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Semi-auto__ticcontrolsystemforhydraulicshovelAbstractAsemi-auto__ticcontrolsystemforahydraulicshovelhasbeendeveloped.Usingthissystemunskilledoperatorscanoperateahydraulicshoveleasilyandaccurately.A__the__ticalcontrolmodelofahydraulicshovelwithacontrollerwasconstructedandacontrolalgorithmwasdevelopedbysimulation.Thisalgorithmwasappliedtoahydraulicshovelanditseffectivenesswasevaluated.Highcontrolaccuracyandhigh-stabilityperfor__n__wereachievedbyfeedbackplusfeedforwardcontrolnonlinearcompensationstatefeedbackandgainsche____ngaccordingtotheattitude.Keywords:Construction__chinery;Hydraulicshovel;Feedforward;Statefeedback;Operation
1.IntroductionAhydraulicshovelisaconstruction__chinerythatcanberegardedasalargearticulatedrobot.Diggingandloadingoperationsusingthis__chinerequireahighlevelofskillandcauseconsiderablefatigueeveninskilledoperators.Ontheotherhandoperatorsgrowolderandthenumberofskilledoperatorshasthusdecreased.Thesituationcallsforhydraulicshovelswhichcanbeoperatedeasilybyanypersonw1–5x.Thereasonswhyhydraulicshovelrequiresahighlevelofskillareasfollows.
1.Morethantwoleversmustbeoperatedsimultaneouslyandadjustedwellinsuchoperations.
2.Thedirectionofleveroperationsisdifferentfromthatofashovel’sattachmentmovement.ForexampleinlevelcrowdingbyahydraulicshovelwemustoperatethreeleversŽarmboombucket.simultaneouslytomovethetopofabucketalongalevelsu_____ŽFig.
1..Inthiscasetheleveroperationindicatesthedirectionoftheactuatorbutthisdirectiondiffersfromtheworkingdirection.Ifanoperatoruseonlyoneleverandother_______sareoperatedauto__ticallytheoperationbecomesveryeasily.Wecallthissystemasemi-auto__ticcontrolsystem.Whenwedevelopthissemi-auto__ticcontrolsystemthesetwotechnicalproblemsmustbesolved.
1.Wemustuseordinarycontrolvalvesforauto__ticcontrol.
2.Wemustcompensatedynamiccharacteristicsofahydraulicshoveltoimprovetheprecisionofcontrol.Fig.
1.Levelcrowdingofanexc__atorandframemodelofanexc__ator.Weh__edevelopedacontrolalgorithmtosolvethesetechnicalproblemsandconfirmtheeffectofthiscontrolalgorithmbyexperimentswithactualhydraulicshovels.Usingthiscontrolalgorithmweh__ecompletedasemi-auto__ticcontrolsystemforhydraulicshovels.Wethenreporttheseitems.
2.HydraulicshovelmodelTostudycontrolalgorithmsweh__eto____yzenumericalmodelsofahydraulicshovel.ThehydraulicshovelwhoseboomarmandbucketjointsarehydraulicallydrivenismodeledasshowninFig.
2.Thedetailsofthemodelaredescribedinthefollowing.Fig.
2.Modelofhydraulicshovel.
2.
1.Dynamicmodel
[6]SupposingthateachattachmentisasolidbodyfromLagrange’sequationsofmotionthefollowingexpressionsareobtained:其中K__1g;andgsgr__itationalac__leration.33g3θiisthejointangleτiisthesupplytorqueliistheattachmentlengthlgiisthedistan__betweengithefulcrumandthe__nterofgr__itymiisthe__ssoftheattachmentIiisthemomentofinertiaaroundthe__nterofgr__itysubscriptsis1–3;meanboomarmandbucketrespectively.
2.
2.HydraulicmodelEachjointisdrivenbyahydrauliccylinderwhoseflowiscontrolledbyaspoolvalveasshowninFig.
3.Wecanassumethefollowing:
1.Theopenareaofavalveisproportionaltothespooldispla__ment.
2.Thereisnooilleak.
3.Nopressuredropoccurswhenoilflowsthroughpiping.
