Ladder logic implementation of Ramadge-Wonham supervisory controller

Abstract

In this paper we present an algorithm to convert a controller automaton synthesized by the Ramadge-Wonham (RW) method to a ladder logic diagram. The subject of conversion from RW controller to ladder logic is not new and has already been addressed by many researchers. Our method takes a new look at this subject. We not only make sure that the same sequences of events can be generated by both the RW controller and its converted ladder logic (as done by other related literature), but we also guarantee the implementation of the converted ladder logic as a PLC program. Specifically, we use the IDEF3 standard, which views a manufacturing system as a set of activities and their required resources. We consider the resource events to define the forcing mechanisms of ladder logic, as the original RW controller cannot model these mechanisms. We also use external signals to resolve the inherent conflicts of RW controller that cannot be tolerated under a forcing controller such as ladder logic. Two examples are presented to illustrate the applicability of the proposed algorithm.