Khepera III Mobile Robot – Practical Aspects
Contents
1. 1 V2 v s Depending on the assignment of v and v9 to the two motors the robot will perform a left or right circular movement with the inner radius r With the remarks on Khepera III C programming given above and the comments included the c code available from http www uni koeln de phil fak muwi sm research k3 khepera html should be readable References 1 Braitenberg Valentino 1984 Vehicles Experiments in Synthetic Psycho logy Cambridge MA MIT Press 2 Burger Birgitta 2007 Communication of Musical Expression from Mobi le Robots to Humans Recognition of Music Emotions by Means of Robot Gestures Master s thesis KTH Stockholm 3 Camurri Antonio Coletta Paolo Varni Giovanna amp Ghisio Simone 2007 Developing multimodal interactive systems with EyesWeb XMI In Pro ceedings of the 2007 Conference on New Interfaces for Musical Expression NIME07 New York NY USA 305 308 4 Ichbiah Daniel 2005 Robots From Science Fiction to Technological Re volution New York Harry N Adams 28 5 6 7 10 11 12 13 14 15 16 17 Intel 2003 Intel PXA255 Processor Developer s Manual Tech rep Intel Intel 2003 Intel PXA255 Processor User s Manual Tech rep Intel Jensenius Alexander Refsum 2006 Using Motiongrams in the Study of Musical Gestures In Proceedings of the 2006 International Computer Music Conference New Orle2. the grid object functions as a controller resembling a joystick The numerical values generated by the slider and grid objects range from 0 to 100 calculation of the actual values sent to the robot is encapsulated in the pd get wheel speed canvas object in the pd move object the values are combined into messages with the appropriate control command setmotspeed 11 display values recieved OSCroute speedA steerA speedB steerB i E E send data within pd Figure 4 Patches for control of the Khepera III via OSC Top separate patches for speed and direction control Bottom patch receiving control data In addition to the patch discussed a set of small Pd applications for movement control of two Khepera III robots via OSC connections shown in Figure 4 was prepared In the patches displayed in the top row numbers in the range 0 to 100 generated by slider objects are combined into messages with keywords indicating the intended use of the numbers the keyword steerA refers to direction control the keyword speedA to speed control and the capital letter A included in both keys indicates the robot addressed Using the sendOSC object the messages are coded according to the OSC specification and sent to the IP address and port defined in the connect message box On the computer indicated by the IP address the messages can be received and decoded us
3. else t KB ERROR knet getCommand KB ERROR KH3SZFMTERR return KH3 ERROR SZFMT 25 4 1 C Programming Initial Steps Short List of C Programs k3 circle test c application that lets K3 move on a circle with a given radius and speed for an amount of time to be entered in milliseconds Ente ring 0 will terminate the program Default value for speed 20 Default value for radius 20 cm Alternative values for speed and radius can be specified as command line parameters k3 circle test radius motspeed i e the first parameter will be interpreted as radius the second parameter if present as speed value A simple form of obstacle avoidance for K3 is implemented in k3 move dur if any of the ir sensors 3 4 5 or 6 returns a proximity value exceeding the value defined in macro K3 IR THRESHOLD K3 moves backward 300 ms turns on the spot away from the obstacle and resumes the original motor speed values k3 neural 2 c perceptron included in control program network configura tion etc provided via command line interaction learning of patterns entered via command line and sensor interaction pdcontrol c control program for Pd interaction with the Khepera3 robots used within the project Different robots denoted by capital letters A and B are distunguished by the port numbers used In addition to these programs the followoing header files will be needed 1 pue 3 k3 def
4. X KF X remark This function requires that kb kh3 init has been called int kh3 sendcommand knet dev t hDev unsigned char in 1 char sizeMsg first byte in the frame is the complete frame size sizeMsg in 0 if knet llwrite hDev in sizeMsg sizeMsg return sizeMsg else KB_ERROR knet_sendCommand KB_ERROR_KH3FRMSNDERR return KH3 ERROR FRMSND 24 Code Fragment kh3_getcommand kh3 getcommand gets a command frame from a given khepera3 device Function flow a retrieve the first byte which is the frame size from the device b retrieve the required bytes Normally an end user don t want to use these function as they are assumed as low level functions param hDev is a handle to an openned knet socket Khepera3 dsPic Mparam out is a pointer to a buffer where the command frame will be stored on return A value 0 on error KH3 ERROR FRMSZERR KH3 ERROR SZFMTERR gt 0 on success returns should be the size of frame remark This function requires that kb kh3 init has been called int kh3_getcommand knet_dev_t hDev unsigned char out char sizeMsg int rc if knet_llread hDev amp sizeMsg 1 1 rc knet_llread hDev out sizeMsg if rc sizeMsg return rc else KB_ERROR knet_getCommand KB_ERROR_KH3FRMSZERR rc sizeMsg return KH3_ERROR_FRMSZ
5. char Buffer MAXBUFFERSIZE if kh3 proximity ir char Buffer dsPic i sprintf irdata proxir 4c 44 4u 44 4u 44 4u 44 4u 44 4u 4 4u 4 4u 4 4 4u 4 4u 1lu n Buffer 0 Buffer 1 Buffer 2 lt lt 8 Buffer 3 Buffer 4 8 Buffer 5 Buffer 6 lt lt 8 Buffer 7 Buffer 8 8 Buffer 9 Buffer 10 8 Buffer 11 Buffer 12 8 Buffer 13 Buffer 14 8 Buffer 15 Buffer 16 8 Buffer 17 Buffer 18 8 Buffer 19 Buffer 20 8 Buffer 21 Buffer 22 lt lt 8 lt lt 16 pdsend 9999 rip irdata else printf r nn error r n First two character arrays are declared the character array Buffer will be used to store data read from the sensors which in turn will be written into the character array irdata together with the keyword proxir It is the array irdata that is sent to the computer hosting the Pd patch where this message is selected according to the keyword by the route proxir object In the head of the if statement another function kh3_proximity_ir is called The integer return value of this function decides which of the branches will be executed for non zero return values data will be processed and sent to the host computer for a zero return value an error message will be printed The function kh3_proximity_ir defined in the file kb khepera3 c of the libko rebot distribution is called with two arguments The first argument is a pointer to the array Buf
