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Real-time piloting of flexible manufacturing systems.

Tawegoum, R.; Castelain, E.; Gentina, J.C.

In: European Journal of Operational Research, Vol. 78, No. 2, pages 252-261. 1994.

Abstract: This paper introduces management functions in real-time monitoring of FMS. We consider FMS in which the control unit is modeled using objects Petri nets. In these systems, machine round-ups connected by complex carriage systems, particular resources behavior and disruption appearance generate considerable data flow. The flexibility of the system is expressed at the control level by nondeterminism, creating resource access conflicts and encouraging parallelism of operations. Particular resource behavior and disruption appearance create dynamic stickings, which need real-time resolution methods. We aim for autonomous decisions of the hierarchical level yielding for the minimization of reflective delays introduced by perturbations. We propose a hierarchical level divided into three parts: a planing level, a schedule level and a real-time piloting level which we will detail in this paper. As the shop floor is steadily perturbed, the piloting level must use both, flexibility of machines and transport system to minimize part traveling duration. We present some efficient methods able to absorb real-time perturbations occurring during production, and to optimize resources management. The major difficulty is the estimation of the consequences induced by correcting actions. Thus, we look for a satisfying solution as a compromise between schedule propositions and current shop state.

Keywords: Petri nets, on-line production control, priority functions, real-time systems, scheduling rules.

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