库存决策培训教材

库存决策CR(2004)PrenticeHall,Inc.Chapter9每一个管理上的失误最后都会变成库存。“Everymanagementmistakeendsupininventory.”MichaelC.BergeracFormerChiefExecutiveRevlon,Inc.1第一页，共一百三十三页。产品计划三角形ProductinthePlanningTriangleCR(2004)PrenticeHall,Inc.PLANNINGORGANIZINGCONTROLLINGTransportStrategy•Transportfundamentals•TransportdecisionsCustomerservicegoals•Theproduct•Logisticsservice•Oc.&info.sys.InventoryStrategy•Forecasting•Inventorydecisions•Purchasingandsupplyschedulingdecisions•Storagefundamentals•StoragedecisionsLocationStrategy•Locationdecisions•Thenetworkplanningprocess计划组织控制TransportStrategy•Transportfundamentals•TransportdecisionsCustomerservicegoals•Theproduct•Logisticsservice•Oc.&info.sys.InventoryStrategy•Forecasting•Inventorydecisions•Purchasingandsupplyschedulingdecisions•Storagefundamentals•StoragedecisionsLocationStrategy•Locationdecisions•Thenetworkplanningprocess库存战略预测客户服务目标采购和供应时间决策存储基础知识存储决策产品物流服务订单管理和信息系统库存决策运输战略运输基础知识运输决策选址战略选址决策网络规划流程2第二页，共一百三十三页。InventoryDecisionsinStrategyCR(2004)PrenticeHall,Inc.PLANNINGORGANIZINGCONTROLLINGTransportStrategy•Transportfundamentals•TransportdecisionsCustomerservicegoals•Theproduct•Logisticsservice•Oc.&info.sys.InventoryStrategy•Forecasting•Inventorydecisions•Purchasingandsupplyschedulingdecisions•Storagefundamentals•StoragedecisionsLocationStrategy•Locationdecisions•ThenetworkplanningprocessPLANNINGORGANIZINGCONTROLLINGTransportStrategy•Transportfundamentals•TransportdecisionsCustomerservicegoals•Theproduct•Logisticsservice•Oc.&info.sys.InventoryStrategy•Forecasting•Inventorydecisions•Purchasingandsupplyschedulingdecisions•Storagefundamentals•StoragedecisionsLocationStrategy•Locationdecisions•Thenetworkplanningprocess3第三页，共一百三十三页。CR(2004)PrenticeHall,Inc.什么是库存WhatareInventories?库存就是在企业生产和物流渠道中各点堆积的原材料、供给品、零部件、半成品和成品。4第四页，共一百三十三页。CR(2004)PrenticeHall,Inc.WhereareInventories?MaterialsourcesInboundtransportationProductionOutboundtransportationFinishedgoodswarehousingCustomersInventorylocationsFinishedgoodsShippingInventoriesin-processReceivingProductionmaterials9-4原料来源生产内向运输外向运输成品储存客户原材料半成品成品库存选址5第五页，共一百三十三页。CR(2004)PrenticeHall,Inc.9.1对库存的评述9.1.1库存原因ReasonsforInventories1.改善客户服务2.降低成本首先，保有库存可以使生产的批量更大、批次更少，运作水平更高，因而产生经济效益其次，保有库存有助于实现采购和运输中的成本节约第三，先期购买可以在当前交易的低价位购买额外数量的产品。第四，抵销生产和运输过程中的不确定性第五，应付突发事件。6第六页，共一百三十三页。CR(2004)PrenticeHall,Inc.9.1对库存的评述9.1.1库存原因ReasonsforInventoriesImprovecustomerserviceProvidesimmediacyinproductavailabilityEncourageproduction,purchase,andtransportation economiesAllowsforlongproductionrunsTakesadvantageofprice-quantitydiscountsAllowsfortransporteconomiesfromlargershipmentsizesActasahedgeagainstpricechangesAllowspurchasingtotakeplaceundermostfavorableprice termsProtectagainstuncertaintiesindemandandleadtimesProvidesameasureofsafetytokeepoperations runningwhendemandlevelsandleadtimescannotbeknown forsureActasahedgeagainstcontingenciesBuffersagainstsucheventsasstrikes,fires,and disruptionsinsupply7第七页，共一百三十三页。CR(2004)PrenticeHall,Inc.9.1.2反对保有库存的原因ReasonsAgainstInventories第一，库存被认为是一种浪费第二，库存可能掩盖质量问题第三，保有库存鼓励人们以独立的观点来看待物流渠道整体的管理问题8第八页，共一百三十三页。CR(2004)PrenticeHall,Inc.9.1.2反对保有库存的原因ReasonsAgainstInventoriesTheyconsumecapitalresourcesthatmightbeputto betteruseelsewhereinthefirmTheytoooftenmaskqualityproblemsthatwouldmore immediatelybesolvedwithouttheirpresenceTheydivertmanagement’sattentionawayfromcareful planningandcontrolofthesupplyanddistribution channelsbypromotinganinsularattitudeabout channelmanagement9第九页，共一百三十三页。流通渠道Pipeline（Inventoriesintransit）投机SpeculativeGoodspurchasedinanticipationofpriceincreases定期性或周期性特征Regular/Cyclical/SeasonalInventoriesheldtomeetnormaloperatingneeds安全SafetyExtrastocksheldinanticipationofdemandand leadtimeuncertainties仓耗Obsolete/DeadStockInventoriesthatareoflittleornovalueduetobeing outofdate,spoiled,damaged,etc.9.2库存类型TypesofInventories10第十页，共一百三十三页。持久性需求PerpetualdemandContinueswellintotheforeseeablefuture季节性需求SeasonaldemandVarieswithregularpeaksandvalleysthroughout theyear尖峰需求LumpydemandHighlyvariable规律性需求RegulardemandNothighlyvariable(3<Mean)终端需求TerminatingdemandDemandgoesto0inforeseeablefuture派生需求DeriveddemandDemandisdeterminedfromthedemandofanother itemofwhichitisapart9.3库存管理类型的分类9.3.1需求特点NatureofDemandAccuratelyforecastingdemandissinglythemostimportantfactoringoodinventorymanagement11第十一页，共一百三十三页。CR(2004)PrenticeHall,Inc.拉动式库存管理法Pull基于每个仓库的特定需求以一定的订货批量补足库存每一个存储点独立Eachstockinglocationisconsideredindependent最大化控制库存Maximizeslocalcontrolofinventories推动式库存管理法Push根据总需求分配产品到库存点鼓励规模生产准时生产制Just-in-time同步库存流量以满足需求Attemptstosynchronizestockflowssoastojust

