Multiple objective scheduling for flexible manufacturing systems using Petri nets and heuristic search

A scheduling method that uses Petri net modeling and heuristic search is extended to simultaneously optimize multiple objectives which exist in flexible manufacturing systems (FMSs). This method formulates the problem with a timed-place Petri net model and applies a search algorithm, a multiple objective version of algorithm L1, to the reachability graph of the Petri net model in order to generate an optimal or near-optimal schedule. A multiple objective version of algorithm L1, Multi-L1, is proposed to optimize the multiple objectives. Multi-L1 employs an evaluation function including multiple objectives. New heuristic functions are developed for efficient search. Experimental results are presented to show the effectiveness of the proposed method.