A Gravity Balancing Passive Exoskeleton for the Human Leg

Abstract

A gravity balancing lower extremity exoskeleton is a simple mechanical device composed of rigid links, joints and springs, which is adjustable to the geometry and inertia of the leg of a human subject wearing it. This passive exoskeleton does not use any motors or controllers, yet can still unload the human leg joints of the gravity load over the full range of motion of the leg. The underlying principle of gravity balancing consists of two steps: (i) Locate the combined system center of mass of the human leg and the exoskeleton, (ii) Add springs to the exoskeleton, one between the center of mass of the combined system and the fixed frame representing the trunk, the others within the links of the exoskeleton so that the potential energy of the combined system is invariant with configuration of the leg. Additionally, parameters of the exoskeleton can be changed to achieve a prescribed level of partial balancing, between 0-gravity and 1-gravity.