庫存管理文獻及翻譯

1、<p>　　本科畢業(yè)設(shè)計（論文）</p><p>　　外文參考文獻譯文及原文</p><p>　　學(xué) 院 經(jīng)濟管理學(xué)院 </p><p>　　專 業(yè) 工商管理 </p><p>　　年級班別 </p><p>　　學(xué) 號

2、 </p><p>　　學(xué)生姓名 </p><p>　　指導(dǎo)教師 </p><p>　　年 月 日</p><p><b>　　目 錄</b></p><p>　　1 什么是庫存管理………………………………………

3、.………………….….…1</p><p>　　2 What is the inventory management……………………………………....………..5</p><p>　　3 庫存控制 ………………………………………………….…………………….10</p><p>　　4 Inventory control……………………………………………….…

4、………..…….15</p><p>　　5 60天庫存精度管理 ……………………………………………….…………..21</p><p>　　6 Inventory Accuracy in 60 Days…………………………….………….…………24</p><p>　　1 什么是庫存管理</p><p>　　Dr. Hermann G

5、ruenwald</p><p>　　公司過去常常用庫存的規(guī)模來測量他們的實力，認為越大越好。倉庫中巨大的貯存量能夠有效地保證裝配線和產(chǎn)品在面對任何困難下都不會停頓，誰會去關(guān)心儲存成本？它們會在增長的銷售中被抵消。但現(xiàn)在這種平衡被改變了。</p><p>　　降低庫存量是最快降低工作資金需求量的一種方法。工作狀況的測定，比如以前的ROA（資產(chǎn)收益率）和新的EVA（經(jīng)濟效益增值），以及其他測

6、量方法都可以作為標(biāo)準(zhǔn)來確定使用多少的資金是最有效率的，這些都越來越普遍地被企業(yè)使用。實際上，很多時候?qū)σ粋€工作的獎勵至少在一方面取決于怎樣有效率地使用資金，建設(shè)高效的資金使用率能迅速滿足變化的客戶需求，使得訂貨－出貨周期越來越短，這些都是你挑戰(zhàn)很多其他企業(yè)所需要的。</p><p><b>　　傾斜經(jīng)濟及其意義</b></p><p>　　在大范圍下，美國的商業(yè)成功之

7、處在于它所尋求的傾斜式運作，但幾乎所有的公司從1981-1991年期間都在增加庫存，且在過去的10年里看不到什么經(jīng)濟效益上提高，庫存在1992到2000年間保持在占GDP的3.8％，從制造商到頂層供應(yīng)者再到底層供應(yīng)者，庫存在供應(yīng)鏈中被降低，但好過被消滅。舉例來說，通用公司，改進庫存周期，用平均庫存來測量銷售商品的總庫存，以得到一個有價值的指標(biāo)，在1996-2001年間，公司售出占其總庫存55.2％的產(chǎn)品所獲得的效果是最好的，然而，該公司

8、供應(yīng)輪胎，旺盛的年度，在同期它的庫存降至21％，換句話說，下層供應(yīng)商不希望留著像通用和沃爾瑪這樣的大麻煩給自己。</p><p><b>　　庫存管理理論：</b></p><p>　　庫存及其管理理論每一個公司都有但是沒有人承認它們，庫存管理理論是真正意義上的跨學(xué)科和跨區(qū)間理論，包括財務(wù)，管理會計，運籌學(xué)和物流，以下是對庫存控制和理論的一些看法：庫存動機：<

9、/p><p>　　庫存維持供給與需求的平衡；</p><p>　　庫存是供應(yīng)臨界點的緩沖器；</p><p><b>　　供應(yīng)者－獲??；</b></p><p><b>　　獲?。a(chǎn)品</b></p><p><b>　　產(chǎn)品－銷售</b></p>

10、;<p><b>　　銷售－分配</b></p><p><b>　　分配－中間商</b></p><p><b>　　中間商－消費者</b></p><p><b>　　庫存允許規(guī)模經(jīng)濟</b></p><p><b>　　購買&

