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TECHNICAL BRIEFS

An Efficient Robotic Tendon for Gait Assistance

[+] Author and Article Information
Kevin W. Hollander

Departments of Mechanical and Aerospace Engineering, and Industrial Design, Arizona State University, Tempe, AZ 85287-6106kevin.hollander@asu.edu

Robert Ilg, Thomas G. Sugar, Donald Herring

Departments of Mechanical and Aerospace Engineering, and Industrial Design, Arizona State University, Tempe, AZ 85287-6106

J Biomech Eng 128(5), 788-791 (Mar 22, 2006) (4 pages) doi:10.1115/1.2264391 History: Received August 18, 2005; Revised March 22, 2006

A robotic tendon is a spring based, linear actuator in which the stiffness of the spring is crucial for its successful use in a lightweight, energy efficient, powered ankle orthosis. Like its human analog, the robotic tendon uses its inherent elastic nature to reduce both peak power and energy requirements for its motor. In the ideal example, peak power required of the motor for ankle gait is reduced from 250 W to just 77 W. In addition, ideal energy requirements are reduced from nearly 36 J to just 21 J. Using this approach, an initial prototype has provided 100% of the power and energy necessary for ankle gait in a compact 0.95kg package, seven times less than an equivalent motor/gearbox system.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Robotic tendon model: motor and spring in series

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Figure 2

Normal ankle gait: kinematics and kinetics

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Figure 3

Optimization of stiffness, K

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Figure 4

The power required for the human ankle in gait versus the input power needed for the motor driving the robotic tendon

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Figure 5

A second generation, powered ankle-orthosis will be designed using a robotic tendon. In this example, the spring and the power unit are separated for compactness.

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Figure 6

The predicted moment is calculated from Fig. 2. The measured moment is calculated knowing the deflection of the spring during the gait cycle.

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Figure 7

Power comparison between predicted and measured power of the motor driving the robotic tendon versus the power required for the human ankle in gait

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