meetdemandasitoccurs最小化库存Minimizestheneedforinventory9.3.2管理思想InventoryManagementPhilosophies12第十二页，共一百三十三页。CR(2004)PrenticeHall,Inc.拉动式库存管理法PullDrawsinventoryintothestockinglocationEachstockinglocationisconsideredindependentMaximizeslocalcontrolofinventories推动式库存管理法PushAllocatesproductiontostockinglocationsbasedon overalldemandEncourageseconomiesofscaleinproduction准时生产制Just-in-timeAttemptstosynchronizestockflowssoastojust meetdemandasitoccursMinimizestheneedforinventory9.3.2管理思想InventoryManagementPhilosophies13第十三页，共一百三十三页。CR(2004)PrenticeHall,Inc.供给驱动Supply-Driven供应量和时间未知Supplyquantitiesandtimingareunknown所有的供应必须接受和处理Allsupplymustbeacceptedandprocessed通过需求控制库存Inventoriesarecontrolledthroughdemand联合控制AggregateControl项目分类项目组根据基于80-20法则确定的销售水平为3个或以上的产品组合允许不同的库存策略9.3.2管理思想InventoryManagementPhilosophies14第十四页，共一百三十三页。PlantWarehouse#1Warehouse#2Warehouse#3A1A2A3A=AllocationquantitytoeachwarehouseQ=Requestedreplenishmentquantity

byeachwarehouseQ1Q2Q3DemandforecastDemandforecastDemandforecastPULL-ReplenishinventorywithordersizesbasedonspecificneedsofeachwarehousePUSH

