Using simplified drum-buffer-rope for re-entrant flow shop scheduling in a random environment

The traditional simplified drum buffer rope (SDBR) does not consider the application of re-entrant flow shop (RFS) in a random environment which might involve variable processing times and machine breakdowns. This paper proposed a weighted layer production buffer and weighted production buffer to monitor the status of the buffer deviation when applying SDBR in a RFS with non-deterministic parameters. The buffer status deviation used the overall urgency and actual urgency to estimate the influence of overall accumulated machine downtime and the influence of actual machine downtime of capacity-constrained-resource (CCR) at different layers. A dispatching rule, called SDBR_DReentry, was applied to decide the priority of all work orders by the buffer status deviation of each CCR machine with the consideration of the re-entry feature. A simulated RFS was designed and four different methods (including ours) were applied in order to demonstrate the effectiveness of our approach. The experimental results show that when compared to six performance indexes related to the due date, our approach has better performance than the other three methods when the product mix with a large proportion of multi-reentrant orders and when the CCR utilization increases from 60 to 90%.