外文翻译--CAD硬件.doc -- 5 元

攀枝花学院本科毕业设计（论文）外语文翻译攀枝花学院本科毕业设计（论文）外语文翻译1外语文献翻译原文3.4.1CADHARDWAREComputersTherearetwomajortypesofhardwareusedinaCADsystem.Computerandinput/outputI/Odevices.IntheearlydaysofCAD.SomecommercialCADsystemsusedproprietarycomputers.Today,nearlyallCADsoftwarerunsonageneralpurposecomputer.DependingonthecomplexityoftheCADpackage,itmayrequireamainframecomputer,aminicomputer,orsimplyamicrocomputer.Ingeneral,themorefunctionalitiesaCADsystemprovides,themorepowerfulthecomputerneeded.Threedimensionalsolidmodelersrequiremuchmorecomputingthandotwodimensionaldraftingsystemsthus,theyneedmorepowerfulcomputers.Systemsthatintegrateengineeringanalysisorsimulationpackagesgenerallyaremorecomputationintensive.ApowerfulcomputernotonlyspeedsuptheresponseofaCADsystem,butalsocansupportmultipleuserswithoutsignificantperformancedegradation.Severalotherparametersandcomponentsconcerningthecomputeralsohavetobeconsidered.CADHARDWARErandomaccessmemoryRAMcapacitypermanentdiskstoragecapacityspecialgraphicsacceleratortapebackupsRAMistheactualphysicalmemoryvs.virtualmemoryofacomputer.Asmallmemorycapacitymeansslowprocessingduetofrequentswappingbetweenthephysicalmemoryandthevirtualmemoryondisk.BecauseCADisextremelystoragedemanding,diskcapacityisimportant.Smalldiskcapacitylimitsthesystemtothestorageofonlyafewdrawings.CADisgraphicsbasedandrequirestremendousdataprocessing.Agraphicsacceleratorcandrasticallyincreasetheperformanceofthesystem.Anothercomponent,theharddisk,istypicallythemajorcostofacomputersystem.Therefore,itisnotcostjustifiabletostorealldrawingsonlineondisk.Magnetictapeisstillthemosteconomicalmediumtouseforofflinedatastorage.ItisnecessaryforaCADsystemtohaveatapebackupsubsystem.Currently,alllevelsofcomputersareusedinCADsystems.Personalcomputersareusedinlowcost,2Ddraftingapplications,andwiththenewpowerofthesecomputers,heyarealsobeingusedforsome3Dsolidmodelingapplications.EngineeringworkstationshavebeenthemainstayinCAD,andareusuallyasingleuserCADworkstationinanetwork.MinicomputersareusedinmultiuserCADsystems.MainframesareusedforlargemultiuserCADsystemstosupportrealtimesimulationandengineeringanalysis.Sometimes,inalargecorporation,alllevels攀枝花学院本科毕业设计（论文）外语文翻译2ofCADsystemsareimplemented.Allthesesystemsarelinkedtogetherthroughahierarchicalcomputernetwork.3.4.2Input.OutputI/ODevicesFigure3.7showsthetypicalI/OdevicesusedinaCADsystem.InputdevicesaregenerallyusedtotransferinformationfromahumanorstoragemediumtoacomputerwhereCADfunctionsarecarriedout.Akeyboardisthestandardinputdeviceusedtotransmitalphanumericdatatothesystem.Functionkeypadsarealsousedtomakeinputeasier.Joysticks,trackballs,andmoussearealsousedtomanipulateacursor.Theycanbeusedtopositionthegraphiccursore.g.crosshaironamonitorandfeedbackthelocationofanobjectonthemonitortothecomputer.Usingthesedevicesallowsanoperatortoaddressterminallocationstointeractivelyinreachinganaccurateposition.Mouseshavebeenusedextensivelywithwindowsandpulldownmenus.TheyareeasytouseforpointingHowever,usingamousetotraceacurveisnotaneasytask.Therearethreebasicapproachestoinputanexistingdrawing1modeltheobjectonadrawing,2digitizethedrawing,or3scantheobject.Digitizingisusuallymucheasierthanmodeling.AdigitizerisadevicethattranslatestheXYlocationsonadrawingthanmodeling.AdigitizerisadevicethattranslatestheXYlocationsonadrawingintoadigitalandfeedsthatsignaltoacomputer.GraphicsscannersscanadrawingandconvertittoaCADsystemreadableformat.SomescannershavebuiltincharacterrecognitionsoftwarethatcanconvertcharactersonpaperintoASCIIcodes.Anotherinputdeviceisasketchpadcalledagraphicstablet.Agraphicstabletisaspecialflatsurfaceonwhichauserdrawswithastylus.Thelocationofthestylusissenttothecomputer.Thetabletisanabsolutecoordinatedevice.Itiseasytoimplementoverlaymenusonthetabletandpulldownmenusonthescreentoimprovetheoperation.Currently.thetabletisthemostpopularinputdeviceusedinCADotherthanthekeyboard.ThestandardoutputdeviceforCADisamonitordisplay.Modernmonitordisplaysarerasterscandisplaymonitors.SimilartoaTVmonitor,anelectrongunSonyTrinitronusesthreegunsforthreebasiccolorssendsanelectronicbeamtothefrontofthemonitor.Easydisplaydotiscalledapixelpictureelement.Forcolordisplays,eachpixelisrepresentedbythreecloselylocateddotswithred,green,andbluecolors.Theelectronicbeamselectsthecolorelementsandtheintensityofeachcolorelement.Theresolutionofthemonitorisdeterminedbythenumberofdifferentcolorsorgrayscalesdisplayableateachpixel,usuallymeasuredinbits,A1bitdisplaycanturneachpixeleitherONorOFF.Agrayscalehasatleastv2bits.A1bitdisplaycanturneachpixeleitherONorOFF.Agrayscalehasatleast2bitswhichallowthreelightintensitiesplusanOFF22.Usually,displaysare4bits16colors,8bits256colors,16bitsthousandsofcolors,and24bitsmillionsofcolors.Theelectronicbeamsweepsthescreenfromthetoptothebottomlinebyline.Becausethedotislitforonlyaveryshortperiodoftime,thesweepmustbedoneveryquicklyinordernottohaveaflickeringimage.Therefreshrateisameasureofhowmanytimesthemonitorisredrawninonesecond.攀枝花学院本科毕业设计（论文）外语文翻译3Thecomputerdoesnotdrawdirectlyonthemonitor.ConnectingthecomputertothemonitorisusuallyaRGBred,green,bluecable.Threeseparatesignallinesareconnected.Onthegraphicsboardinthecomputerarecircuitstogeneratetheanalogsignalsrequiredtodrivethemonitor.Thereisalsoaframebufferthatservesasmemorytostoretheimage.Eachpixelonthescreenhasacorrespondingaddressintheframebuffer.Thedataintheframebufferareconvertedintotheappropriateanalogsignalandsenttothemonitorattherefreshrate.Separately,thecomputerwritesdirectlytotheframebuffertheimageitintendstodraw.Thegreaterthedisplaysizeandnumberofcolors,themoreframebufferisneeded.TheframebufferonthegraphicsboardismadeofrandomaccessmemoryRAM.ThecalculatorlendsupporttoestopaintthesoftwareAutoCADtomakeuscanbewiththesketchthattheastonishingspeeddrawtheengineeringsketchormachinesketchandotherwithaccuracytosophisticate.Thecalculatorpaintstopaintthedifferentplace,oneofthemwithhandicraftthepaintingswithoutthediagramdivideastepproceedof,becauseofbutwouldsometimesappearthetraditionalhandicraftthepaintinghourtheproblemoftheimpossibleemergence.Generalcircumstancebottom,usagetheAutoCADproceedspainting,controltheprecisionpaintingandnotthatdifficult,butwantaccuratethenneedthecertaintechniqueoutthediagram.UsuallypaintoroutsingdiagramtohavenotoneedtochangetomeasuretoAutoCADsystemworthmakethemodificationwithestablish,takeitstheprovinceworthcannormalwork,buthavethespecialrequest,mustmodifytherelatedsystemtochangemeasureToosometimestherequestofthediagrampaperwithmakethediagramswayofdoingtheantinomy,andbetoadoptthetomakethediagrammethodtocantattaintherequestofthediagrampaper,willadoptsometechniqueiquestomodifytherelatedsystemtochangetomeasure,andcanmakethecalculatordrawtoattaintherequestofthediagrampaperwithoutputssketch.AutoCADlinetypeestablishingofcomparisonAtteachingofprocessinsidewouldusuallyrunintowhatthiskindofcircumstance,whileestablishingdiagramlayer,clearlyestablishedthepointlineationed,andconsequentlyoutputtohoweverinvestigateitsreasonforthesolidlined,andisusuallybecauseofthelinetypedtheestablishingofcomparisonisnotappropriateandcausable.ShouldyousoestablishthecomparisonofwhatkindoflinetypeHowtousethelinetypethecomparisoninthepaintingUsageAutoCADpainting,besidescontinuouslinetypeContinuous,theotherlinetypeisallfromthesolidlinesegment,blanksegment,pointseriesforortextthisconstituting.Onlinetypedefinitiondocumenttheinsidehavealreadydefinedtheselinetypesthesegmentsstandardlength,andshowonheldtheactoratprintthemachine\paintingoutput,eachlengthandexportationcomparisonwithlinetypecomparisondirectproportion.Whenshoworprint,thepaintingboundarythatcustomerthatrequest,thishourestablishisoutofaccordancewiththepaintingboundaryoftheprovincedifferencebig,onheldtheactshoworpaintoutputslinetypewouldmatchtheengineeringgraphicstowillpassthechangeslinetypecomparisonthesystemthemethodthatchangethedeal,enlargeor