Reactive Scheduling in FMS: an Integrated Approach based on Petri Nets, Genetic Algorithms and Simulation

This paper focuses on handling disruptions in Flexible Manufacturing Systems (FMS). There are several issues which make this problem especially difficult to translate to real life systems. First the lack of appropriate tools which both capture the essence of such systems and provide optimization tools and second, the complexity of such systems which make the scheduling and re-scheduling process especially hard. We propose an approach, denoted here as AFS Petri Net, which consists of three stages: The first stage concerns the development of a model based on the Petri Net formalism; in the second stage a near optimal schedule is generated by a Genetic Algorithm (GA) which uses the Petri Net model for its chromosomal representation. This GA is also used as a reactive scheduler in the third stage where the system is simulated. In particular we focus on the impact of the arrival of new orders and how there orders are handled by the reactive scheduler. This modeling-optimization approach can also be extended to other systems. Experiments show the validity of the proposed methodology.