数控技术---外文翻译.doc

NUMERICALCONTROLNUMERICALCONTROLN／CISAFORMOFPROGRAMMABLEAUTOMATIONINWHICHTHEPROCESSINGEQUIPMENTISCONTROLLEDBYMEANSOFNUMBERS，LETTERS，ANDOTHERSYMBOLS．THENUMBERS，LETTERS，ANDSYMBOLSARECODEDINANAPPROPRIATEFORMATTODEFINEAPROGRAMOFINSTRUCTIONSFORAPARTICULARWORKPARTORJOB．WHENTHEJOBCHANGES，THEPROGRAMOFINSTRUCTIONSISCHANGED．THECAPABILITYTOCHANGETHEPROGRAMISWHATMAKESN／CSUITABLEFORLOWANDMEDIUMVOLUMEPRODUCTION．ITISMUCHEASIERTOWRITEPROGRAMSTHANTOMAKEMAJORALTERATIONSOFTHEPROCESSINGEQUIPMENT．THEREARETWOBASICTYPESOFNUMERICALLYCONTROLLEDMACHINETOOLSPOINTTOPOINTANDCONTINUOUSPATHALSOCALLEDCONTOURING．POINTTOPOINTMACHINESUSEUNSYNCHRONIZEDMOTORS，WITHTHERESULTTHATTHEPOSITIONOFTHEMACHININGHEADCANBEASSUREDONLYUPONCOMPLETIONOFAMOVEMENT，ORWHILEONLYONEMOTORISRUNNING．MACHINESOFTHISTYPEAREPRINCIPALLYUSEDFORSTRAIGHTLINECUTSORFORDRILLINGORBORING．THEN／CSYSTEMCONSISTSOFTHEFOLLOWINGCOMPONENTSDATAINPUT，THETAPEREADERWITHTHECONTROLUNIT，FEEDBACKDEVICES，ANDTHEMETALCUTTINGMACHINETOOLOROTHERTYPEOFN／CEQUIPMENT．DATAINPUT，ALSOCALLED“MANTOCONTROLLINK”，MAYBEPROVIDEDTOTHEMACHINETOOLMANUALLY，ORENTIRELYBYAUTOMATICMEANS．MANUALMETHODSWHENUSEDASTHESOLESOURCEOFINPUTDATAARERESTRICTEDTOARELATIVELYSMALLNUMBEROFINPUTS．EXAMPLESOFMANUALLYOPERATEDDEVICESAREKEYBOARDDIALS，PUSHBUTTONS，SWITCHES，ORTHUMBWHEELSELECTORS．THESEARELOCATEDONACONSOLENEARTHEMACHINE．DIALSALEANALOGDEVICESUSUALLYCONNECTEDTOASYNCHROTYPERESOLVERORPOTENTIOMETER．INMOSTCASES，PUSHBUTTONS，SWITCHES，ANDOTHERSIMILARTYPESOFSELECTORSAYEDIGITALINPUTDEVICES．MANUALINPUTREQUIRESTHATTHEOPERATORSETTHECONTROLSFOREACHOPERATION．ITISASLOWANDTEDIOUSPROCESSANDISSELDOMJUSTIFIEDEXCEPTINELEMENTARYMACHININGAPPLICATIONSORINSPECIALCASES．INPRACTICALLYALLCASES，INFORMATIONISAUTOMATICALLYSUPPLIEDTOTHECONTROLUNITANDTHEMACHINETOOLBYCARDS，PUNCHEDTAPES，ORBYMAGNETICTAPE．EIGHTCHANNELPUNCHEDPAPERTAPEISTHEMOSTCOMMONLYUSEDFORMOFDATAINPUTFORCONVENTIONALN／CSYSTEMS．THECODEDINSTRUCTIONSONTHETAPECONSISTOFSECTIONSOFPUNCHEDHOLESCALLEDBLOCKS．EACHBLOCKREPRESENTSAMACHINEFUNCTION，AMACHININGOPERATION，ORACOMBINATIONOFTHETWO．