4.Theeffectivesectionalareaofthecylinderisthesameonboththeheadandtherodsides.Inthisproblemforeachjointweh__ethefollowingequationfromthepressureflowcharacteristicsofthecylinder:whenwhereAiseffectivecross-sectionalareaofcylinder;hiscylinderlength;Xisspooldispla__ment;Psissupplypressure;Piscylinderhead-sidepressure;Piscylinderrod-sidepressure;Visoilvolumeinthecylinderandpiping;Bisspoolwidth;γsoildensity;K__ulkmodulusofoil;andcsflowcoefficient.
2.
3.LinkrelationsInthemodelshowninFig.1therelationbetweenthecylinderlengthchangerateandtheattachmentrotationalangularvelocityisgivenasfollows:1leg
2.arm
3.bucket当时,Fig.
3.Modelofhydrauliccylinderandvalve.
2.
4.TorquerelationsFromthelinkrelationsofSection
2.3thesupplytorquetisgivenasfollowstakingcylinderfrictionIintoconsideration:WhereCciistheviscousfrictioncoefficientandFiiskineticfrictionalfor__ofacylinder.
2.
5.ResponsecharacteristicsofthespoolSpoolactionhasagreateffectoncontrolcharacteristics.Thusweareassumingthatthespoolhasthefollowingfirst-orderlagagainstthereferen__input.WhereXXisthereferen__inputofspooldispla__mentandTisatimeconstant.
3.AnglecontrolsystemAsshowninFig.4theangleuisbasicallycontrolledtofollowthereferen__angleubypositionfeedback.Inordertoobtainmoreaccuratecontrolnonlinearcompensationandstatefeedbackareaddedtothepositionfeedback.Wewilldiscussdetailsofthesealgorithmsasfollows.Fig.
4.Blockdiagramofcontrolsystem
3.
1.NonlinearcompensationIntheordinaryauto__ticcontrolsystemsnewcontroldevi__ssuchasservovalvesareused.Inoursemi-auto__ticsysteminordertorealizethecoexisten__of__nualandauto__ticoperationswemustusethe__incontrolvalveswhichareusedin__nualoperation.Inthesevalvestherelationbetweenspooldispla__mentandopenareaisnonlinear.Theninauto__ticoperationusingthisrelationthespooldispla__mentisinverselycalculatedfromtherequiredopenareaandthenonlinearityiscompensatedFig.
5.Nonlinearcompensation.
3.
2.StatefeedbackBasedonthemodeldiscussedinSection2ifthedynamiccharacteristicsforboomanglecontrolarelinearizedinthevicinityofa__rtainstandardconditionŽspooldispla__mentXcylinderdifferential10pressurePandboomangleu.theclosed-looptransferfunctioncanbeexpressedbywhereKispositionfeedbackgain;Thissystemhasacomparatively__allcoefficientsotheresponseisoscillatory.Forinstan__ifinourlargeSK-16hydraulicshovelX10is0thecoefficientsaregivenasas
2.7=10y2a1=
6.010a2=
1.
210.Addingtheac__lerationfeedbackofgainKatothistheupperloopinFig.a
4.theclosedlooptransferfunctionisgivenasAddingthisfactorthecoefficientofs2becomeslargerthusthesystembecomesstable.Inthiswayac__lerationfeedbackiseffectiveinimprovingtheresponsecharacteristics.Howeveritisgenerallydifficulttodetectac__lerationaccurately.Toovercomethisdifficultycylinderfor__feedbackwasappliedinsteadofac__lerationfeedbackthelowerloopinFig.
4..Inthiscasecylinderfor__iscalculatedfromdetectedcylinderpressureandfilteredinitslower-frequencyportion[
7.8].Thisiscalledpressurefeedback.
4.ServocontrolsystemWhenonejointis__nuallyoperatedandanotherjointiscontrolledauto__ticallytofollowthe__nualoperationaservocontrolsystemmustberequired.ForexampleasshowninFig.6inthelevelcrowdingcontroltheboomiscontrolledtokeepthearmandheightZcalculatedfrom81and82tor.Inordertoobtainmoreaccuratecontrolthefollowingcontrolactionsareintrodu__d.
4.
1.FeedforwardcontrolCalculatingZfromFig.1weobtainDifferentiatingbothsidesofEq.
