外文翻译（英语版）-敏捷机器人腿的仿生设计

OntheBiomimeticDesignofAgile-RobotLegsONACCESSAbstract:Thedevelopmentoffunctionalleggedrobotshasencountereditslimitsinhuman-madeactuationtechnology.Thispaperdescribesresearchonthebiomimeticdesignoflegsforagilequadrupeds.Abiomimeticlegconceptthatextractskeyprinciplesfromhorselegswhichareresponsiblefortheagileandpowerfullocomotionoftheseanimalsispresented.Theproposedbiomimeticlegmodeldenestheeffectiveleglength,legkinematics,limbmassdistribution,actuatorpower,andelasticenergyrecoveryasdeterminantsofagilelocomotion,andvaluesforthesevekeyelementsaregiven.Thetransferoftheextractedprinciplestotechnologicalinstantiationsisanalyzedindetail,consideringtheavailabilityofcurrentmaterials,structuresandactuators.Areallegprototypehasbeendevelopedfollowingthebiomimeticlegconceptproposed.Theactuationsystemisbasedonthehybriduseofserieselasticityandmagneto-rheologicaldamperswhichprovidesvariablecompliancefornaturalmotion.Fromtheexperimentalevaluationofthisprototype,conclusionsonthecurrenttechnologicalbarrierstoachieverealfunctionalleggedrobotstowalkdynamicallyinagilelocomotionarepresented.Keywords:leggedrobots;agilequadrupeds;biomimeticdesign;newactuatorsforrobots外文翻译1.State-of-the-ArtAgileLeggedLocomotion1.1.MachinesLeggedlocomotionisattractingtheinterestofresearchersofabroadrangeofareas.Engineers,biologistsandneurologistsareallpoolingtheirknowledgeforthesuccessofaleggedlocomotiondevice1.ThemajorimpetusforthistechnologyiscomingfromthegovernmentoftheUnitedStatesofAmerica,whichhasgivenaboosttothetopicthroughasignicantnumberofprogramssponsoredbytheDefenseAdvancedResearchProjectsAgency(DARPA)inthelasttenyears2.Someoftheseprogramsstartedin2001andendedrecentlywhileothersarestillopen.ThemorerelevantexamplesaretheLearningLocomotionProgram3;TheBigDogProgram4;TheExoskeletonsforHumanPerformanceAugmentationProgram5andthemorerecentLeggedSquadSupportSystemProgram6.However,despitethestrongimpulseintheresearchandtheforecasteddemandfortheserobots7,veryfewadvancesinrealapplicationsexist.Thechallengesofautonomyandthelargepower-to-weightratiodemandedfortheactuatorsmakeconventionalactuationandcontroltechnology,inheritedfromindustrialrobotics,inadequateforthemostpromisingeldandserviceapplicationsofleggedlocomotionwhichexhibitsignicantexpectedimpactonthefuturesociety7.TheHADE(HybridActuatorDevelopment)project8developedattheCentreforAutomationandRoboticsattheSpanishNationalResearchCouncil(CSIC)aimsprimarilyatsolvingthisproblembyestablishinganewlineofresearchfocusedonspecicactuationandcontroltechnologiesforthenewgenerationofleggedrobots:Agile-locomotionrobots.Quadrupedrobots,emulatingtheirbiologicalcounterparts,arethebestchoiceforeldmissionsinanaturalenvironment.However,itiswellknownthatcurrentlegged-locomotiondevicesfeaturehighcomplexityandverylowspeedparticularlyifhighpayloadshavetobetransported,andarefarfromreachingtheperformanceofbiologicalquadrupedsinnaturalenvironments.Table1.Performanceofsignicantquadrupedrobotsdevelopedinthelast12years.RobotSupportsPayload/WeightMax.dimensionlessYeardynamicloadsspeedAibo9No00.351999ScoutII10Yes0.021.171999SILO411No0.590.062002TITANXI12No0.060.0032002TekkenII13Yes00.652003LittleDog14No0a0.232005Tekken3&415Yes0.20.652005Kolt16Yes0.352005Rush17Yes00.642007BigDog4Yes1.410.722008baLittleDogscomplexcomputingisprovidedbyanoff-boardprocessor,itisnotaself-containedautonomousquadruped2;bAlthoughtherstBigDogrobotwasdevelopedin2005,thisdatacorrespondstothe2008BigDogprototype.Table1listsmostrelevantquadrupedrobotsdevelopedinthelast12years,showingtheirpayload-to-weightratiosandmaximumdimensionlessforwardspeed,whichhasbeencomputedfromrobotdimensionsandspeedpublishedbytherobotsauthorsasu=FR,whereFRistheFroudenumber,obtainedfrom18:FR=v2gL(1)beingv,theforwardspeed;g=9.81ms_2;andL,thecharacteristicleglength.Aleggedvehicledesignedtoperforminanaturalterrainshouldbeprovidedwithoptimumperformanceagainstmobility,payload,andendurance.SuchspecicationswereimposedbyDARPAforanAgileGroundVehicleintheUGCVprogram19.Asimilardenominationishereusedforaleggedgroundvehicle,whichwecall“Agile”ifitisabletoreachadimensionlessspeedofu=0.54andfeaturesapayload-to-weightratiolargerthan1,tobecomparablewithbiologicalquadrupeds.Besides,aquadrupedrobottoperformusinghigh-speedgaits(i.e.,trotandgallop)mustmakeathrusttothegroundyieldingdynamicimpactloadsthatcouldexceedthreetimesthestaticloadonthesupportingleg20.Inatrotorinadynamicwalk,wheretwolegsthrustthegroundsimultaneously,bothlegssharethebodyweightandpayload,sothestaticloadoneachlegisonehalftherobotsweightandaddedpayload.Therefore,inatrotgaitdynamicloadsoneachlegcanreach1.5timestherobotsweightandpayload.Foradynamicwalk,dynamicimpactloadsateachlegapproximatelyequaltherobotsweightandpayload.Therefore,thestructuraldesignofanagilerobotlegshouldmakesurealoadcapacity-to-robotsweightratioof11.5dependingontheenvisagedgait.Figure1.State-of-the-artagilerobots:(a)KOLT,jointprojectbyStanfordUniversityandTheOhioStateUniversity,imagecourtesyofProf.Waldron;(b)HyQ,imagecourtesyoftheItalianInstituteofTechnology;(c)BigDog,imagecourtesyofBostonDynamics.(a)(b)(c)Biologicalquadrupedstransitionfromwalkingtorunninggaitsatadimensionlessspeedbetween0.54to0.7.Concretely,horsestransitionfromwalktotrotatu=0.5921.Asexceedingthisdimensionlessspeedrequiresthequadrupedtorun(trotorgallop)andsomecomplexterrainscouldimpedetheuseofthosehigh-speedgaits,wehaveconsideredthedimensionlessspeedof0.54asthelowerspeedlimitforaleggedrobottobeconsideredagile.ByhavingalooktoTable1itisnoticedthatveryfewquadrupedsachieveagilelocomotionperformance,becausethoserobotsfeaturingdimensionlessspeedabove0.54havealmostnegligiblepayload-to-weightratio.Althoughsomeresearchlabsareworkinginthisdirection(StanfordUniversity22,ItalianInstituteofTechnology23),theonlyexistingrobotreachingthosetargetsisBigDog4,aquadrupedunderdevelopmentatBostonDynamics(USA)(seeFigure1).TheBigDogprojectissponsoredbyDARPA,theUSMarineCorpsandtheUSArmy.ThegoaloftheBigDogProjectistobuildaclassofagileunmannedgroundvehicleswithrough-terrainmobilitysuperiortoexistingwheeledandtrackedvehicles.TheBigDogrobotscurrentlybuilt“havetakenthestepstowardthesegoals,thoughthereremainssignicantworktobedone”4.Unfortunately,theinsandoutsofthetechnologyunderlyingBigDogarenotavailabletotheresearchcommunity.1.2.ActuationSystemsSupplyingpowertoahigh-speedleggedmachineusingcurrentlyavailableactuationtechnologyisachallenge.Thisisparticularlytrueifthemachineisexpectedtobeenergeticallyautonomous.Indynamiclocomotion,theloadexperiencedbyeachlegisatleastthreetimesthestaticloadonthatleg,anditmaybemuchmoreforrunninggaits.Thecostofbuildingastructureandactuationsystemcapableofprovidingtheperformanceneededforthedynamiclocomotionofamid-tolarge-sizedmachineisprohibitive,evenwithoutconsideringpayload.Consideringthemammalianmuscleasareference,directmeasurementsofmusclefunctionhaveyieldedinsightintotheversatilewaymusclesoperate.Ithasbeendiscoveredthatmusclesactasmotors,brakes,springs,dampersandstruts24.Themultifunctionalityofnaturalmuscledistinguishesitfromanyhuman-madeactuatoranditmayholdthekeytothesuccessofleggedlocomotion.Inmanybiologicaltissuesitishardtodistinguishbetweenmaterialandstructure.Theuseofviscoelasticmaterialscangivetherobotthespring-massenergy-cyclingcapacitiesoflegged-animallocomotion,whichalsoreducesthecomputationalcomplexityofthecontrol.Viscoelasticmaterialsgreatlysimplifythemechanicsoftherobot,servingsimultaneouslyasshockabsorbers,springsandcompletejoints.Thespring-massenergy-cyclingcapabilitiescanplayakeyroleinthedynamiclocomotionofaleggedvehicle.Kineticenergycanonlybeputintothesystemwhenthefootisontheground.Itisnecessarytokeepthemechanicalenergyinthesystembyusinginternalenergystorage,thatis,compliantactuation.Moreover,thelegisamechanicaloscillator,anditisenergeticallyexpensivetodriveitatafrequencysignicantlydifferenttoitsnaturalfrequency20.Anymeanstomodifythenaturalfrequencyonthelegwouldhelptomakeitoscillateatdifferentfrequencieswithoptimalenergyexpenditure.Thus,inherentadaptablecomplianceisrequired25.Therefore,toefcientlyrunadynamicleggedvehicle,highpower-densityhighforce-densityfastactuatorswithadaptablecompliancearerequired.Addedtothis,energeticautonomyisexpected.Itisevidentthattheserequirementsarenotmettogetherbyconventionaltechnology26.HADEisalong-termproject8aimedatdesigningenergyefcient,largepower-to-weightratioactuatorsandenergy-efcient-locomotioncontrolschemesforthenewgenerationofleggedrobotsfollowingnaturalmusclemultifunctionality.Thismultifunctionalityisapproachedbymeansofmergingdifferenttechnologies(smartmaterialsandconventionaltechnologies)inordertoextractthebestpropertiesofeachone.Someprototypeshavealreadybeentestedandcharacterized27.Thispaperpresentsthedevelopmentofabiomimeticmodelofalegforagilelocomotionofquadrupedrobots.Thekeyprinciplesunderlyingthesuperiorcapabilitiesofstrength,speed,agilityandenduranceofcursorialmammals,likehorses,areanalyzedinSection2andtransferredtotechnologicalinstantiationsinSection3,whereamodelofabiomimeticlegforagilelocomotionispresented.Theproposedconcepthasbeenimplementedonarealprototype.Section4describesthelegdesign,actuationsystemandsensorialsystem.Section5describeshowvariablecomplianceisachievedatthejointsoftheleg.ExperimentalanalysisofthelegperformancetoachieveagilelocomotionisanalyzedinSection6,andnallySection7presentsadiscussiononthetechnologicalbarriersthathavebeenencounteredinthetechnologicalinstantiationofthebiomimeticlegmodelandconcludeswithsomeproposals.2.BiologicalInspirationforEmpoweringRobotLegsAsstatedabove,aquadrupedisconsideredtoperforminagilelocomotionwhenitisabletoachievedimensionlessspeedsupto0.54whilecarryingapayloadatleastequaltoitsownweight.Inordertodesignalegmechanismabletoprovidetherobotwiththosefeatures,natureisthebestsourceforinspiration.Horselegsareadaptedtoprovidespeed,endurance,agilityandstrengthsuperiortoanyotheranimalofequalsize28.Thisadaptationisbasedonlongerlegsthansimilarquadrupedsrelativetothebodysize,whichprovidelongerstridelengths.Thelengthofthehorselegisoptimalforrunning,longerlegswouldprobablybedifculttooscillate(giraffesarenotabletotrot).Thecauseforthehorserelativelylonglegsistheevolutionoftheanatomicalfootandtoe.Horsesfeethaveundergoneextensivemodicationwhichhaveenabledtheseanimalstobecomepowerfulrunners.Themostconspicuouschangeisthereductionofthenumberofdigits:theyhaveretainedonlyonesinglefunctionaldigit.Thisdigitcorrespondstothethirdtoeinhumans(seeFigure2)anditisabletowithstandforceslargelysuperiortothosesupportedbymulti-digittoes.Besides,themetatarsalhasbeensolengthenedthatitseemsmorepartofthelegthanthefoot;humanmetatarsalsarelocatedinthearchasshowninFigure2.Unliketruelegbones,however,itisnotdirectlypoweredbymuscles.Instead,themetatarsalemploysspring-likeforcesfrommassiveligaments.Figure2.Comparisonofhorsefootandhumanfoot28.Thigh