Local modular supervisory control applied to the scheduling of cluster tools

In previous work, we have proposed a methodology for the local synthesis of modular supervisors in the context of timed discrete-event systems. The synthesis of each local supervisor is performed considering only the components of the system that are directly affected by the corresponding control specification, granting a reduction in computational cost in comparison with existing approaches. In addition, the control action of the local supervisors thus obtained is relatively simple, making them easier to implement, comprehend, and modify. In the present paper, we show an application of this methodology for the control and scheduling of cluster tools, which have been increasingly used for wafer fabrication processes in semiconductor manufacturing. We locally enforce the specified behavior for each part of the system, and then design a coordinator that both solves the conflict among the local supervisors and imposes a schedule for wafer production. The resulting global behavior is optimal, in the sense that it ensures maximum wafer throughput while respecting all specifications in a minimally restrictive way.