Modeling FMS by Closed Queuing Network Analysis Methods

The problem of scheduling concurrent lots of different components on a flexible manufacturing system (FMS) structured with a closed transportation network is approached. The production model and hence the decision/control process is seen here decomposed in two hierarchical levels. 1) At the lowest (microscopic) level, with a heuristic closed queuing network analysis, the average throughputs of the different lots contemporaneously present in the system are estimated. Routing of parts has the objective of balancing machine utilization. 2) At the highest (macroscopic) level, given the throughput estimates, lots are scheduled in order to optimize a production performance index and to satisfy release and due date constraints. Time-phased orders formaterials and decisions for sequencing lots on the FMS are generated.