be realized by this control method u t Figure 15 PID Controller Figure 2 2 shows the block diagram of a typical PID controller The PID controller is normally used in a closed loop It fetch the error between the set value and the real value of the output as the input for the controller and return the processed the error to the plant 17 process which is the system itself The system itself could normally be described as a dynamical system which composed of a set of differential equations The PID controller in this project is implemented using Matlab by programming the existed PID model The system is described as differential equations which are derived from the physical law 2 3 2 Implementation in Project PID The detai
7. now clarified as below Motor eDVS PID controller Total system Figure 18 Overview of Whole System As has mentioned already most of the module functions have been realized successfully The component driving and processing has been quite successful the system level integration and tuning require 20 BIBLIOGRAPHY 4 2 Outlook As mentioned before the system level integration and tuning requires urgent improvement This project could be seen as a know how project to understand the balancing mechanism in the robot industry in which the robot could be simply seen as its center point The ball balancing should require to extend to balancing of rigid body of certain shape a step further a multi body balancing could achieved as a direct model of Robot balancing system Bibliography 1 https wiki lsr ei tum de nst programming edvsgettingstarted 2 http support robotis com en product auxdevice interface usb2dx1_manual htm 3 http www nxp com techzones microcontrollers techzone tools ecosystem Ipcxpresso html 4 http en wikipedia org wiki PID_controller 21
8. only limited degree of angle turning is possible In this project both servos are only allowed to turn a maximal from 45 to 45 2 2 2 Connection of Motor with LPC1769 2 2 2 1 Connection to UART To control the Dynamixel actuators the main controller needs to convert its UART signals to the half duplex type In our project we adopt such circuit diagram that is shown below 12 ERROR USE THE HOME TAB TO APPLY UBERSCHRIFT 1 TO THE TEXT THAT YOU WANT TO APPEAR HERE DIRECTION_PORT 74HC126 TXD 74HC126 GND PIN1 74HC04 CM 5 internal circuit HALF DUPLEX UART Figure 9 TTL solution The connector pin assignments are as the following The two connectors on the Dynamixel are connected pin to pin thus the Dynamixel can be operated with only one connector attached MX28 works with half duplex That means RX und TX are in one cable pin DATA In order to connect it to our microcontroller LPC1769 we must first do something before There are three pins on MX28 From above downwards are successively GND VDD and DATA As mentioned and depicted above RX of the microcontroller should be connected directly with motor DATA O TX should first connect to a resister of 10Kohm and then to motor DATA TX and RX should be soldered together O The motor needs a power supply of at least 11 Volt The microcontroller can be linked to computer with a USB 2 0 A Mini B cable in order to get power supply That means
9. BALL BALANCING eingereichte PROJEKTARBEIT von Bsc LI Chao Bsc LIU Yiliang Lehrstuhl fiir STEUERUNGS UND REGELUNGSTECHNIK Technische Universitat Miinchen Univ Prof Dr Ing Univ Tokio Martin Buss Univ Prof Dr Ing Sandra Hirche Betreuer Dipl Inf Nicolai Waniek Beginn 18 04 2013 Zwischenbericht 27 05 2013 Abgabe 18 06 2013 Abstract Ball Balancing is a challenging task concerning high requirement of real time property The Ball Balancing experiment could be seen as a benchmark experiment for the robot balancing which view the robot only as the center point of it The experiment takes one eDVS to get the ball s position and velocity and uses a PID controller fuzzy control from a computer LPC Microcontroller to control the two actuators in order to keep the ball stand still on the center of the plate 2 CONTENTS Contents 1 Introduction 444 4444 H44 44mm 5 1 1 Scheme of Mechanical Structure 5 1 2 eDVS 6 1 3 Dynamixel Servo Motor MX28T 6 1 4 Microcontroller 7 1 4 1 LPC1769 7 1 42 LPCxpresso IDE
10. System Level 19 4 Summary and Outlook 444m Hmmm 19 4 1 Summary 19 4 2 Outlook 20 Bibliography 44444 HH nn 20 CONTENTS 1 Introduction In this project the position and the velocity of the ball is tracked by one eDVS Event based Dynamic Vision Sensor with 2 servo motors driving a plate built in a specific mechanical structure which could be tilted in two dimensions A microcontroller using PID control algorithm is aimed at controlling 2 motors on the basis of received sensor data to make them turn in order to keep the little ball stay within a small area of the plate and balanced at the plate 1 1 Scheme of Mechanical Structure Figure 1 Mechanical structure Figure 1 is the mechanical structure used in this project It is built using two plates with two servos in between and a vertical structure with the eDVS sensor mounted on the top The two servos with each possesses one degree of freedom make sure the round plate could tilt in two dimensions 6 ERROR USE THE HOME TAB TO APPLY UBERSCHRIFT 1 TO THE TEXT THAT YOU WANT TO APPEAR HERE 1 2 eDVS eDVS Event based Dynamical Vision Sensor is used to detect the movement of t
