Design and performance models for end-of-aisle order picking systems

The design of end-of-aisle order picking systems is addressed by focusing on a miniload automated storage/retrieval system. Performance models are developed for the miniload and a design algorithm is presented. The design algorithm has as its objective the minimization of the number of storage aisles subject to two types of capacity constraints: throughput and storage space. Although the system with two pick positions can be modeled directly as a closed queueing network with two servers and two customers, its special structure led to an alternative approach in developing the performance model. For two and more pick positions, the results obtained are compared with those obtainable using simulation and a diffusion approximation.