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Ml!l.1° ,i-: i j' PIII,\\SJ!J.I~ f f.1111:>1!~ I.I!S,IJ,\!Ull-)PII.ly-:tI!.lOI-\i-ISII.l3 ~. ~.";.,,..; L- ..\ßSTI~AL'T In this paper. we address the backlog sequencing problem in a flow-shop CON\VIP production conlrol conlrolled by a system with the objective to mini mise the makespan We characlerise the problem and analyse its similarities and ditlerences with the permutation 110\\-shop problem A comparison of same well-known and a simple and fast dispatching rule is proposed heuristics. the proposed rule Regarding the more simple and laster outperforms those commonly used für the problem! permutation flow-shop Key\vords: dispatching flow-shop heuristics is carried out. Scheduling, Sequencing, Flow-Shop. Constant Work in Process (CONWIP). Heuristics, Dispatching Rules ZUSAMMENFASSUNG In diesem Arbeitspapier wird das Reihenfolgeproblem fur die Einsteuerung von Aufträgen in ein Fenigungssystem (backlog wenn das System durch (CONstanl sequencing) bei Reihenfenigung eine 'Konstanles Work In Process = CONWIP) rung der maximalen Durchlaufzeit rakterisien Seine Ähnlichkeiten Reihenfenigung mit konstanter Shop) werden analysien Arbeitsvolumen gefuhn wird (Flow-Shop) in der Fenigung'-Steuerung Als Zielfunktion (C...J angenommen behandelt, wird die Minimie- ; und Unterschiede zum klassischen Reihenfolgeproblem bei Auftragsfolge auf allen Maschinen (Permutation-Flow- Bekannte Heuristiken fur den Permutation-Flow-Shop werden auf den CONWIP-Flow-Shop übertragen und verglichen regel wird vorgeschlagen Wird diese Regel mit einfachen und schnellen Heuristiken fur den Permutation-Flow-Shop ! Das Problem wird zunächst cha- verglichen. Eine einfache und schnelle Prioritäts- schneidet sie in Simulationsuntersuchungen besser als letztgenannle ab 1. Introduction The production control system CONWIP -acronym für CONstant Work In Process- (Spearman el '1/. 1989) is a pull system thaI appears to share the benefits of Kanban while being applicable in a wider range ofsituations The key poinl ofCONWIP is that it does not limit the single station's WIP or its butTer size, hut the total WIP in the system Several studies (eg Spearman el al. 1989, Lambrecht and Seagert ]990. Chang and Yih Gstettner and Kuhn 1996. and Bonvik "I al. 1994, 1997) indicate thaI in certain production scenarios. this conlrol system is prelerable to others 2 ,;,,;' ):::"1 (S661 c Ul?wJI?;ldS pUl? ddoH) sl:>npoJd IU;lJ;llIIP .10 ;lnUI?J J;)PIM I? ;)lpUl?4 UI?:>I! 11?41S! ul?qul?'I J;)AO S;)nI?IUI?Apl? 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';)U4 dlMNOJ UI?:>11 'AII1!:>lse8 (S661) ,lI) lIlSIIIR4:J;llU II)JIIIO:> "'°[1 Ul!llIJR;)dS P;lI!I!I;)P "41 -~-~ ;, 011 Ihis general CONWIP sequencing problem, very litlle work has been reportcd I)lll:nyas (1994) sludies Ihe most suilable dispalching rules tor a CONWIP nel\\ork queues TarditT (1995) designs an MRP-C based Iramework lilIe by USillg tor sequencing in a C'ONWIP system Finally, Herer and Masin (1997) lormulate a mathematical programming version of the problem of sequencing the back log in a CONWIP of minimising system with the objeclive total costs In this paper we address the backlog sequencing problem in a CONWIP CONWIP framework described by Spearman I!f al (1990). sincc Ihe back log is generaled by an MPS (Master accoum customers demand. so the composilion Ihe production period system in Ihe sequencing is a slatic issue, Production Schedule) taking imo of the backlog is known at the beginning of It is supposed thaI the number of