11、lt;/b></p><p><b>　　運輸</b></p><p><b>　　制造</b></p><p>　　企業(yè)都有著不同的原因持有庫存，庫存在供給與需求波動中和消除供應(yīng)鏈系統(tǒng)錯誤方面扮演著緩沖器的角色，理順你的供應(yīng)鏈運作和使你更好地去預(yù)測你需要維持的最低庫存，除非你是通過規(guī)模經(jīng)濟的購買，運輸，制造來獲利的

12、。</p><p><b>　　庫存的范圍：</b></p><p><b>　　原材料庫存</b></p><p><b>　　在制品庫存</b></p><p><b>　　完成品庫存</b></p><p>　　有三種類型的庫

13、存，過多的庫存對你來說沒有好處除非你因為季節(jié)性、生產(chǎn)正常運作，防止缺貨或改進客戶滿意度這些原因來持有庫存。庫存的種類：</p><p><b>　　周期性庫存；</b></p><p><b>　　在運庫存；</b></p><p><b>　　安全（緩沖）庫存；</b></p>&l

14、t;p><b>　　投機性庫存；</b></p><p><b>　　季節(jié)性庫存；</b></p><p><b>　　呆滯庫存；</b></p><p>　　如果需求量和訂貨時間不變，單周期庫存是必須的。在運庫存通常是指正在船上運輸而未能在目的地使用，在運庫存能夠通過提高運輸模式的速度來減少。

15、安全（緩沖）庫存是為了滿足不確定需求和延遲時間的庫存，維持投機性庫存的的原因不同于滿足確定的需求，常常用來獲得規(guī)模經(jīng)濟效益或滿足季節(jié)性庫存需求，呆滯庫存包括市場對其沒有需求或者是已經(jīng)變壞的物品。</p><p><b>　　庫存管理狀態(tài)：</b></p><p><b>　　確定性；</b></p><p><b&g

16、t;　　不確定性；</b></p><p>　　如經(jīng)濟學(xué)的課本和個案研究中所描述的，通過經(jīng)濟定購批量（EOQ）模型這一方法來使得庫存總成本和定貨成本最小化是最好的方法：</p><p>　　P＝訂貨成本 （$/次）</p><p>　　D＝年需求量

17、 （數(shù)量單位）</p><p>　　C＝年庫存成本 （產(chǎn)品成本的百分比）</p><p>　　V＝單位庫存成本 （$/件）</p><p>　　這一公式能夠調(diào)整總額折扣和需要增加的補給量，在任何條件下都適用。</p><p>

18、;　　大多數(shù)情況下我們都不在一個理想的環(huán)境下工作，經(jīng)常會面對不確定性，生命也是經(jīng)常會因一些微不足道的事情而結(jié)束，因此，你應(yīng)當(dāng)熱衷于看一些運作管理的書和找方法計算補貨周期、安全庫存和背離周期的標(biāo)準(zhǔn)偏差。</p><p>　　低效庫存管理的表現(xiàn)：</p><p><b>　　不斷增加的事后命令</b></p><p><b>　　不斷增加

19、的取消命令</b></p><p><b>　　不斷增加的返品數(shù)量</b></p><p><b>　　高的顧客流轉(zhuǎn)率</b></p><p><b>　　大量的報廢商品</b></p><p><b>　　期性缺乏庫存空間</b></p

20、><p>　　如果你的事后命令在不斷增加以及有時你不得不去取消命令你就知道你有問題了，你的返品數(shù)量增加就是逆向物流增加，以及你將會失去顧客，積聚的廢棄物品會占用其他物品的空間使得庫存空間不足，你必須面對這些庫存信號，但他們可能是由大范圍中的一部分造成的。</p><p>　　降低庫存水平的方法：</p><p><b>　　前置時間分析；</b>&

