Simple blocking prevention for bay type path-based automated material handling systems

This paper proposes a simple blocking prevention method for a path-based automated material handling system (AMHS) such as a semiconductor fabrication line. Here, blocking means the situation in which a vehicle stands and waits without doing anything because the vehicle in front of it is in the process of loading or unloading. Since a typical bay type path-based AMHS has a single path in each bay and no sidetracks, the blocking issue is inevitable in a large complex system with many vehicles. The proposed method is based on the swapping of load assignments between retrieval vehicles on the same path. Our simulation study on an example semiconductor line shows that the proposed method improves the AMHS productivity under various vehicle dispatching rules.