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英文原文ComputerNumericalControlUnitToday,computernumericalcontrol(CNC)machinesarefoundalmosteverywhere,fromsmalljobshopsinruralcommunitiestoFortune500companiesinlargeurbanareas.Truly,thereishardlyafacetofmanufacturingthatisnotinsomewaytouchedbywhattheseinnovativemachinetoolscando.Everyoneinvolvedinthemanufacturingenvironmentshouldbewellawareofwhatispossiblewiththesesophisticatedmachinetools.Inthischapter,wewillexplorethebasicsofthecoreofCNCmachinetool-CNCunit,showingyoumuchofwhatisinvolvedwithitsfunction,workingprinciples,hardwareconfigurationandsoftwarestructure.WithsomanytypesofCNCmachinetoolsandCNCunitsinexistence,itisnexttoimpossibleforthischaptertobeextremelyspecificaboutanyoneparticulartype.ThekeyconceptsallowustoviewthemainfeaturesofCNCunitinmoregeneralterms,stressingwhythingsarehandledthewaytheyareevenmorethanthespecifictechniquesusedwithanyoneparticularCNCmachinetool.Withthisbroadbackground,youshouldbeabletoeasilyzeroinonanykindofCNCmachinetoolyouwillbeworkingwith.11INTRODUCTIONMachinecontrolsaredividedintotwotypes:numericalcontrol(NC)andcomputernumericalcontrol(CNC)NCcontrolshavetoreadtheprogrameachtimeapartisrun;theyhavenomeansofeditingexistingprogramsCNCcontrolscanstoreandalloweditingofloadedprogramsAllmachinesbuilttodayareCNCmachinesCNCunitistheheartofCNCmachine.Nevertheless,inordertoaidtounderstandtheworkingprinciplesofCNCunit,itisnecessarythattheprinciplesofNCsystembeintroducedfirstly111NCsystemTheNCmachinecanbedividedintothreebasicareas.Thefirstareaisthecontrolunit,whichprocessesthecommandsfromtheinputmedia.Thesecondareaisthedrivemechanisms,andthelastareaisthemachineitselfThemostbasicfunctionofanyNCmachineisautomatic,precise,andconsistentmotioncontrolA11formsofNCequipmenthavetwoormoredirectionsofmotion,calledaxesTheseaxescanbepreciselyandautomaticallypositionedalongtheirlengthsoftravelThetwomostcommonaxistypesarelinear(drivenalongastraightpath)androtary(drivenalongacircularpath)Insteadofcausingmotionbymanuallyturningcranksandhandwheelsasisrequiredonconventionalmachinetools,NCmachinesallowmotionstobeactuatedbyservomotorsundercontroloftheNC,andguidedbythepartprogramGenerallyspeaking,themotiontype(rapid,linear,andcircular),theaxestomove,theamountofmotionandthemotionrate(feedrate)areprogrammablewithalmostallNCmachinetoolsFigure11showsthemakeupofalinearaxisofanNCmachineFigure11ThemakeupofalinearaxisofallNCmachineAnNCcommandexecutedwithinthecontrol(commonlythroughaprogram)tellsthedrivemotortorotateapreciseamountofangleTherotationofthedrivemotorinturnrotatestheballscrewAndtheballscrewdrivesthelinearaxisAfeedbackdeviceattheoppositeendoftheballscrewallowsthecontroltoconfirmthatthecommandednumberofrotationshastakenplaceAllNCmachinetoolsneednumericaldataforcontrollingtherelativemotionbetweencuttingtoolandpiecepart,thecomponentdimensionsnormallyemanatingdirectlyfromengineeringdrawings-thegeometricdataOtherdigitizednumericaldatadefinefeedrates,spindlespeeds,toolidentificationnumbers,andmiscellaneousfunctionstoperformsuchoperationsastoolorworkchanging,orcoolantcontrol-thetechnologicaldataThecombinationofallthisnumericalinformationinasequenceunderstoodbythemachinetoolscontrolleriscalledapartprogram,andtheprocessofcreatingthedatainacorrectlystructuredformatiscalledprogrammingNumericalcontrolsusestandardmicroelectronicmodulesthathavebeendevelopedforcomputerhardware。Exceptforspecialmodulesneededinservocontrolcircuits,noindividualmodulesarenecessary,incontrasttotraditionalcontrols,whichemployonlycomponentstailoredtosuitonespecificcontrolfunctionInmodernNCcontrollersextensivecontrolandcalculationtasksareperformedbyoneormoreintegralmicroprocessors。