Echelon-based Inventory Monitoring Schemes in Convergent Supply Chain
           

- 指導教授 黃漢邦 博士 研究生 黃守敬

- Advisor :Dr.Han-Pang Huang Student :Shou-Ching Huang

Lab. of Robotics., Department of Mechanical Engineering National Taiwan University Taiwan
Abstract:

Confronting the variable market demand and the global competition, enterprises must do the plan based on the entire supply chain view, so they can make end products more competitive. For a production system, WIP inventory is a good index to monitor. If WIP inventory control limits of the system are set appropriately, the influence of production variations would be reduced and the target service level would be reached. The upstream stage of convergent supply chain has more then one member. They produce different semi-finished products with different finish time, and then transfer to the downstream factory to assembly. Also, there are many uncertainties during production processes. The above mentioned characters make the convergent supply chain hard to be managed.
Previous researches which mostly focus on the sequent supply chain. Differently, this research focuses on the property of convergent supply chain, that is, multiple suppliers and one assembly factory. This research also attempts to develop a supply chain monitoring scheme based on the concepts of echelon WIP inventory and CONWIP system. The first step in the proposed scheme is to decide the planned lead time of each stage. Then we take the features of uncertainties of production into consideration, and construct a two-echelon model which has two suppliers and one assembly factory. Simultaneously, under the service level constraints, this model is constructed with the goal of minimizing the echelon WIP inventory control limits of the supply chain. In addition, the model is extended to have multiple suppliers and one assembly factory. Finally, an algorithm which solves the developed model is provided by utilizing the property of the positive relationship between standardized WIP inventory control limits and supply chain service level. With the resulting echelon WIP inventory control limits from the model, the proposed monitoring scheme has been validated through the simulation. Conclusions are drawn as follows:
(1) By the algorithm, the proposed scheme can effectively derive the two-echelon WIP inventory limits, which is lower than the stage-based WIP inventory limits of the supply chain.
(2) The proposed echelon-based monitoring scheme can obtain a higher service level under the lower inventory levels.



中文摘要:

面對現今多變的市場需求與全球性的競爭，企業必須以供應鏈的角度出發進行整體規劃，才能讓產品具有競爭力。對於生產系統而言，在製存貨是有效的監督指標， 在製存貨上界設定得當，可以降低生產變異之影響，進而滿足整體供應鏈達交產品給客戶的服務水準目標。組裝式供應鏈上游階段有許多成員，各成員彼此生產不同 的半成品，並在不同的時間內完成。半成品之後輸入共同的下游廠商進行組裝，且在生產過程中存在有不確定性，如此複雜的特性形成管理上的困難。


有別於過往研究多針對序列式供應鏈系統，本研究考慮組裝式供應鏈上游至下游有多對一的特性，應用層級存貨觀點以及CONWIP概念，建構組裝式供應鏈在製 存貨水準之監督機制。首先利用數學方式估計出供應鏈各個階段的規劃生產時間。接著以滿足目標服務水準為前提，並將生產不確定性納入，建構最小化整體在製存 貨上界之二對一兩層級供應鏈模式，再擴展模式至多對一兩層級供應鏈。最後透過模式中標準化在製存貨上界與供應鏈服務水準之間的正向關係，發展模式之求解演 算法。本研究利用求解模型所得到的各層級在製存貨上界作為監督指標，並經由模擬，驗證以該上界進行生產監督之有效性，得到下列結論：


(1) 藉由本研究提出之演算法，可有效得到二對一兩層級供應鏈模式中，各層級之在製存貨上界，且整體上界略小於以階段觀點求得的結果。
(2) 以層級在製存貨取代階段在製存貨作為監督上界，使整體供應鏈系統能夠以較低的在製存貨量，得到較佳的服務水準。