Sequence Control of Essential Siphons for Deadlock Prevention in Petri Nets
Deadlock prevention is crucial to the modeling of flexible manufacturing systems. In the Petri net framework, deadlock prevention is often addressed by siphon-based control (SC) policies. Recent research results show that SC methods can avoid full siphon enumeration by using mixed integer programming (MIP) to greatly increase the computational efficiency so that it can be applied in large systems in computable time. Besides, maximally permissive control solutions can be obtained by means of iterative siphon control (ISC) approaches and MIP. Then the remaining problems are redundancy and MIP iterations. Redundant controllers make the closed-loop system more complicated and each MIP iteration increases the total computational time. This article proposes a revised ISC deadlock prevention policy which can achieve better results than the other reported methods in terms of redundancy and MIP iterations while maintaining the maximal permissiveness. Several benchmark examples are provided to illustrate the proposed approach and to be compared with the other reported methods.