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FORCE

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FORCEforce,FORCE,Force

    FORCE

CHINESEJOURNALOFMECHANICALENGINEERnG

    ;Vo1.21,No.6,2008

    ;DOI:1O.3901/CJME.2008.06.001.availableonlineatwww.cjmenet.com;www.cjmenet.com.an

    ;GONGMingde

    ;ZHAODingxuan

    ;ZHANGHongyan

    ;JIACuiling

    ;CollegeofMechanicalScienceand

    ;Engineering,

    ;JUinUniversity,

    ;Changchun130022.China

    ;FORCEFEEDBACKMODELOF

    ;ELECTRO.HYDRAULICSERVO

    ;TELE.OPERATlONROBOTBASED

    ;ONVELOCITYCONTROL

    ;Abstract:etele.operationroboticsystemwhichconsistsofa

    excavatorastheconsU‟uctionroboL

    ;andtwoioysticksforoperatingtherobotfromasafeplaceareusefu1forperformingrestorationin

    ;damagedareas.Inordertoaccomplishaprecisetask.theoperatorneedstofee1arealisticsenseof

    ;taskforcebroughtaboutfromafeedbackforcebetweentheforkgloveofslaverobotandanfamiliar

    ;environment.Anovelforcefeedbackmode1isproposedbasedonvelocitycontrolofcylinderto

    ;determineenvironmentforceactingonforkglove.Namely,thefeedbackforceisformedbytheerror

    ;ofdisplacementofjoystickwithvelocityanddrivingforceofpiston,andthegainiscalculatedbyfhe

    ;drivingforceandthresholdofdrivingforceofhydrauliccylinder.Moreover,thevariablegain

    ;improvedalgorithmisdevelopedtoovercomethedefectforgraspingsoftobject.Experimentalresults

    ;f0rf0rkglovefreedomofroboticsystemareprovidedtodemonstratethedevelopedalgorithmis

    ;availableforgraspingsoftobject.

    ;Keywords:ConstructionrobotTele.operationB

    ateralelectrohydraulicservocontro1

;Velocitycontro1Forcefeedbackmode1

    ;aD一一Cr0ss-sectionalareaofpiston,m

    ;b——Dampcoefficientofjoystick,N?s/m

    ;G(s)——nansferfunctionofjoystick(Input:torqueto ;joystickandoutput:displacementofjoystick) ;

    ;Gainofservoamplifier,mA/V

    ;——

    ;Difrerentia1gainofmaster,N?m

    ;——

    ;F1owrategain,mZ/s

    ;

    ;GainofseI‟vovalve.m/mA

    ;m——Massofpiston,kg

    ;——

    ;PressuresinBchambersofcylinder,Pa

    ;一一

    ;Loadpressure,Pa

    ;——

    ;Timeconstantofmaster,s

    COntmlinputtoslave,V ;“s

    ;Ym——Displacementsofmasterside,m

    ;V——Vel0cityofpiston,m/s

    ;v0——Nominalquantityofv(v0m=0.10),m/s

    ;——

    ;Nondimensionalquantityofv(=Vm/V0)

    ;——

    ;Nondimensionalquantityofy.(s0s)

    ;fm——Inputtorquetojoystick,N?m

    ;n——Naturalangularfrequency,rad/s

    ;0INTRoDUCTIoN

    ;NoTATIoNS

    ;Atele-operationroboticsystembasedonbilatera1controlis ;usefulforperformingrestorationindamagedareas.andalsoin ;extremeenvironmentssuchasspace,seabed,anddeep ;undergroundL”.Theworld‟sfirstremotecontrolsystemwasa

    ;mechanica1master-slavemanipulatorcalledANL(Argonne ;NationalLaboratory)ModelMldevelopedbvGOERTZ.

    ;Sinceitsintroduction.thefieldoftele.operationhasexpandedits

    ;seope.Forexample.tele.operationhasbeenusedinthehandling

    ;ofradioactivematerials,sub.seaexploration.andservicing.Its

    ;appliancehasalsobeendemonstratedinspace,construction, ;forestry,andmining.Asanadvancedformofteleoperation.the

    ;conceptof”tele.presence”wasproposedbvMINSKYjJ.

