Bio-inspired Open Ligamentous Knee Joint with Extended Pitch and Yaw Range of Motion

This study presents a bio-inspired open knee joint for biofidelic robots with an anatomically correct range of motion. Bio-inspired joints contribute to robot performance and understanding living organisms by providing dynamic motion data as the real-world physical twin. The proposed joint structure features the integration of the open joint and ligamentous constraint. In particular, the spherical envelope of the condyles contributes to the rotation other than pitch rotation. By applying a bio-inspired ligament arrangement, the developed knee joint performed pitch and yaw motion. The relationship between the ligament length and joint orientation was derived by forward kinematics and the ligament wrapping. The arrangement of the bio-inspired collateral ligaments was determined with the iterative calculation method considering the object wrapping, which predicted the yaw range of motion. Verification of the proposed approach includes the evaluation of the range of motion on the robotic knee joint equipped with the motor-driven tendons. The robot validation tests include the rotational motions around the pitch and yaw axes. The tests showed that the proposed joint structure can be a relevant approach for replicating the range of motion of a human knee joint. Future work includes the motion control of the joint system and integration into a real robot.