第九章库存决策

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2InventoryDecisionsinStrategyCR(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•Thenetworkplanningprocess3CR(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。4CR(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5CR(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。6CR(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 disruptionsinsupply7CR(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8CR(2004)PrenticeHall,Inc.9.1.2反对保有库存的原因ReasonsAgainstInventoriesTheyconsumecapitalresourcesthatmightbeputto betteruseelsewhereinthefirmTheytoooftenmaskqualityproblemsthatwouldmore immediatelybesolvedwithouttheirpresenceTheydivertmanagement’sattentionawayfromcareful planningandcontrolofthesupplyanddistribution channelsbypromotinganinsularattitudeabout channelmanagement9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持久性需求求PerpetualdemandContinueswellintotheforeseeablefuture季节性需求求SeasonaldemandVarieswithregularpeaksandvalleysthroughouttheyear尖峰需求LumpydemandHighlyvariable规律性需求求RegulardemandNothighlyvariable(3<Mean)终端需求TerminatingdemandDemandgoesto0inforeseeablefuture派生需求DeriveddemandDemandisdeterminedfromthedemandofanotheritemofwhichitisapart9.3库存存管理类型型的分类9.3.1需求特点点NatureofDemandAccuratelyforecastingdemandissinglythemostimportantfactoringoodinventorymanagement11CR(2004)PrenticeHall,Inc.拉动式库存存管理法Pull基于每个仓仓库的特定定需求以一一定的订货货批量补足足库存每一个存储储点独立Eachstockinglocationisconsideredindependent最大化控制制库存Maximizeslocalcontrolofinventories推动式库存存管理法Push根据总需求求分配产品品到库存点点鼓励规模生生产准时生产制制Just-in-time同步库存流流量以满足足需求Attemptstosynchronizestockflowssoastojustmeetdemandasitoccurs最小化库存存Minimizestheneedforinventory9.3.2管理思想想InventoryManagementPhilosophies12CR(2004)PrenticeHall,Inc.拉动式库存存管理法PullDrawsinventoryintothestockinglocationEachstockinglocationisconsideredindependentMaximizeslocalcontrolofinventories推动式库存存管理法PushAllocatesproductiontostockinglocationsbasedonoveralldemandEncourageseconomiesofscaleinproduction准时生产制制Just-in-timeAttemptstosynchronizestockflowssoastojustmeetdemandasitoccursMinimizestheneedforinventory9.3.2管理思想想InventoryManagementPhilosophies13CR(2004)PrenticeHall,Inc.供给驱动Supply-Driven供应量和时时间未知Supplyquantitiesandtimingareunknown所有的供应应必须接受受和处理Allsupplymustbeacceptedandprocessed通过需求控控制库存Inventoriesarecontrolledthroughdemand联合控制AggregateControl项目目分分类类项目目组组根根据据基基于于80-20法法则则确确定定的的销销售售水水平平为3个个或或以以上上的的产产品品组组合合允允许许不不同同的的库库存存策策略略9.3.2管管理理思思想想InventoryManagementPhilosophies14PlantWarehouse#1Warehouse#2Warehouse#3A1A2A3A=AllocationquantitytoeachwarehouseQ=Requestedreplenishmentquantity

