On controllability and observability of discrete event systems

摘要

In this thesis, we further develop the supervisory control theory of discrete event systems introduced by Ramadge and Wonham. A discrete-event system G is modeled as the controlled generator of a formal language $Lsb{m}$(G). To control G, a supervisor S is developed whose action is to enable and disable the controllable events of G based on a record of occurrences of the observable events of G, in such a way that the resulting closed loop system obeys some prespecified operating rules embodied in a given language $K$. A necessary and sufficient condition is found for the existence of a supervisor S such that $Lsb{m}$(S/G) = $K$. Based on this condition a solution of the supervisory control and observation problem (SCOP) is obtained. In practice, decentralized supervision and hierarchical supervision are more desirable because of their convenience and efficiency. In this thesis, the idea of decentralized supervision and hierarchical supervision is formalized. Conditions are obtained which guarantee that distributed local supervision is equivalent to global supervision. A general procedure to synthesize a supervisor is also given. We apply these results to a small manufacturing system as an example.