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Chapter 11

Chapter 11. 獨立需求 (Independent Demand). 訂購系統. 訂購點系統 (order point system)- for Independent demand 定期訂購系統 (periodic review system) – for Independent demand 物料需求規劃 (MRP) – for Dependent demand. 訂購點系統 (order point system). When 發出訂單 : 存貨量低於 訂購點 ( 預定水準 ) 時 Why 安全存量 : 預防前置時間內的需求大於預期

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Chapter 11

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  1. Chapter 11 獨立需求 (Independent Demand)

  2. 訂購系統 • 訂購點系統 (order point system)- for Independent demand • 定期訂購系統(periodic review system) – for Independent demand • 物料需求規劃 (MRP) – for Dependent demand

  3. 訂購點系統 (order point system) • When 發出訂單: 存貨量低於訂購點(預定水準)時 • Why 安全存量: 預防前置時間內的需求大於預期 • What 公式: OP = DDLT + SS where OP = 訂購點 DDLT = demand during the lead time SS = safety stock

  4. 存貨量 vs. 時間 • 訂購點: 由前置時間內的平均需求與安全存量決定

  5. 訂購點系統的特徵 • 訂購量通常固定 • 由前置時間內的平均需求與安全存量決定訂購點 • 補貨的期間不是固定而是變動的, 依訂購循環的實際需求而定 • 平均存貨 =訂購量/2 + 安全存貨

  6. 安全存量的決定 • 前置時間內的需求變異 • 再訂購的頻率 • 要求的服務水準 • 前置時間的長短 • 前置時間越長, 必須更多的安全存量以維持必要的服務水準 • 儘可能降低前置時間的一重要理由

  7. 常態分配 • 大多數的值都集中在中心點附近 • 對稱於中心點, 向兩邊平均分散

  8. 常態分配的特性 • 集中趨勢 / 平均數 • 實際平均數的變異 / 分散 • 以標準差決定安全存量

  9. 服務水準 • A statement of the percentage of time there is no stock-out • 安全因素:服務水準直接與被提供為安全存量的標準差數量有關

  10. 缺貨成本 stockout cost • Back-order costs • Lost sales • Lost customers • Depending on the item, the market served, the customer, and competition • Difficult to establish • Service level is a senior management decision and is part of the company’s corporate and marketing strategy

  11. 服務水準 VS 訂購次數 • 可能發生缺貨的唯一時間是當存貨很低之際 • 因此 缺貨的機會直接視訂購的次數而定

  12. 不等長的預測區間 VS 前置時間區間 • 如果前置時間為0, 需求的標準差為0 • 當前置時間增加, 標準差增加, 但不會依前置時間增加的量而增加 • LTI = Lead Time Interval • FI = Forecast Interval

  13. 兩箱系統 • 相當於訂購點數量的某品項的數量被保留直到所有的主要存貨用完才被使用 • 當這些存貨需要被使用 採購部門被告知下補貨的訂單

  14. 永續存貨記錄系統 • A continual account of inventory transactions as they occur

  15. 定期訂購系統 • 存貨量由特定的固定時間區間決定, 並下訂單 • 訂購期間固定, 但訂購量允許變動 • 存貨 + 訂購量 必須足以支持到下次的訂貨收到之前 • 存貨 + 訂購量 = 前置時間需求 + 訂購期間需求 + 安全存量

  16. 定期訂購系統

  17. 訂購的目標水準 • 目標水準= 前置時間需求 + 訂購期間需求 + 安全存量 • T = D(R + L) + SS where T = target inventory level D = demand per unit of time L = lead time duration R = review period duration SS = safety stock • 訂購量 Q = T – I , where I = INV on hand

  18. 存貨流通管理的目標 • 提供要求的顧客服務水準 • 極小化運輸與搬運成本 • 與工廠協調以極小化排程的問題

  19. 流通系統 • 除非公司直接從工廠運貨給顧客, 否則工廠的需求直接由中央供應提供

  20. 流通存貨

  21. Decentralized system • Each DC places orders on central supply • Each center orders on its own w/o regard for the needs of other centers, available inv at central supply, or the production schedule of the factory • Pulled system: orders are placed on central supply and “pulled” through the system

  22. Centralized system • All forecasting and order decisions are made centrally • Stock is “pushed” out into the system from central sypply

  23. DRP • A system that forecasts when the various demands will be made by the system on central supply • The system translates the logic of MRP to the distribution system • Planned order releases from the various DCs become the input to the material plan of central supply • The planned order releases from central supply become the forecast of demand for the factory MPS

  24. DRP

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