Assignment 1 - Umeå universitet
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1. Implement a Breitenberg vehicle in Matlab for the Khepera Since there are 8 infra red reflex sensors a somewhat more complicated mapping function from stimuli to response has to be used Use a simple perceptron with linear activation function for each engine m W i Wo 8 Mp Di i Vo Wo OCh vo are offsets that will make the robot move even if the reflex sensors return zero which means there are no close obstacles You may add an amplification factor about 1 400 for all weights to make it easier to experiment with the weights The program should use the routines comm_close comm_open read_proxand set speed from part a Experiment with different weights to get the following behaviors 1 Avoid obstacle the robot should turn away from obstacles 2 Follow the wall the robot should be able to find its way out of a maze by following the left or right wall Can the symmetry left right be used to simplify the weight settings Can the weights be calibrated by showing the robot a wall or an obstacle Can you find other ways to simplify the weight setting More information about Breitenberg vehicles http www mindspring com gerken vehicles Part c Expand the model in Part b with camera data The task for the robot is to track a dark object e g a pencil moving in front of the robot The robot should track the pencil without hitting it Idea let the pixel number decide on turning angle such that a pencil d2. E g gt gt answer ksend N 10 port 1 n 123 32 123 43 2 33 323 666 gt gt The example sends the command Read proximity sensors to the Khepera that returns a string containing data from the 8 IR sensors Note the linefeed character that has to end all commands kclose port Closes the communication channel opened by kopen The parameter port is the handle returned by kopen Umea universitet 901 87 Umea Telefon 090 786 7759 E post thomash cs umu se
3. and receiver may also get out of phase such that a received answer belongs to an old request The remedy to this is extended error handling However in our robot applications a missed incorrect or delayed command does most often not affect the function of the program since new commands with the same or almost the same commands are being transmitted many times per second Support for program development Debug printouts at many levels can simplify both development and usage of the driver routines A global variable can be used to control debug printouts without messing up the parameter lists of the routines Umea universitet 901 87 Umea Telefon 090 786 7759 E post thomash cs umu se Drivers for the Khepera robot Read about the communication protocol for the Khepera and the camera module K213 in their respective manuals in the compendium Command format All commands to the Khepera have a common format PC KHEPERA lt CMD gt lt arg gt lt 1f gt gt lt lt cmd gt lt arg return gt lt lf gt lt CMD gt is an upper case letter defining the type of command lt cmd gt is the same letter but in lower case lt arg gt is a comma separated list with arguments to the command The comma sign should not be sent if lt arg gt is empty lt arg return gt is a comma separated list with results from the Khepera The comma sign is not returned if lt arg return gt is empty lt lf gt is the ascii character line feed char 10
4. initialised port variable the computer may have to be rebooted Test this with sempty port before calling kclose KhepCom Function ok values KhepCom cmd arg N turretID Sends a command cmd with arguments arg to the Khepera robot Retries at most 5 times or until N numbers are read correctly from the Khepera The read values are returned in values A vector with N NaN is returned if unsuccessful ok is returned 1 iff successful Example 1 ok KhepCom D 12 15 0 Set speed Example 2 ok values KhepCom O 8 Read ambient light sensors Example 3 ok values KhepCom N 64 2 Read K213 oe AP ol JP AP AIP oP oO ll oe oe the turretID parameter is used to send commands to turrets instead of to the main Khepera Refer to the T command for details oe Umea universitet 901 87 Umea Telefon 090 786 7759 E post thomash cs umu se a2 When KhepCon is written and tested the following routines should be easy to write about 1 line each function ok set_speed speed Set motor speed The unit is the pulse corresponding to 8 mm s oP o oe speed 1x2 vector containing the speed for the left motor the speed for the right motor See the function D in the Khepera User Manual for details oe oe function values ok read_prox Read the 10 bit values from the proximity meter sensors A vector with 8 NaN are returned if unsuccessful See the function N in the Khe
5. The robot and all its equipment should to be in the black case when it is being moved around The robot must never be left unattended You are responsible for it even if you are not present Never ever Fika over the robot It does not like cookie crumbs and a drip of coffee may be lethal The switch underneath the robot should be in OFF position internal batteries disconnected If you are nice to the Khepera it will also be nice to you It always does its best to understand the commands you are sending to it and misunderstandings are almost always due to HUMAN ERRORS Umea universitet 901 87 Umea Telefon 090 786 7759 E post thomash cs umu se UMEA UNIVERSITY sslve Intelligent Robotics Department of Computing Science SG 2007 03 20 Thomas Hellstr m Drivers for Serial Communication Introduction Drivers are sub routines or functions that are used to communicate with hardware A common standard is serial communication that sends data in serial bit streams between units One example is the communication between a PC and an external modem In the case with our Khepera robots the communication is used to control the motors of the robot and to read values from the sensors and the camera Besides routines for transferring data in both directions a number of other routines are necessary for opening closing the communication channels for checking the number of characters in the data buffers etc Often an ASCII protocol is used All trans