THEENTIREN／CPROGRAMONATAPEISMADEUPOFANACCUMULATIONOFTHESESUCCESSIVEDATABLOCKS．PROGRAMSRESULTINGINLONGTAPESALLWOUNDONREELSLIKEMOTIONPICTUREFILM．PROGRAMSONRELATIVELYSHORTTAPESMAYBECONTINUOUSLYREPEATEDBYJOININGTHETWOENDSOFTHETAPETOFORMALOOP．ONCEINSTALLED，THETAPEISUSEDAGAINANDAGAINWITHOUTFURTHERHANDLING．INTHISCASE，THEOPERATORSIMPLYLOADSANDUNLOADSTHEPARTS．PUNCHEDTAPESALEPREPAREDONTYPEWRITERSWITHSPECIALTAPEPUNCHINGATTACHMENTSORINTAPEPUNCHINGUNITSCONNECTEDDIRECTLYTOACOMPUTERSYSTEM．TAPEPRODUCTIONISRARELYERRORFREE．ERRORSMAYBEINITIALLYCAUSEDBYTHEPARTPROGRAMMER，INCARDPUNCHINGORCOMPILATION，ORASARESULTOFPHYSICALDAMAGETOTHETAPEDURINGHANDLING，ETC．SEVERALTRIALRUNSAREOFTENNECESSARYTOREMOVEALLERRORSANDPRODUCEANACCEPTABLEWORKINGTAPE．WHILETHEDATAONTHETAPEISFEDAUTOMATICALLY，THEACTUALPROGRAMMINGSTEPSALEDONEMANUALLY．BEFORETHECODEDTAPEMAYBEPREPARED，THEPROGRAMMER，OFTENWORKINGWITHAPLANNERORAPROCESSENGINEER,MUSTSELECTTHEAPPROPRIATEN／CMACHINETOOL，DETERMINETHEKINDOFMATERIALTOBEMACHINED，CALCULATETHESPEEDSANDFEEDS，ANDDECIDEUPONTHETYPEOFTOOLINGNEEDEDTHEDIMENSIONSONTHEPARTPRINTARECLOSELYEXAMINEDTODETERMINEASUITABLEZEROREFERENCEPOINTFROMWHICHTOSTARTTHEPROGRAM．APROGRAMMANUSCRIPTISTHENWRITTENWHICHGIVESCODEDNUMERICALINSTRUCTIONSDESCRIBINGTHESEQUENCEOFOPERATIONSTHATTHEMACHINETOOLISREQUIREDTOFOLLOWTOCUTTHEPARTTOTHEDRAWINGSPECIFICATIONS．THECONTROLUNITRECEIVESANDSTORESALLCODEDDATAUNTILACOMPLETEBLOCKOFINFORMATIONHASBEENACCUMULATED．ITTHENINTERPRETSTHECODEDINSTRUCTIONANDDIRECTSTHEMACHINETOOLTHROUGHTHEREQUIREDMOTIONS．THEFUNCTIONOFTHECONTROLUNITMAYBEBETTERUNDERSTOODBYCOMPARINGITTOTHEACTIONOFADIALTELEPHONE，WHERE，ASEACHDIGITISDIALED，ITISSTORED．WHENTHEENTIRENUMBERHASBEENDIALED，THEEQUIPMENTBECOMESACTIVATEDANDTHECALLISCOMPLETED．SILICONPHOTODIODES，LOCATEDINTHETAPEREADERHEADONTHECONTROLUNIT，DETECTLIGHTASITPASSESTHROUGHTHEHOLESINTHEMOVINGTAPE．THELIGHTBEAMSARECONVERTEDTOELECTRICALENERGY，WHICHISAMPLIFIEDTOFURTHERSTRENGTHENTHESIGNAL．THESIGNALSARETHENSENTTOREGISTERSINTHECONTROLUNIT,WHEREACTUATIONSIGNALSARERELAYEDTOTHEMACHINETOOLDRIVES．