毕业设计机械手外文翻译Word格式文档下载.docx
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毕业设计机械手外文翻译Word格式文档下载.docx
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M.
Abou-Samah1
C.
P.
Tang2
R.
Bhatt2
andV.
Krovi2
(1)
MSCSoftwareCorporation,AnnArbor,MI
48105,USA
(2)
MechanicalandAerospaceEngineering,StateUniversityofNewYorkatBuffalo,Buffalo,NY
14260,USA
Received:
5
August
2005
Revised:
25
May
2006
Accepted:
30
Publishedonline:
September
2006
Abstract
Inthispaper,weexaminethedevelopmentofakinematicallycompatiblecontrolframeworkforamodularsystemofwheeledmobilemanipulatorsthatcanteamuptocooperativelytransportacommonpayload.Eachindividuallyautonomousmobilemanipulatorconsistsofadifferentially-drivenWheeledMobileRobot(WMR)withamountedtwodegree-of-freedom(d.o.f)revolute-jointed,planarandpassivemanipulatorarm.Thecompositewheeledvehicle,formedbyplacingapayloadattheend-effectorsoftwo(ormore)suchmobilemanipulators,hasthecapabilitytoaccommodate,detectandcorrectbothinstantaneousandfiniterelativeconfigurationerrors.
Thekinematically-compatiblemotion-planning/controlframeworkdevelopedhereisintendedtofacilitatemaintenanceofallkinematic(holonomicandnonholonomic)constraintswithinsuchsystems.Givenanarbitraryend-effectortrajectory,eachindividualmobile-manipulator'
sbi-levelhierarchicalcontrollerfirstgeneratesakinematically-feasibledesiredtrajectoryfortheWMRbase,whichisthentrackedbyasuitablelower-levelposturestabilizingcontroller.Twovariantsofsystem-levelcooperativecontrolschemes—leader-followeranddecentralizedcontrol—arethencreatedbasedontheindividualmobile-manipulatorcontrolscheme.Bothmethodsareevaluatedwithinanimplementationframeworkthatemphasizesbothvirtualprototyping(VP)andhardware-in-the-loop(HIL)experimentation.Simulationandexperimentalresultsofanexampleofatwo-modulesystemareusedtohighlightthecapabilitiesofareal-timelocalsensor-basedcontrollerforaccommodation,detectionandcorectionofrelativeformationerrors.
Keywords
Compositesystem-Hardware-in-the-loop-Mobilemanipulator-Physicalcooperation-Redundancyresolution-Virtualprototyping
Kinematiccollaborationoftwomobilemanipulators
Wenowexaminetwovariantsofsystem-levelcooperativecontrolschemes—leader-followeranddecentralizedcontrol—thatcanbecreatedbasedontheindividualmobile-manipulatorcontrolscheme.
Leader-followerapproach
Thefirstmethodofmodelingsuchasystemconsidersthemidpointofthemobilebase(MPB)ofthemobile-manipulatorBtoberigidlyattachedtotheend-effectorofmobilemanipulatorA,asdepictedinFig.4.Figure4(b)depictshowtheend-effectorframe{E}ofMPAisrigidlyattachedtotheframe
atMPB(separatedbyaconstantrotationangleβ).
(15)
Fig.4
Schematicdiagramsoftheleader-followerscheme:
(a)the3-linkmobilemanipulatorunderanalysis,and(b)thetwo-modulecompositesystem
MPBnowtakesontheroleoftheleaderandcanbecontrolledtofollowanytrajectorythatisfeasibleforaWMR.Hence,givenatrajectoryoftheleaderMPB
andthepreferredmanipulatorconfigurationof
Eq.(5)canberewrittenas:
(16)
andcorrespondinglyEqs.(6)–(8)as:
(17)
Thus,thetrajectoryofthevirtual(reference)robotforthefollowerMPA
andthederivedvelocities
cannowbedetermined.Thisformstheleader-followerschemeusedforthecontrolofthecollaborativesystemcarryingacommonpayload.
Decentralizedapproach
Thesecondapproachconsiderstheframeattachedtoapointofinterestonthecommonpayloadastheend-effectorframeofboththeflankingmobilemanipulatorsystems,asdepictedinFig.5.Thus,adesiredtrajectoryspecifiedforthispayloadframecanthenprovidethedesiredreferencetrajectoriesforthetwomobileplatformsusingthesimilarframeworkdevelopedintheprevioussectionbytaking
and
where
.ThispermitsEq.(5)toberewrittenas:
(18)
Fig.5
Decentralizedcontrolschemeimplementationpermitsthe(a)compositesystem;
tobetreatedas(b)twoindependent2-linkmobilemanipulators
andcorrespondinglyEq.(6)–(8)as:
(19)
Eachtwo-linkmobilemanipulatornowcontrolsitsconfigurationwithreferencetothiscommonend-effectorframemountedonthepayload.However,thelocationsoftheattachmentsofthephysicalmanipulatorswithrespecttothepayloadreferenceframemustbeknownapriori.
Implementationframework
Weexaminethedesignanddevelopmentofatwo-stageimplementationframework,showninFig.6,thatemphasizesbothvirtualprototyping(VP)basedrefinementandhardware-in-the-loop(HIL)experimentation.
