A new method for modular supervision of timed discrete event systems

Abstract

It is known that modular synthesis for discrete event systems can render better design flexibility than centralized synthesis. This paper extends the author's previous centralized method (1997) to a new method for modular supervision of timed discrete event systems (TDES). Control problems are expressed in terms of forbidden conditions on the base state space of TDES. For tackling such control problems, the proposed modular method, like the centralized method, treats a tick event standing for the passage of a clock tick as an abstract entity in the implementation of control policies. As a result, the implementation of control synthesis can be accomplished without recourse to the construction of exact event trajectories of TDES which may result in state explosion. As such, the proposed method is quite often efficient by trading off an optimal solution for a simpler appropriate solution. The design approach is applied to a modular supervisory control of a simplified model of a manufacturing system with three robots.