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Study On Scheduling Flexible Manufacturing Systems Using Petri Nets

Posted on:2011-07-16Degree:DoctorType:Dissertation
Country:ChinaCandidate:X L RenFull Text:PDF
GTID:1102360302991922Subject:Mechanical Manufacturing and Automation
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Due to stiff competition in today's marketplace and diversified customer demands, scheduling are playing more important roles in modern automated manufacturing systems. The scheduling problems of flexible manufacturing systems (FMS) are very complex because of some complicated relationships existing in a system such as asynchronism, concurrence, resource sharing, and flexible routes. Starting with the modeling methods and scheduling algorithms of Petri net systems, the research makes an intensive study on several problems in the scheduling process of FMS and proposes some models and algorithms. The major results are summarized as follows:1. By the reachability graph of the Petri net that models an FMS, a hybrid heuristic search scheduling algorithm is proposed based on the BF-BT search algorithm and dynamic search window technology. The BF algorithm can ensure the modeling quality. The BT algorithm can realize quick feedback. The dynamic search window can control the system scale and improve operation speed. This algorithm can achieve better modeling effects quickly as shown in an example and can be used to deal with large-scaled FMS's scheduling problems.2. The scheduling problem of FMS with due-date is studied. This research establishes a scheduling model based on Petri-nets with the goal of minimizing total tardiness. Based on dynamic decomposed due-date theory, a heuristic function is proposed with the total tardiness of each job as the indicator so as to render BF algorithm to complete scheduling process.3. Undirected Petri nets are adopted to model the route layout of an AGV system. A time-based reachable state graph is constructed with the combination of time-window. The scheduling method is used to optimize the route of bidirectional multiple AGV systems. A shortest-time routing algorithm is proposed based on BF search, which determines the present state depending on the information of its next step path. The study also studies routing algorithms of the system with multiple AGVs in two dwell modes: work station parking and equipment parking modes. A due-date AGV selection method and routing algorithm are discussed.4. For accompanied, decentralized, and distributing and sharing dispatched AGVs, the Petri net models for FMS whose jobs are integrated with AGVs are built. A Petri net model for selecting AGVs within distributing and sharing dispatchment strategy is established to optimize the control over AGV distpatching and routing. With the hybrid heuristic search algorithm, examples are used to demonstrate of all the strategies. The scheduling effects of all strategies are analyzed and compared.5. Based on the FMS with integrated AGVs, the scheduling problem considering the path traffic in an AGV system is further discussed. For different distribution strategies, the corresponding integrated FMS Petri net models considering route systems are established. We focus on FMS scheduling problems by considering route system when AGVs adopt the distributing and sharing distribution strategy. By an optimal route algorithm, due-date based AGV selection, and routing algorithm, two different scheduling methods are proposed. The scheduling effects of the two methods under different circumstances are analyzed and compared.
Keywords/Search Tags:Flexible Manufacturing Systems (FMS), scheduling, heuristic search, model, Petri nets, Automated Guided Vehicle (AGV), due-date
PDF Full Text Request
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