Fig.6
Paradigmforrapiddevelopmentandtestingofthecontrolschemeonvirtualandphysicalprototypes
Virtualprototypingbasedrefinement
Inthefirststage,weemployvirtualprototyping(VP)toolstorapidlycreate,evaluateandrefineparametricmodelsoftheoverallsystemandtestvariousalgorithmsinsimulationwithinavirtualenvironment.3DsolidmodelsofthemobileplatformsandthemanipulatorsofinterestarecreatedinaCADpackage,4andexportedwiththeircorrespondinggeometricandmaterialpropertiesintoadynamicsimulationenvironment.5Figure7(a)showsanexampleoftheapplicationofsuchframeworkforsimulatingthemotionofamobileplatformcontrolledbyanalgorithmimplementedinSimulink.6However,itisimportanttonotethattheutilityofsuchvirtualtestingislimitedby:
(a)theabilitytocorrectlymodelandsimulatethevariousphenomenawithinthevirtualenvironment;
(b)thefidelityoftheavailablesimulationtools;
and(c)ultimately,theabilityofthedesignertocorrectlymodelthedesiredsystemandsuitablyinterprettheresults.
Fig.7
AsingleWMRbaseundergoingtestingwithinthe(a)virtualprototypingframework;
and(b)hardware-in-the-loop(HIL)testingframework
Hardware-in-the-loopexperimentation
Weemployahardware-in-the-loop(HIL)methodologyforrapidexperimentalverificationofthereal-timecontrollersontheelectromechanicalmobilemanipulatorprototypes.EachindividualWMRisconstructedusingtwopoweredwheelsandtwounactuatedcasters.Conventionaldisc-typerearwheels,poweredbygear-motors,arechosenbecauseofrobustphysicalconstructionandeaseofoperationinthepresenceofterrainirregularities.Passiveballcastersarepreferredoverwheelcasterstosimplifytheconstraintsonmaneuverabilityintroducedbythecasters.Themountedmanipulatorarmhastwopassiverevolutejointswithaxesofrotationparalleltoeachotherandperpendiculartothebaseofthemobileplatform.Thefirstjointisplacedappropriatelyatthegeometriccenterontopframeoftheplatform.Thelocationofthesecondjointcanbeadjustedtoanypositionalongtheslottedfirstlink.Thesecondlinkitselfisreducedtoaflatplatesupportedbythesecondjoint.Eachjointisinstrumentedwithopticalencoderthatcanmeasurethejointrotations.Thecompletelyassembledtwo-linkmobilemanipulatorisshowninFig.1(c).
Thesecondmobilemanipulator(seeleftmoduleofFig.1(b)and(d))employsthesameoveralldesignbutpossessesamotoratthebasejointofthemountedtwo-linkarm.Themotormaybeusedtocontrolthejointmotionalongapredeterminedtrajectory(whichcanincludebraking/holdingthejointatapredeterminedposition).Whenthemotorisswitchedoffthejointnowrevertstoapassivejoint(withmuchgreaterdamping).Themotorisincludedforpermittingfutureforce-redistributionstudies.Inthispaper,however,themotorisusedsolelytolockthejointpreventself-motionsofthearticulatedlinkageforcertainpathologicalcases(Bhattet
al.,2005;
TangandKrovi,2004).
PWM-outputmotordrivercardsareusedtodrivethegearmotors;
andencodercardsmonitortheencodersinstrumentingthevariousarticulatedarms.ThisembeddedcontrollercommunicateswithadesignatedhostcomputerusingTCP/IPforprogramdownloadanddatalogging.ThehostcomputerwithMATLAB/Simulink/RealTimeWorkshop8providesaconvenientgraphicaluserinterfaceenvironmentforsystem-levelsoftwaredevelopmentusingablock-diagrammaticlanguage.Thecompiledexecutableisdownloadedoverthenetworkandexecutesinreal-timeontheembeddedcontrollerwhileaccessinglocallyinstalledhardwarecomponents.
Inparticular,theabilitytoselectivelytestcomponents/systemsatvariouslevels(e.g.individualmotors,individualWMRsorentiresystems)withoutwearingoutcomponentsduringdesigniterationswasveryuseful.Figure7(b)illustratestheimplementationofsuchasystemononeoftheWMRs.Numerouscalibration,simulationandexperimentalstudiescarriedoutwiththisframework,attheindividual-levelandsystem-level,arereportedinAbou-Samah(2001).
Experimentalresults
Forthesubsequentexperiments,9weprescribetheinitialconfigurationofthetwo-modulecompositesystem,asshowninFig.8.Specifically,wepositionthetwoWMRssuchthatMPAislocatedatarelativepositionof
andwitharelativeorientationdifferenceof
withrespecttoMPB.
Forfixedlink-lengthsthisinherentlyspecifiesthevaluesofthevariousconfigurationanglesasshowninTable1.
Table1
Parametersfortheinitialconfigurationofthetwo-modulecompositewheeledsystem(seeFig.8fordetails)
Linklengthsofthearticulation
L1
0.28m(11in)
L2
Relativeanglesoftheconfigura
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