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This paper proposes and evaluates two Petri netbased hybrid heuristic search strategies and their applications to semiconductor test facility scheduling. To reduce the setup time, such as the time spent to bring the test facilities to the required temperatures, scheduling multiple lots for each job type together is desirable. Petri nets can concisely model multiple lot sizes for each job, the strict precedence constraints, multiple kinds of resources, concurrent activities and flexible routes. To cope with the complexities for multiple lots scheduling, this paper presents two Petri net-based hybrid heuristic search strategies. They combine the heuristic best-first strategy with the controlled backtracking strategy based on the execution of the Petri nets. The obtained scheduling results are compared and analyzed through a small-size test facility. The better algorithm is also applied to a more sizable facility containing types of resources with a total of 79 pieces and 30 jobs. The future work includes the real-time implementation of the proposed method and scheduling results in real industrial settings. Index Terms-Heuristic search, hybrid strategy, Petri net, scheduling, semiconductor test. Huanxin Henry Xiong (S'94-M'96) received the B.S. and the M.S.

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