DesignofLowProfile,ModularLowerExtremityExoskeletons

By

YoonJungJeong

Adissertationsubmittedinpartialsatisfactionofthe

requirementsforthedegreeof

DoctorofPhilosophyin

Engineering–MechanicalEngineering

inthe

GRADUATEDIVISION

ofthe

UNIVERSITYOFCALIFORNIA,BERKELEY

Committeeincharge:

PROFESSORHOMAYOONKAZEROONI,CHAIRPROFESSORDENNISLIEUPROFESSORKIMIKORYOKAI

SPRING2014

DesignofLowProfile,ModularLowerExtremityExoskeletons

Copyright2014byYoonJungJeong

1

Abstract

DesignofLowProfile,ModularLowerExtremityExoskeletons

by

YoonJungJeong

DoctorofPhilosophyinEngineering‐MechanicalEngineering

UniversityofCalifornia,Berkeley

ProfessorH.Kazerooni,Chair

Studieshaveshownthatwalkingforaslittleas30minutesofadaycanimproveoverallhealth.However,morethan250,000peopleintheUnitedStatesareparalyzedduetospinalcordinjuries(SCI),andcannolongerwalkwithoutsupport.MostoftheSCIpatientsrelyonwheelchairsaftertheirinjuries,andsufferfromsecondaryinjuriescausedbyprolongedsitting.Moreover,thepatients’reducedmobilityoftenbringsnegativeeffectstotheirindependenceandsociallife.

Theprimaryresearchobjectiveistodeveloppracticalandeffectiveexoskeletontechnologythatenablesparalyzedindividualstoachievemobilityandgainindependenceintheirdailylives.Inthisdissertation,Idiscussdesignsoflowprofileandmodularexoskeletons,withanemphasisondifferentdesignattributesthatincreasedeviceusability.

Aminimally‐actuatedmedicalexoskeletonwasdevelopedwithpoweredhipjointsandpassivekneejoints.Thelowprofileactuationunitsusedforthisexoskeleton’shipactuationallowedthewearertoachievepropulsionandwalkthroughnarrowpassageways.Infact,thisexoskeletonbecamethefirstpoweredmedicalexoskeletonthatweighslessthantwentypounds.Thisexoskeletoncontinuedtoevolveintoasystemwithincreasedmodularitythatmeetsvarioususerneedsbasedondifferentphysicalconditions.Themodulardesignallowseasycustomizationviaitsversatilesupportlevelconfigurationsfordifferentindividuals.Asapartofthisresearch,comprehensiveuserstudiesofthesedevicesandtheuserinterfacewereconductedtocreateapositiveuserexperienceandacomfortablelinkbetweentheuserandtheexoskeleton.

Paralyzedpatientswhoparticipatedinthisstudycorroboratedthatthecompactandlightweightdesignofthesystemenhancestheirmobilityandmaneuverability.Themodularityindesignopensassistiveopportunitiestovariouspeople,suchastheelderlyandotherpeoplewithintactmobility.Iexpectthatassistiveexoskeletontechnologywillcontinuetoadvanceandenhancethequalityoflifeforawidespectrumofcommunitiesinouragingsociety.

i

TableofContents

TableofContents.......................................................................................................................................................i 

ListofFigures............................................................................................................................................................iv 

ListofTables...............................................................................................................................................................v 

Acknowledgements................................................................................................................................................vi 

1.Introduction...........................................................................................................................................................1 

1.1Motivation......................................................................................................................................................................1 

1.2ResearchObjectives...................................................................................................................................................1 

1.3OutlineoftheDissertation......................................................................................................................................2 

2.Background............................................................................................................................................................3 

2.1  SpinalCordInjury...............................................................................................................................................3 

2.2  ConventionalRehabilitationwithPassiveOrthoses..............................................................................4 

2.2.1Knee‐Ankle‐Foot‐Orthoses(KAFO).............................................................................................................4 

2.2.2ReciprocatingGaitOrthoses(RGO).............................................................................................................4 

2.3  PoweredMedicalExoskeletons......................................................................................................................5 

2.3.1PoweredMedicalExoskeletonsontheMarket......................................................................................5 

2.3.2PoweredMedicalExoskeletonsinAcademicDevelopment..............................................................6 

2.4OverviewofHumanWalking..................................................................................................................................7 

2.4.1BodyPlanes...........................................................................................................................................................7 

2.4.2LowerExtremityJointAngles........................................................................................................................8 

2.4.3GaitCycle................................................................................................................................................................8 

2.4.4ClinicalGaitAnalysis(CGA)............................................................................................................................9 

2.4.5PowerConsumedinaJointduringWalking..........................................................................................10 

3.LowProfileExoskeleton................................................................................................................................12 

3.1HipActuationUnitsHardwareDesignOverview.........................................................................................13 

3.1.1  BrushlessDCMotorandStrainWaveGear...................................................................................14 

3.1.2ShaftDesignandSensorMounting............................................................................................................20 

3.1.3  BearingstoHoldExternalLoads........................................................................................................20 

3.2AssemblyProcessandDesignConsiderationforSafety...........................................................................22 

3.2.1AssemblyofaHipActuationUnit..............................................................................................................22 

3.2.2DesignConsiderationsforUserSafety.....................................................................................................26 

3.3IntegrationintoaMinimally‐ActuatedExoskeleton...................................................................................27 

ii3.4LowProfileHipActuatorDesign–SecondRevision..................................................................................29 

4.ModularExoskeleton......................................................................................................................................31 

4.1MobilitySpectrum.....................................................................................................................................................31 

4.2HardwareDesignOverview..................................................................................................................................34 

4.3AssessmentoftheModularSystem...................................................................................................................37 

5.UserInterfaceModuleDesign.....................................................................................................................40 

5.1SchematicsofExplicitUserInterface................................................................................................................41 

5.2OverviewofUIPrototype......................................................................................................................................43 

5.3GloveUIEvaluation:Methods..............................................................................................................................44 

5.3.1PatricipantsOverview....................................................................................................................................44 

5.3.2Interviews............................................................................................................................................................44 

5.3.3UsabilityTests:MaterialsandProcedure...............................................................................................45 

5.4ResultsandDesignRecommendations............................................................................................................46 

5.4.1GloveType...........................................................................................................................................................46 

5.4.2NumberofButtons...........................................................................................................................................46 

5.4.3WalkingOperationScheme..........................................................................................................................47 

5.4.4DisplayModulePosition................................................................................................................................47 

5.5ImplementationoftheUserStudy.....................................................................................................................48 

6.DiscussionsonExoskeletonUserTesting..............................................................................................50 

6.1Minimally‐ActuatedMedicalExoskeletonUserTesting............................................................................51 

6.1.1TestParticipantOverview............................................................................................................................51 

6.1.2UserTestingProceduresandGuideline..................................................................................................52 

6.2TrunkExoskeletonUserTesting.........................................................................................................................55 

6.2.1TestParticipantOverview............................................................................................................................55 

6.2.2UserTestingProcedureandGuideline....................................................................................................55 

6.3DesignConsiderationsforFutureUserTesting............................................................................................56 

6.4ArchetypalPersonasinEachUserCategories...............................................................................................57 

6.4.1Kevin,apoweredwheelchairuser............................................................................................................57 

6.4.2Jennifer,awheelchairuser...........................................................................................................................57 

6.4.3.Samuel,acrutchuser.....................................................................................................................................58 

6.4.4Mary,aseniorcitizen......................................................................................................................................58 

6.4.5Tom,anindustryworker...............................................................................................................................58 

6.4.6Andrew,amilitarysoldier............................................................................................................................58 

7.LimitationsandFutureWork......................................................................................................................59 

7.1HipActuators..............................................................................................................................................................60 

iii7.2Modularity....................................................................................................................................................................60 

7.3UserInterface..............................................................................................................................................................60 

8.ConcludingRemarks.......................................................................................................................................62 

Bibliography............................................................................................................................................................64 

 

iv

ListofFigures

Figure1.Spinalcordinjurylevelsandremainingextremityfunction.............................................3 Figure2.Mostcommonpassivelegorthoses.............................................................................................5 Figure3.Poweredmobilemedicalexoskeletonsonthemarket........................................................6 Figure4.(a)AUSTINExoskeleton(b)MinaExoskeleton.......................................................................7 Figure5.(a)Referenceplanesofthebody(b)Jointangledefinitions...........................................8 Figure6.Illustrationofanormalwalkingcycle.........................................................................................9 Figure7.Variationsintheswingandstanceperiods..............................................................................9 Figure8.ClinicalGaitAnalysisdataatthe(a)knee,(b)hip...............................................................10 Figure9.Kneeandhipjointpowersduringlevelwalking..................................................................11 Figure10.Lowprofileactuationunitdesignprocessflowchart.....................................................13 Figure11.TheBLDCmotorandstrainwavegearusedfortheactuatordesign.......................14 Figure12.Actuatorperformancelinesatisfyingtherequirementforwalking.........................14 Figure13.Motorperformanceplotoftorqueversusangularvelocity...........................................16 Figure14.Strainwavegearcomponents.....................................................................................................18 Figure15.Strainwavegearoperation..........................................................................................................19 Figure16.Ratchetingphenomenon..............................................................................................................19 Figure17.(a)Cross‐sectionalview(b)Apatientwearingasystem...............................................21 Figure18.Loaddiagramforanactuationunitwithapairofangularbearings........................21 Figure19.Anassembledlowprofilehipactuationunit........................................................................23 Figure20.(a)Thesidecross‐sectionalview(b)Sideviewofassembledunit...........................24 Figure21.Explodedviewoflowprofilehipactuationunit................................................................25 Figure22.Experimentalsetupfortestingthehipactuationunit....................................................26 Figure23.Mechanicalhardstopsforhipextensionandflexion......................................................27 Figure24.Lowprofile,minimally‐actuatedmedicalexoskeleton...................................................28 Figure25.Thetestpilotwasabletowalkthroughnarrowaisles...................................................28 Figure26.Cross‐sectionalviewofanactuationunitwiththeMaxonEC90...............................30 Figure27.Mobilityspectrumoftheinjuredusergroup......................................................................32 Figure28.Extendedmobilityspectrum......................................................................................................32 Figure29.(a)HumanUniversalLoadCarrier(HULC)(b)StrideManagementAssist...........33 Figure30.Overviewofthehipmodulewithadditionaljoints..........................................................35 Figure31.Abduction,adduction,androtationjoints............................................................................36 Figure32.Exampleusesofthetrunkexoskeletonmodule................................................................37 Figure33.Thetrunkexoskeletonmodulewornbyahealthy,non‐injuredindividual..........38 Figure34.ThetrunkexoskeletonmodulewornbyaSCIpatient....................................................38 Figure35.Overviewofthehipmodule........................................................................................................39 Figure36.Anexampleofadevice‐coupledUI..........................................................................................41 Figure37.Anexoskeletonfinitestatemachine(Singleton)...............................................................42 Figure38.Alternatingfinitestatemachine................................................................................................42 Figure39.(a)ThecomponentsoftheGloveUI(b)Aparticipantwearingtheprototype....43 Figure40.UsabilitytestofthegloveUIprototype.................................................................................46 Figure41.FingergloveUIoverview.............................................................................................................49 Figure42.FingerGloveUIwithvisualandhapticfeedback..............................................................49 

vFigure43.Sceneoffirsttimeexoskeletontrial........................................................................................51 Figure44.(a)Checkingkneejointalignmentbeforestanding.(b)Thefirsttimestandingup.........................................................................................................................................................................................54 Figure45.(a)Checkingkneejointalignmentafterthefirsttimestandingup.(b)Afteradjustingtorsoandankleangles,thepatientstaysbalancedmoreeasily....................................54 Figure46.(a)Aparaplegicpatienttakingherfirststeps.(b)Anotherparaplegicpatientwearinganexoskeletonwalkingonthestreetwithoutanyassistance.........................................55 

ListofTables

Table1.PoweredexoskeletonsandRGOcomparisonchart.................................................................6 Table2.MotorandTransmissionCharacteristics...................................................................................15 Table3.MaxonEC90FlatMotorCharacteristics...................................................................................29 Table4.ComparisonofTwoMotorDesigns...............................................................................................30 Table5.DifferentExoskeletonFeaturesforDifferentUserGroups...............................................34 Table6.SummaryofUIAssessment..............................................................................................................48 Table7.ArchetypalPersonas...........................................................................................................................59 

vi

Acknowledgements

Foremost,Iwouldliketoexpressmysinceregratitudetomyadvisor,ProfessorHomayoonKazerooni.ProfessorKazerooniwasthereasonthatIcametoBerkeley,andIamthankfulthatIhavehadsuchaninspiring,enthusiastic,supportive,andcaringadvisor.Hisguidancehelpedmethroughoutmygraduatestudiesandresearchendeavors.Iamlookingforwardtocontinuingmycollaborationwithhimafterthisfive‐yearjourney.

Iwouldalsoliketothankthemembersofmythesiscommitteeandqualifyingcommittee:ProfessorsAliceAgogino,DavidDornfeld,DennisLieu,andKimikoRyokai,fortheirencouragementandinsightfulcomments.Ireallyappreciatethetimetheyspentpatientlyguidingmethroughgraduateschool.

MysincerethanksalsogotoallmycolleaguesandfriendsintheRoboticsandHumanEngineeringLaboratory(HEL).TheyhavemademyPh.D.journeytremendouslyfun,memorable,andenriching.Inparticular,IwanttothankMinervaPillai,MichaelMcKinley,andWayneTungforourstimulatingdiscussions,countlessendeavors,andallthefunwehavehadthesepastfiveyears.IamsogratefulthatIhavehadsuchtalented,fun,andkindcolleagueswhosharedtheirdedicationandcamaraderiewithme.IamalsogratefulforthehardworkandfriendshipofJoshCherian,Lee‐HuangChen,StephenMcKinley,JasonReid,KyunamKim,DongjinHyun,NickUm,andPatrickBarnes;andthenewgenerationofHEL‐ChristinaYee,BradleyPerry,MeitingWu,NicholasEricco,LoganVanEngelhoven,GraceLiao,LilyWu,andOctavioNarváezAroche.Myappreciationfurtherextendstoallofthecurrentandpreviousundergraduatestudents,specificallyAlexanderWen,NathanPoon,JonathanMcKinley,andYaseminSarigul‐Klijn.Theyhavebeentremendouslyhelpfulwithmachining,maintaininghardware,andperformingcountlessothertasks.

Mysinceregratitudealsogoestotheamazinginstructorsofthestudentmachineshop–MickFranssen,GordonLong,DennisLee,ScottMcCormick,andJesseLopez.Theyalwayspatientlyhelpedmewithmyhardwarechallenges.Theirincrediblesupportandadvicemadethebestofmylimitedmachiningskills.

Furthermore,IwanttothankDr.LoraOehlberg,Dr.ElizabethGoodman,ProfessorDorAbrahamson,EuiyoungKim,JenniferWang,andSungtaekLimforinsightfuldiscussions.Itwasveryhelpfultoreceivetheirfeedbackonmyresearchfromtheirdifferentpointsofview.Ireallyappreciatetheirprompt,helpfulresponsestomycoldemails,aswellasthetimetheyspentmeetingandtalkingwithme.

Iwanttoexpressmysincerethankstoallofthetestpilotswhopatientlyworkedwithmeandprovidedinvaluablefeedbackalongtheway.AlthoughIcannotnameeveryoneherebecauseoftheprotocols,theirkindparticipationandhonestfeedbackmadealltheamazingprojectspossible.Thankyouallsomuch.

Andfinally,Iamendlesslygratefultomyfamily‐theirguidance,support,andlovethroughoutmylifemademyPh.D.possible.

