J. Lee∗ and J.S. Lee∗
IEC 61131-3, programmable logic controllers, petri net, ladder diagram, function block diagram
We proposed an algorithm that converts the ladder diagrams (LDs) of the programmable logic controller (PLC) to the petri nets (PNs) using the module synthesis technique. By using the enabling arc, the reset arc, and the buffer place, we first converted the LD core functions such as contacts and coils to the corresponding PN modules. We then systematically synthesized these PN modules to convert any general LDs consisting of contacts and coils to the corresponding PNs. The generated PN can be served as an analysis tool for the original LD program. We also converted the counter and the timer function blocks of the function block diagram (FBD) to the PN modules because they were the functions supported by most of the commercially available PLCs. In converting these function blocks, we used the variable weight arc and the variable weight enabling arc.
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