Optimal trajectory generation for reducing structural stress in rotary cranes with multiaxial motion

Automation of rotary crane motion in outdoor worksites, essential due to the declining number of skilled operators, is a challenging issue caused by complex multiaxial operations and residual load sway. This paper proposes an optimal trajectory generation method based on a three-stage S-curve velocity profile that synchronizes boom rotation, luffing, and rope hoisting motions to reduce both load sway and structural stress. The method suppresses dynamic excitation and improves structural durability. Simulations and experiments with a lab-scale crane confirm significant reductions in maximum load sway amplitude and boom stress, with finite element analysis revealing a 17.7 % stress decrease and a 2.7-fold increase in mechanical lifespan. These results extend equipment life and mitigate fatigue-related failure risks, enhancing safety in repeated automated tasks. Furthermore, the method achieves skilled-operator-level efficiency while reducing structural loads, enabling accurate, safe and efficient operation. This contributes to the advancement of practical and reliable crane automation.