DOLLARANDHOWECOMPLIANTGRASPERVIASHAPEDEPOSITIONMANUFACTURING155 Fig1TheSDMprocessCourtesyofMarkCutkoskyThisprocesshasanumberofadvantagesoverotherprototypingtechniquesThedepositionofpartmaterial ID: 355271
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IEEE/ASMETRANSACTIONSONMECHATRONICS,VOL.11,NO.2,APRIL2006ARobustCompliantGrasperviaShapeDepositionManufacturingAaronM.Dollar,StudentMember,IEEE,andRobertD.Howe,Member,IEEEJointcompliancecanenablesuccessfulrobotgraspingdespiteuncertaintiesintargetobjectlocation.Compliancealsoen-hancesmanipulatorrobustnessbyminimizingcontactforcesintheeventofunintendedcontactsorimpacts.Inthispaper,wedescribethedesign,fabrication,andevaluationofanovelcompliantroboticgrasperconstructedusingpolymer-basedshapedepositionmanu- DOLLARANDHOWE:COMPLIANTGRASPERVIASHAPEDEPOSITIONMANUFACTURING155 Fig.1.TheSDMprocess.CourtesyofMarkCutkosky.Thisprocesshasanumberofadvantagesoverotherprototyp-ingtechniques.Thedepositionofpartmaterialallowscompo-nentstobeembeddedintothepartduringproduction,eliminat-ingtheneedforfastenersandreducingthelikelihoodofdamagetothecomponentbyencasingitwithinthepartstructure.Thisisaparticularlydesirablepropertyfortheinclusionoffragilecomponentssuchassensors,greatlyincreasingtherobustnessofthepart.Also,depositingthepartinlayerspermitstheuseofdissimilarmaterials,allowingforvariationofmechanicalpropertieswithinthesamepart.Thispropertycanbeutilizedtocreatecomplexmechanismsfromasinglepart[15]Ð[17].Duetoitsrelativesimplicity,customtoolingisnotrequiredtorealizetheSDMprocess.Complexpartgeometriescanbeattainedusingcommoncomputernumericalcontrolled(CNC)millmachines.B.GrasperDesignandFabricationFig.2showsthestepsoftheSDMprocessusedtoproduceourcompliantgrasperÞngers.PocketscorrespondingtotheshapeofthestifflinksofourÞngersaremachinedintoahigh-grademachinewax(FreemanManufacturingandSupplyCompanyAkron,OH,USA).ThecomponentsinpanelAareputintoplaceinthepockets(panelB)andthepolymerresinpoured.Modelingclayisusedtodamanyareastobeblockedfromtheresin.Afterthelayercures,asecondgroupofpocketsismachined(bothintothesupportwaxandthestiffresin)anddammed(panelC).ThepolymerresinsforthecompliantÞngerjoints(white)andsoftÞngerpads(clear)arethenpoured(panelD)andallowedtocure.Theblockisthenfacedofftolevelthesurfaceandremovesur-faceßaws(panelE),andthecompletedÞngersremovedfromthewaxsupportmaterial.Theentireprocesstakesapproximately30htocomplete,only4ofwhichrequirehumanintervention.Thepolymersusedaretwo-partindustrialpolyurethanes.Dif-ferentcompositionsareusedforthesoftÞngerpads,compliantjoints,andstifflinks(IE35A,IE90A,andIE72DC,respectively,InnovativePolymers,St.Johns,MI).DegassingatHg)wassometimesnecessarytopreventvoidsinthecuredresins.TableIshowsmaterialpropertiesofthesethreepolyurethanesasprovidedbythemanufacturer.Fig.3showsthepartsoftheSDMÞnger.TheconcavesideofeachlinkcontainsasoftÞngerpadtomaximizefrictionandincreasegraspstability[18],[19].Thethinsectionsbetweenlinksarethecompliantjointßexures,designedtobecompliantintheplaneofÞngermotionandstiffoutofplane.Thejointsaredesignedtohavestiffnessesof0.0421and0.224N.m/radfortheproximalanddistaljoints,respectively,resultinginaproximal/distalstiffnessratioof0.19.Conveniently,thepolymerusedforthestifflinksistranspar-ent,allowingtheembeddedcomponentstobeclearlyseen(alsoseeFig2(A)).Jointanglesensingisaccomplishedbyembeddingalow-outputimpedancelinearhall-effectsensor(A3517SUA,AllegroMicroSystems,Inc.,Worcester,MA)ononesideofthejointandarare-earthmagnet(6.35mmdiam3.18mm,Nd-FeB,10,800Gaussstrength,K&DMagnetics,Inc.,BocaRaton,FL)ontheotherside.Jointmotionchangesthedistancebetweenthetwo,varyingthesensoroutput.Thesensorsarewiredtoex-posedconnectors(2.5-mmPCboardheader)forconnectiontoexternalcables.AdovetailprotrusiononthebaselinkallowstheÞngertobesecurelyconnectedtothegrasperbase.Foractuation,eachÞngerhasaprestretchednylon-coatedstainlesssteelcable(77strandcore,0.94mmdiameter,540Nbreakingstrength)anchoredintothedistallink.Thiscablerunsthroughthebodiesoftheproximalandbaselinksthroughlow-frictionnylon11tubing(3.2mmOD,2mmID).Becauseofthejointcompliance,theÞngercanbeunderactuated,allowingforonetendoncabletodrivebothjoints.Thegrasperisintendedtobeunactuateduntilcontactismadewiththetargetobjectandasuccessfulgraspispredictedbasedontheavailablesensoryinformation.Beforeactuation,thetendoncable,whichisinparallelwiththecompliantjoints,remainsslackandtheÞngerisinitsmostcompliantstate.Thismethodpermitstheuseofactuatorsthatarenotbackdrivableandpreventstheinertialloadoftheactuatorfromincreasingthepassivestiffness.Afteractuation,thestifftendontakesmuchofthecomplianceoutoftheÞngers,resultinginagraspwithgreaterstability.Fig.4showsthefullyassembledgrasper(twoÞngers,twomotors,andbase).ThebasewasalsoproducedusingSDM,butispurelystructural.Thelinklengths,measuredfromthecentersofthejointßexures,werechosentobeequaltoenablethetiptoreachthebase.ThejointrestanglesoftheÞngers(25fortheproximalanddistaljoints,respectively)werecare-fullychosenbasedontheresultsofpreviousoptimizationstud-ies[12].Theratioofjointstiffnesses(0.19proximal/distal)wasbasedontheoptimizationstudiesandadditionalmaterialandgeometricconsiderationstocreateafunctionalgrasper.Theseanglesandstiffnesseswereshowntoenablegraspingofthewidestrangeofobjectsizeswiththegreatestamountofuncer-taintyinobjectposition.Thedesignisalmostcompletely2.5dimensional(i.e.,ex-trudedtwo-dimensionalshapes)andsymmetricaboutthecenterplane,allowingforthesameÞngertobeusedontherightorleftsideofthegrasper.Forcomparisontothesingle-partSDMÞnger,asimilargraspermadefromaluminumthatwasusedinpreviouswork IEEE/ASMETRANSACTIONSONMECHATRONICS,VOL.11,NO.2,APRIL2006 Fig.2.StepsoftheSDMprocessusedtofabricatethegrasperÞngers.TABLEIATERIALSPECIFICATIONS