A unified approach to production planning and scheduling

A control theoretic approach to the production planning and scheduling problem of a Flexible Manufacturing System is considered. The proposed method is based on the concept of Gershwin´s hedging point strategy. A hierarchical controller is proposed in which the upper levels use an inventory hedging point for production planning. At the lower level of the controller we introduce the concept of a buffer hedging point and use it to obtain the size of the machine buffers and to derive the schedule for the manufacturing system. The net result is a hedging point concept that is applicable to all levels of the hierarchy. It is also shown how the buffer hedging point concept is related to the Just-In-Time manufacturing strategy. Results are presented from a small, scaled-down computer controlled flexible manufacturing system.