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外文翻译--CAD系统和虚拟装配面层次上几何信息的转换.doc

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外文翻译--CAD系统和虚拟装配面层次上几何信息的转换.doc

TRANSFORMATIONOFGEOMETRYINFORMATIONBASEDONFACEHIERARCHYBETWEENCADSYSTEMANDVIRTUALASSEMBLYENVIRONMENTAbstractTraditionalassemblydependsonmockups,butcreationofthesemockupsistimeconsumingandlaborconsuming.ThedevelopmentofVAbasedonvirtualrealityVRprovidesusalowcostandrapidmethodforassembly.VRisofthreecharacteristicsimmersion,interactionandimagination.WithVRtechnology,geometrymodelsandtoleranceorerrorsvaluesareinputtedintocomputerafterpartsaredesigned.Equipments,toolsandhumanmodelareunitedinVEtoanalyzeandevaluateassemblyperformance.Unqualifiedstructureisthencorrected,assemblyscenarioisoptimizedandbestassemblyplanisselectedtoassurethesuccessofactualassembly.Afterallthesesteps,actualassemblyisimplemented.Thereforeproductdevelopmentcycleisshortenedandproductdevelopmentcostisdecreased.Keywordsvirtualassembly,virtualenvironment,datatransformation,geometryAlthoughCADmodelcanbetransferredintoVE,thesemodelsareofonlytheconceptofbodyandnotofthatofface.Thewholeassemblyorsinglepartcanbeselected,butfacesofpartscannotbeselected.Howeverfaceisanimportantconceptinassembly,anditsfunctionsareasfollows1orientationofpailsorassemblybodies2constraintdefinition3jointdefinition4definitionofshapetoleranceandpositiontolerance5definitionofprecisionandroughness6physicalinformationdefinitione.g.colorandmaterialetc.etc..Withouttheconceptofface,theconceptofassemblybecomesvagueandVAsystemisalsoreducedtoasimplesimulationsystem.SoitisfarfromrequirementwhenVAisofonlytheconceptofbodies.SoconceptoffaceisneededtobecreatedwhilecreatingVRdocument.ThesurfacesofCADmodelcanbediscretizedtoaggregateofpolygontessellationsortriangletessellationsthroughdatetransformationinterfaceofCADsystem.ThenthesetessellationsinformationiswrittenintoVRdocument.UsingtessellationsinformationprovidedbyVRdocument,VRsystemwilldrawallthetessellationstocreateVRobject.Apartcanberegardedasaggregateoffaces,andafacecanberegardedasthatoftessellationsinCADsystem.ThereexistsacorrespondingrelationshipbetweenbodiesandtessellationsinVE,andalltessellationscanformthewholeVRobject,andinthiswaytheinformationofbodiesareconstructedinVE.ButtheredoesntexistcorrespondingrelationshipbetweenfacesandtessellationsinVE,whichconsequentlyresultsinloseoffacesinformation.Inordertocreatetheinformationoffaces,correspondingrelationshipbetweenfacesandtessellationsisneededtobecreatedinVE.ThetechnologyofforwarddevelopmentofCADsystemandColorRecognitionandTransformationMethodCRTMareusedtocreatecorrespondingrelationshipamongfaces,colorsandtessellationsbymeansofcreatinglinkedlistoffacesandlinkedlistoftessellations.InCADsystem,eachfaceofCADmodelingispaintedwithdifferentcolorinvirtueofforwarddevelopmentofCADsystem.Accordingly,tessellationsofthesamecolorbelongtothesameface,andthencorrespondingrelationshipbetweenfacesandtessellationsiscreatedbyconstructinglinkedlistoffacesandlinkedlistoftessellations.Inthisway,facesinformationiscreated.InVEoperationsonfaceswillbetransformedtooperationsontessellations,thustheconceptoffaceisbuiltandgeometryinformationisreconstructedonthebasisofit.InordertorealizeCRTM,Pro/EngineerPro/Eisselectedasplatformofassemblymodeling,WorldToolKitWTKisselectedasplatformofVAdevelopment,andvisualCisselectedasplatformofapplicationdevelopment.VRdocumentinterfacese.g.NFP,3DS,WRL,DXFandSLPetc.areusedtotransfergeometryinformationfromanyotherkindofmodelingsoftwaretoWTK.AlthoughWTKsupportsmanyVRdocumentformat,onlyWRLformatandSLPformatcanbeusedtotransfergeometryinformationfromPro/EtoVE.Inactualapplication,WRLformathasthefollowinglimitationsinWTKenvironment1)Geometryinformationcantbepickedup,soWTKcannotmodifycolorsandtexturesetc.ofvirtualobjects.2WTKcannotcarryoutzoomoperationonvirtualobjects.3PrecisionofcollisiondetectionforvirtualobjectislowfortheinformationofpolygonsofvirtualobjectscantbepickedupinVE.Consequently,SLPformatwrittenintextformat,anotherformatofVRdocumentisused.Fig.1showsthecreationprocessofVRdocument.PartscolorsaremodifiedbymeansofPro/DevelopmoduleofPro/E.Mixingcolorismadeofthreecolorsredr,greengandblueb.Settingdifferentvalueofr,gandbtoeachface,facesofdifferentcolorsarecreated.Inordertodistinguishtwofaces,oneincreasinganotherdecreasingpaintingmethodisused.Ifthevalueofrandgincrease,thenthevalueofbshoulddecreaseaccordingly,andtheextentofincreaseanddecreaseshouldbedifferent.Thusfacesareeasytodistinguishbecauseofbigdifferenceofeachfacescolor.Afterpaintingcolor,VRdocumentofSLPiscreatedthroughPro/InterfacemoduleofPro/E.Withoperationsonallpartsofassemblybody,correspondingVRdocumentswillbecreated.VRdocumentprovidesustessellationsinformation,normalsinformationandcolorsinformationetc..Inordertocreatethecorrespondingrelationshipbetweenfacesandtessellations,twostructuresoflinkedlistareneeded,i.e.,linkedlistoffacesandlinkedlistoftessellations.Linkedlistsoffacesincludethefollowinginformationnumberoffaces,nameoffaces,coloroffacesandlinkedlistoftessellations.Afacescolorcorrespondstothelinkedlistoftessellationsofthisface.Thefunctionoflinkedlistoftessellationsistostoretessellationsofthesamecolor.ByreadingSLPdocumentinturn,informationoffacesandtessellationsispickedupandstoredtolinkedlistoffacesandlinkedlistoftessellationsrespectively.Correspondingrelationshipbetweenfacesandtessellationsisbuiltthroughthemediacolorsoffacesandtessellations.InVE,afaceisselectedbyhighlightingallthetessellationscorrespondingtotheface.Firstly,currentactivetriangletessellationispickedupthroughWTscreen_pickpolyfunction,andnumberofcurrentactivetriangletessellationispickedupbymeansofWTpoly_getidfunction.Thenthefaceincludingthenumberofthetessellationcanbeobtainedbymeansofsearchinglinkedlistoffacesandlinkedlistoftessellations.Whenallthetessellationsofafacetakethesameoperations,thefacewilltakethesameoperation.Forexample,whenallthetessellationsofafacearehighlighted,allthepartsofthefacesarehighlighted,andthenthefaceisselectedinvisualeffectInthisway,geometryinformationisreconstructedbasedonfacehierarchy.

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