Retrieval scheduling in four-directional shuttle-based compact storage and retrieval systems with heterogeneous lifts

As an emerging tier-to-tier shuttle-based system, the four-directional shuttle-based compact storage and retrieval system with heterogeneous lifts utilizes four-directional shuttles for in-tier bin transport; inter-tier movements are executed by two heterogeneous lift types, with shuttle-lifts trans...

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Bibliographic Details
Published in:Computers & industrial engineering Vol. 210; p. 111559
Main Authors: Wang, Rong, Tao, Peiran, Chen, Rui, Zhu, Taoxing, Yang, Peng
Format: Journal Article
Language:English
Published: Elsevier Ltd 01.12.2025
Subjects:
Automated warehouses
Logic-based Benders decomposition algorithm
Logistics
Performance analysis
Retrieval scheduling
Shuttle-based storage and retrieval systems
Shuttle-based storage and retrieval systems
Retrieval scheduling
Logic-based Benders decomposition algorithm
Automated warehouses
Performance analysis
Logistics
ISSN:0360-8352
Online Access:Get full text
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Summary:As an emerging tier-to-tier shuttle-based system, the four-directional shuttle-based compact storage and retrieval system with heterogeneous lifts utilizes four-directional shuttles for in-tier bin transport; inter-tier movements are executed by two heterogeneous lift types, with shuttle-lifts transporting shuttles and bin-lifts transporting bins. Since the bin-lift is typically less expensive than the shuttle-lift, employing two types of lifts can reduce both investment and operational costs. The execution of retrieval requests in this system requires coordinated operation of three types of equipment, making the scheduling optimization problem both complex and challenging. This paper investigates the retrieval scheduling problem, which focuses on determining the task sequences of shuttles and lifts to minimize the makespan. We formulate a mixed integer programming model and propose an exact logic-based Benders decomposition algorithm. Additionally, we develop an effective two-stage heuristic to provide near-optimal solutions for large-scale instances. The two-stage heuristic consistently outperforms alternative scheduling strategies, delivering shorter makespan, lower average retrieval time, and reduced capital investment. Numerical experiments reveal that increasing the number of shuttles and bin-lifts, rather than shuttle-lifts, leads to a more significant reduction in makespan. In addition, bin-lifts demonstrate greater cost-effectiveness compared to shuttle-lifts; partial substitution of shuttle-lifts with bin-lifts yields substantial economic benefits, with the highest benefits observed when bin-lifts account for 20% of the total lift investment. Furthermore, positioning lifts at the midpoint along the picking tracks produces the minimum makespan. These findings provide valuable insights into equipment configuration for optimizing the performance of such systems. •A retrieval scheduling model is proposed for a novel four-directional shuttle system.•An exact logic-based Benders decomposition method is designed for optimal scheduling.•The heuristic cuts makespan by 55.13% versus the genetic algorithm.•Key insights on equipment configuration help minimize makespan and system costs.
ISSN:0360-8352
DOI:10.1016/j.cie.2025.111559