1

1.Introduction

1.1MotivationAsof2013,thereweremorethan273,000individualssufferingfromspinalcordinjuries(SCI)intheUnitedStates.Morethan100,000ofthemareparaplegia,paralyzedintheirlowerbodywithouttheabilitytowalkorstandupright.Oncetheylosetheabilitytowalkorstand,theymainlyrelyonawheelchairformobility[1].However,duetothenatureofthehumanbody,SCIpatientswhospendextensiveamountoftimesittinginwheelchairssignificantlyincreasetheirrisksofincurringsecondaryinjuries,whichincludethefollowing[2]:

Urinarytractinfections. Bloodclots. Reducedcardiovascularfunction. Decreasedbonemineraldensity,bonedensityloss,andosteoporosis. Acutepressureulcerdevelopment. Muscularatrophy,musclespasticity,anddecreasedjointrangeofmotion. Reduceddigestiveandbowlfunctions.

Ithasbeenshownthatthebestwaytodelaytheonsetofsecondaryinjuriesistodelaywheelchairusageandstartrehabilitationassoonaspossibleafteraninjury[3].Moreover,beingabletostanduprightandwalkbringspositivepsychologicalandsocialimpacts.Beinginanuprightpositionforseveralhoursadaynotonlydecreasesthechancesofsustainingsecondaryinjuries,butalsoincreasestheSCIpatients’overallqualityoflifeandlifeexpectancy[4].Forthisreason,rehabilitationtherapy,whichcomprisesvarioustypesofequipmentandlowerextremityorthoses,isstronglyrecommendedforSCIpatients.

1.2ResearchObjectivesBothpassiveandpoweredstate‐of‐the‐artexoskeletonshavelimitationsthatpreventtheirwidespreaduse.Whilepassiveorthosesprovidehealthbenefitsatlowercosts,boththeirperformanceandinherentcharacteristicswhichdemandmoreupperbodystrengthinhibitlong‐termuse.Poweredexoskeletonshavebeendevelopedinanefforttoimprovetheperformanceofpassivedevicesthatrequirelessuserstrength.However,drasticallyincreasedcostslimittheiraccessibility,whilesignificantlyhigherdeviceweightsandsizesdecreasesystemportability.Moreimportantly,larger,heavierdevicesimpedeusers’maneuverabilityinconfinedspaces.Thisnotonlyreducesdeviceusability,butalsosignificantlyaffectsusers’independence.

Inadditiontotheabovementionedcharacteristics,existingexoskeletonshavelowusabilityduetotheirlimitedcustomizablefeatures.Theirdesignsareintendedforpatientswithspecificphysicalconditions.Therefore,abroaderpatientrangewithvaryinglevelsofinjuriesandphysicalconditionsneedstobeaddressedtoallowthistechnologytobenefitawiderpopulation.

2Thus,theprimaryresearchobjectiveistoincreasetheusabilityofassistiveexoskeletonsystems.Toachievethisgoal,theresearchexploresthreemajordesigntopics:

1)Developmentoflowprofilepoweredexoskeletonsthatprovideimprovedmobilityanduserindependenceindailylife.

2)Increasesinmodularityandadjustabilityintheexoskeletondesigntoenhancecustomizationandsatisfycomprehensiveuserneeds.

3)Explorationofuserinterface(UI)designtoprovideanintuitive,comfortablelinkbetweentheuserandthemachine.

1.3OutlineoftheDissertationThisdissertationisorganizedasfollows:

1) Chapter2providesbackgroundonthetopicofspinalcordinjuries(SCI)andexoskeletonrehabilitation.Thischapteralsoprovidesabriefoverviewofthebiomechanicshumanwalking.

2) Chapter3presentsthedesignofalowprofileexoskeletonsystem.Itfocusesontheroleoflowprofilehipactuationunits.Thedesignprocess,hardwaredesign,andanassemblyoverviewarediscussed.

3) Chapter4presentsthedesignofamodularexoskeletonsystem.Itelaboratesonthedesignoflockable,modularjointsystemsthatprovidecustomizablesupportforuserswithdifferentneeds.

4) Chapter5discussestheexoskeletonUIdesign.Itpresentstheuserstudywithaglove‐typeUIprototypeforpeoplewithvaryingneeds.Designrecommendationsfromin‐depthuserinterviewsandusabilitytestsarealsodiscussed.

5) Chapter6describesusertestingproceduresandanalysesbasedonHuman‐Computer‐Interaction(HCI)theories.Interactionsamongagentsinvolvedinusertestingaswellasthepatients’“activitiesofre‐learningtowalk”arediscussed.

6) Chapter7discusseslimitationsandfutureworkforlowprofiledesign,modularity,andUIdesign.

7) Chapter8concludesthisdissertationwithasummaryofresults,contributions,andfutureworkontheassistiveexoskeletontechnology.

3

2.Background

2.1 SpinalCordInjuryASCIconsistsofdamageortraumatothespinalcordandresultsinfunctionimpairmentorloss,whichcausesreducedmobilityorfeeling.Commoncausesofdamagecanbecaraccidents,gunshots,falls,sportsinjuries,orvariousdiseases,whichincludeTransverseMyelitis,Polio,SpinaBifida,andFriedreich’sAtaxia[5].

Thespinalcordisamajorbundleofnervesthatcarriesnerveimpulsestoandfromthebraintotherestofthebody[6].Itisabout18inchesinlengthandextendsfromthebaseofthebraintothewaist,alongthemiddleoftheback.Fig.1showsthespinalcordandtheeffectsofthelocationofinjuryonremainingextremityfunction.Thelevelofinjurycanbemorespecificallydescribedbyindicatingtheinjuredvertebra.“C”indicatescervical,“T”indicatesthoracic,“L”indicateslumbar,and“S”indicatessacral.TheclassificationofcompletenessinSCIisprovidedbytheAmericanSpinalInjuryAssociation(ASIA)andisbasedonneurologicalresponses.“A”indicatesa"complete"spinalcordinjuryinwhichnomotororsensoryfunctionispreservedatS4‐S5.“B”indicatesan"incomplete"spinalcordinjurywheresensorybutnotmotorfunctionispreservedatS4‐S5.“C”indicatesan"incomplete"spinalcordinjurywheremotorfunctionisreduced.“D”indicatesan"incomplete"spinalcordinjurywheremotorfunctionismarginallyreducedbelowthelevelofinjury.“E”indicates"normal"motorandsensoryfunction[7].

Figure1.Spinalcordinjurylevelsandremainingextremityfunction.

4

2.2 ConventionalRehabilitationwithPassiveOrthosesPassiveorthosesareoftenstronglyrecommendedbydoctorsforSCIpatients.Here,twoofthemostcommonlyusedpassiveorthosesareintroduced,withafocusontheirbenefitsandlimitations.

2.2.1Knee‐Ankle‐Foot‐Orthoses(KAFO)

Themostbasictypeofpassivelowerlimborthosesareknee‐ankle‐foot‐orthoses(KAFO),whicharealsoknownaslonglegbraces.KAFOaresomeoftheearliestandstillmostcommonassistivedevicesdesignedtorestorebipedalmobility.Duetotheirmultiplehealthbenefitsandrelativelylowercosts,KAFOarecommonlyprescribedtoSCIpatientsandhighlyrecommendedbydoctors[8].AsshowninFig.2(a),thesebracesarerigidlyfastenedtotheuser’slegstolockboththekneeandanklejointsagainstkneeflexion,ankledorsiflexion,andplantarflexion.Theusercanachieveaquasi‐bipedalgaitwiththeseconstrainedjointdegreesoffreedomandtheassistanceofcrutches,walkers,orparallelbars.However,swingingoneleginfrontoftheotherwhilewearingKAFOrequiresagreatdealofupperbodystrengthandabdominalcontrol.

2.2.2ReciprocatingGaitOrthoses(RGO)

Reciprocatinggaitorthoses(RGO)areanadvancedvariationofKAFO,withatorsounitextendedtotheuser’supperbody(Fig.2(b)).RGOhaveametallinkmountedatthebackofthetorsounitthatactsasatorque‐transferringunit,whichreciprocallycouplesthemotionofthetwohipjoints.Thispassivetransmissionsystemprovidesthecoupledhipmotion–i.e.,whenonehipextends,theenergyisusedtodrivetheotherhiptoflex,andviceversa.Withthismechanism,alongerstridelengthcanbeattainedwithreducedenergyconsumption,ascomparedtothemanuallegswingwithKAFO[9‐11].However,studieshaveshownthatambulationwiththeassistanceofRGOisstillenergeticallyinefficient,requiringapproximately14timesmoreworkincomparisontonormalambulation[12,13].Itappearsthatuserfatigueandslowambulationcontributetoalowlong‐termadoptionrate,despiteahighlevelofphysicalhealthimprovements.Sykesetal.showedthatonly29percentofRGOuserswerestillusingthedevicesafteranaverageof5.4years[14].Theshortcomingsofpassiverehabilitationdevicesoftenovershadowtheirbenefits,preventingalong‐termadoptionrate.

5

(a)(b)

Figure2.Mostcommonpassivelegorthoses.(a)Longlegbraces(KAFO),(b)RGO.

2.3 PoweredMedicalExoskeletonsEventhoughpassiveorthosesprovidehealthbenefitswithrelativelylowcosts,thestate‐of‐the‐arttechnologydoesnotprovidealevelofperformanceandusabilitythatenablestheirwidespreaduseandlong‐termadoptionamongparalyzedpatients.Asanalternative,researchgroupshaveinvestigatedpoweredmedicalexoskeletontechnology,andsomeofthesedeviceshavemadesignificantadvancementsthatareemerginginthecommercialmarket.

2.3.1PoweredMedicalExoskeletonsontheMarket

Fig.3showsthefourmostwell‐knownpoweredexoskeletonsonthemarket:RexbyRexBionicsinNewZealand,ReWalkTMbyArgoMedicalTechnologiesinIsrael,Indego®byIndegogroup,whichisaVanderbiltUniversityspin‐off,andEksoTMbyEksoBionicsinCalifornia.Morespecifically,EksoTMevolvedfrommilitaryexoskeletondevelopmentoftheBerkeleyLowerExtremityExoskeleton(BLEEX),andHumanUniversalLoadCarrier(HULC)[15‐17]intheBerkeleyRoboticsandHumanEngineeringLaboratoryattheUniversityofCaliforniaatBerkeley.Theaforementionedpoweredmedicalexoskeletonsaredesignedforrehabilitationandwalkingoutsidetheclinic.Theyhave4to10poweredelectricjointsthataligntoapatient’sbiologicaljoints.Thesepoweredjointsarepre‐programmedtomimicthehumangaitandambulatethewearerinamannersimilartothatofnaturalwalkingastheusercommands.ThebiggestdifferencesamongtheseexoskeletonslieintheiractuationsystemsandUIs.ReWalkTMcontainspoweredkneesandhips,andexecutesstepsbysensingthetiltoftheuser’storso[18].Indego®operatesinasimilarfashion,byutilizinghipandkneeactuation.Ittakesstepsbymeasuringthewearer’scenterofpressurechangeaccordingtohis/herupperbodymovement[19].EksoTMalsocontainspoweredkneeandhipjoints,andhasvariousoperatingmethods.Whilepushbuttonsareusedforinitial

6trainings,moreimplicitwaysofdetectinguserintentexisttoexecutesteps,usingmultiplesensorsonthepilot'sarmsandcrutches[20].Rex,ontheotherhand,requiresnobalancingaidandhasajoystick‐typeUIlocatedonthearmrest.Withatotaloftenactuatedjointstopowerthehip,knee,andanklealongboththefrontalandsagittalplanes,Rexprovidesself‐balancingofthedeviceandwearer.However,theseadditionalfeaturesalsocomewithtradeoffssuchasslowerambulation,increasedweightandpriceduetothemorecomplexactuationsystems[21,22].Table1summarizesthespecificationsoftheabovementionedpoweredexoskeletonsaswellasthoseoftheRGOforcomparison.

(a)(b)(c)(d)Figure3.Poweredmobilemedicalexoskeletonsthatareavailableonthemarket(a)ReWalkTM,(b)Indego®,(c)EksoTM,(d)Rex.

Table1.PoweredexoskeletonsandRGOcomparisonchart.

Name PoweredDegreesofFreedom Weight ApproximateCost

ReWalkTM 4(1Hip,1Knee) 45Pounds $100,000

Indego® 4(1Hip,1Knee) 27Pounds $140,000

EksoTM 4(1Hip,1Knee) 45Pounds $100,000

Rex 10(2Hip,1Knee,2Ankle) 85Pounds $150,000

RGO 0 15Pounds $10,000

2.3.2PoweredMedicalExoskeletonsinAcademicDevelopment

Severalresearchinstitutionshavedevelopedassistiveexoskeletonsforvariouspurposes.Fig.4showstwoexoskeletonsusedforambulatingparalyzedindividuals.AUSTIN(Fig.4(a))wasdevelopedintheRoboticsandHumanEngineeringLabattheUniversityofCaliforniaatBerkeley.AUSTINcontainsapairofpoweredhipactuatorswithacoupledhip‐and‐knee

7gaitgenerationmechanism.Thekneejointsaredrivenbypoweredhipjointsthroughthecoupledgaitgenerationmechanism,whichisoperatedbyabutton‐integratedUIonawalkerhandle.Thisisthefirstexoskeletonsystemequippedwithonlytwopoweredjointsthathasambulatedaparaplegicpatient[23,24].AUSTINexecutesstepswhenthewearercommandseachstepviabuttonsonthewalkergrip.Mina(Fig.4(b))wasdevelopedbytheFloridaInstituteforHumanandMachineCognition.Minacontainsfouridenticalactuatorsforthehipandkneejoints.Theseactuatorsarepre‐programmedwithgaittrajectories,whichareobtainedbyanable‐bodiedpersonwalkswhilewearingMina.AtMina’scurrentdevelopmentstage,stepsarecommandedbyacontroloperator(practitioner),whilethewearerprovidesverbalandgesturalcues.ThepractitionerusesaMusicalInstrumentsDigitalInterface(MIDI)tocontroleachstep,andthecontrollercantriggerasinglesteporcontinuoussteps,aswellasadjustthewalkingspeeds[25].

(a)(b)Figure4.(a)AUSTINExoskeletonfromUCBerkeley(b)MinaExoskeletonfromtheFloridaInstitute

forHumanandMachineCognition

2.4OverviewofHumanWalkingInthissection,abriefintroductionofhumanwalkingiscoveredtoaidtheunderstandingofthefollowingchapters.Morespecifically,wediscussbodyplanesandjointangledefinitions,thehumangaitcycle,clinicalgaitanalysis,andpowerconsumptionduringthegaitcycle.

2.4.1BodyPlanes

AsshowninFig.5(a),threereferenceplanesareusedtodescribevariousjointmotions.Thecoronalplane,alsoknownasthefrontalplane,verticallyslicesthroughthebodywidth‐wise,andpassesthroughboththearmsandlegs.Thetransverseplanehorizontallyslicesthroughthebodyparalleltothegroundplane.Finally,thesagittalplaneisaverticalplanethatorthogonallyslicesthecoronalplane,andrunsthroughfromthefronttothebackofthebody.

82.4.2LowerExtremityJointAngles

Flexionandextensionaretermscommonlyusedtodescribejointmotion.Theydescribewhetheraparticularrelativejointangleincreasesordecreasesinthesagittalplane.ThesestandardsareillustratedinFig.5(b)forthekneeandhip.

(a)(b)

Figure5.(a)Referenceplanesofthebody[26].(b)Jointangledefinitions.