    ;Tele.presenceenablesahumanoperatortoremotelyperformtasks ;ThisprojectissupposedbyNationalNaturalScienceFoundationofChina ;(No.50475011).ReceivedFebruary13,2007;receivedinrevisedform ;October20;acceptedOctober24,2008

    ;b...........——Viscousdampingcoefficient

    ;ofpiston,N?s/m

    ;——

    ;DriVingforcetoslave,N

    ;——

    ;Pr0portiona1anddifferentialcoecient

    ;ofmaster,N

    ;ktm——T0rquegainofmaster,N?m

    ;——

    ;Pressuregain,m/kg

    ;——

    ;Delaytimeofjoystick,s

    ;P——PressuresinAchamberofcylinder.Pa

    FlOwrate,m/s ;qL——

    ;——

    ;Gain

    ;——

    ;N0ndimensionalquantityof(=Tr/f0r)

    ;——

    ;Displacementofspool,m

    ;s——Displacementsofslaveside,m

    ;——N0mina1quantityofy(.vom=0.06),m

    ;ym——Nondimensionalquantityofy(YmYo)

    ;)——Nominalquantityofy.(yos=0.3),m

    ;——

    ;Dampingratio

    ;——

    ;Reactiontorquetojoystick,N?m

    ;withdexterity,makingtheuserfee1thatshe/heispresentinthe ;remotelocation.Almostatthesametime.”tele.existence”.a

    ;similarconceptwasproposedbyTACHI,etalLqJ.

    ;Intllisstudy,weinvestigatedatele.roboticssystemfora ;constructionmachine.Thesystemconsistsofaservo.conoiled

    ;constructionrobot,andtwoioysticksforoperatingtherobotfrom ;aremoteplace.Aforkgloveisequippedwiththefrontendofthe ;excavatorasahandforgraspingtaskonects.Themasterandthe ;slaveinthissystemcorrespondtothejoysticksandtheforkglove ;controlledbilaterallybyanoperator.

    ;Asanapplicationforexcavatorcontro1.bilateralmatched

    ;impedancetele.operationwasdevelopedattheUniversityof

    ;BritishColumbiaL.Thevalsohavedevelopedavirtual ;excavatorsimulatorsuitableforexperimentationwithuser ;interfaces.controlstrategies.andoperatortrainingt”.This

    ;simulatorcomprisesmachinedynamicsasanimpedancemodel,a ;ground-bucketinteractionmodel,andagraphicaldisplay ;sub-system.Intheirexperiment.anactualexcavatorisoperated ;bybilateralcontrolmethod,andtheforcefeedbackcanbewell ;feltbytheoperator.

    ;„2GONGMingde.etal:Forcefeedbackmodelofelectro—hydraulicservotele-operationrobotbasedonvelocitycontrol

    ;Inorderimprovethecontrollabilityofthesystem.we

    ;examinedthemasterandslavecono1methodbetweenjoysticks

    ;androbotarmst,Refs.8-91bothdiscussedtheforce

    ;presentationofthetaskfieldforalloperatorL….Becausetheforce

    ;presentationistheessentialinforrnationofslavesidetothe ;operator,thosestudiesmainlyfocusedonpositioncontrolof ;master.slavesideanddevelopedforcefeedbackmodels.Namely, ;theoperatorcontrolsthedisplacementofpistonofslavesideby ;thedisplacementofoystick.Thesemethodscanrealizehi2h1y ;sensualforcefeedbacktoioystickt.Butthestrangesensingwill ;befeItwhentheoperatormovedthe{oystickusing

    ;position.positioncontro1.Manyoperatorsgetusedto ;positionvelocitycontro1becausethismethodisastandard ;practiceforbilateralcontro1.Soweapplythisnorma1methodthat ;theoperatorcontrolsthevelocityofpistonofslavesidebythe ;displacementofioystick.Moreover,thenewforcefeedback ;modelisdeveloped.Experimenta1resultsforforkglovefreedom ;ofroboticsystemareprovidedtodemonstratethedeveloped ;algorithmisavailableforgraspingsoRobject.

