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*Processequipmente.g.,machinetools,assemblystations,androbots

*Materialhandlingequipmente.g.,robots,conveyors,andAGVs（automatedguidedvehicles）

*Acommunicationsystem

*Acomputercontrolsystem

Flexiblemanufacturingrepresentsamajorsteptowardthegoaloffullyintegratedmanufacturing.Itinvolvesintegrationofautomatedproductionprocesses.Inflexiblemanufacturin,theautomatedmanufacturingmachineandtheautomatedmaterialshandlingsystemshareinstantaneouscommunicationviaacomputernetwork.Thisisintegrationonasmallscale.

Flexiblemanufacturingtakesamajorsteptowardthegoaloffullyintegratedmanufacturingbyintegratingseveralautomatedmanufacturingconcepts:

*Computernumericalcontrol（CNC）ofindividualmachinetools

*Distributednumericalcontrol（DNC）ofmanufacturingsystems

*Automatedmaterialshandlingsystems

*Grouptechnology（familiesofparts）

Whentheseautomatedprocesses,machines,andconceptsarebroughttogetherinoneintegratedsystem,anFMSistheresult.HumansandcomputersplaymajorrolesinanFMS.Theamountofhumanlaborismuchlessthanwithamanuallyoperatedmanufacturingsystem,ofcourse.However,humansstillplayavitalroleintheoperationofanFMS.Humantasksincludethefollowing:

*Equipmenttroubleshooting,maintenance,andrepair

*Toolchangingandsetup

*Loadingandunloadingthesystem

*Datainput

*Changingofpartsprograms

*Developmentofprograms

Flexiblemanufacturingsystemequipment,likeallmanufacturingequipment,mustbemonitoredforbugs,malfunctions,andbreakdowns.Whenaproblemisdiscovered,ahumantroubleshootermustidentifyitssourceandprescribecorrectivemeasures.Humansalsoundertaketheprescribedmeasurestorepairthemalfunctioningequipment.Evenwhenallsystemsareproperlyfunctioning,periodicmaintenanceisnecessary.

Humanoperatorsalsosetupmachines,changetools,andreconfiguresystemsasnecessary.ThetoolhandlingcapabilityofanFMSdecreases,butdoesnoteliminateinvolvementintoolchangingandsetup.ThesameistrueofloadingandunloadingtheFMS.Oncerawmaterialhasbeenloadedontotheautomatedmaterialshandlingsystem,itismovedthroughthesystemintheprescribedmanner.However,theoriginalloadingontothematerialshandlingsystemisstillusuallydonebyhumanoperators,asistheunloadingoffinishedproducts.

Humansarealsoneededforinteractionwiththecomputer.HumansdeveloppartprogramsthatcontroltheFMSviacomputers.TheyalsochangetheprogramsasnecessarywhenreconfiguringtheFMStoproduceanothertypeofpartorparts.Humansplaylesslabor-intensiverolesinanFMS,buttherolesarestillcritical.

ControlatalllevelsinanFMSisprovidedbycomputers.IndividualmachinetoolswithinanFMSarecontrolledbyCNC.TheoverallsystemiscontrolledbyDNC.Theautomatedmaterialshandlingsystemiscomputercontrolled,asareotherfunctionsincludingdatacollection,systemmonitoring,toolcontrol,andtrafficcontrol.Human/computerinteractionisthekeytotheflexibilityofanFMS.

1HistoricalDevelopmentofFlexibleManufacturing

Flexiblemanufacturingwasborninthemid-1960swhentheBritishfirmMolins,Ltd.DevelopeditsSystem24.System24wasarealFMS.However,itwasdoomedfromtheoutsetbecauseautomation,integration,andcomputercontroltechnologyhadnotyetbeendevelopedtothepointwheretheycouldproperlysupportthesystem.ThefirstFMSwasadevelopmentthatwasaheadofitstime.Assuch,itwaseventuallydiscardedasunworkable.

Flexiblemanufacturingremainedanacademicconceptthroughtheremainderofthe1960sand1970s.However,withtheemergenceofsophisticatedcomputercontroltechnologyinthelate1970sandearly1980s,flexiblemanufacturingbecameaviableconcept.ThefirstmajorusersofflexiblemanufacturingintheUnitedStatesweremanufacturersofautomobiles,trucks,andtractors.