-Allocatesupplytoeachwarehousebasedontheforecastforeachwarehouse拉动式或推动式库存管理思想Pullvs.PushInventoryPhilosophiesCR(2004)PrenticeHall,Inc.9-11推动式——基于每个仓库的预测将供给分配给各个仓库拉动式——基于每个仓库的特定需求以一定订货批量补足库存A—将产品分配到各个仓库Q—每个仓库需要的补货量15第十五页，共一百三十三页。9.3.3产品汇总程度多数库存管理是针对每一种产品的库存进行控制。——自下而上法另一种方法是管理一类产品而不是管理单独一种产品——自上而下法16第十六页，共一百三十三页。9.3.4多层级库存供应链管理鼓励管理者将供应渠道中更多的部分包括到计划过程中来，供应渠道中多个层级的库存也成为核心问题。17第十七页，共一百三十三页。9.3.5虚拟库存虚拟库存即将自己将来所可能需要而又没有的东西的所有相关信息建立档案，包括品名规格价格数量等，在需要时能使用上。18第十八页，共一百三十三页。9.4库存目标InventoryManagementObjectivesGoodinventorymanagementisacarefulbalancingactbetweenstockavailabilityandthecostofholdinginventory.CustomerService,

i.e.,StockAvailabilityInventoryHoldingcostsServiceobjectivesSettingstockinglevelssothatthereisonlya specifiedprobabilityofrunningoutofstockCostobjectivesBalancingconflictingcoststofindthemost economicalreplenishmentquantitiesandtimingCR(2004)PrenticeHall,Inc.19第十九页，共一百三十三页。9.4.1产品的现货供应比率服务水平=1-每年产品缺货件数的期望值/年需求总量20第二十页，共一百三十三页。CR(2004)PrenticeHall,Inc.采购成本Procurementcosts准备订单的成本Costofpreparingtheorder订单传输成本Costofordertransmission产品安装成本Costofproductionsetupifappropriate接受地物料搬运或加工成本Costofmaterialshandlingorprocessingatthe receivingdock商品价格Priceofthegoods9.4.2库存管理相关成本CostsRelevanttoInventoryManagement21第二十一页，共一百三十三页。CR(2004)PrenticeHall,Inc.RelevantCosts(Cont’d)采购成本ProcurementcostsCostofpreparingtheorderCostofordertransmissionCostofproductionsetupifappropriateCostofmaterialshandlingorprocessingatthe receivingdockPriceofthegoods22第二十二页，共一百三十三页。CR(2004)PrenticeHall,Inc.库存持有成本Carryingcosts空间成本。库存成本随时间推移Costforholdingtheinventoryovertime资金成本。库存服务成本库存风险成本23第二十三页，共一百三十三页。CR(2004)PrenticeHall,Inc.9.4.2库存管理相关成本CostsRelevanttoInventoryManagement库存持有成本CarryingcostsCostforholdingtheinventoryovertimeTheprimarycostisthecostofmoneytiedupin inventory,butalsoincludesobsolescence（报废）, insurance,personalpropertytaxes,andstorage costsTypically,costsrangefromthecostofshortterm capitaltoabout40%/year.Theaverageisabout 25%/yearoftheitemvalueininventory.24第二十四页，共一百三十三页。CR(2004)PrenticeHall,Inc.RelevantCosts(Cont’d)缺货成本Out-of-stockcosts销售损失成本Lostsalescost利润损失Profitimmediatelyforegone商誉损失Futureprofitsforegonethroughlossofgoodwill缺货成本Backordercost额外订单处理费用Costsofextraorderhandling额外的运输和处理费用Additionaltransportationandhandlingcosts可能的安装费用Possiblyadditionalsetupcosts25第二十五页，共一百三十三页。Inventory’sConflictingCostPatternsCost补给量Replenishmentquantity缺货成本Stockoutcost采购成本Procurementcost库存持有成本Carryingcost总成本Totalcost最低订货成本MinimumcostreorderquantityCR(2004)PrenticeHall,Inc.9-1626第二十六页，共一百三十三页。术语汇编GlossaryofTermssold

