Visualization of PLC Programs using XML可视化的PLC程序使用XML中英文文献翻译.docx

1、Visualization of PLC Programs using XML 可视化的PLC程序使用XML中英文文献翻译Visualization of PLC Programs using XMLM. Bani Younis and G. FreyJuniorprofessorship Agentenbased AutomationUniversity of KaiserslautemP. 0. Box 3049, D-67653 Kaiserslautem, Germany Abstract - Due to the growing complexity of PLC programs

2、there is an increasing interest in the application of formal methods in this area. Formal methods allow rigid proving of system properties in verification and validation. One way to apply formal methods is to utilize a formal design approach in PLC programming. However, for existing software that ha

3、s to be optimized, changed, or ported to new systems .There is the need for an approach that can start from a given PLC program. Therefore, formalization of PLC programs is a topic of current research. The paper outlines a re-engineering approach based on the formalization of PLC programs. The trans

4、formation into a vendor independent format and the visualization of the structure of PLC programs is identified as an important intermediate step in this process. It is shown how XML and corresponding technologies can be used for the formalization and visualization of an existing PLC program. I. INT

5、RODUCTIONProgrammable Logic Controllers (PLCs) are a special type of computers that are used in industrial and safety critical applications. The purpose of a PLC is to control a particular process, or a collection of processes, by producing electrical control signals in response to electrical proces

6、s- related inputs signals. The systems controlled by PLCs vary tremendously, with applications in manufacturing, chemical process control, machining, transportation, power distribution, and many other fields. Automation applications can range in complexity from a simple panel to operate the lights a

7、nd motorized window shades in a conference room to completely automated manufacturing lines.With the widening of their application horizon， PLC programs are being subject to increased complexity and high quality demands especially for safety-critical applications. The growing complexity of the appli

8、cations within the compliance of limited development time as well as the reusability of existing software or PLC modules requires a formal approach to be developed I. Ensuring the high quality demands requires verification and validation procedures as well as analysis and simulation of existing syst

9、ems to be carried out 2. One of the important fields for the formalization of PLC programs that have been growing up in recent time is Reverse-engineering 3. Reverse Engineering is a process of evaluating something to understand how it works in order to duplicate or enhance it. While the reuse of PL

10、C codes is being established as a tool for combating the complexity of PLC programs, Reverse Engineering is supposed to receive increased importance in the coming years especially if exiting hardware has to be replaced by new hardware with different programming environmentsVisualization of existing

11、PLC programs is an important intermediate step of Reverse Engineering. The paper provides an approach towards the visualization of PLC programs using XML which is an important approach for the orientation and better understanding for engineers working with PLC programs. The paper is structured as fo

12、llows. First, a short introduction to PLCs and the corresponding programming techniques according to the IEC 61131-3 standard is given. In Section an approach for Re-engineering based on formalization of PLC programs is introduced. The transformation of the PLC code into a vendor independent format

13、is identified as an important first step in this process. XML and corresponding technologies such as XSL and XSLT that can be used in this transformation are presented in Section IV. Section V presents the application of XML for the visualization of PLC programs and illustrates the approach with an

14、example. The final Section summarizes the results and gives an outlook on future work in this ongoing project. PLC AND IEC 61131Since its inception in the early 70s the PLC received increasing attention due to its success in fulfilling the objective of replacing hard-wired control equipments at mach

15、ines. Eventually it grew up as a distinct field of application, research and development, mainly for Control Engineering. IEC 61 131 is the first real endeavour to standardize PLC programming languages for industrial automation. In I993 the International Electrotechnical Commission 4 published the I

16、EC 61131 Intemational Standard for Programmable Controllers. Before the standardization PLC programming languages were being developed as proprietary programming languages usable to PLCs of a special vendor. But in order to enhance compatibility, openness and interoperability among different product

