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FuzzyLogicBasedAutonomousSkidSteeringVehicleNavigationL.Doitsidis,K.P.Valavanis,N.C.TsourveloudisTechnicalUniversityofCreteDepartmentofProductionEngineeringandManagementChania,Crete,GreeceGR-73100{Idoitsidis,kimonv,nikost}@dpem.tuc.grAbstract-Atwo-layerfuzzylogiccontrollerhasbeendesignedfor2-DautonomousNavigationofaskidsteeringvehicleinanobstaclefilledenvironment.ThefirstlayeroftheFuzzycontrollerprovidesamodelformultiplesonarsensorinputfusionanditiscomposedoffourindividualcontrollers,eachcalculatingacollisionpossibilityinfront,back,leftandrightdirectionsofmovement.Thesecondlayerconsistsofthemaincontrollerthatperformsreal-timecollisionavoidancewhilecalculatingtheupdatedcoursetobeapplicabilityandimplementationisdemonstratedthroughexperimentalresultsandcasestudiesperformedoarealmobilerobot.Keywords-Skidsteering,mobilerobots,fuzzynavigation.Ⅰ.INTRODUCTIONTheexistseveralproposedsolutionstotheproblemofautonomousmobilerobotnavigationin2-Duncertainenvironmentsthatarebasedonfuzzylogic[1],[2],evolutionaryalgorithms[3],aswellasmethodscombiningfuzzylogicwithgeneticalgorithms[4]andfuzzylogicwithelectrostaticpotentialfields[5].Thepaperistheoutgrowthofrecentlypublishedresults[9],[10],butitstudies2-Denvironmentsnavigationandcollisionavoidanceofaskidsteeringvehicle.Skidsteeringvehiclesarecompact,light,requirefewpartstoassembleandexhibitagilityfrompointturningtolinedrivingusingonlythemotions,components,andsweptvolumeneededforstraightlinedriving.Skidsteeringvehiclemotiondiffersfromexplicitsteeringvehiclemotioninthewaytheskidsteeringvehicleturns.Thewheelsrotationislimitedaroundoneaxisandthebackofsteeringwheelresultsinnavigationdeterminedbythespeedchangeineithersideoftheskidsteeringvehicle.Samespeedineithersideresultsinastraight-linemotion.Explicitsteeringvehiclesturndifferentlysincethewheelsaremovingaroundtwoaxes.ThegeometricconfigurationofaskidsteeringvehicleintheX-YplaneisshowninFig1，whileatistheheadingangle,Wistherobotwidth,θthesenseofrotationandS1,S2arethespeedsintheeithersideoftherobot.Thederivedandimplementedplanneratwo-layerfuzzylogicbasedcontrollerthatprovidespurely”reactivebehavior”ofthevehiclemovingina2-Dobstaclefilledenvironment,withinputsreadingsfromaringof24sonarsensorsandangleerrors,andoutputstheupdatedrotationalandtranslationalvelocitiesofthevehicle.Ⅱ.DESIGNOFTHEFUZZYLOGICCONTROLSYSTEMTheordertothevehiclemovement,atwo-layerMadman-typecontrollerhasbeendesignedandimplemented.Inthefirstlayer,therearefourfuzzylogiccontrollersrepondibleforobstacledetectionandcalculationofthecollisionpossibleilitiesinthefourmaindirections,front,back,leftandright.Thepossibilitiescalculatedinthefirstlayeraretheinputtothesecondlayeralongwiththeangleerror(thedifferencebetweentherobotheadingangleandthedesiredtargetangle),andtheoutputistheupdatedvehicle’stranslationalandtherotationalspeed.Fig.1.GeometricconfigurationoftherobotintheX-Yplane.A.firstlayerofthefuzzylogiccontrollerTheATRV-miniisequippedwithanarrayof24ultrasonicsensorsthatarevehiclesasshowninFig.2.TheultrasonicsensorsthatareusedaremanufacturedbyPolaroid.Afterexperimentwith,andtestingseveralmethodsconcerningsonarsensordategroupingandmanagement,itwasfirstdecidedtofollowthesensorgroupinginpairsasproposedin[8](consideringtheATRV–minitwelvesonargroupAis=1,…..,12,havebeenenumeratedasshowninFig.2)andthendividethesunoftheprovidedpairsensordatabytwotodeterminethedistancefromthe(potential)obstacle.However,thismethodgaveunsatisfactoryresultsduetotheATRV–minisspecificsensorunreliability.Evenincaseswithobstaclespresentinthevicinityofthevehicle,thesensorsweredetectinga“freepath”.Toovercomethisproblem,amodified,simpler,sensorgroupinganddatamanagementmethodwastestedthatreturnmuchbetterandaccurateresults:ThesensorswereagaingroupedinpairsaccordingtoFig.2,buttheminimumofthe(potential)obstacle.EachATRV–minisonarreturnsfromobstaclesatamaximumdistanceof4metres(experimentallyverifiedasopposedtodifferentvalueprovidedbythesonarsensorsmanufacturerFig.2.GroupingoftheSensors.Theformofeachfirstlayerindividualfuzzycontroller,includingtheobstacledetectionmodule,isshowninFig.3.ObservingFig.3,datafromgroupsensorsA1,A2,….,A5(5inputs)andgroupsensorsA7,A8,…,A11(5inputs)serveasinputstotheindividualcontrollersresponsibleforthecalculationofthefrontandbackcollisionpossibilities,respectively.DatafromgroupsensorsA5,A6,A7(3inputs)serveasinputtocalculatetheleftandrightpossibilities,respectively.Theindividualfuzzycontrollersutilizethesamemembershipfunctionstocalculatethecollisionpossibilities.Thelinguisticvaluesofthevariabledistance_from_obstancearedefinedtobethree,near,meium_distance,awaywithmembershipfunctionsasshowninFig.4reflectingthemaximumdistanceof4metersasonarreturnsaccurateinformationaboutpotentialobstacles.Fig.3.Obstacledetectionmodule.Fig.4.InputVariableDistance_From_Obstacle.Thefirstlayeroutputisacollisionpossibilityineachdirectiontakingvaluesfrom0to1.Thelinguisticvariablesdescribingeachdirectionoutputvariablecollisionpossibility(withempiricallyDerivedforbestperformance)membershipfunctionsasshownInFig.5.Apartoft