液压挖掘机的半自动控制系统.docx
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液压挖掘机的半自动控制系统.docx
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液压挖掘机的半自动控制系统
Semi-automaticcontrolsystemforhydraulicshovel
Abstract:
Asemi-automaticcontrolsystemforahydraulicshovelhasbeendeveloped.Usingthissystem,unskilledoperatorscanoperateahydraulicshoveleasilyandaccurately.Amathematicalcontrolmodelofahydraulicshovelwithacontrollerwasconstructedandacontrolalgorithmwasdevelopedbysimulation.Thisalgorithmwasappliedtoahydraulicshovelanditseffectivenesswasevaluated.Highcontrolaccuracyandhigh-stabilityperformancewereachievedbyfeedbackplusfeedforwardcontrol,nonlinearcompensation,statefeedbackandgainschedulingaccordingtotheattitude.q2001ElsevierScienceB.V.Allrightsreserved.
Keywords:
Constructionmachinery;Hydraulicshovel;Feedforward;Statefeedback;Operation
1.Introduction
Ahydraulicshovelisconstructionmachinerythatcanberegardedasalargearticulatedrobot.Diggingandloadingoperationsusingthismachinerequireahighlevelofskill,andcauseconsiderablefatigueeveninskilledoperators.Ontheotherhand,operatorsgrowolder,andthenumberofskilledoperatorshasthusdecreased.Thesituationcallsforhydraulicshovels,whichcanbeoperatedeasilybyanyperson1–5.
Thereasonswhyhydraulicshovelrequiresahighlevelofskillareasfollows.
.1.Morethantwoleversmustbeoperatedsimultaneouslyandadjustedwellinsuchoperations.
Thedirectionofleveroperationsisdifferentfromthatofashovel’sattachmentmovement.
Forexample,inlevelcrowdingbyahydraulicshovel,wemustoperatethreelevers(arm,boom,bucket)simultaneouslytomovethetopofabucketalongalevelsurface(Fig.1.)Inthiscase,theleveroperationindicatesthedirectionoftheactuator,butthisdirectiondiffersfromtheworkingdirection.
Ifanoperatoruseonlyoneleverandotherfreedomsareoperatedautomatically,theoperationbecomesveryeasily.Wecallthissystemasemi-automaticcontrolsystem.
Whenwedevelopthissemi-automaticcontrolsystem,thesetwotechnicalproblemsmustbesolved.
1.Wemustuseordinarycontrolvalvesforautomaticcontrol.
2.Wemustcompensatedynamiccharacteristicsofahydraulicshoveltoimprovetheprecisionofcontrol
Wehavedevelopedacontrolalgorithmtosolvethesetechnicalproblemsandconfirmtheeffectofthiscontrolalgorithmbyexperimentswithactualhydraulicshovels.Usingthiscontrolalgorithm,wehavecompletedasemi-automaticcontrolsystemforhydraulicshovels.Wethenreporttheseitems.
2.Hydraulicshovelmodel
Tostudycontrolalgorithms,wehavetoanalyzenumericalmodelsofahydraulicshovel.Thehydraulicshovel,whoseboom,arm,andbucketjointsarehydraulicallydriven,ismodeledasshowninFig.2.Thedetailsofthemodelaredescribedinthefollowing.
2.1.Dynamicmodel6
Supposingthateachattachmentisasolidbody,fromLagrange’sequationsofmotion,thefollowingexpressionsareobtained:
Where
Andg=gravitationalacceleration.θiisthejointangle,τiisthesupplytorque,liistheattachmentlength,lgiisthedistancebetweenthefulcrumandthecenterofgravity,miisthemassoftheattachment,Iiisthemomentofinertiaaroundthecenterofgravity(subscriptsi=1–3,meanboom,arm,andbucket,respectively).
1.2.Hydraulicmodel
Eachjointisdrivenbyahydrauliccylinderwhoseflowiscontrolledbyaspoolvalve,asshowninFig.3.Wecanassumethefollowing:
1.Theopenareaofavalveisproportionaltothespooldisplacement.
2.Thereisnooilleak.
3.Nopressuredropoccurswhenoilflowsthroughpiping.
4.Theeffectivesectionalareaofthecylinderisthesameonboththeheadandtherodsides.
Inthisproblem,foreachjoint,wehavethefollowingequationfromthepressureflowcharacteristicsofthecylinder:
When
;
where,Ai=effectivecross-sectionalareaofcylinder;hi=cylinderlength;Xi=spooldisplacement;Psi=supplypressure;P1i=cylinderhead-sidepressure;P2i=cylinderrod-sidepressure;Vi=oilvolumeinthecylinderandpiping;Bi=spoolwidth;γ=oildensity;K=bulkmodulusofoil;andc=flowcoefficient.
1.3.Linkrelations
InthemodelshowninFig.1,therelationbetweenthecylinderlengthchangerateandtheattachmentrotationalangularvelocityisgivenasfollows1)boom
(2)arm
(3)bucket
when
时,
1.4.Torquerelations
FromthelinkrelationsofSection2.3,thesupplytorqueτiisgivenasfollows,takingcylinderfrictionintoconsideration:
Where,CciistheviscousfrictioncoefficientandFiiskineticfrictionalforceofacylinder.
1.5.Responsecharacteristicsofthespool
Spoolactionhasagreateffectoncontrolcharacteristics.Thus,weareassumingthatthespoolhasthefollowingfirst-orderlagagainstthereferenceinput.
