Two-layer online scheduling of flexible manufacturing systems

The authors address the scheduling problem in production units which consist of several subsystems, e.g. workshops or flexible manufacturing cells. A two-layer architecture is proposed; on the local level, intelligent control units perform an optimization, and the upper-level scheduler coordinates the subsystems. The coordination problem is solved based on the mathematical description of the overall system in terms of the so-called minimax algebra. The proposed decomposition-and-coordination strategy will be successful if local schedules can be found such that the local deadlines are met. Algorithms that avoid excessive delays for local scheduling problems are discussed