Trajectory generation of rotary cranes based on A* algorithm and time-optimization for obstacle avoidance and load-sway suppression

Rotary cranes are widely utilized for cargo handling of heavy objects in various construction sites by synchronizing two-dimensional boom rotations and rope motion. The crane’s motion is accompanied by undesirable load-sway and constrained by obstacles, which influence the crane motion and may cause collisions and accidents. Therefore, safe and fast motion for rotary cranes are a main demand for reducing operation time and suppressing residual load-sway. Moreover, avoiding collisions is highly required to guarantee safety during load transportation, while sudden acceleration/deceleration motions are basically prohibited. This paper proposes an optimal trajectory generation method for a large crane using a simple nonlinear dynamics to enhance load-sway suppression without collisions. The three-dimensional crane trajectory is generated by two different algorithms; the first one is the A* algorithm, which is used to generate a short-distance load path from a starting position to the destination with avoiding collision with not only the loads but also the crane body and the rope. Using the inverse kinematics of the crane, the shortest-distance paths for boom rotations and rope motion can be determined. The second algorithm is applied to obtain a time-optimal trajectory for the paths generated by the A* algorithm under crane dynamics and load-sway constraints. The proposed trajectory is represented by a polynomial function, which provides practical and smooth motion for the crane. Computational and experimental results confirm the effectiveness of the proposed approach for suppressing residual load-sway and obstacle avoidance.