11. e ground cable TX3 and RX3 Then the actuator and microcontroller can be connected with each other by soldering following the proposed rule Figure 11 Connection between LPC1769 and MX28 both must have extern power supply 15 2 2 2 3 Development on LPCxpresso IDE The LPCXpresso IDE includes several sample code bundles for various development boards In UART c three most important functions are gt UART3_IRQHandler UARTS interrupt handler gt UARTInit Initialize UART port setup pin select clock parity stop bits FIFO etc gt UARTSend Send a block of data to the UART 3 port based on the data length For the configuration of UART3 we must follow the LPC user manual The following must be configured We check each table to see the right bits and right address for certain functions The UARTO 2 3 peripherals are configured using the following registers 1 Power In the PCONP register Table 46 set bits PCUARTO 2 3 Remark On reset UARTO is enabled PCUARTO 1 and UART2 3 are disabled PCUART2 3 0 2 Peripheral clock In the PCLKSELO register Table 40 select PCLK_UARTO in the PCLKSEL1 register Table 41 select PCLK_UART2 3 3 Baud rate In register UO 2 3LCR Table 279 set bit DLAB 1 This enables access to registers DLL Table 273 and DLM Table 274 for setting the baud rate Also if needed set the fractional baud rate in the fractional divider register Table 285 4
12. he ball in this project eDVS could detect the change of the light intensity on the retina and feedback to the microprocessor as event as binary data DVS sensor chip lens removed Lens Capacitors for Bias setup Microcontroller and system clock 52mm UART TWI and SPI connectors Power Management 23mm Figure 2 eDVS128 Figure 2 describes the eDVS128 which is also the one used in this project It contains three major parts The Lens which captures the change of light intensity then the DVS sensor chip could turn the light signal to electrcial signal which could be processed by microcontroller Then microcontroller would process the data and add time stamp Above the microcontroller there is a FTDI chip which is a converter between Uart signal and the USB signal 1 3 Dynamixel Servo Motor MX28T Figure 3 MX28T Dynamixel actuators have been widely used by our Neuron Computation Lab in the TU Munich The actuator has an onboard microprocessor to facilitate bus communication positional feedback temperature and load monitoring The torque peed and response are adjustable In addition position load and voltage feedbacks are also available Usually there are TTL and RS 485 serial communication that allows for daisy chainable bus connections at up to 1 3mbps in the servo motor In our case we operate MX28T which complies with the network interface TTL MX28R is RS485 What is also worth mentioning i
13. he angle the servo should turn and also the turning velocity Mainly through the function of the PID controller the ball should be able to stay within certain area from the middle point BE PIT Gale Figure 17 A picture of the system 3 2 Results of the Project 3 2 1 Component Level The simulation and processing of every main component has worked successfully First the eDVS could fetch data from events changing and the computer is able to process these events to get the real time position and the velocity of the metal ball 19 Secondly UART3 communication has been successfully established Sending data per UART3 with PC can be realized Moreover the motor could be driven successfully to turn to arbitrary angle with arbitrary angular velocity within the physical standard of these servos directly through PC However to control the actuator with LPC is still expected to be realized though the UART protocol and configuration of motor have been finished successfully Possible reasons could be the loop algorithm is not fit enough for the actuator At last the PID controller is successfully implemented in the computer with a descent impulse response 3 2 2 System Level The integration of the PID controller to the system could not function successfully This is the missing Link of this project further work required to be done on this topic 4 Summary and Outlook 4 1 Summary The whole structure of the project is
