塔式起重机有限元分析外文翻译.docx

FEMOptimizationforRobotStructureWangShijun,ZhaoJinjuan*DepartmentofMechanicalEngineering,Xi'anUniversityofTechnologyShaanxiProvince,People,sRepublicofChinaInstituteofPrintingandPackingEngineering,Xi'anUniversityofTechnologyAbstractInoptimaldesignforrobotstructures,designmodelsneedtohemodifiedandcomputedrepeatedly.Becausemodifyingusuallycannotautomaticallyberun,itconsumesalotoftime.ThispapergivesamethodthatusesAPDLlanguageofANSYS5.5softwaretogenerateanoptimalcontrolprogram,whichmikeoptimalprocedurerunautomaticallyandOptimalefficiencybeimproved.1) IntroductionIndustrialrobotisakindofmachine,whichisControlledbycomputers.Becauseefficiencyandmaneuverabilityarehigherthantraditionalmachines,industrialrobotisusedextensivelyinindustry.Forthesakeofefficiencyandmaneuverability,reducingmassandIncreasingstiffhessismoreimportantthantraditionalmachines,instructuredesignofindustrialrobot.Alotofmethodsareusedinoptimizationdesignofstructure.Finiteelementmethodisamucheffectivemethod.Ingeneral,modelingandmodiiyingaremanual,whichisfeasiblewhenmodelissimple.WhenmodeliScomplicated,optimizationtimeislonger.IntheIongeroptimizationtime,calculationtimeisusuallyverylittle,amajorityoftimeisusedformodelingandmodifying.Itiskeyofimprovingefficiencyofstructureoptimizationhowtoreducemodelingandmodifyingtime.APDLlanguageisaninteractivedevelopmenttool,whichisbasedonANSYSandisofferedtoprogramusers.APDLlanguagehastypicalfunctionofsomelargecomputerlanguages.Forexample,parameterdefinitionsimilartoconstantandvariabledefinition,branchandloopcontrol,andmacrocallsimilarIofunctionandsubroutinecall,etc.Besidesthese,ItpossessespowerfulcapabilityofITiathematicalcalcuIation.ThecapabilityofmathematicalCalculationincludesarithmeticcalculation,comparison,rounding,andtrigonometricfunction,exponentialfunctionandhyperbolafunctionofstandardFORTRANlanguage,etc.BymeansofAPDLlanguage,thedatacanbereadandthencalculated,whichisindatabaseofANSYSprogram,andrunningprocessofANSYSprogramcanbecontrolled.Fig.1showsthemainframeworkofaparallelrobotWiththreebars.Whenthelengthofthreebarsarechanged,conjunctendofthreebarscanfollowagiventrack,whererobothandisinstalled.Coreoftopbeamistriangle,owingtothreebarsusedinthedesign,whichisshowedinFig.2.UseofthreebarsmakestopBeamnonsymmetricalalongtheplanethatisdefinedbytwocolumns.AccordingtoaqualitativeanalysisfromFig.!,Stiffnessvaluesalongz-axisaredifferentatthreejointlocationsonthetopbeamandstiffnessatthelocationbetweenbar1andtopbeamislowest,whichisconfirmedbycomputingresultsoffiniteelement,too.Accordingtodesigngoal,stiffnessdifferenceatthreejointlocationsmusthewithinagiventolerance.Inconsistentofstiffnesswillhaveinfluenceonthemotionaccuracyofthemanipulatorunderhighload,soitisnecessarytofindtheaccuratelocationoftopbeamalongx-axis.Tothequestionspresentedabove,thegeneralsolutionistochangethelocationofthetopbeammanytimes,comparetheresultsandeventuallyfindaproperposition,Themodelwillbemodifiedaccordingtothelastcalculatingresulteachtime.Itisdifficulttoavoidmistakesiftheiterativeprocessiscontrolledmanuallyandtheiterativetimeistoolong.Theouterwallandinnerribshapesofthetopbeamwillbechangedafterthemodelismodified.TofindtheappropriateIocationoftopbeam,themodelneedstobemodifiedreetitiously.Fig.1SolutionofOriginalDesignThispapergivesanoptimizationsolutiontothepositionoptimizationquestionofthetopbeambyAPDLlanguageofANSYSprogram.Aftertheanalysismodelfirstfounded,theoptimizationcontrolprogramcanbeformedbymeansofmodelinginstructioninthelogfile.Thelateriterativeoptimizationprocesscanbefinishedbytheoptimizationcontrolprogramanddonotneedmanualcontrol.Thetimespentinmodifyingthemodelcanbedecreasedtotheignorableextent.Theefficiencyoftheoptimizationprocessisgreatlyimproved.2) ConstructionofmodelforanalysisThestructureshowninFig.1consistsofthreeparts:twocolumns,onebeamandthreedrivingbars.ThecolumnsandbeamarejoinedbytheboltsonthefirsthorizontalriblocatedontopofthecolumnsasshowninFig.!.BecausethedrivingbarsaresubstitutedbyequivalentforcesonIhejointpositions,theirstructureisignoredinthemodel.Thecoreofthetopbeamisthreejointsandaholewithspecialpurpose,whichcannotbechanged.TheOtherpartsofthebeammaybechangedifneeded.Fortheconvenienceofmodeling,thecoreofthebeamisfbrmedintoonecomponent.IntheprocessOfoptimization,onlythecorepositionofbeamalongxaxisischanged,thatistosay,shapeofbeamcoreisnotchanged.Itshouldbenoticedthat,intherestofbeam,onlyshapeischangedbutthetopologyisnotChangedandwhichcanautomaticallybeperformedbythecontrolprogram.Fig.l,sixboltsjointhebeamandtwocolumns.Thejointsurfacecannotbearthepullstressinthenon-boltjointpositions,inwhichitisbettertosetcontactelements.Whenthemodelincludescontactelements,nonlineariterativecalculationwillbeneededinIheprocessofsolutionandthecomputingtimewillquicklyincrease.Thetrialcomputingresultnotincludingcontactelementshowsthattheoutsideofbeambearspullingstressandtheinnerofbeambearsthepressstress.Consideringtheprimaryanalysisobjectisthejointpositionstiffnessbetweenthetopbeamandthethreedrivingbars,contactelementsmaynotused,hutconstructsthegeometrymodelofjointsurfaceasFig.2showing.Theuppersurfaceandtheundersurfaceshareonekeypointinbolt-jointpositionsandtheuppersurfaceandtheundersurfaceseparatelypossessownkeypointsinnoboltpositions.Whenmeshed,onenodewillbecreatedatsharedkeypoint,wherecolumnsandbeamarejoined,andtwonodeswillbecreatedatnonsharedkeypoint,wherecolumnandbeamareseparated.Onrightsurfaceofleftcolumnandleftsurfaceofrightcolumn,accordingtotrialcomputingresult,Ihestructurebearspressstress.Therefore,thecolumnsandbeamwillshareallkeypoints,notbutatbolts.ThiscannotonlyomitcontactelementbutalsoshowIhecharacteristicofboltjoining.Thejoiningbetweenthebottomsofthecolumnsandthebasearetreatedasfullconstraint.BecausethemainaimofanalysisisIhestiffnessofthetopbeam,itcanbeassumedthatthejointpositionshearthesameasloadbetweenbeamandthethreedrivingbars.Thestructureisthethinwallcastandsimulatedbyshellelement.ThethicknessoftheoutsidewallofIhestructureandtheribarenotequal,sotwogroupsofrealconstantshouldheset.Fortheconvenienceofmodeling,thetwocolumnsarealsosetintoanothercomponent.Thecomponentscancreateanassembly.Inthisway,thejointpositionsbetweenthebeamcoreandColumnscouldheeasilyselected,inthemodifyingthemodelandmodifyingprocesscanautomaticallybeperformed.AnalysismodelisshowedFig.l.Becausemodelandloadaresymmetric,computingmodelisonlyhalf.Sothetotalofelementsisdecreasedto8927andtheIotalofnodesisdecreasedto4341.Allelementsaretriangle.3) )OptimizationsolutionTheoptimizationprocessisessentiallyacomputingandmodifyingprocess.Theoriginaldesignisusedasinitialconditionoftheiterativeprocess.TheendingConditionoftheprocessisthatstiffnessdifferencesofthejointlocationsbetweenthreedrivingbarsandtopbeamarelessthangiventoleranceoriterativetimesexceedexpectedvalue.ConsideringthespecialityofIhequestion,itisforeseenthatthelocationisexistentWherestiffnessvaluesareequal.Ifiterativeisnotconvergent,thecausecannotbeotherwisethanJnappropriatedisplacementincrementordeficientiterativetimes.Inordertomaketheiterativeprocessconvergentquicklyandefficiently,thispaperusesthebisectionsearchingmethodchangingsteplengthtomodifythetopbeamdisplacement.ThismethodisalittlecomplexbutIherequirementontheinitialconditionisrelativelymild.Theflowchartofoptimizationasfollows:1. Readthebeammodeldataininitialpositionfrombackupfile;2. Modifythepositionofbeam;3Solve;4. Readthedeformofnodeswherebeamandthreebarsarejoined;5. Checkwhethertheconvergentconditionsaresatisfied,ifnot,thencontinuetomodifythebeamdisplacementandreturnto3,otherwise,exittheiterationprocedure.6. Savetheresultsandthenexit.Theprogram,sprimarycontrolcodesandtheirfunctioncommentariesaregiveninit,ofwhichthedetailedmodelinginstructionsareomitted.FortheConvenienceofcomparingwiththecontrolflow,thenecessarynotesareadded,theflagofthebatchfileinANSYSBATCHRESUME,robbak.db,Oreadoriginaldatafromthebackupfilerobbak.dbPREP7enterpreprocessordeletethejointpartbetweenbeamcoreandcolumnsmovethecoreofthebeambyone:steplengthapplyloadandconstraintonthegeometrymeshingthejointpositionbetweenbeamcoreandcolumnsFINISHexitthepreprocessorISOLUentersolverSOLVEsolveFINISHexitthesolverPOSTlenterthepostprocessor*GET,front,NODE,2023,U,ZreadthedeformationofIlrstjointnodeonbeam*GET,back,NODE,1441,U,ZreadthedeformationofsecondjointnodeonbeamintoparameterhackIastdif-Itheabsoluteofinitial(Iifferencebetweenfrontandhacklasttimeflag=-Ithefeasibilityflagoftheoptimizationste=0.05theinitialdisplacementfrominitialpositiontothecurrentpositionD0,1,1,10,1theiterationprocedurebegin,thecyclevariableisIanditsvaluerangeisI-IOandsteplengthis1dif=abs(front-back)theabsoluteofthedifferencebetweenfrontandhackinthecurrentresult*IF,dif,LE,l.OE-6,THENcheckwhethertheabsolutedifferencedifsatisfiestherequestornoflag=lyes,setflagequalto1*EXITexittheiterativecalculation*ELSElF,dif,GEJastdif,THENcheckwhetherthedifvaluebecomesgreatornotflag=2yes,setflag2modifysteplengthbybisectionmethoderfrmthenextiterativecalculation,usethelastpositionasthecurrentpositionandmodifiedlaststeplengthasIhecurrentsteplengthELSEiftheabsoluteofdifferencevalueisnotlessthanexpectedvalueandbecomesmallgradually,continuetomovetopbeamreadtheinitialconditionfrombackupfileenterthepreprocessorMEN,P51X,step,ImovethecoreofthebeambyonestepIengthmodifythejointpositionsbetweenbeamcoreandColumnapplyloadandconstraintmeshingFINISHexitpreprocessorISOLUentersolverSOLVEsolveFINISHexitthesolver/POSTlexitthepostprocessor*GET,fronl,NODE,2013,U,ZreadthedeformationoffirstjointnodeIoparameterfront*GET,back,NODE,1441,U,ZreadthedeformationofsecondjointnodetoparameterbackIastdif-difupdatethevalueofIastdif*ENDIFtheendoftheif-else*ENDDOtheendoftheDOcycleMostofthecontrolprogramaboveiscopiedfromlogfile,whichislong.Thetotaloflinesisuptoabout100OIines.Manycodessuchasmodelingandpost-processcodesareusedrepeatedly.Tomaketheprogramconstructclear,theseinstructionscanhemadeintomacros,whicharecalledbymainprogram.ThisCanefficientlyreducethelengthofthemainprogram.Inaddition,modelinginstructionsfromlogfileincludeslotsofspecialinstructionsthatareonlyusedundergraphicmodebutuselessunderhatchmode.DeletingandmodifyingtheseinstructionswhenunderbatchmodeinANSYScanreducethelengthofthefile,too.Intheprogramabove,thedeformationatgivenpositionisreadfromnodedeformation.Inmeshing,inordertoavoidgeneratinghadelements,trianglemeshisused.Inoptimization,theshapeofjointpositionbetweencolumnsandbeamcontinuallyischanged.Thismakestotalofelementsdifferentaftermeshingeachtimeandthenelementnumberingdifferent,too.DatareadIromdatabaseaccordingtonodenumberingmightnothedatatowant.Therefore,beamcorefirstneedstohemeshed,thensaved.Whenreadnexttime,itsnumberingisthesameaslasttime.Evaluatingwhetherthefinalresultisafeasibleresultornotneedstochecktheflagvalue.IfonlytheflagvalueisI,theresultisfeasible,otherwisethemostproperpositionisnotfound.Thetotaldisplacementoftopbeamissavedinparameterstep.Iftheresultisfeasible,thestepvalueisthedistancefrominitialpositiontothemostproperposition.Thesumofiterativeissavedinparameter1.AccordingtothefinalvalueofI,feasibilityofanalysisresultandcorrectnessofinitialconditioncanheevaluated.4) OptimizationresultsThesumofiterativeinoptimizationisseven,andittakesabout2hourand37minutestofindOptimalposition.Fig.3showsthedeformationcontourofthehalf-construct.InFig.3,thedeformationsinthreeJointsbetweenbeamandthethreedrivingbarsisthesameaslevel,andthecorrespondingdeformationrangeisbetween-0.133E-04and-0.115E-O4m,therequirementofthesamestiffnessisreached.Atthistime,thepositionofbeamcorealongx-axisasshowninFig.1hasmoved-0.7IE-OImcomparedwiththeoriginalUesignedpositionBecausethespeedofcomputerreadinginstructionismuchfasterthanmodifyingmodelmanually,thetimemodifyingmodelcanbeignored.Thetimenecessaryforoptimizationmostlydependsonthetimeofsolution.ComparedwiththeoptimizationprocedureInanuallymodifyingmodel,theefficiencyisimprovedandmistakeoperatinginmodelingisavoided.5) ConclusionTheanalyzingresultrevealsthattheoptimizationmethodgiveninthispaperiseffectiveandreachestheexpectedgoal.Thefirstadvantageofthismethodisthatmanualmistakesdonoteasilyoccurinoptimizationprocedure.Secondly,itisprettyuniversalandthecontrolcodesgiveninthispapermayhetransplantedtouseinsimilarstructureoptimizationdesignWithoutlargemodification.Thedisadvantageisthatthetopologystructureoftheoptimizationobjectcannotbechanged.Themoretheworkloadofmodifyingthemodel,themoretheadvantagesofthismethodareshown.Inaddition,thetopologyoptimizationFunctionprovidedinANSYSisusedtosolvetheoptimizationproblemthatneedstochangethetopologystructure.Thebetteroptimizationresultscanheachievedifthemethodinthispapercombinedwithit.中文译文：机器人机构优化设计有限元分析王世军赵金娟西安大学机电工程系中国陕西西安大学出版社摘要机器人结构最优化设计，设计模型需要反复的修正和计算。应为修改后的模型通常不能自动运行，需要大量的时间进行调试。本论文给出一种采用有限元分析软件ANSYS5.5参数化设计语言生成一种最优化控制的方法，这种方法能给出最优自动运行过程和提高效率。1）简介工业机器人是一种用电脑控制的机械机构。因为效率和可操作性比传统机械要高，因此工业机器人广泛的用于工业生产中。相对传统机械来说，在工业机器人的结构设计中，为了到达高效率和可操作性的目的，减少重量和增加刚度显得更加重要。在结构设计中有很多的方法，一般而言，有限元法是最有效的方法之一。当所需模型比拟简单时，建模和修改采用手工操作是可行的。当模型复杂时，优化时间是比拟长的。在相当长的优化时间内，计算时间是非常少的，大多数时间是用来建模和修改模型的。如何减少结构优化过程中的建模和修改模型所用时间是提高效率的关键所在。ANSYS参数化设计语言是一种基于有限元分析的交互式开发工具，通常被程序设计人员使用。ANSYS参数化设计语言具有一个典型功能及它包含多数大型计算机语言，例如，定义参数像定义常量和变量，条件转移和循环控制，以及宏调用像调用函数和子程序等。除此之外，它具有强大的数学计算控制能力。这种数学计算能力包括算法，计算，比照，凑整和三角函数功能，指数函数功能和标准福传语言的双曲线功能等。依靠ANSYS参数化设计语言，数据能够在ANSYS数据库中被阅读和计算，并且在ANSYS程序运行过程中受到控制。图1表示三连杆平行机器人的主要框架。沿Z轴的刚性值在顶部梁的三个连接处是不一样的。在连杆I和顶部梁连接处得刚性是最小的，这也是通过有限元分析计算结果来确定的。根据设计目的，在三个连接点的不同的刚性必须要有给定的公差。当机械手在进行高强度工作时，一致的刚性会对它的运行精度产生影响，因此在沿X轴设置一个精确的位置是非常有必要的。根据上面提出的问题，一般的解决方法经常是改变顶部梁连接点的位置，比照结果，然后找到一个适宜的位置，模型每次都要根据最后的计算结果进行修改。如果采用人工的控制这个重复的过程且重复时间过长，这样就难免出现错误。当模型被修改时，顶部梁外壁和内部肋板的形状也随之发生改变。模型需要重复的去修改才能找出恰当的位置。图1初始设计方案本论文通过ANSYS程序的参数化设计语言给出一个寻找最优位置问题的最正确解决方法。经过对事先建立的模型进行分析，通过建模系统指令在新的文件里形成一个最正确的控制程序，通过这个最正确的控制程序可以完成以后的重复最优化过程，而且不需要手工控制。在修改模型上消耗的时间可以减少到被忽略的程度。最优化步骤的效率得到很大提高。2建筑模型分析图1所示结构包括了三个局部：两个支柱，一个顶部梁和三个操作连杆。支柱和横梁通过位于支柱上面的水平肋板连接在一起，如图1所示。因为操作连杆被连接位置的等效构件代替，所以在模型中它们的结构被忽略了。顶部横梁的核心是三个连接处和一个特殊作用的孔，这些都是固定不变的。其他部件可以根据需求进行修改。为了建模的方便，横梁的核心被制成一个零件。在进行最优化的过程中，只有沿着X轴的横梁中心位置是变化的，也就是说，横梁核心的形状是不变的.应该注意的是，横梁的其余局部只有形状变化而拓扑是固定的，可以通过控制程序自动执行.图2顶部横梁核心图L六个螺栓连接横梁和支柱。在没有螺栓连接的位置，其结合面不能承受拉应力，最好在该位置设置接触件。当模型中包括接触件，非线性元件时，在解决方案过程中重复计算是必要的，并且计算时间会快速增加。不包括接触件的实验计算结果显示横梁外部承受拉伸应力，横梁内部承受压应力。考虑到主要的分析对象是顶部横梁和三个连杆连接位置的刚性，接触件可能不使用，房屋建设的几何模型的结合面如图2所示。在螺栓连接中，上外表和下外表共享一个关键位置；在没有螺栓连接时，上外表和下外表各自分别拥有一个关键位置。配合的时候，在共享的关键点会产生一个节点，当支柱和横梁连接，在支柱和横梁分开处，没有共享的关键点会产生两个节点。在左侧支柱的右外表和右侧支柱的左外表，根据实验计算结果，结构承受压应力。因此支柱和横梁将分享所有的节点不仅是螺栓。这不仅是忽略连接件而且展示了螺栓连接的特征。在支柱底部和底架之间连接是完整约束。因为主要的分析目的是顶部横梁的刚性,可以假设顶部横梁和三个连杆的连接位置承受同样的载荷。结构是薄壁件和壳件模型。机构外壁厚度和肋板厚度是不相同的。因此两组实常数是要设定的。为了建模的方便，两个支柱可是设置成其它组件。这个组件可以设成一个集合。这样横梁核心和支柱连接位置可以很容易的分辨出来。在修改正程中，建模和修改可以自动执行。分析模型如图1所示。因为模型和负载是对称的，模型计算可以节省一半时间。因此根底组件可以减少到8927,而且总的节点可以减少到4341.所有的组件都是三角形的。3最优化解决方案最优化过程是计算和修改正程的本质。初始设计被用来做重复计算过程的初始条件。计算过程的结束条件是三个连杆和顶部横梁连接位置的刚性偏差小于给定公差或者重复计算时间超出期望值。考虑到问题的特性，可以猜测，刚性值相同的位置是存在的。如果迭代不是收敛的，原因不可能是不相称偏转增大或者是计算时间缺乏。为了使迭代过程快速高效收敛，本论文采用等分搜索的方法改变步长去修改顶梁束位移。