在隨機需求與交貨時間保證下之存貨決策

儘管隨機存貨模型已經被廣泛的研究，在結合時間觀點之服務保證還有隨機存貨之系統之影響還有系統表現卻還是有待研究之主題。在本研究中，我們將交貨時間保證做為競爭條件並且建構隨機存貨模型來展示在確定性投資與運輸延遲風險間平衡點之拿捏。交貨時間由在系統中之等待與生產時間與運輸時間兩者加總。需求是由外界產生的，並且對於價格高低與交貨時間之保證長短有密切關係。相對於在此領域比較熱門之趕工策略，我們藉由建立門檻存貨水準之存貨決策來滿足提供給客戶之交貨時間保證。我們建立一個以最佳利潤為目的之模型，並且探討存貨決策與價格、交貨時間長短等等之關係。我們使用兩個數值分析模型來展示。在以M/G/1建構模型後，我們先使用基本之M/M/1模型展示數值範例。再延伸至M/D/1系統並且與M/M/1系統做比較。有鑒於無存貨策略所能達成之延伸性，例如趕工模型。我們也比較無存貨策略與最佳存貨策略間之改進幅度。本研究顯示出，雖然隨著生產設施的穩定性提升會降低存貨策略所能改進的程度。不過只要需求是隨機的並且著眼點是在時間保證之競爭下，使用存貨策略是更有利的決策。

關鍵字

存貨生產；時間競爭；等候線；存貨策略

並列摘要

Although stochastic inventory model has been well discussed by many researchers, the combination with time based service guarantee and the influence toward system behaviors still remains un-discovered. In this study, we formulate stochastic inventory model with consideration of order lead time guarantee as a competitive strategy and show the trade-off between insured inventory investment and delivery time delay risks. Order lead time is referred as the combination of sojourn time in production facility and delivery time. Demand is exogenous and is sensitive to both price and guaranteed order lead time. In addition to the more popular capacity expansion policy, we satisfy the guarantee by introducing an optimal inventory policy to decide the inventory level threshold. An optimal model is established to observe the relationship between price, order lead time guarantee and the inventory decision with the objective to maximum the total profit. We show the idea in two numerical examples. The basic idea of the study is by M/G/1 system. However, we optimize and analysis it in M/M/1 case and extend it to M/D/1 case. Sensitive analysis is provided to show how optimal inventory decisions are affected by different environment. The results are compared in optimal inventory policies, especially none-inventory policy for the extensional purposes such as capacity boosting policy. The study shows that although the significance of the inventory policy decreases in the production process stability. As long as the demand is stochastic and the competition is about guarantee lead time, it is more profitable to apply inventory policy.

並列關鍵字

Inventory decision ； Time-based competition ； MTS ； Queue

參考文獻

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competition in a supply chain.” Management Science, Vol. 49, Issue 9. 1139-1153.

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在隨機需求與交貨時間保證下之存貨決策

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