Where,
isthereferenceinputofspooldisplacementand
isatimeconstant.
3.Anglecontrolsystem
AsshowninFig.4,theangleθisbasicallycontrolledtofollowthereferenceangleθγbypositionfeedback.Inordertoobtainmoreaccuratecontrol,nonlinearcompensationandstatefeedbackareaddedtothepositionfeedback.Wewilldiscussdetailsofthesealgorithmsasfollows.
3.1.Nonlinearcompensation
Intheordinaryautomaticcontrolsystems,newcontroldevicessuchasservovalvesareused.Inoursemi-automaticsystem,inordertorealizethecoexistenceofmanualandautomaticoperations,wemustusethemaincontrolvalves,whichareusedinmanualoperation.Inthesevalves,therelationbetweenspooldisplacementandopenareaisnonlinear.Then,inautomaticoperation,usingthisrelation,thespooldisplacementisinverselycalculatedfromtherequiredopenarea,andthenonlinearityiscompensated(Fig.5.)
3.2.Statefeedback
BasedonthemodeldiscussedinSection2,ifthedynamiccharacteristicsforboomanglecontrolarelinearizedinthevicinityofacertainstandardcondition(spooldisplacementX10,cylinderdifferentialpressureP110,andboomangleθ10),theclosed-looptransferfunctioncanbeexpressedby
where,Kpispositionfeedbackgain;and
Thissystemhasacomparativelysmallcoefficienta1,sotheresponseisoscillatory.Forinstance,ifinourlargeSK-16hydraulicshovel,X10is0,thecoefficientsaregivenasa0=2.7
10
a1=6.0
10
a2=1.2
10
Addingtheacceleration2feedbackofgainK,tothis(theupperloopinFig.4).theclosedlooptransferfunctionisgivenas
Addingthisfactor,thecoefficientofS
becomeslarger,thus,thesystembecomesstable.Inthisway,accelerationfeedbackiseffectiveinimprovingtheresponsecharacteristics.
However,itisgenerallydifficulttodetectaccelerationaccurately.Toovercomethisdifficulty,cylinderforcefeedbackwasappliedinsteadofaccelerationfeedback(thelowerloopinFig.4).Inthiscase,cylinderforceiscalculatedfromdetectedcylinderpressureandfilteredinitslower-frequencyportion[7,8].Thisiscalledpressurefeedback.
4.Servocontrolsystem
Whenonejointismanuallyoperatedandanotherjointiscontrolledautomaticallytofollowthemanualoperation,aservocontrolsystemmustberequired.Forexample,asshowninFig.6,inthelevelcrowdingcontrol,theboomiscontrolledtokeepthearmendheightZ(calculatedfromθ1andθ2.torefer-12enceZr.Inordertoobtainmoreaccuratecontrol,thefollowingcontrolactionsareintroduced.
Fig.6.BlockdiagramofcontrolsystemŽZ..
4.1.Feedforwardcontrol
CalculatingZfromFig.1,weobtain
DifferentiatingbothsidesofEq.Ž8.withrespecttotime,wehavethefollowingrelation,
Thefirsttermoftheright-handsidecanbetakenastheexpression(feedbackportion)toconvertZ˙to
1,andthesecondtermoftheright-handsideistheexpression(feedforwardportion)tocalculatehowmuchθ1shouldbechangedwhenθ2ischangedmanually
Actually,θ2isdeterminedusingthedifference2valueof△θ2.Tooptimizethefeedforwardrate,feedforwardgainKffistuned
Theremaybeamethodtodetectandusethearmoperating-levercondition(i.e.angle)insteadofarmangularvelocity,sincethearmisdrivenatanangularvelocitynearlyproportionaltothislevercondition.
4.2.Adaptivegainschedulingaccordingtotheattitude
Inarticulatedmachineslikehydraulicshovels,dynamiccharacteristicsaregreatlysusceptibletotheattitude.Therefore,itisdifficulttocontrolthemachinestablyatallattitudeswithconstantgain.To
solvethisproblem,theadaptivegainschedulingaccordingtotheattitudeismultipliedinthefeedbackloop(Fig.6).AsshowninFig.7,theadaptivegain(KZorKθ)ischaracterizedasafunctionoftwovariables,
2andZ.
2meanshowthearmisextended,andZmeanstheheightofthebucket.
5.Simulationresults
ThelevelcrowdingcontrolwassimulatedbyapplyingthecontrolalgorithmdescribedinSection4tothehydraulicshovelmodeldiscussedinSection2.(Inthesimulation,ourlargeSK-16hydraulicshovelwasemployed)Fig.8showsoneoftheresults.Fivesecondsafterthecontrolstarted,loaddisturbancewasappliedstepwise.Fig.9showstheuseoffeedforwardcontrolcanreducecontrolerror.
Fig.7Gainschedulingaccordingtotheattitude.
Fig.8Simulationresultoflevelcrowding
Fig.9EffectoffeedforwardcontroloncontrolerrorofZ.
6.Semi-automaticcontrolsystem
Basedonthesimulation,asemi-automaticcontrolsystemwasmanufacturedfortrial,andappliedtotheSK-16shovel.Performancewasthenascertainedbyfieldtests.Thissectionwilldiscusstheconfigurationandfunctionsofthecontrolsystem.
Fig.10Schemaofcontrolsystem
6.1.Configuration
AsillustratedinFig.10,thecontrolsystemconsistsofacontroller,sensors,man–machineinterface,andhydrauliccontrolsystem.Thecontrol
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