Trajectory Generation with Dynamic Programming for End-Effector Sway Damping of Forestry Machine

When a robot end-effector is attached to the arm via passive joints, undesirable end-effector sway will occur. In a forestry crane, such as the log-loading or harvesting machine, this sway is problematic as it hinders the efficiency and also can harm the machine and environment. Here, we tackle the sway problem of the forestry forwarder by proposing a methodology for generating anti-sway trajectories in fast maneuvers. We employ the dynamic programming algorithm, combined with a suitable linearization approach, the latter identified through a comparative study. The solution has low computational cost and provides excellent performance for residual sway damping. We demonstrate the dynamic programming solution on the virtual model of the forwarder by using a high-fidelity multibody-dynamics simulator to validate its performance. The results show our optimal trajectories can suppress the residual sway effectively to be, on average, less than 10% of the sway when using fifth order polynomial trajectories, in point-to-point maneuvers starting from rest or from initial sway conditions.