(A) study on man-on-board storage and retrieval warehousing system

Abstract

This thesis is concerned with man-on-board (MOB) storage and retrieval (S/R) warehousing system which is suitable for storing the items of small size and light weight. Due to such benefits as lower initial investment cost and flexible nature in S/R operations compared with unit-load automated storage and retrieval system (AS/RS), the MOB systems have been widely used in industries. First part of this thesis is devoted to developing the expected travel time models considering the operating characteristics of the S/R truck. Under three storage assignment policies, random, turnover-based and class-based assignment, the expected travel times are determined for single command cycle. The expected dual command travel times are determined under random storage assignment policy. Second part of this thesis deals with the order sequencing problem. It can be formulated as the traveling salesman problem whose optimal solution can be hardly found for large problems within a computational time limitation. A heuristic procedure is presented for the problem of sequencing a given set of retrieval requests. The validity of the procedure is investigated through computer simulation. Finally, we consider design aspect of the MOB system. A nonlinear integer model is developed for the design parameters such as system length and height, and the number of aisles. We propose a search algorithm to find an optimal values of those parameters. Through experiments, the effects of the storage volume, the system throughput and the predetermined height for the operator``s safety are investigated on the total cost. A comparison of the MOB system is made with the miniload AS/RS.