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附录A:英文资料IntroductiontoAutomationAutomationisthetechnologybywhichaprocessorprocedureisaccomplishedwithouthumanassistance.Itisimplementedusingaprogramofinstructionscombinedwithacontrolsystemthatexecutestheinstructions.Toautomateaprocess,powerisrequired,bothtodrivetheprocessitselfandtooperatetheprogramandcontrolsystem.Althoughautomationcanbeappliedinawidevarietyofareas,itismostcloselyassociatedwiththemanufacturingindustries.ItwasinthecontextofmanufacturingthatthetermwasoriginallycoinedbyanengineeringmanageratFordMotorCompanyin1946todescribethevarietyofautomatictransferdevicesandfeedmechanismsthathadbeeninstalledinFord’sproductionplants.Itisironicthatnearlyallmodernapplicationsofautomationarecontrolledbycomputertechnologiesthatwerenotavailablein1964.Weexaminetechnologiesthathavebeendevelopedtoautomatemanufacturingoperations.ThepositionofautomationandcontroltechnologiesinthelargerproductionsystemisshowninFigure3.1.Inthepresentchapter,weprovideanoverviewofautomation:Whataretheelementsofanautomatedsystem?Whataresomeoftheadvancedfeaturebeyondthebasicelements?Andwhatarethelevelsinanenterprisewhereautomationcanbeapplied?Inthefollowingtwochapters,wediscussindustrialcontrolsystemsandthehardwarecomponentsofthesesystems.Thesetwochaptersserveasafoundationfortheremainingchaptersinourcoverageofautomationandcontroltechnologies.Thesetechnologiesare:(1)numericalcontrol,(2)industrialrobotics,and(3)programmablelogiccontrollers.BasicelementsofanautomatedsystemAnautomatedsystemconsistsofthreebasicelements:(1)powertoaccomplishtheprocessandoperatethesystem,(2)aprogramofinstructionstodirecttheprocess,and(3)acontrolsystemtoactuatetheinstructions.TherelationshipamongsttheseelementisillustratedinFigure3.2.Allsystemthatqualifyasbeingautomatedincludethesethreebasicelementsinoneformoranother.PowertoAccomplishtheAutomatedProcessAnautomatedsystemisusedtooperatesomeprocess,andpowerisrequiredtodrivetheprocessaswellasthecontrols.Theprincipalsourceofpowerinautomatedsystemsiselectricity.Electricpowerhasmanyadvantagesinautomatedaswellasnonautomatedprocesses:Electricalpoweriswidelyavailableatmoderatecost.Itisanimportantpartofourindustrialinfrastructure.Electricalpowercanbereadilyconvertedtoalternativeenergyforms:mechanical,thermal,light,acoustic,hydraulic,andpneumatic.Electricalpoweratlowlevelscanbeusedtoaccomplishfunctionssuchassignaltransmission,informationprocessing,anddatastorageandcommunication.Electricalenergycanbestoredinlong-lifebatteriesforuseinlocationswhereanexternalsourceofelectricalpowerisnotconvenientlyavailable.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.Thecommandsaregenerallytransmittedbymeansoflow-voltagecontrolsignals.Toaccomplishthecommands,theactuatorsrequiremorepower,andsothecontrolsignalsmustbeamplifiedtoprovidetheproperpowerlevelforactuatingdevice.Dataacquisitionandinformationprocessing.Inmostcontrolsystems,datamustbecollectedfromtheprocessandusedasinputtothecontrolalgorithms.Inaddition,arequirementoftheprocessmayincludekeepingrecordsofprocessperformanceorproductquality.Thesedataacquisitionandrecordkeepingfunctionsrequirepower,althoughinmodestamounts.ProgramofInstructionsTheactionsperformedbyanautomatedprocessaredefinedbyaprogramofinstructions.Whetherthemanufacturingoperationinvolveslow,medium,orhighproduction,eachpartofproductstylemadeintheoperationrequiresoneormoreprocessingstepsthatareuniquetothatstyle.Theseprocessingstepsareperformedduringaworkcycle.Anewpartiscompletedduringeachworkcycle(insomemanufacturingoperations,morethanonepartisproducedmultiplepartseachcycleusingamultiplecavitymold).Theparticularprocessingstepsfortheworkcyclearespecifiedinaworkcycleprogram.Workcycleprogramsarecalledpartprogramsinnumericalcontrol.Otherprocesscontrolapplicationsusedifferentnamesofthistypeofprogram.WorkCycleProgramsInthesimplestautomatedprocesses,theworkcycleconsistsofessentiallyonestep,whichistomaintainasingleprocessparameteratadefinedlevel,forexample,maintainthetemperatureoffurnaceatadesignatedvalueforthedurationofaheattreatmentcycle.