Fig.3.DetailsofÞngerpartsandplacementofcomponents.isshowninFig.5[12].EachÞngeronthisgraspercontainsover60distinctparts,40ofwhicharefasteners!ThereisalsoasigniÞcantweightreductionintheSDMÞngers(39geach)versusthealuminumÞngersofsimilarsize(geach). Fig.4.OverheadviewoftheSDMgrasper.C.MechanismBehaviorAnumberoftestswereperformedtocharacterizethebe-havioroftheSDMgrasper.Thepolyurethaneusedforthejoints(IE90A)demonstratessigniÞcantviscoelasticbehavior,asshowninFig.6.Thesampletestedcorrespondstothedimen-sionsofthedistaljointßexure.Astepangulardisplacementof0.54radwasappliedandthejointtorsionalstiffnesswasmeasuredovera30-mininterval.Theresultsshowbehaviorconsistentwithasecond-orderKelvinmodel[20],asshowninFig.6.Notethenonzerooriginoftheverticalaxis,highlightingthesecond-orderÞt176+0isinN.m/radandisinseconds.Overthe30-mintimeintervaltested,thejointtorquedrops29%.Thetimeconstantsaremuchlargerthantypicalgrasptime,sothedampinginthematerialhaslittleeffectoncontrolofthegrasper. DOLLARANDHOWE:COMPLIANTGRASPERVIASHAPEDEPOSITIONMANUFACTURING157 Fig.5.Overheadviewofthealuminumgrasper. Fig.6.ForcerelaxationofthedistaljointoftheSDMÞnger,foranangularstepdisplacementof0.54rad.Theviscoelasticpropertiesofthejointmaterialhavetheben-eÞcialeffectofdampingoutjointoscillationscausedbygrasperaccelerations.Inanundampedcompliantgrasper,theseoscil-lationscanbelargeduetothesigniÞcantmomentofinertiaaboutthejointscausedbylongÞngerlinks.Thiseffectwasobservedinourpreviousprototypethatusedmusicwiretor-sionalspringsinthejoints(Fig.5)[12].Inthisconventionallyassembledgrasper,oscillationsduetolargestepdisplacementspersistedfortensofsecondsafterrelease.Lowjointstiffness,althoughminimizingunwantedcontactforces,increasesthemagnitudeofresonantoscillations.Damp-inginthejointsreducestheseverityoftheseoscillationsandthereforepermitsuseoflowjointstiffness.Fig.7showsthejointresponseoftheSDMÞngertoalargestepdisplacementoftheÞngertip,releasedattime.Notethattheoscillationsarenegligibleafterlessthan1s.Fig.8showsthetorqueandangulardeßectionbehaviorofthejointsofthegrasperfordifferentjointßexuresizes.Loadswereappliedandremovedquicklyinordertominimizetheeffectsofthematerialviscosity.Notethatthejointangulardeßectionsarenearlylinearlyproportionaltoloadtorqueevenacrosslargedeßections,allowingfortheassumptionofsimplecantilevered-beambendingbehavior. Fig.7.JointresponseoftheSDMÞngertoatipstepdisplacementreleasedat Fig.8.AngulardeßectionofSDMjointsastorqueloadisvaried.Samplestestedare15.2-mm(0.6-in)long,12.7-mm(0.5-in)deep,andvariedthicknessinthedirectionofloadapplication.Fig.9showsthebehavioroftheÞngerjointsthroughtheirrangeofmotion.Notethatthecenterofrotationvariesslightlywithjointangle.Fig.10showstheoutputÔVÕofthejointanglesensors(afterampliÞcation)andtheirÞtsversusjointdeßectionforthetwoÞngersusedinthisstudy.TheÞtcurvesareofthearetheÞtcoefÞcients.ThesesensorsgivesufÞcientsensitivityacrosstheentirerangeofmotionofthejointstoallowforuseinthecontrolofthegrasper.NotethatthesensorgivesbetterresolutionastheÞngeropensdecreases)inordertooptimizesensitivityduringpassivecontact.ThisallowsthegraspertobeusedasaÒfeeler.