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IntJAdvManufTechnol200118784–7892001SpringerVerlagLondonLimitedAClampingDesignApproachforAutomatedFixtureDesignJ.CecilVirtualEnterpriseEngineeringLabVEEL,IndustrialEngineeringDepartment,NewMexicoStateUniversity,LasCruces,USAInthispaper,aninnovativeclampingdesignapproachisdescribedinthecontextofcomputeraidedfixturedesignactivities.Theclampingdesignapproachinvolvesidentificationofclampingsurfacesandclamppointsonagivenworkpiece.Thisapproachcanbeappliedinconjunctionwithalocatordesignapproachtoholdandsupporttheworkpieceduringmachiningandtopositiontheworkpiececorrectlywithrespecttothecuttingtool.Detailedstepsaregivenforautomatedclampdesign.Geometricreasoningtechniquesareusedtodeterminefeasibleclampfacesandpositions.TherequiredinputsincludeCADmodelspecifications,featuresidentifiedonthefinishedworkpiece,locatorpointsandelements.KeywordsClampingFixturedesign1.MotivationandObjectivesFixturedesignisanimportanttask,whichisanintegrationlinkbetweendesignandmanufacturingactivities.TheautomationoffixturedesignactivitiesandthedevelopmentofcomputeraidedfixturedesignCAFDmethodologiesarekeyobjectivestobeaddressedforthesuccessfulrealisationofnextgenerationmanufacturingsystems.Inthispaper,aclampdesignapproachisdiscussed,whichfacilitatesautomationinthecontextofanintegratedfixturedesignmethodology.Clampdesignapproacheshavebeenthefocusofseveralresearchefforts.TheworkofChou1focusedonthetwincriteriaofworkpiecestabilityandtotalrestraintrequirement.TheuseofartificialintelligenceAIapproachesaswellasexpertsystemapplicationsinfixturedesignhasbeenwidelyreported2,3.PartgeometryinformationfromaCADmodelhasalsobeenusedtodrivethefixturedesigntask.Bidanda4describedarulebasedexpertsystemtoidentifythelocatingandclampingfacesforrotationalparts.TheclampingmechanismisusedtoperformboththelocatingandclampingCorrespondenceandoffprintrequeststoDrJ.Cecil,VirtualEnterpriseEngineeringLabVEEL,IndustrialEngineeringDepartment,NewMexicoStateUniversity,LasCruces,NM88003,USA.EmailjcecilL50560nmsu.edufunctions.Otherresearcherse.g.DeVoretal.5,6haveanalysedthecuttingforcesandbuiltmechanisticmodelsfordrilling,andothermetalcuttingprocesses.Kangetal.2definedassemblyconstraintstomodelspatialrelationshipsbetweenmodularfixtureelements.Severalresearchershaveemployedmodularfixturingprinciplestogeneratefixturedesigns2,7–11.Otherfixturedesigneffortshavebeenreportedin1,3,9,12–23.Anextensivereviewoffixturedesignrelatedworkcanbefoundin21,24.InSection2,thevariousstepsintheoverallapproachtoautomatetheclampingdesigntaskareoutlined.Section3describesthedeterminationoftheclampsizetoholdaworkpieceduringmachiningandinSection4,theautomaticdeterminationoftheclampingsurfaceorfaceregiononaworkpieceisdetailed.Section5discussesthedeterminationoftheclampingpointsonaworkpiece.2.OverallApproachtoClampDesignInthissection,theoverallclampingdesignapproachisdescribed.Clampingisusuallycarriedouttoholdthepartinadesiredpositionandtoresisttheeffectsofcuttingforces.Clampingandlocatingproblemsinfixturedesignarehighlyrelated.Often,theclampingandlocatingcanbeaccomplishedbythesamemechanism.However,failuretounderstandthatthesetwotasksareseparateaspectsoffixturedesignmayleadtoinfeasiblefixturedesigns.Humanprocessplannersgenerallyresolvethelocatingproblemfirst.Theapproachdevelopedcanworkinconjunctionwithalocatordesignstrategy.However,theoveralllocatorandsupportdesignapproachisbeyondthescopeofthispaper.CADmodelsofthepartdesignforwhichtheclampdesignhastobedeveloped,thetolerancespecifications,processsequence,locatorpointsanddesign,amongotherfactors,aretheinputstotheclampdesignapproach.Thepurposeofclampingistoholdthepartsagainstlocatorsandsupports.Theguidingthemeusedistotrynottoresistthecuttingormachiningforcesinvolvedduringamachiningoperation.Rather,theclampsshouldbepositionedsuchthatthecuttingforcesareinthedirectionthatwillassistinholdingthepartsecurelyduringaspecificmachiningoperation.BydirectingAClampingDesignApproach785thecuttingforcestowardsthelocators,thepartorworkpieceisforcedagainstsolid,fixedlocatingpointsandsocannotmoveawayfromthelocators.Theclampdesignapproachdiscussedheremustbeviewedinthecontextoftheoverallfixturedesignapproach.Priortoperforminglocator/supportandclampdesign,apreliminaryphaseinvolvinganalysisandidentificationoffeatures,associatedtolerancesandotherspecificationsisnecessary.Basedontheoutcomeofthispreliminaryevaluationanddetermination,thelocator/supportdesignandclampdesigncanbecarriedout.Theclampdesignapproachdescribedinthispaperisdiscussedbasedontheassumptionthatlocator/supportdesignattributeshavebeendeterminedearlierthisincludesdeterminationofappropriatelocatorandsupportfacesonaworkpieceaswellasidentificationoflocatorandsupportfixturingelementssuchasVblocks,baseplates,locatingpins,etc.2.1InputstoClampDesignTheinputsincludethewingededgemodelofthegivenproductdesign,thetoleranceinformation,theextractedfeatures,theprocesssequenceandthemachiningdirectionsforeachoftheassociatedfeaturesinthegivenpartdesign,thelocationfacesandlocatordevices,andthemachiningforcesforthevariousprocessesrequiredtoproduceeachcorrespondingfeature.2.2ClampDesignStrategyThemainstepsintheautomationoftheclampingdesigntaskaresummarisedinFig.1.AnoverviewofthesestepsisasfollowsStep1.ConsiderthesetupSUiinthesetupconfigurationlistalongwiththeassociatedprocessH20841featureentries.Step2.Identifythedirectionandtypeofclamping.Theinputsrequiredarethemachiningdirectionvectorsmdv1,mdv2,...,mdvnandidentifiednormalvectorsofsupportfacenvs.Ifthemachiningdirectionsaredownwardwhichcorrespondtothedirectionvector0,0,−1,andthenormalvectorofthesupportfaceisparalleltothemachiningdirection,thenthedirectionofclampingisparalleltothedownwardmachiningdirection0,0,−1.Ifsidewaysclampingisrequired,andiftherearenofeasibleregionsatwhichtopositionaclampfordownwardclamping,thenasideclampdirectionisobtainedasfollows.Letsvandtvbethenormalvectorsofthesecondarysvandtertiarytvlocatingfaces.Then,thedirectionofclampingusedbyasideclampingmechanismsuchasavblockshouldbeparalleltoboththesenormalvectors,i.e.thenormalvectorsoftheeachofthevsurfacesinthevblockwillbeparalleltosvandtv,respectively.Thesideclampingfaceshouldbeapairoffacesparalleltothefacessvandtv,respectively.Step3.DeterminethehighestmachiningforcefromthemachiningforceslistforeachfeatureMFii1,...,n.ThiswillbetheeffectiveforceFEthatmustbebalancedwhiledesigningtheclampforthissetupSUi.Step4.UsingthevalueofthecalculatedhighestmachiningforceFE,thedimensionsoftheclamptobeusedtoholdtheFig.1.Theclampdesignactivities.workpiececanbedeterminedforexample,astrapclampcanbeusedasaclampingmechanism.TheapproachforthistaskisexplainedinSection3.Step5.Determinetheclampingfaceonagivenworkpiece.ThisstepcanbeautomatedasdescribedinSection4.Step6.TheactualpositionoftheclampontheclampingfaceisdeterminedinanautomatedmannerasexplainedinSection5.ConsidernextsetupSUi1andproceedtostep1.3.DeterminationoftheClampSizeInthiswork,theclampsusedbelongtothefamilyofclampsreferredtoasstrapclamps.AstrapclampisbasedonthesameprincipleasthatoftheleverseeFig.2.Inthissection