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外文翻译可视化的PLC程序使用.doc

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外文翻译可视化的PLC程序使用.doc

VisualizationofPLCProgramsusingXMLM.BaniYounisandG.FreyJuniorprofessorshipAgentenbasedAutomationUniversityofKaiserslautemP.0.Box3049,D67653Kaiserslautem,GermanyAbstractDuetothegrowingcomplexityofPLCprogramsthereisanincreasinginterestintheapplicationofformalmethodsinthisarea.Formalmethodsallowrigidprovingofsystempropertiesinverificationandvalidation.OnewaytoapplyformalmethodsistoutilizeaformaldesignapproachinPLCprogramming.However,forexistingsoftwarethathastobeoptimized,changed,orportedtonewsystems.ThereistheneedforanapproachthatcanstartfromagivenPLCprogram.Therefore,formalizationofPLCprogramsisatopicofcurrentresearch.ThepaperoutlinesareengineeringapproachbasedontheformalizationofPLCprograms.ThetransformationintoavendorindependentformatandthevisualizationofthestructureofPLCprogramsisidentifiedasanimportantintermediatestepinthisprocess.ItisshownhowXMLandcorrespondingtechnologiescanbeusedfortheformalizationandvisualizationofanexistingPLCprogram.I.INTRODUCTIONProgrammableLogicControllersPLCsareaspecialtypeofcomputersthatareusedinindustrialandsafetycriticalapplications.ThepurposeofaPLCistocontrolaparticularprocess,oracollectionofprocesses,byproducingelectricalcontrolsignalsinresponsetoelectricalprocessrelatedinputssignals.ThesystemscontrolledbyPLCsvarytremendously,withapplicationsinmanufacturing,chemicalprocesscontrol,machining,transportation,powerdistribution,andmanyotherfields.Automationapplicationscanrangeincomplexityfromasimplepaneltooperatethelightsandmotorizedwindowshadesinaconferenceroomtocompletelyautomatedmanufacturinglines.Withthewideningoftheirapplicationhorizon,PLCprogramsarebeingsubjecttoincreasedcomplexityandhighqualitydemandsespeciallyforsafetycriticalapplications.ThegrowingcomplexityoftheapplicationswithinthecomplianceoflimiteddevelopmenttimeaswellasthereusabilityofexistingsoftwareorPLCmodulesrequiresaformalapproachtobedevelopedI.Ensuringthehighqualitydemandsrequiresverificationandvalidationproceduresaswellasanalysisandsimulationofexistingsystemstobecarriedout2.OneoftheimportantfieldsfortheformalizationofPLCprogramsthathavebeengrowingupinrecenttimeisReverseengineering3.ReverseEngineeringisaprocessofevaluatingsomethingtounderstandhowitworksinordertoduplicateorenhanceit.WhilethereuseofPLCcodesisbeingestablishedasatoolforcombatingthecomplexityofPLCprograms,ReverseEngineeringissupposedtoreceiveincreasedimportanceinthecomingyearsespeciallyifexitinghardwarehastobereplacedbynewhardwarewithdifferentprogrammingenvironmentsVisualizationofexistingPLCprogramsisanimportantintermediatestepofReverseEngineering.ThepaperprovidesanapproachtowardsthevisualizationofPLCprogramsusingXMLwhichisanimportantapproachfortheorientationandbetterunderstandingforengineersworkingwithPLCprograms.Thepaperisstructuredasfollows.First,ashortintroductiontoPLCsandthecorrespondingprogrammingtechniquesaccordingtotheIEC611313standardisgiven.InSectionⅢanapproachforReengineeringbasedonformalizationofPLCprogramsisintroduced.ThetransformationofthePLCcodeintoavendorindependentformatisidentifiedasanimportantfirststepinthisprocess.XMLandcorrespondingtechnologiessuchasXSLandXSLTthatcanbeusedinthistransformationarepresentedinSectionIV.SectionVpresentstheapplicationofXMLforthevisualizationofPLCprogramsandillustratestheapproachwithanexample.ThefinalSectionsummarizestheresultsandgivesanoutlookonfutureworkinthisongoingproject.ⅡPLCANDIEC61131Sinceitsinceptionintheearly70sthePLCreceivedincreasingattentionduetoitssuccessinfulfillingtheobjectiveofreplacinghardwiredcontrolequipmentsatmachines.Eventuallyitgrewupasadistinctfieldofapplication,researchanddevelopment,mainlyforControlEngineering.IEC61131isthefirstrealendeavourtostandardizePLCprogramminglanguagesforindustrialautomation.InI993theInternationalElectrotechnicalCommission4publishedtheIEC61131IntemationalStandardforProgrammableControllers.BeforethestandardizationPLCprogramminglanguageswerebeingdevelopedasproprietaryprogramminglanguagesusabletoPLCsofaspecialvendor.Butinordertoenhancecompatibility,opennessandinteroperabilityamongdifferentproductsaswellastopromotethedevelopmentoftoolsandmethodologieswithrespecttoafixedsetofnotationstheIEC61131standardevolved.ThethirdpartofthisstandarddefinesasuitoffiveprogramminglanguagesInstructionListILisalowleveltextuallanguagewithastructuresimilartoassembler.OriginatedinEuropeILisconsideredtobethePLClanguageinwhichallotherIEC611313languagescanbetranslated.