Abstract
This paper proposes an integrated hierarchical control and scheduling scheme based on Petri net formalism for flexible manufacturing cells (FMCs). The proposed scheme is divided into two main hierarchies: the lower one is the control level and the upper one is the scheduling level. The two levels use a common model representation, colored timed Petri nets (CTPNs), to specify the pallet flows of FMCs graphically. In the control level, the CTPN model can be served as a mechanism to dispatch shop-floor activities within FMCs. In the scheduling level, the same model can be served as a scheduling representation which can describe process precedence relations, resource and time constraints graphically. Dispatching rules are combined with the CTPN simulation to perform the cell-level scheduling. An FMC currently being set up at the Mechanical Industrial Research Laboratories, Taiwan is exemplified to illustrate the proposed methodology throughout this paper. Moreover, under this scheme, detailed refinements concerned with the CTPN-based scheduling, the CTPN-based dispatching and the trace-based monitoring are also described. © 1997 Elsevier Science Ltd.