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Research Papers

Measurement of Six Degrees of Freedom Head Kinematics in Impact Conditions Employing Six Accelerometers and Three Angular Rate Sensors (6aω Configuration)

[+] Author and Article Information
Yun-Seok Kang

Injury Biomechanics Research Laboratory,  The Ohio State University, 3024 Graves Hall, 333 West 10th Ave., Columbus, OH 43210kang.286@osu.edu

Kevin Moorhouse1

 NHTSA/VRTC, 10820 SR 347, PO Box B37, East Liberty, OH 43319Kevin.Moorhouse@dot.gov

John H. Bolte

Injury Biomechanics Research Laboratory,  The Ohio State University, 279 Hamilton Hall, 1645 Neil Ave, Columbus, OH 43210bolte.6@osu.edu

1

Corresponding author.

J Biomech Eng 133(11), 111007 (Dec 08, 2011) (11 pages) doi:10.1115/1.4005427 History: Received February 15, 2011; Revised August 25, 2011; Posted November 02, 2011; Published December 08, 2011; Online December 08, 2011

The ability to measure six degrees of freedom (6 DOF) head kinematics in motor vehicle crash conditions is important for assessing head-neck loads as well as brain injuries. A method for obtaining accurate 6 DOF head kinematics in short duration impact conditions is proposed and validated in this study. The proposed methodology utilizes six accelerometers and three angular rate sensors (6aω configuration) such that an algebraic equation is used to determine angular acceleration with respect to the body-fixed coordinate system, and angular velocity is measured directly rather than numerically integrating the angular acceleration. Head impact tests to validate the method were conducted using the internal nine accelerometer head of the Hybrid III dummy and the proposed 6aω scheme in both low (2.3 m/s) and high (4.0 m/s) speed impact conditions. The 6aω method was compared with a nine accelerometer array sensor package (NAP) as well as a configuration of three accelerometers and three angular rate sensors (3aω), both of which have been commonly used to measure 6 DOF kinematics of the head for assessment of brain and neck injuries. The ability of each of the three methods (6aω, 3aω, and NAP) to accurately measure 6 DOF head kinematics was quantified by calculating the normalized root mean squared deviation (NRMSD), which provides an average percent error over time. Results from the head impact tests indicate that the proposed 6aω scheme is capable of producing angular accelerations and linear accelerations transformed to a remote location that are comparable to that determined from the NAP scheme in both low and high speed impact conditions. The 3aω scheme was found to be unable to provide accurate angular accelerations or linear accelerations transformed to a remote location in the high speed head impact condition due to the required numerical differentiation. Both the 6aω and 3aω schemes were capable of measuring accurate angular displacement while the NAP instrumentation was unable to produce accurate angular displacement due to double numerical integration. The proposed 6aω scheme appears to be capable of measuring accurate 6 DOF kinematics of the head in any severity of impact conditions.

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Figures

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Figure 1

Global coordinate system (XYZ) and body-fixed coordinate system (xyz′)

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Figure 2

Head instrumentation configurations: (a) NAP scheme and (b) 6aω scheme

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Figure 3

(a) Instrumentation configuration (NAP, 3aω, and 6aω) and (b) test setup and coordinate systems

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Figure 4

Angular acceleration in the low-speed head impact test (2.3 m/s): (a) x’ axis, (b) y’ axis, (c) z’ axis, and (d) resultant

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Figure 5

Angular acceleration in the high-speed head impact test (4.0 m/s): (a) x’ axis, (b) y’ axis, (c) z’ axis, and (d) resultant

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Figure 6

Resultant linear acceleration at peripheral clusters in the low-speed head impact test (2.3 m/s): (a) Peripheral cluster 1 and (b) peripheral cluster 2

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Figure 7

Resultant linear acceleration at peripheral clusters in the high-speed head impact test (4.0 m/s): (a) Peripheral cluster 1 and (b) peripheral cluster 2

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Figure 8

Angular displacement in the high speed head impact test (4.0 m/s): (a) Global X axis and (b) global Y axis

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Figure 9

Resultant angular acceleration for the NAP versus the 3aω scheme using different filtering classes

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