工业工程英文文献及外文翻译.docx

工业工程英文文献及外文翻译.docx

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工业工程英文文献及外文翻译

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英文文献

LineBalancingintheRealWorld

Abstract:

LineBalancing（LB）isaclassic,well-researchedOperationsResearch（OR）optimizationproblemofsignificantindustrialimportance.Itisoneofthoseproblemswheredomainexpertisedoesnothelpverymuch:

whateverthenumberofyearsspentsolvingit,oneiseachtimefacinganintractableproblemwithanastronomicnumberofpossiblesolutionsandnorealguidanceonhowtosolveitinthebestway,unlessonepostulatesthattheoldwayisthebestway.Hereweexplainanapparentparadox:

althoughmanyalgorithmshavebeenproposedinthepast,anddespitetheproblem’spracticalimportance,justonecommerciallyavailableLBsoftwarecurrentlyappearstobeavailableforapplicationinindustriessuchasautomotive.WespeculatethatthismaybeduetoamisalignmentbetweentheacademicLBproblemaddressedbyOR,andtheactualproblemfacedbytheindustry.

Keyword:

LineBalancing,Assemblylines,Optimization

LineBalancingintheRealWorld

EmanuelFalkenauer

OptimalDesign

Av.Jeanne19Aboîte2,B-1050Brussels,Belgium

+32（0）26461074

E.Falkenauer@

1Introduction

AssemblyLineBalancing,orsimplyLineBalancing（LB）,istheproblemofassigningoperationstoworkstationsalonganassemblyline,insuchawaythattheassignmentbeoptimalinsomesense.EversinceHenryFord’sintroductionofassemblylines,LBhasbeenanoptimizationproblemofsignificantindustrialimportance:

theefficiencydifferencebetweenanoptimalandasub-optimalassignmentcanyieldeconomies（orwaste）reachingmillionsofdollarsperyear.

LBisaclassicOperationsResearch（OR）optimizationproblem,havingbeentackledbyORoverseveraldecades.Manyalgorithmshavebeenproposedfortheproblem.Yetdespitethepracticalimportanceoftheproblem,andtheOReffortsthathavebeenmadetotackleit,littlecommerciallyavailablesoftwareisavailabletohelpindustryinoptimizingtheirlines.Infact,accordingtoarecentsurveybyBeckerandScholl（2004）,thereappeartobecurrentlyjusttwocommerciallyavailablepackagesfeaturingbothastateoftheartoptimizationalgorithmandauser-friendlyinterfacefordatamanagement.Furthermore,oneofthosepackagesappearstohandleonlythe“clean”formulationoftheproblem（SimpleAssemblyLineBalancingProblem,orSALBP）,whichleavesonlyonepackageavailableforindustriessuchasautomotive.Thissituationappearstobeparadoxical,oratleastunexpected:

giventhehugeeconomiesLBcangenerate,onewouldexpectseveralsoftwarepackagesvyingtograbapartofthoseeconomies.

ItappearsthatthegapbetweentheavailableORresultsandtheirdisseminationinToday’sindustry,isprobablyduetoamisalignmentbetweentheacademicLBproblemaddressedbymostoftheORapproaches,andtheactualproblembeingfacedbytheindustry.LBisadifficultoptimizationproblemevenitssimplestformsareNP-hard–seeGarryandJohnson,1979）,sotheapproachtakenbyORhastypicallybeentosimplifyit,inordertobringittoalevelofcomplexityamenabletoORtools.Whilethisisaperfectlyvalidapproachingeneral,intheparticularcaseofLBitledsomedefinitionsoftheproblemhatignoremanyaspectsofthereal-worldproblem.

Unfortunately,manyoftheaspectsthathavebeenleftoutintheORapproachareinfactcrucialtoindustriessuchasautomotive,inthesensethatanysolutionignoring（violating）thoseaspectsbecomesunusableintheindustry.

Inthesequel,wefirstbrieflyrecallclassicORdefinitionsofLB,andthenreviewhowtheactuallinebalancingproblemfacedbytheindustrydiffersfromthem,andwhyasolutiontotheclassicORproblemmaybeunusableinsomeindustries.

2ORDefinitionsofLB

TheclassicORdefinitionofthelinebalancingproblem,dubbedSALBP（SimpleAssemblyLineBalancingProblem）byBeckerandScholl（2004）,goesasfollows.Givenasetoftasksofvariousdurations,asetofprecedenceconstraintsamongthetasks,andasetofworkstations,assigneachtasktoexactlyoneworkstationinsuchawaythatnoprecedenceconstraintisviolatedandtheassignmentisoptimal.Theoptimalitycriteriongivesrisetotwovariantsoftheproblem:

eitheracycletimeisgiventhatcannotbeexceededbythesumofdurationsofalltasksassignedtoanyworkstationandthenumberofworkstationsistobeminimized,orthenumberofworkstationsisfixedandthelinecycletime,equaltothelargestsumofdurationsoftaskassignedtoaworkstation,istobeminimized.

AlthoughtheSALBPonlytakesintoaccounttwoconstraints（theprecedenceconstraintsplusthecycletime,ortheprecedenceconstraintsplusthenumberofworkstations）,itisbyfarthevariantoflinebalancingthathasbeenthemostresearched.WehavecontributedtothateffortinFalkenauerandDelchambre（1992）,whereweproposedaGroupingGeneticAlgorithmapproachthatachievedsomeofthebestperformanceinthefield.TheGroupingGeneticAlgorithmtechniqueitselfwaspresentedindetailinFalkenauer（1998）.