8.withrespecttotimeweh__ethefollowingrelationThefirsttermoftheright-handsidecanbetakenastheexpressionfeedbackportiontoconvertZ˙toandthesecondtermoftheright-handsideistheexpressionfeedforwardportiontocalculatehowmuchushouldbechangedwhenuischanged__nually.Actuallyu˙isdeterminedusingthedifferen__valueofDu.TooptimizethefeedforwardratefeedforwardgainKistunned.ffThere__ybeamethodtodetectandusethearmoperating-leverconditioniangle.insteadofarmangularvelocitysin__thearmisdrivenatanangularvelocitynearlyproportionaltothislevercondition.
4.
2.AdaptiÕegainsche____ngaccordingtotheattitudeInarticulated__chineslikehydraulicshovelsdynamiccharacteristicsaregreatlysus__ptibletotheattitude.Thereforeitisdifficulttocontrolthe__chinestablyatallattitudeswithconstantgain.Tosolvethisproblemtheadaptivegainsche____ngaccordingtotheattitudeismultipliedinthefeedbackloopFig.
6..AsshowninFig.7theadaptivegainKZorKu.ischaracterizedasafunctionoftwovariablesandZ.meanshowthearmisextendedandZmeanstheheightofthebucket.
5.SimulationresultsThelevelcrowdingcontrolwassimulatedbyapplyingthecontrolalgorithmdescribedinSection4tothehydraulicshovelmodeldiscussedinSection
2.InthesimulationourlargeSK-16hydraulicshovelwasemployed..Fig.8showsoneoftheresults.Fivesecondsafterthecontrolstartedloaddisturban__Fig.
6.BlockdiagramofcontrolsystemZ.Fig.
7.Gainsche____ngaccordingtotheattitude.wasappliedstepwise.Fig.9showstheuseoffeedforwardcontrolcanredu__controlerror.
6.Semi-auto__ticcontrolsystemBasedonthesimulationasemi-auto__ticcontrolsystemwas__nufacturedfortrialandappliedtotheSK-16shovel.Perfor__n__wasthenas__rtainedbyfieldtests.Thissectionwilldiscusstheconfigurationandfunctionsofthecontrolsystem.
6.
1.ConfigurationAsillustratedinFig.10thecontrolsystemconsistsofacontrollersensors__n–__chineinte_____andhydrauliccontrolsystem.Thecontrollerisbasedona16-bitmicrocomputerwhichre__ivesangleinputsignalsoftheboomarmandbucketfromthesensor;determinestheconditionofeachcontrollever;selectscontrolmodesandcalculatesactuatingvariables;andoutputstheresultsfromtheamplifieraselectricalsignals.Thehy-drauliccontrolsystemgenerateshydraulicpressureproportionalFig.
8.Simulationresultoflevelcrowding.totheelectricalsignalsfromtheelectro__gneticproportional-reducingvalvepositionsthespoolofthe__incontrolvalveandcontrolstheflowratetothehydrauliccylinder.Inordertorealizehigh-speedhigh-accuracycontrolanumericdatapro__ssorisemployedfortheFig.
9.EffectoffeedforwardcontroloncontrolerrorofZ.Fig.
10.Sche__ofcontrolsystem.controllerandahigh-resolution__gneticencoderisusedforthesensor.Inadditiontotheseapressuretransdu__risinstalledineachcylindertoachievepressurefeedback.Themeasureddataarestoreduptothememoryandcanbetakenoutfromthecommunicationport.
6.
2.ControlfunctionsThiscontrolsystemhasthreecontrolmodeswhichareauto__ticallyswitchedinaccordan__withleveroperationandselectorswitches.Thesefunctionsarethefollowing
1.Levelcrowdingmode:duringthe__nualarmpushingoperationwiththelevelcrowdingswitchthesystemauto__ticallycontrolstheboomandholdsthearmendmovementlevel.Inthiscasethereferen__positionistheheightofthearmendfromthegroundwhenthearmleverbegantobeoperated.Operationoftheboomlevercaninterruptauto__ticcontroltemporarilybecausepriorityisgivento__nualoperation.2Horizontalbucketliftingmode:duringthe__nualboomraisingoperationwiththehorizontalbucketliftingswitchthesystemauto__ticallycontrolsthebucket.Keepingthebucketangleequaltothatatthebeginningofoperationprevents__terialspillagefromthebucket.3__nualoperationmode:whenneitherthelevelcrowdingswitchnorthehorizontalbucketliftingswitchareselectedtheboomarmandbucketarecontrolledby__nualoperationonly.Theprogramrealizingthesefunctionsispri__rilywritteninClanguageandhaswell-structuredmoduletoimprove__intainability.