byeachwarehouseQ1Q2Q3DemandforecastDemandforecastDemandforecastPULL-ReplenishinventorywithordersizesbasedonspecificneedsofeachwarehousePUSH

-Allocatesupplytoeachwarehousebasedontheforecastforeachwarehouse拉动动式式或或推推动动式式库库存存管管理理思思想想Pullvs.PushInventoryPhilosophiesCR(2004)PrenticeHall,Inc.9-11推动动式式————基基于于每每个个仓仓库库的的预预测测将将供供给给分分配配给给各各个个仓仓库库拉动动式式————基基于于每每个个仓仓库库的的特特定定需需求求以以一一定定订订货货批批量量补补足足库库存存A——将将产产品品分分配配到到各各个个仓仓库库Q——每每个个仓仓库库需需要要的的补补货货量量159.3.3产产品品汇汇总总程程度度多数数库库存存管管理理是是针针对对每每一一种种产产品品的的库库存存进进行行控控制制。。————自自下下而而上上法法另一一种种方方法法是是管管理理一一类类产产品品而而不不是是管管理理单单独独一一种种产产品品————自自上上而而下下法法169.3.4多多层层级级库库存存供应应链链管管理理鼓鼓励励管管理理者者将将供供应应渠渠道道中中更更多多的的部部分分包包括括到到计计划划过过程程中中来来，，供供应应渠渠道道中中多多个个层层级级的的库库存存也也成成为为核核心心问问题题。。179.3.5虚虚拟拟库库存存虚拟拟库库存存即即将将自自己己将将来来所所可可能能需需要要而而又又没没有有的的东东西西的的所所有有相相关关信信息息建建立立档档案案，，包包括括品品名名规规格格价价格格数数量量等等，，在在需需要要时时能能使使用用上上。。189.4库库存存目目标标InventoryManagementObjectivesGoodinventorymanagementisacarefulbalancingactbetweenstockavailabilityandthecostofholdinginventory.CustomerService,

i.e.,StockAvailabilityInventoryHoldingcostsServiceobjectivesSettingstockinglevelssothatthereisonlyaspecifiedprobabilityofrunningoutofstockCostobjectivesBalancingconflictingcoststofindthemosteconomicalreplenishmentquantitiesandtimingCR(2004)PrenticeHall,Inc.199.4.1产产品品的的现现货货供供应应比比率率服务务水水平平=1-每每年年产产品品缺缺货货件件数数的的期期望望值值/年年需需求求总总量量20CR(2004)PrenticeHall,Inc.采购购成成本本Procurementcosts准备订单的成成本Costofpreparingtheorder订单传输成本本Costofordertransmission产品安装成本本Costofproductionsetupifappropriate接受地物料搬搬运或加工成成本Costofmaterialshandlingorprocessingatthe receivingdock商品价格Priceofthegoods9.4.2库库存管理相关关成本CostsRelevanttoInventoryManagement21CR(2004)PrenticeHall,Inc.RelevantCosts(Cont’’d)采购成本ProcurementcostsCostofpreparingtheorderCostofordertransmissionCostofproductionsetupifappropriateCostofmaterialshandlingorprocessingatthereceivingdockPriceofthegoods22CR(2004)PrenticeHall,Inc.库存持有成本本Carryingcosts空间成本。库库存成本随时时间推移Costforholdingtheinventoryovertime资金成本。库存服务成本本库存风险成本本23CR(2004)PrenticeHall,Inc.9.4.2库库存管理相关关成本CostsRelevanttoInventoryManagement库存持有成本本CarryingcostsCostforholdingtheinventoryovertimeTheprimarycostisthecostofmoneytiedupininventory,butalsoincludesobsolescence（报废）,insurance,personalpropertytaxes,andstoragecostsTypically,costsrangefromthecostofshorttermcapitaltoabout40%/year.Theaverageisabout 25%/yearoftheitemvalueininventory.24CR(2004)PrenticeHall,Inc.RelevantCosts(Cont’’d)缺货成本Out-of-stockcosts销售损失成本本Lostsalescost利润损失Profitimmediatelyforegone商誉损失Futureprofitsforegonethroughlossofgoodwill缺货成本Backordercost额外订单处理理费用Costsofextraorderhandling额外的运输和和处理费用Additionaltransportationandhandlingcosts可能的安装费费用Possiblyadditionalsetupcosts25Inventory’sConflictingCostPatternsCost补给量Replenishmentquantity缺货成本Stockoutcost采购成本Procurementcost库存持有成本本Carryingcost总成本Totalcost最低订货成本本MinimumcostreorderquantityCR(2004)PrenticeHall,Inc.9-1626术语汇编GlossaryofTermssold

