塔式起重機(jī)有限元分析外文翻譯

FEMOptimizationforRobotStructureWangShijun,ZhaoJinjuan*DepartmentofMechanicalEngineering,Xi'anUniversityofTechnologyShaanxiProvince,People'sRepublicofChinaInstituteofPrintingandPackingEngineering,Xi'anUniversityofTechnologyAbstractInoptimaldesignforrobotstructures,designmodelsneedtohemodifiedandcomputedrepeatedly.Becausemodifyingusuallycannotautomaticallyberun,itconsumesalotoftime.ThispapergivesamethodthatusesAPDLlanguageofANSYS5.5softwaretogenerateanoptimalcontrolprogram,whichmikeoptimalprocedurerunautomaticallyandoptimalefficiencybeimproved.1〕IntroductionIndustrialrobotisakindofmachine,whichiscontrolledbycomputers.Becauseefficiencyandmaneuverabilityarehigherthantraditionalmachines,industrialrobotisusedextensivelyinindustry.Forthesakeofefficiencyandmaneuverability,reducingmassandincreasingstiffnessismoreimportantthantraditionalmachines,instructuredesignofindustrialrobot.Alotofmethodsareusedinoptimizationdesignofstructure.Finiteelementmethodisamucheffectivemethod.Ingeneral,modelingandmodifyingaremanual,whichisfeasiblewhenmodelissimple.Whenmodeliscomplicated,optimizationtimeislonger.Inthelongeroptimizationtime,calculationtimeisusuallyverylittle,amajorityoftimeisusedformodelingandmodifying.Itiskeyofimprovingefficiencyofstructureoptimizationhowtoreducemodelingandmodifyingtime.APDLlanguageisaninteractivedevelopmenttool,whichisbasedonANSYSandisofferedtoprogramusers.APDLlanguagehastypicalfunctionofsomelargecomputerlanguages.Forexample,parameterdefinitionsimilartoconstantandvariabledefinition,branchandloopcontrol,andmacrocallsimilartofunctionandsubroutinecall,etc.Besidesthese,itpossessespowerfulcapabilityofmathematicalcalculation.Thecapabilityofmathematicalcalculationincludesarithmeticcalculation,comparison,rounding,andtrigonometricfunction,exponentialfunctionandhyperbolafunctionofstandardFORTRANlanguage,etc.BymeansofAPDLlanguage,thedatacanbereadandthencalculated,whichisindatabaseofANSYSprogram,andrunningprocessofANSYSprogramcanbecontrolled.Fig.1showsthemainframeworkofaparallelrobotwiththreebars.Whenthelengthofthreebarsarechanged,conjunctendofthreebarscanfollowagiventrack,whererobothandisinstalled.Coreoftopbeamistriangle,owingtothreebarsusedinthedesign,whichisshowedinFig.2.Useofthreebarsmakestopbeamnonsymmetricalalongtheplanethatisdefinedbytwocolumns.AccordingtoaqualitativeanalysisfromFig.1,Stiffnessvaluesalongz-axisaredifferentatthreejointlocationsonthetopbeamandstiffnessatthelocationbetweenbar1andtopbeamislowest,whichisconfirmedbycomputingresultsoffiniteelement,too.Accordingtodesigngoal,stiffnessdifferenceatthreejointlocationsmusthewithinagiventolerance.Inconsistentofstiffnesswillhaveinfluenceonthemotionaccuracyofthemanipulatorunderhighload,soitisnecessarytofindtheaccuratelocationoftopbeamalongx-axis.Tothequestionspresentedabove,thegeneralsolutionistochangethelocationofthetopbeammanytimes,comparetheresultsandeventuallyfindaproperposition,Themodelwillbemodifiedaccordingtothelastcalculatingresulteachtime.Itisdifficulttoavoidmistakesiftheiterativeprocessiscontrolledmanuallyandtheiterativetimeistoolong.Theouterwallandinnerribshapesofthetopbeamwillbechangedafterthemodelismodified.Tofindtheappropriatelocationoftopbeam,themodelneedstobemodifiedrepetitiously.Fig.1SolutionofOriginalDesignThispapergivesanoptimizationsolutiontothepositionoptimizationquestionofthetopbeambyAPDLlanguageofANSYSprogram.Aftertheanalysismodelfirstfounded,theoptimizationcontrolprogramcanbeformedbymeansofmodelinginstructioninthelogfile.Thelateriterativeoptimizationprocesscanbefinishedbytheoptimizationcontrolprogramanddonotneedmanualcontrol.Thetimespentinmodifyingthemodelcanbedecreasedtotheignorableextent.Theefficiencyoftheoptimizationprocessisgreatlyimproved.2〕ConstructionofmodelforanalysisThestructureshowninFig.1consistsofthreeparts:twocolumns,onebeamandthreedrivingbars.ThecolumnsandbeamarejoinedbytheboltsonthefirsthorizontalriblocatedontopofthecolumnsasshowninFig.1.Becausethedrivingbarsaresubstitutedbyequivalentforcesonthejointpositions,theirstructureisignoredinthemodel.Thecoreofthetopbeamisthreejointsandaholewithspecialpurpose,whichcannotbechanged.Theotherpartsofthebeammaybechangedifneeded.Fortheconvenienceofmodeling,thecoreofthebeamisformedintoonecomponent.Intheprocessofoptimization,onlythecorepositionofbeamalongxaxisischanged,thatistosay,shapeofbeamcoreisnotchanged.Itshouldbenoticedthat,intherestofbeam,onlyshapeischangedbutthetopologyisnotchangedandwhichcanautomaticallybeperformedbythecontrolprogram.Fig.1,sixboltsjointhebeamandtwocolumns.Thejointsurfacecannotbearthepullstressinthenon-boltjointpositions,inwhichitisbettertosetcontactelements.Whenthemodelincludescontactelements,nonlineariterativecalculationwillbeneededintheprocessofsolutionandthecomputingtimewillquicklyincrease.Thetrialcomputingresultnotincludingcontactelementshowsthattheoutsideofbeambearspullingstressandtheinnerofbeambearsthepressstress.Consideringtheprimaryanalysisobjectisthejointpositionstiffnessbetweenthetopbeamandthethreedrivingbars,contactelementsmaynotused,hutconstructsthegeometrymodelofjointsurfaceasFig.2showing.Theuppersurfaceandtheundersurfaceshareonekeypointinbolt-jointpositionsandtheuppersurfaceandtheundersurfaceseparatelypossessownkeypointsinnoboltpositions.Whenmeshed,onenodewillbecreatedatsharedkeypoint,wherecolumnsandbeamarejoined,andtwonodeswillbecreatedatnonsharedkeypoint,wherecolumnandbeamareseparated.Onrightsurfaceofleftcolumnandleftsurfaceofrightcolumn,accordingtotrialcomputingresult,thestructurebearspressstress.Therefore,thecolumnsandbeamwillshareallkeypoints,notbutatbolts.Thiscannotonlyomitcontactelementbutalsoshowthecharacteristicofboltjoining.Thejoiningbetweenthebottomsofthecolumnsandthebasearetreatedasfullconstraint.Becausethemainaimofanalysisisthestiffnessofthetopbeam,itcanbeassumedthatthejointpositionshearthesameasloadbetweenbeamandthethreedrivingbars.Thestructureisthethinwallcastandsimulatedbyshellelement.Thethicknessoftheoutsidewallofthestructureandtheribarenotequal,sotwogroupsofrealconstantshouldheset.Fortheconvenienceofmodeling,thetwocolumnsarealsosetintoanothercomponent.Thecomponentscancreateanassembly.Inthisway,thejointpositionsbetweenthebeamcoreandcolumnscouldheeasilyselected,inthemodifyingthemodelandmodifyingprocesscanautomaticallybeperformed.AnalysismodelisshowedFig.1.Becausemodelandloadaresymmetric,computingmodelisonlyhalf.Sothetotalofelementsisdecreasedto8927andthetotalofnodesisdecreasedto4341.Allelementsaretriangle.3.〕OptimizationsolutionTheoptimizationprocessisessentiallyacomputingandmodifyingprocess.Theoriginaldesignisusedasinitialconditionoftheiterativeprocess.Theendingconditionoftheprocessisthatstiffnessdifferencesofthejointlocationsbetweenthreedrivingbarsandtopbeamarelessthangiventoleranceoriterativetimesexceedexpectedvalue.Consideringthespecialityofthequestion,itisforeseenthatthelocationisexistentwherestiffnessvaluesareequal.Ifiterativeisnotconvergent,thecausecannotbeotherwisethaninappropriatedisplacementincrementordeficientiterativetimes.Inordertomaketheiterativeprocessconvergentquicklyandefficiently,thispaperusesthebisectionsearchingmethodchangingsteplengthtomodifythetopbeamdisplacement.Thismethodisalittlecomplexbuttherequirementontheinitialconditionisrelativelymild.Theflowchartofoptimizationasfollows:1.Readthebeammodeldataininitialpositionfrombackupfile;2.Modifythepositionofbeam;3.Solve;4.Readthedeformofnodeswherebeamandthreebarsarejoined;5.Checkwhethertheconvergentconditionsaresatisfied,ifnot,thencontinuetomodifythebeamdisplacementandreturnto3,otherwise,exittheiterationprocedure.6.Savetheresultsandthenexit.Theprogram'sprimarycontrolcodesandtheirfunctioncommentariesaregiveninit,ofwhichthedetailedmodelinginstructionsareomitted.Fortheconvenienceofcomparingwiththecontrolflow,thenecessarynotesareadded.theflagofthebatchfileinANSYSBATCHRESUME,robbak.db,0readoriginaldatafromthebackupfilerobbak,.db/PREP7enterpreprocessordeletethejointpartbetweenbeamcoreandcolumnsmovethecoreofthebeambyone:steplengthapplyloadandconstraintonthegeometrymeshingthejointpositionbetweenbeamcoreandcolumnsFINISHexitthepreprocessorISOLUentersolverSOLVEsolveFINISHexitthesolverPOST1enterthepostprocessor*GET,front,NODE,2023,U,Zreadthedeformationoffirstjointnodeonbeam*GET,back,NODE,1441,U,Zreadthedeformationofsecondjointnodeonbeamintoparameterhacklastdif-1theabsoluteofinitialdifferencebetweenfrontandhacklasttimeflag=-1thefeasibilityflagoftheoptimizationstep=0.05theinitialdisplacementfrominitialpositiontothecurrentposition*D0,1,1,10,1theiterationprocedurebegin,thecyclevariableisIanditsvaluerangeis1-10andsteplengthis1dif=abs(front-back)theabsoluteofthedifferencebetweenfrontandhackinthecurrentresult*IF,dif,LE,l.OE-6,THENcheckwhethertheabsolutedifferencedifsatisfiestherequestornoflag=lyes,setflagequalto1*EXITexittheiterativecalculation*ELSEIF,dif,GE,lastdif,THENcheckwhetherthedifvaluebecomesgreatornotflag=2yes,setflag2modifysteplengthbybisectionmethodperformthenextiterativecalculation,usethelastpositionasthecurrentpositionandmodifiedlaststeplengthasthecurrentsteplengthELSEiftheabsoluteofdifferencevalueisnotlessthanexpectedvalueandbecomesmallgradually,continuetomovetopbeamreadtheinitialconditionfrombackupfileenterthepreprocessorMEN,,P51X,,,step,,,,1movethecoreofthebeambyonesteplengthmodifythejointpositionsbetweenbeamcoreandcolumnapplyloadandconstraintmeshingFINISHexitpreprocessorISOLUentersolverSOLVEsolveFINISHexitthesolver/POST1exitthepostprocessor*GET,front,NODE,2013,U,Zreadthedeformationoffirstjointnodetoparameterfront*GET,back,NODE,1441,U,Zreadthedeformationofsecondjointnodetoparameterbacklastdif-difupdatethevalueoflastdif*ENDIFtheendoftheif-else*ENDDOtheendoftheDOcycleMostofthecontrolprogramaboveiscopiedfromlogfile,whichislong.Thetotaloflinesisuptoabout1000lines.Manycodessuchasmodelingandpost-processcodesareusedrepeatedly.Tomaketheprogramconstructclear,theseinstructionscanhemadeintomacros,whicharecalledbymainprogram.Thiscanefficientlyreducethelengthofthemainprogram.Inaddition,modelinginstructionsfromlogfileincludeslotsofspecialinstructionsthatareonlyusedundergraphicmodebutuselessunderhatchmode.DeletingandmodifyingtheseinstructionswhenunderbatchmodeinANSYScanreducethelengthofthefile,too.Intheprogramabove,thedeformationatgivenpositionisreadfromnodedeformation.Inmeshing,inordertoavoidgeneratinghadelements,trianglemeshisused.Inoptimization,theshapeofjointpositionbetweencolumnsandbeamcontinuallyischanged.Thismakestotalofelementsdifferentaftermeshingeachtimeandthenelementnumberingdifferent,too.Datareadfromdatabaseaccordingtonodenumberingmightnothedatatowant.