IEEE TRANSACTIONS ON AUTOMATION SCIENCE AND ENGINEERING, VOL. 3, NO. 3, JULY 2006

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Robust Supervisory Control for Production Systems With Multiple Resource Failures
Song Foh Chew, Student Member, IEEE, and Mark A. Lawley, Member, IEEE

Abstract—Supervisory control for deadlock-free resource allocation has been an active area of manufacturing systems research. To date, most work assumes that allocated resources do not fail. Little research has addressed allocating resources that may fail. In our previous work, we assumed a single unreliable resource and developed supervisory controllers to ensure robust deadlock-free operation in the event of resource failure. In this paper, we assume that several unreliable resources may fail simultaneously. In this case, a controller must guarantee that a set of resource failures does not propagate through blocking to stall other portions of the system. That is, the controller must ensure that every part type not requiring any of the failed resources should continue to produce smoothly without disruption. To do this, the controller must constrain the system to states that serve as feasible initial states for: 1) a reduced system when resource failures occur and 2) an upgraded system when failed resources are repaired. We develop the properties that such a controller must possess and then develop supervisory controllers that satisfy these properties. Note to Practitioners—For the past decade or so, researchers have begun to actively address the issue of ensuring smooth and continuous operation for flexibly automated manufacturing systems. This research effort has been motivated by the many failed attempts to implement flexible automation throughout the 1980s. During this time, much has been learned about modeling the control functions of a flexible, automated system. In fact, ladder logic control code can now be generated automatically from mathematical models, such as Petri nets, which compactly capture the required