Vertical Lift Modules for small items order picking: an economic evaluation

Small items order picking is a very labour-intensive activity which is often performed in a dedicated area equipped with carton racks and with the operators walking within the aisles to pick the required products. Recently, improvements in automated solutions have been introduced to ease the picking activities and to reduce the impact of human labor. In this paper, one of these automated systems, called dual-bay Vertical Lift Module (VLM) system, is compared to a manual warehouse with carton racks. Based on the lack reported from the literature analysis, the two order picking solutions are compared according to technical and cost factors, for the first time here. The total annual cost of both systems is modelled by analytical formulations, including fixed terms, related to space and equipment cost, and variable terms, linked to workforce cost. A multi-factorial analysis and an ANOVA permit to study the impact of each factor included in the models. The comparison of the systems leads to the definition of a VLM area of application, which can be used to understand the suitability of the VLM with respect to the warehouse with carton racks. The mathematical models are also applied to an industrial example. Finally, starting from the analysis of the models and from their application, some highlights are derived, and future researches are defined.