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英语原文.docx

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英语原文

FuzzyLogicBasedAutonomousSkidSteeringVehicleNavigation

L.Doitsidis,K.P.Valavanis,N.C.Tsourveloudis

TechnicalUniversityofCrete

DepartmentofProductionEngineeringandManagement

Chania,Crete,GreeceGR-73100

{Idoitsidis,kimonv,nikost}@dpem.tuc.gr

Abstract-Atwo-layerfuzzylogiccontrollerhasbeendesignedfor2-DautonomousNavigationofaskidsteeringvehicleinanobstaclefilledenvironment.ThefirstlayeroftheFuzzycontrollerprovidesamodelformultiplesonarsensorinputfusionanditiscomposedoffourindividualcontrollers,eachcalculatingacollisionpossibilityinfront,back,leftandrightdirectionsofmovement.Thesecondlayerconsistsofthemaincontrollerthatperformsreal-timecollisionavoidancewhilecalculatingtheupdatedcoursetobeapplicabilityandimplementationisdemonstratedthroughexperimentalresultsandcasestudiesperformedoarealmobilerobot.

Keywords-Skidsteering,mobilerobots,fuzzynavigation.

Ⅰ.INTRODUCTION

Theexistseveralproposedsolutionstotheproblemofautonomousmobilerobotnavigationin2-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.DESIGNOFTHEFUZZYLOGICCONTROLSYSTEM

Theordertothevehiclemovement,atwo-layerMadman-typecontrollerhasbeendesignedandimplemented.Inthefirstlayer,therearefourfuzzylogiccontrollersrepondibleforobstacledetectionandcalculationofthecollisionpossibleilitiesinthefourmaindirections,front,back,leftandright.Thepossibilitiescalculatedinthefirstlayeraretheinputtothesecondlayeralongwiththeangleerror（thedifferencebetweentherobotheadingangleandthedesiredtargetangle）,andtheoutputistheupdatedvehicle’stranslationalandtherotationalspeed.

Fig.1.GeometricconfigurationoftherobotintheX-Yplane.

A.firstlayerofthefuzzylogiccontroller

TheATRV-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（experimentallyverifiedasopposedtodifferentvalueprovidedbythesonarsensorsmanufacturer

Fig.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（withempirically

Derivedforbestperformance）membershipfunctionsasshownInFig.5.ApartoftherulesbaseforleftcollisionispresentedinTableⅠ.

Anexampleoftherulesusedtoextractfrontcollisionpossibilitiesis:

IFA1isnearANDA2isnearANDA3isNearANDA4ismedium_distanceANDA5isnearTHENcollision_possibilityishigh.Similarforthebackcollisionpossibility.Forleft（equivalentlyforrightcollision）possibilitiestheruleisoftheform:

IfA5isnearAndA6isnearAndA7isnearTHENcollision_possibilityishigh.

Fig.5.OutputVariablecollision_possibility

TABLEⅠ

PARTOFTHERULESBASEFORLEFTCOLLISION

InputVariables

Output

Variables

A5

A6

A7

Near

Near

Near

High_Possibility

Away

Away

Away

Not_possible

Near

Away

Medium_Distance

Possible

Near

Away

Near

High_Possibility

B.Secondlayerofthefuzzylogiccontroller

Thesecondlayerfuzzycontrollerrecivesasinputsthefourcollisionpossibilitiesinthefourdirectionsandtheangleerror,andoutputsthetranslationalvelocity,whichisresponsibleformovingthevehiclebackwardorforwardandtherotationalspeed,whichisresponsibleforthevehiclerotationasshowninFig.6.

Theangleerrorrepresentsthedifferencebetweentherobot-headingangleandthedesiredangletherobotshouldhaveinordertoreachitstarget.Theangleerrortakesvaluesrangingfrom-1800to1800.Thelinguisticvariablesthatrepresenttheangleerrorare:

Backwards_1,Hard_Left,Left,right,Hard_right,Backwards_2with（empiricallyderivedfromtests）membershipfunctionsasshowninFig.7.

Thetranslationalvelocity（m/sec）,whichisoneoftheoutputsofthesecondlayercontroller,isdescribedwiththefollowinglinguisticvariables:

back_full,back,back_solw,stop,front_slow,front,frontfull,withmembershipfunctionsasinFig.8.

Fig6.Blockdiagramofthe2ndlayerofthefuzzylogiccontroller

Fig7.InputVariableAngleError.

Fig8.OutputVariableTranslational_Velocity.

Therotational_speed（rad/sc）isdescribedwiththefollowinglinguisticvariables:

Right_full,right,no_ratation,left,let_fullwithmembershipfunctionsasinFig.9.

Anexampleoftherulesthatcontrolthevehicleisdemonstrated:

Iffront_collisionisNot_PossibleANDBack_CollisionisNot_possibleAndLeft_CollisionisNot_possibleAndRight_CollisionisNot_possibleAndAngleErrorisAheadTHENTranslational_velocityisFront_FullANDRotational_VelocityisNo_Ratation.

Fig.9.OutputVariableRotational_velocity.

Ⅲ.RUSULTS

ThefuzzylogiccontrollerhasbeendesignedandimplementedusingC++inanATRV-minimanufacturedbyRealWorldInterface（RWI）.Inallexperimentstherobotisconsideredtohavereacheditstargetwhenstoppinginsideacirclewithradiusof30cm.Thisassumptionhasbeendictatedbecauseallcalculationshavebeenmaderelativetothecenteroftherobot.Soiftherobotstopsinsidethatcircleitisassumedthatithasreacheditstarget.

Severalscenariosinanindoor2-Dobstaclefilledenvironmenthavebeentestedtostudytherobotbehaviorandthecontroller’sapplicability.

ThearrowinFig.10,Fig.15,Fig.20isshowingtheinitialdirectionofthevehicle.

Intestcase1weexaminethebehaviorofthevehicleinanenvironmentwiththreeobstacles.Thetestcase1ispresentedinFig.10.Fig.11showsthetranslationalvelocity,whiletherotationalvelocityisgiveninFig.12.Fig.13presentsthefrontcollisionpossibility.InFig.14,thesolidlineindicatestheleftcollisionpossibilitywhilethedotedtherightcollisionpossibility.Thebehaviorofthevehicleisdefinedfromthesurroundingobstacles.

Inthebeginningtheleftcollisionpossibilityishighduetotheobstacleintheleft.Therobotmovesforwardsandit’ssteeringrightinordertoavoidtheobstacle.Thenitsteersleftandmovestowardsitstarget.

InthesecondtestcasepresentedinFig.15,amorecomplicatedenvironmentwiththreeobstacleshasbeentested.Fig.16showsthetranslationalvelocity,whiletherotationalvelocityisgiveninFi