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n)('nsLTSLTCzxsrzMAXTROPQPEspksCISdDLT'zd=====================27第二十七页，共一百三十三页。9.5推动式库存管理1.通过预测或其他手段确定从现在到下一次生产或采购期间的需求量2.找出每个存储点现有的库存量3.设定每个存储点库存的现货供应水平4.计算总需求5.计算净需求6.在平均需求速率的基础上，将超过总净需求的部分分配到各存储点7.在净需求加上分配的超量部分得到需分配到每个存储点的货物总量28第二十八页，共一百三十三页。9.6基本的拉动式库存管理（1）需求是一次性的、高季度性的或持续性的情况（2）订货程序在某一库存水平上启动或由库存盘点程序启动（3）需求和补货提前期存在不同程度不确定性的情况29第二十九页，共一百三十三页。CR(2004)PrenticeHall,Inc.9.6.1一次性订货量SingleOrderPurchasingMakeaone-timepurchaseofanitem.Howmuchtoorder?Procedure:

平衡利润增加额与损失增加额利润=单位价格-单位成本损失=单位成本-单位残值如果考虑一定量产品被售出的概率CPn，预期收益和预期损失在以下点得到平衡CPnx损失=(1-CPn)x利润or

CPn=利润/(利润+损失)CPn代表至多售出n个单位产品的累积概率Dailystockingofnewspapersinvendingmachinesisagoodexample9-1830第三十页，共一百三十三页。CR(2004)PrenticeHall,Inc.9.6.1一次性订货量SingleOrderPurchasingMakeaone-timepurchaseofanitem.Howmuchtoorder?Procedure:Balanceincrementalprofitagainstincrementalloss.Profit=PriceperunitCostperunitLoss=CostperunitSalvagevalueperunitIfCPnisprobabilityofnunitsbeingsold,thenCPnxLoss=(1CPn)xProfitor

CPn=Profit/(Profit+Loss)Now,increaseorderquantityuntilCPnjustmatchescumulativeprobabilityofsellingadditionalunits.Dailystockingofnewspapersinvendingmachinesisagoodexample9-1831第三十一页，共一百三十三页。CR(2004)PrenticeHall,Inc.SingleOrderPurchasing(Cont’d)ExampleAclothingitemispurchasedforaseasonalsale.Itcosts$35,butithasasalepriceof$50.Aftertheseasonisover,itismarkeddownby50%toclearthemerchandise.Theestimatedquantitiestobesoldare:Numberofitems,nProbabilityofsellingexactlynitemsCumulativeprobability100.150.15150.200.35200.300.65250.200.85300.100.95350.05

1.001.009-1932第三十二页，共一百三十三页。CR(2004)PrenticeHall,Inc.9.6.1一次性订货量SingleOrderPurchasing(Cont’d)SolutionProfit=$50-35=$15Loss=$35-(0.5)(50)=$10CPn=15/(15+10)=0.60CPnisbetween15and20items,roundupandorder20items.33第三十三页，共一百三十三页。9.6.2重复订货量1.即刻补货TC—每年总的相关成本（美元）Q—补充存货的订单批量（件）D—对库存产品的年需求量（件）S—采购成本（美元/订单）C—库存产品的价值（美元/件）I—库存持有成本占产品价值的比例（%/年）Developasimplecontrolsystembyfindingthereplenishmentquantity(Q)andthereorderpoint(ROP).Therelevanttotalcostis:总成本=采购成本和库存成本注:需求和提前期确定—周期性的库存管理9-2134第三十四页，共一百三十三页。9.6.2重复订货量1.即刻补货TC—每年总的相关成本（美元）Q—补充存货的订单批量（件）D—对库存产品的年需求量（件）S—采购成本（美元/订单）C—库存产品的价值（美元/件）I—库存持有成本占产品价值的比例（%/年）Developasimplecontrolsystembyfindingthereplenishmentquantity(Q)andthereorderpoint(ROP).Therelevanttotalcostis:总成本=采购成本和库存成本Note:Nouncertaintyindemandorleadtime—manageregular(cycle)stockonly9-2135第三十五页，共一百三十三页。CR(2004)PrenticeHall,Inc.0TimeLeadtimeLeadtimeOrderPlacedOrderPlacedOrderReceivedOrderReceivedInventoryLevelReorderpoint,RQReorderPointMethodUnderCertaintyforaSingleItemQuantityon-handpluson-order9-2236第三十六页，共一百三十三页。9.6.2重复订货量Given:

d=50units/week

I=10%/year

S=$10/order

C=$5/unit

LT=3weeksNote:Nouncertaintyindemandorleadtime—manageregular(cycle)stockonly9-212.有提前期的补货37第三十七页，共一百三十三页。CR(2004)PrenticeHall,Inc.Usingdifferentialcalculus,theoptimalvalueforQwillbe:Thereorderpointis:

