Inventory Management Techniques
介绍了小企业（制造商和零售商）如何利用微型或小型计算机上的库存技术来降低库存相关成本，将技术分为独立需求（成品）和依赖需求（在制品和原材料）两类，并详细讨论了连续检查模型、定期检查模型、混合模型和时相订货点模型。
INVENTORY MANAGEMENT TECHNIQUES Small businesses, both manufacturers and retailers, now have the opportunity to reduce inventory-related costs significantly through the use of various inventory techniques implemented on a micro- or mini-computer. techniques are divided into two categories--those for independent demand items (finished goods) and those for dependent demand items (manufacturing-in-process items and raw material). The use of micro-computers is growing rapidly, with material requirements planning (MRP) systems currently available for use on micro-and mini-computers. These MRP systems assist the small manufacturer in planning and controlling inventory levels of dependent demand items and in scheduling work centers (for example, see Cox and Clark).1 Several techniques offer potential for savings with independent demand items. Independent demand item techniques are subdivided into continuous review models, periodic review models, and mixed models. 1 James F. Cox and Steven J. Clark, Material Requirements Planning System Development,' Computers and Industrial Engineering, vol. 2 (1978), pp. 123-139. The model most frequently presented is the continuous review model (reorder point/economic order quantity model). It is very easy to derive, hence it is extremely popular for classroom exercises and journal articles.2,3 However, an assumption implicit in continuous review models is that a perpetual inventory is maintained so that it is practical to release a replenishment order on the day the reorder point is reached. Thus, continuous review models assume that point-of-sale information is being collected. 2 W. E. Dollan, Purchasing Management and Control for Small Business, Small Business Management Series No. 41, U.S. Small Business Administration (1980). 3 E. Lin, Inventory Control Systems for Small Business,' American Journal of Small Business (spring 1980), pp. 11-19. The continuous review technique, while very practical for a computerized inventory system collecting point-of-sale data, is not practical for manual systems handling numerous different items. Three other techniques are discussed in this article--the periodic review model, the mixed model, and the time-phased order point model. The continuous review model is presented first to give a point of reference. CONTINUOUS REVIEW MODEL There are dozens of variations of the continuous review inventory model.4 The version discussed here is derived from the following assumptions: 4 This article discusses only the simplest model. More complete discussions can be found in Rein Peterson and Edward A. Silver, Decision Systems for Management and Production Planning (New York: John Wiley & Sons, 1979), and E. Naddor, Systems (New York: John Wiley & Sons, 1966). The item under consideration is independent of all other items (no joint replenishment). Demand for the item varies (is random), but the average demand is constant over time. Lead time is known and constant. Holding costs and replenishment costs are known and constant. The inventory position is maintained at all times. Under these circumstances, a continuous review model calls for an order, of size Q, to be placed whenever the reorder point, s, is reached. The formulas for Q and s are as follows: Q = 2dr/h (1) s = D k v, (2) where d = annual demand for the item, r = replenishment cost per occurrence, h = holding cost per item per year, D = average demand during lead time, v = standard deviation of demand during lead time, and k = management determined variable. The formula for s includes an estimate of the demand during the item's lead time and safety stock to protect against stockout. …