Extending the knitting technique to Petri net synthesis of automated manufacturing systems

The modelling or synthesis of ordinary Petri nets has been recognized as a key step for applying Petri nets to performance analysis, control and simulation of industrial production systems. This paper addresses this synthesis problem by adopting a global and incremental synthesis approach: the knitting technique for manufacturing systems. The knitting technique has been applied to Petri net modelling and analysis of communication networks. The idea behind this technique is to introduce details in an incremental way, i.e. by adding new paths and/or cycles to a Petri net. At each step the Petri net model grows according to certain rules which will guarantee such system properties as boundedness, liveness and reversibility. Thus the cumbersome analysis for these properties can be avoided while designers can still build up a Petri net model for a complicated system. The knitting rules are divided into two types: TT and PP with a number of variations. This paper formulates and discusses these rules in the context of manufacturing. The theoretical results on the preservation of system properties using the proposed rules are presented. The results are illustrated through Petri net modelling of an automated manufacturing system which consists of two robots, five machines and two automatic guided vehicles. This approach is compared with other existing synthesis approaches and its distinguishing advantages are indicated in the conclusion. Future research along this direction is also discussed.