SOMEPHOTOELECTRICDEVICESARECAPABLEOFREADINGATRATESUPTO1000CHARACTERSPERSECOND．HIGHREADINGRATESARENECESSARYTOMAINTAINCONTINUOUSMACHINETOOLMOTION；OTHERWISEDWELLMARKSMAYBEGENERATEDBYTHECUTTERONTHEPARTDURINGCONTOURINGOPERATIONS．THEREADINGDEVICEMUSTBECAPABLEOFREADINGDATABLOCKSATARATEFASTERTHANTHECONTROLSYSTEMCANPROCESSTHEDATA．AFEEDBACKDEVICEISASAFEGUARDUSEDONSOMEN／CINSTALLATIONSTOCONSTANTLYCOMPENSATEFORERRORSBETWEENTHECOMMANDEDPOSITIONANDTHEACTUALLOCATIONOFTHEMOVINGSLIDESOFTHEMACHINETOOL．ANN／CMACHINEEQUIPPEDWITHTHISKINDOFADIRECTFEEDBACKCHECKINGDEVICEHASWHATISKNOWNASACLOSEDLOOPSYSTEM．POSITIONINGCONTROLISACCOMPLISHEDBYASENSORWHICH，DURINGTHEACTUALOPERATION，RECORDSTHEPOSITIONOFTHESLIDESANDRELAYSTHISINFORMATIONBACKTOTHECONTROLUNIT．SIGNALSTHUSRECEIVEDALECOMPAREDTOINPUTSIGNALSONTHETAPE，ANDANYDISCREPANCYBETWEENTHEMISAUTOMATICALLYRECTIFIED．INANALTERNATIVESYSTEM，CALLEDANOPENLOOPSYSTEM，THEMACHINEISPOSITIONEDSOLELYBYSTEPPINGMOTORDRIVESINRESPONSETOCOMMANDSBYACONTROLLERS．THEREARETHREEBASICTYPESOFNCMOTIONS,ASFOLLOWSPOINTTOPOINTORPOSITIONALCONTROLINPOINTTOPOINTCONTROLTHEMACHINETOOLELEMENTSTOOLS,TABLE,ETCAREMOVEDTOPROGRAMMEDLOCATIONSANDTHEMACHININGOPERATIONSPERFORMEDAFTERTHEMOTIONSARECOMPLETEDTHEPATHORSPEEDOFMOVEMENTBETWEENLOCATIONSISUNIMPORTANT；ONLYTHECOORDINATESOFTHEENDPOINTSOFTHEMOTIONSAREACCURATELYCONTROLLEDTHISTYPEOFCONTROLISSUITABLEFORDRILLPRESSESANDSOMEBORINGMACHINES,WHEREDRILLING,TAPPING,ORBORINGOPERATIONSMUSTBEPERFORMEDATVARIOUSLOCATIONSONTHEWORKPIECESTRAIGHTLINEORLINEARCONTROLSTRAIGHTLINECONTROLSYSTEMSAREABLETOMOVETHECUTTINGTOOLPARALLELTOONEOFTHEMAJORAXESOFTHEMACHINETOOLATACONTROLLEDRATESUITABLEFORMACHININGITISNORMALLYONLYPOSSIBLETOMOVEINONEDIRECTIONATATIME,SOANGULARCUTSONTHEWORKPIECEARENOTPOSSIBLE,CONSEQUENTLY,FORMILLINGMACHINES,ONLYRECTANGULARCONFIGURATIONSCANBEMACHINEDORFORLATHESONLYSURFACESPARALLELORPERPENDICULARTOTHESPINDLEAXISCANBEMACHINEDTHISTYPEOFCONTROLLEDMOTIONISOFTENREFERREDTOASLINEARCONTROLORAHALFAXISOFCONTROLMACHINESWITHTHISFORMOFCONTROLAREALSOCAPABLEOFPOINTTOPOINTCONTROLCONTINUOUSPATHORCONTOURINGCONTROLINCONTINUOUSPATHCONTROLTHEMOTIONSOFTWOORMOREOFTHEMACHINEAXESARECONTROLLEDSIMULTANEOUSLY,SOTHATTHEPOSITIONANDVELOCITYOFTHECANBETOOLARECHANGEDCONTINUOUSLYINTHISWAYCURVESANDSURFACESCANBEMACHINEDATACONTROLLEDFEEDRATEITISTHEFUNCTIONOFTHEINTERPOLATORINTHECONTROLLERTODETERMINETHEINCREMENTSOFTHEINDIVIDUALCONTROLLEDAXESOFTHEMACHINESNECESSARYTOPRODUCETHEDESIREDMOTIONTHISTYPEOFCONTROLISREFERREDTOASCONTINUOUSCONTROLORAFULLAXISOFCONTROLSOMETERMINOLOGYCONCERNINGCONTROLLEDMOTIONSFORNCMACHINESHASBEENINTRODUCEDFOREXAMPLE,SOMEMACHINESAREREFERREDTOASFOURORFIVEOREVENSIXAXISMACHINESFORAVERTICALMILLINGMACHINETHREEAXESOFCONTROLAREFAIRLYOBVIOUS,THESEBEINGTHEUSUALX,Y,ZCOORDINATEDIRECTIONSAFOURTHORFIFTHAXISOFCONTROLWOULDIMPLYSOMEFORMOFROTARYTABLETOINDEXTHEWORKPIECEORPOSSIBLYTOPROVIDEANGULARMOTIONOFTHEWORKHEADTHUS,INNCTERMINOLOGYANAXISOFCONTROLISANYCONTROLLEDMOTIONOFTHEMACHINEELEMENTSSPINDLES,TABLES,ETCAFURTHERCOMPLICATIONISUSEOFTHETERMHALFAXISOFCONTROL；FOREXAMPLE,MANYMILLINGMACHINESAREREFERREDTOAS25AXISMACHINETHISMEANSTHATCONTINUOUSCONTROLISPOSSIBLEFORTWOMOTIONSAXESANDONLYLINEARCONTROLISPOSSIBLEFORTHETHIRDAXISAPPLIEDTOVERTICALMILLINGMACHINES,25AXISCONTROLMEANSCONTOURINGINTHEX,YPLANEANDLINEARMOTIONONLYINTHEZDIRECTIONWITHTHESEMACHINESTHREEDIMENSIONALOBJECTSHAVETOBEMACHINEDWITHWATERLINESAROUNDTHESURFACEATDIFFERENTHEIGHTSWITHANALTERNATIVETERMINOLOGYTHESAMEMACHINECOULDBECALLEDA2CLMACHINECFORCONTINUOUS,LFORLINEARCONTROLTHUS,AMILLINGMACHINEWITHCONTINUOUSCONTROLINTHEX,Y,ZDIRECTIONSCOULDBETERMEDBEATHREEAXISMACHINEORA3CMACHINE,SIMILARLY,LATHESAREUSUALLYTWOAXISOR2CMACHINESTHEDEGREEOFWORKPRECISIONDEPENDSALMOSTENTIRELYUPONTHEACCURACYOFTHELEADSCREWANDTHERIGIDITYOFTHEMACHINESTRUCTURE．WITHTHISSYSTEM．THEREISNOSELFCORRECTINGACTIONORFEEDBACKOFINFORMATIONTOTHECONTROLUNIT．INTHEEVENTOFANUNEXPECTEDMALFUNCTION，THECONTROLUNITCONTINUESTOPUTOUTPULSESOFELECTRICALCURRENT．IF，FOREXAMPLE，THETABLEONAN／CMILLINGMACHINEWERESUDDENLYTOBECOMEOVERLOADED，NORESPONSEWOULDBESENTBACKTOTHECONTROLLER．