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Cyclic Schedules in Flexible Manufacturing Systems with Flexibilities in Operating Sequences.

Camus, H.; Ohl, H.; Korbaa, O.; Gentina, J.C.

In: Proceedings of CIMAT 1996. May 1996.

Also in: First International Workshop on Manufacturing and Petri Nets, 17th International Conference on Application and Theory of Petri Nets, pages 97-116. June 1996.

Abstract: In this paper, we present an extension of the systematic approach of modeling ratio-driven Flexible Manufacturing Systems with Petri Nets presented in Ohl et al. We enrich our method with the possibility of considering flexibilities in operating sequences. And the aim remains to compute a cyclic and deterministic schedule. The choice of this kind of schedule can be justified by three main reasons: it can be easily implemented. As the state of the system is known at every moment, we can easily react against production change, machine breakdowns, although it is an off-line scheduling. Finally the production constraints (throughput, routing ratios, ...) are satisfied over a minimal set of products.

The fact that we take into account flexibilities can constrain us to increase the production horizon which can be characterized by a multiplying factor n of the minimal set of products defined by Ohl, in order to obtain the optimal performance (throughput minimizing) of the system. However the assumption of a repetitive behavior of the command forces us to work with a production horizon as small as possible. So the approach consists in the optimization of the three criteria: throughput, production horizon and naturally Work In Process.

We focus on the importance of optimizing simultaneously the factor n and the cycle time of the system, considering in a first phase a sufficiently large W.I.P. The second phase consists in the minimization of the W.I.P. We illustrate our approach with an example for a better comprehension.

Keywords: Cyclic Schedule; Flexible Manufacturing Systems, Flexibilities.

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