,theautomateddesignofastrapclampisdescribed.Theclampingforcerequiredisrelatedtothesizeofthescreworathreadeddevicethatholdstheclampinplace.Theclampingforceshouldbalancethemachiningforcetoholdtheworkpieceinposition.LettheclampingforcebeWandthescrewdiameterbed.Thedimensionsofthevariousscrewsizesforvariousclampingforcescanbedeterminedinthefollowingmanner.Initially,theultimatetensilestrengthUTSofthematerialoftheclampdependingonavailabilitycanberetrievedfromadatalibrary.Variousmaterialshavedifferenttensilestrengths.Theselectionoftheclampmaterialcanalsobeperformeddirectlyusingheuristicrules.Forexample,ifthepartmaterialismildsteel,thentheclampmaterialcanbelow786J.CecilFig.2.Thestrapclamp.carbonsteelormachinesteel.Todeterminethedesignstress,theUTSvaluecanbedividedbyasafetyfactorsuchas4or5.TherootareaA1ofthescrewforaclampsuchasascrewclampcanthenbedeterminedClampingforcerequired/DesignStressDS.Subsequently,thefullareaFAoftheboltcrosssectioncanbecomputedasequalto{A1/65}sincetherootareaofthescrewwhereshearingcanoccurisapproximately65ofthetotalareaofthebolt.ThediameterofthescrewdcanthenbedeterminedbyequatingFAto3.14d2/4.AnotherequationwhichcanbeusedinvolvesrelatingthewidthB,heightHandspanLoftheclamptothescrewdiameterdB,H,andLcanbecomputedforvariousvaluesofdd24/3BH2/L.4.TheDeterminationoftheClampingFaceTherequiredinputstodeterminetheclampingregionincludetheCADmodeloftheproduct,theextractedfeaturesinformation,thefeaturedimensionsandfacesonwhichtheyoccur,thelocatingfacesandlocatorsselected.ConsiderapotentialclampingfacePCFasshowninFig.3.Thecrucialcriteriontobesatisfiedisthattheclampingsurfaceshouldnotoverlaporintersectwiththefeaturesonthatface,asshowninFig.4.Theclampingsurfacearea,whichisincontactwiththeworkpiecesurfaceorPCFisa2DprofileconsistingoflinesegmentsseeFig.6.Byusinglinesegmentintersectiontests,itcanbedeterminedwhetherthepotentialclampingareaofcontactoverlapsanyofthefeaturesonthegivenPCF.ThedeterminationofclampingfacescanbeautomatedasfollowsFig.3.Potentialclampingfaceandfeatureprofiles.Fig.4.Potentialclampingfaceandclampboxprofile.Step1.Identifyfacesthatareparalleltothesecondaryandtertiarylocatorfaceslf1andlf2andatthefarthestdistancefromlf1andtcj,respectively.ThisisperformedasshownbelowaIdentifyfacestci,tcjsuchthattciisparalleltolf1andtcjisparalleltolf2.bInsertcandidatefacestciinlistTCF.cByexaminingallfacestcilistedinTCF,determinefacestciandtcjthatarefarthestfromfacelf1andlf2,respectively,anddiscardallotherfacesfromlistTCF.Step2.Identifythefacethatisparalleltothelocationfacesbutnotadjacenttotheadditionallocatorfaces.Itispreferabletoselectaclampfacethatdoesnothavetosharetheadjacentperpendicularfacewithalocator.ThisstepcanbeautomatedasshownbelowaConsidereachfacetciinlistTCFandobtaincorrespondingfacesfcithatareadjacentandperpendiculartoeachtci.Then,inserteachfacefciinlistFCF.bExamineeachfciandperformthefollowingtestIffciisadjacent,perpendiculartolf1orlf2,thendiscarditfromlistFCFandinsertitinlistNTCF.Step3.Determinetheclampingfaces,basedontheavailabilityofpotentialclampingfaces,asdescribedbelow.Casea.IftherearenoentriesinlistNTCF,thenusethefacesinlistTCFandproceedtostep4.Ifanyfaceswerefoundthatwereperpendiculartothesecondaryandtertiarylocationfaceslf1andlf2,suchfacesarethenextfeasiblechoicestobeusedforclamping.Inthiscase,theonlyremainingchoiceistoreexaminethefacesinlistNTCF.Caseb.IfthenumberofentriesinlistNTCFis1,thefeasibleclampingfaceisfci.Thenormalvectorofthecorrespondingadjacent,perpendicularfacetciistheaxisofclamping.Casec.IfnumberofentriesinlistNTCFisgreaterthan1,determinethefacetciwithlargerareaandproceedtostep4.Step4.Dependingonthedirectionofclampingwhichiseitheror−1,0,0oror−0,1,0,theclampcanbepositionedalongthecentreofthefacetci.Thecandidategeometricalpositionsoftheclampcanbedeterminedusingpartgeometryandtopologicalinformation,whichisdescribedinthenextsection.AClampingDesignApproach787Fig.5.Determinationoftheclampprofiledimensions.5.DeterminationoftheClampingPointsonaClampingFaceAftertheclampfacehasbeendetermined,theactualclampingpositionsonthatfacemustbedetermined.Theinputsaretheclampprofiledimensions,clampdirectionsx,y,z,andpotentialclampingfaceCF.TheclampprofiledimensionsareobtainedasincasegusingCFgeometryasfollows.Thefirststepistodetermineaboxsize,whichistestedtodeterminewhetheritcontainsanyfeaturesinsideit.Profileintersectiontestscanalsobeperformedusingthemethoddescribedearlier.Iftheintersectiontestreturnsanegativeresult,thennofeatureintersectswiththeclampboxprofile,asshowninFig.4.Iftheintersectiontestreturnsapositiveresult,thefollowingstepscanbeperformed1.Dividetheclampboxprofileintosmallerrectangularstripsofsize1wFigs5and6.2.PerformtheintersectiontestswiththefeatureprofilesoffeaturesthatoccuronthefaceCFforthegivenpartdesign.Fig.6.Profilesintersectiontestoffeatureandclampregions.3.Therectangularstrips,wherenofeatureintersectionoccurs,arefeasibleclampingregions.Ifthereismorethanonecandidaterectangleforclamping,therectangleprofilethatistowardthemidpointoftheCFfacealongtheclampingaxisistheclampprofileandclamppoints.IfnoprofilePicanbefoundthatdoesnotintersectwiththefeatureprofiles,clampwidthcanbereducedbyhalfandthenumberofclampsincreasedtotwoonthatface.Usingthesemodifiedclampdimensions,performthefeatureintersectiontestdescribedearlier.Ifthistestalsofails,thenthesidefaceadjacenttothePCFcanbeusedastheclampingsurfacetoperformsideclamping.ThesidefacethenbecomesthePCFandthefeatureintersectiontestcanberepeated.5.1TheIntersectionofProfilesTestTherequiredinputsincludethe2DprofileP1another2DprofileP2.Theintersectionofprofilescanbedeterminedinanautomatedmannerusingthefollowingapproach.EachinputprofilePiconsistsofaclosedloopoflinesegmentsLij.ThestepsinthisprofiletestareasfollowsT1ConsideralinesegmentLi,1inP1andanotherlinesegmentL2,jinP2.T2ForinputsLi,1andL2,j,theintersectionofedgescanbeemployed.Iftheedgeintersectiontestreturnsapositivevalue,thenthefeatureprofileintersectswiththecandidateorpotentialclampprofileunderevaluation.Ifitreturnsanegativevalue,proceedtostep3.T3RepeatstepT1forthesamesegmentoredgeLi,1inP1withallremainingsegmentsL2,j1tilljn–1inP2.T4RepeatstepsT1andT2fortheremainingedgesorsegmentsL12,L13,...,L1ninprofileP1.Ifthefeatureprofilesoverlaptheclampingprofiles,thelineintersectiontestswilldeterminethatoccurrence.Theintersectionofedgestestcanbeperformedautomaticallytodetectwhethertwoedgesintersectwitheachother.TheinputsrequiredforthistestarethelinesegmentsL12{connectingx1,y1andx2,y2}andL34{connectingx3,y3andx4,y4}.LettheequationofL12berepresentedbyFx,y01andthatofL34byHx,y02Step1.UsingEq.1computer3Fx3,y3bysubstitutingx3andy3forxandyandcomputer4Fx4,y4bysubstitutingx4andy4forxandy.Step2.Ifr3isnotequalto0,r4isnotequalto0,andthesignsofr3andr4arethesame,whichindicater1andr2lieonsameside,thentheedgesL12andL34donotintersect.Ifthisisnotsatisfied,thenstep3isperformed.Step3.UsingEq.2,computer1Hx1,y1.Then,computer2Gx2,y2andproceedtostep4.Step4.Ifr1isnotequaltozero,r2isnotequaltozero,andthesignsofbothr1andr2arethesame},thenr1,r2lieon
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