Stroage and retrieval policies in carousel storage systems

Abstract

This thesis is concerned with the carousel storage systems with a storage and retrieval (S/R) robot for handling a unit-load. The systems have been used in a broad range of applications in industries. First part of this thesis is devoted to developing a cycle time model for estimating the throughput performance under the situation that a system operator, which is usually a micro-computer, can utilize the information on the succeeding order in carousel system. Under randomized storage assignments policy, the expected cycle times are determined for both single and dual command cycles. In second part of this thesis, two variations of the standard carousel system are introduced. One is the double carousel system and the other the carousel system with two S/R robots. In order to evaluate the throughput performance of both systems, the cycle time models are developed for both single and dual command cycles. These variations can be considered as alternatives at the design stage of carousel system. Third part of this thesis deals with a class-based storage assignment policy in the standard carousel system. Three kinds of boundary shapes are considered. Under 2-class-based storage assignment policy, the cycle time models are developed from which throughput performances are presented for various values of system parameters. Finally, we consider a retrieval sequencing problem, which determines a sequence of retrieval requests to maximize the throughput performance. As a performance measure other than the throughput, energy consumption of the carousel rack is introduced. A simple heuristic procedure is proposed which considers both performance measures. With the simulation experiments, the procedure is compared with the existing ones.