Analysis Of Deadlock Prevention Policies For A Class Of Flexible Manufacturing Systems

Recently Petri nets have been widely used in the modeling, analysis and control of flexible manufacturing systems (FMS). This thesis investigates some deadlock prevention problems in Petri nets. Firstly, we present some popular algorithms, at the same time we discuss the theory of elementary siphons and their applications in the deadlock preventions. On the basis of the theory of elementary siphons, we present a new iterative algorithm for a class of Petri nets called ES3PR (extended from S3PR), by adding two kinds of control places called ordinary control places and weighed control places to the elementary siphons. In this way, we can prevent all elementary siphons from being unmarked and under some given conditions we can make all the strict minimal controlled and get a live net supervisor. Comparing with other policies, we introduce the idea of the elementary siphons and an iterative control policy. As a result we do not have to generate the reachability graph for a net system. The behavior of the net we finally controlled is far less restricted. In addition, we give an optimal algorithm based on the mixed-integer programming techniques. It reduces the restrictions of the control places to the net system by moving the position of the output arcs of control places. Finally we give a flexible manufacturing example to validate the deadlock prevention policy and demonstrate the advantage of our optimal deadlock control algorithm.