Scheduling method with the consideration of machine setup in flexible manufacturing systems

A scheduling method that uses Petri net modeling and heuristic search is extended to handle the tool setup. The machine setup is to attach a tool to a particular machine and detach the tool from the machine, and this is a time-consuming activity. The processing time of operations varies according to the attached tool and the machine used. The method proposed in this paper uses timed-transition Petri net to model these features and applies a search algorithm to the reachability of the Petri net model to generate an optimal or near-optimal schedule. In addition, this method can determine how many tools are needed in order to reduce the makespan. Search algorithm employs an evaluation function to guide the search procedure. New heuristic functions are developed for efficient search. The experimental results that show the effectiveness of the proposed method are presented.