已阅读5页,还剩1页未读, 继续免费阅读
版权说明:本文档由用户提供并上传,收益归属内容提供方,若内容存在侵权,请进行举报或认领
文档简介
IntJAdvManufTechnol(2001)18:7847892001Springer-VerlagLondonLimitedAClampingDesignApproachforAutomatedFixtureDesignJ.CecilVirtualEnterpriseEngineeringLab(VEEL),IndustrialEngineeringDepartment,NewMexicoStateUniversity,LasCruces,USAInthispaper,aninnovativeclampingdesignapproachisdescribedinthecontextofcomputer-aidedfixturedesignactivi-ties.Theclampingdesignapproachinvolvesidentificationofclampingsurfacesandclamppointsonagivenworkpiece.Thisapproachcanbeappliedinconjunctionwithalocatordesignapproachtoholdandsupporttheworkpieceduringmachiningandtopositiontheworkpiececorrectlywithrespecttothecuttingtool.Detailedstepsaregivenforautomatedclampdesign.Geometricreasoningtechniquesareusedtodeterminefeasibleclampfacesandpositions.TherequiredinputsincludeCADmodelspecifications,featuresidentifiedonthefinishedworkpiece,locatorpointsandelements.Keywords:Clamping;Fixturedesign1.MotivationandObjectivesFixturedesignisanimportanttask,whichisanintegrationlinkbetweendesignandmanufacturingactivities.Theautomationoffixturedesignactivitiesandthedevelopmentofcomputer-aidedfixturedesign(CAFD)methodologiesarekeyobjectivestobeaddressedforthesuccessfulrealisationofnextgenerationmanufacturingsystems.Inthispaper,aclampdesignapproachisdiscussed,whichfacilitatesautomationinthecontextofanintegratedfixturedesignmethodology.Clampdesignapproacheshavebeenthefocusofseveralresearchefforts.TheworkofChou1focusedonthetwincriteriaofworkpiecestabilityandtotalrestraintrequirement.Theuseofartificialintelligence(AI)approachesaswellasexpertsystemapplicationsinfixturedesignhasbeenwidelyreported2,3.PartgeometryinformationfromaCADmodelhasalsobeenusedtodrivethefixturedesigntask.Bidanda4describedarule-basedexpertsystemtoidentifythelocatingandclampingfacesforrotationalparts.Theclampingmech-anismisusedtoperformboththelocatingandclampingCorrespondenceandoffprintrequeststo:DrJ.Cecil,VirtualEnterpriseEngineeringLab(VEEL),IndustrialEngineeringDepartment,NewMexicoStateUniversity,LasCruces,NM88003,USA.E-mail:jcecilL50560functions.Otherresearchers(e.g.DeVoretal.5,6)haveanalysedthecuttingforcesandbuiltmechanisticmodelsfordrilling,andothermetalcuttingprocesses.Kangetal.2definedassemblyconstraintstomodelspatialrelationshipsbetweenmodularfixtureelements.Severalresearchershaveemployedmodularfixturingprinciplestogeneratefixturedesigns2,711.Otherfixturedesigneffortshavebeenreportedin1,3,9,1223.Anextensivereviewoffixturedesignrelatedworkcanbefoundin21,24.InSection2,thevariousstepsintheoverallapproachtoautomatetheclampingdesigntaskareoutlined.Section3describesthedeterminationoftheclampsizetoholdawork-pieceduringmachiningandinSection4,theautomaticdetermi-nationoftheclampingsurfaceorfaceregiononaworkpieceisdetailed.Section5discussesthedeterminationoftheclamp-ingpointsonaworkpiece.2.OverallApproachtoClampDesignInthissection,theoverallclampingdesignapproachisdescribed.Clampingisusuallycarriedouttoholdthepartinadesiredpositionandtoresisttheeffectsofcuttingforces.Clampingandlocatingproblemsinfixturedesignarehighlyrelated.Often,theclampingandlocatingcanbeaccomplishedbythesamemechanism.However