cards to be employed in the system has beeIl fixed within the previous WQS module. and thus there is no way to schedule the emrance of jobs into the system once the jobs are arranged in the backlog This means thaI a .job in the backlog will enter whenever there is a card available given it has been sequenced first in the queue in front ofthe system. In Ibis context, a plausible objective für sequencing the backlog seems to be minimising the makespan because: (I) Meaning ofthe backlog in a CONWIP system: thaI is, the set ofjobs to be processed within the next production assigned to a specific job, the completion priorities period thaI are going Thus, unless a high priority is of all jobs is a major issue If different are assigned to the jobs. a relevant objective could be minimisation of the weighted tlow time (2) According to Schonberger (1984) and Spearman I!f al. (1990), period für a pull system in general -and particularly be divided into a regular production the production für a CONWIP system -must time in which the production quota can be achieved and a catch-up time which provides a time-buffer to reach the production quota if, due to unforeseen circumstances (eg materials), machine breakdowns or lack of raw it cannot be accomplished within the regular production time Usually, the catch-up period is used für housekeeping, preventive maimenance, etc In this context, makespan minimisation has the effect of ensuring the production be reached within the regular production basis für a reduction ofthe time On the long run, it also provides a regular production time and für shor1eninglead limes 4 : ~;;:;:":i!i quota to '-' -, -~ -- ;l1!U!JU! Sl1 p;lI;lJdJ;lIII! p:!ull1JISuo:>un J;lllnq ;14.1 ;141 ;lq 148!w S;lSl1:> ;lW;lJIX;I ;lSl1JOIS J;I.unq S 4:J!4M SIUll1JISUO:> J;lJJnq OU aMI P;lI!W!1 ;141 .10 ;lSl1:> 111!:J;lds11 Sl1 p;lI;lJW;lIU! 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Jql ,11111PI1;JP 11 'SdW pou;Jd uoll:>npoJd 1111Äq p;JII1J;JII;J\J1I;J4M (f) ..-, '.- ..~ illlermcdiale butrers) and the zero or no-wait sequencing problem In the two lalter Ihe iJllermediate butTers are zero, but the no-wait sequence problem is even more restriclive in the sense thaI the staning time of a job on the first machine has to be chosen such thaI the job does not have to wait für its processing on any machine The unconstrained sequencing problem has been studied extensively, and a good reference für zero and no-wait problems is pro\ided by Hall and Sriskandarajah (1996) Ht1we\'er, the intermediate case in which butrers are different from zero and not infinite has been addressed by relatively Cunningham Logendran 1975, Reddi despite it is considered (Wismer few researchers für very specific purposes (Dutta and 1976, Papadimitriou and Sriskandarajah and Kanellakis J993, and Sharadapriyadarshini 1980, Leisten and Rajendran the most realistic situation in many manufacturing 1972, and Reddi and Ramamoonhy considered in principle - (o be more difficult 1972) 1990, } .' 1997), environments Besides, this type of problems is than the extreme cases (Mon on and Pentico 1993) With the exception of Dutta and Cunningham, who develop a dynamic programming procedure to generate optimal solutions with the objective of minimising completion limes for the two-station the maximum problem with limited butTers, the rest ofthe papers are mainly devoted to the development ofheuristics für the problems Maybe the most complete work in this direction is done by Leisten, who compares several heuristics für the m-station flow-shop sequencing problem with different intermediate buffer sizes The tested heuristics include buffer-constrained specific (including Dutta and Cunningham, Reddi, and Papadimitriou and Kanellakis and two new heuristics suggested in the paper) as weil as F .,LormuIC""" heuristics heuristic (Nawaz It turns out thaI the NEH ef GI. 1983), employed foT the unconstrained buffeT problem. performs weil according to the objective of minimising makespan. These results suggest thaI same well-known F..lvrmIIIC , heuristics may be suitable also für the CONWIP problem. which is connected to the buffer-constrained sequencing problem with respect to regarding buffer capacities within the system However, in contrast to fixed buffer sizes between each two machines, the CONWIP problem supposes a fixed number of jobs within the entire system being either processed on a machine or waiting for their next operation 3. The structure of the problem To obtain a first insight info the CONWIP-problem, the empirical distributions of all possible makespans obtained by complete enumeration of I 000 instantes of seven machines 6 'Ci, .i:"c '+"iCC,.,:;;j h --, '. .;;; p;J1U;)lUWO:> A,Sno!I\;)Jd ;)41jO snoll\;)Jd IS;)J ;)41 {wnw!ldo ;);)J41 ;)41 jO ;)41 ;Jl\oql! ;)41 U! 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'i'" ..~ ~I patterll~ For instance, the CONWIP six cards curve nearly lits the Ilow-shop makespan di~t ribution However, second pattern jobs from a practical out look it seems there should be a focus primarily onto the thaI is when the card count is neither very low nor close to the number of The first problem is easy to salve and even a 'bad' sequence does not have as much impact on the system performance For the laffer case, we can use numerous techniques developed für the F;'!fJrmIIICmn., problem additional problem Besides of discussing the second pattern itselt: an therefore arises from determining the borderline between the second pattern. ie the 'real' CONWIP-problem, and the third pattern, ie . , 1 li . the ordinary permutation tlow shop case 150 1\ \ \ I -pefm \ ~ 100 f E ~ ; '!! 0 , ' ,', ' ' " \...' .' ..'\ ~ E , ~ '., ,'.:, ':', \ I ' \ 50 g ".' :"'.. I -CONWIP.6cards :', ' \\ " ", ; :' ", " :, ;,'. " """ \..' ., 0 500 700 ftow-shop CONWIP -2 cards CONWIP -3 cards ---CONWIP-4cards -CONWIP.5cards , '. 900 1100 1300 1500 makespan Figure 2: Empirical In figure 2, the distributions are shown The distributions distributions ofthe optimal makespans of the optimal makespan für the I 000 problem instances are almost symmetric While für six cards instances, the optimal values of the makespan coincide with those obtained für the permutation flow-shop, the situation is different when the number of cards is lower A more exhaustive analysis by inspection of the vectors of the optimal job sequences confirms thaI these vectors, within this small numerical problem, study, are identical für the six cards problem and für the flow-shop and almost the same in most of the instances of the five cards problem as compared with the flow-shop problem However, the analysis reveals thaI, in general, the vl:ctor of the optimal solutions für two, three and four cards are different as compared with thosc obtained für the ordinary permutation flow- shop case 8 " , 6 lI\\Oll'l SI S~W!I ilulss~:JOJd ~41,IO lIO!lnq!JISlp S14.L 66 01 ~lIO WOJ) ilu!nul!J S~W!I nlllss~:JoJd WOPUI!J411M p~II!J~u~8 u~~q ;)\1!4 S~:JUI!ISU!U~I ~lN pUl! 