Howeverwellresearched,theSALBPishardlyapplicableinindustry,aswewillseeshortly.ThefacthasnotescapedtheattentionoftheORresearches,andBeckerandScholl（2004）definemanyextensionstoSALBP,yieldingacommondenominationGALBP（GeneralizedAssemblyLineBalancingProblem）.Eachoftheextensionsreportedintheirauthoritativesurveyaimstohandleanadditionaldifficultypresentinreal-worldlinebalancing.WehavetackledoneofthoseaspectsinFalkenauer（1997）,alsobyapplyingtheGroupingGeneticAlgorithm.

ThemajorproblemwithmostoftheapproachesreportedbyBeckerandScholl（2004）isthattheygeneralizethesimpleSALBPinjustoneortwodirections.Therealworldlinebalancing,asfacedinparticularbytheautomotiveindustry,requirestacklingmanyofthosegeneralizationssimultaneously.

3WhatDiffersintheRealWorld?

AlthougheventhesimpleSALBPisNP-hard,itisfarfromcapturingthetruecomplexityoftheprobleminitsreal-worldincarnations.Ontheotherhand,smallinstancesoftheproblem,eventhoughtheyaredifficulttosolvetooptimality,areatrickytargetforlinebalancingsoftware,becausesmallinstancesoftheproblemcanbesolvedclosetoptimalitybyhand.Thatishowevernotthecaseintheautomotiveandrelatedindustries（Bus,truck,aircraft,heavymachinery,etc.）,sincethoseindustriesroutinelyfeatureAssemblylineswithdozensorhundredsofworkstations,andhundredsorthousandsofOperations.Thoseindustriesarethereforetheprimetargetsforlinebalancingsoftware.

Unfortunately,thosesameindustriesalsoneedtotakeintoaccountmanyoftheGALBPextensionsatthesametime,whichmayexplainwhy,despitetheimpressiveORWorkdoneonlinebalancing;onlyonecommerciallyavailablesoftwareseemstubecurrentlyavailableforthoseindustries.

Weidentifybelowsomeoftheadditionaldifficulties（withrespecttoSALBP）thatmustbetackledinalinebalancingtool,inordertobeapplicableinthoseindustries.

3.1DoNotBalancebutRe-balance

ManyoftheORapproachesimplicitlyassumethattheproblemtobesolvedinvolvesanew,yet-to-be-builtassemblyline,possiblyhousedinanew,yet-to-be-builtfactory.Toouropinion,thisisthegravestoversimplificationoftheclassicORapproach,forinpractice,thisishardlyeverthecase.Thevastmajorityofreal-worldlinebalancingtasksinvolveexistinglines,housedinexistingfactories–infect,thetargetlinetypicallyneedstuberebalancedratherthanbalanced,theneedarisingfromchangesintheproductorthemixofmodelsbeingassembledintheline,theassemblytechnology,theavailableworkforce,ortheproductiontargets.Thishassomefar-reachingimplications,outlinedbelow.

3.2WorkstationsHaveIdentities

Aspointedoutabove,thevastmajorityofreal-worldlinebalancingtasksinvolvesexistinglineshousedinexistingfactories.Inpractice,thisseemingly“uninteresting”observationhasonefar-reachingconsequence,namelythateachworkstationinthelinedoeshaveitsownidentity.Thisidentityisnotduetoany“incapacityofabstraction”onpartoftheprocessengineers,butrathertothefactthattheworkstationsareindeednotidentical:

eachhasitsownspaceconstraints（e.g.aworkstationbelowalowceilingcannotelevatethecarabovetheoperators’heads）,itsownheavyequipmentthatcannotbemovedsparehugecosts,itsowncapacityofcertainsupplies（e.g.compressedair）,itsownrestrictionsontheoperationsthatcanbecarriedoutthere（e.g.donotplaceweldingoperationsjustbesidethepaintingshop）,etc.

3.3CannotEliminateWorkstations

Sinceworkstationsdohavetheiridentity（asobservedabove）,itbecomesobviousthatareal-worldLBtoolcannotaimateliminatingworkstations.Indeed,unlesstheeliminatedworkstationswereallinthefrontofthelineoritstail,theireliminationwouldcreategapingholesintheline,byvirtueoftheotherworkstations’retainingoftheiridentities,includingtheirgeographicalpositionsintheworkshop.Also,itsoftensthecasethatmanyworkstationsthatcouldpossiblybeeliminatedbythealgorithmareinfactnecessarybecauseofzoningconstraints.

4Conclusions

Theconclusionsinspection3stemsfromourextensivecontactswithautomotiveandrelatedindustries,andreflectstheirtrueneeds.Other“exotic”constraintsmayapplyinanygivenreal-worldassemblyline,butlinebalancingtoolforthoseindustriesmustbeabletohandleatleastthoseaspectsoftheproblem.Thisisveryfarfromthe“clean”academicSALBP,aswellasmostGALBPextensionsreportedbyBeckerandScholl（2004）.Infact,suchatoolmustsimultaneouslysolve