ÓFig.11showsthejointdeßectionbehaviorastheÞngerisactuatedwithoutobjectcontact.Notethatthedistaljointmovesverylittleuntiltheproximaljointcompletesitsfullrangeofmotion,duetodifferencesinjointstiffnessandcableleverarm.ThisbehaviorissimilartothatofthetwodistaljointsofthehumanÞngerandincreasesthechancesthatbothlinksofthe IEEE/ASMETRANSACTIONSONMECHATRONICS,VOL.11,NO.2,APRIL2006 Fig.9.SuperimposedphotographofjointdeßectionandlinkmotionforthreepositionsacrossthetravelrangeofthedistaljointoftheÞngers.Thecenterimageistherestposition. Fig.10.JointanglesensorcalibrationdataandÞts. Fig.11.JointbehaviorastheÞngerisactuatedwithoutobjectcontact.Þngerareincontactwiththeobject,increasingcontactareaandfriction.TheÒdipÓintheproximaljointcurveiscausedbyout-of-planemotionthatoccurswhenajointhasreacheditstravellimit.Thehall-effectsensorsareonlycalibratedformotionintheplane. Fig.12.Force-deßectioncurveofthetipoftheSDMÞngerwithlineartrend-line.ThedatarepresentsÞvecyclesoftipmotion.Fig.12showstheforcegeneratedatthetipoftheÞngersduetodisplacementintheout-of-planedirection(followingtheconventionofFig.16).Thetipwasdisplacedatarateofapproximately1cm/swhilemountedonanactuatedlinearslidemechanism(R2Dseriesrodlessactuator,IndustrialDevicesCorporation,Petaluma,CA).Forcewasmeasuredwithamultiaxisforce/torquesensor(Gammamodel,ATIIndustrialAutomation,Apex,NC).ThisdatarepresentsforcegeneratedduetomotionofthetipacrossthetestedrangeandbackforatotalofÞvecycles,thenlowpassÞlteredwithacutofffrequencyof1Hz,toremovesensornoise.Notethehysteresisinthecurvesandtheforcerelaxationduetoviscoelasticity.ThedataisÞttedwithatrendlinetogiveanindicationofthetipstiffness.Thesametestswereperformedinthedirections(follow-ingtheconventionofFig.16)andshowsimilarbehavior.Theapproximatetipstiffnessinthex,y,anddirectionsare5.85,7.72,and14.2N/m,respectively.TheSDMÞngers,whileexhibitinglowtipstiffness,canalsoundergolargedeßectionswhileremainingcompletelyfunc-tional.InthetestshowninFig.12,thetipwasdisplacedmorethan3cmintheout-of-planedirectionwithoutanydegradationofmechanicalproperties.Theadvantagesofthispropertyareclearwhenconsideringtheusualresultofunplannedcontactduringuseoftraditionalresearchrobotichands.Thegrasperdoesnotexhibitthisamountofcompliancedur-ingallphasesofthegraspingtask,however.Althoughnotquan-titativelyevaluated,thegrasperbecomesmuchstifferafteritisactuatedbycableÑadesirablecharacteristicallowingformoreaccuratemanipulationofthegraspedobject.Togiveasenseoftherobustnessofthemechanismtoimpactloads,amoreinformaltestwasperformed.AnSDMÞngerwasrepeatedlydroppedfromaheightofover15montoastoneßoor.Aftertwoattempts,nonoticeabledamagehadoccurred.Afterthree,asmallpiecebrokeoffofthedovetailconnector.Aftersixattempts,theouterlinkdevelopedalargecrackandoneofthemagnetsbrokeoff,butthesensorsandjointsremainedintactandfunctional.D.TactileSensorAtactilesensorhasbeendevelopedforintegrationwiththesoftÞngerpads(Fig.13).Thesensorusesareßectiveobject