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"Pli!!' 11!:Ju;)wnll IIl!lllS S!l{ljO ;)UIO:JIIIOlI!l!lll ;11{1. i;i)! -, 11'prOdllCCditlicull schcdulillg prohll'ms «'amphelll'I "i 1970, arId Dannenbring 1977) In lolal, (he tesl-bed contains 180 instances The tested heuristics are those due to Palmer (1965), Gupta (1971), CDS (Campbell el "i 1970), RA or Rapid Access (Dannenbring 1977),and the previously mentionedof NEH Thc Ihree latter perform makespancalculation in several consecutive steps, so the card numher limitation must be explicitly laken into account We will call them CONWIP-CDS, CONWIP-RA and CONWIP-NEH to indicate thaI in the evaluation of partial schedules,the !,.' available number of cards has beenlaken into account For the Palmerand Gupta heuristics, ,.i no specific adaptation is required, since both are based in the construction of indices, taking ;': into account exclusively the processinglimes of thejobs. Besides the above mentioned heuristics, we also test the PF (Profile Fitting) heuristic, introduced by McCormick et al (1989) and proposed in Pinedo (1995) für the flow-shop with limited intermediate storage problem In this heuristic, the first job of the sequenceis the one with the smallest sum of processinglimes This job generatesa ~ determined by ils departure limes from every machine The next job to be sequencedis chosenamong the remainingjobs in order to fit the profile ofthe previous job (that is, to minimise the idle and blocking time in the machines during the processing of this job) The procedure is repeated until all jobs are arranged This heuristic has been also adapted für a CONWIP system in the calculations of the profiles of the jobs taking into account the availability of cards,so in the following it will be namedCONWIP-PF. T 0 compare the relative efficiency of the heuristic, an upper bound of each instancehas beeIl found by long runs (about 10 000 objective function evaluations) of a standard simulated annealingalgorithm The quality of the solutions is representedby the percentage deviation of this upper bound In table 1, the mean percentage deviation from the best known solution of each type of problem is presented The results shown in table 1 reveal that the NEH heuristic is by rar the most suitable among the tested heuristics. The poor performance of the CONWIP-RA heuristic is ., '~. surprising to a certain extent, since it is usually considereda rather suitable heuristic für the FmVJrml/IC..,., problem when short computation limes are required (Taillard, 1990) This reinforccs the idea al ready expressedin section :; thaI suitable methodsfor the f;"VJrmlllr.." problem may not work weil für f;"lcCJllwip!('""" 10 , . 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Besides, the NEH permutation tlow-shop heuristic is by rar the best constructive sequencing problem (Taillard heuristic known für the ~ 1990), although its main shor1coming is the time required to arrive to the solution. compared with other heuristics This is because the NEH heuristic is O(/? m), while Gupta's. RA and Palmer's are O(lIlog(lI) CDS is 0(11 m2 + m 1110g(lI) ) As mentioned before, in CONWIP + 11m), and sequencing, it is not 12 ~"i:;;c;:".' ~, -~ iiii ;141.10 JJllIJ:J SMolloJ ~~ ;)41 1I1 S;)UIII nlllss;):JoJd jO lllll~ jO Pli;) ;)41 1I! JO nll!lIlIln;)q sqof ;)41 ;)nuI1JJI1 'pUOJ;)S 'ISJt/ p;)sl1q 'w~lqoJd J;14n14 411M sqf:!f ;)41 nu!II1:J°1l11 ';)IIlP;)4:>~ ;)41 ;)41 1I1f.1;)I\III1UJ;)1111sqof ;)41 ;)111:>01111 .AIII1U!:! 