Assessment of motion of a swing leg and gait rehabilitation with a gravity balancing exoskeleton.

The gravity balancing exoskeleton, designed at University of Delaware, Newark, consists of rigid links, joints and springs, which are adjustable to the geometry and inertia of the leg of a human subject wearing it. This passive exoskeleton does not use any motors but is designed to unload the human leg joints from the gravity load over its range-of-motion. The underlying principle of gravity balancing is to make the potential energy of the combined leg-machine system invariant with configuration of the leg. Additionally, parameters of the exoskeleton can be changed to achieve a prescribed level of gravity assistance, from 0% to 100%. The goal of the results reported in this paper is to provide preliminary quantitative assessment of the changes in kinematics and kinetics of the walking gait when a human subject wears such an exoskeleton. The data on kinematics and kinetics were collected on four healthy and three stroke patients who wore this exoskeleton. These data were computed from the joint encoders and interface torque sensors mounted on the exoskeleton. This exoskeleton was also recently used for a six-week training of a chronic stroke patient, where the gravity assistance was progressively reduced from 100% to 0%. The results show a significant improvement in gait of the stroke patient in terms of range-of-motion of the hip and knee, weight bearing on the hemiparetic leg, and speed of walking. Currently, training studies are underway to assess the long-term effects of such a device on gait rehabilitation of hemiparetic stroke patients.

Theory and design of an orthotic device for full or partial gravity-balancing of a human leg during motion.

Gravity balancing is often used in industrial machines to decrease the required actuator efforts during motion. In the literature, a number of methods have been proposed for gravity balancing that include counterweights, springs, and auxiliary parallelograms that determine the center of mass. However, these concepts have not yet been seriously applied to rehabilitation machines. This paper presents the underlying theory and design of an orthosis for the human leg that can fully or partially balance the human leg over the range of its motion. This design combines the use of auxiliary parallelograms to determine the center of mass along with springs to achieve a full or partial gravity balanced orthosis design. A first prototype has been constructed to demonstrate the effectiveness of the idea. Future prototypes will have parameters that will be tuned to the geometry and inertia of a human subject and be tailored to an individual's needs.

Gravity balancing rehabilitative robot for the human legs.

People with severe muscle weakness from neurological injury, such as hemiparesis from stroke, often have substantial limitations. The focus of rehabilitation after stroke is often on walking function, however, equipment available to facilitate walking function is severely limited. Most devices move patients through predetermined movements rather than allowing the patient to move under their control. This work presents the design of a gravity balancing rehabilitative robot to assist persons with both leg impairment to walk through elimination of the effects of gravity. The design of the machine is based on a hybrid method for gravity balancing, with two steps: (i) locate the center of mass of a machine using auxiliary parallelograms; (ii) select springs to connect from the center of mass such that the total potential energy of the system is invariant with configuration. The design of the machine considers all motions of the leg and the pelvis by assuming the center of mass of pelvis to be located on the line joining the two hip joints. Preliminary version of this machine, with limited features, is being fabricated.