ROP=d(LT)=3(50)=150unitsFamousEOQformulaRule

Whentheinventoryleveldropsto150units(ROP)thenreorder322units(Q*).9-2338第三十八页，共一百三十三页。3.对不准确数据的敏感性尽管我们不一定总能知道需求和成本的确切水平，经济订货批量的计算对估计错误的数据并不敏感。39第三十九页，共一百三十三页。4.非即刻补货EOQ模型中有一个基本假设，即任何订货批量都可以及时补进。在有些制造和再供应环节中，生产要持续一定时间，并且可能和需求同步进行。p是生产速率，d是需求速率40第四十页，共一百三十三页。CR(2004)PrenticeHall,Inc.9.7高级拉动式库存管理9.7.1需求不确定下的再订货点模型1.计算Q*和ROPGoodmethodforproducts:OfhighvalueThatarepurchasedfromonevendororplantHavingfeweconomiesofscaleinproduction,purchasing,ortransportation9-24FindQ*andROP41第四十一页，共一百三十三页。CR(2004)PrenticeHall,Inc.9.7高级拉动式库存管理9.7.1需求不确定下的再订货点模型Given:

d=50units/weekC=$5/unit

sd=10units/weekLT=3weeks

I=10%/yearP=99%duringleadtime

S=$10/orderFindQ*andROPFromtheEOQformulaGoodmethodforproducts:OfhighvalueThatarepurchasedfromonevendororplantHavingfeweconomiesofscaleinproduction,purchasing,ortransportation9-2442第四十二页，共一百三十三页。CR(2004)PrenticeHall,Inc.ReorderPointControlforaSingleItemROPQuantityonhand0QQReceiveorderPlaceorderStockoutLTTimeLTDDLTP9-2543第四十三页，共一百三十三页。CR(2004)PrenticeHall,Inc.ROPQ0InventorylevelLTLTTimeSafetystockReorderPointControlforaSingleItemActualonhandQuantityonhand+onorderbackordersQuantityforcontrol9-2644第四十四页，共一百三十三页。Weeklydemandisnormallydistributedwithameanofd=100andastandarddeviationofsd=10Leadtimeis3weeksReorderPointControl(Cont’d)Findingthereorderpointrequiresanunderstandingofthedemand-during-lead-timedistributionsd=10d

=100sd=10d

=100sd=10d

=100++=Week3Week2Week1zPDDLTX=300ROPS’=17.39-2745第四十五页，共一百三十三页。CR(2004)PrenticeHall,Inc.ReorderPointControl(Cont’d)where2.33isthenormaldeviateataprobabilityof0.01takenfromanormaldistributiontable.46第四十六页，共一百三十三页。2.平均库存成本平均库存=经常性库存+安全库存A/L=Q/2+z(s'd)在前例中，平均库存=322/2+2.33*17.32=201(个）47第四十七页，共一百三十三页。ReorderPointControl(Cont’d)3.总相关成本TotalrelevantcostThetotalrelevantcostequationisnowextendedtoincludethecostsofsafetystockaswellasout-of-stock.Theout-of-stockcost(k)is$2/unit.Thepricetermisdropped.Hence,whereE(z)=0.0034fromaunitnormallosstableatazvalueof2.339-2948第四十八页，共一百三十三页。4.服务水平服务水平=1-每年产品缺货件数的期望值/年需求总量49第四十九页，共一百三十三页。CR(2004)PrenticeHall,Inc.9.7.2缺货成本已知情况下的再订货成本Withknownstockoutcostsk如果缺货成本已知，就没必要规定客户服务水平了，可以将服务和成本的最佳平衡点计算出来。可用反复迭代的方法1