17、s as well as to promote the development of tools and methodologies with respect to a fixed set of notations the IEC 61131 standard evolved. The third part of this standard defines a suit of five programming languages:Instruction List (IL) is a low-level textual language with a structure similar to a

18、ssembler. Originated in Europe IL is considered to be the PLC language in which all other IEC61 131-3 languages can be translated.Ladder Diagram (LO) is a graphical language that has its roots in the USA. LDs conform to a programming style borrowed from electronic and electrical circuits for impleme

19、nting control logics.Structured Text (STJ is a very powerful high-level language. ST borrows its syntax from Pascal, augmenting it with some features from Ada. ST contains all the essential elements of a modem programming language.Function Block Diagram (FBD) is a graphical language and it is very c

20、ommon to the process industry. In this language controllers are modelled as signal and data flows through function blocks. FBD transforms textual programming into connecting function blocks and thus improves modularity and software reuse.Sequential Function Chart (SFC) is a graphical language. SFC e

21、lements are defined for structuring the organization of programmable controller programs.One problem with IEC 61 131-3 is that there is no standardized format for the project information in a PLC programming tool. At the moment there are only vendor specific formats. This is also one reason for the

22、restriction of formalization approaches to single programs or algorithms. However, recently the PLC users organization PLCopen (see http:/www.plcopen.org) started a Technical Committee to define an XML based format for projects according to IEC 61131-3. This new format will ease the access of formal

23、ization tools to all relevant information of a PLC project. RE-ENGINEERING APPROACHThe presented approach towards re-engineering (cf. Fig.1) is based upon the conception that XML can be used as a medium in which PLC codes will be transformed.This transformation offers the advantage of obtaining aven

24、dor independent specification code. (Even if the PLCopen succeeds in defining a standardized format for PLC applications, there will remain a lot of existing programs that do not conform to this standard.) Based on this code a step-wise transformation to a formal model (automata) is planned. This mo

25、del can then be used for analysis, simulation, formal verification and validation, and finally for the re-implementation of the optimized algorithm on the same or another PLC.Since re-engineering of complete programs will, in most cases, be only a semi-automatic process, intermediate visualization o

26、f the code is an important point. At different stages of the process different aspects of the code and/or formal model have to be visualized in a way that a designer can guide the further work. XML with its powerful visualization and transformation tools is an ideal tool for solving this task.IV. XM

27、L AS A TOOL FOR VISUALIZATIONXML (extensible Markup Language) is a simple and flexible meta-language, i.e， a language for describing other languages. Tailored by the World Wide Web Consortium (W3C) as a dialect of SGML S, XML removes two constraints which were holding back Web developments 6. The de

28、pendence on a single, inflexible document type (HTML) which was being much abused for tasks it was never designed for on one side; and the complexity of full SGML, whose syntax allows many powerful but hard-to-program options on the other side.While HTML describes how data should be presented, XML d

29、escribes the data itself. A number of industries and scientific disciplines-medical records and newspaper publishing among them-are already using XML to exchange information across platforms and applications. XML can be tailored to describe virtually any kind of information in a form that the recipi

30、ent of the information can use in a variety of ways. It is specifically designed to support information exchange between systems that use fundamentally different forms of data representation, as for example between CAD and scheduling applications.Using XML with its powerful parsers and inherent robu

31、stness in terms of syntactic and semantic grammar is more advantageous than the conventional method of using a lexical analyzer and a validating parser (cf. Fig. 2, 7).The conventional method of analysis of program code requires a scanner (lexical analyser) which generates a set of terminal symbols

32、(tokens) followed by a parser thatchecks the grammatical structure of the code and generates an object net. In the object net the internal structure of the program is represented by identified objects and the relations between them. Both the scanner and the parser to be used in this method are docum

33、ent oriented which implies that analysis of different types of documents requires rewriting the generated code for the scanner and the parser. An example of an application of this method can be found in 8.The most promising aspect of using XML instead is that XML and its complementary applications for transfo