Achievement of twist squat by musculoskeletal humanoid with screw-home mechanism

Human knee joint has a yaw-axis rotational DOF and a locking mechanism called screw-home mechanism. We focus on this mechanism and implement it to a musculoskeletal humanoid through hardware design. The importance of developing a knee joint with screw-home mechanism is that such a joint is capable of working yaw-axis properly and generating enough pitch joint torque for supporting whole body motion. In this paper, as an evaluation of our developed knee joint, we first checked the moment arm of the yaw rotational axis of the knee. Moreover, we also checked the yaw angle displacement during squat motion. From these results, we confirmed that the mechanism worked properly. Second, in order to check whether enough pitch joint torque is generated during movement, we conducted several experiments with whole body motions such as squatting. Lastly, as unique and integrated motions that involve the use of yaw DOF derived from the mechanism, we tested knee joint Open-Close, Right-to-Left and whole body twist squat motion. Our results demonstrated the feasibility of musculoskeletal humanoids with screw-home mechanism and showed that we have achieved humanlike twisting motion.