利用基本EOQ公式得出订货量的近似值SolveinitiallyforQ2

通过下式计算提前期内现货供应的概率UsingQ,find如果缺货允许Ifbackorderingisallowedor如果销售出现损失Ifsalesarelost50第五十页，共一百三十三页。CR(2004)PrenticeHall,Inc.ReorderPointControl(Cont’d)3

计算Q的修正值UsingP,findrevisedQ4

重复2,3步直到P和Q不再变化Repeatsteps2and3untilnofurtherchange5

计算ROP和其他所需的统计值ComputeROPandotherstatistics51第五十一页，共一百三十三页。CR(2004)PrenticeHall,Inc.ReorderPointControl(Cont’d)ExampleGiven:每月需求预测,d 11,107units

预测标准差,sd 3,099units

补货提前期,LT 1.5months

产品价值,C $0.11/unit

处理订单的成本,S $10/order

库存持有成本,I 20%/year缺货成本,k$0.01/unitBackorderingisallowed允许缺货FindoptimalQandP52第五十二页，共一百三十三页。CR(2004)PrenticeHall,Inc.ReorderPointControl(Cont’d)ExampleGiven:Monthlydemandforecast,d 11,107units

Std.errorofforecast.,sd 3,099units

Replenishmentlead-time,LT 1.5months

Itemvalue,C $0.11/unit

Costforprocessing

vendororder,S $10/order

Carryingcost,I 20%/yearStockoutcost,k$0.01/unitBackorderingisallowedFindoptimalQandP53第五十三页，共一百三十三页。CR(2004)PrenticeHall,Inc.ReorderPointControl(Cont’d)SolutionEstimateQEstimatePReviseQFindAppA,z@0.82=0.92andfrom

AppB,E(0.92)=0.0968Forthesedata,s'd

waspreviouslycalculatedas3,795units54第五十四页，共一百三十三页。CR(2004)PrenticeHall,Inc.ReorderPointControl(Cont’d)RevisePNow,z@0.79=0.81andE(0.81)=0.118155第五十五页，共一百三十三页。CR(2004)PrenticeHall,Inc.ReorderPointControl(Cont’d)ReviseQContinuetoreviseQandPuntilnofurtherchangeoccurs.P=78%andQ=13,395units.Note

Althoughthein-stockprobabilityduringtheleadtimeis78%,theactualservicelevelisSL=96%56第五十六页，共一百三十三页。9.7.3需求和提前期不确定条件下的再订货点法ReorderpointcontrolwithdemandandleadtimeuncertaintiesCaution:Canresultinveryhighsafetystocklevelswhenlead-timevariabilityishigh9-37在需求和提前期不确定的情况下找到正态分布的标准差s'd。这可以通过将需求波动和提前期波动累加获得。由此s'd得到修正公式sLT是提前期的标准差57第五十七页，共一百三十三页。CR(2004)PrenticeHall,Inc.SupplyChainExample(Cont’d)DistributorOutboundtransportInboundtransportPoolpointSupplierXspp==1012,.Xsii==4102,.Xsoo==20252,.ProcessingtimeTransporttimeTransporttime供应商内向运输集散地加工时间供应商58第五十八页，共一百三十三页。CR(2004)PrenticeHall,Inc.PullMethods(Cont’d)SupplychainexampleSupposethatinventoryistobemaintainedonadistributor’sshelfforanitemwhosedemandisforecastedtobed=100unitsperdayandsd=10unitsperday.Areorderpointisthemethodofinventorycontrol.Thesupplychannelisshowninthediagram.Determinetheaverageinventorytobeheldatthedistributorwherewehave:

I=10%/yearC=$5/unit

S=$10/orderP=0.99duringleadtime59第五十九页，共一百三十三页。CR(2004)PrenticeHall,Inc.SupplyChainExample(Cont’d)SolutionThereorderpointinventorytheoryapplies.However,determiningthestatisticsofthedemand-during-lead-timedistributionrequirestakingthelead-timefortheentirechannelintoaccount.Recall,60第六十页，共一百三十三页。CR(2004)PrenticeHall,Inc.SupplyChainExample(Cont’d)AverageleadtimeNowand61第六十一页，共一百三十三页。CR(2004)PrenticeHall,Inc.9.7.4需求不确定条件下的定期盘点模型Periodicreviewcontrolwithdemanduncertainty

