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Research Papers

Design and Control of a Pneumatic Artificial Muscle Actuated Above-Knee Prosthesis

[+] Author and Article Information
Garrett Waycaster, Sai-Kit Wu

Department of Mechanical Engineering,  The University of Alabama, 290 Hardaway Hall, Box 870276, Tuscaloosa, AL 35487-0276

Xiangrong Shen

Department of Mechanical Engineering,  The University of Alabama, 290 Hardaway Hall, Box 870276, Tuscaloosa, AL 35487-0276xshen@eng.ua.edu

J. Med. Devices 5(3), 031003 (Jul 27, 2011) (9 pages) doi:10.1115/1.4004417 History: Received September 10, 2010; Revised June 02, 2011; Published July 27, 2011; Online July 27, 2011

This paper presents the authors’ investigation results of applying the pneumatic artificial muscle actuation to above-knee prostheses. As a well-known muscle actuator, the pneumatic artificial muscle actuator features a number of unique advantages, including high power density, and similar elastic characteristics to biological muscles. Despite multiple applications in related areas, the application of pneumatic artificial muscle in above-knee prostheses has not been explored. Inspired by this fact, the research presented in this paper aims to develop a pneumatic artificial muscle-actuated above-knee prosthesis, with three specific objectives: (1) demonstrate the pneumatic artificial muscle actuation’s capability in generating sufficient torque output to meet the locomotive requirements; (2) develop an effective control approach to enable the restoration of locomotive functions; (3) conduct preliminary testing of the prosthesis prototype on a healthy subject through a specially designed able-body adaptor. In the prosthesis design, an agonist–antagonist layout is utilized to obtain a bidirectional motion. To minimize the radial profile, an open-frame structure is used, with the purpose of allowing the expansion of the muscle actuators into the center space without interference. Also, the muscle actuator parameters are calculated to provide sufficient torque capacity (up to 140 N m) to meet the requirements of level walking. According to this design, the fabricated prototype weighs approximately 3 kg, with a range of motion of approximately 100°. For the control of the prosthesis, a model-based torque control algorithm is developed based on the sliding mode control approach, which provides robust torque control for this highly nonlinear system. Combining this torque control algorithm with an impedance-based torque command generator (higher-level control algorithm), the fabricated prosthesis prototype has demonstrated a capability of providing a natural gait during treadmill walking experiments.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 3

The maximum available force as a function of the percentage of shortening

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Figure 4

Torque trajectories for level walking at slow and normal cadence (from the data presented in Ref. [1]) compared with the available range of joint actuation torque

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Figure 5

Incorporation of force resistors into the prosthetic foot support to measure the ground contact force. Note that two resistors are used to provide a more reliable measurement in the existence of bending moment.

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Figure 6

Schematic of the actuation structure

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Figure 7

The setup for the control experiments

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Figure 8

Typical tracking performance provided by the torque controller (a) and the corresponding valve command (b)

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Figure 9

Test subject fitted with the prosthesis through an able-body adaptor

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Figure 10

The comparison of the measured walking gait with the prosthesis and the typical walking gait of healthy persons: (a) the measured knee joint angle for five consecutive gait cycles with the prosthesis and (b) the typical trajectory of knee joint angle according to the data in [1]

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Figure 1

The structure (a) and functioning mechanism (b) of the pneumatic artificial muscle. Note that (a) shows the metal fitting on each end and the typical structure of the expandable membrane when deflated. Note also that, when inflated, the membrane expands radially, displaying a larger outer diameter than the metal fitting, as shown in (b).

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Figure 2

A solid model of the prosthesis design (a) and the fabricated prototype (b)

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