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제안 방법
- The changeover time of a lot at each stage can be known from its product type. Further assumptions in this study are: an infinite buffer at each stage; no transportation time between stages; no machine breakdown; and no job split or preemption.
- In this paper, we fOcused on a hybrid flowshop scheduling problem with the objective of minimizing mean tardiness of orders which arrive dynamically and the changeover operations are needed when lots of the different product types are processed consecutively on the same machine. We tested two types of scheduling methods for the hybrid flowshop scheduling problem using the simulation model.
- If an order is not completed by the end of the simulation time, tardiness of the order is obtained with estimated completion time of the order, C, which is calculated as (1+ g)/«, where I is the amount of inventory preceding the order, q is the uncompleted quantity of the order, and 杪 is the production rate of the last stage. In this study, the 4 rules for MVPM and one for OVPM were tested for each problem set. The model was coded with C language and all tests were carried out on a Linux machine with AMD Athlon process of 1.
- generated. In this study, to solve the scheduling problem, our algorithm generates multiple alternative sequences of the target orders and evaluates the generated sequences, obtaining a schedule for each alternative sequence. After the evaluation, one sequence that gives the best performance, i.
- Consequently, to the best of our knowledge, there is no study of HFS scheduling problems considering all these characteristics (dynamic arrival, due date commitment, and changeover times), even though covering such characteristics in a formulation could make the problem more practical. In this study, we focus on the HFS scheduling problem with the objective of minimizing mean tardiness of orders, while orders arrive dynamically and changeover operations between different product types of lots occur.
- The other is Order View Prioritizing Method (OVPM) in which more sophisticated method of prioritizing is used than MVPM. To evaluate the performance of the considered scheduling methods, computational experiments were done with a simulation model. Various results of the experiments showed that an OVPM outperformed all MVPMs.
- same machine. We tested two types of scheduling methods for the hybrid flowshop scheduling problem using the simulation model. One is Machine View Prioritizing Method (MVPM), which is same as the typical list scheduling approach with the dispatching rules.
- That is, a big penalty value is added on the priority value of a lot if the lot causes a changeover operation. With this modification, we rename the above rules as SEDD, SSLACK, and SMDD. For example, when we use SEDD for the prioritizing, the priority value of a lot which causes a changeover operation would be ‘100 xt + df while that of a lot which does not is just ‘ d「.
데이터처리
- To see the impact of the factors (i.e. the number of stages, the due date tightness, and the range of order size) on the performance, an analysis of variance (ANOVA) was done on the solution values (i.e. mean tardiness of orders), and results are given in table 2. The results showed that performance of the scheduling methods was significantly affected by the number of stages and the range of order size at the significance level of 0.
이론/모형
- In addition to the above three rules, we use the ATCS rule which was proposed by Lee and Pinedo (1997). In this study, the priority function of the ATCS, which was originally devised for parallel machine scheduling with sequence-dependent setup times, is modified as
- Therefore, the priorities can be obtained based on up-to-date information of the system status when a list scheduling approach with a dispatching rule is used. In this paper, we call this kind of list scheduling approach, which uses dispatching rules for prioritizing, the Machine View Prioritizing Method (MVPM), because a lot is selected from the machine’s point of view. On the other hand, we suggest an approach, called Order View Prioritizing Method (OVPM), which has a different notion to MVPM.
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