Robust Deadlock Control for Automated Manufacturing Systems Based on the Max-Controllability of Siphons

There have been a variety of deadlock control strategies proposed for automated manufacturing systems (AMSs) without taking unreliable resources into account in the framework of Petri nets. However, in addition to deadlocks, resource malfunction problems may also arise to make a system collapse in the real world. This paper develops a new deadlock control method for a generalized system of simple sequential processes with resources (GS
³
PR), where a class of unreliable GS
³
PR (U-GS
³
PR) is considered. Recovery subnets are used to describe an unreliable resource failure and its recovery process in a Petri net model. First, we compute all the strict minimal siphons (SMSs) in a GS
³
PR net. Second, with the concept of max-controllability of siphons, a monitor is added to each SMS. However, the net loses liveness when unreliable resources are taken into consideration with recovery nets being added for their operation places. Then, by using the concept of constraint set, we add related arcs between the transitions in recovery subnets and original monitors. Finally, a robust deadlock controller is designed for the AMSs according to the max-controllability of siphons.