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TECHNICAL PAPERS

On the Design of a Passive Orthosis to Gravity Balance Human Legs

[+] Author and Article Information
Abbas Fattah

Mechanical Systems Laboratory, Department of Mechanical Engineering,  University of Delaware, Newark, DE 19716fattah@me.udel.edu

Sunil K. Agrawal

Mechanical Systems Laboratory, Department of Mechanical Engineering,  University of Delaware, Newark, DE 19716agrawal@me.udel.edu

J. Mech. Des 127(4), 802-808 (Oct 04, 2004) (7 pages) doi:10.1115/1.1899175 History: Received March 24, 2004; Revised October 04, 2004

This paper presents the design of a passive two leg orthosis to gravity balance human legs for use by subjects with both leg impairment. This design combines the use of auxiliary parallelograms to locate the center of mass along with springs to achieve balancing of each leg. The gravity balancing for all motions of the leg and pelvis is achieved by assuming the center of mass of the pelvis to be located on the line joining the two hip joints. A method for deriving the effectiveness of the gravity balancing due to practical limitations is also outlined. We illustrate the gravity balancing feature of the orthosis and examine the assumptions through computer simulations.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

An AutoCAD drawing of two leg orthosis. The subject uses a portable walking frame. The moving segments of the orthosis straps on to the moving segments of each leg.

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Figure 2

A schematic of the two leg orthosis with coordinate frames

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Figure 3

Locating the center of mass of thigh and shank segments of the right leg

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Figure 4

A schematic of each leg with the attachment of spring k to the leg center of mass

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Figure 5

A schematic of the gravity-balanced leg with all springs

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Figure 6

Joint angles of right leg during single limb support (—knee flexion; ⋯, hip flexion; –– ––, hip abduction; –∙–, hip rotation)

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Figure 7

Joint effectiveness of right leg during single limb support (—, knee flexion; ⋯, hip flexion; –– ––, hip abduction; –∙–, hip rotation)

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