6. contains command name min number of args max number of args the function to call static kb command t cmds i quit 05 0 5 quit exit 30 0s quib s bye 0 9 0 2 qit ciao bella 3 0550s qit setcfg 2 2 4 configure0S getrev 0 0 revisionOS getbat 0 O voltageBAT rststamp 0 O tstampRST getambir 0 O ambIR getproxir 5 0 4 0 proxIR getus 1 1 measureUS setmotspeed 2 2 motSpeed setmotmove 2 2 motMove motstop 0 O MOES EOP help 0 0 help getallus 0 1 getallUS benchmark 1 1 getBenchmark reboot O0 O doReboot alive 0 1 alive NULL 0 O NULL T 17 As can be seen from the first four entries any number of strings can be associated with one function name here quit As also illustrated command names can be arbitrary but should be chosen so as to indicate the function performed The commands defined in our example may pertain to list not exhaustive the operating system of the dsPIC processor setcfg can be used to confi gure the mode of operation e g the number of US sensors active getrev retrieves the current revision of the operating system further information about the current state of the robot getbat in the revision addressed here retrieves the momentary battery voltage in a more recent version
7. interactive applications but also con fronts the developer with a new set of challenges e g dealing with the use of embedded Linux operating systems but partly also resulting from insufficient documentation and the lack of example applications As reported elsewhere Schmidt 2005 21 2007 22 Schmidt Seifert 2006 23 a technical goal of our project is to provide an interface for the Open Sound Control OSC protocol to access the control of the Khepera III robot The OSC protocol was designed to connect sound programming applications via standard internet connections providing a flexible framework to specify messages sent bet ween the applications e g Wright Freed Momeni 2003 29 Wright 2005 28 current state of the protocol specification 27 26 The protocol has been im plemented within popular sound programming environments such as Max MSP Pure Data Pd and SuperCollider but even in general purpose programming languages such as Java or C Thus an OSC interface could enable access to 2 the Khepera III independent of the application programming language used Of particular interest for the implementation and investigation of interaction based on sound related movements gestures may be the possibility afforded by an OSC interface to integrate work presented by Jensenius tools are developed for the analysis of musical gestures to be run within the Max MSP Jitter environment along with the discussion
8. param outbuf is a buffer where the data will be stored on param hDev is a handle to an openned knet socket Khepera3 dsPic return NULL or a pointer to the IR measure x int kh3 proximity ir char outbuf knet dev t hDev int rc i Frame format Size Command Terminator where the command can be more than 1 byte char cmd 3 2 N O if hDev kh3_sendcommand hDev cmd delay to ensure the correct reading of KNET_INTO pin usleep K3_CMD_DELAY while kb_gpio_get KNET_INTO rc kh3_getcommand hDev outbuf return rc I return 0 As evident from the specifier preceding the function name the return value of the function is of type integer but according to the last line of the initial comment it should be a NULL pointer or a pointer to the array holding sensor data This is another example of documentation problems which led to misunderstandings and delay in setting up the Pd interaction As discussed in the previous section the two arguments of the function are poin ters to an array holding data and to the device data will be retrieved from the dsPIC processor In the body of the function a command frame cmd is defined in the form of a character array The array holds as its first element the number of bytes following 21 this element The second element is a character specifying a command of the communication protocol here the capital letter N if required a
9. would set the TCP IP protocol The IP address and receiving port number of the robot need to be edited in the message box containing the connect command The robot s receiving port is defined in the control program running on the KoreBot board the IP address must of course conform to the momentary IP configuration of the KoreBot Data is sent to the robot in the form of messages consisting of sequences of characters including numerals which by the control program are interpreted as 10The shapes and basic functionality of the Pd boxes used in Figure 3 are indicated in the following figure object box function message box message to be sent E number box displaying numbers ix toggle on off switch EA al slider numbers by position of vertical bar peeds TeeuA 393 pd yoolqo SeAu 2 OY ur peunro Iod st Io O13quOO IOJOU 0 juos son e poods enjoe Jo uone JUS IOMOT quouro1nseour Gf 193uo5 quouromnseour YT 3jJo o 3uoo juouroAour JZU Toddn uoryeorunururoo x10439u 0 puodsoxioo ATYSNOI suordo1 popunoqq Hyuemerb setqo 3 1ox2oeq JTLT L00Z u zu y S sn3ob puos p sn3ob puos sn3ob puos z sn306 puos I sn306 puos 293 3eq39b puos 3 h loog ox3 u pump er aural no surad drou pues p ds amstaa it 3obrds obrds Snqep urezboid 312359 jarnb pues feumnuaxod WER 30g OST s amp ox10s2no pd V3oquoi oSAT92ed TI 6666 9AT929
