Publication: A simulation study for job shop scheduling rules in FMC
Abstract
Esnek imalat sistemleri içinde, imal edilecek parçaların yönlendirilmesi, imalat çevreleri ve araştırmacılar tarafından sıklıkla ele alınan kritik bir olgudur. Bu tür imalat sistemlerinde, öngörülen performans kriterlerine ulaşabilmek için değişik çizelgeleme metodları uygulanmaktadır. Bu tezde, Visual Basic programlama dili ile geliştirilen parametrik atölye benzetim yazılımı ile, yaygın olarak bulunan bir esnek imalat hücresi modellenmiştir. Bu çalışmada geliştirilen MAXQ ve MINQ metodları, bu tür imalat ortamlarında ağırlıkla kullanılmakta olan diğer çizelgeleme metodları ile, toplam imalat süresi, ortalama akış süresi, ortalama gecikme, şartlı gecikme, geç kalan iş sayısı ve robot kullanımı gibi performans kriterleri kullanılarak karşılaştırılmıştır. MAXQ metodundan türetilmiş olan iki çizelgeleme politikasının, bahsi geçen metodlar üzerindeki etkisi, yine aynı dinamik atölye ortamında, değişik deney koşulları altında benzetim yoluyla test edilerek kıyaslanmıştır. Çeşitli çizelgeleme metodu kategorilerine ait metodların üç boyutlu performans grafikleri elde edilmiş ve elde edilen sonuçlar istatistiksel olarak test edilerek, değişen koşullardan kaynaklanan farklılıklar incelenmiştir. Elde edilen sonuçlar, MAXQ metodu ve diğer politikaların uygulanması durumunda, esnek imalat hücresi performansında iyileşmeler olduğunu göstermiştir. Özellikle, çizelgeleme politikalarının diğer metodlara uygulandığı durumlarda, ortalama akış süresinde %30 ve gecikmeye bağlı performans kriterlerinde de ortalama %60'ları geçen iyileşmeler gözlemlenmiştir. Bu metod ve politikaların basit olmaları ve yüksek performans sağlayabilme kapasiteleri, gerçek imalat ortamlarında uygulanmalarını kolaylaştıracak ve sistem verimini artıracaktır. Bu çalışmada kullanılan atölye benzetim yazılımı da, içine yerleştirilmiş olan çizelgeleme metodları sayesinde, değişik benzetim parametrelerini test edebilmek için oldukça kullanışlı bir araçtır. Modüler yapısı sayesinde, yazılıma yeni bölümler ilave edilerek, yeteneklerinin artırılması mümkündür.
The routing of parts in a Flexible Manufacturing System (FMS) is a critical issue that is frequently encountered in manufacturing and research environments. Many scheduling rules are commonly used in the job shops to meet the required performance measures. In this study, by means of parametric simulation application software developed in Visual Basic, a commonly found Flexible Manufacturing Cell (FMC) is modeled. The proposed MAXQ and MINQ scheduling rules are benchmarked with the frequently used scheduling rules for six different performance measures, namely; makespan (throughput time), mean flow time, mean tardiness, conditional tardiness, number of tardy jobs and robot utilization. The effects of the two policies that derived from MAXQ rule, on the commonly used scheduling rules are tested and compared in the same dynamic job shop environment under various experimental conditions. The performance and response surface graphs for the representatives of the various categories of the scheduling rules are obtained. The outputs are statistically tested to show the significant differences between the rules under various conditions. The results show that MAXQ rule and the derived policies improve the considered FMC performance in a great extent. When these policies are applied to other scheduling rules, it is observed that more than 30% and 60% improvements are achieved respectively for mean flow and tardiness-based performance measures. Because of the simplicity of the MAXQ rule and the proposed policies and the high performance improvement achievement, it sounds feasible to implement and test them in a similar real manufacturing environment. The job shop simulation package launched is also a very useful tool for testing various simulation parameters with built-in scheduling rules. The modular structure of the application makes it possible to develop the codes further and to add new features.
The routing of parts in a Flexible Manufacturing System (FMS) is a critical issue that is frequently encountered in manufacturing and research environments. Many scheduling rules are commonly used in the job shops to meet the required performance measures. In this study, by means of parametric simulation application software developed in Visual Basic, a commonly found Flexible Manufacturing Cell (FMC) is modeled. The proposed MAXQ and MINQ scheduling rules are benchmarked with the frequently used scheduling rules for six different performance measures, namely; makespan (throughput time), mean flow time, mean tardiness, conditional tardiness, number of tardy jobs and robot utilization. The effects of the two policies that derived from MAXQ rule, on the commonly used scheduling rules are tested and compared in the same dynamic job shop environment under various experimental conditions. The performance and response surface graphs for the representatives of the various categories of the scheduling rules are obtained. The outputs are statistically tested to show the significant differences between the rules under various conditions. The results show that MAXQ rule and the derived policies improve the considered FMC performance in a great extent. When these policies are applied to other scheduling rules, it is observed that more than 30% and 60% improvements are achieved respectively for mean flow and tardiness-based performance measures. Because of the simplicity of the MAXQ rule and the proposed policies and the high performance improvement achievement, it sounds feasible to implement and test them in a similar real manufacturing environment. The job shop simulation package launched is also a very useful tool for testing various simulation parameters with built-in scheduling rules. The modular structure of the application makes it possible to develop the codes further and to add new features.