A generalized Petri net modeling approach for the control of re-entrant flow semiconductor wafer fabrication

Re-entrant flow manufacturing lines, such as occur in semiconductor wafer fabrication, are characterized by a product routing that consists of multiple visits to a workstation or group of workstations during the manufacturing process. In this paper, a modeling approach is based on the use of generalized Petri nets for a re-entrant flow manufacturing line is presented. Specifically, three Petri net models representing a re-entrant flow line with three work centers and six machines are modeled. How these models may be used to represent a variety of queuing disciplines and work release policies is discussed.