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Grafcet or function charts for control systems is an international standard used for the specification and the implementation of logic controllers in manufacturing systems [1], [2]. This model is the basis of the Sequential Function Charts (SFC) international standard used for the implementation of logic controllers. Throughout the twenty years that have passed since it was defined [3], Grafcet is becoming widely used in the industry [4] and in education [5]. The main contribution of Grafcet, which uses a Petri-net like formalism, is that it allows a clear modelling of inputs and outputs and of their relations. It also allows modelling of concurrency and synchronisation. This makes Programmable Logic Controllers (PLCs) more tractable and simplifies the simulation of the control logic of the system. Many PLC builders today use the Grafcet as a specification and/or as a programming language. Among the large companies using it widely or recognising it as an internal standard are: Siemens, Renault, Peugeot, Michelin, and others. However, and in spite of its advantages, Grafcet has long been criticised because it is not supported by a formal foundation that allows to insure correctness and safety requirements on the one hand, and because it lacks adequate methodology that allows an efficient development of high quality models in the case of complex systems on the other. |
