The Robutler a Vision-Controlled Hand-Arm System for Manipulating Bottles and Glasses

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TheRobutler:aVision-ControlledHand-ArmSystemforManipulatingBottlesandGlasses

UlrichHillenbrand,BernhardBrunner,ChristophBorst,andGerdHirzingerInstituteofRoboticsandMechatronicsGermanAerospaceCenter(DLR),82234Wessling,GermanyUlrich.Hillenbrand@dlr.de

Abstract—Wepresentanexperimentalservicerobot,ahand-armsystemwithanthropomorphicfeaturesaswellassomecapabilityforautonomousbehavior.Thesystemintegrateslight-weightconstructionprinciplesofthearmandanarticulateddexterousfour-fingerhandwithreal-timesceneanalysisbystereovision,complianttorquecontrol,andanintuitiveman-machineinterface.Itthuscomprisesmanyofthekeyfeaturesrequiredtorealizethevisionofaroboticservantthatactsandinteractsinahumanenvironment.Thetaskweconsiderhereismanipulationofbottlesandglassesasrequiredforpreparingandservingdrinks.Thepurposeofthisarticleistoprovideacomprehensiveviewofthewholesystem,revealingthesynergiesbetweenitscomponentsthatleadtoreal-worldperformancewithintheaddressedproblemdomain.

I.INTRODUCTION

Inthefieldofservicerobotics,systemsareneededthatcanhandleeverydayobjectsinunconstraintenvironments,inmuchthesamewaytheyarehandledbyhumans.Interactionwithchangingand,hence,onlypartiallyknownenvironmentsre-quiresintelligentsensor-dataprocessingandadvancedcontrolarchitectures.Addressingthisgrandchallengeforrobotics,wepresentahand-armsystemwithanthropomorphicfeaturesaswellassomecapabilityforautonomousbehavior.Thesystemintegrateslight-weightconstructionprinciplesofthearmandanarticulateddexterousfour-fingerhandwithreal-timesceneanalysisbystereovision,complianttorquecontrol,andanintuitiveman-machineinterface.TheworldoftheRobutlerconsistsofvariousbottlesandglassesthatarefreelyarrangedonatable.Itstaskistoprepareandofferdrinks.Initially,aninterpretationofthesceneiscomputedwithinafewseconds.Objectidentitiesandposesareestimatedbymatchingempiricallylearnedmodelsagainst3D-pointdatathathavebeenobtainedfromstereoprocessing.Differenttypesofbottlesandglassesarelocatedanddistinguishedundervaryingconditionsoflighting.Oncethesceneisunderstood,theRobutlerautonomouslyexecutesasequenceofactions.Forinstance,itmayunscrewthecapfromabottle,graspthebottle,andpouradrinkintoaglass;seeFigure1.Ahierarchicalcommandinterfaceenablestheusertoin-structtheRobutleratvariouslevelsofabstraction.Inpar-ticular,theinterfaceprovidesgraphicalrepresentationsoftheobjectsasdetectedinthescene,displayedinavirtual-realityenvironment.Itthusallowstheusertoissuehigh-levelcommandsaboutactionstotakew.r.t.theobjectsinanintuitiveFig.1.TheDLRLight-WeightArmwithFour-FingerHand,pouringwaterintoaglass.manner.Alternatively,theRobutlercanbeinstructedviaaspeechinterface.Weconsiderthepresentexperimentalsystemasignificantsteptowardsdesigningservicerobotsusableinhumanenvi-ronments.II.PREVIOUSWORKThecoreideaoftheGermannationalresearchprojectsDIROKOLandMORPHA[1]wastoprovideadvancedmechatronicsystems,particularlyservicerobots,withtheca-pabilitytocommunicate,interact,andcollaboratewithhumanusersinanaturalandintuitivemanner.Thiscapabilityshouldenablearobottocooperatewithandassistthehumanuserinavarietyoftasks,undertheuser’sguidanceandcontrol.Therobotassistantinthehomeshouldworktogetherwiththeusertoperformsimplehousework.Inadditiontofetch-and-carryduties,thisincludestaskssuchassettingthetableorperformingbasiccleaning.Sofar,robotsystemshaveonlybeenabletodealwiththehighcomplexityandvariabilityofeverydaysurroundingstoalimitedextent.Thiscomplexityandvariabilityposesgreatdemandsontherobot’sintelligenceandautonomy,demandsthathavenotbeenfullysatisfiedbycurrenttechnology.Thecapabilitytointeractwithahumanuserofferstherobotsystemthepossibilityofmakinguseofhumanguidanceandsupporttoexpanditseffectivecompetence.Accordingly,alotofresearchactivityhasbeeninvestedindesigninghuman-machineinterfaces[2],[3].Anotherfocusofresearchhasbeenonnavigationcapabilities,mainlybutnotexclusivelyinbuildings[4],[5].Thepresentstudyiscom-plementarytomostpreviousworkinthatfinemanipulationofobjectsfromthehumanlivingenvironmentisemphasized.Theaimistocommandarobot,inanintuitiveandabstractmanner,toautonomouslycompleteacomplextasklikeservingadrink.Suchataskinvolvesperceptionofasceneandexecutionofasequenceofdelicateactions.III.THEARMServicerobotsneedtooperateinthehumanenvironmentorevencooperatewithhumans.Therefore,somebasicrequire-mentshavetobemetbythemanipulators,makingthemquitedistinctfromindustrialhardware.Serviceroboticapplicationsrequirelight-weightarmsforsafetyreasonsandhuman-friendlyinteraction,aswellastosupportmobility.Interactionwithnotfullyknownenvironmentsdemandscompliantarmsandfingers,controlledbyinformationextractedfrommanydifferentsensors.Tointegratemultisensorycomponentsinarmsandhands,sophisticatedmechatronicconceptsandaflexiblecontrolarchitectureareneeded.Overthelastyears,ourfocusonserviceroboticswasdrivenbystrongconsiderations,howtopushrobotictechnologiesforreal-worldapplications.ThedesignphilosophyofDLR’slight-weightrobots[6]hasbeentorealizeatypeofmanip-ulatorsimilartothekinematicredundancyanddynamicsofthehumanarm,i.e.,with7degreesoffreedom(DOFs),aload-to-weightratioofbetterthan1:2,andahighdynamicperformance;seeFigure2.Alljointshavepositionandtorquesensors.Likeinallmodernapproachestorobotcontrol,commandingjointtorqueshasbeenconsideredasessential,allowingprogrammableimpedance,stiffness,anddamping.Fig.2.The3generationoftheDLRLight-WeightArm.IV.THEHANDForhumans,handsandarmsareuniversalactuatorstointeractwiththeirenvironment.Grasping,carrying,andma-nipulatingawidevarietyofobjects,usingtools,catchingandthrowingthingsarebasicabilitiesthatweneedthemfor.Asrobotsstarttoserveandcollaboratewithman,itisnaturaltoequiprobotswithartificialhands.Theobjectswewanttomanipulate,bottlesandglasses,arechallenging:glasscanbreakanddrinkscanbespilled.Asensitiveandcompliantmanipulatoristhereforerequired.TheDLRhandfeatures4fingerswithanthropomorphickinematics:4jointsperfingerwithacollective3DOFs(distaljointscoupled).AnadditionalDOFresidesinthepalmforadaptationtopowerorprecisiongrasps;seeFigure3.Jointcontrolisaccomplishedwithposition,speed,andtorquesensorsforeachfingerDOF.High-levelcontrolcanbedrivenbysignalsfroma6-DOFforce-torquesensorineachfingertip.