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The rationale für this procedure is as follows in a CONWIP system it is imponant thaI the jobs entering in the first places have a shon processing time, since the cards thaI are 1 " -J attachcd to them must be used für funher jobs This is a critical condi\ion für the first jobs, since a delay of the first jobs is propagated along the sequence On the other hand, entering the jobs with higher processing times at the end causes the makespan 10 be enlarged, and most of the time gained within processing the first jobs is spoiled by large processing limes at the end of the schedule Thus für a CONWIP system, the location of a job with high processing time is less harmful with respect to the makespan of the sequen~.if middle ofthe sequence. ,IlIlIfNT Palme. C.:nl.e SPT LPT 1986() 740:1 17494 22103 12528 26.47t 13829 19990 20.387 t7726 t6790 22116 11.572 17758 20460 24187 19.288 t6.613 26.098 16.614 22085 24841 28126 14817 16793 27932 20894 24631 26290 28357 15/1()/12 13181 16512 28635 21540 25287 26966 29025 2()/10/10 18761 18571 2766() 20196 25561 27019 29458 2()/11)/15 14055 1851XJ 29.<nJ 21573 26.355 27403 29525 20/10/111 1-1055 185tXJ 29'<KJ() 21573 26355 27403 29525 ,()/I()/IO 31)/10/20 179()2 11962 2t.300 18534 28.783 32673 t6.753 20110 2401K) 25276 23481 24944 27826 27441 . 30/10/25 20/2U/10 21)/2U/15 11968 39899 244-18 18539 42797 25823 3267920.115252822495027447 4586(1 33483 42U54 43968 35201 276<17 28.336 31462 411167 31581 .. 2()/21)/18 20469 24925 345111 27686 28234 31468 31178 30/20/10 167116 18.358 19986 13672 17517 175.'8 21829 ,0/2()/20 13732 21093 28.'115 20862 24666 23425 24030 ~0/~0/25 140()-\ 21719 29057 2149-1 25'20 24)167 24677 Me..: t7.362 20.065 29. t(l(, t9.832 24.789 26.010 27.7-16 10/10/115 Gupta CONWIP.RA it is in the 14849 13274 10/IO/lJ8 IIOIJI 15/10/05 21.359 15/10/08 15/10/tO Taille 3 Mean percentage deviation ofthe 14 gIRO 19.322 best solution für the dispatching rules $', SI41 w:llqoJd fiu!:>u:lnb:ls dIM~O') s~ :14101 P;\PU:lIX:I :lq IOUU\!:I w:I\qoJd ""',)I"'I/.I(~'.:I JO,I p:lsn AII"JsS:l:>:>nss:>!ls!Jn:l4 u"ou'I-II:lM 896fv L918t 8(5LI 6Z81l 19L05l 59t08l 09tOl LIII~l 610"Ll IIS~6l aMIs t'JOOtl LI_LI ~O Zt IMMrvl 1955Z R_LLI I-(,tLI oLdl "'ciS :141 1\!41 le:ll\:lJ Slu:lWIJ:ldx:I :141jO sllns:lJ :141 suo!snpu°.:J (p:lI:J:lI:lS :lJe IU pue 11U:I,'!1I \! 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SIU:lIQOJd.10 I:lS P;\l]IJ:>$JpAI~11011\;lJd :11(1Uo :Jlls!Jn~4 SI41 p:lIS:l1 :l1\\!1( :IM ::)" might bc seen as a contirmation dillcrent thaI 1'..,VJrmlll( '..." and 1';'It.'/J/lwipl( '...:, are, in general, problems, as it is derived from the results obtained in section 3 As lar as simple heuristics are concerned, CONWIP-RA to ofter very good clearly outperformed the behaviour results with short computation by the other heuristics of the NEH heuristic, heuristic, which is considered limes in the I'~,v)rmlll( '..." problem, is For more elaborate heuristics, it appears thaI which otTers the best results among the tested heuristics, is partly due to the numerous partial evaluations of sequences, and partly due to the fact that same problem instances are not WIP-constrained .. Finally. a simple dispatching rule is devised for the CONWIP sequencing problem This rule has proven to be panicularly suitable for those instances with lower card count I In -t these situations, the rule also clearly outperforms the more common fast heuristics used for the F;'VJrmIIIC""" problem The study presented here can be extended detinitely: As rar as the relation of n, m and NT as weil as the structure of the processing limes are concemed, the border li ne between simple flow shop