DOLLARANDHOWE:COMPLIANTGRASPERVIASHAPEDEPOSITIONMANUFACTURING159 Fig.13.Tactilesensorprototypewith50gweightplacedoverthesensor.Theangledstrutßexuresseparatethereßectivesurfacefromthesensorface.Notethecurvatureofthereßectivesurfaceduetotheappliedload. Fig.14.Stiffnessofthetactilesensorpadforvarioussphericalindentersensor(OPB608R,660-nmemitterwavelength,OptekTechnol-ogy,Carrolton,TX)whichconsistsofanLEDandphotodetec-tor.AstheÞngerappliesforcetoanobject,thepaddeformsinwards,bringingthereßectiveinnersurfaceoftheÞngerpadclosertotheembeddedsensorandcausingachangeindetectorcurrent.Theslantedstrutsreducestiffnessinthenormalcontactdirection.Thesidesofthesensorareeasilyenclosedtoblockambientlightfromreachingthedetector.Althoughthisproto-typecontainsonlyoneopticalsensor,multiplesensorscanbeembeddedinthepadataboutoneevery15mmunderthecurrentAsshowninFig.13,blackdyewasusedinthesupportma-terial(IE72DC,seeTableIformaterialproperties)toshieldthesensorfromambientvisiblelightcomingthroughtheotherwiseclearmaterial.WhitedyewasusedintheÞngerpadmaterial(IE20AH)toincreasethereßecanceandblockambientlightfromthefrontofthesensor.Fig.14showstheeffectivestiffnessoftheÞngerpadwhenloadeddirectlyabovethesensor.Loadswereappliedwiththreediametersofsphericalindenter:2.5,6.4,and25mm.Thestiff-nessofthepadislow,ontheorderof1kN/m,dependingoncontactlocationandgeometry.Fig.15showsthesensoroutputasafunctionofappliedforceforthevariousindenterdiame- Fig.15.Opticalsensoroutputversuscontactforceforvarioussphericalin-dentergeometries.ters.ItisclearfromtheÞgurethatcontactgeometryplaysaroleinsensoroutput.Thiseffectisduetoboththedifferenceineffectivestiffness(asshowninFig.14)andthecurvatureofthereßectivesurface,whichcandeformwithsmallobjectstodeßectlightawayfromthedetector.Notethehighersensitivitytosmallerloads,apropertyusefulincontactdetection.Thesensitivitytocontactgeometryandlimitedforcerangereducestheusefulnessofthissensorforcontactforcedetermi-nation.However,thesensorprovidesaninexpensivemethodofsensingcontactlocationwithgoodsensitivity.Thisinformationcanbeusefulincontrollingcontactforcewithoutforcesens-ingaswellasindeterminingobjectgeometrybasedoncontactIII.EXPERIMENTALVALUATIONA.ExperimentalApparatusandProcedureInanenvironmentwheresensinguncertaintiesarelarge,me-chanicalcompliancecanallowaroboticgrippertopassivelyconformtotheshapeofthetargetobjectwhileminimizingcontactforces.Tomaximizetheeffectivenessofthegripper,itshouldbedesignedtoaccommodatethelargestrangeoftargetobjectsizeandlocationuncertainty.Weevaluatedtheeffectivenessofourcompliantgripperbymeasuringtheposi-tionsforwhichasuccessfulgraspcouldbeobtainedforvariousobjectsizes.Toaccomplishthis,thegrasperwasmountedonaprecisionscrew-drivenlinearpositioner,whichbroughtthegrasperintocontactwiththetargetobject.Theobjectswerepo-sitionedatincreasingdistancesfromthecenterofthegrasperinthelateraldirection,andsecurelymountedtopreventmo-tionduetogripper-objectcontactforces.Theexperimentalap-paratusisshowninFig.16.Theobjectsweremetalcylinderschosentoreßectthesizesusedinpreviousstudies[12],andweremountedonamultiaxisforce/torquesensor(Gammamodel,ATIIndustrialAutomation,Apex,NC)torecordthecontactforcesintheplane.Forcewasrecordedataresolutionof0.016N.Jointanglesandcontactforceswererecordedasthegraspermovedforwardalongthelinearactuatoratarateof2cm/s.Basedonthejointangleinformationandknowledgeoftheobjectsizeanddistancefromthelineoftravel,theamountofobject IEEE/ASMETRANSACTIONSONMECHATRONICS,VOL.11,NO.2,APRIL2006 Fig.16.Experimentalsetup.Thegrasperismountedonanactuatedlinearsliderandtheobject,afÞxedtoasix-axisforce/torquesensor,canbepositionedatdistancesnormaltotheactuationdirection.TABLEIIOMENCLATURE enclosurewascalculatedusingthekinematicsofthegrasperandgeometryoftheobject.IfthegrasperÞngercontactscanenclosegreaterthan180oftheobjectsurface,anenvelopinggraspwillbeattained,andthegraspisdeemedsuccessful.Forthisevaluationofgrasprange,thegrasperisnotactuated,butisallowedtopassivelyconformtotheshapeofthetargetobject.Thekinematicsofthegrasperandobjectpairdeterminesgraspsuccess.See[12]forfurtherdiscussionofthisgraspingscenarioandsuccessmetric.Theperformanceofthegraspermechanismwasevaluatedfornormalizedobjectradiusr/land0.9,andobjectlocationincrementedby0.023fromthecentertowardtheoutsideofthegraspingrange,whererepresentsthegrasperlinklength(TableII).ThemaximumnormalizeddistanceoftheobjectfromthecenterlineforwhichasuccessfulgraspwasattainedwasrecordedforeachconÞguration.ThisvaluerepresentsthesuccessfulgrasprangeandindicatesthegrasperÕsrobustnesstouncertaintyinobjectlocation.Thecontactforcesappliedtothe Fig.17.Objectforcesduetograspercontact.Thegraspermovesforwardataconstantvelocityof2cm/suntilasuccessfulgraspconÞgurationisreached. Fig.18.SuccessfulgrasprangeoftheSDMgraspercomparedtothealuminumgrasperandsimulation.objectduringthegraspingprocesswerealsorecordedforeachtestedvalueofobjectlocationB.ResultsFig.17showsanexampleplot(r/lofcontactforcesasthegraspermovesforwardagainsttheobjectuntilasuccessfulgraspconÞgurationisobtained.Ascontactismade,theforcecausesdeßectionofthegrasper,occurringpri-marilyattheproximaljoint,whichismorecompliantandisaffectedbyalargerleverarmthanthedistaljoint.Thisdeßec-tioncontinuesasthegraspermovesforward,withobjectforceincreasingnearlylinearly,untilanenvelopingconÞgurationhasbeenreached.ForceontheobjectduetothepassivecontactthendecreasesduetotheviscoelasticityinthejointßexuresandFig.18showsthesuccessfulgrasprangeoftheSDMgrasperandtheanalogousresultsfromthealuminiumgrasper(Fig.5)andsimulation[12]forobjectsofradiusr/land0.9.Theobjectcanbesuccessfullygraspedanywherewithinthisrange,indicatingtheallowableuncertaintyinobjectpositionfora