外文翻译--CAD系统和虚拟装配面层次上几何信息的转换.doc

TRANSFORMATIONOFGEOMETRYINFORMATIONBASEDONFACEHIERARCHYBETWEENCADSYSTEMANDVIRTUALASSEMBLYENVIRONMENTAbstract:Traditionalassemblydependsonmock-ups,butcreationofthesemock-upsistime-consumingandlabor-consuming.ThedevelopmentofVAbasedonvirtualreality(VR)providesusalow-costandrapidmethodforassembly.VRisofthreecharacteristics:immersion,interactionandimagination.WithVRtechnology,geometrymodelsandtolerance(orerrors)valuesareinputtedintocomputerafterpartsaredesigned.Equipments,toolsandhumanmodelareunitedinVEtoanalyzeandevaluateassemblyperformance.Unqualifiedstructureisthencorrected,assemblyscenarioisoptimizedandbestassemblyplanisselectedtoassurethesuccessofactualassembly.Afterallthesesteps,actualassemblyisimplemented.Thereforeproductdevelopmentcycleisshortenedandproductdevelopmentcostisdecreased.Keywords:virtualassembly,virtualenvironment,datatransformation,geometryAlthoughCADmodelcanbetransferredintoVE,thesemodelsareofonlytheconceptofbodyandnotofthatofface.Thewholeassemblyorsinglepartcanbeselected,butfacesofpartscannotbeselected.Howeverfaceisanimportantconceptinassembly,anditsfunctionsareasfollows:(1)orientationofpailsorassemblybodies；(2)constraintdefinition；(3)jointdefinition；(4)definitionofshapetoleranceandpositiontolerance；(5)definitionofprecisionandroughness；(6)physicalinformationdefinition(e.g.colorandmaterialetc.)etc.Withouttheconceptofface,theconceptofassemblybecomesvagueandVAsystemisalsoreducedtoasimplesimulationsystem.SoitisfarfromrequirementwhenVAisofonlytheconceptofbodies.SoconceptoffaceisneededtobecreatedwhilecreatingVRdocument.ThesurfacesofCADmodelcanbediscretizedtoaggregateofpolygontessellationsortriangletessellationsthroughdatetransformationinterfaceofCADsystem.ThenthesetessellationsinformationiswrittenintoVRdocument.UsingtessellationsinformationprovidedbyVRdocument,VRsystemwilldrawallthetessellationstocreateVRobject.Apartcanberegardedasaggregateoffaces,andafacecanberegardedasthatoftessellationsinCADsystem.ThereexistsacorrespondingrelationshipbetweenbodiesandtessellationsinVE,andalltessellationscanformthewholeVRobject,andinthiswaytheinformationofbodiesareconstructedinVE.ButtheredoesntexistcorrespondingrelationshipbetweenfacesandtessellationsinVE,whichconsequentlyresultsinloseoffacesinformation.Inordertocreatetheinformationoffaces,correspondingrelationshipbetweenfacesandtessellationsisneededtobecreatedinVE.ThetechnologyofforwarddevelopmentofCADsystemandColorRecognitionandTransformationMethod(CRTM)areusedtocreatecorrespondingrelationshipamongfaces,colorsandtessellationsbymeansofcreatinglinkedlistoffacesandlinkedlistoftessellations.InCADsystem,eachfaceofCADmodelingispaintedwithdifferentcolorinvirtueofforwarddevelopmentofCADsystem.Accordingly,tessellationsofthesamecolorbelongtothesameface,andthencorrespondingrelationshipbetweenfacesandtessellationsiscreatedbyconstructinglinkedlistoffacesandlinkedlistoftessellations.Inthisway,facesinformationiscreated.InVEoperationsonfaceswillbetransformedtooperationsontessellations,thustheconceptoffaceisbuiltandgeometryinformationisreconstructedonthebasisofit.InordertorealizeCRTM,Pro/Engineer(Pro/E)isselectedasplatformofassemblymodeling,WorldToolKit(WTK)isselectedasplatformofVAdevelopment,andvisualC+isselectedasplatformofapplicationdevelopment.VRdocumentinterfaces(e.g.NFP,3DS,WRL,DXFandSLPetc.)areusedtotransfergeometryinformationfromanyotherkindofmodelingsoftwaretoWTK.AlthoughWTKsupportsmanyVRdocumentformat,onlyWRLformatandSLPformatcanbeusedtotransfergeometryinformationfromPro/EtoVE.Inactualapplication,WRLformathasthefollowinglimitationsinWTKenvironment:1）Geometryinformationcantbepickedup,soWTKcannotmodifycolorsandtexturesetc.ofvirtualobjects.2)WTKcannotcarryoutzoomoperationonvirtualobjects.3)PrecisionofcollisiondetectionforvirtualobjectislowfortheinformationofpolygonsofvirtualobjectscantbepickedupinVE.Consequently,SLPformatwrittenintextformat,anotherformatofVRdocumentisused.Fig.1showsthecreationprocessofVRdocument.PartscolorsaremodifiedbymeansofPro/DevelopmoduleofPro/E.Mixingcolorismadeofthreecolors:red(r),green(g)andblue(b).Settingdifferentvalueofr,gandbtoeachface,facesofdifferentcolorsarecreated.Inordertodistinguishtwofaces,one-increasing-another-decreasing-paintingmethodisused.Ifthevalueofrandgincrease,thenthevalueofbshoulddecreaseaccordingly,andtheextentofincreaseanddecreaseshouldbedifferent.Thusfacesareeasytodistinguishbecauseofbigdifferenceofeachfacescolor.Afterpaintingcolor,VRdocumentofSLPiscreatedthroughPro/InterfacemoduleofPro/E.Withoperationsonallpartsofassemblybody,correspondingVRdocumentswillbecreated.VRdocumentprovidesustessellationsinformation,normalsinformationandcolorsinformationetc.Inordertocreatethecorrespondingrelationshipbetweenfacesandtessellations,twostructuresoflinkedlistareneeded,i.e.,linkedlistoffacesandlinkedlistoftessellations.Linkedlistsoffacesincludethefollowinginformation:numberoffaces,nameoffaces,coloroffacesandlinkedlistoftessellations.Afacescolorcorrespondstothelinkedlistoftessellationsofthisface.Thefunctionoflinkedlistoftessellationsistostoretessellationsofthesamecolor.ByreadingSLPdocumentinturn,informationoffacesandtessellationsispickedupandstoredtolinkedlistoffacesandlinkedlistoftessellationsrespectively.Correspondingrelationshipbetweenfacesandtessellationsisbuiltthroughthemedia-colorsoffacesandtessellations.InVE,afaceisselectedbyhighlightingallthetessellationscorrespondingtotheface.Firstly,currentactivetriangletessellationispickedupthroughWTscreen_pickpolyfunction,andnumberofcurrentactivetriangletessellationispickedupbymeansofWTpoly_getidfunction.Thenthefaceincludingthenumberofthetessellationcanbeobtainedbymeansofsearchinglinkedlistoffacesandlinkedlis