7.Resultsand____ysisoffieldtestWeputthefieldtestwiththesystem.WeconfirmedthatthesystemworkedcorrectlyandtheeffectsofthecontrolalgorithmdescribedinChaps.3and4wereas__rtainedasfollows.
7.
1.Auto__ticcontroltestsofindiÕidualattachmentsForeachattachmentoftheboomarmandbucketthereferen__anglewaschanged58stepwisefromtheinitialvalueandtheresponsesweremeasured;thustheeffectsofthecontrolalgorithmdescribedinChap.3wereas__rtained.
7.
1.
1.EffectofnonlinearcompensationFig.
11.Effectofnonlinearcompensationonboomangle.Becausedeadzonesexistintheelectro-hydraulicsystemssteady-stateerrorre__inswhen______positionfeedbackwithoutcompensationisappliedinthefigure..Additionofnonlinearcompensationinthefigure.canredu__thiserror.
7.
1.
2.EffectofstatefeedbackcontrolForthearmandbucketstableresponsecanbeobtainedbypositionfeedbackonlybutaddingac__lerationorpressurefeedbackcanimprovefast-responsecapability.Asregardstheboomwithonlythepositionfeedbacktheresponsebecomesoscillatory.Addingac__lerationorpressurefeedback__detheresponsestablewithoutimpairingfast-responsecapability.AsanexampleFig.12showsthetestresultswhenpressurefeedbackcompensationwasappliedduringboomlowering.
7.
2.LeÕelcrowdingcontroltestControltestswereconductedundervariouscontrolandoperatingconditionstoobservethecontrolFig.
12.Effectofpressurefeedbackcontrolonboomangle.Fig.
13.EffectoffeedforwardcontroloncontrolerrorofZ.characteristicsandatthesametimetodeterminetheopti__lcontrolparametersŽsuchasthecontrolgainsshowninFig.
6..
7.
2.
1.EffectsoffeedforwardcontrolInthecaseofpositionfeedbackonlyincreasinggainKtodecreaseerrorDZcausesoscillationdueptothetimedelayinthesystemasshownbyAOFFBinFig.
13.ThatisKcannotbeincreased.ApplyingthefeedforwardofthearmlevervaluedescribedinSection
4.1candecreaseerrorwithoutincreasingKasshownbyAONBinthefigure.p
7.
2.
2.EffectsofcompensationinattitudeLevelcrowdingisapttobecomeoscillatoryattheraisedpositionorwhencrowdingisalmostcompleted.ThisoscillationcanbepreventedbychanginggainKaccordingtotheattitudeashasbeenpdiscussedinSection
4.
2.TheeffectisshowninFig.
14.Thisshowstheresultwhenthelevelcrowdingwasdoneataround2maboveground.ComparedtothecasewithoutthecompensationdenotedbyOFFinthefiguretheONcasewiththecompensationprovidesstableresponse.Fig.
14.EffectofadaptivegaincontroloncontrolerrorofZ.
7.
2.
3.EffectsofcontrolinterÕalTheeffectsofcontrolintervaloncontrolperfor__n__wereinvestigated.Theresultsare:
1.whenthecontrolintervalissettomorethan100msoscillationbecomesgreateratattitudeswithlargemomentsofinertia;and
2.whenthecontrolintervalislessthan50mscontrolperfor__n__cannotbeimprovedsomuch.Consequentlytakingcalculationaccuracyintoaccountthecontrolintervalof50mswasselectedforthiscontrolsystem.
7.
2.
4.EffectsofloadAshovelwiththiscontrolsystemcarriedoutactualdiggingtoinvestigatetheeffectsofloading.Nosignificantdifferen__wasfoundincontrolaccuracyfromthatatnoload.
8.ConclusionsThispaperhasshownthatcombiningstatefeedbackandfeedforwardcontrols__kesitpossibletoaccuratelycontrolthehydraulicshovelandalsoshowedthatnonlinearcompensation__kesitpossibletouseordinarycontrolvalvesforauto__ticcontrols.Theuseofthesecontroltechniquesallowsevenunskilledoperatorstooperatehydraulicshovelseasilyandaccurately.Wewillapplythesecontroltechniquestootherconstruction__chinerysuchascrawlercranesandimprovetheconventionalconstruction__chinerytothe__chineswhichcanbeoperatedeasilybyanyone.Referen__s
[1]J.ChibaT.TakedaAuto__ticcontrolinconstruction__chinesJournalofSI__218198240–
46.
