完整版毕业设计机械外文翻译.docx

完整版毕业设计机械外文翻译.docx

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完整版毕业设计机械外文翻译

VisualizationofPLCProgramsusingXML

M.BaniYounisandG.Frey

JuniorprofessorshipAgentenbasedAutomation

UniversityofKaiserslautem

P.0.Box3049,D-67653Kaiserslautem,Germany

Abstract-DuetothegrowingcomplexityofPLCprogramsthereisanincreasinginterestintheapplicationofformalmethodsinthisarea.Formalmethodsallowrigidprovingofsystempropertiesinverificationandvalidation.OnewaytoapplyformalmethodsistoutilizeaformaldesignapproachinPLCprogramming.However,forexistingsoftwarethatapproachthatcanstartfromagivenPLCprogram.Therefore,formalizationofPLCprogramsisatopicofcurrentresearch.Thepaperoutlinesare-engineeringapproachbasedontheformalizationofPLCprograms.ThetransformationintoavendorindependentformatandthevisualizationofthestructureofPLCprogramsisidentifiedasanimportantintermediatestepinthisprocess.ItisshownbeusedfortheformalizationandvisualizationofanexistingPLCprogram.

I.INTRODUCTION

ProgrammableLogicControllers（PLCs）areaspecialtypeofcomputersthatareusedinindustrialandsafetycriticalapplications.ThepurposeofaPLCistocontrolaparticularprocess,oracollectionofprocesses,byproducingelectricalcontrolsignalsinresponsetoelectricalprocess-relatedinputssignals.ThesystemscontrolledbyPLCsvarytremendously,withapplicationsinmanufacturing,chemicalprocesscontrol,machining,transportation,powerdistribution,andmanyotherfields.Automationapplicationscanrangeincomplexityfromasimplepaneltooperatethelightsandmotorizedwindowshadesinaconferenceroomtocompletelyautomatedmanufacturinglines.

Withthewideningoftheirapplication，PLCprogramsarebeingsubjecttoincreasedcomplexityandthecomplianceoflimiteddevelopmenttimeaswellasthereusabilityofexistingsoftwareorPLCmodulesrequiresaformalapproachtobedeveloped[I].Ensuringtheandvalidationproceduresaswellasanalysisandsimulationofexistingsystemstobecarriedout[2].OneoftheimportantfieldsfortheformalizationofPLCprogramsthatgrowingupinrecenttimeisReverse-engineering[3].ReverseEngineeringisaprocessofevaluatingsomethingtounderstandordertoduplicateorenhanceit.WhilethereuseofPLCcodesisbeingestablishedasatoolforcombatingthecomplexityofPLCprograms,ReverseEngineeringissupposedtoreceiveincreasedimportanceinthecomingyearsespeciallyifexitingofexistingPLCprogramsisanimportantintermediatestepofReverseEngineering.ThepaperprovidesanapproachtowardsthevisualizationofPLCprogramsusingXMLwhichisanimportantapproachfortheorientationandbetterunderstandingforengineersworkingwithPLCprograms.

Thepaperisstructuredasfollows.First,ashortintroductiontoPLCsandthecorrespondingprogrammingtechniquesaccordingtotheIECstandardisgiven.InSectionⅢanapproachforRe-engineeringbasedonformalizationofPLCprogramsisintroduced.ThetransformationofthePLCcodeintoavendorindependentformatisidentifiedasanimportantfirststepinthisprocess.XMLandcorrespondingtechnologiessuchasXSLandXSLTthatcanbeusedinthistransformationarepresentedinSectionIV.SectionVpresentstheapplicationofXMLforthevisualizationofPLCprogramsandillustratestheapproachwithanexample.ThefinalSectionsummarizestheresultsandgivesanoutlookonfutureworkinthisongoingproject.

ⅡPLCANDIEC61131

Sinceitsinceptionintheearly‘70sthePLCreceivedincreasingattentionduetoitssuccessinfulfillingtheobjectiveofreplacing,researchanddevelopment,mainlyforControlEngineering.

IEC61131isthefirstrealendeavourtostandardizePLCprogramminglanguagesforindustrialautomation.InI993theInternationalElectrotechnicalCommission[4]publishedtheIEC61131IntemationalStandardforProgrammableControllers.BeforethestandardizationPLCprogramminglanguageswerebeingdevelopedasproprietaryprogramminglanguagesusabletoPLCsofaspecialvendor.Butinordertoenhancecompatibility,opennessandinteroperabilityamongdifferentproductsaswellastopromotethedevelopmentoftoolsandmethodologieswithrespecttoafixedsetofnotationstheIEC61131standardevolved.Thethirdpartofthisstandarddefinesasuitoffiveprogramminglanguages:

InstructionList（IL）isalow-leveltextuallanguagewithastructuresimilartoassembler.OriginatedinEuropeILisconsideredtobethePLClanguageinwhichallotherIEC61131-3languagescanbetranslated.

LadderDiagram（LO）isagraphicallanguagethattheUSA.LDsconformtoaprogrammingstyleborrowedfromelectronicandelectricalcircuitsforimplementingcontrollogics.