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-0.71E-01mcomparedwiththeoriginaldesignedpositionBecausethespeedofcomputerreadinginstructionismuchfasterthanmodifyingmodelmanually,thetimemodifyingmodelcanbeignored.Thetimenecessaryforoptimizationmostlydependsonthetimeofsolution.Comparedwiththeoptimizationproceduremanuallymodifyingmodel,theefficiencyisimprovedandmistakeoperatinginmodelingisavoided.5〕ConclusionTheanalyzingresultrevealsthattheoptimizationmethodgiveninthispaperiseffectiveandreachestheexpectedgoal.Thefirstadvantageofthismethodisthatmanualmistakesdonoteasilyoccurinoptimizationprocedure.Secondly,itisprettyuniversalandthecontrolcodesgiveninthispapermayhetransplantedtouseinsimilarstructureoptimizationdesignwithoutlargemodification.Thedisadvantageisthatthetopologystructureoftheoptimizationobjectcannotbechanged.Themoretheworkloadofmodifyingthemodel,themoretheadvantagesofthismethodareshown.Inaddition,thetopologyoptimizationfunctionprovidedinANSYSisusedtosolvetheoptimizationproblemthatneedstochangethetopologystructure.Thebetteroptimizationresultscanheachievedifthemethodinthispapercombinedwithit.中文譯文：機(jī)器人機(jī)構(gòu)優(yōu)化設(shè)計有限元分析王世軍趙金娟西安大學(xué)機(jī)電工程系中國陜西西安大學(xué)出版社摘要機(jī)器人結(jié)構(gòu)最優(yōu)化設(shè)計，設(shè)計模型需要反復(fù)的修正和計算。應(yīng)為修改后的模型通常不能自動運行，需要大量的時間進(jìn)行調(diào)試。本論文給出一種采用有限元分析軟件ANSYS5.5參數(shù)化設(shè)計語言生成一種最優(yōu)化控制的方法，這種方法能給出最優(yōu)自動運行過程和提高效率。1〕簡介工業(yè)機(jī)器人是一種用電腦控制的機(jī)械機(jī)構(gòu)。因為效率和可操作性比傳統(tǒng)機(jī)械要高，因此工業(yè)機(jī)器人廣泛的用于工業(yè)生產(chǎn)中。相對傳統(tǒng)機(jī)械來說，在工業(yè)機(jī)器人的結(jié)構(gòu)設(shè)計中，為了到達(dá)高效率和可操作性的目的，減少重量和增加剛度顯得更加重要。在結(jié)構(gòu)設(shè)計中有很多的方法，一般而言，有限元法是最有效的方法之一。當(dāng)所需模型比擬簡單時，建模和修改采用手工操作是可行的。當(dāng)模型復(fù)雜時，優(yōu)化時間是比擬長的。在相當(dāng)長的優(yōu)化時間內(nèi)，計算時間是非常少的，大多數(shù)時間是用來建模和修改模型的。如何減少結(jié)構(gòu)優(yōu)化過程中的建模和修改模型所用時間是提高效率的關(guān)鍵所在。ANSYS參數(shù)化設(shè)計語言是一種基于有限元分析的交互式開發(fā)工具，通常被程序設(shè)計人員使用。ANSYS參數(shù)化設(shè)計語言具有一個典型功能及它包含多數(shù)大型計算機(jī)語言，例如，定義參數(shù)像定義常量和變量，條件轉(zhuǎn)移和循環(huán)控制，以及宏調(diào)用像調(diào)用函數(shù)和子程序等。除此之外，它具有強(qiáng)大的數(shù)學(xué)計算控制能力。這種數(shù)學(xué)計算能力包括算法，計算，比照，湊整和三角函數(shù)功能，指數(shù)函數(shù)功能和標(biāo)準(zhǔn)福傳語言的雙曲線功能等。依靠ANSYS參數(shù)化設(shè)計語言，數(shù)據(jù)能夠在ANSYS數(shù)據(jù)庫中被閱讀和計算，并且在ANSYS程序運行過程中受到控制。圖1表示三連桿平行機(jī)器人的主要框架。