6. UMEA UNIVERSITY os IVe Intelligent Robotics Department of Computing Science oe y N ie 2007 03 20 Thomas Hellstr m a Eee gt p Hes Assignment 1 This assignment should be performed in groups consisting of 1 2 students The necessary low level routines kopen ksend and kclose are downloadable from the course web page Khepera_pcdrivers zip in the folder Course material Part a al Write the following drivers in Matlab for communication with the Khepera robot More information can be found in the document Drivers for serial communication comm_open function status comm_open port_id baud timeout debugg function comm_open port_id baud timeout debugg oP ol oe port_id The communication port to be used 0 for COM1 1 for COM2 B baud Set the transfer speed E g 9600 timeout No Of seconds before the read routines timeout debugg Level of debugg printouts 0 for no printouts The first three parameters are the same as for kopen debugg can set a global variable that the other routines can use for debug printouts comm_open calls kopen and defines a global variable port that the other routines can use comm_open can start by calling comm_close to close a possibly opened line The Khepera robots are set to the highest communication speed 38400 baud comm_close function status comm_close o 3 Close the communication port Uses the global variable port Note If kc ose is called with a non
7. a common and hardware related task Important notes Speed The driver routines are normally called very often in an application program In principle execution speed should therefore be of high priority However in many cases such as in the Khepera case the communication intensity is still very low and speed is not really an issue Other applications may require drivers to be written in C or even assembler to achieve necessary speed Stability Drivers may never cause a stop in the program Drivers may not assume that data always arrives or that is has the specified format Faulty or missing data should be handled by resending commands or requests Refer to the section Retransmission below Umea universitet 901 87 Umea Telefon 090 786 7759 E post thomash cs umu se Error handling Write routines Should check input parameters to avoid data outside the specified borders to be sent to the hardware Read routines Received data has to be checked at least at the low level number of parameters and type of parameters alphanumeric or numeric General Check sums are used for certain commands not with the Khepera though Every transmitted data entity command record etc is followed by a checksum with a format that can be checked by the receiver In cases where a checksum is not included in the communication a format check can often serve the same purpose albeit not as safe Example A request for data from the IR sensors on t
8. et 901 87 Umea Telefon 090 786 7759 E post thomash cs umu se UMEA UNIVERSITY g5 IVe Intelligent Robotics Department of Computing Science s y N ie 2007 03 20 Thomas Hellstr m a EEE S KA Q T Handling the Khepera robots The robots are very expensive and very delicate For the equipment to survive it is necessary that everyone is familiar with and obey to the following instructions and rules Booking The robots are booked in a schedule attached on the wall outside the Computing Science corridor on the fourth floor Check out and return The robots are kept at studentexpeditionen over nights The first group for the day checks out their robot there and returns it either to the same place or to the next group in turn The last group for the day returns the robot to studentexpeditionen or to some employee at the computing science department who takes care of returning it to studentexpeditionen The robot may also be handed over to the first group the coming day General e Never lift the robot such that it will fall to the floor if you drop it Always hold it over the table or your maze If the robot falls to the floor it will be severely damaged However these injuries are minor in comparison to the ones that will be inflicted on you when the incident is discovered e NEVER lift the robot in the cable The cables are also very delicate and you do not appreciate working with malfunctioning cables e When disconnecting Pull the con
9. etected in the mid pixel causes the robot to move straight ahead Extra task Implement the ideas described on page 1 3 in the paper Programming by teaching in the compendium The taught behavior should be either Obstacle Avoidance Wall Following or Box Pushing Report e Normal written CS report with source code in appendix e The practical results are inspected by another group that your group don t inspect e The signed inspection protocol is then handed in with the report e Remember to write your name and email on the front page of the report Umea universitet 901 87 Umea Telefon 090 786 7759 E post thomash cs umu se Inspection protocol Assignment 1 Course Intelligent Robotics Group members in block letters Tests a Disconnect the cable from the power unit The robot should now stop if not Contact me and national TV Now return the cable The robot should now resume normal operation If the cable is disconnected for too long the program should time out and stop b Verify assignment part b 1 Avoid obstacles 2 Follow the wall c The robot should track e g a pencil without hitting it Extra task The robot can learn and then repeat a behavior like Obstacle Avoidance Wall Following or Box Pushing Check here if successfully demonstrated gt E Check here if not successfully demonstrated L We have conducted the above tests to our full satisfaction Umea universit
10. he Khepera robot is sent as the following string from the computer N lt 1f gt l e the character N followed by the line feed character ascii 10 A short moment later the robot will reply with a string containing values for the 8 IR sensors E g n 123 43 23 334 677 876 54 32 lt l1f gt There is no checksum but the receiving program can make sure the string starts with the n character and ends with a line feed When values are extracted from the string the number of integers can be checked should be 8 in this case Retransmission f the transmission did not work no or erroneous reply data should be sent again After a fixed number of such attempts a time out should be issued This error condition should be transferred upwards in the call hierarchy as a status or error variable Timing aspects Since external equipment is connected a certain degree of indeterminism is from the computer s perspective introduced After requesting data from an external unit e g an instrument or a robot the reply time may differ depending on the status and load of the external equipment In addition to this delay the communication time has to be considered If the communication speed is 9600 baud a maximum of 870 characters can be transferred per second 8 data bits 2 stop bits 1 start bit If large amounts of data have to be communicated the delay has to be estimated and affect the timeout behavior previously described The sender
