A Statistical Travel Time Model for Miniload Automated Storage and Retrieval Systems with Open-Rack Structure

In customary automated storage and retrieval systems (AS/RSs), stacker cranes (S/R machines) are used to store and retrieve loads into/from the storage cells. In this paper, the open-rack structure with unidirectionalupward mobile loads within the rack is applied in AS/RS, in which the stacker crane is only used for the retrieval operations, and the storage operations are carried out by separate devices namely, storage platforms. Heuristics algorithms and models are developed for load shuffling and travel time of the storage platform, respectively. Then the expected travel time of the proposed AS/RS is derived. The travel time model and the performance of proposed AS/RS are validated using Monte Carlo simulation and are compared with a conventional one. The results show that the open-rack AS/RS represents a higher performance and the proposed models are reliable for the design and analysis of this kind of AS/RS.