,failuretounderstandthatthesetwotasksareseparateaspectsoffixturedesignmayleadtoinfeasiblefixturedesigns.Humanprocessplannersgenerallyresolvethelocatingproblemfirst.Theapproachdevelopedcanworkinconjunctionwithalocatordesignstrategy.However,theoveralllocatorandsupportdesignapproachisbeyondthescopeofthispaper.CADmodelsofthepartdesign(forwhichtheclampdesignhastobedeveloped),thetolerancespecifications,processsequence,locatorpointsanddesign,amongotherfactors,aretheinputstotheclampdesignapproach.Thepurposeofclampingistoholdthepartsagainstlocatorsandsupports.Theguidingthemeusedistotrynottoresistthecuttingormachiningforcesinvolvedduringamachiningoperation.Rather,theclampsshouldbepositionedsuchthatthecuttingforcesareinthedirectionthatwillassistinholdingthepartsecurelyduringaspecificmachiningoperation.BydirectingAClampingDesignApproach785thecuttingforcestowardsthelocators,thepart(orworkpiece)isforcedagainstsolid,fixedlocatingpointsandsocannotmoveawayfromthelocators.Theclampdesignapproachdiscussedheremustbeviewedinthecontextoftheoverallfixturedesignapproach.Priortoperforminglocator/supportandclampdesign,aprelimi-naryphaseinvolvinganalysisandidentificationoffeatures,associatedtolerancesandotherspecificationsisnecessary.Basedontheoutcomeofthispreliminaryevaluationanddetermination,thelocator/supportdesignandclampdesigncanbecarriedout.Theclampdesignapproachdescribedinthispaperisdiscussedbasedontheassumptionthatlocator/supportdesignattributeshavebeendeterminedearlier(thisincludesdeterminationofappropriatelocatorandsupportfacesonaworkpieceaswellasidentificationoflocatorandsupportfixturingelementssuchasV-blocks,baseplates,locatingpins,etc).2.1InputstoClampDesignTheinputsincludethewinged-edgemodelofthegivenproductdesign,thetoleranceinformation,theextractedfeatures,theprocesssequenceandthemachiningdirectionsforeachoftheassociatedfeaturesinthegivenpartdesign,thelocationfacesandlocatordevices,andthemachiningforcesforthevariousprocessesrequiredtoproduceeachcorrespondingfeature.2.2ClampDesignStrategyThemainstepsintheautomationoftheclampingdesigntaskaresummarisedinFig.1.Anoverviewofthesestepsisasfollows:Step1.Considertheset-upSUiintheset-upconfigurationlistalongwiththeassociatedprocessH20841featureentries.Step2.Identifythedirectionandtypeofclamping.Theinputsrequiredarethemachiningdirectionvectorsmdv1,mdv2,.,mdvnandidentifiednormalvectorsofsupportfacenvs.Ifthemachiningdirectionsaredownward(whichcorrespondtothedirectionvector0,0,1),andthenormalvectorofthesupportfaceisparalleltothemachiningdirection,thenthedirectionofclampingisparalleltothedownwardmachiningdirection0,0,1.Ifsidewaysclampingisrequired,andiftherearenofeasibleregionsatwhichtopositionaclampfordownwardclamping,thenaside-clampdirectionisobtainedasfollows.Letsvandtvbethenormalvectorsofthesecondary(sv)andtertiary(tv)locatingfaces.Then,thedirectionofclampingusedbyaside-clampingmechanismsuchasav-blockshouldbeparalleltoboththesenormalvectors,i.e.thenormalvectorsoftheeachofthev-surfacesinthev-blockwillbeparalleltosvandtv,respectively.Thesideclampingfaceshouldbeapairoffacesparalleltothefacessvandtv,respectively.Step3.Determinethehighestmachiningforcefromthemach-iningforceslist(foreachfeature)MFi(i=1,.,n).ThiswillbetheeffectiveforceFEthatmustbebalancedwhiledesigningtheclampforthisset-upSUi.Step4.UsingthevalueofthecalculatedhighestmachiningforceFE,thedimensionsoftheclamptobeusedtoholdtheFig.1.Theclampdesignactivities.workpiececanbedetermined(forexample,astrapclampcanbeusedasaclampingmechanism).TheapproachforthistaskisexplainedinSection3.Step5.Determinetheclampingfaceonagivenworkpiece.ThisstepcanbeautomatedasdescribedinSection4.Step6.TheactualpositionoftheclampontheclampingfaceisdeterminedinanautomatedmannerasexplainedinSection5.Considernextset-upSU(i+1)andproceedtostep1.3.DeterminationoftheClampSizeInthiswork,theclampsusedbelongtothefamilyofclampsreferredtoasstrapclamps.Astrapclampisbasedonthesameprincipleasthatofthelever(seeFig.2).Inthissection,theautomateddesignofastrapclampisdescribed.Theclampingforcerequiredisrelatedtothesizeofthescreworathreadeddevicethatholdstheclampinplace.Theclampingforceshouldbalancethemachiningforcetoholdtheworkpieceinposition.LettheclampingforcebeWandthescrewdiameterbed.Thedimensionsofthevariousscrewsizesforvariousclampingforcescanbedeterminedinthefollowingmanner.Initially,theultimatetensilestrength(UTS)ofthematerialoftheclamp(dependingonavailability)canberetrievedfromadatalibrary.Variousmaterialshavedifferenttensilestrengths.Theselectionoftheclampmaterialcanalsobeperformeddirectlyusingheuristicrules.Forexample,ifthepartmaterialismildsteel,thentheclampmaterialcanbelow786J.CecilFig.2.Thestrapclamp.carbonsteelormachinesteel.Todeterminethedesignstress,theUTSvaluecanbedividedbyasafetyfactor(suchas4or5).TherootareaA1ofthescrew(foraclampsuchasascrewclamp)canthenbedetermined:Clampingforcerequired/DesignStressDS.Subsequently,thefullareaFAoftheboltcross-sectioncanbecomputedasequaltoA1/(65%)(sincetherootareaofthescrewwhereshearingcanoccurisapproximately65%ofthetotalareaofthebolt).ThediameterofthescrewdcanthenbedeterminedbyequatingFAto(3.14d2/4).AnotherequationwhichcanbeusedinvolvesrelatingthewidthB,heightHandspanLoftheclamptothescrewdiameterd(B,H,andLcanbecomputedforvariousvaluesofd):d2=4/3BH2/L.4.TheDeterminationoftheClampingFaceTherequiredinputstodeterminetheclampingregionincludetheCADmodeloftheproduct,theextractedfeaturesinfor-mation,thefeaturedimensionsandfacesonwhichtheyoccur,thelocatingfacesandlocatorsselected.ConsiderapotentialclampingfacePCFasshowninFig.3.Thecrucialcriteriontobesatisfiedisthattheclampingsurfaceshouldnotoverlaporintersectwiththefeaturesonthatface,asshowninFig.4.Theclampingsurfacearea,whichisincontactwiththeworkpiecesurface(orPCF)isa2Dprofileconsistingoflinesegments(seeFig.6).Byusinglinesegmentintersectiontests,itcanbedeterminedwhetherthepotentialclampingareaofcontactoverlapsanyofthefeaturesonthegivenPCF.Thedeterminationofclampingfacescanbeautomatedasfol-lows:Fig.3.Potentialclampingfaceandfeatureprofiles.Fig.4.Potentialclampingfaceandclampboxprofile.Step1.Identifyfacesthatareparalleltothesecondaryandtertiarylocatorfaces(lf1andlf2)andatthefarthestdistancefromlf1andtcj,respectively.Thisisperformedasshownbelow:(a)Identifyfacestci,tcjsuchthattciisparalleltolf1andtcjisparalleltolf2.