外文翻译--生产自动化.doc

共7页第1页ProductionAutomationIntroductiontoproductionAutomationAutomationisawidelyusedterminmanufacturing.Inthiscontext,automationcanbedefinedastechnologyconcernedwiththeapplicationofmechanical,electronic,andcomputerbasedsystemstooperateandcontrolproduction.ExamplesofthistechnologyincludeAutomaticmachinetoolstoprocessparts.AutomatedtransferlinesandsimilarsequentialproductionsystemsAutomaticassemblymachinesIndustrialrobotsAutomaticmaterialhandingandstoragesystemsAutomatedinspectionsystemsforqualitycontrol.Feedbackcontrolandcomputerprocesscontrol.Computersystemsthatautomateproceduresforplanning,datacollection,anddecisionmakingtosupportmanufacturingactivities.Automatedproductionsystemscanbeclassifiedintotwobasiccategoriesfixedautomationandprogrammableautomation.FixedAutomationFixedautomationiswhatHarderwasreferringtowhenhecoinedthewordautomation.Fixedautomationreferstoproductionsystemsinwhichthesequenceofprocessingorassemblyoperationsisfixedbytheequipmentconfigurationandcannotbereadilychangedwithoutalteringtheequipment.Althougheachoperationinthesequenceisusuallysimple,theintegrationandcomplex.Typicalfeaturesoffixedautomationinclude1.highinitialinvestmentforcustomengineeredequipment,2.highproductionrates,3.applicationtoproductsinwhichhighquantitiesaretobeproduced,and4.relativeinflexibilityinaccommodatingproductchanges.Fixedautomationiseconomicallyjustifiableforproductswithhighdemandrates.Thehighinitialinvestmentintheequipmentcanbedividedoveralargenumberofunits,perhapsmillions,thusmakingtheunitcostlowcomparedwithalternativemethodsofproduction.Examplesoffixedautomationincludetransferlinesformachining,dialindexingmachines,andautomatedassemblymachines.Muchofthe共7页第2页technologyinfixedautomationwasdevelopedintheautomobileindustrythetransferlinedatingtoabout1920isanexample.ProgrammableAutomationForprogrammableautomation,theequipmentisdesignedinsuchawaythatthesequenceofproductionoperationsiscontrolledbyaprogram,i.e.,asetofcodedinstructionsthatcanbereadandinterpretedbythesystem.Thustheoperationsequencecanbereadilychangedtopermitdifferentproductconfigurationstobeproducedonthesameequipment.Someofthefeaturesthatcharacterizeprogrammableautomationinclude1.highinvestmentingeneralpurposeprogrammableequipment,2.lowerproductionratesthanfixedautomation,3.flexibilitytodealwithchangesinproductconfiguration,and4.suitedtolowand/ormediumproductionofsimilarproductsorpartse.g.partfamilies.Examplesofprogrammableautomationincludenumericallycontrolledmachinetools,industrialrobots,andprogrammablelogiccontrollers.Programmableproductionsystemsareoftenusedtoproducepartsorproductsinbatches.Theyareespeciallyappropriatewhenrepeatordersforbatchesofthesameproductareexpected.Toproduceeachbatchofanewproduct,thesystemmustbeprogrammedwiththesetofmachineinstructionsthatcorrespondtothatproduct.Thephysicalsetupoftheequipmentmustalsobechangedspecialfixturesmustbeattachedtothemachine,andtheappropriatetoolsmustbeloaded.Thischangeoverprocedurecanbetimeconsuming.Asaresult,theusualproductioncycleforagivenbatchincludes1.aperiodduringwhichthesetupandreprogrammingisaccomplishedand2.aperiodinwhichthebatchisprocessed.Thesetupreprogrammingperiodconstitutesnonproductivetimeoftheautomatedsystem.Theeconomicsofprogrammableautomationrequirethatasthesetupreprogrammingtimeincrease,theproductionbatchsizemustbemadelargersoastospreadthecostoflostproductiontimeoveralargernumberofunits.Conversely,ifsetupandreprogrammingtimecanbereducedtozero,thebatchsizecanbereducedtoone.Thisisthetheoreticalbasisforflexibleautomation,anextensionofprogrammableautomation.Aflexibleautomatedsystemisonethatiscapableofproducingavarietyofproductsorpartswithminimallosttimeforchangeoversfromoneproducttothenext.Thetimetoreprogramthesystemandalterthephysicalsetupisminimalandresultsinvirtuallynolostproductiontime.Consequently,thesystemiscapableofproducingvariouscombinationsandschedules共7页第3页ofproductsinacontinuousflow,ratherthanbatchproductionwithinterruptionsbetweenbatches.Thefeaturesofflexibleautomationare1.highinvestmentforacustomengineeredsystem,2.continuousproductionofmixturesofproducts,3.abilitytochangeproductmixtoaccommodatechangesindemandratesforthedifferentproductsmade,4.mediumproductionrates,and5.flexibilitytodealwithproductdesignvariations.Flexibleautomatedproductionsystemsoperateinpracticebyoneormoreofthefollowingapproaches1.usingpartfamilyconcepts,bywhichthepartsmadeonthesystemarelimitedinvariety2.reprogrammingthesysteminadvanceand/oroffline,sothatreprogrammingdoesnotinterruptproduction3.downloadingexistingprogramstothesystemtoproducepreviouslymadepartsforwhichprogramarealreadyprepared4.usingquickchangefixturessothatphysicalsetuptimeisminimized5.usingafamilyoffixturesthathavebeendesignedforalimitednumberofpartstylesand6.equippingthesystemwithalargenumberofquickchangetoolsthatincludethevarietyofprocessingoperationsneededtoproducethepartfamily.Fortheseapproachestobesuccessful,thevariationinthepartstylesproducedonaflexibleautomatedproductionsystemisusuallymorelimitedthatabatchtypeprogrammableautomationsystem.Examplesofflexibleautomationaretheflexiblemanufacturingsystemsforperformingmachiningoperationsthatdatebacktolate1960s.NumericalControlNumericalcontroloftenabbreviatedNCcanbedefinedasaformofprogrammableautomationinwhichtheprocessiscontrolledbynumbers,letters,andsymbols.InNC,thenumbersformaprogramofinstructionsdesignedforaparticularworkpartorjob.Whenthejobchanges,theprogramofinstructionsischanged.ThiscapabilitytochangetheprogramforeachnewjobiswhatgivesNCitsflexibility.Itismucheasiertowritenewprogramsthantomakemajorchangesintheproductionequipment.NCequipmentisusedinallareasofmetalpartsfabricationandcomprisesroughly15ofthemodernmachinetoolsinindustrytoday.Sincenumericallycontrolledmachinesareconsiderablymoreexpensivethantheirconventionalcounterparts,theassetvalueofindustrialNCmachinetoolsisproportionallymuchlargerthantheirnumbers.Equipmentutilizingnumericalcontrolhasbeendesigned共7页第4页toperformsuchdiverseoperationsasdrilling,milling,turning,grinding,sheetmetalpressworkingspotwelding,arewelding,riveting,assembly,drafting,inspection,andpartshandling.Andthisisbynomeansacompletelist.Numericalcontrolshouldbeconsideredasapossiblemodeofcontrollingtheoperationforanyproductionsituationpossessingthefollowingcharacteristics1.Similarworkpartsintermsofrawmateriale.g.,metalstockformachining.2.Theworkpartsareproducedinvarioussizesandgeometries.3.Theworkpartsareproducedinbatchesofsmalltomediumsizedquantities.4.Asequenceofsimilarprocessingstepsisrequiredtocompletetheoperationoneachworkpiece.Manymachiningjobsmeettheseconditions.Themachinedworkpartsaremetal,theyarespecifiedinmanydifferentsizesandshapes,andmostmachinedpartsproducedinindustrytodayaremadeinsmalltomediumsizelotsizes.Toproduceeachpart,asequenceofdrillingoperationsmayberequired,oraseriesofturningormillingoperations.ThesuitabilityofNCforthesekindsofjobsisthereasonforthetremendousgrowthofnumericalcontrolinthemetalworkingindustryoverthelast25years.BasicComponentsofanNCSystemAnoperationalnumericalcontrolsystemconsistsofthefollowingthreebasiccomponents1.Programofinstructions.2.Controllerunit,alsocalledmachinecontrolunitMCU.3.Machinetoolorothercontrolledprocess.TransferMachinesThehighestdegreeofautomationobtainablewithspecialpurpose,multifunctionmachinesisachievedbyusingtransfermachines.Transfermachinesareessentiallyacombinationofindividualworkstationsarrangedintherequiredsequence,connectedbyworktransferdevices,andintegratedwithinterlockedcontrols.Workpiecesareautomaticallytransferredbetweenthestations,whichareequippedwithhorizontal,vertical,orangularunitstoperformmachining,gagging,workpiecerepositioning,assembling,washing,orotheroperations.Thetwomajorclassesoftransfermachinesarerotaryandinlinetypes.