2.4.3GaitCycle

Humanwalkingisacyclicalprocess.Therearetwofundamentalstatesthateachlegcanhave:stanceandswing.Inthestancephase,thefootisplantedontheground.Duringtheswingphase,thelegswingsforwardwiththefootoffoftheground.Thefirstpartoftheswingischaracterizedbyapositiveaccelerationofthehipflexion(forward),andflexingofthekneebackwardtoallowtheswingfoottocleartheground.Thelattersegmentoftheswinginvolvesnegativeaccelerationofthehipasthekneeextendstoprepareforheel‐strike,whichiswhenthelegagainentersthestancephase.ThiswalkingcycleisillustratedinFig.6.Throughouttheprocess,thetwolegsalternaterolesbetweenstanceandswing.Whenwalkingatslowerspeeds,thereareperiodswhenbothlegsareinstance.Theseperiodsarereferredtoasdouble‐stanceordouble‐support.Therearetwodouble‐stanceperiodsthatconstituteabout10%ofthegaitcyclewhenwalkingat1meterpersecond.Thus,thepureswingperiodconstitutesabout40%ofthewalkingcycle.Asaperson’swalkingspeedincreases,double‐stancetimedecreasesuntilthereisnotimespentindouble‐stance.Runninginvolvesperiodsofflightwherebothlegsareinswing.TherelationshipbetweentheswingandstanceperiodsatdifferentspeedsofambulationisshowninFig.7.Foreachcondition,thebargraphbeginsattheinitialcontactoftheleftleg

9andrepresentstwocompletegaitcycles.Whitebarsindicatetimespentinswing,andbluebarsindicatetimespentinstance[27].

2.4.4ClinicalGaitAnalysis(CGA)

Thejointangledatathroughoutthegaitcycleareavailablefrommanybiomechanicslaboratories.Typically,avideoiscapturedasaparticipantwalks,andlegjointmotionsinthesagittalplaneareextractedusingamotioncapturesystem.ThisisreferredtoasClinicalGaitAnalysis(CGA)data.Fig.8showsCGAdataforkneeandhipjointanglesinthesagittalplanethroughoutthegaitcycle,ascollectedbyWinter,Kirtley,andLinskell[28‐30].

Figure6.Illustrationofanormalwalkingcycle[26].

Figure7.Variationsintheswingandstanceperiodsaswalkingspeedincreases.Imageadaptedfrom

[27].

10

(a)(b)

Figure8.Winter,Kirtley,andLinskellClinicalGaitAnalysisdataatthe(a)knee,(b)hip.

2.4.5PowerConsumedinaJointduringWalking

D.A.Winterandotherresearchershaveinvestigatedpowerconsumptioninjointsduringwalking.Ajoint’sangularvelocityiscalculatedfromjointangledatarecordedovertime,whileajoint’smomentisderivedfrominversedynamics.Jointpoweristhencomputedastheinnerproductofthevelocityandmomentvectors.

Fig.9showsthepoweroftheankle,kneeandhipjointsduringlevelwalking.Jointpowercanbeanegativeorpositivequantity.Powerispositivewhenthejoint’smomentofforceanddirectionofmovement(rotation)areinthesamedirection,meaningtheenergyisgeneratedbyaconcentricactioninmusclescrossingatthatjoint.Incontrast,powerisnegativewhenthejoint’smomentanddirectionofmovementareinoppositedirections.Inthiscase,energyisabsorbedbyaneccentricmuscleactionand/orelongationofothersofttissuescrossingthatpoint.Becausethekneejointisusedformotiondamping,kneepowerisrelativelylowandoftennegative.Meanwhile,asignificantportionofthegaitcyclecomprisesahighlypositivehippowerthatprovidesthepropulsiveforce[31,32].

11

Figure9.Kneeandhipjointpowersduringlevelwalking.Powersarenormalizedbybodyweight.Imageadaptedfrom[31].

12

3.LowProfileExoskeleton

Inadditiontoaddressingthemechatronicconstraints,thedesignmustaccountforacceptanceamonguserswhendevelopingassistiveexoskeletons.Hereareafewquotesfromtheparaplegicpatientswhohaveparticipatedinusabilitytesting:

“Ihadtocrawltomyseatintheairplanebecausemywheelchairdidn’tfitthenarrowaisle.”

“Iwouldn’tweartheexoonthestreetbecauseIdon’twanttolooklikeIamwearingarobot.”

Fromthefeedbackabove,itisclearthattheformfactorofexoskeletonsplaysahugeroleindeviceusability.Thebulkinessofthedevicenotonlyrestrictsauser’sabilitytonavigatenarrowpassages,butalsohis/herabilitytoblendinwithacrowdofablebodiedpeople.Onlylowprofileexoskeletonscanprovideindependencethroughoutthedaybyallowingthewearertopassthroughnarrowaisles,useregularcomputerchairswitharmrests,andbemobileindailylifewithoutassistance.Besidesprovidingindependence,exoskeletonswithsmallerformfactorsallowpatientstowearthedeviceundertheirclothes–respectingone’sformofpersonalexpression.Moreover,minimalhardwareoftheexoskeletonreducesitsweight,whichcanincreasetheefficiencyoftheoverallsystemasamobiledevice.

AsdiscussedinChapter1,humanhipandanklejointsprovidepositivepropulsivepower,whereaskneejointsareusedtodampenthemotionwithnegativepower.However,inbelow‐kneeamputeegaits,itwasobservedthatpropulsionfroma(prosthetic)ankleisverysmall,andcompensatedbypropulsiveenergyfromhipextension[33].Fromthisgaitdata,kneepowercurvesareveryclosetozeroinbelow‐kneeamputeegaits,despitethepresenceofkneemuscles.Also,studieshavedemonstratedthattheamplitudesofmuscleactivationaroundtheanklejointscarcelychangewhenwalkingwitheitheramechanicalorpoweredankle–footorthoses(AFO)[34].Itappearsthatahighlevelofbipedalmobilityisattainableusinghipjointsasthemainsourceofpropulsivepower.Therefore,toachievealowprofile,theexoskeletondesigninthischapterusespoweredelectrichipactuators,andlacksanypoweredactuatorsatthekneeandanklejoints.Thislowprofileexoskeletonhasasimilarambulationstrategytothatoftheamputeegait,andmaximizestheuseofpropulsivepowerfromthehipjoints.

Astheonlypoweredunitforpropulsion,hipactuatorsarethesignificantweightandsizefactorsforthedevice.Therefore,todeveloplowprofileexoskeletons,itiscriticaltoachievealightweight,slimformfactorforthehipactuationunits.Thischapterdiscussesthedesignofminimallyprofiledhipactuationunitsthatpermitambulationofparalyzedindividuals.Theactuationunitsareusedwithpassivekneejointsina“minimally‐actuatedmedicalexoskeleton”.Withlowprofilehipactuators,passivekneejoints,andstandardankle‐foot‐orthoses,thisexoskeletonbecamethefirstpoweredexoskeletonthatweighslessthan20pounds.Furthermore,itscompactformfactormorecloselyresemblesanRGOthanotherpoweredexoskeletons.

13

3.1HipActuationUnitsHardwareDesignOverviewThelowprofilehipactuationunitsdiscussedinthischaptercompriseabrushlessDC(BLDC)motor,transmissionsystem,sensors,load‐bearinginterfacingcomponents,andenclosurecomponents.BarecomponentsofaBLDCmotorandstrainwavegearsystemsareintegratedintoapancakeactuationunitwithcustom‐madeinterfacingparts,andpairsofoff‐the‐shelfradialandangularballbearings.Asasingleintegratedunitwithoutanyredundantbearingstructures,thesystem’sloadratingandformfactorareoptimizedandthisminimizesthesystem’ssizeandweight.TheoveralldesignprocedureisillustratedinFig.10.DesigndecisionsduringeachprocessandabriefoverviewofDCmotordynamicsandstrainwavegearingmechanicsarecoveredinthissection.

Figure10.Lowprofileactuationunitdesignprocessflowchart.

143.1.1BrushlessDCMotorandStrainWaveGear

Therequiredperformancecurvefora200‐poundparaplegicperson’swalkingwasderivedfromCGAdata,amputeegaitdata,andempiricalanalysis.Assumingthatanominal50voltsareappliedusinglithium‐ionbatteries,aBLDCmotorandstrainwavegearwereselectedtofulfilltheperformancecriteria.

Outofalltheoff‐the‐shelfBLDCmotorsthatmeettherequiredspecifications,theEmoteqHT03000‐J01‐Zframelesselectricmotorwasselectedduetoitsrelativelysmallsize.ThisBLDCmotorconsistsofa3‐phase,27‐slotstator,anda12‐polerotor(Fig.11.(a),(b)).Meanwhile,theHarmonicDriveTM(CSD‐25‐160‐2A‐GR‐SP)160‐to‐1unhousedstrainwavegearcomponents(Fig.11.(c))werechosenforthetransmissionsystem.AsillustratedinFig.12,theactuatordynamicslineencompassestherequiredperformancecurveintheplot,whichimpliesthattheselectedcomponentssatisfythespeedandtorquerequirementsofa200‐poundperson’swalking.TechnicalspecificationsofthesecomponentsfrommanufacturersaresummarizedinTable2.Thefundamentalsofmotordynamicsaredetailedbelowtoaidunderstandingofthisplot.

(a)(b)(c)

Figure11.TheBLDCmotorandstrainwavegearusedfortheactuatordesign.(a)12‐polerotormagnet.(b)3‐phase,27‐slotstator.(c)Strainwavegearcomponents[35].

Figure12.Actuatorperformancelinesatisfyingtherequirementforwalking.

15

Table2.MotorandTransmissionCharacteristics.

R(Ω) KT(Nm/A)

KB(V/rad/s)

KM(Nm/√ )

TPR(oC/W)

GearRatio

6 0.2 0.2 0.082 2.89 160

3.1.1.1DCMotordynamics ThedynamicsofaDCmotoraretypicallycharacterizedbythefirstorderdifferentialequation:

V , (1)

whereVisthevoltageacrossamotorwinding,Listhemotorinductance,Ristheresistance, isthebackelectromotiveforceconstant("backEMF"),and istherotationalvelocityofthemotorshaft.Excludingtheeffectofinductanceatsteady‐state,thevoltageequation(1)becomes V . (2)TheBLDCmotorispoweredbyacurrentcontrolamplifierwithaninternalfeedbacklooptotrackacommandedcurrentwithinanacceptablerange.Thereforeitisassumedthatthemotorcurrentcanbedirectlycontrolled.Themotortorquegeneratedisafunctionofthesuppliedcurrent T , (3) whereTisthetorqueandKTisthetorqueconstant,whichisamotor‐specificparameteralongwithK .Substitutingfor inequation(2)fromequation(3)resultsinequation(4)

,(4)

where: .

isreferredtoasthemotorconstant. istheslopeofthemotorwindinglineinFig.13,whichisamotor‐specificparameter.Theinterceptionofthelinewiththehorizontalaxisiscalledtheno‐load‐speed,whichisthespeedwhenthereiszerotorqueonthemotor.Theinterceptofthelinewiththeverticalaxisisthepeaktorque,whichisthetorquethatcanstopthemotorshaftfromspinning.

Themotorwindinglinethatconnectstheno‐load‐speedandthepeaktorquedefinestheboundariesofthemotorperformance.Notethatforagivenmotor,theslopeoftheline

16

doesnotchangewhendifferentvoltagesareapplied.Thisisbecause isafunctionofmotorvolume,andstatesthemotor’sabilitytodissipateheatforagivenamountoftorque.Ahigher representsabetterabilitytodissipateheat.Foragivenmotor,themotorperformancelinetranslatesaccordingtodifferentvoltages,whilemaintainingthesameslope.Theslopeofthislinechangeswhenagearreductionisappliedtothemotor.Motorperformancecanbeimprovedbyapplyingahighervoltagewithinitsheatdissipationability.Toensureaproperlydesignedactuationunit,thedesiredsystemperformance‐torqueversusangularvelocityprofile‐shouldbeencompassedunderthemotorperformanceline(Fig.13).

Figure13.Motorperformanceplotoftorqueversusangularvelocity.

Ontheperformancelimit,excessiveheatmaycausedamagetothemotor’sinternalcomponents.Toaccountforthis,powerdissipation(W)inthemotormustbecalculatedas

W

1. (5)

Acompleteformofequation(5)canbewrittenas

W

1, (6)

where isthedampingthroughthemotor.Theaveragepowerdissipationoverthetimeinterval∆tis

17

W1 1∆

∆ 1∆

∆

, (7)

W1

, (8)

where istherootmeansquared(RMS)torqueand istheRMSspeed.Continuouspowerlimitscanbeobtainedwithasimplerelationship:

∆, (9)

where∆TisanadmissibletemperatureincreaseandTPRisthetemperatureriseperwatt.

Inthislowprofilehipactuationunit,theselectedBLDCmotorallowsapeaktorqueof266.7Nmandano‐load‐speedof1.4rad/secwitha160:1gearreduction.However,whenoperatingthemotor,maximumcontinuousstalltorqueofthemotorshouldalsobeconsideredaccordingtotheheatdissipationlimit.Maximumcontinuousstalltorqueisdefinedas:

Maximumcontinuous stall torque

∆∙ .

(10)

TPRisgivenbyamotor’sspecificationsand∆Tisoftendecidedbytheinsulationratingofthewire.IntheEmoteqHT03000‐J01‐Z,atemperatureriseto125 isadmissibleforanRMSof1.8amperes.Thisresultsinamaximumcontinuousstalltorqueof82.07Nm.Inadditiontothemaximumcontinuousstalltorque,themomentarymaximumtorquepermittedtothetransmissionsystemshouldalsobeconsidered.ThemaximummomentarypeaktorqueoftheHarmonicDriveCSD‐25‐160‐2A‐GR‐SPis152Nm,whichislimitedbytheflexspline[35].Furtherinformationonthestrainwavegearsystemisdiscussedbelow.

3.1.1.2StrainWaveGearingSystemAstrainwavegear,theHarmonicDriveCSD‐25‐160‐2A‐GR‐SP,wasusedinthelowprofilehipactuationunit.Themainreasonsforchoosingastrainwavegearingsystemareitscapabilityofahighgearreductionratioinasmallvolumeanditslightweight.Agearreductionratioupto320:1ispossiblewithstrainwavegears,whileplanterygearscanonlyproducea10:1gearratiointhesamespace.Othertypesofgearssuchaswormgearswereexcludedfromconsiderationduetotheirlowefficiencyandlimitedgearratioinaconfinedspace.

Astrainwavegearcomprisesthreecomponents:awavegenerator,aflexspline,andacircularspline.Thewavegeneratorisathin‐racedballbearingfittedontoanellipticalplug,whichservesasatorqueconvertor.Theflexsplinehasanon‐rigid,shallowcupstructurewithexternalteeth.Thesidesoftheflexsplineareverythin,butthebottomisthickerand

18rigid.Thisresultsinwallflexibility.Theflexsplinefitstightlyoverthewavegenerator,andisheldinanellipticalshape.Thecircularsplineisarigidringwithteethontheinnerside.Theseteethengagewiththeteethontheoutersideoftheflexsplineacrossthemajoraxisofthewavegenerator.

Figure14.Strainwavegearcomponents[35].

Whiletherearemultipleconfigurationsofstrainwavegearstructures,thefollowingconfigurationwasusedinthelowprofileactuationunitdiscussedinthischapter:thewavegeneratorisconnectedtotherotor,whilethecircularsplineisrigidlyattachedtotheenclosingstructure.Therotationoftheflexsplineisusedastheoutputrotationoftheactuationunit.ThemechanismofthisconfigurationisillustratedinFig.15.

