机器人编队.docx

机器人编队.docx

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机器人编队

ModelingandsimulationofformationsofrobotsinDEVSJAVA

Dr.BernardZeigler

ECE575

ByFanYangandTheodoreElhourani

1.Problemstatement

Fromourpreviousexperienceintheareaofroboticswehavelearnedthatthedevelopmentofintelligentcontrolsisatedioustaskrequiringintensiveexperimentation.Tolocateflawsinthebehaviorofamultiagentsystemthesameexperimentmayhavetoberepeatedseveraltimesunderthesamesettings.Inadditiontodiscoveringflaws,simulationisprovedtobeahelpfulandaffordabletoolintheprocessofevaluatingvariousroboticsettingssuchashybridandhomogeneoussystems.Inthisprojecttheproblemofformationcontrolandcollaborativeobstacleavoidanceofahybridroboticsystemisaddressed.

Sixrobotsaretotravelinaknownenvironmentandtopassthroughtunnelsoftheshapegiveninfigure1whilekeepingaformation.

Fig.1Shapeofthetunnelthattherobotwillgothrough.

Ifthecurrentformationcannotpassthroughthetunnelthentherobotsarerequiredtoautonomouslyswitchformation.Forinstance,ifthecurrentformationistriangular（seeFig2.）andthebaseofthetriangleislargerthanthewidthofthetunneltherobotswillneedtoswitchintoeitherformations2and3.

1.Triangularformation

2.Rectangleformation

3.Lineformation

Fig.2.Thethreepossibleformations

Itisdesirabletomaintainthemostcompactformationwhenevertheconstraintsoftheenvironmentallowit.Thetriangularformationisidealhowevergeometricalconstraintsoftheenvironmentsuchasthetunnelwillrequirethesystemtotemporarilyswitchintoalineformation.Aftertherobotsleavethetunneltheyarerequiredtoswitchbacktothedesiredtriangularformation.Formationbehaviorsallowbettersensorfusionandsharingofresources.Inotherwords,dependingonitspositionintheformationarobotcanconcentrateitssensingresourcesononepartoftheenvironment,whileotherrobotsconcentrateontheremainingparts[1].

Inthisprojectwewillshowhowrobotscanmaintainthreegeometricalformationswhilenavigatinginthefreespace.Alsowewilladdresstheproblemofswitchingformationsinordertosatisfygeometricalconstraintslikethetunnel.

2.GeneralDescriptionoftheSystem

Inthissectionwewillgiveageneraloverviewofthesystem.Thesystemconsistsofsixrobotsnavigatingina2Dspaceinaleaderfollowermotion.Hence,theroboticsystemconsistsoftheleaderandfivefollowerrobots.Theleader’sresponsibilityistodetectobstaclesandtosendtheformationcommandstothefollowers.Theleaderisaswellsupposedtosenditspositionandvelocityinformationtoeveryfollower.Herewenotethattheleaderisgivenapredeterminedpath.Thispathisencodedintheformofasequenceofvelocities,whicharesequentiallyfedtotheleaderatsomerate.

Giventheinitialpositionandcurrentvelocityinthe2Dspacetheleadercancalculateitspositionaftertheelapseoftimet.Thefollowingequationisusedtocalculatethepositionoftheleader:

Wherex1isthenextposition,xthecurrentposition,ttheelapsedtimeandvxthevelocityinthex-axisdirection.

Ontheotherhand,everyfollowerrobotcombinesfourparameterstodetermineitsnextpositioninthe2Dspace.Theseparametersare:

currentpositionoftheleader,currentpositionofthefolloweritself,velocityoftheleader,aswellastheformationinformationthatisreceivedfromtheleader.Thefollowercanchooseoneofthreedifferentkinematicsequations,respectivelyrepresentingeachofthethreeformations.Forexample,infigure3wecanseethesimplecaseofalineformation.Therobotsareoriginallymovinghorizontally.Thentheleaderdecidestochangeitsdirectionasshown.Thenextcoordinatesoftheleaderare（x1,y1）andthenewpositionofthefollower2iscalculatedusingequationR2forlineformations（seeappendixA）.

Fig.3.Lineformationchangeofdirection.

Knowingitscurrentandnextpositionalongwiththetimestepttherobotcancalculateatwhatspeedandinwhatdirectionitshouldmove.