DOLLARANDHOWE:COMPLIANTGRASPERVIASHAPEDEPOSITIONMANUFACTURING161successfulgrasp.Theresultsshowthatthecenterofanobjectofradiusr/lcanbelocatedanywherewithintherangefromthecenterlineofthegrasper.Similarly,alargeobjectr/lcanbelocatedanywherewithinthe.ThevaluesoftheSDMgrasprangeshowgoodagreementwiththealuminumandsimulatedgraspers.IV.CONCLUSIONANDPassivecomplianceconfersanumberofadvantagesforrobotichands.Previousstudiesshowedthatcarefullytunedjointcompliancemaximizestherangeofobjectpositionsthatresultinasuccessfulgraspandminimizesthemagnitudeofforcesthatthegrasperappliestotheobject[12].ThesebeneÞtsareparticularlyimportantinunstructuredenvironments,whereob-jectlocationandsizemaybepoorlyknown.Inthispaper,wepresentagripperfabricatedusingasimpleprototypingtechniquethatminimizesconstructioncomplexityandincreasesrobustness,whilepreservingtheadvantagesofpassivejointcompliance.RobustnessisalimitingfactorinexperimentaldevelopmentofmultiÞngeredrobothands:theexpenseandfragilityofthesehandsprecludescasualexperi-mentation,restrictingthetypeofexperimentaltasksthatcanbereasonablyattemptedandslowingimplementationduetotheneedforcarefulvalidationofprograms.Thegrasperdesignpre-sentedheredemonstratesthatpolymer-basedSDMallowstheconstructionofÞngerswiththefunctionalityofconventionalmetalprototypesbutfarsuperiorrobustnessproperties.Thisstudydescribedthedesign,fabrication,andevaluationofacompliantgrasperthathaspropertiesdesirableforgrasp-ingwithinherentuncertainty:largesuccessfulgrasprange,lowpassivecontactforcesduetomechanicalcompliance,andro-bustconstruction.However,theperformanceofthegrasperhasonlybeenevaluatedinstructuredtasksthatforeshadowtheper-formanceinunstructuredtasks.Thenaturalextensionofthiswork,therefore,istestingwithmoreunstructuredtasks,relax-ingtheassumptionsofobjectgeometryandposition,andtherequirementofanenvelopinggraspforgraspsuccess.CKNOWLEDGMENTTheauthorswouldliketothankMarkCutkosky,MotoHatanaka,andMiguelPiedrahitafortheiradviceandassis-tancewithimplementingtheSDMprocess.Also,wewouldliketothankChrisJohnsonforhisassistanceinimplementingtheprocess,andFranciscoIsenbergforhisworkontheconstructionofthetactilesensor.[1]K.J.Salisbury,ÒActivestiffnesscontrolofamanipulatorinCartesiancoordinates,ÓinProc.19thIEEEConf.DecisionControl,1980,pp.95Ð[2]M.R.CutkoskyandI.Kao,ÒComputingandcontrollingthecomplianceofarobotichand,ÓIEEETrans.Robot.Autom.,vol.5,no.2,pp.151Ð165,Apr.1989.[3]J.P.DesaiandR.D.Howe,ÒTowardsthedevelopmentofahumanoidarmbyminimizinginteractionforcesthroughminimumimpedancecontrol,ÓProc.2001IEEEInt.Conf.Robot.Autom.,2001,pp.4214Ð4219.[4]J.LoncaricÒGeometricalanalysisofcompliantmechanismsinrobotics,ÓPh.D.thesis,HarvardUniv.,Cambridge,MA,1985.[5]D.E.Whitney,ÒQuasi-staticassemblyofcompliantlysupportedrigidJ.Dyn.Syst.Meas.Control,vol.104,pp.65Ð77,1982.[6]J.M.SchimmelsandS.Huang,ÒApassivemechanismthatimprovesroboticpositioningthroughcomplianceandconstraint,ÓRobot.Comput.-Integr.Manuf.,vol.12,no.1,pp.65Ð71,1996.