Asthewavegeneratorrotates,theflexsplineteethengagementwiththecircularsplineteethchange;i.e.,themajoraxisoftheflexsplinerotates.Becausetherearefewerteethontheflexsplinethanthecircularspline,everyfullrotationofthewavegeneratorresultsinaslightbackwardrotationoftheflexsplinerelativetothecircularspline.Thus,therotationspeedoftheflexsplineismuchslowerthanthatofthewavegenerator,whichcreatesahighgearreduction.Thegearreductionratioiscalculatedby:

GearReductionRatio

.

Forexample,ifthereare202teethonthecircularsplineand200teethontheflexspline,thegearreductionratiois‐0.01.Thismeanstheflexsplinespinsat1/100ofthespeedofthewavegeneratorintheoppositedirection.

Inadditiontothestrainwavegears’lightweight,compactdesign,andhighgearreductionratio,otheradvantagesincludenobacklash,highefficiency,back‐drivability,goodresolution,andhighrepeatability.Meanwhile,disadvantagesincludehighcostandflexibilityintheirmechanicalstructures,whichcanresultinpotentialdegradationsuchastheratchetingphenomenonfromenvironmentalandmechanicalshocks[36,37].Theratchetingphenomenoncanoccurwhenanexcessivetorque(atorabovetheratcheting

19torque)isappliedwhilethegearisinmotion.Theteethbetweenthecircularsplineandflexsplinemaynotengageproperlyandlosetheirconcentricity(Fig.16).Thismaydamagetheflexsplineandloweritslifespan,aswellastheratchetingtorque.Ratchetingtorqueisacriticalfactorthatmustbeconsideredwhendesigninganactuationunitwithastrainwavegear.

Figure15.Strainwavegearoperation.

Figure16.Ratchetingphenomenon[35].

203.1.2ShaftDesignandSensorMounting

Therearetwoshaftsinthisactuationsystem,the“innershaft”andthe“outershaft”.Theoutershaft,illustratedinblueinFig.17(a),transmitstorqueandrotationfromtherotor(coloredinyellow)tothestrainwavegearinput,whichisthewavegenerator(coloredinlightgreen).Fourscrewsclamptheoutershaft;thescrewscrossthroughthewavegenerator,outershaft,androtorwiththreadedholesontherotor’ssteelbody.Rotationissupportedbytworadialbearingslocatedontheouterandinnersideoftheoutershaft(coloredinblack).Theinnershaft,illustratedinorange,isusedtoencodetherotationalangledataoftheactuationunit’sfinaloutput(i.e.,thehipjointangle).Amagnet(coloredinred)fortheabsoluterotarymagneticencoderispressedonthetipofinnershaft.ThismagnetprovidesangularrotationdatatoAustriaMicrosystem’sAS5145B12‐bitencoder,whilerotatingwiththeenclosingcomponent(coloredinpink)andtheflexspline(coloredindarkgreen)‐theoutputoftheactuationunit.Theinnershaftlocatesitselfinsidetheoutershaft,andbecomesasingleentitywiththeoutputoftheentireactuationunitwhenfullyassembled.Locatingtheinnershaftinsidetheoutershafthastwoadvantages:

1) Itreducestheoverallthicknessoftheactuationsystembyutilizingthespaceinsidethehollowoutershaftfortheencoderversusaddinganexternalencodermountingstructure.

2) ItallowsthesystemtoefficientlyroutewiresbyplacingthewiresfromtheabsoluteencoderandBLDCmotorclosetothewearer’slowerback,wherethecontrollercircuitboardandbatteriesarelocated.Fig.17(b)showsacompleteassemblyofalowprofilehipactuationunitinstalledontheexoskeleton.Withthisconfiguration,theencoderandmotorconnecttothecontrollercircuitboardandbatterieswithoutexposinganywires.

3.1.3BearingstoHoldExternalLoads

Inadditiontoapairofradialballbearingsthattaketheinternalloads,apairofangularcontactballbearingswasusedtowithstandexternalloads.Here,weassumethattheworst‐caseexternalloadingscenariooccurswhenthewearerleanstothesidewithhis/herbodyweightinthefrontalplane(Fig18).Inthiscase,calculationofthemomentappliedtotheactuationunitisrathersimple.Westartbyassumingthatthewearer’sweightis200poundsandthedistancebetweenthemid‐planesofthehipactuatorsoneachside(paralleltothesagittalplane)is20inches.Inthisloadingscenario,weneglecttheaxialloadappliedtothesystem.Therefore,themomentappliedtothesystempurelyresultsfromtheradialloadfromthewearer’supperbody.Knowingthatthewearer’supperbodyweightis55%ofthewholebodyweight[38]andthemomentarmlengthis10inches,wecalculatethemomentappliedtothebearingstobe1,100lb‐in,orabout125Nm.Apairofangularcontactbearings,KaydonBearingKA035AR0,waschosenandinstalledwithaback‐to‐backorO‐configurationsuchthattheactuationunitssafelysustainthesystemunderthisloadingandpreventstructuralfailure,whichcanbeinjurioustothewearer.Theseselectedbearingsareabletotake552lbofdynamicradialloadand1,350lbofdynamicaxialload.

21

(a)(b)

Figure17.(a)Cross‐sectionalviewofanactuationunit.(b)Apatientwearingalowprofileexoskeletonsystem.

Figure18.Loaddiagramforanactuationunitwithapairofangularbearingsinstalledback‐to‐back.

22

3.2AssemblyProcessandDesignConsiderationforSafetyWithconsiderationsforachievingalowprofilesystemanddesignforassembly[39,40],atotalofsevencustom‐madecomponentsweredesigned.Withsystemsthatrequireassemblyprocesses,itisimportanttoconsidereaseofassemblyearlyinthedesignstage.Insection3.2.1,therecommendedassemblyprocessofthelowprofilehipactuationunitsisdiscussed.Section3.2.2coversthedesignconsiderationstakenintoaccountforsafety.

3.2.1AssemblyofaHipActuationUnit

Therearethreeenclosingcomponents(EC)andtwointerfacingcomponents(IC)inthehipactuationunit.Thesefivecustom‐madepartswerefabricatedoutofeitherAluminum7075‐T6orStainlessSteel17‐4PH.Cross‐sectionandsideviewsareshowninFig.20,whileanexplodedviewisshowninFig.21.Designforassemblywasconsideredfromanearlystageinthedesign,andtherecommendedassemblyprocessisasfollows:

1) Installtheradialbearing(large)ontheoutershaft(pressfit),andslideIC#2alongtheouterraceoftheradialbearing.

2) InstallthecircularsplineontheIC#1.3) SlideIC#2fromstep1)overIC#1.4) InstalloneangularbearingonEC#2,andtheotherangularbearingonIC#1;make

suretheorientationofangularbearingsformsaback‐to‐backconfiguration.5) Combinetheproductsofstep3)and4).6) Installtheradialbearing(small)ontheinnerraceoftheoutershaft.7) PressinthestatoronIC#2;makesurethewirealignmentiscorrect.8) Assemblethewavegenerator,outershaft(assembledwithIC#2andtheradial

bearing),androtor.9) Presstheencodermagnetontotheinnershaft.10) Slidetheproductofstep9)throughtheinnerraceoftheradialbearing,whichwas

installedinstep6).11) Assemblethebearingretainertotherotor.12) InstalltheabsoluteencodermoduleontheEC#3.13) AssembleEC#3andIC#2.14) Preloadtheangularbearing.15) AssembleEC#1andtheflexspline.16) Assembletheproductof15)withtheinnershaftandEC#2.

Whenassembled,EC#3isconnectedtothetorsoadaptorwithsafetystops,whichisexplainedinsection3.2.2.

23

Figure19.Anassembledlowprofilehipactuationunit.

24

Figure2

0.(a)T

hesid

ecross‐sectionalview

ofalowprofileh

ipactu

ationunit.(b

)Sideview

ofalowprofileh

ipactu

ationunit

assembly.

25

Figure2

1.Exp

lodedview

oflowprofileh

ipactu

ationunit.

26

3.2.2DesignConsiderationsforUserSafety

Multiplemotortest‐runswereconductedwithoutahumantestpilotbeforeexoskeletonsystemintegration.Tosimulatenaturalhumanwalkingandverifythehipactuationunit’sperformance,anexperimentalsetupwasarrangedasshowninFig.22.Compensatoryweightswereattachedtothethighandshanklinkstomatcha200‐poundperson’slegweight.Althoughtheexoskeletonwasintendedtohavepassivekneejoints,ahipactuatorwasusedtosimulatekneejointmovementinthissetuptofacilitatetheexperiment,whilethepassivekneejointtechnologywasunderdevelopment.Thistestprovidedempiricalvalidationthatthehipactuationunitcouldprovidesufficientspeedandtorqueduringtheswingphaseofwalking.

Asidefromtest‐runningthehipactuatorsundercomparableloads,mechanicalhardstopsweredesignedintoatorsoadaptorunit.Thisistoensurethehipactuator’srangeofmotionislimitedtoanatural,biologicalrangeofmotioninthesagittalplane(Fig.23).However,unexpectedcollisionswiththehardstopscancreatehighmomentarytorquestothehipactuator,whichcanpotentiallycauseratchetingofthestrainwavegear.Therefore,inadditiontomechanicalhardstops,itisimportanttohaveelectricsafetystopsinthecontrollertolimitthecurrentprovidedtotheactuator.

Figure22.Experimentalsetupfortestingthehipactuationunit.

27

Figure23.Mechanicalhardstopsforhipextensionandflexion.

3.3IntegrationintoaMinimally‐ActuatedExoskeletonApairoflowprofilehipactuationunitswasintegratedintoaminimally‐actuatedmedicalexoskeleton(Fig.24).Thisexoskeletonalsoconsistsofpassivekneejointsandacarbonfibertorsoframe,whichcontainsacontrollercircuitboardandbatteries.Also,asetofstandardlegbracescustom‐moldedforeachpatientwasused.Detailsofthepassivekneejointdesigncanbefoundin[41].

Thisdevicewastestedbyatestpilotwhowasa28‐year‐oldmale,5’10”talland170pounds,whohadsustainedacompleteT12injuryfor12years.Whenwornbythetestpilot,theactuatorswereabletoprovideaspeedofupto1secondperstep,withvaryingstepsizesfrom14to16inches.Theoverallwalkingspeedoftheexoskeletonwearervariedsignificantlyaccordingtothebalancingtimebetweeneachstep,whichappearedtoberelatedtothewearer’sphysicalconditions.Inthisstudy,thetestpilotwasabletowalkataspeedof0.22m/s.Thetorqueprovidedfromtheactuatorsprovedtobesufficientforwalking,aswellasforprovidingmoderateassistanceduringsittingandstanding(withthehelpofbalancingaids).

Thegeometryoftheactuatorswasofasufficientlylowprofiletoallowthewearertositinaregularcomputerchairwitharmrests,partiallyconcealthedeviceunderhisclothing,andwalkthroughnarrowaisles(Fig.25).Thetotalweightoftheactuatoris3.5pounds,whichenablestheweightofthewholeexoskeletonsystemtobe19.5pounds.Thisexoskeletonisthelightestpoweredexoskeleton,weighinglessthan20pounds,withacompactformfactorthatmorecloselyresemblesanRGOthanotherpoweredexoskeletons.

28

Figure24.Lowprofile,minimally‐actuatedmedicalexoskeleton.

Figure25.Withlowprofileactuators,thetestpilotwasabletowalkthroughthenarrowaisleofa

localstore.Thismedicalexoskeletoniswornpartiallyunderneathhisclothing.

29

3.4LowProfileHipActuatorDesign–SecondRevisionLowprofilehipactuationunitswiththeEmoteqHT03000‐J01‐ZandHarmonicDriveTMCSD‐25‐160‐2A‐GR‐SPallowacompactprofile,lightweight,andhighusermaneuverability.Infact,giventheirspecifications,theactuationunitsdiscussedinthischapterarethemostcompactunitscomparedtootheractuationunitsonthemarket.Meanwhile,thedesign’sdisadvantagesincludeitscomplicatedassemblyprocessandhighcostduetomanycustom‐madecomponents.Toimproveupontheseshortcomings,anothersetofhipactuatorswasdeveloped(Fig.26).Theseactuatorsuseoff‐the‐shelfhousedcomponents:aMaxonEC90FlatmotorandHarmonicDriveTMSHD‐20‐100‐2SH.Asaresult,theactuatorcontainsfewercustom‐madeparts,andhasaneasierassemblyanddisassemblyprocess.Asatradeoff,adoptingtheseactuationunitsresultedinanincreaseintheexoskeletonhipwidthofabout1.9inchesandadecreaseduserweightlimitduetothestrainwavegear’sbearings.TechnicalspecificationsaresummarizedinTable3.ThecharacteristicsoftheMaxonEC90FlatmotorarecomparabletotheEmoteqHT03000‐J01‐Z,andthegearratiowasselectedtobe100:1insteadof160:1,toachieveamoreoptimaldynamicswingofthepassivekneejoints.Although,neitheractuationunitrequiresanymodification,exceptforthedisassemblyandre‐assemblyprocessforinterchangingthestrainwavegearsbetween100:1and160:1.

Whilethedesignusesanoff‐the‐shelfBLDCmotorandstrainwavegearthathavetheshaftandbearingsintegrated,somemodificationsontheBLDCmotorstructureweremadetooptimizeinterfacingwithminimalthickness.Therecommendedassemblyandmodificationprocessofthisactuationunitisdescribedbelow.

1) MillouttheholepatternandshoulderonthemetalinterfaceoftheMaxonEC90flatmotorforthestrainwavegear.

2) CuttheshaftlengthoftheMaxonEC90to0.592in.3) PressIC#2ontotheshaftoftheMaxonEC90.4) AssembleIC#1andthewavegeneratorofthestrainwavegear.5) Aligntheflexsplineandcircularsplineassemblywiththehole‐patternfrom1).6) InstallIC#3ontheproductofstep5).7) Slidetheproductofstep4)ontotheproductofstep3),andfastenthescrews.8) PressthemagnetontotheOutputLink.9) Installtheproductofstep8)ontotheproductofstep5)10) InstalltheabsolutemagneticencoderonEC#1.11) Installtheproductofstep10)ontoIC#3.

AcomparisonofthetwohipactuationunitsissummarizedinTable4.Futureworkremainstofurtherdevelopcost‐effectiveandlowprofileactuationunitsthatcanbeusedbyuserswhoweighmorethan170pounds.

Table3.MaxonEC90FlatMotorCharacteristics

R(Ω) KT(Nm/A)

KB(V/rad/s)

KM(Nm/√ )

TPR(oC/W)

2.26 0.217 0.217 0.144 2.99

30

Figure26.Cross‐sectionalviewofanactuationunitwiththeMaxonEC90.

Table4.ComparisonofTwoMotorDesigns

DCMotor Emoteq,Frameless MaxonEC90,Housed

StrainWaveGear UnhousedComponents Housed,AssembledGearset

Assembly Complicated Simple

Diameter 4.5” 3.8”

Thickness 1.8” 2.5”+cover(notshown,0.25”)

Weight 3.5lb 3lb

UserWeightLimit 200lb 170lb

31

4.ModularExoskeleton

Targetusers’specificconditionsandneedsmustbethouroughlyconsideredtodevelopaneffective,widelyacceptedmobileexoskeletonsystem.Amongparalyzedindividuals,onecrucialuserneedthatvariessignificantlyistheamountofsupportrequiredfromtheexoskeletonforbalancing.Evenwithinaparaplegicpatientgroup,thereisabroadrangeofpatientabilitiesforsustainingupperbodycontrolafterinjury.Whileagivenamountofsupportfromtheexoskeletonmightnotsufficeforcertainpatients(inwhichcasethepatientmaynotbeabletousethedevice),thesameamountofsupportcouldbeexcessiveandimpedingforotherpatientswhosustainmoremusclecontrol.