21、lt;/p><p><b>　　交貨時間分析；</b></p><p><b>　　消除低周轉(zhuǎn)產(chǎn)品；</b></p><p><b>　　消除報廢品</b></p><p><b>　　包裝規(guī)模分析；</b></p><p><b

22、>　　分析結(jié)構(gòu)折扣；</b></p><p><b>　　檢查退貨商品程序；</b></p><p>　　應(yīng)單位維持庫存（SKU）測量補貨頻率；</p><p><b>　　分析消費者需求；</b></p><p>　　10、提高庫存預(yù)測；</p><p>

23、　　11、改進買賣雙方的電子數(shù)據(jù)交換。</p><p>　　以上將的庫存水平的建議是提高庫存管理理論方法的一部分庫存管理系統(tǒng)/分析：</p><p><b>　　ABC分析法；</b></p><p><b>　　庫存預(yù)測；</b></p><p><b>　　訂單處理系統(tǒng)；</b

24、></p><p><b>　　企業(yè)資源計劃；</b></p><p><b>　　電子數(shù)據(jù)交換；</b></p><p><b>　　知識管理系統(tǒng)；</b></p><p><b>　　供應(yīng)商庫存管理；</b></p><p&g

25、t;　　ABC分析法是根據(jù)物品的重要性/收益率來對其進行分類的工具（A類物資比B類物資重要，依此類推），以價值為依據(jù)來分類是ABC分類法的基本方法，把良好的銷售預(yù)測和先進的訂貨處理系統(tǒng)作為市場計劃的一部分可以降低庫存，企業(yè)資源規(guī)劃( ERP )系統(tǒng)和企業(yè)知識管理( KM )系統(tǒng)，如SAP將消除庫存積壓及資訊滯留和促進信息共享。高層管理人員可以看到供應(yīng)商管理庫存( VMI )作為一種外在的庫存問題。但都必須非常小心,因為它需要合伙人之間有

26、高度的透明度和一體化。就像婚姻一樣在蜜月期有很多好處，但是背后也隱藏著昂貴的離婚危險。</p><p>　　庫存是相對現(xiàn)金來說一種低效的投資，但也必須達到一定的服務(wù)水平，保持適當(dāng)數(shù)量和種類的庫存是必要的,以為你的顧客提供高質(zhì)量的產(chǎn)品,及時的服務(wù)和產(chǎn)品。防止缺貨,需要一個嚴格的過程和信息系統(tǒng),以動態(tài)地維持這一平衡，優(yōu)化庫存量的兩個關(guān)鍵是改進客戶可靠性和滿足顧客需求來使得成本有效，以使庫存剛好到達準(zhǔn)時和足量水平。&l

27、t;/p><p>　　2 What Is Inventory Management?</p><p>　　Dr. Hermann Gruenwald</p><p>　　Companies used to measure their muscle by the size of their inventory. Bigger was better. Vast wareh

28、ouses filled to capacity ensured efficient assembly lines and guaranteed that, come hell or high water, production would never stop. Who cared about carrying costs? They would be erased by increased sales. But now that e

29、quation has changed. </p><p>　　Lowering inventories is one of the quickest ways to decrease working capital needs. Performance measurements, such as the old standby ROA (return on assets) and the newer EVA (

30、economic value added), as well as other measures that gauge how efficiently capital is used, have become more common organizational drivers. In fact, many times an executive's bonus depends, at least in part, on how

31、efficiently capital is used. Couple the drive for efficient capital use with the need to respond more quickl</p><p>　　Leaner and Meaner</p><p>　　In the big picture, American business has succeed

32、ed in its quest to run lean. But almost all these gains in inventory reduction happened from 1981 to 1991, and the past 10 years have not seen much improvement. Inventory as a percent of GDP held steady at 3.8 percent fr

33、om 1992 to 2000. Rather than being eliminated, inventory has been pushed down into the lower reaches of the supply chain, from manufacturers to top-tier suppliers to lower-tier suppliers. GM, for example, improved invent

