Designing of a Passive Knee-Assisting Exoskeleton for Weight-Bearing

Weight-bearing exoskeleton can effectively help the wearer to bear heavier burden, while assisting his ambulation. However, current researches in this field are relatively scarce on the passive weight-bearing exoskeleton. This research aims to design an unpowered knee-assisting exoskeleton used for weight-bearing, which can store human metabolic energy and assist human locomotion, through utilization of Teflon string, pulley, and compression spring. Biomechanical analysis of human weight-bearing locomotion shows that knee-flexion angle can be used to identify level walking or ascending movement of a person, where the largest sagittal flexion angle in level walking does not exceed 60º. Hence, the contour of pulley used for winding string is designed to be eccentric, in which the assisting torque varies nonlinearly according to the knee-flexion angle. Through mechanical modeling of eccentric pulley, we predict the assisting torque of the device and compare it with actual experimental statistics. Results show that such passive exoskeleton exhibits multi-stage nonlinear assisting augmentation under different knee-flexion angles; with least possible knee assistance during level walking, and remarkable assistance during climbing.