外文翻译-可编程逻辑控制器图形软件的开发

英文原文GraphicalDevelopmentofSoftwareforProgrammableLogicControllersAbstractGraphicallanguagesarestandardinthefieldofcomputerprogramming.Complexsoftwaredevelopmentisbesthandledbygraphicallyconnectingpre-built,fullytestedandhighlyspecializedsoftwarecomponents,insteadofwritinganddebuggingthousandsoflinesofcode.Modernprogrammingenvironmentsincludecompletelibrariesofsuchcomponents.InthefieldofProgrammableLogicControllers(PLCs),thisisnotthecase.PLCprogramscanbedevelopedusinggraphicallanguages,asLadderDiagrams(LD)orFunctionBlockDiagrams(FBD),butthestandardlibrariesareverylimited,sotheprogrammermustdevelophisownlibraries,buildingsoftwareobjectsfromscratch.Inthispaper,aframeworkispresentedforautomaticallybuildingcomplexsoftwaremodulesusingbasedontwokeypillars:ontheonehand,usingobjectorientedconceptsasencapsulation,inheritanceandgenericprogramming,and,intheotherone,closelyfollowingthephysicalmodeloftheobjectsusedinbuildingelectricalcontrolcabinets(ECBs).I.INTRODUCTIONThedevelopmentofPLCprogramsisacrucialpointintheconstructionofmodernautomationinstallations.AsPLCOpenorganizationstatesin1,“softwareplaysanever-increasingroleinindustrialautomation.Withthis,theassociatedsoftwarecostsincrease,eventothepointthatitbecomesthehighestpartofthetotalsystem”.Oldprogramminglanguagesgivealimitedsupporttothistask:thecodetendstobeobscure,withlimitedcapabilitiesofflowcontrol,andinternalinterdependenciesmakeanyminormodificationanightmare.Tosolvethisproblem,anewstandardhasbeenestablished,theIEC-61131-3.Itdefineselementsthatcanbeusedasblocksforbuildingnewprograms,suchasFunctionBlocks(FBs),andbringssomeofthebenefitsofOOP,suchasencapsulation,asLewis2orJohnandTiegelkamp3pointout.Nevertheless,othermajorOOPfeatureslikeinheritance,genericprogrammingandpolymorphismarenotsupportedinthestandard.Inspiteofthislimitedsupport,Brendel4developssoftwarecomponentsusingIEC-61131FBmodules.BonfeandFantuzzi5presentanobject-oriented(OO)programforamanufacturingmachine,andHVanderWalH6developsacompleteOOlibraryofmotioncontrolcomponents,asaresultofPLCOpeneffort.OOP,besidesbeingawayfordevelopingwellstructuredPLCprograms,bringsalsoaddedbenefitsasself-explanatoryprograms,Plompetal.7,orgraphicalprogramming,Lewis8.Therearedifferentapproachesforchoosingthesoftwareobjectsthatcanserveasthebuildingblocksforconstructingwellstructured,failure-proofPLCprograms:Mathematicalmethods,whichformalizethestructureofthesoftwarecomponentsandtheirrelationshipfromamathematicalpointofview.Feldmannetal.9,PolicandJezernik10usePetrinetsasthetoolformodelingdiscreteeventsystems(DES).Bridgemethods,whichdevelopthecontrolprogramusinghighlevel,objectorientedprogramlanguagesandtranslatetheresultingcodetoIEC-61131-3FBmodules.PlazaandMedrano11useClanguageasthesource,HeverhagenandTracht12useUnifiedModelingLanguage(UML).JammesandSmith13followinsteadthemodelofWebServices.MIM(ModelIntegratedMechatronics)considerseachobjectasacompleteunitwhichintegratestheelectricalmechanicalandsoftwareaspects.Thramboulidis1415andVyatkin16developsuchMechatroniccomponents.Aninteractive“IntelligentMechatronicTestbed”canbefoundat17.Archimedes18,CORFU19andOONEIDA20aregeneralframeworksbuiltuponthisconcept.TheseapproacheshavedrawbacksfromthepointofviewofthetechnicianthatdevelopsPLCprograms.Mathematicalmethodsareoftentooabstractanddifficulttotrack.RealtimeconstraintsarealientogeneralpurposelanguageprogramssuchasCorJava.AndMechatronicsmodelstendtobefartoocomplex,becausetheytrytomodelallthebehavioralaspectsofaspecificdevice.Whatitisneededisasimple,clear,robustandflexibleOOPmodelthatallowsfortheassemblyofPLCprogramsfollowingthesameprocedureusedtobuildmodernECBs:bycablingpre-built,fullytestedcomponents.Thatswayanewframework,ObjectOrientedFrameworkforPLCSoftwareDevelopment(OOPLC),hasbeendevelopedandispresentedinthispaper.ItsgoalistobuildPLCprogramsbyassemblingpre-built,fullytestedsoftwarecomponentsinasimple,graphicalway,analogtothedrawingofelectricalschemas.Thestructureofthispaperisasfollows:sectionIistheintroduction.SectionIIestablishesthemainOOPLCframeworkfeatures,whicharefullydevelopedinsectionIII.InsectionIVanexampleprogramdevelopedwiththeproposedmethodisshown,andinsectionVtheconclusionsarepresented.II.OOPLCFEATURESOOPLCisfoundedonthephysicalcomponentsusedtobuildECBs.AsFarins21pointsout,eachideamustberelatedwiththeprincipleonamaterialsystem,howeversimpleandprimitiveitmaylook,onwhichavariablesolutioncouldbebased.TheelectionoftheECBasthephysicalmodelalsoguaranteesthatthesystemcanbeeasilyunderstoodbythepersonnelwhowillapplyandmaintainit.WithOOPLC,buildinganewprogramisjustaprocessofinstallingandconnectingpre-built,fullytestedsoftwaremodules,inagraphicalway(thesameasdrawingelectricalcontrolcabinetdiagrams),insteadofwritinganddebugginglinesofcode.Asitissaid,ashortsketchisbetterthanalongreport.ThebasicelementusedforassemblingECBsistherelay.Ithasbeenakeycomponentofindustrialautomationinstallationssinceitsconception.Infact,themostwidelyusedPLCprogramminglanguageistheladderone,builtaroundtherepresentationofrelayscoilsandcontacts,asinFig.1.Modernrelayshaveevolvedfromtheoriginal,electromechanicalone,andnowtheyareelectronicdevicesthatcanperformcomplexcontroltasks.ThereareeveninthemarketsmallPLCsthataresoldas“intelligentrelays”.Therearesomecommonfeaturestoallthisvarietyofrelays:Modulardesign.Modernrelaysarecomposedoftwoparts:the“base”containstheconnectionswiththeinput/outputconductors,andiscommontoalltherelaysfromagivenseries.Theotherpartisthe“body”oftherelay,whichcontainstheelementsthatperformthedesiredfunctionality.Differentbodiescanbeconnectedtothesamebase,whichaddsflexibilitytothedesignandmaintenanceofECBs.Besides,oldelementscanbereplacedwithmoreadvancedoneswithoutmodifyingthecablingofthecabinet.Parallelism.ECBconstructionisspeededusingarraysofrelays,groupedincards,interconnectedwithcablesinsteadofsingleconductors.Theuseofstandardarrayconnectorsallowsforafast,error-freeassemblyofthecabinet.Communicationcapabilities.ECBsarenotisolatedelementsinamodernautomationinstallation.Theymustcommunicatewithexternaldevices,mainlycomputers,fortheset-upoftheiroperationaldeviceparametersandalsoforsupervisingtheoperationoftheinstallation.Modernrelayshavebuilt-incommunicationcapabilities,andareabletocommunicatethroughstandardindustrialbuses.Therearesomemodulesinthemarketthatcanevenactasautonomouswebservers.Toimplementthesefeatures,OOPLCdefinesthreeelements:relay,cardandconnectors,whicharefullydescribedinthenextsections.Besidescloselyresemblingtheirphysicalcounterparts,OOPLCelementsarebuiltusingasimple,error-freeprocedure,basedonthefeaturesofOOP:Encapsulation.Anyobjectintegratesboththedataandthemethodsthatprocessit.Externalinputsandoutputsareaccessibleonlythroughwelldocumentedinterfaces.Inheritance.Newobjectsarederivedfromexistingones,addingnewfeaturestospecializethem.Polymorphism.Differentobjectscanreacttothesameeventsinadifferentway.Templateprogramming.Theuseofgenericobjectsandalgorithmsallowsthegenerationofobjectsfrompredefinedtemplates,withanautomatic,error-freeprocess.ThepresentnormforPLCsoftwaredevelopment,theIEC61131-3,offersalimitedsupportforthesefeatures:TheFBdefinitionestablishesacleardistinctionbetweentheinterface(whichcontainstheexternalinputs,outputs,andtheinternal,hiddenvariablesofthefunction),andthebody,(whichcontainsthealgorithmthatoperatesontheinterfaceelements).OnlyoneprogramcanbedefinedperFB.Thereisalimitedsupportofthepolymorphism.Onlysomeofthestandardfunctionscanprocessparametersoftype“any”(asumfunction,forexample,canaddintegerandrealnumbers).Thereisnosupportforinheritanceortemplateprogramming.InOOPLC,thesecharacteristicsareimplementedandusedtobuildtheobjectsthatintegratetheframework.III.OOPLCELEMENTSA.ModularDesign:theRelayElementTheOOPLCmodelofaphysicalrelayhastwocomponents,asitsphysicalcounterpart:theexternalinterface,orthe“base”,whichiscommontoeveryrelay,anditsinternalcomponents,or“body”,whichisspecifictoeachone.Thebase_relayelementdefinesthecommonsetofconnectionsofeveryrelayinOOPLC.Physicalrelaysareconnectedusingconductors,whichcancarrysignalsofdifferenttypes(digital,analog),evenmixedonesusingtimeorfrequencymultiplexingtechnology.Tomimicthisbehavior,anewdatatypeisdefined:theconductordatatype,showninFig.2,whichcantransportsimultaneouslydataunitsofthemostcommontypes.Thebase_relaycomponentdefinestheconnectionsoftherelay,anditiscommontoeveryspecificrelay.Havingthesameconnector,allofthemareinterchangeable,fromthepointofviewoftheirgraphicalinterconnection.ThedefinitionandgraphicalrepresentationofthiselementareshowninFig.3.Thebodyofthebase_relayisaprogramwhichonlyhasanemptyline(;).Anyotherrelayisderivedfromthisonebyinheritingitsinterface,throughathree-stepprocessthatconstitutestheinheritancemechanisminOOPLC:1)Duplicatethebase_relaycomponentwiththenameofthenewrelay(inheritance)2)Addanynecessaryinternalvariables(dataencapsulation)3)Programthebodyofthenewrelay(methodencapsulation)Thefactthatalltherelayshaveacommoninterfaceguaranteesthatanynewrelayderivedfromthebase_relaycanbesubstitutedbyanotherone,withoutneedingtochangeanyconnections.Fig.4showsatimerrelaywithdelaytotheconnection,whichisgeneratedusingthisalgorithm.ItencapsulatesastandardFBoftheIECnorm,theTONtimer,whichhasbeenconnectedinternallytotheinputandoutputconductorsoftheOOPLCbase_relay.Thereisamajordrawbackwiththismethod:anymodificationtothebase_relayisnotautomaticallypropagatedtotheinheritedrelays,likeafullyOOPlanguageasC+does.Amanual,error-proneworkisrequiredtomodifyalltherelaysofthelibrary(thechildren),ifthereisanymodificationofthebase_relay(theparent).TrueinheritancecouldbeachievedifafutureadditiontotheIEC-61131-3normincorporatesaconstructorforderivinginheritedobjects,withsyntaxsimilartotheonepresentedinFig.5.B.Parallelism:theCardElementParallelismisacommongoalintheconstructionofECBs,duetothehugesavingsoftimeinthetaskofconnectingtheelements.Conductorsaregroupedformingcables,andrelaysaregroupedincards.Arrayconnectorsfastentheconnectionofthecardsbetweenthemandwithexternalinputsandoutputs.AnewelementisusedinOOPLCtorepresentaphysicalcable:thecabledatatype,definedasanarrayoftenconductors,asshowninFig.6.TheOOPLCcardisatemplateelementwhichholdsanarrayoftenbase_relays,whereanyOOPLCrelaycanbepluggedin.Itsalgorithmconnectstheconductorsofeachoftherelaystothecorrespondingconductorsofthecardscables,asshowninFig.7.Toderiveanewcardwithrelaysofagiventype,asxx_relay,justatwostepsprocessisneeded,whichconstitutesthetemplatemechanisminOOPLC:1)Duplicatethetemplate_cardandgiveitanewname.2)Changetheword“base_relay”to“xx_relay”.Asanexampleofthisprocess,inFig.8ithasbeenappliedtogenerateacardthatcontainston_relays.Thetemplatemechanismguaranteesthatanynewcardiserror-free,becausenomodificationsaredonetotheinternalprogramofthetemplatecard.Onlythesymbolbase_relaymustbesubstitutedwiththetypeofthedesiredrelay(inthiscaseaton_relay).Thereisalsoadrawbackinthismethod:anewcardmustbeconstructedforeverytypeofrelay.InrealOOPlanguages,likeC+,thecompilerwhobuildsautomaticallynewcomponentsfromtemplateswhentheyarefirstdeclared.ShouldtheIECnormsupportthisfeature,thedeclarationofanewcard,Card_1,withton_relayswouldbe:Card_1:template_card;C.Communications:theConnectorElementOOPLCobjects,liketheirphysicalcounterparts,mustbeabletocommunicatewith:Eachother,toperformthePLCcontroltasks.Thecontrolledprocess,viainputandoutputsignals.Othercontrolequipment,mostlycomputers,tosuperviseandadjusttheprocessparameters.TheinterconnectionoftheobjectsinsideanOOPLCprogramisachievedeithergraphically,usingthetoolsprovidedbythevendorsofIECcompliantPLCs,orinatextualway,withlanguagesasSTL.OOPLCfacilitatesthisprocessbecause:Allthecardscanbeinterconnectedusingthesamedatatypeelement,thecable.Asacablecontainstenconductors,graphicalschemasaregreatlysimplified,inthesamewaythatunifilarelectricalschemasallowforagreatlysimplifiedrepresentationofelectricalinstallations.Aseverycardobjectinheritsthesameexternalinterface,anygivencardcanbereplacedwithanotheronewithouthavingtomodifyitsconnections.ToconnectanOOPLCcardwiththeprocessinputandoutputsignals,newselementsareneeded:aninputconnector,whichcollecttheinputsandfeedthemthroughcablestothecardobjects,andanoutputone.Theirphysicalcounter-partarethescrewconnectorsusedforcouplinganECBtoamachineorprocess.AcommonpracticeinECBconstructionistogroupsignalsofthesametypeinasingleconnector(forexample,on/offsignalsfromendswitches,oranalogonesfromtemperaturesensors).So,adifferentconnectorisbuiltforeachtypeofthecablesdata:bool,integer,timeandreal.Fig.9showsaninputconnectorforboolsignals.Theseconnectorscanbetailoredtoeachinstallation,byrepresentingonlythephysicallyconnectedpinsandassigningthemmeaningfulnames.Forexample,aninputboolconnectorathree-axismachinewouldbedefinedasinFig.10.TheconnectionofOOPLCobjectswithexternalcontrollersandcomputersismadeusingOPC(OleforProcessControl)technology.OPCserversareprovidedbythevendorsofeverymajorPLCbrandinthemarket.OPCclientscanbeembeddedinmostwindows-basedcomputerprograms,includingSCADAs,Worksheets,DataBases,etc.Nevertheless,OPChassomeconstraintsthathavetobecarefullymatchedtoimprovetheperformanceofdatatransmission:Onlydataofelementarytype(BOOL,INT,REAL,etc.)canbeaccessed.DatamustbelocatedinthePLCglobalmemory.Thedatatransmissionrateishigherwhentransferringmultipleandcontiguousunitsofdatainoneoperationinsteadofexchangingsingleonesrepeatedly,becauseoftheoverheadofthefixedframesthatthesystemuses.Datashouldbeself-explanatory.Iftheusercangetnotonlytheactualvaluesbutalsoadescriptionofthem,thenautomaticpresentationprogramscanbedeveloptoactinteractivelyuponthem.Memoryconnectorsareusedtoconnectthedataofthesearrayswiththeobjectcards.Theyhavetwoinputparameters:anumberforlocatingthearrayelementtobetransferred,andanameforexternalidentificationpurposes.Thenumbermustbeassignedmanuallytotheconnector,whichmeansthatafixedmemorylayoutisneededbeforebuildingtheprogram.Furtherresearchisbeingcarriedouttodevelopamemorymanagerthatcanassignautomaticallymemoryresourcestothecardswhentheyaredeclaredforthefirsttime.Aswiththeexternalconnector,memoryconnectorscanbedefinedeitherasinputconnector,transferringdatafromthememorytothecardinputsforparameterssetting,orasanoutputconnector,movingdatafromthecardtothememoryforsupervisionpurposes.TheactualcodeandthegraphicalrepresentationofaninputmemoryconnectorisshowninFig.11.IV.APPLICATIONOFTHEPROPOSEDMETHODTOIMPLEMENTANEXAMPLEPLCPROGRAMInFig.12,asimpleprogramwhichfiltersoutdigitalsignalswithadurationlessthanapresettimeisshown.Itfiltersthesignalsfromtheendswitchesofathree-axismachine,amustinnoisyenvironments.Asitcanbeobservedinthisfigure,specializedconnectorsareselfexplanatory.Forexample,thephysicalinputsignalcorrespondstotheend_switch(nameoftheconnector)ofaxisnumber2(nameoftheconnectorspin).So,thereisnoneedofworkingwithseparatesymbolliststhatassignanametoeveryprocesssignal.Inthisway,thepossibilitiesofmismatchesandlackofsynchronizationaftertheadditionofnewsignalsaregreatlyreduced.Thecommunicationwithexternalcomputers,forexampletosetthefiltertimeinaSCADAprogram,sachievedthroughtheuseofthememoryconnector,whichassignsafixedglobalmemoryspacetothetentimersoftheton_card,accessiblefromOPCservers.TheexampleprograminFig.12hasbeenbuiltliketheelectricaldrawingofanECB,inagraphicalway.New,complexmodulescanbederivedinthesameway,andtheycanbereusedtodevelopnewprograms,inthesamewayaspre-builtICchipsareusedtobuildhardwareequipment.V.CONCLUSIONSInthispaper,aframeworkforgraphicallydevelopingPLCcontrolprograms,usingobjectorientedtechniques,hasbeenpresented,OOPLC.Thesoftwareobjectsarebuiltwithinthisframeworkfollowingthephysicalmodelofthecomponentsofelectricalcontrolcabinets,withfeaturessuchasmodularity,parallelismandcommunicationcapabilities,bothwiththeprocessandwithexternalcomputers.Toderivenewobjectsfromexistingones,OOtechniquessuchasencapsulation,polymorphism,inheritanceandtemplateshavebeenapplied.LimitedsupportoftheIEC-61131-3normofthesetechniqueshasbeenpointedout,andsuggestionsforfutureextensionstoimplementthemhavebeenpresented.OOPLCenablesthedevelopmentofaPLCprograminagraphicalway,byinterconnectingpre-built,fullytestedsoftwarecomponents,inthesamewaythatmodernECBsaredesignedandbuilt.Asimpleexampleofsuchaprogramhasbeengiveninthispaper,butthisframeworkhasbeenalsosuccessfullyappliedfordevelopingcomplexindustrialprograms。中文翻译可编程逻辑控制器图形软件的开发摘要在计算机编程领域图形语言是标准的。复杂的软件开发靠图形连接预先建立，充分测试和高度专业化的软件组件得到最佳处理，而不是靠编写和调试成千上万行的代码。现代编程环境包含了这些成分的完整库。在可编程逻辑控制器（PLC）领域中，情况并非如此。可编程控制器编程是用图形语言开发的，梯形图（LD）或功能块图（FBD），然而标准库是非常有限的，因此，程序员必须开发自己的库，以构建软件对象。本文提出了一种基于两个重要支柱的自动建立复杂软件模块的构架：一方面，使用面向对象的概念进行封装和通用编程，另外一方面，紧随对象的物理模型以建立电气控制柜（ECBs）。一、导言在现代自动化装置的建设中，PLC编程的发展是一个关键点。正因为PLCOpen的开发1，“软件在工业自动化发挥了越来越多的作用。有了它，相关软件的费用增加，甚至这成为整个系统最高的一部分”。老的编程语言对任务有局限性：代码往往令人费解，因为流量控制的能力很有限，并且内部的相互依存使得不能进行任何轻微修改。为了解决这一问题，一个新的准,IEC-61131-3已经确立。它定义了可以用作编程的模块元素，如功能模块，并给OOP带来了一些好处，比如Lewis2或John和Tiegelkamp3提出的封装。不过，其他主要面向对象的功能，比如继承，通用编程和多态性就不为这个标准所不支持。尽管有这种局限性，Brendel4使用IEC-61131-3功能模块开发了软件组件。由于PLCOpen的作用，Bonfe和Fantuzzi5为生产机器提出了一种面向对象的编程，VanderWal6为运动控制组件开发了一种完整的面向对象库。面向对象，除了是开发PLC合理结构编程的一种方式外，也有程序注释的优势，Plomp等，或图形化编程，Lewis8。对于选择可以作为构建合理结构的PLC程序模块的软件对象，有许多种方法：数学方法，运用数学观点形成软件组件的结构及其相互关系。对于建模离散事件系统，Feldmann9,Polic和Jezernik10利用Petri网作为工具。桥式方法，使用高层次，面向对象的编程语言开发控制程序，并将产生的代码转换到IEC-61131-3功能模块中。Plaza和Medrano11使用C语言作为源程序，Heverhagen和Tracht使用统一建模语言（UML）。Jammes和Smith13用的是网络服务建模。MIM（模型集成机电）将每个对象作为一个完整的单元，集成了电气机械和软件方面的问题。Thramboulidis和Vyatkin研发了这种机电一体化的组成部分。一个互动的“智能机电试验”在17.Archimedes18中提及,CORFU19和OONEIDA20是建立在这一概念上的通用框架。这些方法从开发PLC程序的技术观点来看存在缺点，数学方法往往过于抽象，并且很难跟踪。实时限制与通用语言程序不兼容，如C或Java语言。机电模型往往过于复杂，因为他们要对所有专用设备的行为进行建模。它所需要的是一个允许与构建现代ECBs的程序相同的简单，明确，强有力和灵活的面向对象编程的模式：由布线预先建立，经过全面测试的组成部分。这是一个新的PLC软件开发的面向对象的框架，已经开发并在本文提出。其目标是通过用简单，图形化方式汇集预建立，充分测试软件组件，类似于绘制电气架构。本文的结构如下：第一部分是导言。第二节描述了主要OOPLC框架的功能，这在第三节中将全面介绍。在第四节中举例了一个程序，用的是上文提出的方法。第五节中阐述结论。二、OOPLC特征OOPLC是建立在用来构建ECBs物理成分之上的。正如Farins所指出的那样，每一个想法，必须与本身系统原则相关，不管它看上去如何简单而原始，总会有基于它的不同解决办法。作为物理模型的EBC的选择同样保证，该系统可很容易地被运用它的工作人员所理解。有了OOPLC，建立一个新的程序只是安装和连接预置，充分测试的软件模块的过程，以图形方式（与绘图电器控制柜图表相同），而不是编写和调试代码行。用于组装ECBs的基本要素是继电器。这是一个工业自动化装置的关键组成部分。事实上