10. 439u v3OqOo3 eATe2ed JOS6t SII OL S6 T TI 329uuoj pezriou3neun qTTxew ouo o o 33odur od HueqpeotT A1o33 eq 93noi v3oquo1g puos Figure 3 Pd patch implementing the wireless communication with the Khepera III robot 10 names and arguments of robot control commands Whenever any of the message boxes containing a message that starts with send is activated by clicking or by an activating impulse bang from another component of the patch the part of the message following send e g quit or getambir is transmitted to the robot by the netsend object Incoming data from the robot is received by the netreceive object The first creation argument of netreceive sets the port of the host computer listened to in the control program running on the KoreBot this is defined as the sendport number In a setting involving more than one robot different sendport numbers are specified in the resp control programs to keep apart data from the different sources Within the patch data received from the robot is distributed using the Pd internal send and receive objects data transmitted from the send frombotA object will be processed by any receive frombotA object in any currently opened Pd patch Data to be processed is selected using the Pd route function the need for the consecutive route objects in the context of IR measurement will become clear in the discussion of low level control below The evaluatio
11. Khepera III Mobile Robot Practical Aspects Liider Schmidt in cooperation with Benjamin Buch Birgitta Burger Son Hwa Chang Andreas Gernemann Paulsen Jochen Arne Otto Uwe Seifert As a first step towards the investigation of robotic artifacts within artistic sound related contexts it was decided as a part of the project Artistic Interactivity in Hybrid Networks subproject C10 of the collaborative research project SFB FK 427 Media and Cultural Communication funded by the national german re search foundation DFG to utilize a pair of Khepera II robots One aim is the investigation of patterns of interaction at least at a rather small scale and to gain some insight into the technological issues relating to problems of human animat artifact interaction in general The Khepera II robot is a popular device widely used for the investigation of behaviors such as obstacle avoidance or wall line following see examples in Pfeifer Scheier 1999 19 Chapter 5 or the implementation of the so called Braitenberg vehicles Braitenberg 1984 1 Pfeifer Scheier 1999 19 Chapter 6 Even evolutionary techniques have been attacked Nolfi Floreano 2001 18 and not least the Khepera II platform has functioned as an educational tool in the field of robotics Ichbiah 2005 4 page 420 As a consequence a substantial body of project descriptions and applications for the Khepera II is available on the internet As a rathe
12. ans Jensenius Alexander Refsum Camurri Antonio Castagn Nicolas Mae stre Esteban Malloch Joseph McGilvray Douglas Schwarz Diemo amp Wright Matthew 2007 a Panel The Need of Formats for Streaming and Storing Music Related Movement and Gesture Data In Proceedings of the 2007 International Computer Music Conference Copenhagen Jensenius Alexander Refsum Castagn Nicolas Camurri Antonio Mae stre Esteban Malloch Joseph amp McGilvray Douglas 2007 b A Summary of Formats for Streaming and Storing Music Related Movement and Ge sture Data In Proceedings of the 4th International Conference on Enactive Interfaces Grenoble Jensenius Alexander Refsum Godoy Rolf Inge amp Wanderley Marce lo M 2005 Developing Tools for Studying Musical Gestures within the Max MSP Jitter Environment In Proceedings of the International Music Computer Conference Barcelona 282 285 Jones Joseph L Flynn Anita M amp Seiger Bruce A 1999 Mobile Robots Inspiration to Implementation Second Edition Natick MA A K Peters Kohler Achim 2007 Der C C Projektbegleiter Heidelberg dpunkt verlag Kriiger Guido 2007 C Programmierung Bonn et al Addison Wesley Lambercy Fredric amp Bureau Pierre 2007 Khepera HI User Manual Tech rep K Team Corporation Yverdon les bains www k team com Microchip 2003 PIC18F2331 2431 4331 4431 Data Sheet 28 40 44 Pin Enhanced Flash Microcontrollers w
13. d in the discussion Further extensions available for the Khepera III and displayed in Figure 2 lower right panel include the KoreSound card providing audio input and output and a USB camera 2 Pd Interaction with Khepera III We will start our discussion of interaction with the Khepera III robot with the description of a pure data pd application providing a high level interface The patch shown in Figure 3 was originally prepared by Tobias Grewenig and Ralf Baecker within the research project mentioned above some additions and corrections were introduced by the present author In the figure four regions enclosed by polygons are displayed These regions correspond roughly to different types of functionality 1 In the upper right area functions pertaining to network interaction are collected 2 the area on the left is related to movement control of the robot 3 functions in the lower right area address the ultrasonic sensors and display data obtained from US measurement 4 the functions collected in the lower middle evaluate data retrieved from the infrared sensors Network communication with the Khepera III is established using the Pd netsend and netreceive objects Here they are used with a non zero creation argument the argument following the function name in the corresponding object boxes specifying the network protocol to be used as the UDP User Datagram Protocol protocol a zero or missing creation argument
14. dmissible followed by any arguments of the command none in our case The last element of the command frame is 0 used as a terminating symbol The function kh3 proximity ir makes use of two other functions kh3_getcommand and kh3 sendcommand which too are defined within the file kb_khepera3 c As the names indicate the first of these is used to pass the command frame to the dsPIC processor the second retrieves the answer produced by the dsPIC and writes it to the array Buffer referenced by the pointer outbuf Between the passing and retrieving commands a delay is inserted consisting of a fixed amount of time defined by the constant K3_CMD_DELAY and a variable part determined by the condition of a while loop In the file kb_khepera3 h the constant K3_CMD_DELAY is set to 300 ps the while loop waits for a certain pin to signal readiness 22 3 4 Interacting with the dsPIC kh3_sendcommand and kh3_getcommand The functions kh3_sendcommand and kh3_getcommand are as far down as we will have to go All sensor related functions defined in the control program eventually make use of these functions because the sensors are controlled by the dsPIC processor Although appropriate commands for motor control are available in the commu nication protocol these can not be used in the manner described here Since the dsPIC processor operates in the I2C slave mode in connection with the KoreBot board no commands will be issued to the I2C de