Humanhipjointsareoftendescribedasballjoints,whichhavedegreesoffreedominallthreebodyplanes:flexionandextensioninthesagittalplane,adductionandabductioninthefrontalplane,andexternalandinternalrotationinthetransverseplane.Whilehipextensionandflexionarethemainsourcesofbipedallocomotion,ab/adductionandinternal/externalrotationalsocontributetonumerouskindsofmaneuversandbalancing,aslongastheindividualretainsthecontrol.Beingabletoprovideanadequatelevelofsupportandfreedombasedonthewearer’sphysicalconditioniscriticalfordeviceusability.

Existingpoweredexoskeletonshavea“oneexoskeletonforall”approach,withafixedamountofsupport.Thislimitstheusergrouptothosewhoneedtheexactlevelofsupportthedeviceprovides,whichoftentimesisnotoptimalforpatients.Moreover,beingabletochangethesupportlevelsisbeneficialforbothusersandpractitioners.Thisallowspractitionerstorecommendfirsttimeuserstostartwithfullsupport,thengraduallylowerthesupportlevelformorenaturalmovementasthepatientgetsaccustomedtothedeviceanddevelopsbalancingskills.

Inlightofthis,atrunkexoskeletonmodulethatcomprisespoweredhipactuatorsandlockablejointsthatprovidedifferentsupportlevelswasdeveloped.Thisexoskeletonmodulecanbeusedeitherbyitselforwithotherkneemodules.Itsconfigurablearchitecturecreatesversatilesupportlevelsforpatientsandnon‐injuredusers.Thetrunkexoskeletonmodule,apairofkneemodules,andapairofAFOcanbecombinedtoformafullbodyexoskeleton.Thischapterdiscussesanoverviewofthehardwaredesignandpossibleconfigurationsofthedesign,whichopensassistiveopportunitiestoseveraltypesofuserswhichincludesnon‐injuredpeople.

4.1MobilitySpectrumAsbrieflyexplainedabove,itappearsthateachparalyzedpatient’ssustainingmobilitylevelvariessignificantly.Therefore,therecommendeddevice’srangeofmotionhastobefittedaccordingtoanindividual’sinjurylevelandphysicalconditions.Fig.27illustratesthe“mobilityspectrum”toaidintheunderstandingofthedifferentuserconditionsandneeds.Thecolordensityofthespectrumstandsforthemobilityoftheuser.Forexample,aparalyzedusergroupwithahighinjurylevelandlowresidualmusclecontrolfallsonthe

32leftsideofthespectrum.Patientsinthisusersegmentmayrequirealargeramountofsupportfromthedevicewhichcanconstraintheiruncontrolledmovementswithhigherdevicerigidity.Thisisachievedusinglockedjoints(exceptforthehipandkneeduringextensionandflexion),shoulderstraps,acorset,shinguards,etc.Patientswithlowerinjurylevelswhosustaingreatermusclecontrolfallontherightsideofthespectrum.Alimitedrangeofmotion,lockedjoints,andadditionalstrappingsmayimpedetheirnaturalmovements.

Figure27.Mobilityspectrumoftheinjuredusergroup.ItwasnotedthatpatientsattaininghighmobilitywhoareontheveryrightsideofthemobilityspectruminFig.27havesimilarneedsastheelderly,orthosewhoarenotseverelyinjuredyetrequireanassistiveexoskeletonsystem.Thisoverlapinneedsandpreferencesdespitebeingunderdifferentphysicalconditionsnaturallyraisesaquestiontous‐whatifwefurtherextendthismobilityspectrumtotherightside?Totherightsideofthismobilityspectrum,therewillbeindividualswithhighermobility,suchasindustryworkersandsoldiers(Fig.28).

Figure28.Extendedmobilityspectrum.Currently,technologyexistsonlyforafewdiscretesegmentsofthisspectrum.However,designmodularitycanfulfillthefullrangeofthespectrumandfillgapsindeviceavailabilitybetweensegmentsonthespectrum.

ExoskeletonsforparalyzedpatientswerediscussedinSection2.3andChapter3.Asmentionedinprevioussections,theyhavelimiteduseforpatientswithcertainconditions.

33Fig.29(a)showstheHumanUniversalLoadCarrier(HULC)[42],anexoskeletonforsoldiers.HULCevolvedfromtheUCBerkeley’sBerkeleyLowerExtremityExoskeleton(BLEEX)[15‐17],andislicensedtotheLockheedMartinCorporation.TheHULCuseshydraulicactuatorswithhighpowerdensitytohelpsoldiers’heavyloadscarrying.Fig.29(b)showsHonda’sStrideManagementAssist.Ithastwoelectrichipactuatorswithoutkneejoints,andassistsflexionduringwalking[43].Itisdesignedfor“individualswithweakenedmuscleswhoarestillabletowalk”[44],andiscurrentlyundergoingaclinicaltrialforstrokerehabattheRehabilitationInstituteofChicago.EventhoughHonda’soriginaltargetusergroupincludespeoplewithvariousphysicalconditions,thedevicedoesnotincludecustomizablefeaturesintermsofrangeofmotionandlevelofsupportfordifferentindividuals[45].

(a)(b)

Figure29.(a)HumanUniversalLoadCarrier(HULC)[42].(b)StrideManagementAssist[44].Table5showsthemajordifferencesamongexoskeletonsystemsfordifferentusergroupswhichrequirevaryingrangesofmotion,levelsofbalancingsupport,speedsofwalking,andtypesofuserinterfaces.Forexample,alimitedrangeofmotionandasubstantialamountofbalancingsupportisrequiredforaparaplegicpatientwithahighinjurylevel.Forthispatient,therecommendedwalkingspeedwouldbeslowerthanthatofasoldier.Thesuggesteduserinterfacesforthesetwousersarealsohighlydifferent.Fortheparaplegicpatient,itisrecommendedthatmorecautiousstepsbetakenwhentheuserorpractitionerexplicitlycommandsthestep,forinstance,bypressingbuttons.Incontrast,asoldierwithcompletemusclecontrolandhighagilitywouldprefertowalkwithoutexplicitstepcommandstothedevice.Amongthesefourvaryingdevicecharacteristics,threefeatures–recommendedrangeofmotion,levelofsupport,andspeed/power–arecloselyrelatedtothehipjointdesign.Therefore,thetrunkexoskeletonmodulewithlockablejoints,whichessentiallycreatesvaryinglevelsofsupportandrangesofmotion,wasdesignedtosatisfydifferentuserneedswithoutrequiringcompletelyre‐customizedsystemsforeachuser.

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Table5.DifferentExoskeletonFeaturesforDifferentUserGroups.

*RefertoChapter5formoreinformationonexplicitandimplicitUIs.

4.2HardwareDesignOverviewTodifferentiatedevicesupportlevelsforuserswithvaryingmobility,thedeviceshouldincludeallbiologicaldegreesoffreedom,butallowuserstodisableanydegreesoffreedomatanytime.Onewayofachievingthisfunctionisthroughpoweredactuatorswhicharecontrolledbyauserorpractitioner.Mostpoweredexoskeletons,includingtheminimally‐actuatedlowprofileexoskeletondiscussedinChapter3,alreadyhavethispoweredactuationforhipextensionandflexion.However,addingadditionalpowereddegreesoffreedomincreasessize,weight,andcostofthedeviceduetoadditionalrequiredinfrastructuresuchasbatteries,sensors,andcontrollers.Sincehipadduction,abduction,androtationhavelittleinfluenceonbipedalambulation,itwasdecidedtoachievetheseadditionaldegreesoffreedomviapassive,unactuatedmechanicaljointswithlockingfeatures.Thisminimizesthesize,weight,andcostofthedevicewhileallowingdifferentdevicesupportlevels.

Ideally,alljointsthatprovidedegreesoffreedomshouldbelocatedwithinthebiologicalhipjointtoachievenaturalmovement.However,orthoticdevices(unlikeprosthetics)havegeometriclimitationswhichrequireoffsettingthedevicejointfromthebiologicaljointinthefrontalplane.Also,itisverychallengingtocreateaballjointsystemwithcomparablesizeandweightthatmimicsthehumanhipjointwithpartiallypoweredandpartiallypassivecomponents.Therefore,itwasdecidedtolocatethehipadductionandabductionjointsattwodifferentplacesontheexoskeleton–oneonthelowerbackandtheotherontheupperthighascloseaspossibletothehipjoint.Whilethelowerbackabductionjoint

35provideslimitedabductionandadduction,theadditionaljointontheupperthighisequippedwithahigherrangeofmotiontocompensateforinaccuraciesindevicemovements.Arotationaljointisalsolocatedontheupperthighinconjunctionwiththeabductionjoint(Fig.30,Fig.31).

Thesejointsareallfree,passive,mechanicaljointsthatcomplywiththewearer’smotionwithoutimpedingoramplifyingmovement.Specificdegreesoffreedomcanbeconstrainedbyinsertingpinsintopre‐designedlocationsonthedevice.

Figure30.Overviewofthehipmodulewithadditionalabduction,adduction,androtationjoints.

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Figure31.Abduction,adduction,androtationjoints.Thistrunkexoskeletonmodule,whichisequippedwithadditionallockablejoints,canbeworneitherbyitselforincombinationwithmultipledifferentkneetechnologies,whichweredevelopedintheBerkeleyRoboticsandHumanEngineeringLabatUCBerkeley.Certaintypesofpatients(suchaspatientswhoretaincontrolintheirlowerlegsortheelderly)canbenefitfromthetrunkexoskeletonmodulebyitself,withoutaddedkneeandanklesupports.Similarly,anyable‐bodieduserwithmobilitycanreceivegaitassistanceandlowerenergyconsumption,asthesimilareffectwasachievedinpreviousmilitaryexoskeletonsystemsusinghydraulicactuators[15‐17].Thedevicecanalsoprovideassistanceoraugmentvarioususermaneuversassociatedwithindustrialwork.Theconfigurablearchitectureandprogrammablecontrollerofthesystemallowindustryworkerstowearthisexoskeletontogainsupportforrepetitive,strenuousworkmovements–forexample,liftingworkinawarehouseorassemblyworkinamanufacturingfacilitywheretheworkerneedstobendhis/herback.However,furtherdevelopmentofdifferentmodesofoperationaccordingtotheuser’spostureisrequiredfortheseapplications.

37Fig.32summarizesexampleoftheusesofthetrunkexoskeletonmodulewithadditionallockablejoints.Thedesignaccommodatesvariouscombinationsofactuationunitswithdifferentpowerlevels,andseveralkindsofkneemodules.

1. GaitAssistKneeModuleisapassivekneemoduledevelopedfor

alowprofileexoskeleton,discussedinChapter3.2. SquatAssistKneeModuleisapassivekneemoduledevelopedin

theBerkeleyRoboticsandHumanEngineeringLab.Figure32.Exampleusesofthetrunkexoskeletonmodule,byitselfandincombinationwithtwo

differentkneemodules.

4.3AssessmentoftheModularSystemThetrunkexoskeletonmodulewastestedbya32‐year‐oldmalewhoretainedpartialmusclecontrolinhislegsafterhisT9incompleteSCI.Forthisindividual,theabductionandrotationjointontheupperthigh(6inFig.30andFig.31)weredisabled,whilethead/abductionjointonthelowerback(1)wasactivated.Fig.34showsphotosofthehipmodulewornbythetestpilotwhilewalkingwiththetrunkexoskeletonmodule.

Thedevice’srangeofmotionanddegreesoffreedomwereexperimentallyverifiedbytwohealthyindividualswithoutmobilitydisorders.Whenjoints1,5,and6wereactivated,able‐bodiedwearerswereabletoperformvariousmovementsandachievedifferentpostureswithoutdeviceimpedance.SomeoftheposturesareshowninFig33.

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Figure33.Thetrunkexoskeletonmodulewornbyahealthy,non‐injuredindividual.

Figure34.ThetrunkexoskeletonmodulewornbyanincompleteT9SCIpatient.

However,whentheable‐bodiedwearerfullysquattedwithhis/herhipsabducted,thedeviceconformationwasnotideal.Withjoints1,5,and6activated,thedevicewasnotabletofullycomplywithasquattingpostureeventhoughthewearerwasabletoachieveandmaintaintheposture.Throughoutthisempiricalanalysis,itwasfoundthatadditional

39abductionjointsalongaxis9inFig.35withalimitedrangeofmotionsignificantlyincreaseconformitytothewearerduringsquatting.Thebenefitofafullrangeoffreedomonjoints9and1remainsdebatable.

Figure35.Overviewofthehipmodulewithacompensatedabductionjointaxisindicated.Systemmodularitysimplifiesthecustomizationforeachuser’sspecificneedsbymerelyaddingorswappingdifferentmodulesbasedonuserabilities.Accuratelyaligningdevicejointstothewearer’sbiologicalhipjointswhileprovidingpropulsionassistancewithpoweredactuatorsappearstobeachallengingproblem.Especiallyinregardtohipabductionandadductionforable‐bodiedusers,itiscriticaltocomplywithjointmovementstoaugmentendurance.Therefore,exploringmorepossibilitiesforjointlocationstopermitvariousmovements,suchassquatting,lunging,andhipabductionwalking,anddiversifyingactuationunitsremainasfuturework.Enhancingmodularityindesignwillnotonlyaugmentavailablemobilitysolutionsforvariouskindsofindividuals,butalsofillthegapsofavailabledevicesacrossthemobilityspectrum.

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5.UserInterfaceModuleDesign

State‐of‐the‐artmedicalexoskeletonsusevarioususerinputreceivingmethodswhichcanbecategorizedintotwodifferentgroups:

1) Sensingauser’sintenttowalkfromhis/herposture.Forexample,thesystemcanmeasurethegroundreactionforce,centerofpressure,etc.

2) Receivingexplicitcommandsfromthewearerviadirectuserinput,suchasbuttons.

Theadvantageofthefirstmethodisthatitrequiresminimaluserefforttoissuecommands.However,becauseofthelimitedmobilityandmusclecontroloftheintendedusers,thisimplicitUIhasthepotentialriskofmisinterpretingthewearer’sposture,whichcanresultinfalling.StudieshaveshownthattheimplicitUIofReWalkTMresultsinauniquepatternofcontrolforwalkinginindividualswithSCI;patientswithlowerinjurylevelsshowbetterwalkingperformancesandalsoprogressmorerapidly[46].Meanwhile,explicitUIssuchasthesystemsusedinRexandAUSTIN,requiremoreuserefforttocommandstepsviajoysticksorbuttons.Still,theyarethepreferredexoskeletonoperationmethodsforpatientswithhigherinjurylevelsbecausetheyminimizethemistriggeringrisksresultingfromtheuser’sweakenedmotorcontrol.Yet,thisdevice‐coupledUIdesignalsocouldresultinlimitedusabilitybydifferentuserswhosehand/fingersizesvary(Fig.36).

AsmentionedinChapter4,designmodularityincreasesdeviceusabilitybyprovidingopportunitiestoaugmentsolutionsfordifferentusergroups.Therefore,thischapterdiscussesanexplicit,user‐coupledUIdesignasanexclusivemoduleforparalyzedindividuals.Herethetermcoupledderivesfromthetermcouplingofmechanicalcomponentsinmechanicalengineering.Inparticular,wefocusonauserstudythatconsistsofinterviewsandusabilitytestsofaprototype.Basedonobservationsandinterviewsconductedasapartofthisstudy,theprimaryuserneedsforaUIaredefinedasfollows:

1) Intuitiveness:Theinterfaceshouldbeeasytolearnanduse.