Asmentionedearlierthisisahybridsystemofrobots.Infreespacecase,thereisnocameraused.Leaderrobotwillactfollowingthemotionplanned,anditwillsendtheformationanditscurrentpositionandvelocityinformationtoallfivefollowers,sofollowerswilltrytokeeptheformationandmovewiththeleaderrobot.Alltheobstacleexperimentsweareconducting,oneormorecamerasaremounted.Insecondexperiment,acamerawillbemountedonsite,whichmeansthatitcanwatchthemovementofrobotsandthepositionofobstacles（suchastunnels）.Whenthevisionsystemdetectethereistunnelinfrontofthemotiondirectiontotherobotsgroup,neccessaryformationchangingcommandwillbegeneratedtoavoidcollisionswiththetunnelbycomparingthedimensionoftunnelwiththesizeofrobotsgroup.Whentherobotsgroupleavingthetunnel,thevisionsystemwilldetectitandissuescommandtorecoverthedefaultformation.Thirdexperimentlettheleaderrobot（ingreen）willalwayshaveacameraasitsmainsensor.Conversely,otherfollowerrobotsintheformationwillnothaveacamera.Theleadercameraandtheassociatedvisionsystemcandetectobstaclesinfrontoftheleader.Whenthevisionsystemindicatesthatatunnelisahead,theleaderrobotordersallfollowerstochangeformationifnecessary.Itcandecidewhetheraformationchangeisnecessaryornotbycomparingthedimensionsofthetunnelandtheformation.Whentheitleavesthetunneltheleader（orfollower6insomeexperiments）isrequiredtodetectthateventandgenerateappropriateoutputstoreconstructtheoriginalformation.Thereissomeuncertaintythatwhentheleaderrobotleftthetunnel,otherfollowingrobotsarestillintunnel.Sochangingformationundersuchsituationwillresultincollisionbetweenrobotsandtunnel.Thiswillbeshownintheexperiment.Inordertoovercomethisshortcoming,wemountanothercameraonthelastrobot,whichwilldetectedwhetherthelastrobothasleftthetunnelornotandgeneratethecommandofreconstructthedefaultformation.

Theexperimentalframecontainsavelocitygeneratortodrivetheleaderrobot.Italsocontainstheenvironmentmodel,whichiscomposedofzeroormoreobstacles.Theenvironmentmodelcanreceivepositioninformationfromallsixrobots,butmainlythepositionofleaderandlastrobots.Itisresponsiblefortriggeringthevisionsystemoftheleaderrobot（andfollowerinsomeoftheexperiments）whenthedistanceseparatingrobotandobstacleexceedsacertainthreshold.Theexperimentalframewillbediscussedinmoredetaillaterinthisreport.

3.ObjectivesoftheModelingandSimulationStudy

Asmentionedearlier,simulationisconsideredtobeaveryusefultoolinthedevelopmentofmultiagentroboticsystems.Throughsimulation,flawsinthedesignoftheagentscanbedetectedintheearlystages.Suchflawsrangefromtrivialcalculationandlogicerrorstomorecomplexfailuresinthehighlevelbehaviorsofthesystem.Forexample,inthesystemwedescribeheremodelingandsimulatingouragentshelpsustodiscovererrorsinthemathematicalmodel（kinematicsequations..etc）wederived.Simulationcanalsoproveordisprovethatacertainmodelissuccessfulinachievingitsgoals.Inourcase,wecanknowiftheRobotsmodelwedesignediscapableofmaintainingthemostcompactformationandatthesametimeproperlytraverseatunnel.

Anotherimportantgoalofthemodelingandsimulationofamultiagentsystemistheevaluationofavarietyofroboticsettings.Thesameexperimentcanberunwithdifferentrobotconfigurations.Inthisprojectthesameexperimentisrunwithtwodifferentconfigurations:

leaderonlyhasacameraorbothleaderand“follower6”havecameras.Thustheadvantagesanddisadvantagesofeachconfigurationcanbeassessed.

4.TheSimulationModel

a.SystemEntityStructure–seeFig.4ofnextpage

b.ExplanationofOperations

world–itisthedescriptionoftheexperimentsworld,itincludesfreespaceworldandworldwithobstacles.

experimentalframe–itwillgivetheexperimentalframe,whichincludesagenerator,environmentorencamera.

Fig.4SystemEntityStructure

generator–thismodelwillgivetheinitialformation,T（timeperiodtosendoutpositioninformation）,L（lengthusedtocontrolthesizeofformation）,velocitycontroloftheleaderrobotandcontrolwhenthestartoftheexperiments.

environment–thismodelwillgivetheenvironmentsoftherobotsstay,itcontainsseveralobstacles.

encamera–thismodelwillwatchtheobstaclesandthepositionofleaderrobotandthelastrobot（r6）.

Robots–itwillgivethe6robotsinformation.

r1–itwillincludear1cameraandar1controller,wherer1camerawatchestheobstaclesandthepositionofr1,r1controllerwillguider1movefollowingthemotiongivenbygenerator.

followers-itoffersinformationabout5followingrobots.

r6–itwillincludear6cameraandar6controller,wherer6camerawatchestheobstaclesandthepositionofr6,r6controllerwillguider6movefollowingtheleaderwithsomekindofformation.

r2,r3,r4andr5–thecontrollerofrobots2to5,willguidethoserobotsmovingfollowingtheleaderwithsomekindofformation.

display–itwillprocessthepositiondatareceivedanddisplayobstaclesand6robots’positionintheCellSpace.Theobstacleswillbedisplayedbeforetherobots’running.Thedisplayorderof6robots’positionisfromtheleaderrobot（r1）tolastrobotr6.Fromitwecanseetheformationofrobotsgroupkeep.BecausetheDEVSJAVAIu