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n)('nsLTSLTCzxsrzMAXTROPQPEspksCISdDLT'zd=====================279.5推动式式库存管理1.通过预测测或其他手段段确定从现在在到下一次生生产或采购期期间的需求量量2.找出每个个存储点现有有的库存量3.设定每个个存储点库存存的现货供应应水平4.计算总需需求5.计算净需需求6.在平均需需求速率的基基础上，将超超过总净需求求的部分分配配到各存储点点7.在净需求求加上分配的的超量部分得得到需分配到到每个存储点点的货物总量量289.6基本的的拉动式库存存管理（1）需求是是一次性的、、高季度性的的或持续性的的情况（2）订货程程序在某一库库存水平上启启动或由库存存盘点程序启启动（3）需求和和补货提前期期存在不同程程度不确定性性的情况29CR(2004)PrenticeHall,Inc.9.6.1一一次性订货量量SingleOrderPurchasingMakeaone-timepurchaseofanitem.Howmuchtoorder?Procedure:平衡利润增加加额与损失增增加额利润=单位价格-单单位成本损失=单位成本-单单位残值如果考虑一定定量产品被售售出的概率CPn，预期收益和和预期损失在在以下点得到到平衡CPnx损失=(1-CPn)x利润orCPn=利润/(利润+损失)CPn代表至至多售出n个个单位产品的的累积概率Dailystockingofnewspapersinvendingmachinesisagoodexample9-1830CR(2004)PrenticeHall,Inc.9.6.1一一次性订货量量SingleOrderPurchasingMakeaone-timepurchaseofanitem.Howmuchtoorder?Procedure:Balanceincrementalprofitagainstincrementalloss.Profit=PriceperunitCostperunitLoss=CostperunitSalvagevalueperunitIfCPnisprobabilityofnunitsbeingsold,thenCPnxLoss=(1CPn)xProfitorCPn=Profit/(Profit+Loss)Now,increaseorderquantityuntilCPnjustmatchescumulativeprobabilityofsellingadditionalunits.Dailystockingofnewspapersinvendingmachinesisagoodexample9-1831CR(2004)PrenticeHall,Inc.SingleOrderPurchasing(Cont’’d)ExampleAclothingitemispurchasedforaseasonalsale.Itcosts$35,butithasasalepriceof$50.Aftertheseasonisover,itismarkeddownby50%toclearthemerchandise.Theestimatedquantitiestobesoldare:Numberofitems,nProbabilityofsellingexactlynitemsCumulativeprobability100.150.15150.200.35200.300.65250.200.85300.100.95350.051.001.009-1932CR(2004)PrenticeHall,Inc.9.6.1一次次性订订货量量SingleOrderPurchasing(Cont’d)SolutionProfit=$50-35=$15Loss=$35-(0.5)(50)=$10CPn=15/(15+10)=0.60CPnisbetween15and20items,roundupandorder20items.339.6.2重复复订货货量1.即即刻补补货TC——每年年总的的相关关成本本（美美元））Q—补补充存存货的的订单单批量量（件件）D—对对库存存产品品的年年需求求量（（件））S—采采购成成本（（美元元/订订单））C—库库存产产品的的价值值（美美元/件））I—库库存持持有成成本占占产品品价值值的比比例（（%/年））Developasimplecontrolsystembyfindingthereplenishmentquantity(Q)andthereorderpoint(ROP).Therelevanttotalcostis:总成本本=采采购成成本和和库存存成本本注:需求和和提前前期确确定—周期性性的库库存管管理9-21349.6.2重复复订货货量1.