Level scheduling under limited resequencing flexibility

Abstract

A mixed-model assembly line requires the solution of a short-term sequencing problem, which decides on the succession of different models launched down the line. A famous solution approach stemming from the Toyota Production System is the so-called Level Scheduling (LS), which aims to distribute the part consumption induced by a model sequence evenly over the planning horizon. LS attracted a multitude of different researchers, who, however, invariably treat initial sequence planning where all degrees of freedom in assigning models to production cycles exist. In the real-world, conflicting objectives and restrictions of preceding production stages, i.e., body and paint shop, simultaneously need to be considered and perturbations of an initial sequence will regularly occur, so that the sequencing problem often becomes a resequencing problem. Here, a given model sequence is to be reshuffled with the help of resequencing buffers (denoted as pull-off tables). This paper shows how to adapt famous solution approaches for alternative LS problems, namely the Product-Rate-Variation (PRV) and the Output-Rate-Variation (ORV) problem, if the (re-)assignment of models to cycles is restricted by the given number of pull-off tables. Furthermore, the effect of increasing re-sequencing flexibility is investigated, so that the practitioner receives decision support for buffer dimensioning, and the ability of the PRV in reasonably approximating the more detailed ORV in a resequencing environment is tested.