StructuredText（STJisaverypowerfulBlockDiagram（FBD）isagraphicallanguageanditisverycommontotheprocessindustry.Inthislanguagecontrollersaremodelledassignalanddataflowsthroughfunctionblocks.FBDtransformstextualprogrammingintoconnectingfunctionblocksandthusimprovesmodularityandsoftwarereuse.

SequentialFunctionChart（SFC）isagraphicallanguage.SFCelementsaredefinedforstructuringtheorganizationofprogrammablecontrollerprograms.

OneproblemwithIEC61131-3isthatthereisnostandardizedformatfortheprojectinformationinaPLCprogrammingtool.Atthemomentthereareonlyvendorspecificformats.Thisisalsoonereasonfortherestrictionofformalizationapproachestosingleprogramsoralgorithms.However,recentlythePLCusers’organizationPLCopen（see.org）startedaTechnicalCommitteetodefineanXMLbasedformatforprojectsaccordingtoIEC.ThisnewformatwilleasetheaccessofformalizationtoolstoallrelevantinformationofaPLCproject.

Ⅲ.RE-ENGINEERINGAPPROACH

Thepresentedapproachtowardsre-engineering（cf.Fig.1）isbasedupontheconceptionthatXMLcanbeusedasamediuminwhichPLCcodeswillbetransformed.

Thistransformationofferstheadvantageofobtainingavendorindependentspecificationcode.（EvenifthePLCopensucceedsindefiningastandardizedformatforPLCapplications,therewillremainalotofexistingprogramsthatdonotconformtothisstandard.）

Basedonthiscodeastep-wisetransformationtoaformalmodel（automata）isplanned.Thismodelcanthenbeusedforanalysis,simulation,formalverificationandvalidation,andfinallyforthere-implementationoftheoptimizedalgorithmonthesameoranotherPLC.

Sincere-engineeringofcompleteprogramswill,inmostcases,beonlyasemi-automaticprocess,intermediatevisualizationofthecodeisanimportantpoint.Atdifferentstagesoftheprocessdifferentaspectsofthecodeandorformalmodelawaythatadesignercanguidethefurtherwork.XMLwithitspowerfulvisualizationandtransformationtoolsisanidealtoolforsolvingthistask.

IV.XMLASATOOLFORVISUALIZATION

XML（extensibleMarkupLanguage）isasimpleandflexiblemeta-language,i.e，alanguagefordescribingotherlanguages.TailoredbytheWorldWideWebConsortium（W3C）asadialectofSGML[S],XMLremovestwoconstraintswhichwereasingle,inflexibledocumenttype（HTML）whichwasbeingmuchabusedfortasksitwasneverdesignedforononeside;andthecomplexityoffullSGML,whosesyntaxallowsmanypowerfulbuttheotherside.

WhileHTMLdescribesacrossplatformsandapplications.XMLcanbetailoredtodescribevirtuallyanykindofinformationinaformthattherecipientoftheinformationcanuseinavarietyofways.Itisspecificallydesignedtosupportinformationexchangebetweensystemsthatusefundamentallydifferentformsofdatarepresentation,asforexamplebetweenCADandschedulingapplications.

UsingXMLwithitspowerfulparsersandinherentrobustnessintermsofsyntacticandsemanticgrammarismoreadvantageousthantheconventionalmethodofusingalexicalanalyzerandavalidatingparser（cf.Fig.2,[7]）.

Theconventionalmethodofanalysisofprogramcoderequiresascanner（lexicalanalyser）whichgeneratesasetofterminalsymbols（tokens）followedbyaparserthat

checksthegrammaticalstructureofthecodeandgeneratesanobjectnet.Intheobjectnettheinternalstructureoftheprogramisrepresentedbyidentifiedobjectsandtherelationsbetweenthem.Boththescannerandtheparsertobeusedinthismethodaredocumentorientedwhichimpliesthatanalysisofdifferenttypesofdocumentsrequiresrewritingthegeneratedcodeforthescannerandtheparser.Anexampleofanapplicationofthismethodcanbefoundin[8].

ThemostpromisingaspectofusingXMLinsteadisthatXMLanditscomplementaryapplicationsfortransformationsarestandardizedsoastoprovidemaximumflexibilitytoitsuser.

TheXMLbasedmethodisadvantageous,sincethelexicalspecificationisaninvariantcomponentofXML;thereforethewell-formednessisindependentfromtherespectiveindividualapplication.

Hence,anXML-Parseralsocantransferwell-shapedXMLdocumentsinanabstractrepresentationcalledDocumentObjectModel（DOM）withoutusingagrammar.DOMisanapplicationprogramminginterface（APII）forvalidHTMLandwell-formedXMLdocuments.Itdefinesthelogicalstructureofdocumentsandthewayadocumentisaccessedandmanipulated.IntheDOMspecification,theterm"document"isusedinabroadsenseincreasingly.XMLisusedasawayofrepresentingmanydifferentkindofinformationthatmaybestoredindiversesystems,andmuchofthiswouldtraditionallybeseenasdataratherthanasdocuments.Nevertheless,XMLpresentsthisdataasdocuments,andtheDOMcanbeusedtomanagethisdata［5］.

XSLT,thetransformationlanguageforXMLiscapableoftransformingXMLnotonlytoanotherXMLorHTMLbuttom