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Improvement of delivery times by dynamic vehicle routing in automated material handling systems for semiconductor industry
In the last couple of years, a high level of automation was integrated in the factories of semiconductor industry. This implies the whole production process as well as the material delivery process. An automated material handling system (AMHS) is such an integrated automated transport solution of today's 300mm semiconductor waferfabs. These AMHS are based on a direct delivery approach (unified) model with alternative flexible storage systems to handle surges of lots in process or unplanned events. As the 300mm fabs are very large and the number or process and handling steps is rising, a fast and reliable transport system with short delivery times is required which, in addition, minimizes its footprint inside the expensive clean room. Currently, the implemented transport solutions are based on overhead hoist vehicles (OHV) which have to cope with several problems. On one hand there is an increasing traffic on the whole track system caused by the increasing number of processsteps. On the other hand there is a higher number of hoist-actions as a result of new storage strategies. Instead of large central stockers, distributed tool assigned Under Track Storages (UTS) are used. Both issues mentioned can result in vehicles blocking track sections frequently. This can cuase accumulations which lead to high variances in delivery times and make the delivery time for loads in this system less predictable. An additional effect might be the increased idle times of expensive process equipments, which need to minimized. This paper describes an approach of dynamic vehicle routing and identifies simulation based improvements of the AMHS performance. Furthermore different vehicle routing strategies are presented and compared.