對於提昇倉儲管理的效率而言，揀貨作業是最重要的關鍵因素。過去對於揀貨作業的研究，大都只考量到單一揀貨員；但在實際的倉儲系統中，通常都會有多個揀貨員同時在同一區域內進行作業。這種多人作業的倉儲系統，有可能會發生阻塞的情況，所以僅使用行走時間或距離無法評估揀貨的績效，必需加入人員的等候時間，才能反映整體作業的效率。本研究視揀貨模式為一個等候網路，同時考慮揀貨人員的等候時間與行走時間，並提出一種啟發式儲位指派法則，使得訂單平均完成揀貨的時間為最小。本研究利用eM-plant模擬軟體發展倉儲模式，以執行啟發式儲位指派法則，並進行模擬測試，以比較所提出啟發式法則的績效，而結果顯示啟發式法則的確優於傳統指派法則。

Order picking is one of the most important key factors for an efficient warehouse management. Most of previous research in order picking considered only single-picker operation; however, there are often multiple pickers concurrently working at the same region in a real warehouse system. Since congestion may occur in such a multiple picker system, waiting time must be taken into account together with travel time or travel distance in the evaluation of the efficiency for the picking operations.
The purpose of this research is to study the effect of congestion on the order picking operations in a multiple picker warehouse where the picking follows the walk-and-pick method of order retrieval with sequential one-way travel. The picking model can be treated as an closed queueing network and this research subsequently develops a heuristic storage assignment policy by considering both the travel time and the waiting time simultaneously by minimizing the average time of order fulfillment. This paper compares the mean travel time for different storage assignment policy. A simulation model is proposed and developed to implement the heuristic assignment storage policy using eM-plant software. The simulation results show that the proposed heuristic policy outperform the existing traditional storage assignment policies in a multiple picker warehouse environment.

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