An Algorithm About Translating From Sequential Function Chart To Ladder Diagram

The standard IEC61131-3defines four programming languages for PLC, and the Ladder Diagram and Sequential Function Chart are the most predominate graphical languages among them. Comparing with the Ladder Diagram, The sequential function chart is a structured program language, which maintains its overall logic of a control plant and uses process approach to describe the composition of the system, as well as the relationship between functional modules. So it can effectively respond to the large scale of PLC software. After years of the IEC61131-3standard popularized, many foreign programming development platforms, e.g. SIEMENS S7, MITSUBISHI Gx Programmer, have made great progress. However, there is not yet our own independent PLC programming system, it has great application value and market potential to develop a proprietary PLC programming system for sequential function chart, so studying the convert algorithm from sequential function chart to ladder program is an important issue.The paper in-depth studies the two graphical languages according to IEC61131-3standard. On this basis, a convert algorithm is proposed. Firstly, this article depth studied of the IEC61131-3programming language standard, analyzed sequential function chart and ladder diagram languages, and discussed feasibility and type of the convert algorithm; then defined the description of sequential function chart graphical network strictly, this article proposed a new definition for the AOV node, that abstract step component and its connection information to the AOV vertex, and abstract transition components to the arc, based on this form I defined the sequential function chart’s different structures into a unified, sample expression. In this way, using AOV digraph as a mapping format of sequential function chart and obtain the Start-Retention-Stop(SRS) electric circuit design rules, it can generate ladder program in the way of SRS electric circuit according to the IEC61131-3standard. At last, I discussed the connection checking method of the SFC’s inspection and the way for syntax errors checking and also.In summary, the paper proves that it is feasible to convert sequential function chart into ladder diagram. Finally, in order to check correctness of this algorithm, I designed a sorter control project with the platform; and this machine has a good result in the testing and acceptance phase.