外文翻译--电脑数值控制单元.doc -- 5 元

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