(b)InsertcandidatefacestciinlistTCF.(c)ByexaminingallfacestcilistedinTCF,determinefacestciandtcjthatarefarthestfromfacelf1andlf2,respect-ively,anddiscardallotherfacesfromlistTCF.Step2.Identifythefacethatisparalleltothelocationfacesbutnotadjacenttotheadditionallocatorfaces.Itispreferabletoselectaclampfacethatdoesnothavetosharetheadjacentperpendicularfacewithalocator.Thisstepcanbeautomatedasshownbelow:(a)ConsidereachfacetciinlistTCFandobtaincorrespond-ingfacesfcithatareadjacentandperpendiculartoeachtci.Then,inserteachfacefciinlistFCF.(b)Examineeachfciandperformthefollowingtest:Iffciisadjacent,perpendiculartolf1orlf2,thendiscarditfromlistFCFandinsertitinlistNTCF.Step3.Determinetheclampingfaces,basedontheavailabilityofpotentialclampingfaces,asdescribedbelow.Case(a).IftherearenoentriesinlistNTCF,thenusethefacesinlistTCFandproceedtostep4.Ifanyfaceswerefoundthatwereperpendiculartothesecondaryandtertiarylocationfaceslf1andlf2,suchfacesarethenextfeasiblechoicestobeusedforclamping.Inthiscase,theonlyremainingchoiceistore-examinethefacesinlistNTCF.Case(b).IfthenumberofentriesinlistNTCFis1,thefeasibleclampingfaceisfci.Thenormalvectorofthecorrespondingadjacent,perpendicularfacetciistheaxisofclamping.Case(c).IfnumberofentriesinlistNTCFisgreaterthan1,determinethefacetciwithlargerareaandproceedtostep4.Step4.Dependingonthedirectionofclampingwhichiseither(+or)1,0,0or(+or)0,1,0,theclampcanbepositionedalongthecentreofthefacetci.Thecandidategeometricalpositionsoftheclampcanbedeterminedusingpartgeometryandtopologicalinformation,whichisdescribedinthenextsection.AClampingDesignApproach787Fig.5.Determinationoftheclampprofiledimensions.5.DeterminationoftheClampingPointsonaClampingFaceAftertheclampfacehasbeendetermined,theactualclampingpositionsonthatfacemustbedetermined.Theinputsaretheclampprofiledimensions,clampdirectionsx,y,z,andpoten-tialclampingfaceCF.Theclampprofiledimensionsareobtained(asincase(g)usingCFgeometryasfollows.Thefirststepistodetermineaboxsize,whichistestedtodeterminewhetheritcontainsanyfeaturesinsideit.Profileintersectiontestscanalsobeperformedusingthemethoddescribedearlier.Iftheintersectiontestreturnsanegativeresult,thennofeatureintersectswiththeclampboxprofile,asshowninFig.4.Iftheintersectiontestreturnsapositiveresult,thefollowingstepscanbeperformed:1.Dividetheclampboxprofileintosmallerrectangularstripsofsize(1w)(Figs5and6).2.PerformtheintersectiontestswiththefeatureprofilesoffeaturesthatoccuronthefaceCFforthegivenpartdesign.Fig.6.Profilesintersectiontestoffeatureandclampregions.3.Therectangularstrips,wherenofeatureintersectionoccurs,arefeasibleclampingregions.Ifthereismorethanonecandidaterectangleforclamping,therectangleprofilethatistowardthemid-pointoftheCFfacealongtheclampingaxisistheclampprofile(andclamppoints).IfnoprofilePicanbefoundthatdoesnotintersectwiththefeatureprofiles,clampwidthcanbereducedbyhalfandthenumberofclampsincreasedtotwoonthatface.Usingthesemodifiedclampdimensions,performthefeatureintersectiontestdescribedearlier.Ifthistestalsofails,thenthesidefaceadjacenttothePCFcanbeusedastheclampingsurfacetoperformsideclamping.ThesidefacethenbecomesthePCFandthefeatureintersectiontestcanberepeated.5.1TheIntersectionofProfilesTestTherequiredinputsincludethe2DprofileP1another2DprofileP2.Theintersectionofprofilescanbedeterminedinanautomatedmannerusingthefollowingapproach.EachinputprofilePiconsistsofaclosedloopoflinesegmentsLij.Thestepsinthisprofiletestareasfollows:(T1)ConsideralinesegmentL(i,1)inP1andanotherlinesegmentL(2,j)inP2.