A novel scheduling approach to dual-arm cluster tools with wafer revisiting

It has been shown that, for dual-arm cluster tools with wafer revisiting, a swap strategy may not be optimal. To improve the performance of such a system, a Petri net model is developed in this work. Based on it, dynamical behavior of the wafer production process is analyzed. Then, two new scheduling methods called 2-wafer cyclic schedules are presented. Cycle time analysis shows that, under some conditions, the performance obtained by the 2-wafer cyclic schedules is better than that obtained by a swap strategy. Thus, the methods presented in this paper and the swap strategy can be used to complement each other in optimally scheduling dual-arm cluster tools with wafer revisiting. Illustrative examples are presented to show the results.