Design of a passive lower limb exoskeleton for walking assistance with gravity compensation

In this paper, a passive lower limb exoskeleton with hip and knee joints is proposed for walking assistance. The exoskeleton is designed with built-in spring mechanisms for gravity compensation of the human leg. A pair of mating gears is used to convert the tension force from the built-in springs into balancing torques at the hip and knee joints in order to overcome the influence of gravity. With the novel design, the exoskeleton has a compact layout with small protrusion, which improves its user acceptance and safety. In this paper, the working principle of the design for gravity compensation is described. A model is developed to analyze the effects of the design parameters. Simulations are conducted and the results show that the average absolute driving torque was reduced by 79.0% at the hip joint and 66.4% at the knee joint, with the use of this exoskeleton. Parametric study shows that lower gait speed, lower stiffness with larger pretension of the springs contribute to the maintenance of balance. A prototype of the leg exoskeleton was fabricated, and preliminary tests on healthy subjects verified usability of the exoskeleton. (C) 2020 Elsevier Ltd. All rights reserved.