Abstract
This paper focuses on solving deadlock problems in flexible manufacturing systems modeled with Petri nets by adding a set of recovery transitions. Different from the traditional deadlock control policies that add control places to a net model, this paper employs transitions to recover all the deadlock markings to be legal ones. A live net system can be obtained with all reachable markings. First, according to reachability graph analysis, a set of recovery transitions is obtained for each deadlock marking to be recovered. Second, we present a vector intersection approach to compute a recovery transition to recover multiple deadlock markings. Then, an iterative method is developed to find a set of recovery transitions to recover all deadlock markings. At each iteration step, a recovery transition is found to recover more than one deadlock markings. This iterative method cannot obtain the minimal number of recovery transitions in theory, but it can usually lead to a minimal one supported by extensive experimental studies. Finally, several widely used examples are provided to demonstrate the presented approach. The experimental results show that the reported deadlock recovery technique is effective and efficient.