Petri-Net based modeling and scheduling of a flexible manufacturing system

In this paper, a timed place Petri-net (TPPN) model for flexible manufacturing systems with the components of machines, limited buffers, robots and the material handling systems, automated guided vehicles (AGV´s) is constructed. Since a firing sequence of the TPPN from the initial marking to the final marking can be seen as a schedule of the modeled FMS, by using an A* based search algorithm, namely, Limited-Expansion A algorithm, a near-optimal schedule of the part processing can be obtained using reasonable computing time and memory requirement. For a large volume of parts, the authors also propose an adaptive scheduling approach to generate a near-optimal schedule in an economical computing time. In order to show the effectiveness of the proposed method, a prototype FMS in the Automation Lab of the Department of Mechanical Engineering, National Taiwan University, is used as a target system for implementation