即即刻补补货TC——每年年总的的相关关成本本（美美元））Q—补补充存存货的的订单单批量量（件件）D—对对库存存产品品的年年需求求量（（件））S—采采购成成本（（美元元/订订单））C—库库存产产品的的价值值（美美元/件））I—库库存持持有成成本占占产品品价值值的比比例（（%/年））Developasimplecontrolsystembyfindingthereplenishmentquantity(Q)andthereorderpoint(ROP).Therelevanttotalcostis:总成本本=采采购成成本和和库存存成本本Note:Nouncertaintyindemandorleadtime—manageregular(cycle)stockonly9-2135CR(2004)PrenticeHall,Inc.0TimeLeadtimeLeadtimeOrderPlacedOrderPlacedOrderReceivedOrderReceivedInventoryLevelReorderpoint,RQReorderPointMethodUnderCertaintyforaSingleItemQuantityon-handpluson-order9-22369.6.2重重复复订订货货量量Given:d=50units/weekI=10%/yearS=$10/orderC=$5/unitLT=3weeksNote:Nouncertaintyindemandorleadtime——manageregular(cycle)stockonly9-212.有有提提前前期期的的补补货货37CR(2004)PrenticeHall,Inc.Usingdifferentialcalculus,theoptimalvalueforQwillbe:Thereorderpointis:ROP=d(LT)=3(50)=150unitsFamousEOQformulaRuleWhentheinventoryleveldropsto150units(ROP)thenreorder322units(Q*).9-23383.对对不不准准确确数数据据的的敏敏感感性性尽管管我我们们不不一一定定总总能能知知道道需需求求和和成成本本的的确确切切水水平平，，经经济济订订货货批批量量的的计计算算对对估估计计错错误误的的数数据据并并不不敏敏感感。。394.非非即即刻刻补补货货EOQ模模型型中中有有一一个个基基本本假假设设，，即即任任何何订订货货批批量量都都可可以以及及时时补补进进。。在在有有些些制制造造和和再再供供应应环环节节中中，，生生产产要要持持续续一一定定时时间间，，并并且且可可能能和和需需求求同同步步进进行行。。p是是生生产产速速率率，，d是是需需求求速速率率40CR(2004)PrenticeHall,Inc.9.7高高级级拉拉动动式式库库存存管管理理9.7.1需需求求不不确确定定下下的的再再订订货货点点模模型型1.计计算算Q*和和ROPGoodmethodforproducts:OfhighvalueThatarepurchasedfromonevendororplantHavingfeweconomiesofscaleinproduction,purchasing,ortransportation9-24FindQ*andROP41CR(2004)PrenticeHall,Inc.9.7高高级拉动动式库存存管理9.7.1需求求不确定定下的再再订货点点模型Given:d=50units/weekC=$5/unitsd=10units/weekLT=3weeksI=10%/yearP=99%duringleadtimeS=$10/orderFindQ*andROPFromtheEOQformulaGoodmethodforproducts:OfhighvalueThatarepurchasedfromonevendororplantHavingfeweconomiesofscaleinproduction,purchasing,ortransportation9-2442CR(2004)PrenticeHall,Inc.ReorderPointControlforaSingleItemROPQuantityonhand0QQReceiveorderPlaceorderStockoutLTTimeLTDDLTP9-2543CR(2004)PrenticeHall,Inc.ROPQ0InventorylevelLTLTTimeSafetystockReorderPointControlforaSingleItemActualonhandQuantityonhand+onorderbackordersQuantityforcontrol9-2644Weeklydemandisnormallydistributedwithameanofd=100andastandarddeviationofsd=10Leadtimeis3weeksReorderPointControl(Cont’d)Findingthereorderpointrequiresanunderstandingofthedemand-during-lead-timedistributionsd=10d=100sd=10d=100sd=10d=100++=Week3Week2Week1zPDDLTX=300ROPS’=17.39-2745CR(2004)PrenticeHall,Inc.ReorderPointControl(Cont’d)where2.33isthenormaldeviateataprobabilityof0.01takenfromanormaldistributiontable.462.平均库库存成本平均库存=经常性库库存+安全全库存A/L=Q/2+z(s'd)在前例中，，平均库存=322/2+2.33*17.32=201(个）47ReorderPointControl(Cont’d)3.