2) Comfort:Thephysicalinterfaceshouldbecomfortableandcomplywiththeuser’sbodyshapeandskeletalstructure.

3) Informationfeedback:Informationfeedbackallowsthewearertobetterengagewiththeexoskeletonsystem.Unliketheclosed‐loopnervoussystemofthehumanbody,exoskeletonsareexternalandartificial.Ideally,thefeedbacksystemwillcompensateforauser’simpairedperceptionofhis/herownposition,pressure,andorientationwithrespecttogravityforbalancing.Moreover,forsafety,theusershouldbeabletomonitorandmaintainfullcontroloverthemotionoftheexoskeleton.

4) Independence:TheUIshouldinterfereminimallywiththeuser’sothernaturalmovementsandallowtheusertodon,doff,andoperatetheexoskeletonbyhimself/herself.

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Figure36.Anexampleofadevice‐coupledUI.Atwo‐waybuttonisattachedonawalkerhandle.Notethattheswitchisintegratedintoawalkerhandle(device‐coupled).Thetwo‐wayswitchgivestwo

differentsignalsaccordingtothedirectionausertriggerstheswitch(upordown).

5.1SchematicsofExplicitUserInterfaceTheexplicitUIoftheexoskeletonswitchesthestateofthemachinefromonestatetotheotherwhentheuserissuesinputcommandsviameansofinput,suchasbuttons.Inasimpleformofwalkingoperationwithexoskeletons,therearefourdifferentstatesofthemachine:1)leftlegforward,2)rightlegforward,3)feettogether(standing),and4)seateddown.WiththewalkingschemeshowninFig.37,atleasttwobuttons‐thesimplestwayofgivingtwodifferentsignals‐arerequiredfortheusertoswitchbetweenstates.Forexample,whenthewearerisstanding(feettogether),he/shecanpresseitherbuttonAtostartwalkingbymovinghis/herleftlegforward,orbuttonBtositdown.Withthiswalkingscheme,theusercansitdownonlyifhis/herfeetaretogether,andtheweareralwaysmuststartwalkingwithhis/herleftleg.Clearly,therearemultipleapproachestomappingthesecommands,possiblyusingmorebuttons.

Twodifferentexoskeletonfinitestatemachines(i.e.,walkingoperationschemes)weresuggestedandevaluatedviausabilitytestsandinterviews.Thefirstfinitestatemachineiscalled“Singleton”,asshowninFig.36.IntheSingletonmethod,theuserpressesthesamebuttonforeachstep.Forexample,theuserpressesbuttonAforthefirststep→buttonAagainforthesecondstep→(continue)→buttonBtostandup(feettogether)→buttonBagaintositdown.

Thesecondfinitestatemachineiscalled“Alternating”,becausetheuseralternatesbuttonsas his/her stepping legs alternate. Essentially, different buttons are used to step withdifferentlegs.Forexample,inanalternatingscheme,theuserpressesbuttonAfortheleftstep→buttonBfortherightstep→buttonAagainfortheleftstep→(continue)→bothbuttons(oranallocatedthirdbutton,buttonC)tobringthefeettogetherandsitdown.ThisprocedureisillustratedinFig.38.

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Figure37.Anexoskeletonfinitestatemachine(Singleton).

Figure38.Alternatingfinitestatemachine.

Thetwoaforementionedmethodsweresuggestedandevaluatedbyeightindividualswithmobilitydisorders,viainterviewsandusabilitytestswiththelow‐fidelityUIprototype,whichisdescribedinthefollowingsections.Becausethepotentialusers’preferenceinwalkingschemesmayhighlyaffectthehardwaredesign,itwasimportanttoidentifythepreferredmappingpriortohigh‐fidelityprototypedevelopment.

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5.2OverviewofUIPrototypeSeveralversionsoflow‐fidelityprototypeshavebeendevelopedtosimulateanewUIandelicitfeedbackfrompotentialusersduringthetestingphase.Internalconceptscoringwasconductedtoselectthenew,user‐coupledUIconcept.Thescoringusedcriteriabasedontheprimaryuserneeds–intuitiveness,comfort,feedback,andindependence.Throughoutthisprocess,a“gloveUI”featuringaglovewithbuttonsattachedtothefingertipsandanLEDdisplaymountedontheinsideofthewrist(Fig.39(a))wasselectedasaproposednextgenerationUIformedicalexoskeletons.ThisgloveUIretainstheconceptofusingthewearer’sfingerstooperateanexoskeleton,whileitisnolongerdevice‐coupledasitwasinthepreviousUIdesign.Fig.39(b)showsawheelchairuserwearingtheprototype.Thisprototypeuseswhitestripesforbettervisualizationoftheblackglove,whilebuttonsareattachedtoallfivefingerstodeterminepreferredbuttonlocations.

ThisnewUIconceptisdesignedtobemoreuser‐centeredthanpreviousdevice‐coupledUIs,andaccommodatesdifferentusers’handsizesandgrippingpreferences.Also,itisintendedtoprovidevisualfeedbacktotheuserviaadisplaymonitor.InformationshownonthemonitorincludesOn/Offstatus,batterylife,andquickinstructionsforexoskeletonoperation.

(a)(b)Figure39.(a)ThethreecomponentsoftheGloveUIprototype.(b)Aparticipantwearingthe

prototype.

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5.3GloveUIEvaluation:MethodsThegoalofthisevaluationwastofindthepotentialusers’preferencesregardingglovetypes,buttonnumbers,displaylocations,andwalkingschemes.Ourhypothesiswasthatthepotentialuserswouldprefertohavethesimplesthardwareandwalkingschemewithlimitedmaneuvers,ratherthanmorecomplexwalkingschemeswithmoreelaboratemaneuvers.

5.3.1PatricipantsOverview

Atotalofeightindividualswithmobilitydisordersparticipatedinthisevaluation.Abriefprofileoftheparticipantsisasfollows:

1) Participant1:30‐year‐oldmaleandrelativelynewcrutchuserduetohisrecentankleinjury.

2) Participant2:28‐year‐oldmaleand12‐yearcrutchuserafterSCIresultingfromasnowboardingaccident.

3) Participant3:34‐year‐oldfemaleandlifetimecaneorsinglecrutchuserduetocongenitallegabnormalities.

4) Participant4:24‐year‐oldmaleand5‐yearmanualwheelchairuserafterSCIresultingfromacaraccident.

5) Participant5:27‐year‐oldmaleand12‐yearwheelchairuserafterSCIresultingfromamotorcycleaccident.

6) Participant6:24‐year‐oldfemaleand2‐yearwheelchairuserafterSCIresultingfromacaraccident.

7) Participant7:42‐year‐oldmaleand20‐yearpoweredwheelchairuserafterSCIresultingfromacaraccident.

8) Participant8:33‐year‐oldfemaleand2‐yearsinglecrutchandKAFOuserafterkneeinjury.

Feedbackwascollectedfromalltheparticipantsviainterviewsandusabilitytestswithparticipants1),2),3),and4).

5.3.2Interviews

Interviewswereconductedatseverallocationswherepeoplewithmobilitydisordersfrequentlyvisit.OneoftheseplacesistheEdRobertsCampuslocatedinBerkeley,California.Bothguerillaandscheduledinterviewswereconductedwithavarietyofpotentialuserswithmobilitydisorders.Ashortlistofquestionnaireswaspreparedtoobtainbasicdemographicdatafromtheparticipantsbeforetheinterviews.Giventherelativelysmallsamplesize,itwascriticaltocoordinatein‐depthinterviewssuchthattheywereimmediatelyfollowedbyusabilityteststothoroughlyexploreopinionsonthegloveUIprototype.

455.3.3UsabilityTests:MaterialsandProcedure

Usabilitytestswereconductedwithfourindividualswithmobilitydisorders–participants1),2),3),and4).Forusabilitytesting,theparticipantsweregiventhegloveUIprototypeshowninFig.39,andaskedtodemonstratehowtheywouldwalkwiththeirmobilityaidwhilewearingthegloveUI.Detailedfociontheusabilitytestaredescribedasfollows:

1)GloveTypeThegloveprototypeusedforthisusabilitytestisshowninFig.39.Theparticipantswereaskedfortheiropinionsontheglovematerial.Inparticular,whetherthefabricwastoothickorthin,andwhetherthecoverageofthegloveoverthehandwastoomuchortoolittle.

2)GripandButtonsThegripusedbyindividualswithmobilitydisorderstoholdtheircrutchesorwalkersvarieswidelywithhandsize,mobilityaidtype,andgriptype.Dependingonthesefactors,auser’spreferenceforbuttonlocationsmaydifferforeaseofuseandaccuratetriggering.Todeterminetheirpreferences,participantswereaskedtoholdthegripoftheirmobilityaidwhilewearingthegloveUIprototype,andtoselecttheirpreferredbuttonsamongthoseattachedtothefingertipsofthegloveUIprototype.

Theparticipantswerealsoaskedfortheiropinionsonthenumbersandtypesofbuttons.Theywereaskedtochooseatleasttwobuttonsforsimpleoperations,andmorebuttonsforotherpossiblefunctionsormoreelaborateexoskeletonmaneuvers.

3)UIScheme,orWalkingMethodPreferenceTwodifferentUIschemesdescribedinSection5.1wereexplainedtotheparticipants.Then,participantswereaskedtosimulatewalkingwiththetwodifferentschemesusingtheirbuttonpreferencesfromthepreviouspartoftheusabilitytest.TheparticipantswereaskedtofolloweachwalkingschemeinFig.37andFig.38threetimes.Afterthissimulation,theparticipantswereaskedtodescribetheirpreferencesandopinionsregardingthetwodifferentschemes.

4)FeedbackDisplayModulePositionThedisplaymodulecontainsanLEDscreenthatiscapableofdisplayingvarioustypesofinformation,suchasthesystemstatus,batterylife,wirelessconnectivity,anderrordiagnosticswhenapplicable.Theparticipantswereaskedtofindthepositionofthedisplaymodulewheretheycouldreceiveinformationataglancewhileoperatingtheexoskeleton.Thistestwasintendedtolearntheusers’preferencesforlocationsofthedisplaymodule,whichmaydifferfromthetypeofmobilityaidanditsgrip.

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Figure40.UsabilitytestofthegloveUIprototype.

5.4ResultsandDesignRecommendationsBasedonfeedbackfromtheinterviewandusabilitytestuserresearch,designsuggestionsregardingfourdifferentcomponentsofthenextgenerationgloveUIaresummarizedinthissection(Table6).

5.4.1GloveType

Basedonfindingsfromtheusabilitytestsandinterviews,adoptingonetypeofall‐inclusivegloveforthisapplicationtomeetvarioususerneedsappearstobechallengingduetoconflictingpreferencesamongpotentialusers.Manualwheelchairuserspreferredthick,durableglovestoprotecttheirhandswhileusingawheelchairandwearingamedicalexoskeleton.However,afullglove,evenwiththinmaterialwasnotfavoredbyotherusergroupsbecauseofitsunnecessarycoveragewhichcancauseunpleasantheatingoftheuser’shand.Therefore,fingersleevesarerecommendedinsteadofafullglove.Fingersleevesbetterfacilitatevariationsinusers’handsizes,grippreferences,andpreferencesforglovematerialforbothwheelchairusersandnon‐wheelchairusersbyofferingtheoptionofwearingthegloveUIontopofanyothergloves.

5.4.2NumberofButtons

Allparticipantsrespondedfavorablytowardtactilefeedbackfrommomentaryswitchesontheprototype.Giventhepossiblefinitestatemachinesofanexoskeleton,atleasttwobuttonsarerequired(asstatedinSection5.1).Formoreelaboratemaneuveringofthemachine,threebuttonscanbeconsidered.However,itappearsthatpotentialusersprefer

47twobuttonsduetoitsinherentsimplicityandminimalinterface.Sixoutofeightparticipantsrespondedthattheywouldprefertohaveasimple,minimalUIwithlimitedfunctionratherthanmorebuttonswithadditionalmaneuvers.Regardingthepotentialusers’limitedcontroloftheirlowerbodyandlackofexperiencewithexoskeletontechnology,simplicityshouldbeconsideredasoneofthemostimportantattributesinUIdesign.

5.4.3WalkingOperationScheme

TheSingletonmethodwasthepreferredwalkingoperationscheme;amajorityoftestparticipantsperceivedtheSingletonmethodasmoreintuitiveandeasiertooperate.Despiteitsflexibility,theAlternatingmethodwasdeemedtoocomplicatedforbeginners.AnargumentremainstokeeptheAlternatingmethodasanoptionformoreexperiencedusers.Keyquotationsfromtheparticipantsonthesepotentialwalkingschemesareasfollows:

“I’mthinkingaboutacomputergame.Somepeoplepreferusingfewerbutmoreintuitivecommands,butIliketousemoregranularones.Butforrightnow,IliketheSingletonoptionsinceIamnewtothissystem.”

“AfterawhileifitwassomethingthatIhadtodoregularly,like,say,driveacar,itwouldprobablyjustbecomesecondnaturebecauseIwouldtrainmyselftoclickonlyone.”

Similartotheresultoftheprevioususertesting,itappearedthatsimplicityandintuitivenesswerethekeyfactorsforthepotentialusers’preferences,especiallyforthosewhohavenoexperiencewearingexoskeletons.

5.4.4DisplayModulePosition

Participantsshoweddifferentpreferencesregardingthedisplaymodule’sangleandposition.Walker,crutch,andwheelchairusersviewthedisplayfromdifferentanglesduetotheirdifferentgrips.Therefore,itisrecommendedtohaveanadjustabledisplaymodulepositionwitheasyattachmentmethods,suchasVelcro.

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Table6.SummaryofUIAssessment

5.5ImplementationoftheUserStudyFingergloves,twobuttons,thesingletonwalkingmethod,andanadjustabledisplaypositionwerethefinaldesignrecommendationsbasedontheUIassessment.Ahigh‐fidelityprototypewasdevelopedtoincorporatemostoftheseresultsofthisuserstudy.Detailsoftheelectriccomponentsusedinthisdesigncanbefoundin[47].AsshowninFig.41and42,thisUIcontainstwobuttons(1)attachedtofingersleeves(2),andisaSingletonfinitestatemachine.Itfurthercomprisesadisplaymodule(5)andcontrollerbox(6)whichenclosesacontrollerthatwirelesslycommunicateswiththemaincontrolleroftheexoskeleton(3).Thecontrollerboxalsocontainsavibrationmotortoprovidehapticfeedbacktothewearer(notshown).Twofingersleevescanbewornonanyfingersoftheuser’spreferredhand.Thedisplaymodule(5)providesthestatusoftheexoskeletontothewearerasvisualfeedback.Informationmayincludeswing/stancelegstates,kneejointstatus,andbatterylife.

Withfurtherimplementationofsensors,thisUIcanprovidefurtherinformationonthewearer’scenterofpressure,whichcouldaidwithbalanceforwearerswithhigherinjurylevels.OtherfutureworkonthisUIdesignincludespreventingmistriggerviaatime‐outlockand/orobject‐dependenttrigger,andmodifyingthedesigntoeasilyrelocatethedisplaymoduletoeachuser’spreferredlocation.

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Figure41.FingergloveUIoverview.

Figure42.FingerGloveUIwithvisualandhapticfeedback.

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6.DiscussionsonExoskeletonUserTesting

Thischaptercoversusertestingoftheminimally‐actuatedmedicalexoskeletonandthetrunkexoskeletonmodulewithparaplegicindividuals.Abriefoverviewoftestparticipantsisgiven,anddetailsofusertestingproceduresarediscussedtoprovideausertestingguideline.Sixarchetypalpersonasbasedonusertestingareintroducedattheendofthischapter.

