Optimal class boundaries, number of aisles, and pick list size for low-level order picking systems

This article considers a two-block warehouse with low-level aisles having dedicated pickers who follow a return routing policy within the aisle. Travel distance models are formulated assuming a given product density distribution in aisles for multi-item picks. An analytical recursive procedure is developed to find optimal n-class partitions of each warehouse aisle. A range on the number of classes and number of picks for which class-based storage is an attractive option over the random storage policy is determined through a computational study. The article also presents an iterative hierarchical framework to simultaneously obtain pick list size, number of aisles, and class storage boundaries. A sensitivity analysis of optimal pick travel distance against important warehouse design parameters is presented.