(Weassumethatloadingandunloadingoftheworkunitsintoandfromthefurnaceisperformedmanuallyandisthereforenotpartoftheautomaticcycle.)Inthiscase,programmingsimplyinvolvessettingthetemperaturedialonthefurnace.Tochangetheprogram,theoperatorsimplychangesthetemperaturesetting.Anextensionofthissimplecaseiswhenthesingle-stepprocessisdefinedbymorethenoneprocessparameter,forexample,afurnaceinwhichbothtemperatureandatmospherearecontrolled.Inmorecomplicatedsystems,theprocessinvolvesaworkcycleconsistingofmultiplestepsthatarerepeatedwithnodeviationfromonecycletothenext.Mostdiscretepartmanufacturingoperationsareinthiscategory.Atypicalsequenceofsteps(simplified)is:(1)loadthepartintotheproductionmachine,(2)performtheprocess,and(3)unloadthepart.Duringeachstep,thereareoneormoreactivitiesthatinvolvechangesinoneormoreprocessparameters.Processparametersareinputstotheprocess,suchastemperaturesettingofafurnace,coordinateaxisvalueinapositioningsystem,valveopenedorclosedinafluidflowsystem,andmotoronoroff.Processparametersaredistinguishedfromprocessvariables,whichareoutputsfromtheprocess;forexample,theactualtemperatureofthefurnace,theactualpositionoftheaxis,theactualflowrateofthefluidinthepipe,andtherotationalspeedofthemotor.Asourlistofexamplessuggests,thechangesinprocessparametervaluesmaybecontinuous(\gradualchangesduringtheprocessingstep;forexample,graduallyincreasingtemperatureduringaheattreatmentcycle)ordiscrete(stepwisechanges;forexample,on/off).Differentprocessparametersmaybeinvolvedineachstep.AnAutomatedTurningOperationConsideranautomatedturningoperationinwhichacone-shapedgeometryisgenerated.Assumethesystemisautomatedandthatarobotisusedtoloadandunloadtheworkunit.Theworkcycleconsistsofthefollowingsteps:(1)loadstartingworkpiece,(2)positioncuttingtoolpriortoturning,(3)turn,(4)repositiontooltoasafelocationatendofturning,and(5)unloadfinishedworkpiece.Identifytheactivityandprocessparameterineachstepoftheoperation.Solution:Instep(1),theactivitiesconsistoftherobotmanipulatorreachingfortherawworkpart,liftingandpositioningthepartintothechuckjawsofthelathe,thenparametersfortheseactivitiesaretheaxisvaluesoftherobotmanipulator,thegrippervalue,andthechuckjawvalue.Instep(2),theactivityinvolvesthemovementofthecuttingtooltoa“ready”position.Theprocessparametersassociatedwiththisactivityarethex-andz-axispositionofthetool.Step(3)istheturningoperation.Itrequiresthesimultaneouscontrolofthreeprocessparameters:rotationalspeedoftheworkpiece,feed,andradialdistanceofthecuttingtoolfromtheaxisofrotation.Tocuttheconicalshape,radialdistancemustbechangedcontinuouslyataconstantrateofeachrevolutionoftheworkpiece.Foraconsistentfinishonthesurface,therotationalspeedmustbecontinuouslyadjustedtomaintainaconstantsurfacespeed,andforequalfeedmarksonthesurface,thefeedmustbesetaconstantvalue.Dependingontheangleofthecone,multipleturningpassesmayberequiredtograduallygeneratethedesiredcontour.Eachpassrepresentsanadditionalstepinthesequence.Step(4)and(5)involvethereverseactivitiesassteps(2)and(1),respectively,andtheprocessparametersarethesame.Manyproductionoperationsconsistofmultiplesteps,sometimesmorecomplicatedthanourtruingexample.Examplesoftheseoperationsincludeautomaticscrewmachinecycles,sheet
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