数字机床控制系统中英文对照外文翻译文献.docx
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数字机床控制系统中英文对照外文翻译文献
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原文:
NumericalControl
Oneofthemostfundamentalconceptsintheareaofadvancedmanufacturingtechnologiesisnumericalcontrol(NC).PriortotheadventofNC,allmachinetoolsweremanualoperatedandcontrolled.Amongthemanylimitationsassociatedwithmanualcontrolmachinetools,perhapsnoneismoreprominentthanthelimitationofoperatorskills.Withmanualcontrol,thequalityoftheproductisdirectlyrelatedtoandlimitedtotheskillsoftheoperator.Numericalcontrolrepresentsthefirstmajorstepawayfromhumancontrolofmachinetools.
Numericalcontrolmeansthecontrolofmachinetoolsandothermanufacturingsystemsthoughtheuseofprerecorded,writtensymbolicinstructions.Ratherthanoperatingamachinetool,anNCtechnicianwritesaprogramthatissuesoperationalinstructionstothemachinetool,Foramachinetooltobenumericallycontrolled,itmustbeinterfacedwithadeviceforacceptinganddecodingthep2ogrammedinstructions,knownasareader.
Numericalcontrolwasdevelopedtoovercomethelimitationofhumanoperator,andithasdoneso.Numericalcontrolmachinesaremoreaccuratethanmanuallyoperatedmachines,theycanproducepartsmoreuniformly,theyarefaster,andthelong-runtoolingcostsarelower.ThedevelopmentofNCledtothedevelopmentofseveralotherinnovationsinmanufacturingtechnology:
1.Electricaldischargemachining.
2.Lasercutting.
3.Electronbeamwelding.
Numericalcontrolhasalsomademachinetoolsmoreversatilethantheirmanuallyoperatedpredecessors.AnNCmachinetoolcanautomaticallyproduceawidevarietyofpar4s,eachinvolvinganassortmentofundertaketheproductionofproductsthatwouldnothavebeenfeasiblefromaneconomicperspectiveusingmanuallycontrolledmachinetoolsandprocesses.
Likesomanyadvancedtechnologies,NCwasborninthelaboratoriesoftheMassachusettsInstituteofTechnology.TheconceptofNCwasdevelopedintheearly1950swithfundingprovidedbytheU.SAirForce.Initsearlieststages,NCmachineswereabletomakestraightcutsefficientlyandeffectively.
However,curvedpathswereaproblembecausethemachinetoolhadtobeprogrammedtoundertakeaseriesofhorizontalandverticalstepstoproduceacurve.Theshorteristhestraightlinesmakingupthestep,thesmootheristhecurve.Eachlinesegmentinthestepshadtobecalculated.
Thisproblemledtothedevelopmentin1959oftheAutomaticallyProgrammedTools(APT)languageforNCthatusesstatementssimilartoEnglishlanguagetodefinethepartgeometry,describethecuttingtoolconfiguration,andspecifythenecessarymotions.ThedevelopmentoftheAPTlanguagewasamajorstepforwardinthefurtherdevelopmentofNCtechnology.TheoriginalNCsystemwerevastlydifferentfromthoseusedpunchedpaper,whichwaslatertoreplacedbymagneticplastictape.Atapereaderwasusedtointerprettheinstructionswrittenonthetapeforthemachine.Together,allofthisrepresentedgiantstepforwardinthecontrolofmachinetools.However,therewereanumberofproblemswithNCatthispointinitsdevelopment.
Amajorproblemwasthefragilityofthepunchedpapertapemedium.Itwascommonforthepapercontainingtheprogrammedinstructionstobreakortearduringamachiningprocess,Thisproblemwasexacerbatedbythefactthateachsuccessivetimeapartwasproducedonamachinetool,thepapertapecarryingtheprogrammedinstructionshadtorerunthoughtthereader.Ifitwasnecessarytoproduce100copiesofagivenpart,itwasalsonecessarytorunthepapertapethoughtthereader100separatetimes.Fragilepapertapessimplycouldnotwithstandtherigorsofshopfloorenvironmentandthiskindofrepeateduse.
Thisledtothedevelopmentofaspecialmagnetictape.Whereasthepapertapecarriedtheprogrammedinstructionsasaseriesofholespunchedinthetape,theThismostmportantofthesewasthatitwasdifficultorimpossibletochangetheinstructionsenteredonthetape.Tomakeeventhemostminoradjustmentsinaprogramofinstructions,itwasnecessarytointerruptmachiningoperationsandmakeanewtape.Itwasalsostillnecessarytorunthetapethoughtthereaderasmanytimesastherewerepartstobeproduced.Fortunately,computertechnologybecomearealityandsoonsolvedtheproblemsofNC,associatedwithpunchedpaperandplastictape.
Thedevelopmentofaconceptknownasnumericalcontrol(DNC)solvethepaperandplastictapeproblemsassociatedwithnumericalcontrolbysimplyeliminatingtapeasthemediumforcarryingtheprogrammedinstructions.Indirectnumericalcontrol,machinetoolsaretied,viaadatatransmissionlink,toahostcomputerandfedtothemachinetoolasneededviathedatatransmissionlinkage.Directnumericalcontrolrepresentedamajorstepforwardoverpunchedtapeandplastictape.However,itissubjecttothesamelimitationasalltechnologiesthatdependonahostcomputer.Whenthehostcomputergoesdown,themachinetoolsalsoexperiencedowntime.Thisproblemledtothedevelopmentofcomputernumericalcontrol.