15. erson manipulating the other control parameter of the robot needs to be established other persons might be interfering with one operator s actions technical problems include reaction times of the robots and delays in the transmission of control commands It is intended to replace the sliders by other input devices such as sensors registe ring body movements or motion tracking applications as developed by Jensenius see above the EyesWeb system Camurri et al 2007 3 A first motion tracking application based on the patch described has been implemented by Jo chen Arne Otto see Section 2 1 More sophisticated robot behaviors will be taken into account as well 13 2 1 Motion Tracking Using SoftVNS Movement control of the Khepera III robot by camera based motion tracking was implmented in the patch shown on the next page The patch is based on a one to one port with the exception of the grid object of the Pd patch of Figure 3 to the MaxMSP environment also provided by Tobias Grewening and Ralf Baecker Motion tracking functionality has been incorporated by use of the softVNS external objects for MaxMSP by David Rokeby Here a region of the camera image shown on the right can be selected and tracked by the video processing objects collected in the subpatch p softvns x and y positions of the tracked region are mapped to the sliders for direction and speed control of the robot Motion tracking components of
16. fer defined locally within the function prixIR The second argu ment is a pointer to the device addressed and is defined globally for the complete control program As the name of the second argument suggests the device ad dressed is the dsPIC 30F5011 processor running the communication protocol The handling of data retrieved by the function kh3_proximity_ir closely reflects the way data is returned when the command N is entered in the communication protocol see above page 6 The first element of Buffer Buffer 0 which 19 encodes the small letter n is processed independently The following elements of Buffer are combined in eleven pairs each pair encoding the reading of an IR sensor in two bytes The bit shifting operation performed on the second element of each pair points at the fact that numbers are encoded in the little endian format The inclusion of the element Buffer 0 necessitates the presence of the route n object in the part of the Pd patch evaluating IR sensor data 14 8 shifting 8 bits one byte to the left 20 3 3 Integrating the Communication Protocol kh3_proximity_ir Turning to the function kh3 proximity ir will illustrate the way commands of the communication protocol are accessed by control programs running on the KoreBot board The definition of this function including comments is presented in the following code fragment kh3 proximity ir retrieves an instant IR measure
17. floor as follows for an illustration see Figure 6 v1 speed of inner wheel T wheel distance 13 cm radius of circle Figure 6 Driving a circle with a Khepera III robot The radius of the circle is measured as the distance from the center to the inner wheel and the speed v is measured for this wheel The desired radius r of the circle is specified as the distance from the center of the circle to the wheel closer to the center henceforth inner wheel The distance rg to the farther wheel will then be T9 r1 d http www ipem ugent be ISSSM2007 ISSSM2007 html http bricxcc sourceforge net nbc 1TNXC programming was done jointly using a collaborative text editing tool by B Buch B Burger S Chang J Kim J A Otto L Schmidt and U Seifert 27 where d is the distance between the two robot wheels which amounts to d 13 cm For the robot to stay on the circular track both wheels will have to move around the center of the circle with a common angular velocity w Therefore the speeds v of the inner wheel and v of the outer wheel will be vi wr U2 WT 2 Calculating the ratio of the speeds will cancel out the common factor w U2 T2 ri d 14 d iE n T U1 Ti Ti Ti Thus specifying the inner radius r of the circle and the speed v of the inner wheel the appropriate speed v2 for the outer wheel to keep the robot on the desired circular course will be d
18. hich can be connected to the RS 232 connector of the KoreConnect adapter intended for operation of the Khepera III in the basic configuration without a KoreBot extension The major innovation introduced with the Khepera III robot is the possibility to connect a KoreBot board via the KB 250 extension bus i e by stacking the KoreBot board on top of the robot The main component of the KoreBot board is an Intel PXA255 XScale pro cessor running at 400 MHz with 60 MB RAM and 32 MB flash memory The PXA255 processor was developed for handheld computing applications 5 page 1 1 supporting an ARM embedded Linux operating system for technical details concerning the processor see PXA255 User s Developer s Manual 6 5 In addition the KoreBot board provides a PCMCIA slot to which in our case a standard wireless network card is connected In Figure 2 top row the topmost level of the robot is formed by another version of the KoreBot board carrying two PCMCIA slots in the actual version Figure 2 bottom row the layout has been changed allowing to stack further extensions on top of the KoreBot board which is situated within the robot s chassis When the KoreBot board is mounted on the Khepera III robot the dsPIC micro controller running the communication protocol switches to the I2C slave mode As a consequence the control commands described above can no longer be ente red directly Instead commands have to be transmitted to