总相关关成本TotalrelevantcostThetotalrelevantcostequationisnowextendedtoincludethecostsofsafetystockaswellasout-of-stock.Theout-of-stockcost(k)is$2/unit.Thepricetermisdropped.Hence,whereE(z)=0.0034fromaunitnormallosstableatazvalueof2.339-29484.服务水水平服务水平=1-每年年产品缺货货件数的期期望值/年年需求总量量49CR(2004)PrenticeHall,Inc.9.7.2缺货成本本已知情况况下的再订订货成本Withknownstockoutcostsk如果缺货成成本已知，，就没必要要规定客户户服务水平平了，可以以将服务和和成本的最最佳平衡点点计算出来来。可用反反复迭代的的方法1利用基本EOQ公式式得出订货货量的近似似值SolveinitiallyforQ2通过下式计计算提前期期内现货供供应的概率率UsingQ,find如果缺货允允许Ifbackorderingisallowedor如果销售出出现损失Ifsalesarelost50CR(2004)PrenticeHall,Inc.ReorderPointControl(Cont’d)3计算Q的修修正值UsingP,findrevisedQ4重复2,3步直到P和Q不再再变化Repeatsteps2and3untilnofurtherchange5计算ROP和其他所所需的统计计值ComputeROPandotherstatistics51CR(2004)PrenticeHall,Inc.ReorderPointControl(Cont’d)ExampleGiven:每月需求预预测,d11,107units预测标准差差,sd3,099units补货提前期期,LT1.5months产品价值,C$0.11/unit处理订单的的成本,S$10/order库存持有成成本,I20%/year缺货成本,k$0.01/unitBackorderingisallowed允许缺货FindoptimalQandP52CR(2004)PrenticeHall,Inc.ReorderPointControl(Cont’d)ExampleGiven:Monthlydemandforecast,d11,107unitsStd.errorofforecast.,sd3,099unitsReplenishmentlead-time,LT1.5months

Itemvalue,C$0.11/unit

Costforprocessingvendororder,S$10/order

Carryingcost,I20%/yearStockoutcost,k$0.01/unitBackorderingisallowedFindoptimalQandP53CR(2004)PrenticeHall,Inc.ReorderPointControl(Cont’d)SolutionEstimateQEstimatePReviseQFindAppA,z@0.82=0.92andfromAppB,E(0.92)=0.0968Forthesedata,s'dwaspreviouslycalculatedas3,795units54CR(2004)PrenticeHall,Inc.ReorderPointControl(Cont’d)RevisePNow,z@0.79=0.81andE(0.81)=0.118155CR(2004)PrenticeHall,Inc.ReorderPointControl(Cont’d)ReviseQContinuetoreviseQandPuntilnofurtherchangeoccurs.P=78%andQ=13,395units.NoteAlthoughthein-stockprobabilityduringtheleadtimeis78%,theactualservicelevelisSL=96%569.7.3需求和提提前期不确确定条件下下的再订货货点法ReorderpointcontrolwithdemandandleadtimeuncertaintiesCaution:Canresultinveryhighsafetystocklevelswhenlead-timevariabilityishigh9-37在需求和提提前期不确确定的情况况下找到正正态分布的的标准差s'd。这可以通过过将需求波波动和提前前期波动累累加获得。。由此s'd得到修正公公式sLT是提前期的的标准差57CR(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58CR(2004)PrenticeHall,Inc.PullMethods(Cont’d)SupplychainexampleSupposethatinventoryistobemaintainedonadistributor’sshelfforanitemwhosedemandisforecastedtobed=100unitsperdayandsd=10unitsperday.Areorderpointisthemethodofinventorycontrol.Thesupplychannelisshowninthediagram.Determinetheaverageinventorytobeheldatthedistributorwherewehave:I=10%/yearC=$5/unitS=$10/orderP=0.99duringleadtime59CR(2004)PrenticeHall,Inc.SupplyChainExample(Cont’d)SolutionThereorderpointinventorytheoryapplies.However,determiningthestatisticsofthedemand-during-lead-timedistributionrequirestakingthelead-timefortheentirechannelintoaccount.Recall,60CR(2004)PrenticeHall,Inc.SupplyChainExample(Cont’d)AverageleadtimeNowand61CR(2004)PrenticeHall,Inc.9.7.4需求不确确定条件下下的定期盘盘点模型Periodicreviewcontrolwithdemanduncertainty按预先确定定的周期（（T)核查查某种产品品的库存。。