Bio-inspired Knee Joint of a Lower-limb Exoskeleton for Misalignment Reduction

Abstract

Misalignment between an exoskeletal robot and the wearers body must be minimal to prevent injury and discomfort during active assistance. It is particularly difficult for the robot to imitate the knee joint motion of a human because the human knee joint has a complex structure, which cannot be realized with a single revolute joint. In this paper, a knee joint mechanism that closely realizes the human knee joint motion using the curved guide rail and bearings is proposed. For the optimal design of the proposed mechanism, the motions of the tibia and the femur are captured, and the guide rail of the proposed mechanism is designed to realize the captured human knee joint motion. A simulation study is performed based on kinematic calculations, and the shape of the guide rail is optimized for the proposed device to precisely imitate the human motion. This paper also introduces an experimental method for the quantitative evaluation of the misalignment; the pressure inside the brace is measured using an air-pressure sensor pad, and the pressure measurements are utilized for objective comparison of the misalignment with respect to the joint mechanism. An additional experiment is performed to verify the non-interfering of the human walking motion.