19. ing the command A will result in the robot entering the Braitenberg mode which instantiates some form of wande ring behavior including obstacle avoidance no detailed description is given in the User Manual and returning the small letter a on the command line As another example which will be taken up below consider the command N entering N will result in the retrieval of the current proximity measurements of the IR sensors The answer displayed on the command line consists of the small letter n followed by eleven numbers representing the sensor readings in the order described above and another number specifying the relative time stamp i e the value of the relative time counter User Manual page 36 indicating the time of measurement Further commands are used to configure the mode of operation of the Khepera III 5Even the format of the numbers returned is not specified coherently according to Section 3 3 the values are 12 bit numbers without type specification in Appendix A describing the built in commands the values are defined as 10 bit numbers to set various options for the motor controllers or the desired speed position values or to retrieve other data from the robot see Appendix A of the User Manual for a complete list To access the command line e g via a serial connection a terminal emulator should be running on the host computer and be connected to a serial port w
20. ing the dumpOSC listening to the port defined in the sending patches see bottom row of Figure 4 Here the message received is transmitted further within the Pd application using the s rcvOSC object A corresponding r revOSC object is included in the control patch of Figure 3 again using the route function to select data for speed and direction control according to the keywords speedA and steerA These patches were informally tested in a playful classroom situation serving as an example to illustrate possible applications of the OSC protocol The slider patches were running on five or six different laptop computers and there was a host computer running control patches for both robots Participants were given Ils is used as an abbreviated form of send likewise r is used as a shorthand for receive 12 the task to collaborate in controlling the robots in order to push a small box in a certain direction collaboration of at least two operators is required to steer one robot because only one slider can be operated on any computer at a time The task turned out to be tricky for the following reasons since the robots look alike the operators first need to find out which one reacts to the objects they are manipulating and keep track of their robot once they found out operators can not be certain whether the reaction observed was a result of their action coordination with the p
21. initions h pdsend h percept2 h C programs can be retrieved from http www uni koeln de phil fak muwi sm research k3 khepera html following the link C Programme 4 2 Driving Circles The movement patterns developed by Burger 2007 2 for the LEGO NXT robot M e X contained as one major component circular segments Originally the patterns were implemented in the graphical programming environment NXT G provided by LEGO 26 In preparation for an observational experiment performed at the International Summer School in Systematic Musicology ISSSM 2007 in Ghent the programs were re written in the textual programming language Not eXactly C NXC One of the questions addressed in this experiment concerned the impact of the robots shape on the outcome of observational data It appears meaningful to re write the programs once again in the language C for an implementation for the Khepera III robot in order to include the Khepera III in an extended comparison As a building block we will present here a short program implementing movement of the Khepera III on a circle with a given radius Since the direction of the robot s movement is determined by the speed settings of the two motor controllers it is necessary to provide a formula calculating the appropriate relationship between motor speeds for a desired circle radius The formula is derived from simple geometrical considerations assuming ideal contact between robot wheels and
22. ith nano Watt Technology High Perfor mance PWM and A D Tech rep Microchip Technology Incorporated Nehmzow Ulrich 2000 Mobile Robotics A Practical Introduction Lon don Springer Nichols Bradford Buttlar Dick amp Proulx Farrell Jacqueline 1996 Pthreads Programming Beijing et al O Reilly 29 18 19 20 21 22 23 24 25 26 27 28 29 Nolfi Stefano amp Floreano Stefano 2000 Evolutionary Robotics The Bio logy Intelligence and Technology of Self Organizing Machines Cambridge MA MIT Press Pfeifer Rolf amp Scheier Christian 1999 Understanding Intelligence Cam bridge MA MIT Press Philips Semiconductors 2000 The I C Bus Specification Version 2 1 Tech rep Schmidt Liider 2005 Towards an Embodied Cognitive Science of Mu sic Incorporating Mobile Autonomous Robots Into Musical Interaction In APSCOMOS Seoul Schmidt Liider 2007 Embodied Cognitive Science as a Paradigm for Mu sic Research In Lischka Christoph amp Sick Andrea eds Machines as Agency Artistic Perspectives Bielefeld transcript Verlag University of the Arts Bremen Press Series 04 48 62 Schmidt L der amp Seifert Uwe 2006 K rperlichkeit und Musik In Neue Zeitschrift f r Musik 4 44 45 Tanenbaum Andrew S 2009 Modern Operating Systems Pearson Pren tice Hall Webb Barbara Reeve Richard Horchler Andrew amp Qui