[2]H.NakamuraA.__tsuzakiAuto__tioninconstruction__chineryHitachiReview573197555–
62.
[3]T.Nakanoetal.Developmentoflargehydraulicexc__ator.MitsubishiHe__yIndustriesTechnicalReview222198542–
51.
[4]T.MoritaY.SakawaModelingandcontrolofpowershovelTransactionsofSI__221198669–
75.
[5]H.Arayaetal.Auto__ticcontrolsystemforhydraulicexc__atorRDKobeSteelEngineeringReports372198774–
78.
[6]P.K.VahaM.J.SkibniewskiDynamicmodelofexc__atorJournalofAerospa__Engineering621990April.
[7]H.HanafusaDesignofelectro-hydraulicservosystemforarticulatedrobotJournaloftheJapanHydraulicsandPneu__ticsSociety13719821–
8.
[8]H.B.Kuntzeetal.Onthemodel-basedcontrolofahydrauliclargerangerobotIFACRobotControl1991207–
212.液压挖掘机的半自动控制系统摘要:__出了一种应用于液压挖掘机的半自动控制系统采用该系统,即使是不熟练的操__也能容易和精确地操控液压挖掘机构造出了具有控制器的液压挖掘机的精确数学控制模型,同时通过模拟实验研发出了其控制算法,并将其应用在液压挖掘机上,由此可以估算出它的工作效率依照此法,可通过正反馈及前馈控制、非线性补偿、状态反馈和增益调度等各种手段获得较高的控制精度和稳定性能关键词施工机械;液压挖掘机;前馈;状态反馈;操作1.引言液压挖掘机,被称为大型铰接式机器人,是一种施工机械采用这种机器进行挖掘和装载操作,要求司机要具备高水平的操作技能,即便是熟练的司机也会产生相当大的疲劳另一方面,随着操__年龄增大,熟练司机的数量因而也将会减少__出一种让任何人都能容易操控的液压挖掘机就非常必要了[1-5]液压挖掘机之所以要求较高的操作技能,其理由如下
1.液压挖掘机的操作,至少有两个操作手柄必须同时操作并且要协调好
2.操作手柄的动作方向与其所控的臂杆组件的运动方向不同例如,液压挖掘机的反铲水平动作,必须同时操控三个操作手柄(动臂,斗柄,铲斗)使铲斗的顶部沿着水平面(图1)运动在这种情况下,操作手柄的操作表明了执行元件的动作方向,但是这种方向与工作方向不同如果司机只要操控一个操作杆,而其它自由杆臂自动的随动动作,操作就变得非常简单这就是所谓的半自动控制系统__这种半自动控制系统,必须解决以下两个技术难题
1.自动控制系统必须采用普通的控制阀
2.液压挖掘机必须补偿其动态特性以提高其控制精度现已经研发一种控制算法系统来解决这些技术问题,通过在实际的液压挖掘机上试验证实了该控制算法的作用而且我们已采用这种控制算法,设计出了液压挖掘机的半自动控制系统具体阐述如下2.液压挖掘机的模型为了研究液压挖掘机的控制算法必须分析液压挖掘机的数学模型液压挖掘机的动臂、斗柄、铲斗都是由液压力驱动,其模型如图2所示模型的具体描述如下
2.1动态模型
[6]假定每一臂杆组件都是刚体,由拉格朗日运动方程可得以下表达式其中g是重力加速度;θi铰接点角度;τi是提供的扭矩;li组件的长度;lgi转轴中心到重心之距;mi组件的质量;Ii是重心处的转动惯量下标i=1-3;依次表示动臂,斗柄,铲斗
2.2挖掘机模型每一臂杆组件都是由液压缸驱动,液压缸的流量是滑阀控制的,如图3所示可作如下假设
