Circular rail-guided vehicle scheduling considering multi-type composite operations and task release times

This paper investigates the scheduling of Circular Rail-Guided Vehicle (CRGV) in a real-world tobacco warehouse logistics system. In this system, CRGVs are required to transport materials among multiple material-handling units distributed across different areas. Since transportation are synchronised with material-handling operations, each task can only be transported after being released by the corresponding unit. Moreover, the diverse tasks among different units create a multi-type composite operation environment. These characteristics make efficient CRGV scheduling challenging, and fixed rule-based scheduling is therefore adopted in current industrial practice. To address the challenges, this study formulates a mathematical model with the objective of minimising the total flow time, which enables the processing of multi-type composite operations under task release time constraints. To improve solution quality, a heuristic-guided sequential small perturbation and a staged exponential cooling mechanism are proposed, resulting in an improved simulated annealing (ISA). Experiments based on real data demonstrate that, compared with the standard simulated annealing, ISA improves solution quality by 1.89% and obtains superior solutions relative to other methods. Furthermore, in scenarios with different task densities, the proposed approach achieves solutions approximately 10.75% better than existing rule-based scheduling, indicating strong robustness under varying task-density conditions and promising applicability in practical engineering.