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Research Papers

The Design and Initial Experimental Validation of an Active Myoelectric Transfemoral Prosthesis

[+] Author and Article Information
Carl D. Hoover

 Elder Research, Inc., Charlottesville, VA 22903hoover@datamininglab.com

George D. Fulk

Department of Physical Therapy,  Clarkson University, Potsdam, NY 13699gfulk@clarkson.edu

Kevin B. Fite

Department of Mechanical and Aeronautical Engineering,  Clarkson University, Potsdam, NY 13699kfite@clarkson.edu

J. Med. Devices 6(1), 011005 (Mar 13, 2012) (12 pages) doi:10.1115/1.4005784 History: Received May 23, 2011; Revised December 20, 2011; Published March 12, 2012; Online March 13, 2012

This paper describes a single degree-of-freedom active-knee transfemoral prosthesis to be used as a test bed for the development of architectures for myoelectric control. The development of an active-knee transfemoral prosthesis is motivated by the inability of passive commercial prostheses to provide the joint power required at the knee for many activities of daily living such as reciprocal stair ascent, which requires knee power outputs of up to 4 W/kg. Study of myoelectric control based on surface electromyogram (EMG) measurements of muscles in the residual limb is motivated by the desire to restore direct volitional control of the knee using a minimally-invasive neuromuscular control interface. The presented work describes the design of a transfemoral prosthesis prototype including the structure, actuation, instrumentation, electronics, and real-time control architecture. The performance characteristics of the prototype are discussed in the context of the requisite knee energetics for a variety of common locomotive functions. This paper additionally describes the development of a single-subject diagnostic socket with wall-embedded surface EMG electrodes and the implementation of a control architecture for myoelectric modulation of knee impedance. Experimental results of level walking for a single subject with unilateral transfemoral amputation demonstrate the potential for direct EMG-based control of locomotive function.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Average normal knee joint behavior of four subjects (19 trials per subject) during reciprocal stair ascent, including (a) mass normalized power, (b) angle, (c) speed, and (d) mass normalized extensive moment. Dashed lines indicate one standard deviation bands.

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Figure 2

Powered transfemoral prosthesis, including: (1) knee, (2) motor revolute joint, (3) axial load cell, (4) motor, (5) ball nut revolute joint, (6) ball screw, (7) knee revolute joint and potentiometer, (8) tibia pylon, (9) pyramid connector, and (10) prosthetic foot. The inset shows the limb positioned at various angles of flexion: 0°, 30°, and 90°. Mechanical stops limit the range of motion.

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Figure 3

Angle-dependent transmission ratio between knee torque and motor torque. Motor torque is amplified by a gain of approximately 200 at mid-range and 140 at the mechanical limits.

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Figure 4

Average normal knee moment versus knee angle for various locomotive functions with the configuration-dependent torque bound of the actuator (dashed)

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Figure 5

Knee specifications transformed to rectified actuator-space requirements. The recommended actuator operation region is bounded by a combination of the maximum motor speed (dark) and the motor’s nominal power of 150 W (light). The dashed line bounds the peak motor output at its nominal voltage of 48 V. Average strides of normal walking, stair ascent, stair descent, and sit-stand are shown as scatter plots.

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Figure 6

Diagnostic myo-socket with wall-embedded surface EMG electrodes: (a) posterior view and (b) donned by an amputee subject with an early version of the transfemoral prosthesis prototype

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Figure 7

Amputee EMG (linear envelope) signals of amputee donning myo-socket for static voluntary muscle contractions of the (a) rectus femoris, (b) vastus lateralis, and (c) biceps femoris

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Figure 8

Stride-normalized average amputee EMG (linear envelope) signals and ± 1 standard deviations of the (a) rectus femoris, (b) vastus lateralis, and (c) biceps femoris for level walking

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Figure 9

(a) Lateral and (b) medial views of the transfemoral prosthesis prototype with electronics, batteries, and prosthetic foot

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Figure 10

Functional block diagrams of (a) low-level force-controlled servo-actuator and (b) high-level myoelectric controller. The servo-actuator uses a proportional plus feed-forward control law. The high-level limb controller includes myoelectric control and limb friction compensation with a linear damping coefficient CD .

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Figure 11

(a) Standing and (b) walking on level ground under myoelectric impedance control with support harness

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Figure 12

Results of level walking with an 83 kg adult male subject with unilateral transfemoral amputation for five consecutive strides. Stride-normalized average (a) knee angle, (b) normalized flexor EMG, and (c) normalized extensor EMG are shown with 1 standard deviation bands (dashed). Note that each stride begins and ends with heel contact of the prosthetic-side leg.

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Figure 13

Results of level walking with an 83 kg adult male subject with unilateral transfemoral amputation for five consecutive strides. Stride-normalized average (a) desired knee angle and (b) effective knee stiffness are shown with 1 standard deviation bands (dashed). Note that each stride begins and ends with heel contact of the prosthetic-side leg.

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