Theevelopmentofthemicroprocessorallowedforthedevelopmentofprogrammablelogiccontrollers(PLC)andmicrocomputers.Thesetwotechnologiesallowedforthedevelopmentofcomputernumericalcontrol(CNC).WithCNC,eachmachinetoolhasaPLCoramicrocomputerthatservesthesamepurpose.Thisallowsprogramstobeinputandstoredateachindividualmachinetool.CNCsolvedtheproblemsassociateddowntimeofthehostcomputer,butitintroducedanotherproblemknownasdatamanagement.Thesameprogrammightbeloadedontendifferentmicrocomputerswithnocommunicationamongthem.ThisproblemisintheprocessofbeingsolvedbylocalareanetworksthatconnectDigitalignalProcessors.
Therearenumeroussituationswhereanalogsignalstobeprocessedinmanyways,likefilteringandspectralanalysis,Designinganaloghardwaretoperformthesefunctionsispossiblebuthasbecomelessandpractical,duetoincreasedperformancerequirements,flexibilityneeds,andtheneedtocutdownondevelopment/testingtime.Itisinotherwordsdifficultpmdesignanaloghardwareanalysisofsignals.
Theactofsamplingansignalintothehatarespecialisedforembeddedsignalprocessingoperations,andsuchaprocessoriscalledaDSP,whichstandsforDigitalSignalProcessor.TodaytherearehundredsofDSPfamiliesfromasmanymanufacturers,eachonedesignedforaparticularprice/performance/usagegroup.Manyofthelargestmanufacturers,likeTexasInstrumentsandMotorola,offerbothspecialisedDSP’sforcertainfieldslikemotor-controlormodems,andgeneralhigh-performanceSP’sthatcanerformbroadrangesofprocessingtasks.Developmentkitsansoftwarearealsoavailable,andtherearecompaniesmakingsoftwaredevelopmenttoolsforDSP’sthatallowstheprogrammertoimplementcomplexprocessingalgorithmsusingsimple“drag‘n’drop”methodologies.
DSP’smoreorlessfallintotwocategoriesdependingontheunderlyingarchitecture-fixed-pointandfloating-point.Thefixed-pointdevicesgenerallyoperateon16-bitwords,whilethefloating-pointdevicesoperateon32-40bitsfloating-pointwords.Needlesstosay,thefixed-pointdevicesaregenerallycheaper.Anotherimportantarchitecturaldifferenceisthatfixed-pointprocessorstendtohaveanaccumulatorarchitecture,withonlyone“generalpurpose”register,makingthemquitetrickytoprogramandmoreimportantly,makingC-compilersinherentlyinefficient.Floating-pointDSP’sbehavemorelikecommongeneral-purposeCPU’s,withregister-files.
TherearethousandsofdifferentDSP’sonthemarket,anditisdifficulttaskfindingthemostsuitableDSPforaproject.Thebestwayisprobablytosetupaconstraintandwishlist,andtrytocomparetheprocessorsfromthebiggestmanufacturersagainstit.
The“bigfour”manufacturersofDSP’s:
TexasInstruments,Motorola,AT&TandAnalogDevices.
Digital-to-analogconversion
InthecaseofMPEG-Audiodecoding,digitalcompresseddataisfedintotheDSPwhichperformsthedecoding,thenthedecodedsampleshavetobeconvertedbackintotheanalogdomain,andtheresultingsignalfedanamplifierorsimilaraudioequipment.Thisdigitaltoanalogconversion(DCA)isperformedbyacircuitwiththesamename&DifferentDCA’sprovidedifferentperformanceandquality,asmeasuredbyTHD(Totalharmonicdistortion),numberofbits,linearity,speed,filtercharacteristicsandotherthings.
TheTMS320familyDQPofTexasInstruments
TheTLS320familyconsistsoffixed-point,floating-point,multiprocessordigitalsignalprocessors(DSP’s),andfoxed-pointDSPcontrollers.TMS320DSPhaveanarchitecturedesignedspecificallyforreal-timesignalprocessing.TheF/C240isanumberofthe’C2000DSPplatform,andisoptimizedforcontrolapplications.TheC24xseriesofDSPcontrollerscombinesthisreal-timeprocessingcapabilitywithcontrollerperipheralstocreateanidealsolutionforcontrolsystemapplications.ThefollowingcharacteristicsmaketheTMS320familytherightchoiceforawiderangeofprocessingapplications:
---Veryflexibleinstructionset
---Inherentoperationalflexibility
---High-speedperformance
---Innovativeparallelarchitecture
---Costeffectiveness
DeviceswithinagenerationoftheTMS320familyhavethesameCPUstructurebutdifferenton-chipmemoryandperipheralconfigurations.Spin-offdevicesusenewcombinationsofOn-chipmemoryandperipheralstosatisfyawiderangeofneedsintheworldwideelectronicsmarket.Byintegratingmemoryandperipheralsontoasinglechip,TMS320devicesreducesystemcostsandsavecircuitboardspace.
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