Robust deadlock control for automated manufacturing systems based on elementary siphon theory

Abstract

Resource failures may happen from time to time in an automated manufacturing system (AMS) in production practice, leading to that most of deadlock control methods in the literature are not applicable. For a generalized system of simple sequential process with resources (GS3PR), this paper develops a robust deadlock control strategy when there exists a type of unreliable resources. To do so, after computing the system’s elementary and dependent strict minimal siphons (SMSs), by using the concept of max′-controllability of siphons, we then check whether an elementary SMS is self-max′-controlled or not, and whether it contains unreliable resources. Afterwards, a constraint set for a siphon is introduced and a monitor is designed for each non-max′-controlled elementary SMS and self-max′-controlled elementary one that contains unreliable resources. Then, if a dependent SMS is max′-controlled with respect to the control depth variables of its elementary siphons, it needs no monitor; otherwise, we add a monitor for such a dependent SMS. Finally, a robust deadlock control algorithm is developed to keep each SMS to be max′-controlled, even if there exists a type of unreliable resources. The proposed method is demonstrated by using examples.