DEALING WITH BLOCKING IN SUPERVISORY CONTROL OF DISCRETE-EVENT SYSTEMS

Blocking occurs in the supervisory control of discrete-event systems when the controlled system can generate admissible traces of events that cannot be extended to any member of the set of desired marked (e.g., complete) traces. It is often the case that due to the presence of uncontrollable events, blocking is unavoidable or nonblocking solutions do not yield good performance. We study the issue of blocking in the context of a general "supervisory control problem with blocking" introduced in a previous paper. The admissible solutions of this problem are characterized and their properties analyzed. We then consider strategies to improve the performance of a given blocking supervisor. Performance is characterized in terms of two sets termed satisficing measure and blocking measure. We present techniques for improving each of these two conflicting measures. We also present techniques to improve both measures successively in order to optimize a given supervisor.