Biomechanical-design-of-the-Berkeley-lower-extremi

128IEEE/ASMETRANSACTIONSONMECHATRONICS,VOL.11,NO.2,APRIL2006BiomechanicalDesignoftheBerkeleyLowerExtremityExoskeleton(BLEEX)AdamB.Zoss,H.Kazerooni,Member,IEEE,andAndrewChuAbstract—Wheeledvehiclesareoftenincapableoftransportingheavymaterialsoverroughterrainorupstaircases.Lowerextrem-ityexoskeletonssupplementhumanintelligencewiththestrengthandenduranceofapairofwearableroboticlegsthatsupportapayload.ThispapersummarizesthedesignandanalysisoftheBerkeleylowerextremityexoskeleton(BLEEX).Theanthropo-morphicallybasedBLEEXhas7DOFperleg,fourofwhicharepoweredbylinearhydraulicactuators.TheselectionoftheDOF,criticalhardwaredesignaspects,andinitialperformancemeasure-mentsofBLEEXarediscussed.IndexTerms—Biomimetics,exoskeletons,mechatronics,robotics.I.INTRODUCTIONHEAVYobjectsaretypicallytransportedbywheeledvehi-cles.However,manyenvironments,suchasrockyslopesandstaircases,posesignificantchallengestowheeledvehicles.Withinthesesettings,leggedlocomotionbecomesanattrac-tivemethodoftransportationsincelegscanadapttoawiderangeofextremeterrains.Berkeley’slowerextremityexoskele-ton(BLEEX)isthefirstfield-operationalroboticsystemthatcanbewornbyitsoperatorandprovidestheabilitytocarrysig-nificantloadswithminimaleffortoveranytypeofterrain.Thisisaccomplishedthroughfourcriticalfeatures:anovelcontrolscheme,high-poweredcompactpowersupplies,specialcom-municationprotocolandelectronics,andadesignarchitecturetodecreasethecomplexityandpowerconsumption.Thispaperfocusesonthedesignarchitecture.BLEEXcomprisestwopoweredanthropomorphiclegs,apowersupplyandabackpack-likeframeonwhichavarietyofheavypayloadscanbemounted(Fig.1).BLEEXprovidesload-carryingcapabilitythroughleggedlocomotionguidedbyhumaninteraction;butinsteadofactively“driving”thevehicle,BLEEXshadowstheoperator’smovementashe/she“wears”itlikeapairofartificiallegs.Bycombiningthestrengthcapabili-tiesofroboticswiththenavigationalintelligenceandadaptabil-ityofhumans,BLEEXallowsheavyloadstobecarriedoverrough,unstructured,anduncertainterrains.Possibleapplica-tionsincludehelpingsoldiers,disasterreliefworkers,wildfirefighters,andotheremergencypersonneltocarrymajorloadswithoutthestraintypicallyassociatedwithdemandinglabor.ManuscriptreceivedSeptember15,2005;revisedNovember30,2005.Rec-ommendedbyGuestEditorsS.AgarwalandV.Krovi.ThisworkwassupportedinpartbyDefenseAdvancedResearchProjectsAgency(DARPA)underGrantDAAD19-01-1-509.A.B.ZossandH.KazerooniarewiththeMechanicalEngineeringDe-partment,UniversityofCalifornia,Berkeley,CA94720USA(e-mail:[e-mail];[e-mail]).A.ChuiswithSiemens,Concord,CA94520USA(e-mail:[e-mail]).DigitalObjectIdentifier10.1109/TMECH.2006.871087Fig.1.Conceptualsketchofalowerextremityexoskeleton.Properactuationoftheroboticlegsremovesthepayloadweightfromthewearer,whileallowingthewearertoeffortlesslycontrolandbalancethemachine.II.BACKGROUNDInthelate1960s,thefirstactiveexoskeletonsweredevel-opedalmostsimultaneouslyatGeneralElectric(GE)[1]andtheMihajloPupinInstituteinBelgrade[2].SafetyconcernsandcomplexitypreventedtheHardimanprojectatGEfromwalkingandtheBelgradeexoskeletonfollowedonlypreprogrammedwalkingmotions.Bothprojectsweretetheredtoastationarypowersource.Morerecently,alightweightpowerassistdevice,HAL,hasbeendevelopedattheTsukubaUniversity[3].Althoughthedevicesuccessfullywalksandcarriesitsownpowersupply,itisdesignedtoonlyassistthewearer’smuscles;itcannotcarryanexternalload.TheKanagawaInstituteofTechnologyhasdevelopedafull-body“wearablepowersuit,”poweredbyuniquepneumaticactuators[4].Ithasbeendemonstratedinlimitedapplicationswithoutaportablepowersupply.Stillindevelopmentareseveralotherlowerextremityex-oskeletonsdesignedtoaiddisabledpeople[5]–[7].Similartoexoskeletons,avarietyofpoweredorthosesarebeingdevelopedfortheknee[8],[9],lowerback[10],andankle[11].TheBLEEXprojectisanenergeticallyautonomousexoskele-toncapableofcarryingitsownweightplusanexternalpayload.Allpreviousexoskeletonsareeithertetheredtoafixedpowersupplyornotstrongenoughtocarryanexternalload.Unlikeorthosesandbraces,BLEEXtransfersthepayloadforcestotheground,insteadofthewearer.III.EXOSKELETONCONTROLTheBLEEXcontrolalgorithmensuresthattheexoskeletonshadowstheoperatorwithminimalinteractionforcesbetween1083-4435/$20.00©2006IEEEZOSSetal.:BIOMECHANICALDESIGNOFBERKELEYLOWEREXTREMITYEXOSKELETON129TABLEIBLEEXELECTRONICSREQUIREMENTSthetwo.Thehighlightofthecontrolschemeisthatitissolelybasedonmeasurementsfromtheexoskeleton;therearenodirectmeasurementsfromtheoperatororfromwheretheoperatorcontactstheexoskeleton(e.g.,noforcesensorsbetweenthetwo)[12].Thiseliminatestheproblemsassociatedwithmeasuringinteractionforcesorhumanmuscleactivity.Throughthecontrolalgorithm,BLEEXinstantaneouslyshad-owsthewearer’svoluntaryandinvoluntarymovements.Thisre-quiresthecontrollertobeverysensitivetoallforcesandtorquestheoperatorimposesontheexoskeleton.Toachievethis,theBLEEXcontrolincreasestheclosedloopsystemsensitivitytotheoperator’sforcesandtorques[12].TheBLEEXcontrolschemeusesafulldynamicmodeloftheexoskeletonandutilizesasignificantnumberofsensorstosolvethed