关于PLC的毕业设计外文翻译.docx

关于PLC的毕业设计外文翻译.docx

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关于PLC的毕业设计外文翻译

毕业设计（外文翻译）

英文题目ThedevelopmentandfutureofPLC中文题目PLC的发展和未来

系（院）自动化系

专业电气自动化技术

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二〇一三年六月

ThedevelopmentandfutureofPLC

Part1PLCoverview

Programmablecontrolleristhefirstinthelate1960sintheUnitedStates,thencalledPLCprogrammablelogiccontroller（ProgrammableLogicController）isusedtoreplacerelays.Fortheimplementationofthelogicaljudgment,timing,sequencenumber,andothercontrolfunctions.TheconceptispresentedPLCGeneralMotorsCorporation.PLCandthebasicdesignisthecomputerfunctionalimprovements,flexible,genericandotheradvantagesandrelaycontrolsystemsimpleandeasytooperate,suchastheadvantagesofcheappricescombinedcontrollerhardwareisstandardandoverall.Accordingtothepracticalapplicationoftargetsoftwareinordertocontrolthecontentoftheuserproceduresmemorycontroller,thecontrollerandconnectingtheaccusedconvenienttarget.

Inthemid-1970s,thePLChasbeenwidelyusedasacentralprocessingunitmicroprocessor,importexportmoduleandtheexternalcircuitsareused,large-scaleintegratedcircuitsevenwhenthePLCisnolongertheonlylogical（IC）judgmentfunctionsalsohavedataprocessing,PIDconditioninganddatacommunicationsfunctions.InternationalElectrotechnicalCommission（IEC）standardspromulgatedprogrammablecontrollerforprogrammablecontrollerdraftmadethefollowingdefinition:

programmablecontrollerisadigitalelectroniccomputersoperatingsystem,specificallyforapplicationsintheindustrialdesignenvironment.Itusedprogrammablememory,usedtoimplementlogicintheirinternalstorageoperations,sequencecontrol,timing,countingandarithmeticoperations,suchasoperatinginstructions,andthroughdigitalandanaloginputandoutput,thecontrolofvarioustypesofmachineryorproductionprocesses.Programmablecontrollerandrelatedperipherals,andindustrialcontrolsystemseasilylinkedtoformawhole,toexpanditsfunctionaldesign.Programmablecontrollerfortheuser,isanon-contactequipment,theprocedurescanbechangedtochangeproductionprocesses.Theprogrammablecontrollerhasbecomeapowerfultoolforfactoryautomation,widelypopularreplication.Programmablecontrollerisuser-orientedindustriesdedicatedcontrolcomputer,withmanydistinctivefeatures.

Part2HistoryofPLC

ProgrammableLogicControllers（PLC）,acomputingdeviceinventedbyRichardE.Morleyin1968,havebeenwidelyusedinindustryincludingmanufacturingsystems,transportationsystems,chemicalprocessfacilities,andmanyothers.Atthattime,thePLCreplacedthehardwiredlogicwithsoft-wiredlogicorso-calledrelayladderlogic（RLL）,aprogramminglanguagevisuallyresemblingthehardwiredlogic,andreducedtherebytheconfigurationtimefrom6monthsdownto6days[MoodyandMorley,1999].

AlthoughPCbasedcontrolhasstartedtocomeintoplace,PLCbasedcontrolwillremainthetechniquetowhichthemajorityofindustrialapplicationswilladhereduetoitshigherperformance,lowerprice,andsuperiorreliabilityinharshenvironments.Moreover,accordingtoastudyonthePLCmarketofFrostandSullivan[1995],anincreaseoftheannualsalesvolumeto15millionPLCsperyearwiththehardwarevalueofmorethan8billionUSdollarshasbeenpredicted,thoughthepricesofcomputinghardwareissteadilydropping.TheinventorofthePLC,RichardEMorley,fairlyconsidersthePLCmarketasa5-billionindustryatthepresenttime.

ThoughPLCsarewidelyusedinindustrialpractice,theprogrammingofPLCbasedcontrolsystemsisstillverymuchrelyingontrial-and-error.Alikesoftwareengineering,PLCsoftwaredesignisfacingthesoftwaredilemmaorcrisisinasimilarway.Morleyhimselfemphasizedthisaspectmostforcefullybyindicating

`Ifhouseswerebuiltlikesoftwareprojects,asinglewoodpeckercoulddestroycivilization.”

Particularly,practicalproblemsinPLCprogrammingaretoeliminatesoftwarebugsandtoreducethemaintenancecostsofoldladderlogicprograms.ThoughthehardwarecostsofPLCsaredroppingcontinuously,reducingthescantimeoftheladderlogicisstillanissueinindustrysothatlow-costPLCscanbeused.

Ingeneral,theproductivityingeneratingPLCisfarbehindcomparedtootherdomains,forinstance,VLSIdesign,whereefficientcomputeraideddesigntoolsareinpractice.ExistentsoftwareengineeringmethodologiesarenotnecessarilyapplicabletothePLCbasedsoftwaredesignbecausePLC-programmingrequiresasimultaneousconsiderationofhardwareandsoftware.Thesoftwaredesignbecomes,thereby,moreandmorethemajorcostdriver.Inmanyindustrialdesignprojects,morethanofthemanpowerallocatedforthecontrolsystemdesignandinstallationisscheduledfortestinganddebuggingPLCprograms.

