This paper presents a deadlock prevention method for a class of flexible manufacturing systems (FMS) where deadlocks are caused by unmarked siphons in their petri net models. This method is an iterative approach consisting of two main stages. At each iteration, a fast deadlock detection technique developed by mixed integer programming (MIP) is used to find an unmarked maximal siphon. The first stage, called siphons control, of the proposed method is to add, for each unmarked minimal siphons, a control place to the original net to prevent a minimal siphon from being unmarked. The second stage, called augmented siphons control, is to add a control place to the modified net. The second stage is required since adding control places in the first stage may create new unmarked siphons. In addition, the second stage assures that there are no new unmarked siphons generated. We have obtained the relation of the proposed method and the liveness and reversibility of the controlled net. Finally, manufacturing examples are presented for illustrating the method and allow us to compare with prior methods.
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