MA Yunfeng, YU Jing, Zhang Jiayi, Hou Wenjie, Ren Liang, Gao Dongpo
Accepted: 2025-09-16
The shuttle-based storage and retrieval system with two lifts exhibits remarkable features such as compactness and high efficiency. Dual-command operation, favored for its effectiveness in minimizing equipment idle time, is commonly employed in warehouse system scheduling. However, incorporating dualcommand operations while managing conflicts between the two lifts introduces significant complexity into the scheduling decisions. This paper addresses the scheduling challenges of the shuttle-based storage and retrieval system with two lifts by focusing on minimizing the makespan through a comprehensive consideration of dual-command operations and dual-lift constraints. A mixed-integer programming model is formulated to tackle these issues. Given the NP-hard nature of this problem, a two-stage algorithm is proposed by combining the adaptive large neighborhood search algorithm and dynamic programming. To align with real-world scenarios, three types of instances, namely small, medium, and large-scale, are designed, and the two-stage algorithm is benchmarked against the Gurobi solver, the Sequential Matching algorithm, and the Particle Swarm Optimization algorithm to evaluate its efficacy. The findings indicate that: (1) Lift speed exerts a significant impact on system efficiency, yet its marginal benefits decline with increasing speed; (2) For a given input/output point, there exists an optimal speed ratio between the upper and lower lifts; (3) Dual-command operations enhance efficiency by 42.72% compared to single-command operations, while dual-lift systems achieve a 47.09% improvement over single-lift systems. The study provides a scientific foundation and algorithmic basis for managers to develop effective scheduling strategies and offers theoretical support for optimizing the configuration of shuttle-based storage and retrieval systems with two lifts.