Thesearetermedcomputernumericalcontrolsystem(CNCs)112CNCsystemandfunctionsofCNCunitControlsystemsbasedonindustrialPC(abbreviationforpersonalcomputer)areincreasinglyusedinautomationtechnologyMachinecontrolshavechangedgreatlywiththe“ageofthecomputer”Controlstodayare“softwired”,whichallowsgreaterflexibilityinchangingandupgradingthecomputercontrolInfact,manyofmachinesoperatingcharacteristicscanbechangedbytheoperator,sothatthemachineoperatesthewayheshewantsitto.ParametertablesinCNCmachinestodayalloweachmachinetobepersonalizedtotheneedsofthejobtoberunThemodernCNCmachinetoolissoftwaredrivenSimplyspeaking,computercontrolsareprogrammedinsteadofhard-wiredDefinition:AccordingtoElectronicIndustriesAssociation(EIA),CNCsystemisaspecialcomputersystemthatisequippedwithcertaininterfacecircuitsandservodrivers,andcandopartora11theworksanNCsystemdobyrunningthesoftwarestoredinitsmemoriesCNCshaveexpandablememoriesthatcanstorelargenumbersofprograms,plussubroutinesandcorrectiondata。SophisticatedgraphicdisplaysanddynamicsimulationhavealsonowbecomeavailableasaresultoftheextensivememorycapacitybeingbuiltintocurrentCNCsWithinonlyfewyears,thecapabilityandefficiencyofmachinecontrollershasincreasedtosuchanextentthatthename“numericalcontrol”isnolongerappropriate;“computernumericalcontrol”ismoreaccuratelydescriptiveGenerally,CNCscomprisesCNCunit,feedmotionservosubsystem,spindleservosubsystemandsomeauxiliarycontrolcells,asshowninFigure1.2,CNCunitisthecoreofthewholeCNCsystemItiscomposedofhardwareandsoftware。ThehardwarecomprisingaCNCunitismadeupofmicroprocessors,electronicmemorymodules,I0interfaces,andpositioncontrolmodules,etcCNCsoftwarecontrolsallfunctionsofthemachineanditsefficiencyofoperation,andmanagesalllocalprogrammingatthemachinetoolandgraphicsimulationofthecuttingprocessifavailableThehardwareandthesoftwareworktogethertodoallfunctionsofCNCunit,whichanordinaryNCsystemcanneverdo,suchasgraphicdisplayHMI(Human-MachineInterface),systemdiagnosis,implementingofvariouscomplextool-pathcontrollingandcompensationalgorithms,intelligentcontrolling,onlineprogramming,andWebcommunications,etcThemainfunctionsandfeaturesofCNCunitaredescribedasfollows:Figure12CNCmachiningsystem(1)Controllingfunction(thenumberofcontrolaxesandsynchronouslycontrolaxes)Controllingfunctionindicatesthemaximumaxis-numbertheCNCunitcancontrolandthenumberofaxestheCNCunitcancontrolsynchronouslyItisalsothemarefeaturesofCNCmachineAxestobecontrolledbyCNCunithavelinearaxesandrotateaxes,basicaxesandauxiliaryaxesGenerally,CNCmachineneedsonly2axestobecontrolledsynchronouslyIncaseofdoubletoolslides,fouraxesareneededCNCmillingmachine,boringmachine,andCNCmachinecenterneed3ormorecontrolledaxesThemorethenumberofControlledaxes,especiallythenumberofaxesbeingcontrolledsynchronously,themorepowerfulfunctionsoftheCNCunit,andthemorecomplexstructureoftheCNCunit,themoredifficultyofprogramming(2)PreparatoryfunctionPreparatoryfunction,alsocalledGfunction,describesthemotionmodesofCNCmachineThemotionmodescompriseinstructionsofbasicmotions,dwell,planeselections,coordinatesystemsettings,toolcompensations,referencepointreturn,fixedoperationcircles,andmetricinchunittransfer,etcAccordingtoISOstandard,thereare100typesofGcodes(fromG00toG99)usedinCNCunit,whichcanbedividedintotwoclasses-nonmodalcodes(whichfunctionsarevalidonlyinthecodesegmentincludingthecodesthemselves)andmodalcodes(whichcankeepeffectivebeforethecomingofnextGcodeofthesamegroup)FortheexactfunctionofeachGcodeusedinyourmachinetools,youmustreferenceyourcontrolmanufacturersmanualtofindthelistoffunctionsforyourmachine(3)InterpolationfunctionCNCunitdoesinterpolationbyusingsoftwarerealtimecalculationsLinearinterpolation,circularinterpolation,helicalinterpolation,andpolarcoordinateinterpolationwilldotheirbesttohelpCNCunitgeneratetooltrackasclosetovariouspathsaspossible(4)FeedfunctionFeedfunctionusesF(Feedratedesignation)todesignatethe.feedratetoaxisThemethodbywhichfeedrateisprogrammedvariesfromonemachinetypetothenextGenerallyspeaking,machiningcentersonlyallowthefeedratetobespecificinper-minuteformat(inchesormillimetersperminute),suchas,F15000meansthefederateis15000millimetersperminuteTurningcenters,whichhavepositionencodersintheirspindles,alsoallowfeedratetobespecifiedinper-revolutionformat(inchesormillimetersperrevolution)thatisnamedsynchronousfeedrate(5)SpindlefunctionAn“S”wordisusedtospecifythespindlespeed(inRPMformachiningcenters).AnM03isusedtotur
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