1.液压阀的开度与阀芯的位移成比例
2.系统无液压油泄漏
3.液压油流经液压管道时无压力损失
4.液压缸的顶部与杆的两侧同样都是有效区域在这个问题上,对于每一臂杆组件,从液压缸的压力流量特性可得出以__程当时;其中,Ai是液压缸的有效横截__;hi是液压缸的长度;Xi是滑芯的位置;Psi是供给压力;P1i是液压缸的顶边压力;P2i是液压缸的杆边压力;Vi是在液压缸和管道的油量;Bi是滑阀的宽度;γ是油的密度;K是油分子的黏度;c是流量系数
2.3连杆关系在图1所示模型中,液压缸长度改变率与杆臂的旋转角速度的关系如下1动臂2斗柄3铲斗当时,
2.4扭矩关系从
2.3节的连杆关系可知,考虑到液压缸的摩擦力,提供的扭矩τi如下 其中,Cci是粘滞摩擦系数;Fi是液压缸的动摩擦力
2.5滑阀的反应特性滑阀动作对液压挖掘机的控制特性产生会很大的影响因而,假定滑阀相对参考输入有以下的一阶延迟其中,是滑芯位移的参考输入;是时间常数3角度控制系统如图4所示,θ角基本上由随动参考输入角θγ通过位置反馈来控制为了获得更精确的控制,非线性补偿和状态反馈均加入位置反馈中以下详细讨论其控制算法
3.1非线性补偿在普通的自动控制系统中,常使用如伺服阀这一类新的控制装置在半自动控制系统中,为了实现自控与手控的协调,必须使用手动的主控阀这一类阀中,阀芯的位移与阀的开度是非线性的关系因此,自动控制操作中,利用这种关系,阀芯位移可由所要求的阀的开度反推出来同时,非线性是可以补偿的(图5)
3.2状态反馈建立在第2节所讨论的模型的基础上,若动臂角度控制动态特性以一定的标准位置逼近而线性化(滑芯位移X10,液压缸压力差P110,动臂夹角θ10),则该闭环传递函数为其中,Kp是位置反馈增益系数;由于系统有较小的系数a1所以反应是不稳定的例如,大型液压挖掘机SK-16中X10是0,给出的系数a0=
2.710a1=
6.010a2=
1.
210.加上加速度反馈放大系数Ka,因而闭环(图4的上环)的传递函数就是加入这个因素系数S就变大,系统趋于稳定可见,利用加速度反馈来提高反应特性效果明显但是,一般很难精确的测出加速度为了避免这个问题,改用液压缸力反馈取代加速度反馈(图4的下环)于是,液压缸力由测出的缸内的压力计算而滤掉其低频部分[7,8]这就是所谓的压力反馈4伺服控制系统当一联轴器是手动操控,而其它的联轴器是因此而被随动作控制时,这必须使用伺服控制系统例如,如图6所示,在反铲水平动作控制中,动臂的控制是通过保持斗柄底部Z(由θ1与θ2计算所得)与Zr的高度为了获得更精确的控制引入以下控制系统
4.1前馈控制由图1计算Z,可以得到将方程
(8)两边对时间求导,得到以下关系式,右边第一个式子看作是表达式(反馈部分)将替换成1,右边第二个式子是表达式(前馈部分)计算当θ2手动地改变时,θ1的改变量实际上,用不同的△θ2值可确定1通过调整改变前馈增益Kff,可实现最佳的前馈率采用测量斗柄操作手柄的位置(如角度)取代测斗柄的角速度,因为驱动斗柄的角速度与操作手柄的位置近似成比例
4.2根据位置自适应增益调度类似液压挖掘机的铰接式机器人,其动态特性对位置非常敏感因此,要在所有位置以恒定的增益稳定的控制机器是困难的为了解决这个难题,根据位置的自适应增益调度并入反馈环中(图6)如图7所示,自适应放大系数(KZ或Kθ)作为函数的两个变量,2和Z、2表示斗柄的伸长量,Z是表示铲斗的高度5模拟实验结论反铲水平动作控制的模拟实验是将本文第4节所描述的控制算法用在本文第2节所讨论的液压挖掘机的模型上(在SK-16大型液压挖掘机进行模拟实验)图8表示其中一组结果控制系统启动5秒以后,逐步加载扰动图9表示使用前馈控制能减少控制错误的产生.6半自动控制系统建立在模拟实验的基础上,半自动控制系统已制造出来,应用在SK-16型挖掘机上试验通过现场试验可验证其操作性这一节将讨论该控制系统的结构与功能
