Some Issues About Petri Net Application to Manufacturing and Process Supervisory Control

After some general considerations concerning modeling issues , the paper concentrates on the fact that places are generally interpreted as logical conditions. There are various kind of logical propositions , some (the resources) are consumed when they are used in the same way tokens are removed from places when transitions are red. Linear logic has pointed out the fact that resources had to be handled with a restricted set of logical rules and that they could not easily be handled concurrently with classical logic propositions. This can be exploited for developing modeling methods based on Petri nets. Then two cases of combining Petri nets and other formal tools are examined: Petri nets and fuzzy sets and Petri nets and diierential algebraic equations. It is shown that it is better to avoid a complex integration of the various approaches in order to keep the analytical capabilities of Petri nets. 1 Theory, tool and application When an industrial application is addressed, the major issue concerns the trade-oo between delity to reality and tractability. Typically, the theoretical results are only valid for speciic cases which do not exactly map to the actual system. The major issue is therefore to obtain a model which can be analyzed and whose behavior is not too far from that of the physical system. It is also clear that in order to cope with the complexity, a tool is required. In a nutshell, dealing with a complex application implies solving three problems: { nd theoretical results which could aid the engineers, { nd a method in order to obtain a good model of the system, { nd a tool to support the approach. Figure 1 illustrates the complexity of the relationships between theory, tool and application and allows to reene the issues arising from complex applications. When an academic group or a commercial rm decides to develop a tool, a general application domain is generally considered. However, the natural trend is that the tool has to be as general as possible. Tools such as Design/CPN, MISS-RdP or AMI may be used for manufacturing systems as well as for protocols etc. As a consequence, when a speciic application is concerned, the issues concerning modeling are twofold: