Evaluation of a coplanar 6a3ω configuration in the Hybrid III 50th percentile male head

Abstract

Objectives: In order to understand the mechanisms of traumatic brain injury (TBI) and develop proper safety measures, it is essential that accurate instrumentation methods are utilized. The brain injury criterion (BrIC) has been developed and validated to predict brain injuries in combination with the head injury criterion (Takhounts et al. 2011(Takhounts et al. , 2013. Because the validated BrIC is heavily dependent on angular motion, the accuracy of any head instrumentation technique should be judged in part by its ability to measure angular motion. The main objective of this study was to evaluate a method of accurately measuring 6-degree-offreedom (DOF) anthropomorphic test device (ATD) head kinematics using a coplanar 6 accelerometers and 3 angular rate sensors (6a3ω) configuration. Methods: A coplanar 6a3ω configuration (c6a3ω) was implemented via a newly designed fixture. The c6a3ω fixture was placed at the center of gravity (CG) of a Hybrid III 50th percentile ATD (HIII 50) head. In addition, a tetrahedron fixture with 9 installed accelerometers (tNAAP) was externally mounted on the posterior surface of the HIII 50 skull cap. The c6a3ω setup also allowed for comparison to the 3a3ω configuration (i3a3ω) by subsequently treating the c6a3ω fixture as an i3a3ω fixture by only using accelerations and angular rates from select sensors. A total of 63 tests were conducted by impacting the head-neck apparatus at various high speeds and directions by a pneumatic ram. Normalized root mean square deviation (NRMSD), peak differences, and uncertainty were used for quantitative evaluation of the 3 configurations (e.g., c6a3ω, i3a3ω, and tNAAP). Results: The average NRMSD and peak differences between the calculated angular accelerations were less than 5% between the tNAAP and the c6a3ω with 5.6% of uncertainty but greater than 18% for NRMSD and 20% for the peak differences between the tNAAP and i3a3ω with 58.2% uncertainty. Average NRMSD and peak differences between transformed resultant linear accelerations and gold standards (accelerations directly measured by accelerometers at the origin of tNAAP or c6a3ω fixtures) were also calculated. The c6a3ω had both NRMSD and peak differences less than 3% (uncertainty of 2.5%), and i3a3ω had NRMSD, peak values, and uncertainty on the order of 20% and higher. The tNAAP was slightly less accurate than the c6a3ω for transformed accelerations (NRMSD and peak differences <6%, uncertainty of 4.6%) and showed NRMSD and peak differences in the 7-8% range for angular velocity and rotation (uncertainty of 4.3 and 6.7%, respectively). Conclusions: The c6a3ω configuration exhibited much better accuracy for calculating angular acceleration and transformed linear acceleration than the i3a3ω configuration. The tNAAP showed slightly less accurate transformed linear acceleration than the c6a3ω and was demonstrated to have less accuracy than c6a3ω and i3a3ω for calculating angular velocity and rotation. The c6a3ω configuration could be a potential alternative to specialized NAAP ATD heads...

Consensus Head Acceleration Measurement Practices (CHAMP): Laboratory Validation of Wearable Head Kinematic Devices

“…Applications that require 6DOF kinematics should choose reference arrangements capable of making these measurements. 39 , 62 Applications that focus on impact counting or measuring impact direction may require only linear acceleration or high-speed video for validation. 94 Select a laboratory-grade reference sensor that is capable of measuring the range of kinematics expected in the conditions tested.…”

“… 40 The 3 a 3ω has lower cost due to the use of fewer sensors and is relatively easy to mount to a surrogate; however, the derivative is used to approximate angular acceleration, which can amplify noise under higher frequency excitation, which should be considered when validating wearable devices that measure angular acceleration. 14 , 25 , 39 , 57 While angular acceleration is algebraically calculated using the NAP and 6 a 3ω, 40 integration is used to approximate angular velocity from the NAP, which can manifest error due to signal drift. 14 , 75 The advantage of the 6 a 3ω over the NAP is that it enables direct measurement of angular velocity, which is important for validating wearable devices that measure angular rate.…”

Characteristics and Estimation of Dew in the Loess Hilly Region of Northern Shaanxi Province, China

“…The normalized root-mean-square deviation (NRMSD) is a metric used to measure the accuracy of predictive models [54,55]. The NRMSD at the monthly and annual scales was used to determine how well the simulated values of dew matched the measured values using Equation ( 8) [56].…”