Transforming time constraints of a GRAFCET graph into a suitable Petri net formalism

GRAphe Fonctionnel de Commande Etape Transition (GRAFCET) is a powerful graphical modeling language for the specification of controllers in discrete event systems and an international standard since 1988. It contributes to a more structural and model driven approach in the design of logic controllers but still lacks an exhaustive formal definition. As a step towards an exhaustive formal definition of GRAFCET this paper discusses time dependencies, as they are defined in IEC 60848, by comparing them to time constraints of timed Petri nets and Time Petri nets. Based on this analysis the authors propose an extension of a formal model for GRAFCET, which is a specific type of a control interpreted Petri net.