On-line Deadlock Avoidance for Complex Routing Flexible Manufacturing Cells

The time for electronically connecting business and manufacturing has come. Advancements in e-commerce have requested that business decisions on web be the direct driving info to the corresponding manufacturing activities without human interventions. Since orders from the web may arrive in random sequence and with a range of specifications, flexible manufacturing systems (FMS) may be the proper automata for the basis of e-manufacturing. An FMS is designed to handle orders having moderate variations in both part style and quantity. The computerized nature of the FMS makes it readily adaptive to the web-based information system. However, processes run by the FMS may not be fully automatic because of potential resource conflict, i.e. a floating characteristic relationship between system facility and production orders. Since coordination between system facility and unpredictable orders is difficult, this paper will present an off-line simulation approach to reveal the embedded relationship and then avoid the conflicts on-line. The method employs three dispatching rules individually to direct the process flows inside a flexible manufacturing cell (FMC), and acquires potential deadlock patterns of part processing sequence from an off-line simulation. Then an on-line matching/reordering process is used to keep the incoming orders dissimilar to the deadlock patterns. Two major advantages have been achieved by the proposed method: it provides an effective routing mechanism for deadlock-free production on randomly arrived orders, and it improves the feasibility of any planned schedules by removing the potential of resource deadlock. This research uses timed Petri nets to simulate the flexible manufacturing cell. Three dispatching rules, which generate pull tendency at cell exit, are employed and compared to demonstrate the routing mechanism.