During the last decade, in the area of material handling, unit-load automated storage/retrieval systems(AS/RSs) have been the subject of many researches. The needs for automated warehouses which handle small parts often found in electronic, pharmaceutical and chemical industries are expected to increase in the near future. In this regard, this thesis deals with the problems arising in the design and operation aspects of small-part handling warehouses such as storage carousels and man-on-board(MOB) AS/R systems.
First part of this thesis is devoted to developing a design model of a storage carousel in which storage racks are rotating so that items can be picked without any travel of the S/R machine in the warehouse. We develop an analytic model to evaluate throughput performance of the system. And then, based on the results, we present a mathematical model for designing an economical configuration of the system which satisfies the required throughput. The model incorporates both initial investment and operating costs. A partial search procedure is employed to obtain an optimal solution and implemented on an IBM PC.
Three fundamental policies in warehouse operation are where to store items (storage policy), how to combine orders to form batches (batching policy) and how to sequence items within a batch (batching policy) and how to sequence itemswithin a batch (picking policy). These policies are closely related to system efficiency and often required in simple form to ensure fast and efficient results. Second part of this thesis focuses on developing efficient rules for each policy in an MOB AS/RS. For the batching policy, an optimization model is derived with the objective of minimizing total processing time. Then, taking into account of the operation characteristics in the S/R system, heuristics are developed for the model based on cluster analysis, and compared with existing algorithms through computer simulation.
Next, a heuristic procedure is developed for item storage assignments considering both order frequency and order structure. The heuristic consists of two stages: one is related to the generation of an initial storage layout, and the other, the improvement of the initial layout by pairwise exchanges.
Finally, we consider the order picking problem in which both storages and retrievals are performed together in a trip of the S/R machine. The problem is formulated as a variant of the classical traveling salesman problem due to some additional constraints involved. A dynamic programming approach is developed to solve the problem.
70년대 후반부터 각종 자동창고에 대한 수요가 증대되고 그에 대한 연구가 활발히 진행되어 왔다. 향후에는 전자제품이나 의약품등과 같은 소형의 물품을 저장하는데 적합한 캐러젤(Carousel) 시스템이나 작업자 탑승식(MOB : Man-On-Board) 자동창고들에 대한 상대적인 수요가 점차 커지리라고 전망된다. 본 연구는 이러한 시스템들을 다루고 있는 데, 크게 캐러젤 시스템의 경제적 설계 모형 개발과 MOB 시스템의 효과적인 운영 방안 제시등의 두부분으로 구성된다.
우선, 캐러젤 시스템의 설계를 위한 성능평가 모형으로서, 단위 시간당 작업물량 (혹은 단위작업당 소요시간)을 추정하는 분석적 모형을 개발하고, 다음으로 이러한 성능평가 모형을 사용하여, 요구되는 성능수준을 만족하면서 초기 투자비용과 운영비용의 합을 최소로 하는 수리적 설계 모형을 정립하였다. 아울러 최적 설계안을 구하기 위한 해법으로서 부분적 탐색절차(partial search procedure)를 제시하였다.
MOB 시스템의 운영상 고려해야 할 전략으로는, "물품의 불출 주문 처리를 위한 주문 그룹 형성(batching policy)", "개별 주문 그룹 처리를 위한 입출고 기기(S/R machine)의 주행 행로 결정(picking policy)" 및 "물품의 창고내 저장 장소 결정(storage policy)"등 에 대한 것들을 들 수 있다.
각각의 운영 전략에 대하여 본 연구는 최적해를 보장하는 수리적 모형을 정립하고, 규모가 큰 실제 문제를 해결하기 위한 효과적인 발견적(heuristic) 해법을 제시함과 함께, 기존 방법들과의 비교를 통해서 그 효용성을 평가하였다.
