An improved hybrid approach for the PLC-based implementation of reduced RW supervisors

A successful application of a hybrid (mixed Petri net/automaton) approach for the real-time supervisory control of an experimental manufacturing system was reported recently. The hybrid approach includes a Ramadge-Wonham (RW) supervisor in the form of an automaton. The reduced RW supervisor offers fewer states for the programmable logic controller (PLC) implementation of the hybrid controller with less memory requirements, but due to a problem called the avalanche effect, the PLC implementation of the hybrid controller with the reduced RW supervisor was not possible. This paper proposes a method to both detect and eliminate the avalanche effect problem for a RW supervisor in the form of an automaton, which enables the PLC implementation of the hybrid controller with the reduced RW supervisor. In addition, this paper improves the recently proposed hybrid approach by including the reduced RW supervisor and the avalanche effect detection and elimination method. The applicability of the improved hybrid approach is demonstrated by the PLC-based real-time control of an experimental manufacturing system.