An algorithm for hoist scheduling

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1、INT.J.PROD.RES.,1994,VOL.32,No.3,501-516AnalgorithmforhoistschedulingproblemsY.YIHThispaperproposesanalgorithmforhoistschedulingproblemsinaflexiblePCBelectroplatinglinewherethereisnobufferamongworkstations.Duetoitschemicalprocessnature,theprocessingtimeshavetobecontrolledwithinaspecifiedrange(i.

2、e.betweenamaximumprocessingtimeandaminimumprocessingtime).Theproductwillbecomedefectiveifthisconstantisviolated.Theobjectiveistomaximizethroughputwithnodefectiveproduct.Theproposedalgorithmschedulesjobsenteringthesystembasedonthespecifiedrangeofprocessingtime.Asimulationstudyshowsthattheproposed

3、algorithmoutperformsthebasicalgorithmthatschedulesjobsbasedontheminimumprocessingtimes.1.IntroductionMaterialhandlinghoistsarecommonlyusedinsmeltingandplatingprocessestotransportmaterialsamongworkstations(e.g.furnaces,chemicaltanks).Thecontrolandscheduleofsuchhoistsisverycrucialtothesystemperfor

4、mance,especiallywheretherearechemicalprocessesinvolved.Inprintedcircuitboard(PCB)manufacturingfacilities,veryoftentheplatingprocessisoneofthemajorbottlenecks.Thehoistschedulingproblemsareusuallyverycomplex.ThehoistschedulingproblemhasbeenproventobeNP-completeareusuallyverycomplex.Thehoistschedul

5、ingproblemhasbeenproventobeNP-completeevenifthereisonlyonehoistandoneproducttypeinthesystem(LeiandWang1989).Thisresearchismotivatedbyasingle-hoistschedulingprobleminaflexibleprintedcircuitboard(PCB)electroplatingsystemasshowninFig.I.Thehoisttransportsmaterialsthroughaseriesofchemicaltanks.Jobs(P

6、CBs)randomlyarriveatthesystemandhavetogothroughtheworkstationssequentiallyfromlefttorightwhileskippingworkstationsisallowed.Inaddition,eachjobhasitsspecifictimewindows(specifiedbyaminimumprocessingtimeandamaximumprocessingtime)forprocessingineachworkstation.Iftheprocessingtimeforajobinaworkstati

7、ondoesnotreachtheminimumprocessingtimeorexceedthemaximumprocessingtime,thejobwillbecomeadefect.Thehoistisinchargeoftransportingjobs,oneatatime,throughtheworkstationscorrespondingwiththoseboundedprocessingtimes.Thetravellings