Skin deformation caused by muscle motion is a common source of error for body-mounted sensors. A new method of measuring joint angles using a combination of two-axial accelerometers and reaction force sensors is presented. In this study, the effect of soft tissue deformation was minimized using a new reaction force sensor that is bound onto the body segment. The force sensor was designed using a pressure-sensitive electric conductive rubber. A Fourier transform of the total pressure forces induced by the body-mounted motion sensor modules was implemented to analyze the frequency property of soft tissue deformation on the human body surface. We processed the data of two-axial accelerations measured by the accelerometers using the measurements of soft tissue deformation including the total pressure force and two-directional coordinates of the center of pressure. An experimental study with ten subjects was implemented to verify the new sensor system proposed for estimating the joint angle of the knee. The effectiveness of this system is illustrated by the experimental results using an optical motion analysis system as a reference. If we use the accelerometers alone, the root mean square (RMS) difference and the coefficient of multiple correlation (CMC) over all the subjects walking at each of the three speeds (slow, average, and fast) are and , and , and and , respectively. If we compensate for soft tissue deformation using the surface pressure measurements, the RMS difference and the CMC in each of the three conditions are and , and , and and , respectively. Measurement results of the developed sensor system showed high correlation with results from two alternative methods including an optical motion analysis system and the goniometer system in walking analysis experiments. The results support the effectiveness of the proposed method in the measurement of the flexion and extension angle of the knee. The compensation for soft tissue deformation using the surface pressure measurements improved the accuracy of the body-mounted sensor in the experiments.
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September 2009
Design Innovations
Measurement of Soft Tissue Deformation to Improve the Accuracy of a Body-Mounted Motion Sensor
Tao Liu,
Tao Liu
Department of Intelligent Mechanical Systems Engineering,
e-mail: liu.tao@kochi-tech.ac.jp
Kochi University of Technology
, 185 Miyanokuchi, Tosayamada-cho, Kochi 782-8502, Japan
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Yoshio Inoue,
Yoshio Inoue
Department of Intelligent Mechanical Systems Engineering,
Kochi University of Technology
, 185 Miyanokuchi, Tosayamada-cho, Kochi 782-8502, Japan
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Kyoko Shibata
Kyoko Shibata
Department of Intelligent Mechanical Systems Engineering,
Kochi University of Technology
, 185 Miyanokuchi, Tosayamada-cho, Kochi 782-8502, Japan
Search for other works by this author on:
Tao Liu
Department of Intelligent Mechanical Systems Engineering,
Kochi University of Technology
, 185 Miyanokuchi, Tosayamada-cho, Kochi 782-8502, Japane-mail: liu.tao@kochi-tech.ac.jp
Yoshio Inoue
Department of Intelligent Mechanical Systems Engineering,
Kochi University of Technology
, 185 Miyanokuchi, Tosayamada-cho, Kochi 782-8502, Japan
Kyoko Shibata
Department of Intelligent Mechanical Systems Engineering,
Kochi University of Technology
, 185 Miyanokuchi, Tosayamada-cho, Kochi 782-8502, JapanJ. Med. Devices. Sep 2009, 3(3): 035001 (6 pages)
Published Online: August 28, 2009
Article history
Received:
June 18, 2008
Revised:
July 30, 2009
Published:
August 28, 2009
Citation
Liu, T., Inoue, Y., and Shibata, K. (August 28, 2009). "Measurement of Soft Tissue Deformation to Improve the Accuracy of a Body-Mounted Motion Sensor." ASME. J. Med. Devices. September 2009; 3(3): 035001. https://doi.org/10.1115/1.3212558
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