Buffer sizing models for end-of-aisle order picking systems

We study an end-of-aisle order picking system with inbound and outbound buffer positions. The system is referred to as a miniload system with a horse-shoe front-end configuration, and is modeled as a two-stage cyclic queueing system with limited capacity. We analyze the system by utilizing known queueing results. Closed form expressions are developed for system performance measures, including the steady-state probability and system throughput. To provide some decision criteria in the design of buffer capacity, we examine the effect of the buffer size on system throughput. We give examples to illustrate how the results developed can be applied to solving real world problems. It is also shown that under heavy retrieval system demand, the system naturally achieves its optimal operating condition in the long run and it always performs dual command cycles.