Petri Net and Hybrid Heuristic Search-Based Method for Energy-Minimized Scheduling of Flexible Assembly Systems with Tool Change Processes

With the increasing concerns about energy consumption and environmental protection, minimizing energy consumption while ensuring desired productivity becomes more and more important in flexible assembly systems (FASs) design and operation. However, because of the complexity of deadlock-prone FASs, only a few researchers have addressed their scheduling problems. Besides, no existing literature in the field of scheduling of deadlock-prone FASs takes energy consumption minimization as the optimization criterion to our best knowledge. This paper presents an A^*-based hybrid heuristic search algorithm to minimize the total energy consumption of FASs with tool change processes. Based on a developed Petri net (PN) model, two energy functions are proposed to calculate the energy consumption of FASs. To achieve better performance, six new heuristic functions are designed to guide the search process by considering the features of FASs. Besides, two selection functions are proposed to evaluate the prospects of vertexes and choose the promising ones. Moreover, a dynamic window is applied in the algorithm to limit the search space, and a deadlock prevention policy is used to ensure feasible schedules. Experimental results show that the proposed algorithm can effectively find feasible schedules for FASs, and a well-designed heuristic function is likely to obtain schedules to meet industrial application requirements.