6.1结构图10的例子中,控制系统由控制器、传感器、人机接口和液压系统组成控制器是采用16位的微处理器,能接收来自动臂、斗柄、铲斗传感器的角度输入__,控制每一操作手柄的位置,选择相应的控制模式和计算其实际改变量,将来自放大器的__以电__形式输出结果液压控制系统控制产生的液压力与电磁比例阀的电__成比例,主控阀的滑芯的位置控制流入液压缸液压油的流量为获得高速度、高精度控制,在控制器上采用数字处理芯片,传感器上使用高分辨率的磁编码器除此之外,在每一液压缸上__压力传感器以便获得压力反馈__以上处理后的数据都存在存储器上,可以从通信端口中读出
6.2控制功能控制系统有三种控制模式,能根据操作杆和选择开关自动切换其具体功能如下
(1)反铲水平动作模式用水__铲切换开关,在手控斗柄推动操作中,系统自动的控制斗柄以及保持斗柄底部的水平运动在这种情况下,当斗柄操作杆开始操控时,其参考位置是从地面到斗柄底部的高度对动臂操作杆的手控操作能暂时中断自动控制,因为手控操作的优先级高于自动控制
(2)铲斗水平举升模式用铲斗水平举升切换开关,在手控动臂举升操作中,系统自动控制铲斗保持铲斗角度等于其刚开始举升时角度以阻止原材料从铲斗中泄漏
(3)手控操作模式当既没有选择反铲水平动作模式,也没有选择铲斗水平举升模式时,动臂,斗柄,铲斗都只能通过手动操作系统主要采用C语言编程来实现这些功能,以构建稳定模组提高系统的运行稳定性7现场试验结果与分析通过对系统进行现场试验,证实该系统能准确工作核实本文第
3、4节所阐述的控制算法的作用,如下所述
7.1单个组件的自动控制测试对于动臂、斗柄、铲斗每一组件,以±5º的梯度从最初始值开始改变其参考角度值,测量其反应,从而确定第3节所描述的控制算法的作用
7.
1.1非线性补偿的作用图11表明动臂下降时的测试结果因为电液系统存在不灵敏区,当只有简单的位置反馈而无补偿时(图11中的关)稳态错误仍然存在加入非线性补偿后(图11中的开)能减少这种错误的产生
7.
1.2状态反馈控制的作用对于斗柄和铲斗,只需位置反馈就可获得稳定响应,但是增加加速度或压力反馈能提高响应速度以动臂为例,仅只有位置反馈时,响应趋向不稳定加入加速度或压力反馈后,响应的稳定性得到改进例如,图12表示动臂下降时,采用压力反馈补偿时的测试结果
7.2反铲水平控制测试在不同的控制和操作位置下进行控制测验,观察其控制特性,同时确定最优控制参数(如图6所示的控制放大系数)
7.
2.1前馈控制作用在只有位置反馈的情况下,增大放大系数Kp,减少△Z错误,引起系统不稳定,导致系统延时,例如图13所示的“关”,也就是Kp不能减小采用第
4.1节所描述的斗柄臂杆前馈控制能减少错误而不致于增大Kp如图示的“开”
7.
2.2位置的补偿作用当反铲处在上升位置或者反铲动作完成时,反铲水平动作趋于不稳定不稳定振荡可根据其位置改变放大系数Kp来消除,如第
4.2节所讨论的图14表示其作用,表明反铲在离地大约2米时水平动作结果与不装补偿装置的情况相比较,图中的关表示不装时,开的情况具有补偿提供稳定响应
7.
2.3控制间隔的作用关于控制操作的控制间隔的作用,研究结果如下
1.当控制间隔设置在超过100ms时,不稳定振荡因运动的惯性随位置而加剧
2.当控制间隔低于50ms时,其控制操作不能作如此大提高因此,考虑到计算精度,控制系统选定控制间隔为50ms
7.
2.4受载作用利用控制系统,使液压挖掘机执行实际挖掘动作,以研究其受载时的影响在控制精度方面没有发现与不加载荷时有很大的不同8结论本文表明状态反馈与前馈控制组合,使精确控制液压挖掘机成为可能同时也证实了非线性补偿能使普通控制阀应用在自动控制系统中因而应用这些控制技术,允许即使是不熟练的司机也能容易和精确地操控液压挖掘机将这些控制技术应用在其它结构的机器上,如履带式起重机,能使普通结构的机器改进成为可让任何人容易操控的机器____
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