34、ory turns, </p><p>　　Inventory Management Theory</p><p>　　Inventory and the management thereof belong to everyone in the company but nobody wants to own it.  Inventory Management is truly i

35、nterdisciplinary and spans from financial and managerial accounting, to operations research, material handling to logistics. The following is a quick overview of Inventory Control/Management terminology and theory. </

36、p><p>　　Reasons for Holding Inventory: </p><p>　　Inventory balances supply and demand.</p><p>　　Inventory acts as a buffer between critical Supply Chain interfaces.</p><p>

37、;　　supplier – procurement</p><p>　　procurement – production </p><p>　　production – marketing</p><p>　　marketing – distribution </p><p>　　distribution – intermediary <

38、;/p><p>　　intermediary – user</p><p>　　Inventory allows for economies of scale in.</p><p>　　Purchasing </p><p>　　Transportation</p><p>　　manufacturing </p&

39、gt;<p>　　There are various reasons for holding inventory. Inventory acts as a buffer between supply and demand fluctuations and irons out supply chain system failures.  The smoother your supply chain operates

40、 and the better you are able to forecast the less inventory you have to hold, unless you gain some economies of scale in purchasing, transportation and or manufacturing.   </p><p>　　Categories of I

41、nventory </p><p>　　Raw Material Inventory </p><p>　　Work-in-progress Inventory </p><p>　　Finished Goods Inventory </p><p>　　There are three categories of inventory; too

42、 much in either may be a bad thing unless you have reasons for it such as seasonality, production runs, and prevention of stockouts or improvement of customer satisfaction levels. </p><p>　　Types of Inventor

43、y/Stock</p><p>　　Cycle stock </p><p>　　In-transit stock </p><p>　　Safety or buffer stock </p><p>　　Speculative stock </p><p>　　Seasonal stock</p>&

44、lt;p>　　Dead stock </p><p>　　If demand and lead time is constant, only cycle stock is necessary. In transit inventory is usually accounted for on the place of shipment as it is not available at the destina

45、tion. In-transit stock can be reduced through faster modes of transportation. Safety or buffer stock is a result of uncertainty of demand and lead time. Speculative stock is inventory held for reasons other than satisfyi

46、ng current demand, often acquired to reach economies of scale or to generate seasonal stock. Dead stock </p><p>　　Inventory Management Conditions</p><p>　　Certainty </p><p>　　Uncert

47、ainty </p><p>　　In a perfect world as described in business school text books and case studies one manages in a world of certainty. And the best ordering policy can be determined by minimizing the total of i

48、nventory carrying costs and ordering costs using the Economic Order Quantity (EOQ) model. </p><p>　　P = ordering cost   ($/order) </p><p>　　D = annual dem

49、and  (number of units) </p><p>　　C = annual inventory carrying cost  (% of product cost) </p><p>　　V = average cost of one unit of inventory

50、  ($/unit) </p><p>　　This formula can be adjusted for volume discounts and incremental replenishment, as well as other conditions. </p><p>　　Most of us don’t work in a place cal

51、led perfect, and are facing uncertainties. Life ends up throwing monkey wrenches into the production of widgets. For those of you who love math look at the operations management literature and you will find ways to calcu

52、late fill rates, safety stock, and standard deviation of replenishment cycles. </p><p>　　Symptoms of Poor Inventory Management:</p><p>　　Increasing number of backorders </p><p>　　In

53、creasing cancelled orders </p><p>　　Increasing numbers of returns </p><p>　　High customer turnover rate </p><p>　　Large number of obsolete items </p><p>　　Periodic lack

54、 of storage space </p><p>　　You know you have a problem if your backorders continue to increase and at the same time you are faced with increasing cancelled orders. Reverse logistics may be tasking as well a

55、s your number of returns increase, and you end up loosing customers, while accumulating obsolete items which among other things may lead to lack of storage space. You may face these inventory symptoms, but the causes may

