第七章柔顺控制

对于一个被约束的机械手进行控制要比一般的机械手的控制更为复杂和困难：1）约束使自由度减少，以致再不能规定末端的任意运动；2）约束给手臂施加一个反作用力，必须对这个力进行有效控制，以免它任意增大，甚至损害机械手或与其接触的表面；3）需要同时对机械手的位置和所受的约束反力进行控制。第七章机器人柔顺控制§7.1概述—柔顺控制目的1.位置控制的局限性当机械臂末端与工作环境有任何接触时，只依靠位置控制是不能满足要求的。Consideramanipulatorwashingawindowwithasponge.Thecomplianceofthespongemightmakeitpossibletoregulatetheforceappliedtothewindow.Imaginethatthemanipulatorisscrapingpaintoffaglasssurface,usingarigidscrapingtool.Ifthereisanyerrorinthepositionofthemanipulator,thistaskwouldbecomeimpossible.第七章机器人柔顺控制§7.1概述—柔顺控制目的Ifthestiffnessoftheend-effector,tool,orenvironmentishigh,itbecomesincreasinglydifficulttoperformoperationsinwhichthemanipulatorpressesagainstasurface.Itwouldbemorereasonablenottospecifythepositionoftheplaneoftheglass,butrathertospecifyaforcethatistobemaintainednormaltothesurface.第七章机器人柔顺控制§7.1概述—柔顺控制目的2.工业机器人装配作业应用装配作业中要求部件间的相互精确定位，而目前工业机器人还不具备精确的位置控制能力，保证装配任务的完成。Simpleapplication:suchasspotwelding,spraypainting,andpick-and-placeoperations.Forcecontrolhasalreadyappearedinafewapplications,forexample,capableofsimpleforcecontrolallowsthemtodosuchtasksasgrindinganddeburring.Assembly-linetasks:Apparently,thenextbigareaofapplication.Inwhichoneormorepartsaremated.Insuchparts-matingtasks,monitoringandcontroloftheforcesofcontactareextremelyimportant.第七章机器人柔顺控制§7.1概述—柔顺控制目的测量和控制机器人末端与环境的表面接触力是提高位置有效精度的有效方法。–与位置控制系统不同的是，接触力的测量是相对的，而不需要绝对的位置误差测量。–当部件间具有一定刚度接触时，小的相对位置误差会产生大的接触力，所以力的控制对位置控制精度还有很大帮助。第七章机器人柔顺控制§7.1概述—柔顺控制目的1、被动柔顺：将弹簧和消振器构成的无源机械装置安装在机械手的末端上，使机械手能够维持适当的方位。限于应用于一些专门的任务。2、主动柔顺：通过控制方法使末端呈现需要的刚度和阻尼或力作用要求，达到柔顺控制的目的。能够对不同类型的零件进行操作，或者能够根据装配作业不同阶段的要求来修改末端装置的弹性性能。第七章机器人柔顺控制§7.1概述—柔顺控制方法机器人的工作任务可根据机器人末端与工作环境间的不同接触状态而划分为系列子任务，对于每一个子任务定义相应的约束集，称为自然约束，来源于子任务构型的机械和几何性能约束。–Ahandincontactwithastationary,rigidsurfaceisnotfreetomovethroughthatsurface;hence,anaturalpositionconstrainsexist.–Ifthesurfaceisfrictionless,thehandisnotfreetoapplyarbitraryforcestangenttothesurface,thus,anaturalforceconstraintexist.第七章机器人柔顺控制§7.2作业约束—自然约束Inthemodelofcontactwiththeenvironment,foreachsubtaskconfiguration,ageneralizedsurfacecanbedefinedwithpositionconstraintsalongthenormalstothissurfaceandforceconstraintsalongthetangents.Thesetwotypesofconstraint,forceandposition,partitionthedegreesoffreedomofpossibleend-effectormotionsintotwoorthogonalsetsthatmustbecontrolledaccordingtodifferentcriteria.Thetermnaturalconstraintsisusedtoindicatethattheseconstraintsarisenaturallyfromtheparticularcontactingsituation.Theyhavenothingtodowiththedesiredorintendedmotionofthemanipulator.第七章机器人柔顺控制§7.2作业约束—自然约束根据自然约束状态，必须设计需要的位置控制或力控制，即每一时刻都要设计期望的位置轨迹或力的约束，定义为人为约束。Theseconstraintsalsooccuralongthetangentsandnormalsofthegeneralizedconstraintsurface.Butunlikenaturalconstraints,artificialforceconstraintsarespecifiedalongsurfacenormals,andartificialpositionconstraintsalongtangents..第七章机器人柔顺控制§7.2作业约束—人为约束约束坐标系{C}根据任务环境设定，也可以固定在机器人末端，形成移动坐标系。机器人的工作任务是相对约束坐标系定义的，即自然约束和人为约束是定义在约束坐标系的。–In(a),{C}isattachedtothecrankwiththeXdirectionalwaysdirectedtowardthepivot.–In(b),{C}isattachedtothetipofthescrewdriverandmoveswithitasthetaskproceeds.第七章机器人柔顺控制§7.2作业约束—约束坐标系Example:Atasktopullupapegfromahole.Theproblemistofindnaturalandartificialconstraints.Assume:–Thepegcanmoveintheverticaldirectionwithoutfrictionwhenslidinginthehole.–Thetaskprocessisquisi-staticinthatanyinertialforceisnegligiblysmall.第七章机器人柔顺控制§7.2作业约束—举例ConstrainsinkinematicdomainNaturalconstrains:•Thepegcannotbemovedinthexandydirectionsduetothegeometricconstraint:•Thepegcannotberotatedaboutthexandyaxes:Artificialconstrains:•Theremainingdirectionsarelinearandangularzaxes.Velocitiesalonethesetwodirectionscanbeassignedarbitrarily,andmaybecontrolledwithpositioncantrolmode.Weselect:.0xyvv0xy0,0zzvV第七章机器人柔顺控制§7.2作业约束—举例ConstrainsinthestaticsdomainNaturalconstrains:–Inthestaticsdomain,forcesandtorquesarespecifiedinsuchawaythatthequasi-staticconditionissatisfied.Thismeansthatthepegmotionmustnotbeacceleratedwithanyunbalancedforce:Artificialconstrains:–Theremainingdirectionsaregeometricallyconstrained.Inthesedirections,forcesandtorquescanbeassignedarbitrarily,andmaybecontrolledwithforcecontrolmode.Wecanselectthereferenceinput:0,0zzf0,0xyxyff第七章机器人柔顺控制§7.2作业约束—举例Itisclearthattheaxesinvolvedinthenaturalconstraintsandtheartificialconstraintsareorthogonaltoeachotherinbothkinematicandstaticdomains.Moreover,theaxesinvolvedinthenaturalkinematicconstraintsandtheartificialstaticconstraintsarethesame.KinematicStaticNaturalconstrainsArtificialconstrains0xyvv0xy00zzvV00zzf00xyxyff第七章机器人柔顺控制§7.2作业约束—举例Example:Figureshowsthenaturalandartificialconstraintsfortwotasks.Notethatwhenanaturalpositionconstraintsisgivenforaparticulardegreeoffreedomin{C},anartificialforceconstraintsshoudbespecified,andviceversa.Atanyinstant,anygivendegreeoffreedomintheconstraintsframeiscontrolledtomeeteitherapositionoraforceconstraints.第七章机器人柔顺控制§7.2作业约束—举例Assemblystrategyisatermthatreferstoasequenceofplannedartificialconstraintsthatwillcausethetasktoproceedinadesirablemanner.–Mustincludemethodsbywhichthesystemcandetecta