按预先确定的周期（T)核查某种产品的库存。盘点后的订货量就是最大值（M)与盘点时所持有的库存量之差。因此可以通过设定T*和M*控制库存。Given:

d=50units/weekC=$5/unit

sd=10units/weekLT=3weeks

I=10%/yearP=0.99

S=$10/orderk=$2/unitGoodmethodforproducts:OflowvalueThatarepurchasedfromthesamevendorHavingeconomiesofscaleinproduction,purchasing,andtransportation9-3862第六十二页，共一百三十三页。9-39Q1StocklevelreviewedTTLTLTOrderreceivedQ2Mq0QuantityonhandTime

M=maximumlevel最高库存M-q=replenishmentquantity补货量

LT=leadtime提前期T=reviewinterval盘点周期q=quantityonhand持有库存量Qi=orderquantity订购量~单一产品定期盘点PeriodicControlforaSingleItem盘点时库存63第六十三页，共一百三十三页。CR(2004)PrenticeHall,Inc.EstimateQ*fromtheEOQformulaasifunderdemandcertaintyconditions.RecallthatthisisQ*=322units.Now,

T*=Q*/d=322/50=6.4weeksConstructthedemand-during-lead-time-plus-order-cycle-timedistribution.TisorderreviewtimePeriodicReview(Cont’d)64第六十四页，共一百三十三页。CR(2004)PrenticeHall,Inc.PeriodicReview(Cont’d)PDD(T*+LT)X=d(T*+LT)MAXs′Z(s′)65第六十五页，共一百三十三页。PeriodicReview(Cont’d)whereFindMAX

MAX=d(T*+LT)+z(s’)=50(6.4+3)+2.33(30.66)=470+71.44=541unitsRuleReviewtheinventoryevery6.4weeksandplaceanorderforthedifferencebetweentheMAXlevelof541unitsandthequantityonhand+quantityonorder–backorders.CR(2004)PrenticeHall,Inc.9-4266第六十六页，共一百三十三页。CR(2004)PrenticeHall,Inc.PeriodicReview(Cont’d)总相关成本Thetotalrelevantcostforthisdesignis:

TC=DS/Q+ICQ/2+ICr+ks’(D/Q)E(z)

=2600(10)/322+(.10)(5)(322/2)+(.10)(5)(71)+2(30.66)(2600/322)(.0034)=$198Note

与再订货的点的方法比（$182），定期盘点因为安全程度更高，所以成本相对较高（$198）67第六十七页，共一百三十三页。PullMethods(Cont’d)9-4468第六十八页，共一百三十三页。PullMethods(Cont’d)联合订货联合订货的库存管理包括确定联合订货的所有产品的共同盘点时间，然后根据其成本和服务水平求出每种产品的最高库存水平。whereO=commonprocurementcost,$/order订购采购的联合成本下标i代表某种特定产品Note:

Q*=T*xdCR(2004)PrenticeHall,Inc.9-4969第六十九页，共一百三十三页。每种产品的最高库存水平总相关成本=订购成本+经营性库存持有成本+安全库存持有成本+缺货成本70第七十页，共一百三十三页。CR(2004)PrenticeHall,Inc.JointOrderingExample

