A HIERARCHICAL MODEL FOR CONTROL OF FLEXIBLE MANUFACTURING SYSTEMS

Flexible Manufacturing Systems (FMSs) are usually composed of general purpose machines with automatic tool changing capability and integrate d material handling. The complexity of FMSs requires sophisticated con trol. In this paper we present a four-level control hierarchy and outl ine computationally feasible control algorithms for each level. The to p level is concerned with the choice of part types and volumes to be a ssigned to the FMS over the next several months. The second level plan s daily or shift production. Production levels are set and tools are a llocated to machines so as to minimize holding and shortage costs. Var ious FMS environments are presented. The third level determines proces s routes for each part type in order to minimize material handling. Ad ditional tools are loaded on machines when possible to maximize altern ate routeing. Routes are then assigned to parts to minimize workload a ssignment, and these are used by level four for actual routeing, seque ncing and material handling path control. The level three model is for mulated as a linear program, and heuristics are used for level four. A n example is provided to illustrate the completeness of the decision h ierarchy and the relationships between levels.