11. in Matlab Example set the robot engine s speed PC KHEPERA D 5 15 lt 1f gt gt lt d lt lf gt Commands to K213 and other turrets A separate command T x is tells the Khepera that the next command should be interpreted by a turret with turret_id x The camera K213 has turret_id 2 Available subroutines For the Khepera drivers we will use a set of routines that can open the communication channel send a command and wait for a reply from the Khepera The manufacturer of the Khepera K team supplies these routines They implement the low level and some of the mid level functionality above and you will as part of one assignment write the other necessary routines The drivers from K team are downloadable from the course web page port kopen com_port baud_rate timeout Opens the communication channel for serial communication through COM1 or COM2 on the PC Parameters com_ port 0 for COM1 1 for COM2 baud_rate 9600 for 9600 baud etc time_out Controls the timeout function for ksend Number of seconds before ksend times out Example for COM2 with 38400 baud and 0 1 seconds timeout port kopen 1 38400 0 1 answer ksend s port 1 Sends a command s to the Khepera and waits for a reply that is returned as a string If no answer arrives before the set timeout set in kopen ksend returns an empty string The parameter port is the handle returned by kopen GC
12. mitted messages are in this case streams of mainly human readable characters and a few control characters such as line feed and carriage return Other protocols are binary and use data coded at bit level The Khepera uses an ASCII protocol The physical connection between Khepera and PC is a cable from the serial port of the PC to the gray colored communication module that comes with the Khepera This module connects further to the Khepera through a multi colored cable NOTE The power adapter must NOT be connected to the communication module when the other cables are being connected or disconnected Layers Drivers perform data communication between the computer and the connected equipment and are often implemented as modules handling different layers of abstraction in the communication Low level Communicates with the hardware i e reading and writing data with no concern of the meaning of the data Routines to initiate and close the communication are also on this level Mid level Calls low level routines extracts data read routines and packs data write routines E g sendfloat v may be a routine sending a real number according to a hardware dependent standard to the hardware High level Calls routines from the mid level and performs commands close to the application E g turn degrees could be a routine executing communication necessary to make the robot turn To be regarded as a driver routine the function has to perform
13. nectors instead of pulling the cables e The camera module may not be detached from the Khepera since the connectors are very delicate and easy to ruin e The communication speed is set to 38400 baud on the Khepera switches and should not be changed Connection The robot is connected to the PC as follows 1 The long thin cable should be connected to the rotating device The other end of the cable is connected to the gray interface 2 The cable that goes from the rotating device is connected to the Khepera robot Please observe the latch on the red connector that fits into a small hole on the Khepera connector Umea universitet 901 87 Umea Telefon 090 786 7759 E post thomash cs umu se The long cable with a 9 pin male connector is connected to the serial port marked COM1 or COM2 on the PC the choice affects the value of the port_id parameter in the comm_open routine 4 The other side of the cable is connected to the interface 5 6 The cable from the power adapter is plugged into the interface The power adapter is connected to the mains 230 volt The rotating device sometimes fails You may in such case remove it and connect the thin cable straight from the Khepera to the interface Disconnection The important thing when disconnecting the cables is that the power adapter is first disconnected either from the interface or from the wall This operation can also be used as a master reset of the robot General
14. pera User Manual for details oe oe oe oe function values ok read_amb Read the 10 bit values from the ambient light meter sensors A vector with 8 NaN are returned if unsuccessful See the function O in the Khepera User Manual for details oe oe oe oe function values ok read_vision Read the 64 8 bit values from the K213 camera turret A vector with 64 NaN are returned if unsuccessful See the function N in the Khepera User Manual for details oP oe oe Finally Write a test program using the developed routines To display the camera image mshow can be used image ok read vision figure 2 xmul 30 ymul 6 imshow repmat reshape repmat image ymul 1 64 ymul 1 1 xmul 0 255 The call to reomat duplicates image along y and x to a suitable size General tips e sscanf str d canbe used to extract integers from str e Use tryoch catch for error handling in Matlab e Test KhepCom properly with simulated correct and incorrect readouts from the Khepera Then test with the robot connected e Use the debugger Make a breakpoint where ksend is called to check the format of the transmitted string Step forward and check the string that ksend returns e Remember The routines have to work no matter what the Khepera returns including no return Correct time out handling is very important Umea universitet 901 87 Umea Telefon 090 786 7759 E post thomash cs umu se Part b
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