經濟訂購量條件下的存貨調節機制

Transshipment Mechanism Using EOQ

張智超(Chih-Chao Chang)

指導教授 ： 陳靜枝

國立臺灣大學/管理學院/資訊管理學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.02442

摘要

在存貨管理問題中，供應鏈成員(例如零售商)都常利用經濟訂購量模式或最小最大政策來管理存貨。然而，由於等待貨品從上游供應商送達的可能需要相當長的前置時間，導致大量的安全存貨來因應需求的不確定性。本研究提出存貨調節機制，地理位置相近的供應鏈成員會自動形成群組。群組內的成員可以互相轉運存貨，藉以將存貨水準調整至正常的範圍內。在存貨調節機制下，當本期需求量過低時，供應鏈成員可以將過剩的存貨轉運給同群組內的其它成員，因此可以節省存貨持有成本。另一方面，當本期需求量過高時，及時地從同群組其它成員補充到存貨可以增加銷售量並維持顧客的滿意度。
利用轉運進行存貨調節機制會產生額外的成本支出。對於存貨調節機制的賣方來說，主要的成本為作業成本。賣方可以藉由轉運降低存貨持有成本並賺取賣出商品的價差。對於存貨調節機制的買方而言，相關的成本包含了查詢成本、作業成本、轉運價差、及運輸成本。然而，買方可以藉由轉運增加額外的銷售而獲利。
本研究建立數量模式來找出最佳的轉運數量，並利用數值分析區分適合應用存貨調節機制的狀況。分析結果發現賣方如果將多的藉由轉運運送給買方是有利的話。此種狀況下，群組內可以採用存貨調節機制。
由於無法直接從數量模式得到封閉解，故改由搜尋的方法找最佳解。本研究根據需求分配特性的不同，提出單峰二分搜尋法與全域搜尋法二種不同的演算法來找最佳的轉運數量。另一方面也利用模擬的方式進行驗證。在基本經濟訂購量模式下設計16種不同的情境、在非一次送達經濟訂購量模式下設計32種情境、而在數量折扣經濟訂購量下設計32種情境。模擬的結果發現當需求不穩定時，採用存貨調節機制可以提高供應鏈成員的淨收益，同時也亦能提高群組的總收益。

關鍵字

轉運 ； 群組 ； 供應鏈水平整合

並列摘要

More often than not, a member in a supply chain(e.g. a retailer) manages its inventory based on the traditional EOQ model, or the min-max inventory policy, with simple modifications. However, since the lead time could be long, a member usually has to keep high safety stocks for so many merchandise items to meet the high service level requested by the customers. This study suggests differently that the member nearby in the same echelon should form a cluster to encourage the transshipment of stocks, so as to adjust every member’s inventory to the regular target level. Under this mechanism, the members with excess inventory are able to sell these surplus stocks, due to lower-than-expected demand, to those in short supply in the same cluster, and hence to reduce the carrying costs from keeping the excess inventory. On the other hand, the members in the same cluster running out of stocks also benefit by the timely supplies, which normally come faster than those from their suppliers, to serve and keep their customers.
The transshipment itself incurs additional costs. For the members with excess stocks, called “sellers”, to provide, the major cost incurred is the operation cost for the transshipment operation. Yet sellers also benefit from clearing up excess inventory, and by doing this, it leads to a lower carrying cost. Moreover, they are able to earn margins from the difference between their own purchase and selling prices. For the members requesting the transshipment, called “buyers”,, the costs include the communication / query cost, operation cost, the price difference and the transportation cost. However, buyers benefit from the orders they would have lost without those supplies, and hence revenue is increased by the transshipment.
This study constructed a mathematic model to find the optimal transshipment quantity for both parties and present the quantitative analysis to clarify the proper use of the transshipment mechanism. Because the mathematic model is too complicated to obtain a close-form solution, two search algorithms, BSA and GSA, were proposed in this study to find the optimal transshipment quantity based on the shape of the demand density functions. As results, the search algorithms provided the same optimal solution as the one found by using simulation model in 16 scenarios with basic EOQ model, 32 scenarios with non-instantaneous EOQ model, and 32 scenarios with quantity discount EOQ model. The results show that it is reasonable to adopt a transshipment mechanism to increase a member’s own net profit when facing abrupt demand, and even to benefit the cluster as a whole.

並列關鍵字

Transshipment ； Cluster ； Inventory Management ； EOQ Model ； Horizontal Supply Chain Management

參考文獻

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