Efficiency Analysis and Optimization of Layer-Switching Strategies for Automated Vehicle Storage and Retrieval Systems

To investigate the impact of shuttle performance and layer-switching strategies on the efficiency of the tier-to-tier automated vehicle storage and retrieval system (TTAVS/RS), a parameterized and modular efficiency evaluation model is developed based on discrete event simulation. Using the control variable approach, the model analyzes the effects of shuttle quantity, shuttle speed, and rack layout on system efficiency, and further examines the influence of four layer-switching strategies. Simulation experiments with increasing shuttle quantities reveal that the goods lift is the primary bottleneck constraining system efficiency, and that excessive shuttles reduce per-shuttle utilization; compared with the tier-captive mode, the tier-to-tier mode more effectively balances the handling capacity between shuttles and lifts, thereby enhancing shuttle utilization. Comparative experiments on layer-switching strategies demonstrate that the "shortest origin distance first" strategy outperforms the commonly adopted "first-come-first-served" strategy in engineering practice improving system efficiency by 3.1%–5.8%.