56、 be part of the bigger picture. </p><p>　　Ways to Reduce Inventory Levels:</p><p>　　Lead-time analysis </p><p>　　Delivery-time analysis </p><p>　　Eliminate low turnover

57、 items</p><p>　　Eliminate obsolete items </p><p>　　Analysis of package size </p><p>　　Analysis of discount structure </p><p>　　Examine returned goods procedures </p&

58、gt;<p>　　Measurement of fill rate by stock-keeping unit (SKU) </p><p>　　Analysis of customer demand </p><p>　　Improve forecasting </p><p>　　Improve electronic data interchang

59、e with vendors/suppliers </p><p>　　The above mentioned ways to reduce inventory levels should be part of a system approach to improving Inventory Management </p><p>　　Inventory Management System

60、s/Analysis</p><p>　　ABC Analysis </p><p>　　Forecasting </p><p>　　Advanced Order Processing Systems </p><p>　　Enterprise Resource Planning (ERP)</p><p>　　El

61、ectronic Data Interchange (EDI) </p><p>　　Knowledge Management (KM) </p><p>　　Systems Vendor-Managed inventory (VMI)</p><p>　　ABC analysis is a tool to classify items according to t

62、heir relative importance/profitability (Category A items are more important than category B items, and so on). A distribution by value report usually forms the basis of an ABC analysis. Better sales forecasting and advan

63、ced order processing systems as part of a larger marketing plan will reduce inventory. And Enterprise Resource Planning (ERP) system such as SAP will eliminate stove pipes and information silos and contribute to informat

64、ion s</p><p>　　Inventory is a poor investment alternative for cash, but imperative to achieve required service levels. Maintaining the appropriate levels and types of inventory is essential to providing qual

65、ity, timely service and products to your customers. Preventing stock-outs without overstocking products requires a disciplined process and information system that can dynamically manage this balance. Two of the keys to o

66、ptimizing inventories are to improve reliability and reduce variability in the supply ch</p><p><b>　　3 庫存控制</b></p><p>　　J. E. Beasley</p><p>　　庫存的基本功能就是使生產(chǎn)過程遠離環(huán)境變化造成的影

67、響，如下圖3.1所示：</p><p><b>　　圖3.1 庫存功能</b></p><p>　　在此說明，雖然本文我們只涉及到制造業(yè)的庫存，而其他企業(yè)也有著庫存，比如銀行里可用的庫存現(xiàn)金分配給客戶，一個區(qū)域的警察儲備等等。</p><p>　　有一點值得注意的是，從上圖看出大多數(shù)活動都是一種成本――只是它在最終點（銷售最終產(chǎn)品）時我們用來抵

68、消我們的成本和希望以此獲得利潤（＝收入－成本）。因此如果我們計算成本總價值，我們就需要涉及到庫存的有效性，效率性和經(jīng)濟形式（我習(xí)慣稱之為3E’s）</p><p>　　隨后產(chǎn)生的問題是：我們應(yīng)該持有多少庫存？庫存控制理論就是試圖回答這樣一個簡單的問題。 </p><p>　　對這個問題有兩個極端的回答：</p><p><b>　　1、大量庫存</b

69、></p><p>　　確保我們生產(chǎn)不會中斷；</p><p>　　這是一種管理庫存的簡單方法；</p><p>　　這樣會是昂貴的庫存成本，低廉的管理成本。</p><p>　　2、沒有/非常少庫存</p><p>　　像準(zhǔn)時制（JIT）一樣有效率；</p><p>　　是一種困難的管理

70、庫存方法；</p><p>　　這樣會是低廉的庫存成本和高昂的管理成本；</p><p><b>　　決定完成品庫存；</b></p><p>　　決定一個生產(chǎn)過程中產(chǎn)品的規(guī)模 。</p><p>　　我們應(yīng)該考慮的是定購原材料的問題，但是相同的基本理論也能夠應(yīng)用在以下問題上：</p><p>　