behaviour of a problem relevance of the CONWIP constraints dispatching the CONWIP developed rules exploiting or a problem instance respectively can be explored problem Additionally, and the heuristics and structure in more detail might be We plan work on these aspects However, the study presented here gives a first insight into the structure ofthe sequencing problem ofCONWIP problem settings References Berkley, B. J., 1992, A review of the Kanban production Prcldllction and Operations Management, I, 393-411 control research literature Bonvik, A M, Couch, C, and Gershwin, S, B, 1997, A comparison of production-line control mechanisms /11/ernational Jolln/al (1 Prod/lction Research, 35, 789-804 Campbell, H G, Dudek, R A, and Smith, M, L, 1970, A heuristic algorithm for the n-job, m-machine sequencing problem Management oS'cience,16, B630-B637 . Chang, T M, and Yih, Y" 1994, Generic kanban system for dynamic environment Intemalional.fo/lrnal 0/ Prod/lction Research, 32, 889-902 Dannenbring, D G" 1977, An evaluation of flow-shop sequence heuristics ManaXl!nlel/1 ~; St.'il!nt.'e,23,1174-1182 Dar-EI, E M, Herer, Y T, and Masin, M, 1992, CONWIP-based production lines with multiple bottlenecks performance and design implications Technical report, Israel Institute ofTechnology, Duenyas, 1,1994, Haifa, Israel, A simple release policy for networks ofqueues with controllable input O,Jeralic)/l,\" '~e,\"l!arch, 42, 1162-1171 Dudek, R A, and Teuton, 0 F, 1964, Development of m stage decision rule for scheduling n jobs through m machines (J,Jl!rat;c)/l,\"l?e\"l!arch, 12, (3) 16 -::' -91, 'u L~ LI' ',}>II,}!,J,\,/11,}/U,};J'/J//IJrv ;Jn\!JOIS;J1\!!p;JIlIJ',}IU!41!M nuIJu',}l1b~S'9L61 's ~rN 's.lIllJ S '!PP;J~I (II\!H ;JJIIU;lJd pooM',}lnu3) ,IIU,J/I,;{IPi/V ,IIUIf/!,I/h'i/IJ ',{JIi,JIf/ :,il/!//lp,JIf,7,\, 'S661 '~ 'oP',}uld 6~~-ff~ 'L'l ',{JiJll!If,JIJrv;J'11!/lldIIJ'},),/lJjllli!/V!,7/}I,;I'V ,JIf/ ji} //J//.I/lIi[ ;ln\!IS ,\J\!JOdUI',}1P;lIIWII 41!M fiuIII1pa4JS d04S-MOI:l '0861 'd 'S!)j\!llaul!)t pUl! 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S .JaUllaIS!) ,II,\\NO'> 9Z[-L8Z 's ",7!//J/U;JIf/v}'V;J/,JJ,7,'!(/ji} l/pmlV A:1'1JI1S 11 nlllll1pa4:J~ PU\! nlllJII;ll1bas J!ISIUllIlJalap UI UO!II!WIXOJddl! pUl! 1I011l!SIlIlIIdO 'hL(, I ") 11 V "lm)l AO()IIIII~1 Pli\! ')I r '\!JlslIa1 '1 3 'JalM\!l '1 ~I "lIII1I(I1.1~) 966-686 'I 'l ';J}I/;J/7S 111;J//I;J,iPI/Vrv;lnI!JOIS;lII!IP;lIlIJ;l11I1 :11111~1 1(11'11 sdol(s-'IIOll ;l1I1I1:J11111-0'l11 nlll:JII;)l1h:1S'SL61 .\1 "l1I\!l(nllllllll1,) PII\!.)I S .\!III1(1 ~."'f", I{.:ddi. S S. and I{amamoorthy. C V, 1972. On the flow-shop sequencing problem with no wail in process ()IJt!ratilJllal'~ex('ar('h <!'Iar/erl>', 23, 323-331 I{ccves, (' I{, 1995. A genetic algorithm for tlowshop sequencing ('vmIJllter' ()per(l/itlll(11 1<"""11"', 22, )-1 '; Schonberg.:r, I~ J, 1984, ~I/vrhl .Ia.'" m(l/IlljiIL'/llril"l,': /he le.\:'lIlIX llr ,impliL'I/) , appl;,'J (NY, Thc Free Press) Sharadapriyadarshini, B, and Rajendran, C. 1997, Scheduling in akanban controlted Ilowshop wilh dual blocking mechanism and missing operations for part-types Illtema/iV/lal ,!clllmal llf PrlJd/lc/io/l/~e.~em'ch, Spearman, M architecture L, Hopp, W J. 35, 3133-3156 and Woodrufl: for Constant Work-ln-Process 0 L., (CONWIP) ""al/1!fact//rillga/ldOperatio/l.~Ma/lageme/lt, 1990, A hierarchical production control .. system~, :JlI//mal llf 2,147-171 Spearman. M L., Woodruff. 