    ;1MATHEMATICALMoDELoFMASTER.-

    ;SLAVESYSTEM

    ;Experimentalapparatusconsistsoftheioystickandthe ;tele.operatedconstructionrobot.Thejoystickf‟‟SideWinderForce

    ;Feedback2”,MicrosoRCo.,Ltd.)canbeoperatedtotheX.axis

    ;andYaxisdirections.Displacementsofthejoystickaredetected ;bypositionsensors.ADCmotorisconnectedundertheioystick, ;andthereactionforcefromtheforkgloveisfedbacktothe ;operatorthroughareducerconnectedtotheDCmotor~The ;hydrauliccylindersfordrivingtheconstructionrobotare ;controlledbytheservovalves.Thedisplacementsofthecylinders ;aredetectedbymagneticstrokesensorswhichareembeddedin ;thepistons.Thedrivingforcesaredetectedbyapairofpressure ;sensorsattachedtothecylinders.

    ;1.1Mathematicalmodelofmastersystem

    ;Inordertogetthemathematicalmodelofthemastersystem. ;weperformedaparameteridentificationoftheioystick.The ;identificationresultshowedastepresFIprisecurveofthe ;displacementYmtotheinputtorqueoftheioystick.Fromthis ;result,theansferfunctionofthe{oystickwasestimatedasoneof ;thefirstorderlagsystem(=O.125s,=0.18N)withatime ;lagelement(=O.08s).Transferfunctionofjoystickisas ;?)=exp()(1)

    ;1.2Mathematicalmodelofslavesystem

    ;Inthisstudythesameslavesystemastheoneinprevious ;pal:}erswasused.Therefore.themathematicaImodeltusedfor ;thisslavesystemisalsothesameasinthepreviousone. ;Experimentalresultsforonedegree.of-freedomaregivento ;demonstratetocylinderoff0rkglove.

    ;ThemotionequationoftheservovalveisasEq.(2)

    ;+2i+:x=kakco:”(2)

    ;TheequationofmotionofthepistonisasEq.(3)

    .PI ;my+=

    ;PlPapb

    ;TherelationsforflowrateqLareasfollows

    ;qt:kxxkpPL

    ;qI=ap

    ;(3)

    ;(4)

    ;(5)

    ;Astheresult,themathematicalmodeloftheslavesystemis ;representedbyEq,(2)toEq.(5).

    ;2FoRCEFEEDBACKMoDELBASEDoN

    ;VELoCITYCoNTRoL

    ;2.1Constantthresholdofdrivingforcefeedbackmodel ;Inthjsart,wecomparedpositioncontrolmethodand

    ;developedvelocityeontro1method.Thedifferenceofismethod

    ;isthatthefeedbackvalueisthenon.dimensiona1valueofvelocity ;ofpistoninsteadofthenon.dimensiona1valueofdisplacementof ;piston.Thecono1erroristhedifferencebetweenthe

    ;non.dimensionalvalueofvelocityofpistonandthe ;nondimensionalvalueofdisplacementof{oystick.Theposition ;ofioystickreachesmiddleposition(zeroposition),theveloeityof ;pistonequalstozero.Themorethedisplacementofioystickis, ;themorethevelocityofpistonis.Sowegotthevelocityofpiston ;trackingonthedisplacementofioystick.ThecontrollerisalsoPD ;controller.Theblockdiagramforrepresentingthecontrolmethod ;isillustratedinFig.1.Inthisstudy,thedampofioystickbis ;consideredtobezerobecausethevalueofitrelativelyverysmal1.

    ;ThereactiontorquetothejoystickisgivenbyEq.f6) ;=

    ;Tr=[(ym)+t(6)

    ;Masterside

    ;3c?)?)t

    ;)t,

    ;f<

    ;Fig.1Schematicdiagramofmasterslavesystemofforce

    ;feedbackmodelbasedonvelocitycontrol

    ;InEq.(7),theparameters/thataresummationoffriction, ;inertialforceandweightofpistonarecalledexpanding/ ;contractingmotionsthresholdofdrivingforces.Thevaluecannot ;beeasilygotandberegardedasconstantvalueinthisresearch. ;Whenanexternalforcegeneratedforgraspingataskobjectbythe ;fbrkgloveisabsent,thevalueis=2.0kN,=1.4kN).

    ;Furthermore.themaximumdrivingfcIrcetothecylinderin ;expandingandcontractingmotionsisdefinedasma)andm”

    ;11.7kN,mi=-6.8l(N).Therefore,thegainTis

    ;determinedbydrivingforceofpiston.

