(A) study on automated warehouse systems considering the operating characteristics of the storage and retrieval machine

Abstract

During the recent several years, a considerable number of unit load automated storage/retrieval systems(AS/RS) has been installed in the domestic industries. It is expected that the demand for automated carousels will be increasing in the near future due to its capability to handle small-sized parts often found in electronic and pharmaceutical industries. The installation costs of these automated warehouse systems are usually very expensive. Thus acurate estimation of the throughput rate and high utilization of the systems once installed become key issues since they are closely related to design and operation of the systems. In this regard, this thesis deals with the throughput estimation of both systems and storage assignment policy of unit load AS/RS. First part of this thesis is devoted to developing the continuous analytical models of travel time which integrate the operating characteristics of storage/retrieval(S/R) machine such as maximum velocity and acceleration/deceleration rate in unit load AS/RS. Under a randomized assignment policy, the expected travel times are determined for both single and dual command cycles. The models developed are evaluated through simulation results. Second part of this thesis is an extension of the first part to automated carousel. The travel time models are developed which take into account of the operating characteristics. Each of the distributions of storage, interleave and retrieval time is obtained. Finally, we propose an energy-consumption-based storage assignment rule characterzed by finding the storage location to which S/R machine travels with minimum energy consumption. Randomized and full turnover-based storage assignment policies are evaluated considering the operating characteristics of the S/R machine. The proposed rule is compared with the existing assignment rules from the viewpoint of energy consumption. The results show the significant energy savings of the proposed rule over the others.