An inverse kinematics method of a soft robotic arm with three-dimensional locomotion for underwater manipulation

Soft robots have several promising features for underwater manipulation, e.g., safe interaction with surroundings, lightweight, low inertia, etc. In this paper, we proposed a method for the inverse kinematics of the soft manipulator that can move in the three-dimensional space. By controlling the two bending segments to move with opposing curvatures and one elongation segment to move up and down, our method enabled the real-time solution of the inverse kinematics and allowed the tip of the manipulator executing point-point movements in three dimensions. We performed the trajectory planning ability of the soft manipulator following the straight line and circle paths. Furthermore, we investigated the hydrodynamic functions of the soft manipulator underwater including forces, and the wake flows when the soft arm stroked at different amplitudes and frequencies. We found that the hydrodynamic force (<1N) and the torques (<0.1Nm) were quite small during locomotion — which led to a negligible inertial impact on the underwater vehicle compared to the traditional rigid underwater manipulator. Finally, we demonstrated that the soft manipulator successfully picked and placed sea animals at 10m depth.