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Gravity-Balancing Leg Orthosis and Its Performance Evaluation
Banala, S.K.
Agrawal, S.K.
Fattah, A.
Krishnamoorthy, V.
Wei-Li Hsu
Scholz, J.
Rudolph, K.
Dept. of Mech. Eng., Delaware Univ., Newark, DE;
This paper appears in: Robotics, IEEE Transactions on
Publication Date: Dec. 2006
Volume: 22,
Issue: 6
On page(s): 1228-1239
ISSN: 1552-3098
INSPEC Accession Number: 9214796
Digital Object Identifier: 10.1109/TRO.2006.882928
Current Version Published: 2006-12-04
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In this paper, we propose a device to assist persons with hemiparesis to walk by reducing or eliminating the effects of gravity. The design of the device includes the following features: 1) it is passive, i.e., it does not include motors or actuators, but is only composed of links and springs; 2) it is safe and has a simple patient-machine interface to accommodate variability in geometry and inertia of the subjects. A number of methods have been proposed in the literature to gravity-balance a machine. Here, we use a hybrid method to achieve gravity balancing of a human leg over its range of motion. In the hybrid method, a mechanism is used to first locate the center of mass of the human limb and the orthosis. Springs are then added so that the system is gravity-balanced in every configuration. For a quantitative evaluation of the performance of the device, electromyographic (EMG) data of the key muscles, involved in the motion of the leg, were collected and analyzed. Further experiments involving leg-raising and walking tasks were performed, where data from encoders and force-torque sensors were used to compute joint torques. These experiments were performed on five healthy subjects and a stroke patient. The results showed that the EMG activity from the rectus femoris and hamstring muscles with the device was reduced by 75%, during static hip and knee flexion, respectively. For leg-raising tasks, the average torque for static positioning was reduced by 66.8% at the hip joint and 47.3% at the knee joint; however, if we include the transient portion of the leg-raising task, the average torque at the hip was reduced by 61.3%, and at the knee was increased by 2.7% at the knee joints. In the walking experiment, there was a positive impact on the range of movement at the hip and knee joints, especially for the stroke patient: the range of movement increased by 45% at the hip joint and by 85% at the knee joint. We believe that this orthosis can be potentially used to desig-
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n rehabilitation protocols for patients with stroke
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