    ;Theexperimentalresultsformovingioysfickineespace

    ;withoutgraspingobjectareshowninFig.2.InFig.2athesolid ;lineisthedisplacementofioystickandthebroken1ineisthe ;velocityofpiston.Wecanfindtheerroroftwo1inesisverysmal1. ;ThereactionforcetoioystickcanbeinferredfromEqs.(61and ;(7).AsshowninFig.2bdrivingforceisintherangeofthreshold ;ofdrivingforces,Tequalstozero.Thereactionforcetooystick ;equalstozero.

    ;Fromtheexperimentalresults,whentheexternalforceis ;absentintheforkglove,meioystickbecomessmoothbecausethe ;reactionforcetoioystickiszero.Theresultcanbeseenflr0mFig. ;2d,thatis,theactLIa1fbrceinf-0m1atiOnofslavesidecanbewel1 ;feltbytheopemt0r.

    ;一一一一

    ;CHINESEJOURNALOFMECHANICALENGINEERING?3?

    ;1.0

    ;1O

    ;010203040506065

    ;Timet/s

    ;(a)Displacementofjoystickandvelocityofpiston ;Timet/s

    ;1Drivingforceofpiston

    ;Timet/s

    ;(c)Displacementofpiston

    ;10203040506O65

;Timet/s

    ;(d)Reactionforcetojoystick

    ;Fig.2Movejoystickinfreespace

    ;Ontheotherhand,whentheforkglovegraspssoftobiect ;stepbystep,especiallywithslowspeed,thereactionforceto ;joystickisnotsatisfactory.Theexperimentalresultsmovingthe ;joysticktograspsoftobjectareshowninFig.3.InthepartAof ;Fig.3a,thejoystickdoesn‟tmove;inthepartB,movingthe

    ;joystickgraspsthetire;inthepartC,thetireisgrasped,andinthe ;partD,thetireisunlocked.Thereactionforcetojoystickcanbe ;inferredfromEq.(6)andEq.(7).Fig.3bshowsthedrivingforce ;isnotintherangeofthresholdofdrivingforcesandTdoesnot ;equaltozero.Thereactionforcetooystickisnotzero.Fromthe ;experimentalresults,wecanfindtheresultfromFig.3d,ivthe ;partC.operatorcanfee1reactionforcebutitissosmal1that ;operatorcannotfee1theactualforcestepbysteDtof0rkglove. ;Whentheexternalforceisexistandchangesslowlyinthefork ;glove.theactua1forceinformationofslavesidecannotbewell ;feltbyoperator.

    ;Themainlyreasonisthatthedrivingforcedoesnot

    ;necessarilyexceedtheregionof??.n1isunsatisfa.

    ;ctorysituationoccursinataskwhenthefbrkglovegraspsasoft ;objectinaslowvelocity.First,displacementsofthejoystickand ;velocityofthefbrkglovepiston,rmand,areshowninFig.3 ;againsttimetintheabscissa.TheshortverticallinemarkedinFig. ;3indicatesthestartingpointofthetask.AtierstartingthepartC. ;asisshowninFig.3.thetaskofgraspingthetirecontinuesinthis ;mannerinwhichthedisplacementofpistonreachesgrasping ;maximalpositionandunlocksitstepbystepandthen.atabout ;90s,thetireiscrushedcompletely.Fromthedrivingforceand ;reactionforcefigure.itisobservedthatthedrivingforceand ;reactionarealsomaxima1.Butinthepictureofthedrivingforce ;totheforkgloveisshowninFig.3b.ThebrokenlinesinFig.3 ;denotethethresholdofdrivingforces,.AsisseeninFig.3, ;thedrivingf0rceisinrangeofthresholdofdriving ;forces?fs?,whenthedrivingforceissmallatbeginningof

    ;grasping.InEqs.(6)and(7),thegainTequalstozero,andthe ;reactionforceto1oysfickalsoequalstozero.Thereforethe ;proposedalgorithmcannotreflectthefactua1forcetoforkglove. ;Inmisstudy,wefoCUSonsuchaproblemasisseenhereandaim ;atovercomingtheproblembyusingvelocitycontrolmethod. ;

    ;

    ;>

;

    ;.

    ;g

    ;E

    ;

    ;?