沿Z軸的剛性值在頂部梁的三個連接處是不一樣的。在連桿1和頂部梁連接處得剛性是最小的，這也是通過有限元分析計算結(jié)果來確定的。根據(jù)設(shè)計目的，在三個連接點的不同的剛性必須要有給定的公差。當(dāng)機(jī)械手在進(jìn)行高強(qiáng)度工作時，一致的剛性會對它的運行精度產(chǎn)生影響，因此在沿X軸設(shè)置一個精確的位置是非常有必要的。根據(jù)上面提出的問題，一般的解決方法經(jīng)常是改變頂部梁連接點的位置，比照結(jié)果，然后找到一個適宜的位置，模型每次都要根據(jù)最后的計算結(jié)果進(jìn)行修改。如果采用人工的控制這個重復(fù)的過程且重復(fù)時間過長，這樣就難免出現(xiàn)錯誤。當(dāng)模型被修改時，頂部梁外壁和內(nèi)部肋板的形狀也隨之發(fā)生改變。模型需要重復(fù)的去修改才能找出恰當(dāng)?shù)奈恢?。圖1初始設(shè)計方案本論文通過ANSYS程序的參數(shù)化設(shè)計語言給出一個尋找最優(yōu)位置問題的最正確解決方法。經(jīng)過對事先建立的模型進(jìn)行分析，通過建模系統(tǒng)指令在新的文件里形成一個最正確的控制程序，通過這個最正確的控制程序可以完成以后的重復(fù)最優(yōu)化過程，而且不需要手工控制。在修改模型上消耗的時間可以減少到被忽略的程度。最優(yōu)化步驟的效率得到很大提高。2〕建筑模型分析圖1所示結(jié)構(gòu)包括了三個局部：兩個支柱，一個頂部梁和三個操作連桿。支柱和橫梁通過位于支柱上面的水平肋板連接在一起，如圖1所示。因為操作連桿被連接位置的等效構(gòu)件代替，所以在模型中它們的結(jié)構(gòu)被忽略了。頂部橫梁的核心是三個連接處和一個特殊作用的孔，這些都是固定不變的。其他部件可以根據(jù)需求進(jìn)行修改。為了建模的方便，橫梁的核心被制成一個零件。在進(jìn)行最優(yōu)化的過程中，只有沿著X軸的橫梁中心位置是變化的，也就是說，橫梁核心的形狀是不變的.應(yīng)該注意的是，橫梁的其余局部只有形狀變化而拓?fù)涫枪潭ǖ?，可以通過控制程序自動執(zhí)行.圖2頂部橫梁核心圖1.六個螺栓連接橫梁和支柱。在沒有螺栓連接的位置，其結(jié)合面不能承受拉應(yīng)力，最好在該位置設(shè)置接觸件。當(dāng)模型中包括接觸件，非線性元件時，在解決方案過程中重復(fù)計算是必要的，并且計算時間會快速增加。不包括接觸件的實驗計算結(jié)果顯示橫梁外部承受拉伸應(yīng)力，橫梁內(nèi)部承受壓應(yīng)力?？紤]到主要的分析對象是頂部橫梁和三個連桿連接位置的剛性，接觸件可能不使用，房屋建設(shè)的幾何模型的結(jié)合面如圖2所示。在螺栓連接中，上外表和下外表共享一個關(guān)鍵位置；在沒有螺栓連接時，上外表和下外表各自分別擁有一個關(guān)鍵位置。配合的時候，在共享的關(guān)鍵點會產(chǎn)生一個節(jié)點，當(dāng)支柱和橫梁連接，在支柱和橫梁分開處，沒有共享的關(guān)鍵點會產(chǎn)生兩個節(jié)點。在左側(cè)支柱的右外表和右側(cè)支柱的左外表，根據(jù)實驗計算結(jié)果，結(jié)構(gòu)承受壓應(yīng)力。因此支柱和橫梁將分享所有的節(jié)點不僅是螺栓。這不僅是忽略連接件而且展示了螺栓連接的特征。在支柱底部和底架之間連接是完整約束。因為主要的分析目的是頂部橫梁的剛性,可以假設(shè)頂部橫梁和三個連桿的連接位置承受同樣的載荷。結(jié)構(gòu)是薄壁件和殼件模型。機(jī)構(gòu)外壁厚度和肋板厚度是不相同的。因此兩組實常數(shù)是要設(shè)定的。為了建模的方便，兩個支柱可是設(shè)置成其它組件。這個組件可以設(shè)成一個集合。這樣橫梁核心和支柱連接位置可以很容易的分辨出來。在修改正程中，建模和修改可以自動執(zhí)行。分析模型如圖1所示。因為模型和負(fù)載是對稱的，模型計算可以節(jié)省一半時間。因此根底組件可以減少到8927，而且總的節(jié)點可以減少到4341.所有的組件都是三角形的。3〕最優(yōu)化解決方案最優(yōu)化過程是計算和修改正程的本質(zhì)。初始設(shè)計被用來做重復(fù)計算過程的初始條件。計算過程的結(jié)束條件是三個連桿和頂部橫梁連接位置的剛性偏差小于給定公差或者重復(fù)計算時間超出期望值?？紤]到問題的特性，可以猜測，剛性值相同的位置是存在的。如果迭代不是收斂的，原因不可能是不相稱偏轉(zhuǎn)增大或者是計算時間缺乏。為了使迭代過程快速高效收斂，本論文采用等分搜索的方法改變步長去修改頂梁束位移。這種方法有點復(fù)雜但是在初始條件上的要求不苛刻。以下是最優(yōu)化生產(chǎn)的流程圖：1在備份文件中確定橫梁初始位置的模型基準(zhǔn)2修改橫梁位置3解決4確定橫梁和三個連桿連接處的節(jié)點變形5檢查收斂條件是否適宜，如果不適宜，那么繼續(xù)去修改束位移并且返回到步驟3，否那么退出迭代程序。6保存數(shù)據(jù)然后退出程序的主要控制代碼和功能評注要保存一起，詳細(xì)的建模指令被忽略。為了比擬的方便，要添加必要的注釋。BATCHRESUME,robbak.db,0從備份文件中讀取原始資料/PREP7預(yù)處理程序刪除橫梁核心和支柱連接局部以一個步長移動橫梁核心應(yīng)用載荷和約束橫梁核心和支柱嚙合FINISH退出預(yù)處理程序ISOLU進(jìn)入計算器SOLVE解答FINISH退出解答POST1進(jìn)入后處理程序*GET,front,NODE,2023,U,Z讀取橫梁第一個節(jié)點的變形*GET,back,NODE,1441,U,Z讀取橫梁第二個節(jié)點的變形lastdif-1前后時間差計算flag=-1