A CTPN-BASED SCHEDULER FOR A FLEXIBLE MANUFACTURING CELL

摘要

This paper first presents hierarchical scheduling and control ar-chitecture for a flexible manufacturing cell (FMC) that is currently set up at the Mechanical Industrial Research Laboratories of the Industrial Technology Research Institute at Hsinchu,Taiwan. With this architec-ture, we focus on the scheduling problem of the FMC and present a scheduling mechanism based on a colored timed Petri net (CTPN) model. The CTPN model has three functions in the proposed mecha-nism: the first one is to formally describe pallet flows and resource constraints in the FMC by the event-condition relation; the second one is to analyze conflict points among the pallet flows; the third one is to evaluate the used dispatching rules concerned with the selection of machine routings, the selection of work-in-process pallets in inter-medium buffers and the assignment of the commonly used material-handling device. Using the CTPN-based scheduler, an ap-propriate combination of dispatching rules for each given batch can be selected to fit given criteria, e.g. minimum batch completion time, maximum resource utilization or minimum tardiness, etc. More-over, real-time status of the FMC can be represented in the mechanism for obtaining the on-line scheduling effect.