挖掘式装载机外文文献.docx
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挖掘式装载机外文文献.docx
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挖掘式装载机外文文献
Developmentofawalkingmachine:
mechanical
designandcontrolproblems
TeresaZielinska*,JohnHeng
Abstract
Thispaperdescribes:
anoveldesignofthelegdrivemechanism,hardwarearchitectureand
thelegcontrolmethodforawalkingmachinebeingdevelopedtostudyvariouswalkinggait
strategies.Thelegmechanismemploysaninversedifferentialgeardrivesystemprovidinglarge
legliftandswingsweepangleaboutacommonpivotalpointwhilebeingdrivencollectivelyby
apairofmotors.Thedevelopmentplatformconsistsofapairoflegsmountedadjacentlyto
eachotheronalinearslide.Athree-axispiezotransducerismountedonthefeettomeasure
thevariousvectorforcesinthelegsduringthesupportphase.Theforcesensingresultsare
presentedanddiscussed.Currentlyonesmallfour-leggedprototypeandonehexapodareused
forthetestsofdifferentgaitpatterns._2002ElsevierScienceLtd.Allrightsreserved.
Keywords:
Walkingmachines;Mechanicaldesign;Controlsystemdesign;Forcesensing
1.Introduction
Incomparisonwiththeindustrialmanipulators,thetaskofbuildinganadaptable,
autonomouswalkingmachineismoredifficult.Walkingmachineshavemore
activedegreesoffreedom(DOF)thanindustrialrobots.Toenlargethework-space
oftheleg-end,andthusenhancethemachine’sabilitytoadapttotheterrain,eachlegshouldhaveatleastthreeDOF,whichresultsinatotalof12DOFforaquadruped
or18DOFforahexapod.Allthosejointsmustbecontrolledadequatelyinreal
time.Thisalsomeansthatthehardwareandsoftwaresystemsmustmeetmorecritical
requirementsthanthoseformulatedforindustrialrobotcontrollers.Moreover,fully
autonomousvehiclesuseonlyon-boardcontrollersandsothosecontrollershaveto
beminiaturizedtoanutmostextent.Thereisnosuchrequirementinthecaseofnonmobile
controllersofmanipulators.Theoreticalproblemsthatmustbesolvedare
numerous.Fromanoverviewofthepublicationsconcerningthesubjectofmultilegged
walkingmachinesitcanbenoticedthatthemainattentionispaidto:
•general(technical)descriptionofprototypes,e.g.,[1],
•methodsoffreegaitplanning,e.g.,[2,3],
•problemsofgaitsynthesisusingdynamicalorquasi-dynamicalmodelling,(e.g.,
forcedistributionproblems)–[4–7],
•theproblemsofmotionoptimization–[8,9],
•thephilosophyofcontrolsystemsfunctionaldecompositionandmechanismsof
machines’adaptivebehavior–[10,11].
Thedescriptionofcontrolsoftwarecomponentislacking.Suchadescription
isnecessaryinthesystematicdevelopmentofwalkingmachines,whichshouldbe
treatedasmechatronicsystems.
Mechanicalstructureofawalkingmachineshouldnotonlyimitatethelegstructure
oflivingcreatures(e.g.,insects,spiders),butshouldalsotakeintoaccountthe
actuatingsystemsproperties(e.g.,size,weightandpowerofthemotors)andconstraints
(e.g.,sizeofthebodyandthelegwork-space).
Fig.1.LAVAusingthemultipurposelegbeingdevelopedatRRC(RoboticsResearchCentre–Nanyang
TechnologicalUniversity,Singapore).
Inthispaper,wearepresentingthemechanicalstructureofamultileggedmachine
andwearegivingabriefdescriptionofjoint,legandgaitlevelsofthecontrol
system.
2.Mechanicaldesign
2.1.Mechanicalproblems
Theneedforageneralsolutiontotheproblemofrobotlegsdesign,thatcanbe
usedeitherbytwo-,four-orsix-leggedvehicles,isclear.Howevertheabilitytomeet
thisneedhasbeenhamperedbythelackofadequatejointmechanismsandcontrols.
Jointtechnologyisakeyprobleminthedevelopmentofsuchvehicles,becausehip
andanklejointsrequire,ataminimum,pitchandyawmotionaboutacommon
centerwithremotelocationofactuationsourcesanalogoustoourmusclesandjoints.
Thelackofsimple,compact,cost-effectiveandreliableactuatorpackageshasalso
beenamajorstumblingblockincurrentdesigns.Ineffectivejointdesignleadsto
unwieldyvehiclesthatcompensatefortheinstabilityoftheirsimplejointsbymeans
ofadditionallegs.
2.2.Uniquedifferentiallegmechanism
Thegeneralstructureofawalkingmachineleggedautonomousvehicularagent
(LAVA)[12,13]isshowninFig.1.Thethighsectionemploysadifferentialgeardrive
systemtoachievebothlegswingandlegliftfunctions(Fig.2).Thisdrivesystem
offerstwodistinctfeaturesthataresuperiortoconventionallegdesign.Firstly,leg
liftandlegswingfunctionsoperatefromacommongeometricalpivotpoint.This
featurewillprovebeneficialwhenperformingworkspaceandkinematicmodeling.
