数控外文翻译.docx

数控外文翻译.docx

《数控外文翻译.docx》由会员分享，可在线阅读，更多相关《数控外文翻译.docx（15页珍藏版）》请在冰豆网上搜索。

数控外文翻译

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,thesmootheris4hecurve.Eachlinesegment

inthestepshadtobecalculated.

Thisproblemledtothedevelopmentin1959oftheAutomaticallyProgrammedTools（APT）languageforNCthatusesstatementssimilartoEnglishlanguagetodefinethepartgeometry,describethecuttingtoolconfiguration,andspecifythenecessarymotions.ThedevelopmentoftheAPTlanguagewasamajorstepforwardinthefurtherdevelopmentofNCtechnology.TheoriginalNCsystemwerevastlydifferentfromthoseusedpunchedpaper,whichwaslatertoreplacedbymagneticplastictape.Atapereaderwasusedtointerprettheinstructionswrittenonthetapeforthemachine.Together,all/fthisrepresentedgiantstepforwardinthecontrolofmachinetools.However,therewereanumberofproblemswithNCatthispointinitsdevelopment.

Amajorproblemwasthefragilityofthepunchedpapertapemedium.Itwascommonforthepapercontainingtheprogrammedinstructionstobreakortearduringamachiningprocess,Thisproblemwasexacerbatedbythefactthateachsuccessivetimeapartwasproducedonamachinetool,thepapertapecarryingtheprogrammedinstructionshadtorerunthoughtthereader.Ifitwasnecessarytoproduce100copiesofagivenpart,itwasalsonecessarytorunthepapertapethoughtthereader100separatetimes.Fragilepapertapessimplycouldnotwithstandtherigorsofshopfloorenvironmentandthiskindofrepeateduse.

Thisledtothedevelopmentofaspecialmagnetictape.Whereasthepapertapecarriedtheprogrammedinstructionsasaseriesofholespunchedinthetape,theThismostimportantofthesewasthatitwasdifficultorimpossibletochangetheinstructionsenteredonthetape.Tomakeeventhemostminoradjustmentsinaprogramofinstructions,itwasnecessarytointerruptmachiningoperationsandmakeanewtape.Itwasalsostillnecessarytorunthetapethoughtthereaderasmanytimesastherewerepartstobeproduced.Fortunately,computertechnologybecomearealityandsoonsolvedtheproblemsofNC,associatedwithpunchedpaperandplastictape.

Thedevelopmentofaconceptknownasnumericalcontrol（DNC）solvethepaperandplastictapeproblemsassociatedwithnumericalcontrolbysimplyeliminatingtapeasthemediumforcarryingtheprogrammedinstructions.Indirectnumericalcontrol,machinetoolsaretied,viaadatatransmissionlink,toahostcomputerandfedtothemachinetoolasneededviathedatatransmissionlinkage.Directnumericalcontrolrepresentedamajorstepforwardoverpunchedtapeandplastictape.However,itissubjecttothesamelimitationasalltechnologiesthatdependonahostcomputer.Whenthehostcomputergoesdown,themachinetoolsalsoexperiencedowntime.Thisproblemledtothedevelopmentofcomputernumericalcontrol.

Thedevelopmentofthemicroprocessorallowedforthedevelopmentofprogrammable

logiccontrollers（PLC）andmicrocomputers.Thesetwotechnologiesallowedforthedevelopmentofcomputernumericalcontrol（CNC）.WithCNC,eachmachinetoolhasaPLCoramicrocomputerthatservesthesamepurpose.Thisallowsprogramstobeinputandstoredateachindividualmachinetool.CNCsolvedtheproblemsassociateddowntimeofthehostcomputer,butitintroducedanotherproblemknownasdatamanagement.Thesameprogrammightbeloadedontendifferentmicrocomputerswithnocommunicationamongthem.ThisproblemisintheprocessofbeingsolvedbylocalareanetworksthatconnectDigitalSignalProcessors

Therearenumeroussituationswhereanalogsignalstobeprocessedinmanyways,likefilteringandspectralanalysis,Designinganaloghardwaretoperformthesefunctionsispossiblebuthasbecomelessandpractical,duetoincreasedperformancerequirements,flexibilityneeds,andtheneedtocutdownondevelopment/testingtime.Itisinotherwordsdifficultpmdesignanaloghardwareanalysisofsignals.

Theactofsamplingansignalintothehatarespecialisedforembeddedsignalprocessingoperations,andsuchaprocessoriscalledaDSP,whichstandsforDigitalSignalProcessor.TodaytherearehundredsofDSPfamiliesfromasmanymanufacturers,eachonedesignedforaparticularprice/performance/usagegroup.Manyofthelargestmanufacturers,likeTexasInstrumentsandMotorola,offerbothspecialisedDSP’sforcertainfieldslikemotor-controlormodems,andgeneralhigh-performanceDSP’sthatcanperformbroadrangesofprocessingtasks.Developmentkitsan`softwarearealsoavailable,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”manufacturersofDSPs:

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（D[Ps）,andfoxed-pointDSPcontrollers.TMS320DSPhaveanarchitecturedesignedspecificallyforreal-timesignalprocessing.The’F/C240isanumberofthe’C2000DSPplatform,andisoptimizedforcontrolapplications.The’C24xseriesofDSPcontrollerscombinesthisreal-timeprocessingcapabilitywithcontrollerperipheralstocreateanidealsolutionforcontrolsystemapplications.ThefollowingcharacteristicsmaketheTMS320familytherightchoiceforawiderangeofprocessingapplications:

---Veryflexibleinstructionset

---Inherentoperationalflexibility

---High-speedperformance

---Innovativeparallelarchitecture

---Costeffectiveness

DeviceswithinagenerationoftheTMS320familyhavethesameCPUstructurebutdifferenton-chipmemoryandperipheralconfigurations.Spin-offdevicesusenewcombinationsofOn-chipmemoryandperipheralstosatisfyawiderangeofneedsintheworldwideelectronicsmarket.Byintegratingmemoryandperipheralsontoasinglechip,TMS320devicesreducesystemcostsandsavecircuitboardspace.

The16-bit,fixed-pointDSP