Design of a Lightweight and Flexible Knee Exoskeleton with Compensation Strategy

The lower-limb exoskeleton is promising for gait rehabilitation training and reducing metabolism. A lightweight and lexible knee exoskeleton with Bowden cables as the power transmission is designed. The designed device is highly integrated and convenient to wear, which also combines the advantages of the convenient installation of sensors in a rigid exoskeleton. The block diagram of the human-machine system is established to analyze the factors that affect the exoskeleton assistance. Based on the above analysis, a force control framework based on a position loop is proposed. Besides, the compensation strategy corresponding to the exoskeleton designed in this paper is further considered. Firstly, a feedforward compensation that uses the encoder as the signal source is proposed to account for the subject's active movements. Secondly, the nonlinear deformation compensation is proposed to compensate for the human-machine interface's elastic deformation, which ensures the force loading performance. Thirdly, the iterative force control is used to compensate for the inelastic deformation. The experiments on three subjects demonstrate the effectiveness.