Tothebestofourknowledge,thereisnofundamentalanalysisofusertestingprocedureformedicalexoskeletonswithparalyzedpatients.Thegoaloftheusertestingistonotonlytesttheperformanceoftheexoskeletonsdevices,butalsotoprovideuserexperienceof“re‐learningtowalk”viafieldofpromotedaction.Thus,theimportanceoftheeffectiveandstructuredearlystageusertesting,orpatients’learningprocesses,shouldbeacknowledged.Also,theusertestingprocessaswellastheoutcomesshouldbeconsideredduringthedesignstagetofacilitatelearningandtesting.

Exoskeletonwearerstendtolearnattheirownpace,whichcanrangefromrelativelyfasttorelativelyslow.Learningcurvescanbeinfluencedbyvariousfactors,suchasusers’injurylevels,physicalconditions,timesofinjury,pastrehabilitationexperiences,andmotivations.Duringmedicalexoskeletontraining,patientsdevelopnewutilizationschemasviascaffoldedinteractionsthataremediatedbythetechnology,andguidedbythetrainersconsistingofengineerswhodevelopedthemedicalexoskeleton.Herethetermscaffoldedisusedfromscaffoldingtheory[48]introducedbyJ.Bruner,acognitivepsychologist.Inhisscaffoldingtheory,instructionalscaffoldingisalearningprocessdesignedtopromoteadeeperleveloflearning.Scaffoldingtheorywasdevelopedtobetterunderstand,explainandfacilitatechildren’slearningprocedures.Scaffoldingisthesupportgivenduringthelearningprocess,whichistailoredtotheneedsofthestudentwiththeintentionofhelpingthestudentachievehis/herlearninggoals[49].Whenappliedtoexoskeletontraining,scaffoldingtheoryallowsengineers’/trainers’trainingsessionstobecomebetterstructuredandfacilitateapatient’slearning.Inmedicalexoskeletonusertesting,apatient(student)uses(orlearnshowtouse)anexoskeletontostandup,walkandachievehealthbenefits(thelearninggoals).

Inthisprocessoflearningactivitywithexoskeletons,thefollowingagentsparticipateasscaffolding,andinteractwiththepatient(student).ThisisalsoshowninFig.43.

1) Tether;theweareristetheredwiththeexoskeletonstructuretoensurefallsafety.2) Parallelbars;thewearerholdsontotheparallelbarstobalancehimself/herself.3) Twotrainers;tospotthewearerinfrontandbehind.4) Apractitioner;tooperatetheexoskeleton,andtunethegaittrajectory.5) Designersofthetechnology.6) Anexoskeleton.

Notethat3),4),and5)canbeinterchangeable,forexample,oneofthetrainersin3)canbeapractitioneroradesignerofthetechnology.Throughouttheusertesting,orthepatients’relearningtowalkprocedure,humanagentsfulfillavarietyofroles;theytakesomeofthe

51distributedactions,suchasmanipulatingthedevice,spotting,takingactions,andcueingforactions.

Figure43.Sceneoffirsttimeexoskeletontrial.

6.1Minimally‐ActuatedMedicalExoskeletonUserTestingInmanysenses,theminimally‐actuatedmedicalexoskeletonusertestingisakintotheprocessoflearningtorideabicycle.Bothinvolvelearningviamotorproblemsolving,ratherthanrepetitionthroughoutthescaffoldedlearningprocess,untilthewearerachievestheabilitytobalancehimself/herselfandwalk(ride).

6.1.1TestParticipantOverview

Fortheminimally‐actuatedmedicalexoskeleton,itiseasiertoworkwithindividualswithoutjointcontracture,spasticity,andmuscletone.Theyactasexternalfactorsthatincreaseanatomicjointdamping,andoftennegativelyaffectthebehaviorofpassivekneejointsofminimally‐actuatedmedicalexoskeletons.Thekneejointsmaycreateaggressive,moderate,orhamperedswingextensiondependingonthewearer’sanatomicjointdamping.Aggressiveswingextensioncanbetunedbyaddingdampingelementstothekneejoints[41].Whilehamperedswingextensioncanbetunedbymodifyingthehipswingtrajectorytomatchthepatient’sspecificconditionsandcancompensateforanatomicdampingtoacertaindegree,anatomicjointdampingshouldnotbesignificantenoughtolockupthekneejointstoachieveeffectiveambulation.

Threeindividualswithparalysisintheirlowerbodyhavetriedtheminimally‐actuatedmedicalexoskeleton.Theyhavevaryingdegreesofinjurylevels,upperbodystrength,physique,andexperiencewithpreviousrehabilitation.

1) Testpilot#1‐isa28‐year‐oldmale,5’10”tall,and170lbs.HesustainedacompleteT12injury12yearspriortothetesting.Insteadofawheelchair,hismainmobility

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comprisesaswing‐throughgaitusingcrutchesandpassivelegbraces.Becauseofthispriorexperience,hisbalancingskillsareexceptionallyhigh.Hehasamoderateamountofmuscletone,buthasnosignsofspasticityorjointcontracture.

2) Testpilot#2‐isa27‐year‐oldmale,6’tall,and110lbs.AlthoughhesustainedacompleteT10injuryeightyearspriortothefirsttesting,hemaintainedabdominalcontrol.Hehasasubstantialmuscleatrophy,whichmeanshiskneejointshaveminimalmuscletoneresistance.Sincediscontinuinghisrehabilitationwithlegbracesaboutsixyearsagoduetoexcessivephysicalexertion,hehasprimarilyreliesonawheelchair.

3) Testpilot#3‐isa24‐year‐oldfemale,5’2”tall,and140lbs.ShesustainedacompleteT5injurylevelthreeyearspriortothefirsttesting.Shehasverylittletoalmostnoabdominalcontrol,andacomparativelyhighamountofmuscletone.Sheiscurrentlyparticipatinginastemcellclinicaltrial.Sheistestingtheexoskeletonasapotentialmethodforrehabilitation.

6.1.2UserTestingProceduresandGuideline

Whenapatientdonstheminimally‐actuatedmedicalexoskeletonforthefirsttime,therearethreecriticalpointsthatneedtobesatisfiedbeforethepatientcanstarttakingsteps.

First,thedistancesbetweenthepatient’shipandkneejoints,aswellaskneeandanklejointsneedtobemeasuredinadvance.Inaddition,thelengthoftheexoskeleton’sthighandshanklinksmustbeadjustedaccordingly.Thetrainercanverifytheaccuracybycheckingthekneejointalignmentbetweentheexoskeletonandthepersoninthesagittalplanewhilethepatientissitting,asshowninFig.44(a).Thisalignmentcanbeachievedonlyifboththighandshanklengtharecorrect,andiscriticalforenablingthewearertobothstandupandusetheexoskeletonproperly.

Thesecondcriticalpointistore‐checkthisalignmentwhenthepatientstandsup.Standingwithanexoskeletonatfirstmayrequiresomeeffortbyutilizingthemechanicaladvantageofexoskeletonlegsandauxiliarybalancingwithhis/herarms(Fig44(b)).Whenthewearerisstandingwiththeexoskeleton,thedevice’skneejointshouldbefullyextendedandalignedtothebiologicalkneejoint.Ifthedevice’skneejointisnotfullyextended,thethighandshanklinklengthsoftheexoskeletonneedtobeadjustedaccordingly.Thedevice’skneejointalignmentshouldbeverifiedinboththefrontalandsagittalplanes.Ifthejointsarenotalignedwhenextended,strappingsorpaddingonthethighandcalfbracemayhavetobeadjusted.Ideally,thereshouldbenogapbetweenthewearer’sthighandtheexoskeleton’sthighbrace.Thesameholdsforthecalf.UsingapairofKAFObracingsthatiscustommadeforthepatientisrecommendedforthebestresult.Utilizingaccessibletechnologies,suchas3‐dimensionalscanningandprinting,isalsoanoptionforprovidinghighlyfunctionalbracings.Theamountofpaddingshouldbeaddressedsothatwearingtheexoskeletondoesnotcauseanyexcessivepressure.Especiallyforparalyzedpatientswho

53lacktactilesenseintheirlowerbodies,unnoticedexcessivepressurecanbeprolonged,causingsecondaryinjuriessuchaspressuresores.

Thefinalpointthatneedstobeaddressedatthebeginningofusertestingistheadjustmentofthedefaultankleangleandtorsoangle.Oncetheseanglesareadjusted,theintegratedsystemofthewearer,exoskeleton,andbalancingaidcanachieveastateofstaticequilibriuminthesagittalplane,sothatthewearercanholdastandingpositionmorecomfortablywithlittleeffort.Theseanglesneedtobetunedfordifferentwearers,sincethephysiqueofeachwearerandexoskeletonpaddingscreatedifferentcentersofmassfortheintegratedsystem.Fig.45(b)showstestpilot#3describedinSection6.1.1standingatthestaticbalancingpoint.

Assoonasaweareriscomfortablewiththestandingpositionandallalignmentsaretuned,takingstepscanbeinitiated.Totakeeffectivesteps,thepatientmustlearntoconstantlyshifthis/herbodyweightbetweentheswinglegandstancelegefficiently.Thisisatfirstobtainedviaexaggeratedweightshiftingmovementsfromsidetoside,requiringratherslow,exaggeratedmovementswithpausesinbetween.Fig.46(a)showsthisactivityoftestpilot#3.Atthisstageoftesting,itisrecommendedtohavethewearersupportedbyatether,withatleastonepersonspottingandanotherpersonoperatingtheexoskeletonwhilecueingthesignaltothewearerfortakingsteps.

Asthepatientgetsaccustomedtothisactivity,exaggerationsinweightshiftingandbalancingreduceandbecomemorenatural.Asthewearergainsexperiencewithside‐to‐sideweightshifting,he/shewillalsolearnhowtocontrolhis/herupperbodymovementsbackandforthinthesagittalplane.AsmentionedinChapter3,theminimally‐actuatedexoskeletonhaspassivekneejoints,whicharedynamicallydrivenbyhipactuations.Thus,placementofthewearer’storsocanchangethesteplengthbyaffectingthisdynamicswing.Forexample,stepsizewillbesmallerifthewearerleansfartherbackwardsthanthenormalstandingangle.Untilthewearerisabletoshifthis/herweightnaturally,itisrecommendedtohavethewearertetheredandinbetweenparallelbarswhileatraineroperatestheexoskeletonandcuesthewearer.

Assoonasthepatientovercomesexaggeratedweightshifting,he/shecantakestepsoutsidetheparallelbars,witheithercrutchesorawalker.Thewearercannowoperatehimself/herself.Asthewearerlearnshowtooperatethedeviceandwalkwithit,thetethercanberemovedandhe/shemayonlyneedoneindividualforspotting.Inotherwords,thenumberofsupportingagents,orscaffolds,isnowreducedcomparedtothebeginningoftesting.Theamountofthetrainingnecessarytoreachthisstagevariessubstantiallywithpatients’variousconditions.Fromthisstageoftrainingon,thedecisionmakerintheactivityofwalkingstartstobecomethewearerhimself/herself,ratherthanthetrainer.Fig.46(b)showstestpilot#1(describedinSection6.1.1)walkingonthestreetusingamedicalexoskeletonafterthreemonthsoftraining.Here,thedecisionmakerinthisactivityofcontinuouswalkingisthewearerhimself,withengineers’knowledgeencodedinthedevice.

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(a)(b)

Figure44.(a)Checkingkneejointalignmentbeforestanding.(b)Thefirsttimestandingup.

(a)(b)Figure45.(a)Checkingkneejointalignmentafterthefirsttimestandingup.(b)Afteradjustingtorso

andankleangles,thepatientstaysbalancedmoreeasily.

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(a)(b)Figure46.(a)Aparaplegicpatienttakingherfirststeps.(b)Anotherparaplegicpatientwearingan

exoskeletonwalkingonthestreetwithoutanyassistance.

6.2TrunkExoskeletonUserTesting

6.2.1TestParticipantOverview

ThetrunkexoskeletonmodulediscussedinChapter4wastestedbya32‐year‐oldmale,5’6”tall,and135lbs.HeisaT9incompleteparaplegicpatientwithreducedsensoryandmotorfunctionsduetoTransverseMyelitis.Thetrunkexoskeletonmodulewithoutakneemodulewasapplicabletothispatientovertheminimally‐actuatedexoskeletonfortworeasons:

1)Thefullbodyexoskeletoniscumbersomeforthepatientwhoretainscontrolsofhislowerleg.

2)Thepatientisalessidealcandidateforanexoskeletonwithpassivekneejointsbecauseheexhibitsspasticityandasubstantialamountofuncontrolledjointdampinginhisknees.Thisanatomicdampinghamperstheperformanceofpassivekneejointsusedintheminimally‐actuatedexoskeleton.

6.2.2UserTestingProcedureandGuideline

Sincethepatientexhibitssubstantiallyhighermusclecontrolcomparedtotestpilots#1,#2,and#3inSection6.1.1,fewersupportingagentswererequiredforthistesting.Also,becausethisdevicesetupdoesnotincludethekneemodule,thelengthadjustmenttoachievekneejointalignmentisnolongernecessary.However,itshouldbenotedthatwithoutanAFO,thewearersupportsthedeviceweight,asopposedtothefull‐bodymedicalexoskeleton.Thus,thelevelofcomfortintheupperbodyiscritical.Specifically,the

56lowerbackandshouldersaretheprimarycontactsurfaceswherethewearersupportstheloadofthedevice.Inthetestingwiththeaforementionedpatient,memoryfoampaddingforthelowerbackandlight‐duty,elasticshouldersuspenderswereused.Regardinghislevelofupperbodycontrol,theshoulderstrapsusedfortheminimally‐actuatedmedicalexoskeletonwerenotnecessaryandfoundtobecumbersometothewearer.

TheorderofoperationswouldbesimilartotheonefortestingthemedicalexoskeletondiscussedinSection6.1.Thelengthofthethighlinkandthefittingofbracesneedtobeverifiedbeforethewearercantakeanysteps.Also,thetorsoanglemustbeadaptedtothewearer’scomfortablestandingposture.Althoughthewearerretainssensoryandmotorfunctionsinhislowerbody,itisrecommendedtostarttestingwhiletheweareristetheredwiththeexoskeletonandinbetweenparallelbars,withindividualsspottingthewearer.Oncetheweareriscomfortablewithstandingandbalancingwhilewearingtheexoskeleton,atrainercaninitiatesteptaking.Afterthewearerisaccustomedtotakingstepsandshiftingweightside‐to‐sideandbackandforth,he/shecantrytakingstepsoutsideoftheparallelbars,operatingtheexoskeletonbyhimself/herself.Asthewearerimprovesbalancingandoperatingtheexoskeletonwhilewalking,thetethercanberemoved.Nowthewearerbecomesthedecisionmakerofthewalkingactivitybyoperatingthedeviceandinteractingwiththedeviceencodedbyengineers.

6.3DesignConsiderationsforFutureUserTestingThroughouttheusertesting,itwasfoundthatcertaindesignfeaturesandtrainingstrategiessignificantlyfacilitatetheusertesting.Theseconsiderationsshouldbetakenintoaccountforfuturegenerationsofexoskeletondesignsandusertestingsetupstoacceleratethelearningexperience.

1) Designfeaturesfortetheringandspotting:Intheearlystageofusertesting,thepatientshouldalwaysbetetheredandspotted.Afeaturefortetheringandspottingshouldbeincorporatedintoexoskeletondesign.Fortethering,itisimportanttoincludeanadapterthatcantaketheweightofboththeexoskeletonandthepatient.Forspotting,thetorsoframeshouldincludeasufficientamountofsurfaceareathatatrainercanholdduringtesting.

