Hierarchical planning of operational decisions in flexible manufacturing systems

Abstract

This study proposes a hierarchical planning model for the operational problems in Flexible Manufacturing Systems (FMSs). The functional problems included in the model are part type selection (hatching), loading and scheduling. The top level of the hierarchy deals with the hatching decisions, the second level solves the machine loading and tool allocation problem, and the lowest level detennines machine and material handling equipment scheduling. The hatching and loading levels are formulated as linear mathematical mcxiels where the loading model considers various objective functions. A Lagrangian relaxation based solution approach is also applied to the loading level, and since it is not always possible to obtain feasible solutions by this method, a Lagrangian heuristic is developed to make the solutions feasible. On the other hand, the effect of aggregation/disaggregation of information between the hatching and the loading levels upon the feasibility of top-down commands is of particular importance in the study. Finally in the scheduling level, a dispatching algorithm is developed, and various dispatching rules are tested under various performance criteria In order to perform this analysis, some mcxiel parameters are varied, and certain conclusions are drawn about these dispatching rules.