Item

ABAveragedailydemand(d)30

75unitsDemandstd.dev.(sd)8

10unitsAverageleadtime(LT)14

14daysAnnualcarryingcost(I)25

25%Procurementcost(S)30

20$/orderwithcommoncost(O)80$/orderIn-stockprobability(P)80

92%Productvalue(C)170

200$/unitOut-of-stockcost(k)25

45$/unitSellingdaysperyear365

365daysGiven71第七十一页，共一百三十三页。CR(2004)PrenticeHall,Inc.JointOrderingExample(Cont’d)FindcommonreviewtimeFindtargetquantity(MAX)foritemAthenz@80%=0.8472第七十二页，共一百三十三页。JointOrderingExample(Cont’d)whichhasanaverageinventoryofFindtargetquantity(MAX)foritemBthenforz@90%=1.41whichhasanaverageinventoryofCR(2004)PrenticeHall,Inc.73第七十三页，共一百三十三页。CR(2004)PrenticeHall,Inc.9.7.5实用拉动式库存管理方法PullMethods(Cont’d)1.最低-最高库存管理法TheMin-Maxvariant当库存水平达到再订货点时，要订购的货物数量就是目标库存量M（最高点）与所持库存量q之差。74第七十四页，共一百三十三页。CR(2004)PrenticeHall,Inc.Min-MaxInventoryControl~Q1Q2Q*ROPqLTLTTimeQuantityonhandMAddincrementROPqtoordersize9-5475第七十五页，共一百三十三页。CR(2004)PrenticeHall,Inc.PullMethods(Cont’d)TheT,R,MvariantThisisacombinationofthemin-maxandtheperiodicreviewsystems.Thestocklevelsarereviewedperiodically,butcontrolthereleaseofthereplenishmentorderbywhetherthereorderpointisreached.Thismethodisusefulwheredemandislow,suchthatsmallquantitiesmightbereleasedunderaperiodicreviewmethod.76第七十六页，共一百三十三页。CR(2004)PrenticeHall,Inc.PullMethods(Cont’d)T,R,MvariantLTLTTTTimeRqInventorylevelT=reviewtimeR=reorderpointM–Q=replenishmentquantity补给量Q1Q2InventorynotbelowR,sodon’tplaceanorder9-5677第七十七页，共一百三十三页。CR(2004)PrenticeHall,Inc.PullMethods(Cont’d)2.按需存储Stocktodemand(aperiodicreviewmethod)对某种产品的需求速率进行预测。预测值乘以一个代表盘点周期、补货提前期，以及包含需求预测和提前期不确定性的时间增量的因子，就得到目标值。预测时还要记录所持库存量，而订购量就等于目标值减去所持库存量。按需存储库存控制法实际上是一种定期盘点的方法。78第七十八页，共一百三十三页。CR(2004)PrenticeHall,Inc.PullMethods(Cont’d)3.多产品、多地点的库存管理Multipleitem,multiple-locationcontrolThetheorythathasbeendiscussedpreviouslyisusefulwhendesigninginventorycontrolsystemsforthepracticalproblemofcontrollingmanyitemsatmanylocations.Considerhowaspecialtychemicalcompanydesignedsuchapracticalsystem.TASO（订单积累时间）isthetimetoaccumulateastockorder(truckload)forallitemsinwarehouse.79第七十九页，共一百三十三页。Q1StockorderTASOTASOLTOrderreceivedLTQ2M0QuantityonhandTime

M=maximumlevelTASO=timetoaccumulatestockorder

Qi=orderquantityLT=leadtimeTASO~~Q3Multiple-Item,Multiple-LocationControlCR(2004)PrenticeHall,Inc.9-6080第八十页，共一百三十三页。CustomerServiceLevelForindividualitemsTheservicelevel(stockavailability)actuallyachievedbyinventorycontrolmethodsisnotbestrepresentedbytheprobability(P)ofastockoutduringtheleadtime.Itismoreaccuratetocomputeitasfollows.Usingdatafromthereorderpointunderuncertaintyexample,theservicelevelwouldbe:Note:HigherthanPCR(2004)PrenticeHall,Inc.9-6181第八十一页，共一百三十三页。CR(2004)PrenticeHall,Inc.CustomerServiceLevel(Cont’d)ThisactuallevelishigherthanP=0.99thatwasusedtosettheinventorylevel.Thereasonisthatthereareperiodsoftimewhenthestocklevelisabovethereorderpointandthereisnoriskofbeingoutofstock.Methodsfordefiningstockavailabilityinclude:ProbabilityoffillingallitemdemandProbabilityoffillinganordercompletelyProbabilityoffillingapercentofallitemdemandWeightedaverageofitemsfilledonanorder(fill rate)82第八十二页，共一百三十三页。CR(2004)PrenticeHall,Inc.CustomerS