An Algorithm for Estimating Acceleration Magnitude and Impact Location Using Multiple Nonorthogonal Single-Axis Accelerometers

[+] Author and Article Information
Joseph J. Crisco

Department of Orthopaedics, Brown Medical School/Rhode Island Hospital, Providence, RI

Jeffrey J. Chu

Simbex LLC, Lebanon, NH

Richard M. Greenwald

Simbex LLC, Lebanon, NHThayer School of Engineering, Dartmouth College, Hanover, NH

J Biomech Eng 126(6), 849-854 (Feb 04, 2005) (6 pages) doi:10.1115/1.1824135 History: Received November 20, 2003; Revised June 09, 2004; Online February 04, 2005
Copyright © 2004 by ASME
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An impact generates linear acceleration of an object (a player’s head in the field application) whose shape is approximated here as a hemisphere. The acceleration of the geometrical center (O) of the hemisphere is defined by the vector, H , and the direction of the sensing axis of each accelerometer, defined to be normal to the surface, ai, are defined in a spherical coordinate system, referred to as the HCS, using angles of azimuth and elevation angles. Azimuth (θ) is defined from −180 to 180 deg with 0 deg at the X axis and positive (θ) to the right. Elevation (α) is defined from 0 deg (horizontal plane passing through O) to 90 deg (crown of sphere at the Y axis).
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In the computer simulation, the standard deviation of the errors in predicting acceleration magnitude (A) and impact location [azimuth (B) and elevation (C)] varied with impact location and HMAS configuration (see Table 1)
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In the experimental study, the 11 HMAS, 6 HMAS, and 5 HMAS configurations exhibited similar errors. The error in predicting the acceleration magnitude (A) was generally not sensitive to impact location, while the error in predicting impact location varied strongly with the impact location [azimuth (B) and elevation (C)].
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Individual HMAS accelerations (A) from a typical impact to the hemispherical headform with the 6 HMAS configuration. By iteratively applying Eq. (4) over time, the estimated linear acceleration is calculated [calculated curve in (B)] and shown to be an accurate estimate of the linear acceleration measured by the triaxial accelerometer of the hemispherical headform [experimental curve in (B)].




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