Research And Implementation Of Software PLC Ladder Programming System

Programmable Logic Controller(PLC) in Numerical Control Machine assists the Numerical Controller(NC) to control certain equipments. With the devopment of NC from exclusive and enclosed architecture to open-ended structure, the traditional PLC can't meet the need of open development direction of the NC. Then, software PLC technology based on PC is developed and becomes the key techonology in the open NC. The IEC61131-3 standard issued by International Electrotechnical Commission promotes the development of the software PLC technology greatly.The software PLC system is generally composed of develoment system and operational system. The development system provides the operating interface for users to edit, debug and compile logic programs. The development system built in the LanTian NC is limited by the hardware platform and then it brings inconvenience to related operation about PLC. Besides, it uses array to store the Ladder, going against the active editing operation and wasting storage resource to some extent.Directed at the problems above and using general PC as hardware platform and Windows as software resource, the paper designs and implements the software PLC Ladder programming system. Its main content is listed as follows.Firstly, the whole logical structure of the system is designed. It is modularized into Ladder editing subsystem and Instruction List compiling subsystem.Secondly, the Ladder editing subsystem is telled at length. The OOP method is used to draw the graphic object; serialization mechanism is adopted to load and preserve the Ladder; the location and type of the graphic object is maked full use of to check the validity of the logical relationship; According to the straight and deep traversal algorithm, the Ladder program is converted to equivalent IL program.Thirdly, the compiling process of the IL program is presented at length. Lexical analysis, syntax and semantic analysis is implemented by Flex and Bison; and then traverse the syntax tree to generate object code distinguished by operational system.Finally, the software PLC Ladder programming system is tested by in practice.