Shop Floor Scheduling in Combination with Forward and Backward Methods

Abstract

An approach to the scheduling of a shop Floor which may involve assembly machines is proposed. The objective of this approach is firstly to maximize productivity by avoiding idle time on the bottleneck machine which has maximum workload, and secondly to minimize average net flow time by making consecutive operations as close as possible. Initially the operation sequence on the bottleneck machine is determined by applying a dispatching rule. On the basis of this sequence, remaining operations are assigned to the specified machines using forward and backward methods to minimize average net flow time. As the initial schedule does not consider the conflict, the human scheduler modified this schedule interactively until it becomes feasible. From the experiment the following four points are clarified : ( 1 ) schedulers can change the initial schedules to feasible ones steadily, ( 2 ) performance of the minimization of idle time and the average net flow time largely depends on the scheduler's scheduling ability, ( 3 ) schedulers having aptitude for scheduling often seem to produce near optimal schedules, and ( 4 ) the proposed approach is suitable for shop floors where the workload ratio of nonbottleneck to bottleneck machines is small.