Liveness-enforcing Supervisor Design For Flexible Manufacturing Systems Based On Petri Nets

In order to improve production efficiency, it is a trend for enterprises to adopt flexible manufacturing systems (FMS). However, because of the sharing and competition of limited resources, if there is lack of effective control, it is likely to cause circular wait of resources when the system is running, thus resulting in deadlock. This will lead to the standstill of partial or whole system, which not only reduces productivity, sometimes it may even cause major economic losses. For this reason, dealing with deadlock problems in an effectively way is important.As a mathematical modeling tool, Petri net can describe the sharing, conflict, mutual exclusion, concurrency and uncertainty of system resources due to its inherent advantages. Therefore, in recent decades Petri net has been widely used to study the method of analyzing and controlling of the deadlock of resource allocation system. Traditional strategy for deadlock prevention is based on Petri net, with the idea of preventing all the strict minimal siphons from being emptied, so as to make the system deadlock-free. But with the expanding of the network system, an increasing number of strict minimal siphons require the addition of control places, making the scale of the controlled network system more complex. As a result, this study is conducted to reduce the number of the siphons which require the addition of control places, and also to achieve the control effect.This thesis adopts a common model S3PR in Petri net to model and analyze FMS. The main research work is as follows:1) As for S3PR, deadlock is closely related to siphons. If all the strict minimal siphons are controlled, then the entire system will be deadlock-free. But the computation of all the strict minimal siphons is quite time-consuming. In light of this, this paper proposes a method based on matrix manipulation, which can compute the maximal siphons emptied in the network system, and then extract the strict minimal siphons from it. In addition, this method does not need to compute all the strict minimal siphons, so it is more efficient and visualized.2) Based on the theory of elementary siphon and matrix manipulation, this paper proposes strategies for deadlock prevention based on matrix manipulation and elementary siphon set.