摘要
基于Petri网的结构特性分析 ,研究了FMS(柔性制造系统 )一种预防死锁方法 .提出了Petri网的一种特殊拓扑结构———基本信标的概念 .在Petri网中基本信标的集合是SMS(严格极小信标 )集合的一个真子集 .尤其在大型Petri网系统中 ,基本信标的集合比SMS的集合要小得多 .对于Petri网的一个子类S3PR ,只对每一个基本信标添加一个库所使其不被清空 ,就可实现预防死锁 ,也就是说无须控制S3PR的所有SMS而达到无信标被清空的目的 .此外 ,对于S3PR ,还提出了一种求取SMS和基本信标的方法 .相对于现在普遍采用的控制所有SMS来预防死锁的策略 ,其具三方面优势 .1)只需控制少量的SMS即所谓的基本信标 .相应地 ,添加少量的控制库所和连接弧 ,就可得到无死锁或活的Petri网 .2 )不需要先行计算出极小信标的集合 .3)明显地 ,这种方法更适合大型Petri网系统 .我们通过穿插在文中的一个例子来说明这些方法 .
A deadlock prevention strategy for flexible manufacturing systems is developed based on Petri nets and their structural analysis. The concept of elementary siphons is proposed, it is a class of SMS (strict minimal siphons) with a smaller cardinality, particularly in the Petri net models of large-scale systems. By adding a control place for each elementary siphon to make it never be emptied, deadlocks can be prevented for a special class of Petri nets, namely S 3 PR. That means not all SMS need to be considered when ensuring no siphon loses its tokens. For S 3 PR, An approach is proposed for finding elementary siphons and SMS. Compared with the existing methods that control all SMS in a Petri net, the deadlock prevention policy has at least three advantages: 1) only a smaller number of SMS need to be controlled, hence the deadlock-freeness or live Petri net model obtained has less additional places and arcs; 2) not need to compute the set of siphons beforehand; and 3) this policy is more suitable for large-scale Petri nets. These methods are illustrated with an example.
出处
《自动化学报》
EI
CSCD
北大核心
2003年第5期733-740,共8页
Acta Automatica Sinica
基金
SupportedbytheYoungWorkstationFundsofXidianUniversityofP .R .China(YWF2 0 0 2 0 10 0 1)