71、　我們需要考慮成本是為了我們能夠通過如下的庫存維持成本和訂貨（收貨）成本來決定庫存數(shù)量。在這里指出，習(xí)慣地，管理成本是可以忽略的。</p><p>　　1、維持成本－隨著庫存的增加而增加</p><p><b>　　儲存成本</b></p><p><b>　　租借費/折舊</b></p><p>

72、<b>　　勞動力費用</b></p><p>　　一般管理費用（比如保溫、照明、安全管理費）</p><p>　　資金占用（機會成本損失）</p><p>　　無形損耗費（如果再生產(chǎn)末期還剩下庫存）</p><p>　　庫存老化（如果庫存物資在保存時老化而損耗的資金）</p><p><b

73、>　　防盜/保險費</b></p><p>　　2、訂貨成本－隨著訂貨和收貨次數(shù)增加而增加</p><p>　　定貨過程中的記錄/人工成本</p><p>　　檢查和返修低質(zhì)量產(chǎn)品</p><p><b>　　運輸成本</b></p><p><b>　　訂貨手續(xù)費&l

74、t;/b></p><p>　　在這里指出當(dāng)我們的存貨不足以供應(yīng)給客戶時就會發(fā)生存貨短缺現(xiàn)象，通常庫存短缺發(fā)生在訂貨的前置時間，這個時間是指作出訂貨指令至到貨這一段時間。</p><p>　　發(fā)生缺貨時可能會完全失去客戶或者客戶會選擇退定，也就是說，我們要準(zhǔn)備充足的庫存來滿足客戶的訂貨要求。</p><p>　　在這里指出，雖然在理念上我們知道成本與這些因素有

75、關(guān)，但是卻很難得到一個適當(dāng)合理的庫存指數(shù)（舉例來說，如果產(chǎn)品存儲在一幢有多種使用目的的大樓里，我們應(yīng)當(dāng)怎樣去合理安置保溫/照明/保安成本）</p><p>　　通過考慮以下簡單的模型來決定我們的庫存水平：</p><p><b>　　基本模型：</b></p><p>　　在這個基本模型我們設(shè)想處于以下情形：</p><p&

76、gt;　　1、我們的公司從一個外部供應(yīng)商那里訂貨；</p><p>　　2、外部供應(yīng)商剛好能夠提供我們所需的定貨數(shù)量；</p><p>　　3、我們的庫存產(chǎn)品流通到客戶（無論是在一個相同公司的外部客戶還是內(nèi)部客戶（例如定購在生長過程中使用的原材料））。</p><p><b>　　假想：</b></p><p>　　1、

77、庫存以一個持續(xù)的速率消耗；</p><p>　　2、每次訂貨的成本固定為co －常常稱之為訂貨成本；</p><p>　　3、從發(fā)出訂貨命令到貨物到達沒有前置時間；</p><p>　　4、每單位每年的儲存可變成本為ch；</p><p>　　5、然后我們必須確定每次訂貨的數(shù)量Q，常常稱之為定購批量。</p><p>

78、　　在這些假設(shè)條件下隨著時間的推移可以得到如圖3.2的庫存水平：</p><p>　　考慮在上圖Q/2處劃一條線，如果你劃這條線就能清楚地表示當(dāng)庫存量在Q/2附近波動時，此時的庫存量是均衡的，換句話說，我們同樣可以認為上圖表示隨著時間的推移庫存量持續(xù)維持在Q/2的水平上。</p><p><b>　　因此我們可以得到：</b></p><p>

79、　　年庫存成本＝ch(Q/2)</p><p>　　Q/2是平均庫存水平</p><p>　　年定貨成本＝co(R/Q) （R：年總需求量，Q：定購量）</p><p>　　R/Q是指每年的訂貨次數(shù)</p><p>　　所以 年庫存總成本＝ch(Q/2) + co(R/Q)</p><p>　　我們可以通過選擇一個最合

80、適的Q值來實現(xiàn)年庫存總成本最小</p><p>　　在這里指出，顯然地，進貨成本與R單位每年有關(guān)，然而R是一個持續(xù)不變的固定值，所以我們在這里可以忽略它。</p><p>　　圖3.3 庫存成本曲線</p><p>　　上圖舉例說明了兩個部分（年維持成本和年訂貨成本）的改變對Q，訂貨數(shù)量的改變，隨著Q的增加，維持成本在增加，但是訂貨成本卻在下降，因此總成本曲線如圖2

81、.3所示，曲線上的一個Q值能夠?qū)崿F(xiàn)最小總成本。</p><p>　　我們能夠視Q為0時來區(qū)分總成本以準(zhǔn)確地計算出哪一個Q值能夠?qū)崿F(xiàn)最小總成本，</p><p>　　成本最小化公式：d(總成本)/dQ = ch/2 - coR/Q² = 0</p><p>　　使得Q² = 2coR/ch</p><p>　　因此最優(yōu)定購量

82、Q（總定購量＝總庫存量）如下所示：</p><p>　　Q =(2Rco/ch)0.5</p><p>　　這個就成為經(jīng)濟定購批量（EOQ）</p><p><b>　　注釋：</b></p><p>　　1、EOQ公式被認為是起源與十二十世紀初的大規(guī)模的裝配線生產(chǎn)時期。</p><p>　　2、

83、從年庫存總成本與EOQ有關(guān)我們可以把公式Q =(2Rco/ch)0.5代入年總庫存成本＝ch(Q/2) + co(R/Q)中，從而得到以下年總成本公式：</p><p>　　ch((2Rco/ch)0.5/2) + co(R/(2Rco/ch)0.5) = (Rcoch/2)0.5 + (Rcoch/2)0.5 = (2Rcoch)0.5 </p><p>　　因此年庫存總成本是(2Rco

84、ch)0.5 就意味著當(dāng)定購最佳數(shù)量（EOQ），其總成本就與一些有關(guān)因素(R, co and ch)的乘積的平方根成比例。比如，如果我們降低四個因素中的其中一個因素co，我們就能降低總成本中一個因素的兩倍，（EOQ也是同樣道理），實際上準(zhǔn)時制生產(chǎn)（JIT）的基本原理也是在于（不斷地）減少co和ch 以致于降低整個成本。</p><p>　　3、回到管理成本被忽略這一問題，如果我們考慮上圖的總成本曲線可知其基本理由

85、是－假如我們不推行政策使得Q非常低（JIT）或Q非常高－我們可以說管理成本整合在一個固定的廣義上的Q值里面，如果是這樣的話,那么這些費用將不影響決定采用什么訂貨量q最合適，此外，如果我們需要數(shù)量上更加接近，我們需要一些能力來確定由此招致的管理成本和定購批量Q之間的關(guān)系－估計這是一個不可能的任務(wù)。</p><p>　　4 Inventory control</p><p>　　J E Be

86、asley</p><p>　　The basic function of stock (inventory) is to insulate the production process from changes in the environment as shown below.</p><p>　　Note here that although we refer in this not

87、e to manufacturing, other industries also have stock e.g. the stock of money in a bank available to be distributed to customers, the stock of policemen in an area, etc. </p><p>　　One point to note from the a

88、bove diagram is that most of the activities are a cost. it is only at the final point (sales of finished goods) that we get revenue to set against our costs and hopefully make a profit (= revenue - cost). Hence if we hav

89、e cost associated with stock we need to deal with that stock in an Effective, Efficient and Economic manner (the 3E's as I tend to term it). </p><p>　　The question then arises: how much stock should we h

90、ave? It is this simple question that inventory control theory attempts to answer. </p><p>　　There are two extreme answers to this question: </p><p>　　a lot this ensures that we never run out <

91、;/p><p>　　is an easy way of managing stock </p><p>　　is expensive in stock costs, cheap in management costs </p><p>　　none/very little </p><p>　　this is known (effectively