盘点后的的订货量就就是最大值值（M)与与盘点时所所持有的库库存量之差差。因此可可以通过设设定T*和和M*控制制库存。Given:d=50units/weekC=$5/unitsd=10units/weekLT=3weeksI=10%/yearP=0.99S=$10/orderk=$2/unitGoodmethodforproducts:OflowvalueThatarepurchasedfromthesamevendorHavingeconomiesofscaleinproduction,purchasing,andtransportation9-38629-39Q1StocklevelreviewedTTLTLTOrderreceivedQ2Mq0QuantityonhandTimeM=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~单一产品定期期盘点PeriodicControlforaSingleItem盘点时库存63CR(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)64CR(2004)PrenticeHall,Inc.PeriodicReview(Cont’d)PDD(T*+LT)X=d(T*+LT)MAXs′Z(s′)65PeriodicReview(Cont’’d)whereFindMAXMAX=d(T*+LT)+z(s’)=50(6.4+3)+2.33(30.66)=470+71.44=541unitsRuleReviewtheinventoryevery6.4weeksandplaceanorderforthedifferencebetweentheMAXlevelof541unitsandthequantityonhand+quantityonorder––backorders.CR(2004)PrenticeHall,Inc.9-4266CR(2004)PrenticeHall,Inc.PeriodicReview(Cont’’d)总相相关关成成本本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与再再订订货货的的点点的的方方法法比比（（$182）），，定定期期盘盘点点因因为为安安全全程程度度更更高高，，所所以以成成本本相相对对较较高高（（$198））67PullMethods(Cont’’d)9-4468PullMethods(Cont’’d)联合合订订货货联合合订订货货的的库库存存管管理理包包括括确确定定联联合合订订货货的的所所有有产产品品的的共共同同盘盘点点时时间间，，然然后后根根据据其其成成本本和和服服务务水水平平求求出出每每种种产产品品的的最最高高库库存存水水平平。。whereO=commonprocurementcost,$/order订购购采采购购的的联联合合成成本本下标标i代代表表某某种种特特定定产产品品Note:Q*=T*xdCR(2004)PrenticeHall,Inc.9-4969每种种产产品品的的最最高高库库存存水水平平总相相关关成成本本=订订购购成成本本+经经营营性性库库存存持持有有成成本本+安安全全库库存存持持有有成成本本+缺缺货货成成本本70CR(2004)PrenticeHall,Inc.JointOrderingExampleItemABAveragedailydemand(d)3075unitsDemandstd.dev.(sd)810unitsAverageleadtime(LT)1414daysAnnualcarryingcost(I)2525%Procurementcost(S)3020$/orderwithcommoncost(O)80$/orderIn-stockprobability(P)8092%Productvalue(C)170200$/unitOut-of-stockcost(k)2545$/unitSellingdaysperyear365365daysGiven71CR(2004)PrenticeHall,Inc.JointOrderingExample(Cont’d)FindcommonreviewtimeFindtargetquantity(MAX)foritemAthenz@80%=0.8472JointOrderingExample(Cont’d)whichhasanaverageinventoryofFindtargetquantity(MAX)foritemBthenforz@90%=1.41whichhasanaverageinventoryofCR(2004)PrenticeHall,Inc.73CR(2004)PrenticeHall,Inc.9.7.5实用用拉动动式库库存管管理方方法PullMethods(Cont’d)1.最最低-最高高库存存管理理法TheMin-Maxvariant当库存存水平平达到到再订订货点点时，，要订订购的的货物物数量量就是是目标标库存存量M（最最高点点）与与所持持库存存量q之差差。