    ;

    ;——

    ;

    ;8B.(

    ;1

    ;[

    ;

    ;I

    ;i

    ;0Timet/s130

    ;(a)Displacementofjoystickandvelocityofpiston ;Timet/s

    ;(b)Drivingforceofpiston

    ;2

    ;&

    ;C

    ;

    ;

    ;Timet/s

    ;(C)Displacementforceofpiston

    ;Timet/s

    ;(d)ReactionforcetoJoystick

    ;Fig.3Graspingatirewithconstantthresholdofdrivingforces

    ;Thisproblemisconsideredtobeoriginatedfromthenext ;reasons.InthecontrolmethodbasedonEq.(7),eachvalueof ;505

    ;OO

    ;50

    ;E,{芒量uBIds(

    ;OO0

    ;00

    ;2岔口0l18

    ;„4‟GONGMingde.etal:Forcefeedbackmodelofelectro

    ~draulicservotete-operationrobotbasedonvelocitycontrol ;thresholdofdriivingf0rces,istreatedasconstant.Forthis ;reason,thereactiontorquecanappearasseenjtnFig.3whenthe

    ;drivingfo)rceofthef0rkglovefsexceedsthethresholdasseenin

    ;Fig.6.Ontheotherhand.intheregionof??sincethe

    ;gainTbecomeszerointhdssituation.thereactionforcedoesnot ;appearthoughtheforkgloveisgraspingataskobject. ;2.2Improvedthresholdofdrivingforcefeedbackmodel ;Inordertoovercometheprobleminthepreviousmexhod.in ;thebeginning,thedrivingforceofthehydrauliccylinderwas ;measuredaltongwiiththepistonvelociItyv,thustoobtainv

    ;character]istics.

    knownthatthedrivingforceisindicatedasa ;Itiswell

    ;functionofthevelocityv.Soiitiisbettertoadoptavariable ;thresholdofdrivingfc)rcechangingwitththevelocityv.j~nsteadof ;fixedthresholds,.Intheimprovedmethod,.therefore,we ;adoptthevariablethresholdDre.Fromtheexperimental,the

    ;thresholdfpisdescribedbyEq.(8)

    ;18v6v:m10.0?l/=

    ;(9.+5.0.4)×y<

    ;ByapplyingEq.(8),itisexpectedthatthenewmethodis ;abletodealwithagraspingmotionoftimedependence,e.g., ;slowmovinggrasping,andalsotofeedbacksensitivelyareaction ;fo:)rceofanextemallfo:)rce,.moreoverjncreasingmaneuverabilitty ;throughcontrollingvelocil[,,ofpiston.

    ;Invelocitycontrolmet1)od,thereactionforcetojoysticksf, ;isshownjtnEq.f61.desoribedbytherelationdependingonthe ;differencebetweenthtedisplacementofioystickandthevelocity ;ofpistonaswellasthedrivingfo.rce.Atthesametime.theinertia ;fo:rceandfrictionofpistonarenotconsidered.Asaresult,the ;reactionforcetoioystickfoftheimprovedalgori(thmis ;writtenbyEq.(9)andthegainTisdeterminedbyEq.(10) ;T=

    ;O

    ;r=丁【(ym)+](9)

    ;0<二盘

    ;.

    ;0

    ;

    ;

    ;?If

    ;?l0nfl0)

    ;?1<0n<

    ;AsisshowninEq.(9),thegainTchangesiItsvaluewith ;thechangeinthedrivingforcethreshold

    ;ThefeaturesoftheimprovedmethodbasedonEqs.f91and ;(10)alestatedasfollows.ifthedrivingforcetopistonfisbigger ;thanthethresholdregivenbyEq.(10),thedifferencebetween ;themitsregardedastheexternalforcetothepiston,andthusthe

    ;correspondingreactionfolrcecanbegenerated.Itistherefcpre ;expectedinthismethodthattheoperatorcanfeelthegrasping ;forcetothefolgloveverywel1.evenift‟tisdoingaslow—move

    ;ingraspingofsoftobject.

    ;AItierapplydngtheimprovedmethodtothemaster.slave ;system,.weconfirmtheavailab41ityofthemethodbyexperiment. ;CorrespondingtotheexperimentalresultsshowninFig.4,a ;taskofgraspingatirewithslowvelo@tywastestedbythe ;velocitycontrolmethodstepbystep.InFig.4athepartA.the ;joystickdoesn‟tmove;inthepartB,movingthejoystickgrasps

    ;thetire;inthepartC,thetireisgrasped,andinthepartD.thetire ;:isunlocked.

    ;A,fterstartingthepartC,asisshowninFig.4.operatorcan ;feelreactionfo)teeverywell,thetaskofgraspingthetire ;continuesinthdsmann

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