Heuristic search based on Petri net structures for FMS scheduling

A heuristic search method using Petri net structures for flexible manufacturing system (FMS) scheduling is presented. To minimize makespan, an FMS scheduling problem is formulated as finding a firing sequence from the initial state to the final state of a timed Petri net model, such that the sequence reveals the minimal cost. The reachability graph is partially generated and searched. The search process is guided by a heuristic function based on firing count vectors of the state equation, predicting the total cost. Since this heuristic search exploits the linear characteristics of the state equation, which contains sufficient global information, it can efficiently generate a near-optimal or optimal solution. To deal with large systems, the proposed algorithm exploits the concurrency information to reduce the searched state space.