(T2)ForinputsL(i,1)andL(2,j),theintersectionofedgescanbeemployed.Iftheedgeintersectiontestreturnsapositivevalue,thenthefeatureprofileintersectswiththecandidateorpotentialclampprofileunderevaluation.Ifitreturnsanegativevalue,proceedtostep3.(T3)Repeatstep(T1)forthesamesegmentoredge(Li,1)inP1withallremainingsegments(L2,j+1)tillj=n1inP2.(T4)Repeatsteps(T1)and(T2)fortheremainingedgesorsegmentsL12,L13,.,L1ninprofileP1.Ifthefeatureprofilesoverlaptheclampingprofiles,thelineintersectiontestswilldeterminethatoccurrence.Theinter-sectionofedgestestcanbeperformedautomaticallytodetectwhethertwoedgesintersectwitheachother.TheinputsrequiredforthistestarethelinesegmentsL12connecting(x1,y1)and(x2,y2)andL34connecting(x3,y3)and(x4,y4).LettheequationofL12berepresentedby:F(x,y)=0(1)andthatofL34by:H(x,y)=0(2)Step1.UsingEq.(1)computer3=F(x3,y3)bysubstitutingx3andy3forxandyandcomputer4=F(x4,y4)bysubstitut-ingx4andy4forxandy.Step2.Ifr3isnotequalto0,r4isnotequalto0,andthesignsofr3andr4arethesame,(whichindicater1andr2lieonsameside),thentheedgesL12andL34donotintersect.Ifthisisnotsatisfied,thenstep(3)isperformed.Step3.UsingEq.(2),computer1=H(x1,y1).Then,computer2=G(x2,y2)andproceedtostep4.Step4.Ifr1isnotequaltozero,r2isnotequaltozero,andthesignsofbothr1andr2arethesame,thenr1,r2lieon788J.CecilFig.7.Sampleparttoillustratetheclampingdesignapproach.thesamesideandtheinputlinesegmentsdonotintersect.Else,ifthisconditionisnotsatisfied,proceedtostep5.Step5.Thegivenlinesegmentsdointersect.Thiscompletesthetest.ConsiderthesamesamplepartshowninFig.7.Thefeaturestobeproducedareastepandhole.Initially,thelocatordesigniscompleted.Thesupportlocator(orprimarylocator)isabaseplate(placedagainstfacef4)andthesecondaryandtertiarylocatorsareplacedagainstfacesf6andf5(whichcorrespondtothelocatorfaceslf1andlf2discussedinSection4).Anancillarylocatorisalsoused,whichisav-block(positionedagainsttheancillaryfacesf3andf5),showninFig.8.BasedonthestepsoutlinedintheclampdesignFig.8.FixturedesignforthesamplepartinFig.7.approachdiscussedearlier,thecandidatefaces(whichareparallelandatthefarthestdistancefromlf1andlf2)arefacef3andf5.Therearenofaceswhichareparalleltothelocatorfacesbutnotadjacenttothem.Usingthepriorityrulesinsuchcases(asdiscussedinstep3ofSection4),theremainingcandidatefaceisfacef2.Theclampdirectionisdownward;thev-blockradiallocatorandotherlocatorsprovidetherequiredlocationwiththeclampholdingtheworkpiecedown-wardagainstthebaseplate.ThepositionoftheclampisdeterminedbasedonthestepsdescribedinSection5.Astherearenofeauresoccurringonfacef2,thereisnoneedforfeatureintersectionteststodeterminecollision-freeclamping.Thepositionoftheclampshouldbeawayfromthev-locator(whichispositionedalongtheancillarylocationfaces)astheclampingfaceisadjacenttotheancillarylocationfaces(thisensuresbetteraccessforquickclamping).ThefinallocationandclampingdesignisshowninFig.8.Themethoddiscussedinthispapercomparesfavourablywiththeotherclampdesignmethodsdiscussedintheliterature.Theuniquenessofthediscussedapproachisthesystematicidentificationoftheclampingfacesbasedonpartgeometry,topology,andtheoccurrenceoffeaturestobemachined.Whileotherapproacheshavenotexploitedthepositionofthelocatorsadequately,theproposedmethodusesthelocatorstoholdtheworkpieceduringmachiningagainsttheprimary,secondary,andtertiarylocators.Anotheradvantageofthisapproachisthedeterminationofcandidatefeasiblelocationsonclampfacesusingthedetectionofprofileintersectionstest(describedearlier),whichquicklyandefficientlyidentifiespotentialdown-streamproblemswhichmayoccurduringclampingandmach-iningoffeatures.6.ConclusionInthispaper,theclampingdesignaspectsintheoverallcontextofafixturedesignmethodologywasdiscussed.Thelocatordesign,thepartdesignspecifications,andotherinputsareconsideredinidentifyingtheclampingfacesanddirections.Thevariousstepstoautomatethisapproacharealsodiscussed.References1.Y.C.Chou,V.ChandruandB.Barash,“Amathematicalapproachtoautomaticconfigurationofmachiningfixtures:analysisandsynthesis”,TransactionsASME,JournalofEngineeringforIndus-try,111(4),pp.299306,1989.2.Y.Kang,Y.RongandM.Sun,“Constraintbasedmodularfixtureassemblymodellingandautomateddesign”,ProceedingsoftheASMEManufacturingScienceandEngineeringDivision,8,pp.901908,1998.3.M.ManiandW.R.D.Wilson,“Automateddesignofworkholdingfixturesusingkinematicconstraintsynthesis”,16thNAMRC,pp.437444,1988.4.B.BidandaandP.H.Cohen,“Developmentofacomputeraidedfixtureselectionsystemforconcentricrotationalparts,”AdvancesinIntegratedDesignandManufacturing,Proceedings1990ASMEWinterAnnualMeeting,SanFrancisco,CA,vol.231,pp.151162,1990.AClampingDesignApproach7895.R.E.DeVor,V.ChandrasekharanandS.G.Kapoor,“Mechanisticmodeltopredictthecuttingforcesystemforarbitrarydrillpointgeometry”,TransactionsASMEJournalofManufacturingScienceandEngineering,120,pp.563570,1998.6.R.E.DeVor,S.G.KapoorandW.J.Endres,“Adualbasedapproachtothepredictionofmachiningforcesformetalcuttingprocesses:PartII,Modelvalidationandinterpretation”,Trans-actionsJournalofEngineeringforASMEIndustry,117,pp.534541,1995.7.M.V.GandhiandB.S.Thompson,“Automateddesignofmodularfixturesforflexiblemanufacturingsystems”,JournalofManu
温馨提示
- 1. 本站所有资源如无特殊说明,都需要本地电脑安装OFFICE2007和PDF阅读器。图纸软件为CAD,CAXA,PROE,UG,SolidWorks等.压缩文件请下载最新的WinRAR软件解压。
- 2. 本站的文档不包含任何第三方提供的附件图纸等,如果需要附件,请联系上传者。文件的所有权益归上传用户所有。
- 3. 本站RAR压缩包中若带图纸,网页内容里面会有图纸预览,若没有图纸预览就没有图纸。
- 4. 未经权益所有人同意不得将文件中的内容挪作商业或盈利用途。
- 5. 人人文库网仅提供信息存储空间,仅对用户上传内容的表现方式做保护处理,对用户上传分享的文档内容本身不做任何修改或编辑,并不能对任何下载内容负责。
- 6. 下载文件中如有侵权或不适当内容,请与我们联系,我们立即纠正。
- 7. 本站不保证下载资源的准确性、安全性和完整性, 同时也不承担用户因使用这些下载资源对自己和他人造成任何形式的伤害或损失。
最新文档
- 智慧博物馆解决方案V1.6
- 离散数学图与树
- 防水班组考试卷及答案
- 小学数学试卷三年级上册数学期末测试卷及参考答案(夺分金卷)
- 二年级上册数学期末测试卷及参考答案(综合题)
- 小学四年级下册数学期末测试卷附答案(基础题)
- 教科版科学三年级下册第一单元《 物体的运动》测试卷含完整答案(各地真题)
- 人教版小学四年级下册数学期末测试卷附参考答案(综合卷)
- 小学三年级上册数学期末测试卷及答案(名师系列)
- 二年级上册数学期末测试卷及参考答案
- 外加剂掺合料试题带答案
- 物业工程维修部门培训内容
- 机床行业培训资料
- 《工伤保险条例》课件
- 摄影课件美学基础
- 成本控制和效益改进风险评估
- 市政弱电施工方案
- 绝交协议书模板
- 《保持乐观心态》课件
- 轮机维护与修理 第七章(培训教材)
- 安全生产专项资金台账
评论
0/150
提交评论