LadderDiagramLOisagraphicallanguagethathasitsrootsintheUSA.LDsconformtoaprogrammingstyleborrowedfromelectronicandelectricalcircuitsforimplementingcontrollogics.StructuredTextSTJisaverypowerfulhighlevellanguage.STborrowsitssyntaxfromPascal,augmentingitwithsomefeaturesfromAda.STcontainsalltheessentialelementsofamodemprogramminglanguage.FunctionBlockDiagramFBDisagraphicallanguageanditisverycommontotheprocessindustry.Inthislanguagecontrollersaremodelledassignalanddataflowsthroughfunctionblocks.FBDtransformstextualprogrammingintoconnectingfunctionblocksandthusimprovesmodularityandsoftwarereuse.SequentialFunctionChartSFCisagraphicallanguage.SFCelementsaredefinedforstructuringtheorganizationofprogrammablecontrollerprograms.OneproblemwithIEC611313isthatthereisnostandardizedformatfortheprojectinformationinaPLCprogrammingtool.Atthemomentthereareonlyvendorspecificformats.Thisisalsoonereasonfortherestrictionofformalizationapproachestosingleprogramsoralgorithms.However,recentlythePLCusersorganizationPLCopenseehttp//www.plcopen.orgstartedaTechnicalCommitteetodefineanXMLbasedformatforprojectsaccordingtoIEC611313.ThisnewformatwilleasetheaccessofformalizationtoolstoallrelevantinformationofaPLCproject.Ⅲ.REENGINEERINGAPPROACHThepresentedapproachtowardsreengineeringcf.Fig.1isbasedupontheconceptionthatXMLcanbeusedasamediuminwhichPLCcodeswillbetransformed.Thistransformationofferstheadvantageofobtainingavendorindependentspecificationcode.EvenifthePLCopensucceedsindefiningastandardizedformatforPLCapplications,therewillremainalotofexistingprogramsthatdonotconformtothisstandard.Basedonthiscodeastepwisetransformationtoaformalmodelautomataisplanned.Thismodelcanthenbeusedforanalysis,simulation,formalverificationandvalidation,andfinallyforthereimplementationoftheoptimizedalgorithmonthesameoranotherPLC.Sincereengineeringofcompleteprogramswill,inmostcases,beonlyasemiautomaticprocess,intermediatevisualizationofthecodeisanimportantpoint.Atdifferentstagesoftheprocessdifferentaspectsofthecodeand/orformalmodelhavetobevisualizedinawaythatadesignercanguidethefurtherwork.XMLwithitspowerfulvisualizationandtransformationtoolsisanidealtoolforsolvingthistask.IV.XMLASATOOLFORVISUALIZATIONXMLextensibleMarkupLanguageisasimpleandflexiblemetalanguage,i.e,alanguagefordescribingotherlanguages.TailoredbytheWorldWideWebConsortiumW3CasadialectofSGMLS,XMLremovestwoconstraintswhichwereholdingbackWebdevelopments6.Thedependenceonasingle,inflexibledocumenttypeHTMLwhichwasbeingmuchabusedfortasksitwasneverdesignedforononesideandthecomplexityoffullSGML,whosesyntaxallowsmanypowerfulbuthardtoprogramoptionsontheotherside.WhileHTMLdescribeshowdatashouldbepresented,XMLdescribesthedataitself.AnumberofindustriesandscientificdisciplinesmedicalrecordsandnewspaperpublishingamongthemarealreadyusingXMLtoexchangeinformationacrossplatformsandapplications.XMLcanbetailoredtodescribevirtuallyanykindofinformationinaformthattherecipientoftheinformationcanuseinavarietyofways.Itisspecificallydesignedtosupportinformationexchangebetweensystemsthatusefundamentallydifferentformsofdatarepresentation,asforexamplebetweenCADandschedulingapplications.UsingXMLwithitspowerfulparsersandinherentrobustnessintermsofsyntacticandsemanticgrammarismoreadvantageousthantheconventionalmethodofusingalexicalanalyzerandavalidatingparsercf.Fig.2,7.Theconventionalmethodofanalysisofprogramcoderequiresascannerlexicalanalyserwhichgeneratesasetofterminalsymbolstokensfollowedbyaparserthatchecksthegrammaticalstructureofthecodeandgeneratesanobjectnet.Intheobjectnettheinternalstructureoftheprogramisrepresentedbyidentifiedobjectsandtherelationsbetweenthem.Boththescannerandtheparsertobeusedinthismethodaredocumentorientedwhichimpliesthatanalysisofdifferenttypesofdocumentsrequiresrewritingthegeneratedcodeforthescannerandtheparser.Anexampleofanapplicationofthismethodcanbefoundin8.ThemostpromisingaspectofusingXMLinsteadisthatXMLanditscomplementaryapplicationsfortransformationsarestandardizedsoastoprovidemaximumflexibilitytoitsuser.TheXMLbasedmethodisadvantageous,sincethelexicalspecificationisaninvariantcomponentofXMLthereforethewellformednessisindependentfromtherespectiveindividualapplication.Hence,anXMLParseralsocantransferwellshapedXMLdocumentsinanabstractrepresentationcalledDocumentObjectModelDOMwithoutusingagrammar.DOMisanapplicationprogramminginterfaceAPIIforvalidHTMLandwellformedXMLdocuments.Itdefinesthelogicalstructureofdocumentsandthewayadocumentisaccessedandmanipulated.IntheDOMspecification,theterm

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