Petri net based dynamic scheduling of an elevator system

In this paper, a hybrid model of a multiple elevator system is proposed, consisting of a timed place Petri net (TPPN) model and a set of control rules implemented via the so-called control places in the TPPN model. The Petri net model is a highly modulized structure, whose constituent modules can be classified into three types: basic movement module, loading/unloading module, and direction reversing module. The whole complete model is a combination of the copies of the above three modules. Since the firing sequences of the TPPN equate the evolution of the modeled system, they can be regarded as a schedule. A heuristic search algorithm, A* search, is thus used on the reachability graph of the TPPN model to obtain the desirable schedule. To show the feasibility of the proposed method, an emulator of the elevator system is constructed for demonstration. The experiment result for a 15-floor building with four elevators is shown to be satisfactory