bone(Femur)KneeShank bone(Tibia)HeelHock jointFetlock jointHeelHUMANHORSEMetatarsalsSensors2011,1111310Thehorserearlegsarerelativelylightweight,yetstrongenoughtodeliververylargethrustsandtosustaintremendouslyheavyloads.Again,theleghasevolvedtooptimizetheuseofitsjointsforloadbearing.Thehorsehipjointismainlyahingetoturnthethighforwardandbackward.Theabduction/adductionmovementispracticallynegligible28,29.Similarly,knee,ankleandfetlockjoints(thejointbetweentoeandmetatarsal)are1DoFjoints.Thus,allthemusclesandtendonsfocustheireffortinsimplejointmotions.Andallthiswithenougheconomyofefforttoprovideendurance,whichisachievedbymeansofelasticenergystorageintendonsduringcertainphasesofthelocomotioncycleandthelaterreturnofthisenergytothemoreexigentphases.Intheprocessofcopyingfromnatureadesiredsystemperformance,onehastobecarefulinwhatissuesmustbeextractedandtranslatedtoatechnologicaldesign.Thejobofthebiomimeticististoidentifythoseelementsresponsibleforproducingthedesiredcharacteristicsonbiologicalsystemsandtoextractthekeyprinciplesunderlyingtheirbiologicalfunctionandthentranslatethemtoatechnologicalinstantiationthatislimitedbyitsownhumanengineering30.Onecannotsimplycopynature,butrathercarefullyextractconceptsatthelevelofdescriptionthataretechnicallypossibletoimplement.Otherwise,theresultofadirectcopywouldyieldasub-optimalapproximationtothedesiredperformance.Whendesigningpowerfulrobotlegs,theengineercoulddecidetoextractthedesiredcharacteristicsofhorselegswhicharetheirsuperiorspeed,endurance,agilityandstrength.Inordertotranslatethesecharacteristicstoarticialquadrupedlegs,thekeyelementsthatshouldbecopiedhavebeensummarizedinTable2andenumeratedasfollows:(1)Effectiveleglengthdirectlyaffectsspeedandendurance.Longereffectiveleglengthimprovesstridelengthandconsequentlylegspeed,whilelongerlegsreducetheenergeticcostoftransport.Theaverageeffectiveleglengthofhorsesis1.24m31anditrepresentsthe60%ofthehorizontalhorselengthfromnosetotail32.(2)Massdistributionalongthelegdeterminesthenaturalfrequencyoflegmovementandthereforeaffectsspeed.Itwasdemonstratedthathighspeedrunnerbreedsofhorseshavegreatermasslocatednearthehipjointthanotherbreeds.Concretelythe80%90%oflegmassislocatedinthethighinrunners.Thisfeaturefavorsahighnaturalfrequencyoflegmovementandfacilitatesahigherstridefrequency33.Addedtothis,thelegmassrelativetobodymassinuencesagilityofmotion.Thisratioisbetween5%to8%inhorses.(3)Legkinematicsinuencesgaitenergeticsandendurance.Movementsintheequinelimbsoccurpredominantlyinthesagittalplane,whichisenergeticallyadvantageousincursorialspecies29.Besides,theuseof1-DOFjointsoptimizetheuseofitsjointsforloadbearing,thusimprovingthestructuralstrengthoftheanimal.(4)Elasticenergystorageintendonsprovidesagilityandelasticenergystorage,reducingthepowerrequirementsatmusclesforthemoreenergeticexigentmotionsandimprovingendurance34.Theinherentstiffnessoftendonsalsoaffectsthelimbnaturalfrequency,whichdeterminesthedurationofthesupportphase35andconsequentlyinuenceslegspeed.