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毕业设计（论文）外文文献翻译文献、资料中文题目：数控技术文献、资料英文题目：NumericalControl文献、资料来源：文献、资料发表（出版）日期：院（部）：专业：班级：姓名：学号：指导教师：翻译日期：2017.02.14NumericalControlNumericalcontrol(N/C)isaformofprogrammableautomationinwhichtheprocessingequipmentiscontrolledbymeansofnumbers,lettersandothersymbols.Thenumbers,letters,andsymbolsarecodedinanappropriateformattodefineaprogramofinstructionsforaparticularworkpartorjob.Whenthejobischanged,theprogramofinstructionsmustbechanged.ThecapabilitytochangetheprogramiswhatmakesN/Csuitableforlow-volumeandmedium-volumeproduction.Itismucheasiertowriteprogramsthantomakemajoralterationsoftheprocessingequipment.Therearetwobasictypesofnumericallycontrolledmachinetools:point—to—pointandcontinuous—path(alsocalledcontouring).Point—to—pointmachinesuseunsynchronizedmotors,withtheresultthatthepositionofthemachiningheadCanbeassuredonlyuponcompletionofamovement,orwhileonlyonemotorisrunning.Machinesofthistypeareprincipallyusedforstraight—linecutsorfordrillingorboring.TheN/Csystemconsistsofthefollowingcomponents:datainput,thetapereaderwiththecontrolunit,feedbackdevices,andthemetal—cuttingmachinetoolorothertypeofN/Cequipment.Datainput,alsocalled“man—to—controllink”,maybeprovidedtothemachinetoolmanually,orentirelybyautomaticmeans.Manualmethodswhenusedasthesolesourceofinputdataarerestrictedtoarelativelysmallnumberofinputs.Examplesofmanuallyoperateddevicesarekeyboarddials,pushbuttons,switches,orthumbwheelselectors.Thesearelocatedonaconsolenearthemachine.Dialsaleanalogdevicesusuallyconnectedtoasynchronization-typeresolverorpotentiometer.Inmostcases,pushbuttons,switchesandothersimilartypesofselectorsaredigitalinputdevices.Manualinputrequiresthattheoperatorsetthecontrolsforeachoperation.Itisaslowandtediousprocessandisseldomjustifiedexceptinelementarymachiningapplicationsorinspecialcases.Inpracticallyallcases,informationisautomaticallysuppliedtothecontrolunitandthemachinetoolbycards,punchedtapes,orbymagnetictape.Eight—channelpunchedpapertapeisthemostcommonlyusedformofdatainputforconventionalN/Csystems.Thecodedinstructionsonthetapeconsistofsectionsofpunchedholescalledblocks.Eachblockrepresentsamachinefunction,amachiningoperation,oracombinationofthetwo.TheentireN/Cprogramonatapeismadeupofanaccumulationofthesesuccessivedatablocks,Programsresultinginlongtapesallwoundonreelslikemotion-picturefilm.Programsonrelativelyshorttapesmaybecontinuouslyrepeatedbyjoiningthetwoendsofthetapetoformaloop.Onceinstalled,thetapeisusedagainandagainwithoutfurtherhandling.Inthiscase,theoperatorsimplyloadsandunloadstheparts.Punchedtapesalepreparedontypewriterswithspecialtape—punchingattachmentsorintapepunchingunitsconnecteddirectlytoacomputersystem.Tapeproductionisrarelyerror-free.Errorsmaybeinitiallycausedbythepartprogrammer,incardpunchingorcompilation,orasaresultofphysicaldamagetothetapeduringhandling,etc.Severaltrialrunsareoftennecessarytoremoveallerrorsandproduceanacceptableworkingtape.Whilethedataonthetapeisfedautomatically,theactualprogrammingstepsaledonemanually,Beforethecodedtapemaybeprepared,theprogrammer,oftenworkingwithaplanneroraprocessengineer,mustselecttheappropriateN/Cmachinetool,determinethekindofmaterialtobemachined,calculatethespeedsandfeeds,anddecideuponthetypeoftoolingneeded.Thedimensionsonthepartprintarecloselyexaminedtodetermineasuitablezeroreferencepointfromwhichtostarttheprogram.Aprogrammanuscriptisthenwrittenwhichgivescodednumericalinstructionsdescribingthesequenceofoperationsthatthemachinetoolisrequiredtofollowtocuttheparttothedrawingspecifications.Thecontrolunitreceivesandstoresallcodeddatauntilacompleteblockofinformationhasbeenaccumulated.Ittheninterpretsthecodedinstructionanddirectsthemachinetoolthroughtherequiredmotions.Thefunctionofthecontrolunitmaybebetterunderstoodbycomparingittotheactionofadialtelephone,where,aseachdigitisdialed,itisstored.Whentheentirenumberhasbeendialed,theequipmentbecomesactivatedandthecalliscompleted.Siliconphotodiodes,locatedinthetapereaderheadonthecontrolunit,detectlightasitpassesthroughtheholesinthemovingtape.Thelightbeamsareconvertedtoelectricalenergy,whichisamplifiedtofurtherstrengthenthesignal.Thesignalsarethensenttoregistersinthecontrolunit,whereactuationsignalsarerelayedtothemachinetooldrives.Somephotoelectricdevicesarecapableofreadingatratesupto1000characterspersecond.Highreadingratesarenecessarytomaintaincontinuousmachine—toolmotion;otherwisedwellmarksmaybegeneratedbythecutteronthepartduringcontouringoperations.Thereadingdevicemustbecapableofreadingdatablocksataratefasterthanthecontrolsystemcanprocessthedata.AfeedbackdeviceisasafeguardusedonsomeN/Cinstallationstoconstantlycompensateforerrorsbetweenthecommandedpositionandtheactuallocationofthemovingslidesofthemachinetool.AnN/Cmachineequippedwiththiskindofadirectfeedbackcheckingdevicehaswhatisknownasaclosed-loopsystem.Positioningcontrolisaccomplishedbyasensorwhich,duringtheactualoperation,recordsthepositionoftheslidesandrelaysthisinformationbacktothecontrolunit.Signalsthusreceivedalecomparedtoinputsignalsonthetape,andanydiscrepancybetweenthemisautoma