逆向工程英文资料

IntJAdvManufTechnol(2000)16:635–6422000Springer-VerlagLondonLimitedThePre-ProcessingofDataPointsforCurveFittinginReverseEngineeringMing-ChihHuangandChing-ChihTaiDepartmentofMechanicalEngineering,TatungUniversity,Taipei,TaiwanReverseengineeringhasbecomeanimportanttoolforCADmodelconstructionfromthedatapoints,measuredbyacoordi-natemeasuringmachine(CMM),ofanexistingpart.Amajorprobleminreverseengineeringisthatthemeasuredpointshavinganirregularformatandunequaldistributionarediffi-culttofitintoaB-splinecurveorsurface.Thepaperpresentsamethodforpre-processingdatapointsforcurvefittinginreverseengineering.TheproposedmethodhasbeendevelopedtoprocessthemeasureddatapointsbeforefittingintoaB-splineform.TheformatofthenewdatapointsregeneratedbytheproposedmethodissuitablefortherequirementsforfittingintoasmoothB-splinecurvewithagoodshape.Theentireprocedureofthismethodinvolvesfiltering,curvatureanalysis,segmentation,regressing,andregeneratingsteps.Themethodisimplementedandusedforapracticalapplicationinreverseengineering.TheresultofthereconstructionprovestheviabilityoftheproposedmethodforintegrationwithcurrentcommercialCADsystems.Keywords:Curvefitting;Pre-processingofdatapoints;Reverseengineering1.IntroductionWiththeprogressinthedevelopmentofcomputerhardwareandsoftwaretechnology,theconceptofcomputer-aidedtech-nologyforproductdevelopmenthasbecomemorewidelyacceptedbyindustry.Thegapbetweendesignandmanufactur-ingisnowbeinggraduallynarrowedthroughthedevelopmentofnewCADtechnology.Inanormalautomatedmanufacturingenvironment,theoperationsequenceusuallystartsfromproductdesignviageometricmodelscreatedinCADsystems,andendswiththegenerationofmachininginstructionsrequiredtoconvertrawmaterialintoafinishedproduct,basedonthegeometricmodel.Torealisetheadvantagesofmoderncom-Correspondenceandoffprintrequeststo:Ming-ChihHuang,Depart-mentofMechanicalEngineering,TatungUniversity,40ChungshanNRoad,3rdSection,Taipei104,Taiwan.E-mail:mindyKmgher.ttit.edu.twputer-aidedtechnologyintheproductdevelopmentandmanu-facturingprocess,ageometricmodeloftheparttobecreatedintheCADsystemisrequired.However,therearesomesituationsinproductdevelopmentinwhichaphysicalmodelorsampleisproducedbeforecreatingtheCADmodel:1.Whereaclaymodel,forexample,indesigningautomobilebodypanels,ismadebythedesignerorartistbasedonconceptualsketchesofwhatthepanelshouldlooklike.2.Whereasampleexistswithouttheoriginaldrawingordocumentationdefinition.3.WheretheCADmodelrepresentingtheparthastoberevisedowingtodesignchangeduringmanufacturing.Inallofthesesituations,thephysicalmodelorsamplemustbereverseengineeredtocreateorrefinetheCADmodel.Incontrasttothisconventionalmanufacturingsequence,reverseengineeringtypicallystartswithmeasuringanexistingphysicalobjectsothataCADmodelcanbededucedinordertoexploittheadvantagesofCADtechnologies.Theprocessofreverseengineeringcanusuallybesubdividedintothreestages,i.e.datacapture,datasegmentationandCADmodellingand/orupdating[1,2].Aphysicalmock-uporprototypeisfirstmeasuredbyacoordinatemeasuringmachineoralaserscannertoacquirethegeometricinformationintheformof3Dpoints.Themeasuredresultsarethensegmentedintotopologicalregionsforfurtherprocessing.Eachregionrepresentsasinglegeometricfeaturethatcanberepresentedmathematicallybyasimplesurfaceinthecaseofmodelreconstruction.CADmodellingreconstructsthesurfaceofaregionandcombinesthesesurfacesintoacompletemodelrepresentingthemeasuredpartorprototype[3].Inpracticalmeasuringcases,however,therearemanysitu-ationswherethegeometricinformationofaphysicalprototypeorsamplecannotbemeasuredcompletelyandaccuratelytoreconstructagoodCADmodel.Somedatapointsofthemeasuredsurfacemaybeirregular,havemeasurementerrors,orcannotbeacquired.AsshowninFig.1,themainsurfaceofmeasuredobjectmayhavefeaturessuchasholes,islands,orroughnesscausedbymanufacturinginaccuracy,consequentlytheCMMprobecannotcapturethecompletesetofdatapointstoreconstructtheentiresurface.636M.-C.HuangandC.-C.TaiFig.1.Thegeneralproblemsinapracticalmeasuringcase.Measurementofanexistingobjectsurfaceinreverseengin-eeringcanbeachievedbyusingeithercontactprobingornon-contactsensingprobingtechniques.Whatevertechniqueisapplied,therearemanypracticalproblemswithacquiringdatapoints,forexamples,noise,andincompletedata.Withoutextensiveprocessingtoadjustthedatapoints,theseproblemswillcausetheCADmodeltobereconstructedwithanunde-siredshape.InordertorebuildtheCADmodelcorrectlyandsatisfactorily,thispaperpresentsausefulandeffectivemethodtopre-processthedatapointsforcurvefitting.Usingtheproposedmethod,thedatapointsareregeneratedinaspecifiedformat,whichissuitableforfittingintoacurverepresentedinB-splineformwithouttheproblemspreviouslymentioned.Afterfittingallofthecurves,thesurfacemodelcanbecompletedbyconnectingthecurves.2.TheTheoryofB-splineMostofthesurface-basedCADsystemsexpressshapesrequiredformodellingbyparametricequations,suchasinBe´zierorB-splineforms.ThemostusedistheB-splineform.B-splinesarethestandardforrepresentingfreeformcurvesandsurfacesincurrentcommercialCADsystems.B-splinecurvesandBe´ziercurveshavemanyadvantagesincommon[4].