[7]L.Biagiotti,F.Lotti,C.Melchiorri,andG.Vassura,ÒMechatronicdesignofinnovativeÞngersforanthropomorphicrobothands,ÓinProc.2003IEEEInt.Conf.Robot.Autom.,2003,pp.3187Ð3192.[8]S.HiroseandY.Umetani,ÒThedevelopmentofsoftgripperforthever-satilerobothand,ÓMach.MachineTheory,vol.13,pp.351Ð359,1978.[9]iRobotCorporationGovernmentandIndustrialRoboticsDivision,(www.irobot.com/governmentindustrial),Burlington,MA,USA.[10]D.F.Hougenetal.,ÒAminiatureroboticsystemforreconnaissanceandsurveillance,ÓinProc.IEEEInt.Conf.Robot.Autom.,SanFrancisco,CA,Apr.2000,pp.501Ð507.[11]D.A.Theobaldetal.,ÒAutonomousrockacquisition,ÓpresentedattheAIAAForumonAdvancedDevelopmentsinSpaceRobotics,Madison,WI,Aug.1Ð2,1996.[12]A.M.DollarandR.D.Howe,ÒTowardsgraspinginunstructuredenviron-ments:GraspercomplianceandconÞgurationoptimization,ÓAdv.Robot.vol.19,no.5,pp.523Ð544,2005.[13]R.Merz,F.B.Prinz,K.Ramaswami,M.Terk,andL.Weiss,ÒShapedepositionmanufacturing,ÓpresentedattheSolidFreeformFabricationSymp.,UniversityofTexas,Austin,TX,Aug.8Ð10,1994.[14]M.BinnardandM.R.Cutkosky,ÒAdesignbycompositionapproachforlayeredmanufacturing,ÓASMETrans.,J.Mech.Design,vol.122,no.1,pp.91Ð101,2000.[15]C.Stefanini,M.R.Cutkosky,andP.Dario,ÒAhighforceminiaturegripperfabricatedviashapedepositionmanufacturing,Ópresentedatthe2003Int.Conf.Robot.Autom.,Taipei,Taiwan,2003.[16]J.E.Clark,J.G.Cham,S.A.Bailey,E.M.Froehlich,P.K.Nahata,R.J.Full,andM.R.Cutkosky,ÒBiomimeticdesignandfabricationofahexapedalrunningrobot,ÓpresentedattheInt.Conf.Robot.Autom.,Seoul,SouthKorea,2001.[17]B.H.Park,M.Shantz,andF.B.Prinz,ÒScalablerotaryactuatorswithembeddedshapememoryalloys,ÓProc.SPIE.,vol.4327,pp.79Ð87,2001.[18]K.B.ShimogaandA.A.Goldenberg,ÒSoftmaterialsforroboticÞngers,ÓProc.1992IEEEInt.Conf.RoboticsandAutomation,1992,pp.1300Ð[19]M.R.Cutkosky,J.M.Jourdain,andP.K.Wright,ÒSkinmaterialsforroboticÞngers,ÓinProc.IEEEInt.Conf.Robot.Autom.,1987,pp.1649Ð[20]Y.C.Fung,Biomechanics:MechanicalPropertiesofLivingTissues2nded.NewYork:Springer-Verlag,1993. AaronM.Dollar(SÕ02)receivedtheB.S.degreeinmechanicalengineeringfromtheUniversityofMassachusetts,Amherst,in2000,andtheS.M.de-greeinengineeringfromHarvardUniversity,Cam-bridge,MA,in2002.HeiscurrentlypursuingthePh.D.degreeattheDivisionofEngineeringandAp-pliedSciences,HarvardUniversity.Hisresearchfocusesonmechanicallycompliantrobotgraspersandtheirapplicationinunstructuredenvironments.Mr.DollarisastudentmemberoftheASMEandASEE. RobertD.Howe(SÕ88ÐMÕ99)receivedtheB.A.de-greeinphysicsfromReedCollege,Portland,OR,andthePh.D.degreeinmechanicalengineeringfromStanfordUniversity,Stanford,CA,in1990.HehasworkedintheelectronicsindustryasananaloganddigitalDesignEngineer.Currently,heistheGordonMcKayProfessorofEngineeringtheDivisionofEngineeringandAppliedSciences,HarvardUniversity,Cambridge,MA.Hisresearchinterestsfocusonrobotandhumanmanipulationandthesenseoftouch.Bioengineeringapplicationsin-cludethecharacterizationofthemechanicalpropertiesofsofttissuesandde-velopmentofnewtechniquesforimage-guidedsurgery.