An assembly scheduler for TFT LCD manufacturing

This paper presents development of a scheduling system for Thin Film Transistor Liquid Crystal Display (TFT LCD) assembly process. With given daily production plan that is rough-cut capacitated, the scheduler generates shift-based capacity feasible schedules at each assembly step. The scheduling problem is a parallel-machine scheduling problem with sequence dependent setups and some manufacturing environments, which make the problem considerably difficult. The scheduling objective is to minimize the mean flow time and maximize the production progressiveness. Two scheduling heuristics are proposed for each production step of assembly process. The first scheduling heuristic is applicable for the first three steps of assembly process, i.e. coating, rubbing, and attaching step, and for the later steps another similar heuristic is employed. We also propose a simple method for computing production requirements for each step where daily production demand is unknown. The proposed scheduling procedures are implemented in a real TFT LCD manufacturing line and their performances are investigated. The experimental results show that the proposed scheduler provides quite better schedules than the current practice employed in the line in terms of both mean flow time and fulfillment of production demands. (C) 2001 Elsevier Science Ltd. All rights reserved.