On decentralized on-line scheduling of FMS

Abstract

The scheduling problem is considered for medium sized (5-10 machines or workplaces) flexible manufacturing systems which are part of a larger production process. The general philosophy is to divide the scheduling problem into a number of local decentralized problems: the optimal sequencing and routing of the jobs within flexible manufacturing systems or small workshops. The subsystems are coordinated by an upper-level scheduler. It assigns the due dates for the completion of operations in the subsystems and determines the earliest possible starting times from the dependencies among the operations and the externally determined starting conditions. Based on the mathematical description of decision-free manufacturing systems in terms of minimax algebra, the coordination of the subsystems can be achieved in a very simple manner. In this study the behavior of local on-line scheduling algorithms is investigated. The local control laws are based on priority rules augmented by look-ahead strategies.<>