Automated Storage/ Retrieval Systems (AS/RS) are widely adopted in warehouses due to the advantages of reduced labor cost, high space utilization and efficient material handling. There is a recent trend in which some major air-cargo terminals and distribution centers incorporate Integrated Automated Storage and Retrieval Systems (IAS/RS), consisting of several AS/RS and some processing stations, to handle the increasing volume of international goods....[ Read more ]

Automated Storage/ Retrieval Systems (AS/RS) are widely adopted in warehouses due to the advantages of reduced labor cost, high space utilization and efficient material handling. There is a recent trend in which some major air-cargo terminals and distribution centers incorporate Integrated Automated Storage and Retrieval Systems (IAS/RS), consisting of several AS/RS and some processing stations, to handle the increasing volume of international goods.

Similar to AS/RS, the tasks in IAS/RS are to store or retrieve shipments and the operation generally consists of automated S/R machines. The difference between the two systems is that IAS/RS involves an additional transfer task and the amount of equipment required to transfer shipments is larger. Due to the small amount of equipment in AS/RS, most researchers focus on the sequence of tasks to be handled by the S/R machine. However, shipment routing is rarely addressed in the literature. Shipment routing refers to the way a shipment is transferred from an entry point to the exit point. It is a significant and difficult operation in IAS/RS. Considering the fact that many shipments are routed through the system, any traffic congestion owing to poor shipment co-ordination can hinder the shipments from completing their routes, and the congestion eventually worsens the system performance. Hence, an effective shipment routing strategy, which enhances shipment co-ordination, is vital to improve the system performance of IAS/RS.

In this thesis, we have studied and evaluated several routing strategies including static single shortest path (SSSP), adaptive single shortest path (ASSP) and the proposed strategies of flow diversion among multiple paths (FMP) and adaptive flow diversion among multiple paths (AFMP). We have conducted simulation experiments to evaluate several routing strategies. When compared with SSSP, the proposed strategy of AFMP achieves 14.1% and 32.7% improvement of total shipment traveling time in the two simulation experiments.