14. l description of the system remains unknown which means the relation between turning angle and the velocity of the ball remains unknown x t Mechanical Communication systeme PID controllere Figure 16 System Scheme The relation between 0 and x is unknown in this system As the mass and also diameter of the ball is unknown In this project the relation between them are determined experimentally As different velocity v are tested with different angles the following relation has been determined 0 0 5 10 20 30 40 v 0 2 7 5 5 8 5 9 10 The unit of the angle is degree and the unit of velocity is pixel per meter There is no need to match every unit to the international standard unit as the parameter of PID controller could also function as a correct factor The displacement x is the integral of v with time t As the relation between v and is clear it is relative easy to derive also the relation between t and x 18 BIBLIOGRAPHY 3 Results 3 1 Connecting the System The system is built by connecting two servos and the eDVS to the computer and is placed two sensors and the eDVS on the mechanical structure The eDVS detects the ball and transmits the data to the computer the events sent from eDVS will be processed by the computer to get the position and velocity of the ball The position and velocity of the ball would be processed by the PID controller programmed within computer to send t
15. oard consists of two parts LPC Link debug interface and an NXP LPC ARM based microcontroller target The LPCXpresso target board includes an integrated JTAG debugger LPC Link so there s no need for a separate JTAG debug probe The target portion of the board can connect to expansion boards to provide a greater variety of interfaces and I O devices The on board LPC Link debugger provides a high speed USB to JTAG SWD interface to the IDE and it can be connected to other debug targets such as a customer prototype In our project we use the LPCXpresso IDE to better perform the debugger as well as the target 1 4 2 LPCxpresso IDE LPCXpresso is a development platform available from NXP The software consists of an enhanced elipse based IDE a GNU C compiler linker libraries and an enhanced GDB debugger The LPCXpresso IDE is based on the Eclipse development platform and includes several LPC specific enhancements It is an industry standard GNU tool chain with an optimized C library With these tools we can develop software solutions quickly and cost effectively LPCXpresso is based on Eclipse with many LPC specific enhancements It also features the latest version of the industry standard GNU tool chain with a proprietary optimized C library providing professional quality tools The LPCXpresso IDE can build an executable of any size with full code optimization LPCXpresso supports the full embedded product design cycle by moving beyond
16. s that MX28T complies with PID Additionally the operating angle ranges from 0 to 360 But one thing that should be mentioned is that in our entity the angle is quite limited less than 40 As a whole MX28 is a high performance networked actuators for robots fully integrated with feedback function and programmability Figure 4 USB2Dynamixel What figure 4 is showing is USB2Dynamixel which is used to be connected between the actuator and the computer directly Thus a PC can directly communicate with the actuator 1 4 Microcontroller 1 4 1 LPC1769 The LPC1769 is a Cortex M3 microcontroller developed by NXP Semiconductors for embedded applications featuring a high level of integration and low power consumption at frequencies of 120 MHz Some important features include 512 kB of flash memory 64 kB of data memory 4 UARTs 2 CAN channels motor control PWM ultra low power Real Time Clock with separate battery supply and up to 70 general purpose I O pins The LPC1769 is pin compatible to the 100 pin LPC2368 ARM7 MCU 8 ERROR USE THE HOME TAB TO APPLY UBERSCHRIFT 1 TO THE TEXT THAT YOU WANT TO APPEAR HERE Figure 5 LPC1769 It can be applied in many areas such as e metering lighting industrial networking alarm systems white goods and motor control and so on In our project we use LPC1769 to operate the MX28 LPC Link Figure 6 Debugger and Target As figure 6 already shows the whole LPCXpresso development b
17. we don t need VDD pin 2 2 2 2 UART and Pin Assignment There exists 4 UART in the LPC1769 Because UARTO and UARTI in some cases may have its specific functions in this project we have chosen UART3 as our communication interface 13 LPC LINK side Expansion Connector superset of mbed pinning mbed LPCXpresso OEI AE AS AO LPCXpresso mbed RO Kap art ee 2020 a AO Were Th a nasies wasser M a Le pepe a wenden ie dr VE tater mar a ce gt nnd Tr rn SEN wein eas 21 va sueca ae vai rom Ins n r so RD tere are aor y Cas snt Ms TR are SI mae uo gt res we mar sa 1 gt 10 7 TD Phere ae a or jiti WS Toms Tue ET mar nay A u Ta ruca Tau wo 1 gt ree Fa ne o A er ni TER Te BIETER TEN CO gt sea ne TREE UIST aA ARTAR TE gt ai LN Rae LATA ese Hs ML 1 a E77 u 75 am RT no zu 7 mm a an 00 1 lem Cr mans ma TIEN EN 27 0 et nn fr u A sesa A m u mi m aes nor sns mi PA PA Rr 1 o gt ma mu ies al a wi Cr 1 gt Pam Er eu 1 Pao e sa a ne uF Orne Orso Orne Orn gt szu aT vo om Oro Ort A ran ne 9 Qonsu ua s es gran Oro a Figure 10 TTL solution Here is the whole schematic for the LPCXpresso According to what have been analyzed above on the left side the pin GND pin P0 0 and pin p0 1 are chosen which is respectively th
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