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1、CAD/CAMandApplicationsBeforewepresentthebasicsofCAD,itisappropriatetogiveabriefhistory.CADisaproductofthecomputerera.Itoriginatedfromearlycomputergraphicsystemstothedevelopmentofinteractivecomputergraphics.TwosuchsystemsincludetheSageProjectattheMassachusettsInsti
2、tuteofTechnology(MIT)andSketchpad.TheSageProjectwasaimedatdevelopingCRTdisplaysandoperatingsystems,SketchpadwasdevelopedundertheSageProject.ACRTdisplaysandlightpeninputwereusedtointeractwiththesystem,thiscoincidentallyhappenedataboutthesametimethatNCandAPT(Automat
3、icallyProgrammedTool)firstappeared.Later,X-Yplotterswereusedasthestandardhard-copyoutputdeviceforcomputergraphics.AninterestingnoteisthatanX-YplotterhasthesamebasicstructureasanNCdrillingmachineexceptthatapenissubstitutedforthetoolonNCspindle.Inthebeginning,CADsys
4、temswerenomorethanagraphicseditorwithsomebuilt-indesignsymbols.Thegeometryavailabletotheuserwaslimitedtolines,circulararcs,andthecombinationofthem.Thedevelopmentoffree-formcurvessurfaces,suchasCoon'spatch,Bezier'spatch,andB-spline,enablesaCADsystemtousedforsophist
5、icatedcurvesandsurfacedesign.Three-dimensionalCADsystemsallowadesignertomoveintothethirddimension.Becauseathree-dimensionalmodelcontainsenoughinformationforNCcutter-pathprogramming,thelinkagebetweenCADandNCcanbedevelopment.SocalledturnkeyCAD/CAMsystemsweredevelope
6、dbasedonthisconceptandbecamepopularinthe1970sand1980s.The1970smarkedthebeginningofanewareainCAD一theinventionofthethree-dimensionalsolidmodeling.Inthepast,three-dimensional,wire-framemodelsrepresentedanobjectonlybyitsboundingedges.Theyareambiguousinthesensethatseve
7、ralinterpretationsmightbepossibleforasinglemodel.Thereisalsonowaytofindthevolumetricinformationforamodel.Solidmodelscontaincompleteinformation;therefore,notonlycantheybeusedtoproduceengineeringdrawing,butengineeringanalysiscanbeperformedonthesamemodelaswell.Later,
8、manycommercialsystemsandresearchsystemsweredeveloped.QuiteafewofthesesystemswerebasedonthePADLandBUILDsystems.Althoughtheyarepowerfulinrepresentation,ma
