Design of a personalized knee rehabilitation exoskeleton with high motion compliance

Abstract

During the motion of a knee joint, the instantaneous center of rotation (ICR) of the tibia relative to the femur is not fixed but moves along a curve decided by the joint structure. Adapting to wearer’s personalized knee joint structure is important to improve the wearing comfort and rehabilitation effect of the exoskeleton. The paper proposes a design method of a personalized knee rehabilitation exoskeleton with high human-machine compliance. Firstly, an instantaneous center curve (ICC) generation algorithm is proposed, which extracts feature points of the tibia from the medical images of the wearer’s knee joint, generates ICRs of the tibia at different knee joint angles, and then fits the ICRs into the ICC of the knee joint. Secondly, a four-bar linkage model for the knee joint is applied, and the structure parameters of the linkage are optimized by minimizing the deviations between the ICRs of the linkage and the wearer. Finally, a lower limb rehabilitation exoskeleton is implemented, adopting a lightweight transmission scheme using conjugate cams combined with Bowden cables. The experimental results show that the designed exoskeleton is lightweight and has small relative movement and small interaction forces with the wearer, realizing good wearing comfort and motion compliance.