0 L., and Hopp, W J, 1989, CONWIP a pult alternative to kanban fII/ema/io/lal Jollrnal 01 Prodllctio/l Research, 28, 879-894 Spearman. M L, and Zazanis, M A, comparisons 1992, rush and pult production syste~s issues and OperatiO/l.5 Research, 40, 521-532 Tailtard, E, 1990, Same efficient heuristic methods for the flow-shop l~lIrlllJt!a/l,!ll/lr/lall?f Operatio/lal Research, 47, 65-74 Tailtard, E, 1993, Benchmark for basic scheduling ()peratilmal Re.~earch, 64, 278-285 problems, sequencing problem El/ropea/l Tardiff, V, 1995, Detecting scheduling infeasibilities in multi-stage, production environments, PhD Thesis, Northwestern University, USA Wismer, 0 A, 1972, Solution of the flow-shop queue ()peratiO/l.5 Research, 20, 689-697 Jol/r/lal finite lI/ capacity sequencing problem with no intermediate WoodrutT, 0 L., and Spearman, M L., 1992, Sequencing and batching for two classes of jobs with due dates and set-up limes Jo//r/lal l?f Prodl/c/io/l a/ld Operativ/ls Ma/lageme/l/, 1, 87-102 Zegordi, S.H, Itoh, K, and Enkawa, T, 1995, Minimizing makespan for flow-shop scheduling by combining simulated annealing with sequencing knowledge E//ropea/l Jo/trllal llf Operatio/lal Research, 85, 515-531 -'~{:ii.:;il~~ (,: , '\1'5" ~:;;; I3IJf)9l ,~\i~1 /-: t ,:)1),,)\ \\:: 18 ':.'i Il.cddi, S S, and I~amamoorthy, C V, 1972, On the flow-shop sequencing problem with 1111 wail in process ()/lerOli(llloll?exeor(..h (j1(O/"lerf}', 23, 323-331 Il.ccves, C' I~, 1995, A genetic algorithm tor tlowshop sequencing I(""'"r,"', 22, 5-11 Schonbergcr, I~ J, 1984, UI(lrl,/ L'I"" (NY, The Free Press) ('(Inllllller, ()p,'mli(l/kll 1//001/(/LI("(llril,x Ihe 1",",'(111,'(Ir ,il//pli('II)" ,'ppli,',} Sharadapriyadarshini, B, and Rajendran, C, 1997, Scheduling in akanban controlled tlowshop \vith dual blocking mechanism and missing operations für part-\ypes /l11"/"IIOli(l/Iol ,IVIIrIIOI v( Pr(idIIClioll/?e,\"earch, 35, 3133-3156 Spearman. M L, Hopp, W J, and Woodrutl: D L., 1990, A hierarchical control architecture für alld Constant Work-ln-Process Nlolll!(aClllrillg OperaliO/I.\" Mallagemelll, (CONWIP) 2,147-171 production systems, '.J(mmol v( Spearman, M L, Woodrutf, kanban IIIlenlaliol/al D L., and Hopp, W J, 1989, CONWIP Jollrl/al 01 ProdllCliol/ a pull alternative to Research, 28, 879-894 Spearman, M L., and Zazanis, M A, 1992, rush and pull production systelrls: issues and comparisons Operaliol/,\" Research, 40, 521-532 Taillard, E, 1990, Some efficient heuristic methods für the flow-shop 1;;,lr(I/iL'OI/.!ollrl/al C?(Operaliol/al Re~'earch, 47, 65-74 Taillard, E, 1993, Benchmark für basic scheduling Operoliol/al Re,\"earch, 64, 278-285 Tarditf, V, production problems, sequencing problem E/lropeal/ 1995, Detecting scheduling infeasibilities in multi-stage, environments, PhD Thesis, Northwestern University, USA Wismer, D A, ] 972, Solution of the flow-shop queue ()peraliol/,~ Research, 20, 689-697 Jo/lrl/al finite (if capacity sequencing problem with no intermediate Woodrutf, D L., and Spearman, M L., 1992, Sequencing and batching für two classes of jobs with due dates and set-up times Jo/lmal 01 Prod/lcliol/ al/d Opera!iul/,~ Mallaxemel/l, 1,87-102 Zegordi, S.H, Itoh, K, and Enkawa, T, 1995, Minimizing makespan für flow-shop scheduling by combining simulated annealing with sequencing knowledge Ellropeal/ Jvllrllal o( Operaliol/al Re~'earch, 85, 5] 5-531 "::: ", ...t:iJ\" i ,\14," :JO:"{', ,. , ~~ .~\\~j "t '~)II..))\ \It 18 -- "nl!;)/I -IUSI;)Jd run ;)gU;)WPI;)D 'S;)PI;)D S;)P 1!;)JjgIPuIM4:>s;)gSjnI!IWOU;)4:>S!MZSUI!4 86/8 "U;)W4;)W;)IUO J;)P JnJJjruls -sguru;)!ZUI!U!~ ;)IP jnl! guru;)!UO!II!JI!P;)J)! 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