23. l of speed measuring the number of pulses in time the maximum speed is specified as 1 m s For both control modes different options and values including proportionality constants for PID controllers can be set The motor controllers act as I2C slave devices for a detailed description of the I2C bus see 20 gt All technical details if not explicitly stated otherwise are taken from the Khepera III User Manual Lambercy Bureau 14 the version referred to here is dated 2007 03 12 and the specifications published on the website of K Team Corporation http www k team com The material referred to can be retrieved in the latest revision from this site 6691 2 pulses correspond to 27r therefore 691 2 110 01 pulses correspond to r On the other hand 110 pulses correspond to 20mm therefore the radius r equals 20 mm and the diameter will be 40 mm The value of 22 pulses per 1 mm robot movement given in the online specification does not appear to be compatible with the User Manual the actual size of the wheels Tresp 0 5 m s following the online specifications 4 Figure 2 Khepera III mobile robot Top row Prototype still without chassis Bottom row Left panel standard form right panel with KoreSound card and USB camera Even the IR sensors provide two modes of measurement Every sensor consists of one receiver for infrared radiation and one emitter In the mode using only the receiver part of the sensors the inten
24. n the following we will specifically discuss the command for retrieving an am bient IR measurement which involves both receiving and sending data on the side of the robot in order to gain some insight into the control architecture im plemented in the libkorebot distribution The complete listing of the code for the control application can be retrieved from our websitet We will only look at functions specific to the Khepera III platform i e details of setting up the network connection will be left out Phttp www uni koeln de phil fak muwi sm research k3 khepera html link to c programs file pdcontrol c 16 3 1 Decoding Messages Command Table and Command Parser Messages sent to the robot via an existing network connection will be written into a character array This array will be parsed by a function defined in the file kb commandparser c of the libkorebot distribution for names and arguments to be executed the parsing function is invoked by the line kb parse command sbuf cmds NULL sbuf is the name of the buffer containing the data and cmds is the name of a structure defining the available command names More specifically the command table cmds maps arbitrary strings to a minimum and a maximum number of arguments to be entered and the name of a function to be called The actual function call is issued by the command parser program The command table of our application is defined as follows The command table
25. n ultrasonic measurement in the application shown is restricted to the display of sensor values the geometrical arrangement of the number boxes in the patch reflects the placement of the corresponding US sensors on the robot Even the number boxes displaying the reading of the IR sensors red boxes in the lower middle area are arranged corresponding to the placement on the robot discarding the data retrieved from the ground sensors The values in this patch are used for two different purposes whenever any sensor reading exceeds the value of 300 an activating impulse is generated On the one hand this is sent to the pd sounds canvas object triggering the playback of a short sound sample boing the functions used are encapsulated within the canvas object On the other hand the impulse is sent to the pd autopilot canvas object that implements an automatic movement control of the robot including obstacle avoidance When the autopilot is turned on and receives an impulse resulting from an IR sensor reading higher than 300 indicating the presence of some object in the vicinity of the robot the robot s direction of movement is inverted until new speed and direction values are generated randomly When the autopilot is turned off movement of the robot can be controlled in two different ways using this patch the green slider objects are used to generate values for speed vertical slider and direction horizontal slider independently
26. nn Roger 2003 Testing a model of cricket phonotaxis on an outdoor robotic platform In Proceedings of TIMRO3 Wright Matthew The Open Sound Control Specification http opensoundcontrol org spec 1_0 Wright Matthew OpenSound Control Specification http www cnmat berkeley edu OpenSoundControl 0SC spec html Wright Matthew 2005 Open Sound Control an enabling technology for musical networking In Organised Sound 10 3 193 200 Wright Matthew Freed Adrian amp Momeni Ali 2003 OpenSound Con trol State of the Art 2003 In Proceeding of the 2003 Conference on New Interfaces for Musical Expression NIME 03 Montreal 30
27. of relevant features for the analysis and appropriate formats for streaming related data e g Jensenius Godoy Wanderley 2005 10 Jensenius 2006 7 Jensenius et al 2007a b 8 9 4 At the time of writing the goal of providing an OSC interface has not been achieved yet A preliminary solution using a network connection via a Pd patch however can be presented and will be described in some detail below This de scription will include aspects of the robot s control architecture the knowledge of which is a prerequisite for setting up an OSC interface Mastery of these steps should render the design of the OSC interface a technicality albeit probably still rather time consuming We will start with a superficial technical description of the Khepera III next turn to the Pd application for interacting with the robots and finally take an intense look at the underlying low level control programs http www infomus org EywIndex html 3 1 Technical Description of Khepera III The Khepera III is a small circular mobile robot running on two wheels and a sliding support The diameter is about 130 mm the height about 70 mm and the weight without extensions amounts to ca 690 g Different view of the Khepera III are presented in figure 2 the top row showing a prototype and the bottom row the current commercially available version In its basic configuration the Khepera III is equipped with two motors with asso ciated controller
