Synthesis of an event based supervisor for deadlock avoidance in semiconductor manufacturing systems

With the emerging of highly automated and flexible manufacturing systems in semiconductor fabrication, reliability and optimal productivity of such systems require very intelligent and complex control systems. Deadlock issue arises easily in these systems due to shared equipment usage and high production flexibility. This work presents a new event-based deadlock avoidance supervisor. The supervisor is able to efficiently and smartly avoid the deadlock state space explosion problem. The method is built upon a directed graph model of process flows. Concepts such as compound events, operation strings and deadlock strings are introduced. Major features in the proposed method include: i) it enables the optimal deadlock free operation of regular systems; and ii) it runs in polynomial time (fast online computation) provided that the set of deadlock strings is calculated offline. Examples are provided to show the effectiveness of the method.