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英文原文ComputerNumericalControlUnitToday,computernumericalcontrolCNCmachinesarefoundalmosteverywhere,fromsmalljobshopsinruralcommunitiestoFortune500companiesinlargeurbanareas.Truly,thereishardlyafacetofmanufacturingthatisnotinsomewaytouchedbywhattheseinnovativemachinetoolscando.Everyoneinvolvedinthemanufacturingenvironmentshouldbewellawareofwhatispossiblewiththesesophisticatedmachinetools.Inthischapter,wewillexplorethebasicsofthecoreofCNCmachinetoolCNCunit,showingyoumuchofwhatisinvolvedwithitsfunction,workingprinciples,hardwareconfigurationandsoftwarestructure.WithsomanytypesofCNCmachinetoolsandCNCunitsinexistence,itisnexttoimpossibleforthischaptertobeextremelyspecificaboutanyoneparticulartype.ThekeyconceptsallowustoviewthemainfeaturesofCNCunitinmoregeneralterms,stressingwhythingsarehandledthewaytheyareevenmorethanthespecifictechniquesusedwithanyoneparticularCNCmachinetool.Withthisbroadbackground,youshouldbeabletoeasilyzeroinonanykindofCNCmachinetoolyouwillbeworkingwith.1.1INTRODUCTIONMachinecontrolsaredividedintotwotypesnumericalcontrolNCandcomputernumericalcontrolCNC.NCcontrolshavetoreadtheprogrameachtimeapartisruntheyhavenomeansofeditingexistingprograms.CNCcontrolscanstoreandalloweditingofloadedprograms.AllmachinesbuilttodayareCNCmachines.CNCunitistheheartofCNCmachine.Nevertheless,inordertoaidtounderstandtheworkingprinciplesofCNCunit,itisnecessarythattheprinciplesofNCsystembeintroducedfirstly.1.1.1NCsystemTheNCmachinecanbedividedintothreebasicareas.Thefirstareaisthecontrolunit,whichprocessesthecommandsfromtheinputmedia.Thesecondareaisthedrivemechanisms,andthelastareaisthemachineitself.ThemostbasicfunctionofanyNCmachineisautomatic,precise,andconsistentmotioncontrol.A11formsofNCequipmenthavetwoormoredirectionsofmotion,calledaxes.Theseaxescanbepreciselyandautomaticallypositionedalongtheirlengthsoftravel.Thetwomostcommonaxistypesarelineardrivenalongastraightpathandrotarydrivenalongacircularpath.Insteadofcausingmotionbymanuallyturningcranksandhandwheelsasisrequiredonconventionalmachinetools,NCmachinesallowmotionstobeactuatedbyservomotorsundercontroloftheNC,andguidedbythepartprogram.Generallyspeaking,themotiontyperapid,linear,andcircular,theaxestomove,theamountofmotionandthemotionratefeedrateareprogrammablewithalmostallNCmachinetools.Figure1.1showsthemakeupofalinearaxisofanNCmachine.Figure1.1ThemakeupofalinearaxisofallNCmachineAnNCcommandexecutedwithinthecontrolcommonlythroughaprogramtellsthedrivemotortorotateapreciseamountofangle.Therotationofthedrivemotorinturnrotatestheballscrew.Andtheballscrewdrivesthelinearaxis.Afeedbackdeviceattheoppositeendoftheballscrewallowsthecontroltoconfirmthatthecommandednumberofrotationshastakenplace.AllNCmachinetoolsneednumericaldataforcontrollingtherelativemotionbetweencuttingtoolandpiecepart,thecomponentdimensionsnormallyemanatingdirectlyfromengineeringdrawingsthegeometricdata.Otherdigitizednumericaldatadefinefeedrates,spindlespeeds,toolidentificationnumbers,andmiscellaneousfunctionstoperformsuchoperationsastoolorworkchanging,orcoolantcontrolthetechnologicaldata.Thecombinationofallthisnumericalinformationinasequenceunderstoodbythemachinetoolscontrolleriscalledapartprogram,andtheprocessofcreatingthedatainacorrectlystructuredformatiscalledprogramming.Numericalcontrolsusestandardmicroelectronicmodulesthathavebeendevelopedforcomputerhardware。Exceptforspecialmodulesneededinservocontrolcircuits,noindividualmodulesarenecessary,incontrasttotraditionalcontrols,whichemployonlycomponentstailoredtosuitonespecificcontrolfunction.InmodernNCcontrollersextensivecontrolandcalculationtasksareperformedbyoneormoreintegralmicroprocessors。ThesearetermedcomputernumericalcontrolsystemCNCs.1.1.2CNCsystemandfunctionsofCNCunitControlsystemsbasedonindustrialPCabbreviationforpersonalcomputerareincreasinglyusedinautomationtechnology.Machinecontrolshavechangedgreatlywiththeageofthecomputer.Controlstodayaresoftwired,whichallowsgreaterflexibilityinchangingandupgradingthecomputercontrol.Infact,manyofmachinesoperatingcharacteristicscanbechangedbytheoperator,sothatthemachineoperatesthewayhe/shewantsitto.ParametertablesinCNCmachinestodayalloweachmachinetobepersonalizedtotheneedsofthejobtoberun.ThemodernCNCmachinetoolissoftwaredriven.Simplyspeaking,computercontrolsareprogrammedinsteadofhardwired.DefinitionAccordingtoElectronicIndustriesAssociationEIA,CNCsystemisaspecialcomputersystemthatisequippedwithcertaininterfacecircuitsandservodrivers,andcandopartora11theworksanNCsystemdobyrunningthesoftwarestoredinitsmemories.CNCshaveexpandablememoriesthatcanstorelargenumbersofprograms,plussubroutinesandcorrectiondata。SophisticatedgraphicdisplaysanddynamicsimulationhavealsonowbecomeavailableasaresultoftheextensivememorycapacitybeingbuiltintocurrentCNCs.Withinonlyfewyears,thecapabilityandefficiencyofmachinecontrollershasincreasedtosuchanextentthatthenamenumericalcontrolisnolongerappropriatecomputernumericalcontrolismoreaccuratelydescriptive.Generally,CNCscomprisesCNCunit,feedmotionservosubsystem,spindleservosubsystemandsomeauxiliarycontrolcells,asshowninFigure1.2,CNCunitisthecoreofthewholeCNCsystem.Itiscomposedofhardwareandsoftware。ThehardwarecomprisingaCNCunitismadeupofmicroprocessors,electronicmemorymodules,I/0interfaces,andpositioncontrolmodules,etc.CNCsoftwarecontrolsallfunctionsofthemachineanditsefficiencyofoperation,andmanagesalllocalprogrammingatthemachinetoolandgraphicsimulationofthecuttingprocessifavailable.ThehardwareandthesoftwareworktogethertodoallfunctionsofCNCunit,whichanordinaryNCsystemcanneverdo,suchasgraphicdisplayHMIHumanMachineInterface,systemdiagnosis,implementingofvariouscomplextoolpathcontrollingandcompensationalgorithms,intelligentcontrolling,onlineprogramming,andWebcommunications,etc.ThemainfunctionsandfeaturesofCNCunitaredescribedasfollowsFigure1.2CNCmachiningsystem1ControllingfunctionthenumberofcontrolaxesandsynchronouslycontrolaxesControllingfunctionindicatesthemaximumaxisnumbertheCNCunitcancontrolandthenumberofaxestheCNCunitcancontrolsynchronously.ItisalsothemarefeaturesofCNCmachine.AxestobecontrolledbyCNCunithavelinearaxesandrotateaxes,basicaxesandauxiliaryaxes.Generally,CNCmachineneedsonly2axestobecontrolledsynchronously.Incaseofdoubletoolslides,fouraxesareneeded.CNCmillingmachine,boringmachine,andCNCmachinecenterneed3ormorecontrolledaxes.ThemorethenumberofControlledaxes,especiallythenumberofaxesbeingcontrolledsynchronously,themorepowerfulfunctionsoftheCNCunit,andthemorecomplexstructureoftheCNCunit,themoredifficultyofprogramming.2PreparatoryfunctionPreparatoryfunction,alsocalledGfunction,describesthemotionmodesofCNCmachine.Themotionmodescompriseinstructionsofbasicmotions,dwell,planeselections,coordinatesystemsettings,toolcompensations,referencepointreturn,fixedoperationcircles,andmetric/inchunittransfer,etc.AccordingtoISOstandard,thereare100typesofGcodesfromG00toG99usedinCNCunit,whichcanbedividedintotwoclassesnonmodalcodeswhichfunctionsarevalidonlyinthecodesegmentincludingthecodesthemselvesandmodalcodeswhichcankeepeffectivebeforethecomingofnextGcodeofthesamegroup.FortheexactfunctionofeachGcodeusedinyourmachinetools,youmustreferenceyourcontrolmanufacturersmanualtofindthelistoffunctionsforyourmachine.3InterpolationfunctionCNCunitdoesinterpolationbyusingsoftwarerealtimecalculations.Linearinterpolation,circularinterpolation,helicalinterpolation,andpolarcoordinateinterpolationwilldotheirbesttohelpCNCunitgeneratetooltrackasclosetovariouspathsaspossible.4FeedfunctionFeedfunctionusesFFeedratedesignationtodesignatethe.feedratetoaxis.Themethodbywhichfeedrateisprogrammedvariesfromonemachinetypetothenext.Generallyspeaking,machiningcentersonlyallowthefeedratetobespecificinperminuteformatinchesormillimetersperminute,suchas,F15000meansthefederateis15000millimetersperminute.Turningcenters,whichhavepositionencodersintheirspindles,alsoallowfeedratetobespecifiedinperrevolutionformatinchesormillimetersper.revolutionthatisnamedsynchronousfeedrate.5SpindlefunctionAnSwordisusedtospecifythespindlespeedinRPMformachiningcenters.AnM03isusedtoturnthespindleoninaclockwiseforwardD1a11ner.M04turnsthespindleoninacounterclockwisemanner.M05turnsthespindleoff.Notethatturningcentersalsohaveafeaturecalledconstantsurfacespeed,whichallowsspindlespeedtobespecifiedinsurfacefeetperminuteormetersperminute.Onoperationpanel,thereisabuttontoturnthespindleonandoff,aswellasarheostattocontrolspindlespeed.Allofthesefunctionsareactivatedmanually,throughtheManualorJogmode.6MiscellaneousfunctionLikepreparatoryfunctions,miscellaneousfunctionsMwords,fromM00toM99allowavarietyofspecialfunctions.Miscellaneousfunctionsaretypicallyusedasprogrammableswitches1ikespindleon/off,coolanton/off,andsoon.7CompensationfunctionAlltypesofCNCmachinetoolsrequiresomeformsofcompensation.Thoughappliedfordifferentreasonsondifferentmachinetypes,allformsofcompensationallowtheCNCusertoallowforunpredictableconditionsrelatedtotooling.8Enhancedgraphicdisplayfunction
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