Secondlyduringlegswingandlegliftmotions,bothmotorsareconstantlyworking
togethertoachievethedesiredmotion.Nomotorisleftidleandsoisnotcarried
aroundasadeadweight,whenonlyoneparticularlegmotionisinuse.Theadvantage
wouldbethattwosmallerlightermotorscanbeutilizedwhichcanbe
combinedtoprovideacooperativeeffortinsteadoftheconventionalindependent
motordrivedesign.Theresultwouldprovidesavingsinpowerconsumption,weight
penaltyandsizeconstraints.Otherpower-savingfeaturesincludeusingwormgears
ataparticulargearratiotodrivethevariousappendages.Thisprovidesaself-lock
featurethusremovingtheneedtokeepthemotorscontinuouslypoweredwhen
holdingthewalkingmachineataparticularorientation.Toprovidemaximumfoot
placementflexibilitywithpreciseturningfunctions,fullthreeDOFwereincorporated
intoeachleg.
2.3.Fullyinvertablewalkingmachineplatformwithamphibiousadaptability
Thelargelegliftandswinganglecomplementsthesymmetricallegdesign,which
enablesthewalkingmachinetobeinvertable.Thisfeatureisseenasbeingessential,
Fig.2.Thedifferentialgeardrivesystem
ifthewalkingmachineistooperatewithinthesurfzoneofaseashore.Theabsence
ofawkwardlyexposedmechanicaldrivesystemsallowsthewalkingmachinetobe
economically‘‘waterisolated’’andhenceobtainsamphibiouscapability.Thewalking
machinecanbeconfiguredtowalkontheseabedorspreaditslimbstoincrease
buoyancyandhenceswimonthesurface(Fig.3).
2.4.Convertibletoinsect/mammalianconfigurationwithsegmentablelegpair
Thewidelegliftandswingcapabilityallowthemodularlegtobeadaptedfor
useineitheraninsectormammalianlegconfiguration(Fig.4).Utilizingthelegin
mammalianconfigurationrequiresonlyasmalladjustmenttotheleggeometry.The
addedbenefitofhavingawidelegliftandswingcapabilityisthatthefronttwolegs
canbeadaptedtoperformprobingorpickandplacefunctions(Fig.5).Themodular
Fig.3.Thewalkingmachineinswimmingmode.
Fig.4.ConfigurationofLAVA’slegs:
(a)insectlegconfiguration;(b)mammalianlegconfiguration.
legcanbeadaptedtoafour-orsix-leggedvehicleoremployedinanomnidirectional
hexapodconfiguration.
2.5.Conclusion
Themodularapproachfollowedinthelegdevelopmentoffersseveraladditional
benefits.Thethighandlowerleglengthcanbeadjustedquicklytoassumedifferent
leglengthrequirements.Thereisfreespaceinthecentralcolumnofthelegtoaccommodate
varioussensors,dataandpowercables.Thecurrentimplementationof
thelegdesigncanaccommodatetwodifferentgearratiosfordifferentialgeardrive
units.Ifanincreaseindrivemotorpowerisrequiredinthefuture,onlyminor
modificationsarerequiredtoaccommodatethebiggermotors.Similarly,legsupporting
beamscaneconomicallyberesizedbychanginggeometricallysimplecomponents.
Finally,withalargelegliftandswinganglethewalkingmachinecanbe
manipulatedina‘‘prone’’modetooperateinrestrictivespacesorbeneatlyfolded
foreasystorageordeployment(Fig.6).Thelegservodriveactuatorsystemisdesigned
aroundamodifieddifferentialgearsystemthusallowinglargelegliftand
swingmotionstobeachievedaboutthesamepivotalpointthusprovidingsimpler
leggeometrythanconventionallegdesigns.
Fig.5.Pickandplaceoption.
3.Controlsystem
3.1.Functionaldecomposition
Thefunctionalstructureofthecontrolsoftwarewasdecomposedintohierarchically
relatedlevels(Fig.7).Thelowestlevelincludesjointcontrol.Theangular
jointpositionsareevaluatedfromtheleg-endtrajectoryshapedefinedinCartesian
space.Inversekinematicsmodelisimplementedtheretoevaluatethejointangular
positions.Incrementalrotaryopticalencodersmountedonmotorshaftsareused
asthefeedbackdevices.ThemotorcontrollersusethePIDalgorithmtocompute
theangularpositions.Inthesolutionofinversekinematics,simplesingularitiesand
problemsofnon-uniquechoicesofconfigurationswereconsidered.
Theupperlevel–leglevelproducestheleg-endtrajectoryaccordingtotheproper
timingscheme.Thenextlevelisthegaitlevel.Therhythmicandfreegaitwillbe
generatedbyit.Inthecaseofpickandplaceoperations,thislevelwillalsogenerate
trajectoriesoffrontlegstreatedasmanipulators.Theuppermostlevelofthecontrol
softwarewillberesponsibleforthegenerationofthebody(bodylevel)trajectories
accordingtotheusercommandsoraccordingtothesensoryreadings.Forthegait
andbodylevel,themostseriousproblemistoelaboratethemethodoffreegait
generationtakingintoaccountthatthereareobstaclesofdifferentsizeanddensity,
whichmustbeavoided[16].Itwasassumedthatmotionplanningmustbedone
inrealtime(neithertheleg-endtrajectoryispre-plannednorthesequenceoflegs
Fig.6.Lavalegposition:
(a)proneconfiguration;(b)foldedconfiguration
transfersisfixed).Thetransitionfromonestatetoanotherisperformedt
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