多種服務組合考量下發散式多階(S-1,S)存貨系統之研究

Abstract

本研究探討發散式多階(S-1,S)存貨系統，在此存貨系統中假設最下游組裝點的顧客需求服從卜氏分配且各自獨立；及各組裝點的加工及運送時間為任意的分配。在給定了最下游組裝點顧客要求的服務水準與等待時間限制後，以最小化系統總持有成本為目標，求解整個系統的存量最佳配置。本研究發展了一套啟發式演算法，第一步驟：將多階的存貨系統化簡為二階(S-1,S)存貨系統，求解在服務水準限制下，此簡化的二階(S-1,S)存貨系統的最佳配置；第二步驟：將第一步驟的下游組裝點往下展開為二階存貨系統，由第一步驟求得的下游組裝點(即此二階存貨系統的上游組裝點)最佳存貨水準，在服務水準的限制下求解下游組裝點的存貨水準；第三步驟：重複步驟二，直到展開到最下游組裝點為止；第四步驟：由最下游組裝點驗證是否滿足等待時間的限制，若滿足則停止，否則由最下游組裝點再往上推演，以計算滿足等待時間限制之最佳存貨配置。隨之，以一案例說明此演算法。最後，並探討成本與等待時間及服務水準的關係。

The problem that we address is to determine appropriate safety stocks in a multistage divergent system for a high cost and low demand item. In this study, we proposed an approach for determining appropriate of safety stocks regarding holding cost objectives and service level and waiting time restrictions. The multistage divergent (S-1,S) inventory model assumes that customer demands of final stage are independent Poisson process, and the distributions of processing and transportation time of each stockpoint are arbitrary. The proposed approach are developed according the following steps, Step 1: Simplified the multistage inventory system to a two-echelon (S-1,S) inventory system. Thus, under the consideration of service level restriction, we determine appropriate safety stocks for the two-echelon (S-1,S) model; Step 2: Expand the nodes in second echelon to a two-echelon (S-1,S) inventory system. To determine appropriate safety stocks for the nodes of second echelon in the two-echelon (S-1,S) inventory system; Step 3: Repeat Step 2 to the final stage; Step 4: Verify whether or not the safety stocks satisfy the waiting time constraints. Finally, an example is given to illustrate the proposed approach.