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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.EachinputprofilePiconsist