FMS scheduling based on timed Petri net model-minimization of total deadline over-time

Scheduling of manufacturing process is one of the significant problems in FMSs. Requirements for the FMSs´ scheduling are as follows: (1) it is easy to formulate a problem; and (2) semi-optimal solution can be found within short time. However, no scheduling method which meets these requirements, has been proposed yet. This paper presents a new scheduling method for a manufacturing system based on a Petri net model and a reactive fast search algorithm. The following two typical problems are addressed in this paper: (1) minimize the maximum completion time; (2) minimize the total deadline over-time. As for problem (1), a search algorithm which combines RTA^* and rule-based supervisor is proposed. Since both RTA^* and rule-based supervisor can be executed in a reactive manner, machines and AGVs allocations can be scheduled reactively, and simultaneously. As for problem (2), original Petri net model is converted to its reverse model and the algorithm developed in problem (1) is applied with regard to the due time as a starting time in the reverse model, and then some minor refinements are considered to get a feasible solution. The usefulness of the proposed algorithm is also shown through some numerical experiments