BECAUSESTEPPINGMOTORSARENOTSENSITIVETOLOADVARIATIONS，MANYN／CSYSTEMSAREDESIGNEDTOPERMITTHEMOTORSTOSTALLWHENTHERESISTINGTORQUEEXCEEDSTHEMOTORTORQUE．OTHERSYSTEMSAREINUSE，HOWEVER，WHICHINSPITEOFTHEPOSSIBILITYOFDAMAGETOTHEMACHINESTRUCTUREORTOTHEMECHANICALSYSTEM，ALEDESIGNEDWITHSPECIALHIGHTORQUESTEPPINGMOTORS．INTHISCASE，THEMOTORSHAVESUFFICIENTCAPACITYTO“OVERPOWER’’THESYSTEMINTHEEVENTOFALMOSTANYCONTINGENCY．THEORIGINALN／CUSEDTHECLOSEDLOOPSYSTEM．OFTHETWOSYSTEMS，CLOSEDANDOPENLOOP，CLOSEDLOOPISMOREACCURATEAND，ASACONSEQUENCE，ISGENERALLYMOREEXPENSIVE．INITIALLY，OPENLOOPSYSTEMSWEREUSEDALMOSTENTIRELYFORLIGHTDUTYAPPLICATIONSBECAUSEOFINHERENTPOWERLIMITATIONSPREVIOUSLYASSOCIATEDWITHCONVENTIONALELECTRICSTEPPINGMOTORS．RECENTADVANCESINTHEDEVELOPMENTOFELECTROHYDRAULICSTEPPINGMOTORSHAVELEDTOINCREASINGLYHEAVIERMACHINELOADAPPLICATIONS．MILLINGMILLINGISABASICMACHININGPROCESSINWHICHTHESURFACEISGENERATEDBYTHEPROGRESSIVEFORMATIONANDREMOVALOFCHIPSOFMATERIALFROMTHEWORKPIECEASITISFEDTOAROTATINGCUTTERINADIRECTIONPERPENDICULARTOTHEAXISOFTHECUTTER．INSOMECASESTHEWORKPIECEISSTATIONARYANDTHECUTTERISFEDTOTHEWORK．INMOSTINSTANCESAMULTIPLETOOTHCUTTERISUSEDSOTHATTHEMETALREMOVALRATEISHIGH，ANDFREQUENTLYTHEDESIREDSURFACEISOBTAINEDINASINGLEPASSOFTHEWORK．THETOOLUSEDINMILLINGISKNOWNASAMILLINGCUTTER．ITUSUALLYCONSISTSOFACYLINDRICALBODYWHICHROTATESONITSAXISANDCONTAINSEQUALLYSPACEDPERIPHERALTEETHTHATINTERMITTENTLYENGAGEANDCUTTHEWORKPIECE．INSOMECASESTHETEETHEXTENDPARTWAYACROSSONEORBOTHENDSOFTHECYLINDER．BECAUSETHEMILLINGPRINCIPLEPROVIDESRAPIDMETALREMOVALANDCANPRODUCEGOODSURFACEFINISH，ITISPARTICULARLYWELLSUITEDFORMASSPRODUCTIONWORK，ANDEXCELLENTMILLINGMACHINESHAVEBEENDEVELOPEDFORTHISPURPOSE．HOWEVER，VERYACCURATEANDVERSATILEMILLINGOFAGENERALPURPOSENATUREALSOHAVEBEENDEVELOPEDTHATAREWIDELYUSEDINJOBSHOPANDTOOLANDDIEWORK．ASHOPTHATISEQUIPPEDWITHAMILLINGMACHINEANDANENGINELATHECANMACHINEALMOSTANYTYPEOFPRODUCTOFSUITABLESIZE．TYPESOFMILLINGOPERATIONS．MILLINGOPERATIONSCANBECLASSIFIEDINTOTWOBROADCATEGORIES，EACHOFWH