Load Shuffling and Travel Time Analysis of a Miniload Automated Storage and Retrieval System with an Open-rack Structure

Automated storage and retrieval systems (AS/RSs) are major material handling systems, which have been widely used in distribution centers and automated productions. This paper studies the characteristics of a miniload AS/RS with an open-rack structure and unidirectional-upward mobile loads within the rack. In this warehousing system, the stacker crane is used for the retrieval operations and shuffling procedures, while the storage operations are carried out by separate devices namely, storage platforms. The proposed AS/RS has one storage platform for each rack to unload several loads at the same time into the rack. The stacker crane shuffling processes are used to provide more available locations for increasing the storage capacity of the storage platform. Heuristic algorithms and models are developed for load shuffling processes and travel time of the storage platform. Subsequently, travel time of the proposed AS/RS is analyzed under randomized storage policy and by using Monte Carlo simulation. The results show that the proposed models and algorithms are reliable for the design and analysis of this kind of AS/RS.