Look ahead batching to minimize earliness/tardiness measures in batch processes

Scheduling problems involving earliness/tardiness (E/T) measures have received significant attention in recent years. This type of problem became important with the advent of the just-in-time (JIT) manufacturing philosophy, where early or tardy deliveries are highly discouraged. In this paper we examine the single batch processing machine-scheduling problem in a dynamic environment for minimizing the E/T measures. We propose a look ahead batching (LAB) method where the scheduling decisions are made considering the arrival epochs and due dates of incoming lots, which are easily predictable in a computer integrated manufacturing environment, especially in the semiconductor industry. The results of the proposed method are compared with the dynamic batching heuristic (DBH) and next arrival control heuristic (NACH), which are look ahead strategies developed based on arrival information alone. The E/T performance is measured by minimization of the absolute sum of earliness and tardiness of the lots (|E|+|T|) and the minimization of their square sum (E²+T²). The steady state simulation results show that exploiting the knowledge of future arrivals and their due dates leads to a significant reduction in the E/T measures for tight and loose due date settings at two different utilization levels.