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外文翻译自动化的介绍.doc

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外文翻译自动化的介绍.doc

附录A英文资料IntroductiontoAutomationAutomationisthetechnologybywhichaprocessorprocedureisaccomplishedwithouthumanassistance.Itisimplementedusingaprogramofinstructionscombinedwithacontrolsystemthatexecutestheinstructions.Toautomateaprocess,powerisrequired,bothtodrivetheprocessitselfandtooperatetheprogramandcontrolsystem.Althoughautomationcanbeappliedinawidevarietyofareas,itismostcloselyassociatedwiththemanufacturingindustries.ItwasinthecontextofmanufacturingthatthetermwasoriginallycoinedbyanengineeringmanageratFordMotorCompanyin1946todescribethevarietyofautomatictransferdevicesandfeedmechanismsthathadbeeninstalledinFordsproductionplants.Itisironicthatnearlyallmodernapplicationsofautomationarecontrolledbycomputertechnologiesthatwerenotavailablein1964.Weexaminetechnologiesthathavebeendevelopedtoautomatemanufacturingoperations.ThepositionofautomationandcontroltechnologiesinthelargerproductionsystemisshowninFigure3.1.Inthepresentchapter,weprovideanoverviewofautomationWhataretheelementsofanautomatedsystemWhataresomeoftheadvancedfeaturebeyondthebasicelementsAndwhatarethelevelsinanenterprisewhereautomationcanbeappliedInthefollowingtwochapters,wediscussindustrialcontrolsystemsandthehardwarecomponentsofthesesystems.Thesetwochaptersserveasafoundationfortheremainingchaptersinourcoverageofautomationandcontroltechnologies.Thesetechnologiesare1numericalcontrol,2industrialrobotics,and3programmablelogiccontrollers.BasicelementsofanautomatedsystemAnautomatedsystemconsistsofthreebasicelements1powertoaccomplishtheprocessandoperatethesystem,2aprogramofinstructionstodirecttheprocess,and3acontrolsystemtoactuatetheinstructions.TherelationshipamongsttheseelementisillustratedinFigure3.2.Allsystemthatqualifyasbeingautomatedincludethesethreebasicelementsinoneformoranother.PowertoAccomplishtheAutomatedProcessAnautomatedsystemisusedtooperatesomeprocess,andpowerisrequiredtodrivetheprocessaswellasthecontrols.Theprincipalsourceofpowerinautomatedsystemsiselectricity.ElectricpowerhasmanyadvantagesinautomatedaswellasnonautomatedprocessesElectricalpoweriswidelyavailableatmoderatecost.Itisanimportantpartofourindustrialinfrastructure.Electricalpowercanbereadilyconvertedtoalternativeenergyformsmechanical,thermal,light,acoustic,hydraulic,andpneumatic.Electricalpoweratlowlevelscanbeusedtoaccomplishfunctionssuchassignaltransmission,informationprocessing,anddatastorageandcommunication.Electricalenergycanbestoredinlonglifebatteriesforuseinlocationswhereanexternalsourceofelectricalpowerisnotconvenientlyavailable.Alternativepowersourcesincludefossilfuels,solarenergy,water,andwind.However,theirexclusiveuseisrareinautomatedsystems.Inmanycaseswhenalternativepowersourcesareusedtodrivetheprocessitself,electricalpowerisusedforthecontrolsthatautomatetooperation.Forexample,incastingorheattreatment,thefurnacemaybeheartedbyfossilfuels,butthecontrolsystemtoregulatetemperatureandtimecycleiselectrical.Inothercases,theenergyfromthesealternativesourcesisconvertedtoelectricpowertooperateboththeprocessanditsautomation.Whensolarenergyisusedasapowersourceforanautomatedsystem,itisgenerallyconcertedinthisway.PowerfortheProcessInproduction,thetermprocessreferstothemanufacturingoperationthatisperformedonworkunit.Inadditiontodrivingthemanufacturingprocessitself,powerisalsorequiredforthefollowingmaterialhandlingfunctionsLoadingandunloadingtheworkunit.Thesepartsmustbemovedintotheproperpositionandorientationfortheprocesstobeperformed,andpowerisrequiredforthistransportandplacementfunction.Attheconclusionoftheprocess,theworkunitmustsimilarlyberemoved.Iftheprocessiscompletelyautomated,thensomeformofmechanizedpowermaybeusedtopositionandlocatetheworkunit.Materialtransportbetweenoperations.Inadditiontoloadingandunloadingatagivenoperation,theworkunitsmustbemovedbetweenoperations.Weconsiderthematerialhandlingtechnologiesassociatedwiththistransportfunction.PowerforAutomationAboveandbeyondthebasicpowerrequirementsforthemanufacturingoperation,additionalpowerisrequiredforautomation.TheadditionalpowerisusedforthefollowingfunctionsControllerunit.Modernindustrialcontrollersarebasedondigitalcomputers,whichrequireelectricalpowertoreadtheprogramofinstructions,makethecontrolcalculations,andexecutetheinstructionsbytransmittingthepropercommandstotheactuationdevices.Powertoactuatethecontrolsignals.Thecommandssentbythecontrollerunitarecarriedoutbymeansofelectromechanicaldevices,suchasswitchesandmotors,calledactuators.Thecommandsaregenerallytransmittedbymeansoflowvoltagecontrolsignals.Toaccomplishthecommands,theactuatorsrequiremorepower,andsothecontrolsignalsmustbeamplifiedtoprovidetheproperpowerlevelforactuatingdevice.Dataacquisitionandinformationprocessing.Inmostcontrolsystems,datamustbecollectedfromtheprocessandusedasinputtothecontrolalgorithms.Inaddition,arequirementoftheprocessmayincludekeepingrecordsofprocessperformanceorproductquality.Thesedataacquisitionandrecordkeepingfunctionsrequirepower,althoughinmodestamounts.ProgramofInstructionsTheactionsperformedbyanautomatedprocessaredefinedbyaprogramofinstructions.Whetherthemanufacturingoperationinvolveslow,medium,orhighproduction,eachpartofproductstylemadeintheoperationrequiresoneormoreprocessingstepsthatareuniquetothatstyle.Theseprocessingstepsareperformedduringaworkcycle.Anewpartiscompletedduringeachworkcycleinsomemanufacturingoperations,morethanonepartisproducedmultiplepartseachcycleusingamultiplecavitymold.Theparticularprocessingstepsfortheworkcyclearespecifiedinaworkcycleprogram.Workcycleprogramsarecalledpartprogramsinnumericalcontrol.Otherprocesscontrolapplicationsusedifferentnamesofthistypeofprogram.WorkCycleProgramsInthesimplestautomatedprocesses,theworkcycleconsistsofessentiallyonestep,whichistomaintainasingleprocessparameteratadefinedlevel,forexample,maintainthetemperatureoffurnaceatadesignatedvalueforthedurationofaheattreatmentcycle.Weassumethatloadingandunloadingoftheworkunitsintoandfromthefurnaceisperformedmanuallyandisthereforenotpartoftheautomaticcycle.Inthiscase,programmingsimplyinvolvessettingthetemperaturedialonthefurnace.Tochangetheprogram,theoperatorsimplychangesthetemperaturesetting.Anextensionofthissimplecaseiswhenthesinglestepprocessisdefinedbymorethenoneprocessparameter,forexample,afurnaceinwhichbothtemperatureandatmospherearecontrolled.Inmorecomplicatedsystems,theprocessinvolvesaworkcycleconsistingofmultiplestepsthatarerepeatedwithnodeviationfromonecycletothenext.Mostdiscretepartmanufacturingoperationsareinthiscategory.Atypicalsequenceofstepssimplifiedis1loadthepartintotheproductionmachine,2performtheprocess,and3unloadthepart.Duringeachstep,thereareoneormoreactivitiesthatinvolvechangesinoneormoreprocessparameters.Processparametersareinputstotheprocess,suchastemperaturesettingofafurnace,coordinateaxisvalueinapositioningsystem,valveopenedorclosedinafluidflowsystem,andmotoronoroff.Processparametersaredistinguishedfromprocessvariables,whichareoutputsfromtheprocessforexample,theactualtemperatureofthefurnace,theactualpositionoftheaxis,theactualflowrateofthefluidinthepipe,andtherotationalspeedofthemotor.Asourlistofexamplessuggests,thechangesinprocessparametervaluesmaybecontinuous\gradualchangesduringtheprocessingstepforexample,graduallyincreasingtemperatureduringaheattreatmentcycleordiscretestepwisechangesforexample,on/off.Differentprocessparametersmaybeinvolvedineachstep.AnAutomatedTurningOperationConsideranautomatedturningoperationinwhichaconeshapedgeometryisgenerated.Assumethesystemisautomatedandthatarobotisusedtoloadandunloadtheworkunit.Theworkcycleconsistsofthefollowingsteps(1)loadstartingworkpiece,(2)positioncuttingtoolpriortoturning,(3)turn,(4)repositiontooltoasafelocationatendofturning,and(5)unloadfinishedworkpiece.Identifytheactivityandprocessparameterineachstepoftheoperation.SolutionInstep(1),theactivitiesconsistoftherobotmanipulatorreachingfortherawworkpart,liftingandpositioningthepartintothechuckjawsofthelathe,thenparametersfortheseactivitiesaretheaxisvaluesoftherobotmanipulator,thegrippervalue,andthechuckjawvalue.Instep(2),theactivityinvolvesthemovementofthecuttingtooltoareadyposition.Theprocessparametersassociatedwiththisactivityarethexandzaxispositionofthetool.Step3istheturningoperation.Itrequiresthesimultaneouscontrolofthreeprocessparametersrotationalspeedoftheworkpiece,feed,andradialdistanceofthecuttingtoolfromtheaxisofrotation.Tocuttheconicalshape,radialdistancemustbechangedcontinuouslyataconstantrateofeachrevolutionoftheworkpiece.Foraconsistentfinishonthesurface,therotationalspeedmustbecontinuouslyadjustedtomaintainaconstantsurfacespeed,andforequalfeedmarksonthesurface,thefeedmustbesetaconstantvalue.Dependingontheangleofthecone,multipleturningpassesmayberequiredtograduallygeneratethedesiredcontour.Eachpassrepresentsanadditionalstepinthesequence.Step4and5involvethereverseactivitiesassteps2and1,respectively,andtheprocessparametersarethesame.Manyproductionoperationsconsistofmultiplesteps,sometimesmorecomplicatedthanourtruingexample.Examplesoftheseoperationsincludeautomaticscrewmachinecycles,sheet

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