自动制造系统Petri网的公平活性控制策略

基于Petri网的不变式理论,针对典型的自动制造系统,提出了Petri模型强制公平性 和活性的方法.首先,基于网论T-不变式的概念,把系统的网模型设计为一个公平网.此后,利 用P-不变式把一个公平网设计为一个活的且公平网.同时,提出了非冗余严格极小信标的概念, 大大简化了系统的分析与设计.一般说来,非冗余严格极小信标是系统严格极小信标一个小的 子集,尤其对于复杂系统的网模型.研究结果表明,只要使非冗余的严格极小信标受控,则系统 所有的严格极小信标就不会被清空.文中举例说明了这些控制方法的应用.研究结果适用于一 大类柔性制造系统,具有相当的普遍性.这种方法对于自动制造系统的调度设计也具有一定意义 和价值.

A Fairness and Liveness Control Policy of Petri Net Models for Automated Manufacturing Systems

Based on invariants of Petri nets, an approach to the enforcement of fairness and liveness is presented for classic automated manufacturing systems. First of all, a fair net is obtained by adding some places that make the net have only one T-invariant. Then, a fair net is enforced to be live through controlling minimal siphons by P-invariants. Importantly, the concept of redundant strict minimal siphons is put forward, which can greatly simplify the synthesis and analysis of Petri net model of the system considered. Generally, the set of non-redundant strict minimal siphons is a much small subset of the set of strict minimal siphons in a Petri net, particularly in large-scale ones. The results show that all strict minimal siphons cannot be emptied if non-redundant strict minimal siphons are controlled. Examples are presented to illustrate these approaches. The results obtained can be applied to a larger class of flexible manufacturing systems and are of significance to Petri nets based scheduling problems for automated manufacturing systems.