Research Papers

Design of an Ankle Rehabilitation Device Using Compliant Mechanisms

[+] Author and Article Information
Edward Sung, Alexander H. Slocum, Raymond Ma, Martin L. Culpepper

Department of Mechanical Engineering, Precision Compliant Systems Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139

Jonathan F. Bean

Harvard Medical School, Department of Physical Medicine and Rehabilitation, Spaulding Cambridge Outpatient Center, Cambridge, MA 02138

J. Med. Devices 5(1), 011001 (Jan 06, 2011) (7 pages) doi:10.1115/1.4002901 History: Received August 09, 2010; Revised October 21, 2010; Published January 06, 2011; Online January 06, 2011

In this paper, we present the design, analysis, and testing of an ankle rehabilitation device (ARD), the purpose of which is to improve the efficacy of ankle joint complex (AJC) injury diagnosis and treatment. The ARD enables physicians to quantitatively measure the severity of an injury. This is done by measuring deficiencies in the joint’s range of motion, as well as force, torque, and power output. Evaluation of the relative degree of recovery over time can also reduce the error associated with current methodologies for rehabilitation, which rely on measurements based on the patient’s verbal response. A Wheatstone bridge circuit is used for the measurement of the various parameters as applied to the blades of complementary rotational flexures; the device is designed to measure motion about three axes of rotation in the ankle joint: pitch, roll, and yaw. A full bridge circuit is applied to each axis of rotation, and the use of multiple axes increases anatomically accurate measurement, enabling characterization of coupled motions. The device has flexibility and a range of motion such that it can be adjusted to take measurements of multiple different degrees of plantar or dorsiflexion of the AJC. The ARD is able to measure both range of motion, force, and torque output simultaneously. Experimental results show that there is significant coupled motion among the ankle joint rotations but that it is highly dependent on a subject’s own physical development.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Gait pressure device (top left), (6) Rutgers ankle interface (top right), (8) hand-held dynamometer (bottom left), (10) and isokinetic dynamometer (bottom right) (12)

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Figure 2

Ankle joint complex (13)

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Figure 3

Wire-frame solid model of prototype; the malleolus is aligned with the axis labeled in the figure as such

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Figure 4

Basic cartwheel flexure design (15)

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Figure 5

Cartwheel flexure calibration setup

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Figure 6

Concept 1 solid model

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Figure 7

Concept 2 solid model

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Figure 8

Pugh chart for concepts

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Figure 9

Fatigue curve of 7075-T6 aluminum alloy

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Figure 10

Deformed flexure blade

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Figure 11

Finite element analysis of plantar/dorsiflexion cartwheel flexure (top) and inversion/eversion cartwheel flexure (bottom)

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Figure 12

Solid model of the α-prototype ankle rehabilitation device

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Figure 13

Detail view of cartwheel flexure

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Figure 14

Prototype ankle rehabilitation device in use. The patient's free foot is not in its normal position.

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Figure 15

Ankle joint torque output for subject 1

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Figure 16

Solid model of the beta-prototype design




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