2RationaleforFlexibleManufacturing

Inmanufacturingtherehavealwaysbeentradeoffsbetweenproductionratesandflexibility.Atoneendofthespectrumaretransferlinescapableofhighproductionrates,butlowflexibility.AttheotherendofthespectrumareindependentCNCmachinesthatoffermaximumflexibility,butarecapableonlyoflowproductionrates.Flexiblemanufacturingfallsinthemiddleofcontinuum.Therehasalwaysbeenaneedinmanufacturingforasystemthatcouldproducehighervolumeandproductionrunsthancouldindependentmachines,whilestillmaintainingflexibility.

Transferlinesarecapableofproducinglargevolumesofpartsathighproductionrates.Thelinetakesagreatdealofsetup,butcanturnoutidenticalinapartcancausetheentirelinetobeshutdownandreconfigured.Thisisacriticalweaknessbecauseitmeansthattransferlinescannotproducedifferentparts,evenpartsfromwithinthesamefamily,withoutcostlyandtime-consumingshutdownandreconfiguration.

Traditionally,CNCmachineshavebeenusedtoproducesmallvolumesofpartsthatdifferslightlyindesign.Suchmachinesareidealforthispurposebecausetheycanbequicklyreprogrammedtoaccommodateminororevenmajordesignchanges.However,asindependentmachinestheycannotproducepartsinlargevolumesorathighproductionrates.

AnFMScanhandlehighervolumesandproductionratesthanindependentCNCmachines.Theycannotquitematchsuchmachinesforflexibility,buttheycomeclose.Whatisparticularlysignificantaboutthemiddlegroundcapabilitiesofflexiblemanufacturingisthatmostmanufacturingsituationsrequiremediumproductionratestoproducemediumvolumeswithenoughflexibilitytoquicklyreconfiguretoproduceanotherpartorproduct.Flexiblemanufacturingfillsthislong-standingvoidinmanufacturing.

Flexiblemanufacturing,withitsgroundcapabilities,offersanumberofadvantagesformanufacturers:

*Flexibilitywithinafamilyofparts

*Randomfeedingofparts

*Simultaneousproductionofdifferentparts

*Decreasedsetuptimeandleadtime

*Moreefficientmachineusage

*Decreaseddirectandindirectlaborcosts

*Abilitytohandledifferentmaterials

*Abilitytocontinuesomeproductionifonemachinebreaksdown

3FlexibleManufacturingSystemComponents

AnFMShasfourmajorcomponents:

*Machinetools

*Controlsystem

*Materialshandlingsystem

*Humanoperators

（1）MachineTools

Aflexiblemanufacturingsystemusesthesametypesofmachinetoolsasanyothermanufacturingsystem,beitautomatedormanuallyoperated.Theseincludelathes,mills,drills,saws,andsoon.ThetypeofmachinetoolsactuallyincludedinanFMSdependsonthesettinginwhichthemachinewillbeused.SomeFMSaredesignedtomeetaspecific,well-definedneed.Inthesecasesthemachinetoolsincludedinthesystemwillbeonlythosenecessaryfortheplannedoperations.Suchasystemwouldbeknownasadedicatedsystem.

Inajob-shopsetting,oranyothersettinginwhichtheactualapplicationisnotknownaheadoftimeormustnecessarilyincludeawiderangeofpossibilities,machinescapableofperformingatleastthestandardmanufacturingoperationswouldbeinclude.Suchsystemsareknownasgeneralpurposesystems.

（2）ControlSystem

ThecontrolsystemforanFMSservesanumberofdifferentcontrolfunctionsforsystem:

*Storageanddistributionofpartsprograms

*Workflowcontrolandmonitoring

*Productioncontrol

*System/toolcontrol/monitoring

ThecontrolareawiththecomputerrunningtheFMScontrolsystemisthecenterfromwhichallactivitiesintheFMSarecontrolledandmonitored.TheFMScontrolsoftwareisrathercomplicatedandsophisticatedsinceithastocarryoutmanydifferenttaskssimultaneously.Despitetheconsiderableresearchthathasbeencarriedoutinthisarea,thereisnogeneralanswertodesigningthefunctionsandarchitectureofFMSsoftware.

TheschedulerfunctioninvolvesplanninghowtoproducethecurrentvolumeofordersintheFMS,consideringthecurrentstatusofmachinetools,work-in-process,tooling,andsoon.Theschedulingcanbedoneautomaticallyorcanbeassistedbyanoperator.MostFMScontrolsystemscombineautomaticandmanualscheduling;

thesystemgeneratesaninitialschedulethatcanbechangedmanuallybytheoperator.Thedispatcherfunctioninvolvescarryingoutthescheduleandcoordinatingtheactivitiesontheshopfloor,thatis,decidingwhenandwheretotransportapallet,whentostartaprocessonamachiningcenter,andsoon.

Themonitorfunction