28. program is required running on the KoreBot board that decodes the messages sent to the robot into appropriate control commands and corresponding arguments and on the other hand encodes the responses from the robot into messages that can be put to use within the Pd application The control program to be discussed is based on a test application for the Khepera III provided by K Team Corporation as part of the libkorebot libraries the C source code is contained in the file khepera3 test c Along with the preparation of the Pd patch this application was modified by Tobias Grewenig and Ralf Baecker to incorporate functions for network interaction and coding decoding messages sent between computer and robot Networking functionality was established by importing source code for the Pd netsend object by Miller Puckette Some changes and additions had to be introduced by the present author Grewenig Baecker started from the application as provided with the libkorebot 1 8 distribution Since the return values of some low level functions were changed from pointer to integer type with the libkorebot 1 9 1 distribution the functions in our application had to be adapted Even the syntax and return values of some commands of the communication protocol running on the dsPIC 30F5011 seem to have been changed so that the functions making use of these had to be revised too A minor change concerns the definition of different sendport numbers for different robots I
29. r advanced example for the use of the Khepera II platform an ap plication presented by Webb Reeves Horchler 2003 25 can be considered Here the Khepera II which in its standard configuration is not equipped for outdoor operation is supplemented with sound sensors and a chassis with an extra controller and motor moving on so called whegs rotating sets of legs see Figure 1 This setup was devised to test principles of cricket phonotaxis relating the orienting behavior of female crickets towards males making use of acoustic signals to the layout of their auditory and nervous systems l http www uni koeln de phil fak muwi ci0 http www fk 427 de only in german Built by K Team Corporation http www k team com 1 Compliant foot Mast for tracker tethers PC104 wireless ethernet y Khepera robot ears circuit t n Ves icrophones 60cm long chassis Figure 1 Khepera II robot extended for an outdoor test implementing theoretical assumptions about cricket phonotaxis Described by Webb Reeve Horchler 2003 25 The choice of the Khepera II was at least partly motivated by the popularity of the platform see Schmidt 2005 21 At the time of the beginning of the project however K Team Corporation released a successor to the Khepera II the Khepera III robot This new device offers greatly enhanced possibilities for the development of control structures and
30. s a ring of 9 infrared IR sensors attached to the bottom layer of the robots internal structure another ring of ultrasonic US sensors attached to the second layer and an additional pair of IR sensors pointing downward called ground sensors Communication with and control of these devices is mediated by a dsPIC 30F5011 microprocessor For a textbook description of hardware devices for mobile robots see e g Jones Flynn Seiger 1999 11 or Nehmzow 2000 16 More specifically each of the motors is equipped with an incremental shaft en coder producing 16 pulses per revolution of the motor axis since the motor is connected to the wheels with a 43 2 1 reduction i e 43 2 motor axis revoluti on corresponding to 1 revolution of the wheel one revolution of the wheel will correspond to 691 2 pulses produced by the shaft encoder Because 55 pulses are stated to correspond to 10 mm of distance covered by the robot Khepera III User Manual 14 Section 3 2 the diameter of the wheels can be calculated to be 40 mm The incremental encoder together with a PIC 18F4431 microprocessor technical data in 15 reading the encoder pulses and controlling the pulse width of a 20 MHz pulse which provides the electrical power of the motor allows for two dif ferent modes of motor control control of position making use of the number of pulses registered which can be converted into distances according to the calcu lations indicated above and contro
31. sity of infrared radiation present in the robot s environment will be measured This mode which is called ambient ir mea surement may e g be used to implement heat following or avoiding behavior as classically described by Braitenberg 1984 1 Vehicles 2 4 In the mode referred to as proximity ir measurement the IR emitters are used to obtain a comparison between ambient infrared radiation and radiation reflected from surfaces nearby More specifically the value returned from the sensor is the difference in intensi ty measured between the conditions with IR emitter turned on and IR emitter turned off Thus proximity IR measurement does not directly provide a measure of distance to an object For identical surface conditions the sensor reading will increase when the distance is diminished for different surfaces however sensor readings will differ according to the reflecting absorbing properties of the sur 5 faces even if distance is kept constant According to the online specification the measuring range for proximity IR measurement is up to 25 cm the measurement is mainly intended for the implementation of obstacle avoidance Khepera III User Manual Section 3 3 The 11 sensors are read consecutively starting at the rear left and going clockwise along the ring to the sensor pointing straight backwards taking the right and left ground sensors last it is in this order in which the sensor readings are returned as a list when
32. some more information including the battery temperature can be obtained retrieval of sensor data getambir and getproxir retrieve ambient resp proximity IR measurements getus retrieves the ultrasonic measurement of the sensor whose number is entered as argument getusall reads all US Sensors setting of certain control values for example setmotspeed sets the desired speed values for the motors thus requiring two arguments in a similar way setmotmove sets the desired position values as an exception in this list the command reboot leads to the restart of the ARM Linux operating system of the KoreBot board The commands possibly included in messages sent by the Pd patch are getproxir getambir getbat getus 1 5 quit help and setmotspeed the last is used within the object pd move of the patch We will concentrate on the command getproxir As can be seen in the command table no arguments are required or allowed Upon finding the string getproxir in the input array without arguments the command parser will call the function proxIR defined as shown below within the control program 18 3 2 Retrieving IR Data getproxir proxIR The function proxIR which is called when a message containing the command getproxir is received is defined by the following code fragment proxIR retrieves proximity ir measure using kb_khepera3 c library int proxIR int argc char argv void data char irdata 512
