パレツトを積載保管する倉庫における部品の保管位置割当問題

摘要

本研究で対象とする倉庫は，組立直前に必要な部品を取り揃えるフォワードエリアと，そこへ補充するために比較的長期間に渡り部品を保管しているリザーブェリァに分かれている.このリザーブエリアでは，保管する部品量の增加に伴い，数段に渡りパレットの状態で積み重ねられているため部品の入出庫に伴うハンドリング時間が問題となっている.この時間を減らすためにはできるだけ広いスペースを使ってパレツトの積み重ねを行わないようにすればよいが，フォヮードエリアへ部品を補充するためのフォークリフトによる移動時間が長くなつてしまうという問題が生じる.そこで本研究ではこれらを考慮した部品の保管位置割当問題を考える.%The present case study was conducted in an automobile factory to examine improvement of total operational time. The factory warehouse described in this paper is divided into two areas: the forward area, where the appropriate parts are selected just before the assembly stage, and the reserve area, where parts can be stored for long periods of time before being used to replenish the forward area. In the reserve area, the handling time spent for loading and unloading pallets is a problem. As more parts are stored over time, an increasing number of pallets are stacked and the time taken to load and unload these pallets increases. In order to reduce this time, excessive stacking of pallets should be avoided by using as much free space as possible. However, using more space increases the travel time for the forklift when it is replenishing parts in the forward area. In this paper, we propose two policies (a storage efficiency priority policy and a handling efficiency priority policy) to direct the manner in which pallets are stored and reduce the handling time involved in the storage and retrieval of pallets. The effectiveness of these policies is evaluated by assessing the relationship between storage location and unit-load to handling time and travel time. The results of our investigation reveal that handling time is the most time-demanding task in the warehouse when stacking pallets. Therefore, increasing the effectiveness of the storage stage should be based on reducing handling time.