Variability Aspects in Flowshop Scheduling Systems

In this paper different aspects of variability in a job scheduling system are discussed. Unlike an ideal manufacturing system a real-world system requires an efficient mix of different buffers to balance the influence of variability. The focus in this paper is to observe the effects of non-uniformity of processing times on the performance measures Makespan, Flowtime and Squared Variability of Completion Time Differences (=CTDVB2). In addition, the behavior of Waiting Time and Idle Time regarding these measures is analyzed. An example is used to illustrate the influence of variability: A nonuniform permutation flow shop is smoothed in different ways. First a linear step-by-step harmonization is executed. Furthermore, non-uniform processing times are modified with a logarithmic and a quadratic optimization model.