92、) as Just-in-Time (JIT) </p><p>　　is a difficult way of managing stock </p><p>　　is cheap in stock costs, expensive in management costs </p><p>　　We shall consider the problem of o

93、rdering raw material stock but the same basic theory can be applied to the problem of: </p><p>　　deciding the finished goods stock; </p><p>　　and deciding the size of a batch in a batch producti

94、on process.</p><p>　　The costs that we need to consider so that we can decide the amount of stock to have can be divided into stock holding costs and stock ordering (and receiving) costs as below. Note here

95、that, conventionally, management costs are ignored here. </p><p>　　Holding costs - associated with keeping stock over time</p><p>　　storage costs </p><p>　　rent/depreciation </p&

96、gt;<p><b>　　labour </b></p><p>　　overheads (e.g. heating, lighting, security) </p><p>　　money tied up (loss of interest, opportunity cost) </p><p>　　obsolescence

97、costs (if left with stock at end of product life) </p><p>　　stock deterioration (lose money if product deteriorates whilst held) </p><p>　　theft/insurance</p><p>　　Ordering costs -

98、associated with ordering and receiving an order</p><p>　　clerical/labour costs of processing orders </p><p>　　inspection and return of poor quality products </p><p>　　transport cost

99、s</p><p>　　handling costs </p><p>　　Note here that a stockout occurs when we have insufficient stock to supply customers. Usually stockouts occur in the order lead time, the time between placing

100、 an order and the arrival of that order. </p><p>　　Given a stockout the order may be lost completely or the customer may choose to backorder, i.e. to be prepared to wait until we have sufficient stock to sup

101、ply their order. </p><p>　　Note here that whilst conceptually we can see that these cost elements are relevant it can often be difficult to arrive at an appropriate numeric figure (e.g. if the stock is store

102、d in a building used for many other purposes, how then shall we decide an appropriate allocation of heating/lighting/security costs).</p><p>　　To see how we can decide the stock level to adopt consider the v

103、ery simple model below. </p><p>　　Basic model</p><p>　　In this basic model we have the situation where:</p><p>　　our company orders from an outside supplier; </p><p>　　

104、that outside supplier delivers to us precisely the quantity we ask for; and </p><p>　　we pass that stock onto our customers (either external customers, or an internal customer within the same company (e.g. i

105、f ordering raw materials for use in the production process)). </p><p><b>　　Assume: </b></p><p>　　Stock used up at a constant rate (R units per year) </p><p>　　Fixed set-

106、up cost co for each order - often called the order cost </p><p>　　No lead time between placing an order and arrival of the order </p><p>　　Variable stock holding cost ch per unit per year </p

107、><p>　　Then we need to decide Q, the amount to order each time, often called the batch (or lot) size. </p><p>　　Consider drawing a horizontal line at Q/2 in the above diagram. If you were to draw t

108、his line then it is clear that the times when stock exceeds Q/2 are exactly balanced by the times when stock falls below Q/2. In other words we could equivalently regard the above diagram as representing a constant stock

109、 level of Q/2 over time.</p><p>　　With these assumptions the graph of stock level over time takes the form shown below. </p><p>　　Hence we have that: </p><p>　　Annual holding cost =

110、 ch(Q/2) </p><p>　　where Q/2 is the average (constant) inventory level </p><p>　　Annual order cost = co(R/Q) </p><p>　　where (R/Q) is the number of orders per year (R used, Q each o

111、rder) </p><p>　　So total annual cost = ch(Q/2) + co(R/Q) </p><p>　　Total annual cost is the function that we want to minimise by choosing an appropriate value of Q.</p><p>　　Note he

112、re that, obviously, there is a purchase cost associated with the R units per year. However this is just a constant as R is fixed so we can ignore it here.</p><p>　　The diagram below illustrates how these two

113、 components (annual holding cost and annual order cost) change as Q, the quantity ordered, changes. As Q increases holding cost increases but order cost decreases. Hence the total annual cost curve is as shown below - so