Stochastic cyclic scheduling problem in synchronous assembly and production lines
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Stochastic cyclic scheduling problem in synchronous assembly and production lines S Karabati and B Tan KocË University, Istanbul, Turkey In this paper we address the stochastic cyclic scheduling problem in synchronous assembly and production lines. Synchronous lines are widely used in the production and assembly of various goods such as automobiles or household appliances. We consider cycle time minimisation (or throughput rate maximisation) as the objective of the scheduling problem with the assumption that the processing times are independent random variables. We ®rst discuss the two-station case and present a lower bounding scheme and an approximate solution procedure for the scheduling problem. For the general case of the problem, two heuristic solution procedures are presented. An extension of the two-station lower bound to the general case of the problem is also discussed. The performance of the proposed heuristics on randomly generated problems is documented, and the impact of scheduling decisions on problems with different levels of variability in processing times are analysed. We also analyse the problem of sequence determination when the available information is limited to the expected values of individual processing times. Keywords: cyclic scheduling; stochastic scheduling; synchronous ¯ow lines
Introduction Synchronous lines are designed mostly to meet the assembly or production requirements of a single product, which is usually in the maturity stage of its life cycle, and ef®ciency is always considered as the primary objective in the design process. With the single-product focus, ef®ciency can be achieved by appropriately assigning operations of the product to stations of the line. Changes experienced in the nature of competition in various markets have decreased the relative importance of the ef®ciency criterion, and increased the weights of criteria such as product range ¯exibility, volume ¯exibility, and delivery speed. As a result of these changes, the line concept has shifted its focus from a single product to a mix of products that are in different stages of their life cycles, and therefore simultaneous production of a mix of products has become an important issue in the management of assembly and production lines. The shift to mixed-model production has also changed the practice, and operational decisions, such as scheduling, have gained more importance. For example, in the mixed-model setting, the performance of the line now also depends on the scheduling decisions. One of the recent approaches to the management of mixed-model environments is to employ a cyclic scheduling policy at the operational level. Cyclic scheduling policies have proved to be very effective in repetitive
Correspondence: Dr S Karabati KocË University College of Administrative Sciences and Economics Istinye. 80860 Istanbul, Turkey. E-mail: [email protected]
manufacturing environments within the JIT conte
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