An approximation schema for the estimation of buffer sizes for manufacturing facilities

A unified approach to the production planning and scheduling problem of a flexible manufacturing system with failure-prone machines 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 the concept of a buffer hedging point is introduced and used to obtain the size of the machine buffers and to derive the schedule for the manufacturing system. The estimation of the buffer size is not based on any optimization procedures; instead, it relies on an argument that allows decoupling of the operation of every machine. 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 and from several simulated cases