Energy efficient dual command cycles in Automated Storage and Retrieval Systems

Sustainable manufacturing claims for more energy efficient operations in warehouse management. In AS/RSs they can be pursued by optimizing storage and retrieval cycles so that the least energy is required to move the crane. While picking operations have been traditionally optimized in order to minimize picking times directly linked to the service level perceived by customers, a sustainable approach leads to change this perspective by optimizing storage and retrieval cycles to lower energy requirements. In this paper we propose an energy-based heuristic to re-sequence retrievals in order to perform dual command cycles with the least energy requirements. Impact on both energy savings and round trip times is assessed when moving from single command to dual command cycles, if storage and retrieval operations are combined by the common first-come first-served policy. Further improvements on energy and time performances achievable by adopting different re-sequencing heuristics are then investigated. Factors affecting energy consumption and round trip times such as the storage allocation strategy, the re-sequencing time-based or energy-based policies, the demand distribution, and the shape of the rack, are analyzed by a 24 factorial design of experiments.