2) Easyadjustment:AsdescribedinSection6.1.2,therearemanyadjustmentsthathavetobemadefordifferentpatients–lengthadjustmentstoalignbiologicaljointswithdevicejoints,paddingamountadjustments,andtheangleadjustmentsforcomfortablestanding.Itiscriticalforthedesigntoincludeeasyaccessandsimpleproceduresfornecessaryadjustments.

3) Patient’sturn‐aroundmaneuver:Itshouldbenotedthattherearespaceconstraintsinthelaboratorywhenusingatetherandparallelbars.Oftentimes,thepatientneedstoturn180degreesattheendoftheparallelbarsorwhenthetetherropereachesitsendoftravel.Inthebeginningstagesoflearning,theturn‐aroundmaneuvercanbeverychallengingforpatients.Therefore,itishighlyrecommendedfortrainerstoplanthewalkingpathinadvancetominimizethismaneuver.

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6.4ArchetypalPersonasinEachUserCategoriesThroughouttheusertesting,theexoskeletondeviceswereevaluatedbydifferentindividualswithvaryinginjurylevels.Structuredusertestingprovided“re‐learningtowalk”experiencestopatients,whileallowingpatientstoactivelyengagewiththedevices,trainersanddesigners.However,theusertestingwaslimitedtofourindividualswithvaryinglevelsofparalysis,eventhoughthereareothersegmentsofusergroupswhocanpotentiallybenefitfromthistechnology.

Here,sixarchetypalpersonasaredevelopedtorepresenteachpotentialusergroupsegment.Asoneofthehuman‐centered‐designmethodologies,creationanduseofarchetypalpersonasthatrepresentimportantclassesofusersprovideaclearwaytodefinetargetuserswhosharecommondesires,goals,andbehaviors,andwhowillbenefitfromthetechnology[50‐53].Thepersonasarebasedontheresultsofexoskeletonusertesting,medicalexoskeletonUIusabilitytesting,andotherinterviewswithindustryworkersandsoldiers.Table7summarizesthesixarchetypalpersonaswiththeirkeyattributes.

6.4.1Kevin,apoweredwheelchairuser

Kevinisa35‐year‐oldmale,anincompleteT3quadriplegicpatientwithacentralcordsyndromefromacaraccidenteightyearsago.Althoughheretainsalimitedamountofsensoryandmotorfunctioninhislowerbodyincludingabdominalcontrol,theinjuryresultedinthelossofarmfunction.Becauseofhisimpairedarmfunction,hehasbeenusingapoweredwheelchairsincetheinjury.Unfortunately,hisphysicalconditionofimpairedupperbodycontrolprecludestheuseoftheminimally‐actuatedmedicalexoskeletonorthetrunkexoskeletonmodule.Moreover,thelongerhestaysinapoweredwheelchair,thehigherhislikelihoodofmusclecontractureandreducedrangeofjointmotions,whichwillmakeKevinanevenlessidealexoskeletonwearercandidate.

6.4.2Jennifer,awheelchairuser

Jenniferisa31‐year‐oldfemale,acompleteT9paraplegicpatientfromamotorbikeaccidentoneyearago.SheiscurrentlyparticipatinginrehabilitationwithanRGO.Asofnow,herupperbodystrengthisnothighenoughtosupportandambulateherselfwithanRGO.Eventhoughsheisawareofthenecessitytocontinuerehabilitationactivitiestodelaytheonsetofsecondaryinjuries,sheisconsideringdiscontinuingtherehabduetoanexcessiveamountofphysicalexertion.SheusesawheelchairashermainmobilityaidexceptforthetimesinrehabwhensheusesanRGO,whichisfivehoursperweek.Aminimally‐actuatedmedicalexoskeletoncanpotentiallybeausefulrehabilitationtoolandmotivationforJennifertocontinueherrehabactivity,becausepoweredexoskeletonusewillnotrequireasmuchupperbodystrength.HerexperienceusinganRGOwillaccelerateherlearningexperiencewiththemedicalexoskeletonintermsofbalancingandweightshifting.

586.4.3.Samuel,acrutchuser

Samuelisa27‐year‐oldmale,acompleteT12paraplegicpatientasaresultofanaccidentwhilesnowboardingtenyearsago.HehasbeenparticipatinginvariousrehabactivitieswithaKAFOsincehisaccident.HehasbeenusingaKAFOandcrutchesashismainmobilityaidinsteadofawheelchair,whichkeepshimmoreactiveandprovideshealthbenefits.Hisathleticlifestylebeforetheinjurycoupledwithhisbalancingabilityacquiredfromhisextensive,professionalsnowboardingexperiencegreatlycontributedtohisrehabilitation.Samuelisagoodcandidatefortheminimally‐actuatedmedicalexoskeleton.AlthoughheisalreadyabletoachieveahighlevelofambulationwithhisKAFOandcrutches,theexoskeletonwillalleviatehisexhaustiveupperbodyuse,andenablehimtotravellongerdistanceswithoutgettingtired.

6.4.4Mary,aseniorcitizen

Maryisa60‐year‐oldfemaleseniorcitizenandaretiredaccountant.Shehasnotsustainedanyseriousdiseasesorinjuries,althoughshehasalightamountofarthritisduetoaging.Herpreviousoccupationdemandedsittingforlonghoursduringwork,andshehasnotbeenregularlyworkingoutforthelast35years.Asaresult,herbodystrengthisrelativelylowandshewishessheweremorefittoplaywithhergrandkidsattheplayground.ThetrunkexoskeletonmodulewithextralockabledegreesoffreedomisidealforMary,eitherwithorwithoutakneemodule,dependingonherpreference.

6.4.5Tom,anindustryworker

Tomisa40‐year‐oldmalewhoworksforalogisticscompanydeliveringpackages.Hehasmaintainedagoodphysique,but,attheendoftheday,hehaspaininhislowerbackfromrepetitivebendingandliftingactivitiesduringhisworkday.Hisjobdoesnotdemandliftingheavyboxesthataremorethan50pounds,butrepetitivebending,squatting,andwalkingthroughoutthedaytireshimout.ForTom,thetrunkexoskeletonmoduleisrecommendedforassistinghisbendingandwalking,becauseitfeaturesmoredegreesoffreedomwhichallowvariousmovementsusingmodifiedsoftwarefordifferentfinitestatemachines.

6.4.6Andrew,amilitarysoldier

Andrewisa25‐year‐oldmaleriflemanwhoservesintheU.S.ArmyInfantry.Onpatrol,theaverageweighthecarriesisabout100pounds.Hemustcarrytheseheavyweightlongdistances,whichoftenexhaustshimeventhoughhehasveryhighphysicalstrengthandendurance.Hefeelsthattheweightoftheloadhecarriesimpedeshismobilityandagility,andplaceshimatriskofinjurywhentraversinguneventerrain.TheidealexoskeletonforAndrewissimilartoTom’s(6.3.5),butwithhigherperformanceintermsofpowerandrangeofmotion.Also,forAndrew,afull‐bodyexoskeletonishighlyrecommendedtoreducetheloadhecarriesbytransferringittothegroundthroughtheexoskeleton.

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Table7

.Arch

etypalP

ersonas

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7.LimitationsandFutureWork

Thischapterdiscusseslimitationsandfutureworkforenhancingthepracticalityandusabilityofassistiveexoskeletons.

7.1HipActuatorsLowprofilehipactuatorsandpassivekneejointsincreasemedicalexoskeletons’practicalityandusability.AsdiscussedinChapter3,twodifferentactuationunitsweredevelopedforthispurpose:1)AdesignwithbarecomponentsofBLDCmotorsandstrainwavegears:theEmoteqHT03000‐J01‐ZandHarmonicDriveTMCSD‐25‐160‐2A‐GR‐SPand2)Adesignwithoff‐the‐shelfhousedcomponents:theMaxonEC90FlatmotorandHarmonicDriveTMSHD‐20‐100‐2SH.Thefirstdesignhasthemostcompactprofilecomparedtoavailableproductsonthemarketwithcomparablespecifications.Meanwhile,thedesign’sdisadvantagesincludeitscomplicatedassemblyprocessandhighcostduetomanycustom‐madecomponents.Theseconddesignimprovesupontheseshortcomings,withfewercustom‐madepartsandaneasierassemblyanddisassemblyprocess.Asatradeoff,adoptingtheseactuationunitsresultsinanincreaseintheexoskeletonhipwidthofabout1.9inchesandadecreaseduserweightlimitduetothestrainwavegear’sbearings.Futureworkremainstoimproveonbothdesigns’limitations.Giventhecurrentlyavailableproductsonthemarket,itisanticipatedthatincreasingtheuserweightlimitwithahousedstrainwavegearwillmostlikelyfurtherincreasetheformfactoroftheactuationunit.Therefore,reducingthenumberofcustommadepartsofthefirstdesignandsimplifyingtheassemblyprocessisrecommended.Exploringothercombinationsofmotorsandtransmissions,forexample,utilizingtheMaxonEC90motorwiththeCSDseriesstrainwavegears,isneededtofurtheroptimizethedeviceprofileandcost.

7.2ModularityAsdiscussedinChapter4,itisimportanttoprovideeasy‐to‐usecustomizationfeaturestomeetusers’differentconditionsandneeds.Thetrunkexoskeletonmodulewithadditionallockablejointsallowssimplebutversatileconfigurationsfordifferentuserswithvaryingmobilities.However,accuratelyaligningab/adductiondevicejointstothewearer’sbiologicalhipjointswhileprovidingpropulsionassistanceisachallengingproblem.Thisiscritical,especiallytoaugmenttheenduranceofable‐bodiedusers.Exploringmorepossibilitiesforjointlocationstopermitvariousmovementssuchassquatting,lunging,hipabduction,walking,anddiversifyingactuationunitsremainasfuturework.Enhancingmodularityaswellasdevelopingvariouskindsofmodulesfordifferentuserswillaugmentmobilitysolutionsandfillgapsindeviceavailabilityacrossthemobilityspectrum.

7.3UserInterfaceAglovetypeuser‐coupledUIdesignformedicalexoskeletonsprovidesflexibilityinthegripandfeedbackfromtheexoskeletontotheuser.However,furtherimplementingsensors

61andimprovingcommunicationsbetweentheexoskeletonandtheUImoduleremainasfuturework.Utilizinginertialmeasurementunits(IMU)orpressuresensorstodetectawearer’sbalancingstatusandtransmitthesignaltotheuserinanenergeticallyefficientmannerwillbebeneficialforuserswithhighinjurylevels.Also,preventingfalsetriggerswithatime‐outlockordevice‐dependenttrigger,aswellaslocatingthedisplaymoduleattheuser’sdesiredpositionareimportantfutureworktomaturethistechnology.Currently,thedisplaymoduleisdesignedtobelocatedonauser’swrist.However,beingabletoadjustthislocationbasedontheuser’spreference,orprojectonanopticalheadmountdisplay(OHMD)willfurtherincreasetheusabilityofthisdevice.Finally,modifyingthisUItobemodular–i.e.,separatingthegloveandfeedbackdisplaymodule–sothatapractitionercanweartheglovetooperateanexoskeletonwhilefeedbackisgiventothewearerwouldbehighlybeneficialforfirsttimewearers’re‐learningtowalkactivities.

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8.ConcludingRemarks

Thisdissertationcoveredthreedifferentdesigntopicsthatcontributetoincreasingtheusabilityofassistivelowerextremityexoskeletonsystems.Adesignofaminimally‐actuatedmedicalexoskeletonwasintroduced,withspecialemphasison“lowprofilehipactuationunits”.Thelowprofilehipactuationunitsenabledthesystemtobethemostcompactpoweredmedicalexoskeleton,andfirstofitskindtoweighlessthantwentypounds.Thisexoskeletonevolvedtoanexoskeletonsystemwithincreasedmodularityandadjustabledegreesoffreedom.Themodulardesignopensanopportunitytoexpandusersegmentstoindividualswithvariousconditionsandneedsbyallowingeasycustomizationbymeansofcombiningdifferentmodules.AcomprehensiveuserstudyoftheexoskeletonUIwasconductedinanefforttocreateacomfortable,intuitivelinkbetweentheuserandthemachine.Theintentoftheresearchwasnotonlytodevelopassistivedevices,butalsotocreatepositiveuserexperiencesbyprovidingstructuredlearningactivitieswherethepatients,devices,andengineerswhodevelopedthedevicesactivelyinteract.

Theminimally‐actuatedmedicalexoskeletonusesthelowprofilehipactuationunitsandpassivekneejoints.Thepassivekneejointsaredynamicallydrivenbythemomentumcreatedbythehipactuationunits.ThreeindividualswithcompleteSCIwithinjurylevelsrangingfromT5toT12wereabletoachievebipedallocomotionandahigherlevelofmaneuverabilitywithextendeduse.Itshouldbenotedthatthesystemisveryminimalwithonlyonepairofpoweredactuators,whichprovidessimpleambulationwithajointcouplingmechanismwithcompactandlightweighthardware.Eventhoughitdoesnotprovideanyelaboratejointmovements,suchasself‐balancing,stairascending,andstairdescending,thisambulation‐centrictechnologycanprovidehigherlevelsoffreedomandmaneuverabilitythankstoitslightweightandcompactsize.

Thetrunkexoskeletonmoduleincludessimplecustomizingfeaturesthatpermitandincreasemodularityindesign,withsimplecustomizingfeatures.Lockablefeaturesallowvarioustypesofusers–fromcompleteparaplegicpatientstoindividualswithintactmobility–tobenefitfromthistechnology.Itsmodularityandcapabilitiesforexclusiveuseenableeasycustomizationbycombiningdifferentkneemodulesfordifferentpurposes.Developingvariousmoduleswithdistinctivefinitestatemachinesandexploringmoredesignoptionsforcomplyingwithvariousmovementsassociatedwiththehumanhipjointremainasfuturework.

AconceptualUIprototypethatcontainsthekeycomponentsforevaluationwascreatedandassessedbypotentialusers.Threeresearchmethodswereusedinthisresearch:interviews,guerillatests,andusabilitytests.EightintervieweesandusertestparticipantsweredrawnfromthoseworkingwiththeBerkeleyRoboticsandHumanEngineeringLaboratoryandtheEdRobertsCampusforthedisabledinBerkeley,California.Evenwiththissmallnumber,itwaspossibletofinddistinctuserneedsandpreferences.Throughouttheusertests,designrecommendationsweredrawn,andahigh‐fidelityprototypewasdeveloped.TheUIprototypeuserstudyaddressesthenextgenerationUIdesignformedicalexoskeletons,whichcanimprovetheirusabilityandlearnability.

63Futureworkinthefieldofassistiveexoskeletonsincludesperformanceenhancementsandvariousmoduledevelopmentsthatfurtherexpandtheusergroupswhocanbenefitfromthetechnology.Currently,thetechnologyisstilllimitedtoindividualswhoretainacertainlevelofupperbodycontrol,excludingKevinfromthepersonasinSection6.3.Safetyfeatures,suchasreliableself‐balancingwhilemaintainingthelowprofileofthesystem,wouldbehighlybeneficialtothosewhosufferfromhigherlevelsofSCI.Also,increasedambulationspeedwouldincreasepracticalityforthedailyuseofmedicalexoskeletons.Applyingmachinelearningadaptationforexperiencedwearerstograduallyacceleratetheambulationspeedisapromisingsolution.Withperformanceenhancementandmodularity,theexoskeletontechnologycanfurtherextenditsbenefitstoamorediversepopulation,includingparalyzedindividualswithhigherinjurylevels,theelderly,industryworkers,andsoldiers.Ihopethattheassistiveexoskeletontechnologywillcontinueadvancingtoenhancethequalityoflifeforawidespectrumofcommunitieswithadiversearrayofneeds.

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