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，F(xiàn)15000meansthefederateis15000millimetersperminuteTurningcenters，whichhavepositionencodersintheirspindles，alsoallowfeedratetobespecifiedinper-revolutionformat(inchesormillimetersperrevolution)thatisnamedsynchronousfeedrate(5)SpindlefunctionAn“S”wordisusedtospecifythespindlespeed(inRPMformachiningcenters).AnM03isusedtotur