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外文翻译--自动控制器.doc

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外文翻译--自动控制器.doc

附加外文翻译外文文献I,robotcontrollerAsophisticatedapproachtokinematicsiswhatdifferentiatesrobotcontrollersfrommoregeneralpurposemotionequipment.Aninterestingsituationemergedrecentlywhenamanufacturertriedtoputavisionsystemonanassemblyline.Theideawastolocatepartsonamovingconveyorwithavisionsystem,thenpositionaroboticsarmtopickthemuplineatatime.Engineerstherediligentlyworkedoutnumerousdisplacementfudgefactorstorelatethelocationsoftheconveyorendeffectorsandpartsimagedbythecamera.Thefudgefactorsletthemotioncontrollerinferthephysicallocationofapartfromthevisionsystemdata,thendirectthearmtotherightplacetopickitup.Problemwas,therelativepositionofthevariouscomponentsallchangedeverytimetheconveyorwentbackonlineafterservicingormaintenance.Thefactorssocarefullycomputedbecameuseless.Thisnecessitatedregularroundsofrecalculatingnewdisplacements.Attherootofthesedifficultiesweresomefundamentalmisunderstandingsabouthowgeneralpurposemotioncontrollersdifferfrommorespecializedrobotcontrollers.Hardwarewise,thetwocanlooksimilar.BothfrequentlyemployPentiumbasedprocessorsoradoptahybridapproachwithageneralCPUsupervisingoneormoredigitalsignalprocessorsdedicatedtoservoloops.However,thesoftwarearchitectureofarobotcontrollerdiffersdramaticallyfromthatofanordinarymotioncontrollersoftwareItgenerallyconsistsofaroutineforclosedlooppositionorvvelocitycontrol,operatorinterfacefunctions,androutineforsupervisorytasks.Animportantpointtonoteisatthesupervisorylevelofcontrol.Taskstherethatrelatetohandlingmotiondonotextendmuchpastsimplyissuingpositioncommandsandindividualaxes.Inotherword,thesupervisorylevelisrelativelysimply.Thesupervisorylevelofrobotcontrollerismoresophisticated.Foronething,itiswrittenwiththeideathat,postroboticsystemsincorporatefeedbackfromhighlevelsensorsthatresideoutsidethepositionencoderfeedbackservoloopsofindividualaxes.Typicalexamplesincludeindustrialvisionsystemandforcesensors.Mostroboticworkinvolvesusinginformationfromthesesensorstocalculatethetrajectoryofarobotarm.Tohandlethiscalculationprocess,supervisorylevelsoftwareimplementsatrajectoryplanningalgorithm.Thisalgorithmrelatesthephysicallocationofpositioningelements,sensorfeedback,andtheobjectsbeingpositionedintermsofwhatscalledaworldcoordinatesystem.Thisisincontrasttogeneralpurposemotionequipmentwhichtendstouseaseparatereferenceframeforeachaxisofmotion.Onebenefitofaworldcoordinatesystemisthatitcaneliminatetheneedforfudgefactorsrelatingsensordatatothepositionofvariouscomponents.Thestateoftheartissuchthatstraightforwardsetuproutinescancomputesuckinformationautomatically.Moreover,datagatheredduringsetupgoesintotransformationcalculationsthatdetermineworldcoordinatesandwhicharemoreprecisethananymanuallydeducedfudgefactors.REFEENCEKINEMATICSItisusefultobrieflyreviewthewayarobotcontrollerimplementsworldcoordinates.Readerswillprobablyrecallfromengineeringmechanicsthatthepositionofanarbitrarypointexpressedinonecoordinatesystemcanbemappedinanotherthroughuseofa4x4transformation.InthecaseofScasarobotarm,thepositionofapointattheendofthearmcanbeexpressedintermsoftheproductof4x4matrices,onematrixforeachlinkintherobotarm.Matrixcoefficientsforthearmitselfaredeterminedbylinklengthandgeometry,andjointangle.Obviouslylinkgeometryisknown.Jointanglecoefficientscomefromfeedbackprovidedbyjointservoencoders.Inananalogousmanner,thecoordinatesinferredfromtheimageofanindustrialvisionsystemcanbeexpressedinworldcoordinatesviaanothersetof4x4transformations.Thecoefficientsforthetransformationmatricescomefrominformationdeterminedduringequipmentsetup.Take,asanexample,thecaseofpartslayingonaconveyor.Therobotarmwilllocatethreepointsontheconveyoraspartofthesetupprocess.Thesepoints,ofcourse,definetheconveyorplane.Therobotcontrollerusesthisinformationtodeducethetransformationcoefficientsthatwillrelateconveyorpositioninworldcoordinates.Apointtonoteisthateveniftheconveyorisonananglethisfactwillbereflectedinthetransformationcoefficientscalculatedautomaticallyduringsetup.Thereisnoneedforcomputingadditionaldisplacementsorothercompensatingoffsets.Modernrobotcontrollersuseprogramminglanguagesthatalsoworkinworldcoordinates.Toolcommands,visioncommands,andconveyordefinitionsallgetexpressedthisway.Putanotherway,theworldcoordinatesystemandthetransformationsthatmakeitpossibleareembeddedinthecontrollerprogramminglanguage.Oneadditionalmanifestationofthisapproachisthatwhenprogrammingmovesoperatorsofsucksystemsneednotconcernthemselveswithtimingrelationshipsattheoperatingsystemlevel.Thisisalsoonereasonwhyrobotcontrollerscanimplementahighlevelcalibrationmethodology.Oncerepositioned,arobotanditsancillarysystemscanfindtheirbearingsthroughuseofafewsoftwaresetuputilitiesthatrecalculatetransformationcoefficients.Thisprocesscontrastswiththatnecessaryformoregeneralpurposemotioncontrollers.Thoughthesesystemsalsotendtoemployspecialpurposeautomationsoftware,positioningcommandstendtoassumecoordinatesystemsthatcenteroneachaxisofmotion.Itiscertainlypossibletodefineworldcoordinatesystemforthesecontrollers.ButcontrolvendersgenerallyleavethistasktoOEMshandingapplicationswhereitspecificallycomesinhandy.Thereasonisthatroboticpositioningisaspecialcaseofmotioncontrol.WorldcoordinatesofferlimitedutilityinsimplerbutmoretypicalpositioningapplicationsthatcanrangefromconvertingmachinestocardreadersinATMs.Allinall,theprocessoffittinggeneralpurposecontrollerstoroboticapplicationsputstheburdenonOEMsforcoordinatetransformationrelationshipsalreadyavailableinrobotcontrollers.Alternativelytheycansimplytrytomakedowithaseriesoflossrobustphysicaloffsetsanddisplacements.TRAJECTORYPLANNINGTheservoloopsoftwarethatpositionsanaxisonarobotisfairlyconventional.Eachaxishasitsownservoloop.Anerrortermdrivesaxismotion,derivedfromthedifferencebetweenpositionfeedbackandapositioncommand.Theremaybefeedforwardconstantstoadjustthepositionerrorundercertainconditions.Andaswithgeneralpurposemotioncontrollers,roboticservoloopsexecuteontheorderofonceeverymillisecond.Thesoftwarethatfeedspositioncommandstoeachservoloopiscalledthetrajectoryplanner.Itisthetrajectoryplannerthatcomputesamodelofwhereatooltipmustgofromwhereitcurrentlyresides.Todoso,itmusttakeinformationoutofworldcoordinateformandtranslateitintojointanglesforaScasarobotorintodisplacementsformoregeneralpurposeautomationequipment.Thetrajectoryplannerrepeatsthisprocessaboutevery16mses.Trajectoryandservocycletimeentersintonotonlysystembandwidthconcerns,butalsosafetyconsiderations.Theroboticindustryhasissuedstrictsafetystandardsthatdictateminimumlevelsofperformanceinemergencysituations.Perhapsmostobviousoftheseistheemergencystop.Roboticcontrollersemployanemergencystopalgorithmthatbypassesthetrajectoryplannerandits16msescycletimeandexecutescontrolledstoproutinesinfirmware.Thispowersdowneachaxistoacontrolledstopinafewmilliseconds.Thisfastbutcontrolledemergencystopcanbecontrastedwiththetechniqueusedbymanygeneralpurposemotioncontrollers.Thesimplerapproachistojustdrivealargemomentarysurgeofnegativehaltpowertotheamplifier.Thiscertainlystopsthepositioningequipment.Butinthecaseofarobot,itcouldeasilysnapoffawristmechanismifthereisenoughinertia.Finally,robotcontrollersemployothersafety,measuresthatarecommonlyfoundinNCequipmentbutwhicharerareinmoregeneralpurposepositions.Forexample,lossofencoderfeedbackwillgenerateanemergencystop.Dittoforreachingend–of–travellimits.Theselimitsmaybeseteitherbyhardwarelimitswitches,orbydeclaringpositionsoftherobotworkenvelopofflimits.外文文献翻译自动控制器对于运动的一个很久的处理是如何去辨别自动控制与通用的一般的运动设备的不同之处。最近出现了一个令人感兴趣的情况,一个制造者尝试给一条组装线设置一个辨认系统。这目的是为了用一个监控系统去找到正在移动的物体。那时,一个机器人手臂作每次取它们中间的一个出来的动作。这时,工程师们孜孜不倦地去计算多众相关的各个位置运动的假设因素。最后,这些结果和运动影像用照相机照下来。这些假设的因素让动作控制器推理出其物理的位置,部分位置的数据是来自虚拟系统数据,那时直接控制手臂到正确的位置来取出它们之中的一件。但问题就是,各种相关联的位置必须在每次工作和维修后回到同一线位置。这些如此细致的计算的数据变得无用的,这需要重新计算新的移位。最主要的困难是不理解一些基本的原理,是如何区别一般大致的运动和众多的特殊的自动控制运动,这两者看起来是相类似的,通常使用Pentium信息处理器或者使用Hybird处理器配备一个普通的CPU的信息处理机专门用于处理一个或者更多数字信号。然而,自动控制器的软件结构与通用的运动设备是不相同。首先,辨别运动控制的软件,其大致由闭环位置和速度控制,操作协调职责和协调监督这些常规的程序来控制工作。一个最重要的情况必须记下来,就是监督协调的程度如何。这种连接和操纵相关联的监督工作不是简单的延伸发出位置要求和常规的单轴程序。另一种说法,这种监督程序的程度是相对简单的。自动控制器的监督系统是更加复杂的。首先,很多自动控制系统反馈信息到高级的传感器,这些传感器是设置在单独轴的位置,反馈的数据记录。典型的

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