74CR(2004)PrenticeHall,Inc.Min-MaxInventoryControl~Q1Q2Q*ROPqLTLTTimeQuantityonhandMAddincrementROPqtoordersize9-5475CR(2004)PrenticeHall,Inc.PullMethods(Cont’d)TheT,R,MvariantThisisacombinationofthemin-maxandtheperiodicreviewsystems.Thestocklevelsarereviewedperiodically,butcontrolthereleaseofthereplenishmentorderbywhetherthereorderpointisreached.Thismethodisusefulwheredemandislow,suchthatsmallquantitiesmightbereleasedunderaperiodicreviewmethod.76CR(2004)PrenticeHall,Inc.PullMethods(Cont’d)T,R,MvariantLTLTTTTimeRqInventorylevelT=reviewtimeR=reorderpointM–Q=replenishmentquantity补给量Q1Q2InventorynotbelowR,sodon’’tplaceanorder9-5677CR(2004)PrenticeHall,Inc.PullMethods(Cont’d)2.按需存存储Stocktodemand(aperiodicreviewmethod)对某种产品品的需求速速率进行预预测。预测测值乘以一一个代表盘盘点周期、、补货提前前期，以及及包含需求求预测和提提前期不确确定性的时时间增量的的因子，就就得到目标标值。预测测时还要记记录所持库库存量，而而订购量就就等于目标标值减去所所持库存量量。按需存存储库存控控制法实际际上是一种种定期盘点点的方法。。78CR(2004)PrenticeHall,Inc.PullMethods(Cont’d)3.多产品品、多地点点的库存管管理Multipleitem,multiple-locationcontrolThetheorythathasbeendiscussedpreviouslyisusefulwhendesigninginventorycontrolsystemsforthepracticalproblemofcontrollingmanyitemsatmanylocations.Considerhowaspecialtychemicalcompanydesignedsuchapracticalsystem.TASO（订单积累累时间）isthetimetoaccumulateastockorder(truckload)forallitemsinwarehouse.79Q1StockorderTASOTASOLTOrderreceivedLTQ2M0QuantityonhandTime

M=maximumlevelTASO=timetoaccumulatestockorder

Qi=orderquantityLT=leadtimeTASO~~Q3Multiple-Item,Multiple-LocationControlCR(2004)PrenticeHall,Inc.9-6080CustomerServiceLevelForindividualitemsTheservicelevel(stockavailability)actuallyachievedbyinventorycontrolmethodsisnotbestrepresentedbytheprobability(P)ofastockoutduringtheleadtime.Itismoreaccuratetocomputeitasfollows.Usingdatafromthereorderpointunderuncertaintyexample,theservicelevelwouldbe:Note:HigherthanPCR(2004)PrenticeHall,Inc.9-6181CR(2004)PrenticeHall,Inc.CustomerServiceLevel(Cont’d)ThisactuallevelishigherthanP=0.99thatwasusedtosettheinventorylevel.Thereasonisthatthereareperiodsoftimewhenthestocklevelisabovethereorderpointandthereisnoriskofbeingoutofstock.Methodsfordefiningstockavailabilityinclude:ProbabilityoffillingallitemdemandProbabilityoffillinganordercompletelyProbabilityoffillingapercentofallitemdemandWeightedaverageofitemsfilledonanorder(fillrate)82CR(2004)PrenticeHall,Inc.CustomerServiceLevel(Cont’d)FormultipleitemsonthesameorderIfallitemsonanorderhavethesameservicelevel,whatistheprobabilityoffillingtheordercomplete?Theservicelevelformultipleitemsisthecombinationoftheindividualitemserv