Inaddition,currentPLCbasedcontrolsystemsarenotproperlydesignedtosupportthegrowingdemandforflexibilityandreconfigurabilityofmanufacturingsystems.Afurtherproblem,impellingtheneedforasystematicdesignmethodology,istheincreasingsoftwarecomplexityinlarge-scaleprojects.

TheobjectiveofthisthesisistodevelopasystematicsoftwaredesignmethodologyforPLCoperatedautomationsystems.Thedesignmethodologyinvolveshigh-leveldescriptionbasedonstatetransitionmodelsthattreatautomationcontrolsystemsasdiscreteeventsystems,astepwisedesignprocess,andsetofdesignrulesprovidingguidanceandmeasurementstoachieveasuccessfuldesign.Thetangibleoutcomeofthisresearchistofindawaytoreducetheuncertaintyinmanagingthecontrolsoftwaredevelopmentprocess,thatis,reducingprogramminganddebuggingtimeandtheirvariation,increasingflexibilityoftheautomationsystems,andenablingsoftwarereusabilitythroughmodularity.Thegoalistoovercomeshortcomingsofcurrentprogrammingstrategiesthatarebasedontheexperienceoftheindividualsoftwaredeveloper.

Part3NowofPLC

FromthestructureisdividedintofixedPLCandModulePLC,thetwokindsofPLCincludingCPUboard,I/Oboard,displaypanel,memoryblock,power,theseelementsintoadonotremoveoverall.ModuletypePLCincludingCPUmodule,I/Omodules,memory,thepowermodules,bottomoraframe,thesemodulescanbeaccordingtocertainrulescombinationconfiguration.

Intheuserview,adetailedanalysisoftheCPU'sinternalunnecessary,butworkingmechanismofeverypartofthecircuit.TheCPUcontrolworks,byitreadsCPUinstruction,interpretstheinstructionandexecutesinstructions.Butthepaceofworkbyshocksignalcontrol.

Unitworkunderthecontrollercommandusedinadigitalorlogicoperation.Incomputingandstorageregisterofcomputationresult,itisalsoamongthecontrollercommandandwork.CPUspeedandmemorycapacityistheimportantparametersforPLC,itsdeterminesthePLCspeedofwork,IOPLCnumberandsoftwarecapacity,solimitstocontrolsize.

CentralProcessingUnit（CPU）isthebrainofaPLCcontroller.CPUitselfisusuallyoneofthemicrocontrollers.Aforetimethesewere8-bitmicrocontrollerssuchas8051,andnowtheseare16-and32-bitmicrocontrollers.Unspokenruleisthatyou’llfindmostlyHitachiandFujicumicrocontrollersinPLCcontrollersbyJapanesemakers,SiemensinEuropeancontrollers,andMotorolamicrocontrollersinAmericanones.CPUalsotakescareofcommunication,interconnectednessamongotherpartsofPLCcontrollers,programexecution,memoryoperation,overseeinginputandsettingupofanoutput.

Systemmemory（todaymostlyimplementedinFLASHtechnology）isusedbyaPLCforaprocesscontrolsystem.Asideform.thisoperatingsystemitalsocontainsauserprogramtranslatedformaladderdiagramtoabinaryform.FLASHmemorycontentscanbechangedonlyincasewhereuserprogramisbeingchanged.PLCcontrollerswereusedearlierinsteadofPLASHmemoryandhavehadEPROMmemoryinsteadofFLASHmemorywhichhadtobeerasedwithUVlampandprogrammedonprogrammers.WiththeuseofFLASHtechnologythisprocesswasgreatlyshortened.Reprogrammingaprogrammemoryisdonethroughaserialcableinaprogramforapplicationdevelopment.

Usermemoryisdividedintoblockshavingspecialfunctions.Somepartsofamemoryareusedforstoringinputandoutputstatus.Therealstatusofaninputisstoredeitheras“1”oras“0”inaspecificmemorybit/eachinputoroutputhasonecorrespondingbitinmemory.Otherpartsofmemoryareusedtostorevariablecontentsforvariablesusedinusedprogram.Forexample,timevalue,orcountervaluewouldbestoredinthispartofthememory.

PLCcontrollercanbereprogrammedthroughacomputer（usualway）,butalsothroughmanualprogrammers（consoles）.ThispracticallymeansthateachPLCcontrollercanprogrammedthroughacomputerifyouhavethesoftwareneededforprogramming.Today’stransmissioncomputersareidealforreprogrammingaPLCcontrollerinfactoryitself.Thisisofgreatimportancetoindustry.Oncethesystemiscorrected,itisalsoimportanttoreadtherightprogramintoaPLCagain.ItisalsogoodtocheckfromtimetotimewhetherprograminaPLChasnotchanged.Thishelpstoavoidhazardoussituationsinfactoryrooms（someautomakershaveestablishedcommunicationnetworkswhichregularlycheckprogramsinPLCcontrollerstoensureexecutiononlyofgoodprograms）.

AlmosteveryprogramforprogrammingaPLCcontrollerpossessesvarioususefuloptionssuchas:

forcedswitchingonandoffofthesysteminput/outputs（I/Olines）,programfollowupinrealtimeaswellasdocumentingadiagram.Thisdocumentingisnecessarytounderstandanddefinefail