33. the built in commands for retrieval of sensor data are issued see below The time to jump from one sensor to the next is specified as 3 ms thus each sensor is read every 33 ms In its present state the Khepera III User Manual does not give any precise interpretation of the IR sensor values returned Longer range distance measurements 20 cm to 4 m are performed by the ultra sonic sensors In the default operation mode of the Khepera III only the sensor pointing forward is active Due to the low speed of sound as compared to the speed of light ultrasonic measurement requires inherently longer time than IR measurement for a maximum distance of 4 m to an obstacle i e a traveled di stance of 8 m for a reflected ultrasonic sound burst and a speed of sound of 320 m s the required time for one measurement is at least 25 ms thus in situations requiring rapid interaction ultrasonic measurement shouldn t be employed too frequently In the basic configuration of the Khepera III the dsPIC 30F5011 processor ope rates as an I2C master device controlling the motor controllers and reading the sensors To access the various control functions and to retrieve sensor data a communication protocol has been implemented consisting of single character com mands which can be followed by additional parameters Commands are entered as capital letters producing an effect on the robot and evoking a response on the command line As a simple example enter
34. the dsPIC processor via the I2C bus For this purpose a C library containing functions implementing the low level communication with the I2C devices is provided by K Team Cor poration The latest version of this library is libkorebot 1 10 in the following we are referring to libkorebot 1 9 1 Access to the ARM Linux command line can again be established via a seri al connection as described above but now using the RS 232 connector of the KoreConnect adapter intended for use with the KoreBot board Alternatively standard wireless network connections can be used such as telnet ssh resp ftp sftp The first of the new challenges mentioned above that are posed by the Khepera III platform more precisely concerns the setup of a cross compilation toolchain for the ARM Linux system running on the KoreBot board i e an environment The libraries can be retrieved from the K Team ftp server http ftp k team com korebot libkorebot that allows to compile executable programs e g from C or C source code for the ARM Linux system on a different e g Mac OS X or Windows platform Here we will refrain from further discussion of this topic simply asserting that we have successfully compiled the C code discussed below for the Khepera III robot extended with a KoreBot board The other challenge the still incomplete and at times at least apparently inconsistent state of the Khepera III documentation has been illustrate
35. this patch were developed by Jochen Arne Otto Two problems were encountered with this approach 1 Too fast movement of the selected region could lead to losing track 2 In more advanced versions of this patch repeatedly the connection between robot and computer got lost Reasons for this problem are not clear yet first ideas concern internal timing issues and the loss of data packages during transmission due to the use of the UDP network protocol http homepage mac com davidrokeby softVNS html 14 uama serqo Aexoeeqj e4 007 S4osuas Ayivurxoad paae jur AIxo4d ajno4 J0quI04 3A18284 30quu04 puas jeqjab puas DOS 04jou G snjab puas t snjab puas iuonisod ey 3e 2 fqo ue Bulyx924 1461s 0 U 19S y O1UI H212 ii LOBOM JHL dO 1S S weAboad 46 524 bueqpeo oapia ajeAnje o 32112 x 3oquio4 puad M io A48 jeq ajno4 056 OSI P91 S6 p6 jouuos Bupjoea 1oefqo suA3Jos yum es d yy Buses 0S6t p02 S6 v 19auuoo iiij u4apuae assaape di Bueqpeo 30qUJ04J 3A139834 TENE 1 6666 2A18934 3U e BITEGHUA SUAYOS ET GO Z00Z eee NS externals for movement control of the tion tracking Figure 5 MaxMSP patch using softV Khepera III robot by camera based mo 3 The libkorebot C Programming Library As repeatedly mentioned in the previous section for interaction with the Khepera III robot using the Pd patches described a control
36. vices controlling the motors the PIC 18F4431 processors Instead special functions defined in the file kmot c of the libkorebot distribution have to be employed The code defining kh3 sendcommand and kh3 get command is included as an illus tration in the code fragments at the end of this section The first argument of kh3 sendcommand is a pointer to the dsPIC device the second argument points to the command frame defined within kh3 proximity ir The pointer to the array Buffer defined in the function proxIR is passed as second argument to kh3 getcommand eventually writing data into Buffer which then can be sent to the host computer as described above These remarks may suffice as an overview to give an impression how interaction with the Khepera III can be implemented For actual programming work e g preparing an OSC interface as proposed above of course more detailed work will be required but the general framework should be clear 23 Code Fragment kh3 sendcommand kh3 sendcommand sets a command frame to a given khepera3 device Normally and end user doesn t want to use these function as they are assumed as low level functions param hDev is a handle to an opened knet socket Khepera3 dsPic Mparam in is a pointer to a buffer where the command frame to be sent is stored on return A value 0 on error KH3_ERROR_FRMSNDERR gt 0 on success returns should be the size of frame X X X X X X X X X X
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