(5)Musclepowercapacitydirectlydeterminesjointspeedandlimbstrength.Table2.Keyelementsandtheirinuenceondesiredcharacteristicsofhorselegs.SpeedEnduranceAgilityStrengthEffectivelengthXXMassdistributionXXKinematicsXXElasticityXXXMusclepowerXXTakingintoconsiderationthesekeyelementsandtheirroleinagilelocomotion,aconceptualmodelofalegforanagilequadrupedhasbeenoutlinedanditsperformancehasbeensimulated.Thisisdetailedinthenextsection.3.DerivingtheBiomimeticLegConceptTheaboveprinciplesunderlyinghorsepowercapabilitieshavebeenextractedandtranslatedtotechnologicalimplementation.Firstly,alegconceptwhichencompassesthekeyelementshasbeendesignedandafterwards,itsperformancehasbeenanalyzedthroughdynamicsimulation.3.1.EffectiveLegLengthTakingintoconsiderationthatbuildingaquadrupedwiththesizeofahorsewouldbedifculttohandleinthelaboratory,scalingoftheleglengthmakingsurethattheeffectiveleglengthisthe60%ofthebodysizewouldcomplywiththespecications.Foratrade-offbetweenreproducinghorsesdimensionsandhavingareliableprototype,ascalingfactorof65%hasbeenappliedtothedesign,thereforearobotlengthof1.2mwasconsidered,havinganeffectiveleglengthof0.8m.3.2.LegKinematicsThecomplexityofcontrollingaplanar4-DoFredundantkinematicchainaddedtothecostofelectronicsandactuatorsandthedirectconsequenceofincreasinglegmassasthenumberofdegreesoffreedomincreasesmakeunfeasiblethedevelopmentofanexacthorse-likeleg.However,theelectionofredundantkinematicsfavorsreducingjointtorquesandthusactuatorrequirementsandpowerconsumption.Apossiblesolutionistousepassiveelasticelementstodriveoneormorejoints,however,theanalysisofjointpowerrequirementsforaslowtrot(seeSection3.4)advisesagainstpurelypassiveactuation.Asatrade-off,aplanar3-DoFleghasbeenoutlinedcomposedofthreelinks:thigh,crusandhoof,connectedthrough1-DoFjoints:thehip,kneeandfetlockjoints.Thelengthsofthigh,crusandhoofareproportionaltorealhorselegsplusascalingfactortoreachthedesiredeffectiveleglength,takingintoconsiderationthattheuseofa3-DoFmodeloflegshortensthetotalleglengthina34%comparedtoahorseleg.The35%reductionineffectiveleglengthplustheincreaseof34%inlimblengthresultsinanal1%decreaseineachleglinklength.Table3liststhenallinklengths.Table3.Characteristicrobotlengths(inmeters)basedonbiomimetism.BodyEffectivelegThighCrusHoof0.360.19Figure3andTable4showDenavitHartenbergparametersforthelegkinematics,whichcorrespondtoaconventionalthree-linkplanarstructure.Followingthisconvention,thedirectkinematicmodelprovideshoofpositionandorientationfromjointanglesasfollows:x0y0f=a1C1a2C12a3C123a1S1a2S12a3S123q1q2q3(2)where(x0,y0,f)arehoofxandypositionandorientationrespectivelyinthelegsbasereferenceframe,andqiwithi=1.3arejointanglesnumberedfromhiptofetlockjoint.Parametersaiaretherespectivelinklengthsmeasuredasthedistancebetweenadjacentjointaxes,andcorrespondtothevalueslistedinTable3.InEquation(2)CiandSimeancos(qi)andsin(qi)respectively,whileexpressionCijkmeanscos(qi+qj+qk)andSijkmeanssin(qi+qj+qk).Figure3.Kinematicmodelofrobotleg.Table4.DenavitHartenbergparametersofthelegmodel.Jointaidi_i_iHip(1)a100q1Knee(2)a200q2Fetlock(3)a300q33.3.MassDistributionPublishedworkontheexperimentaldeterminationofequinelimbinertialpropertiesshowwiderangesofaveragevaluesforlegsegmentmassesfordifferenthorsebreeds.Table5summarizesaverageresultsofanexperimentalworkperformedonsixDutchWarmbloodhorses36.Consideringthatourlegmodelaccountswiththreelinks,thesele