Research And Implementation Of PLC Ladder Programming System

Industrial automation is the important symbol of both the country’s industrymodernization and comprehensive national power. As one of the pillars of industrialautomation, Programmable Logical Controller (PLC) plays an important role in the industrialautomation. PLC ladder programming system is one of the key technologies of ProgrammableLogical Controller. Aimed at improving the equipment development efficiency, a new PLCladder programming system based on IEC61131-3standard is designed.According to the editing, compiling and simulating functions of it, PLC ladderprogramming system is divided into three modules. Based on Windows XP system and MFCMDI, this paper accomplished the designing work of the system.The editing module is the editing environment of PLC ladder programming system. Inorder to implement a friendly editing user interface, this paper designed the editing logicalgorithm, graph library, the document and project manager, ladder diagram data structure,structure and the destructor algorithm and loading and saving algorithm.The compiling moduleis in charge of converting the ladder diagram program into objectcode. The compiling module includes two submodules. Firstly, based on the sequential andhierarchical characteristics of ladder diagram, this paper designed a block recursion dividingalgorithm with high efficiency and self-adaption ability to convert the ladder diagramprogram into IL. Secondly, according to the requirement of PLC running core, object codewith specific format was established.A IL traversal algorithm is designed to convert it into thetarget code. Meanwhile, syntax and logic checking function is provided to improve thedevelop efficiency.The simulation module is composed by off line simulation submodule and on linesimulation submodule. The off line simulation submodule is used to simulate the runningprocess without a machine. The on line simulation submodule is used to monitor the realrunning process of a machine. To accomplish the simulation function, the simulatingrefreshing algorithm and simulating register management were designed.Finally, a throuthout testing on the whole programing system is conducted to verify thefeasibility and effectiveness of the system. A PLC ladder diagram program for MR65slottingmachine was designed, programmed and compiled on this system then downloaded into themotion control card to control a MR65machine.