Six-Degree-of-Freedom Accelerations: Linear Arrays Compared with Angular Rate Sensors in Impact Events

Paper #:
  • 2017-01-1465

Published:
  • 2017-03-28
Abstract:
At present, SAE J211 provides no definitive guidance as to the appropriate procedures for filtering angular rate sensor data prior to differentiation into angular acceleration data, especially for very short duration or impact data. Accordingly, a 3-2-2-2 array of linear accelerometers and a triaxial angular rate sensor were mounted into a Hybrid III 50th percentile male ATD headform and compared in a variety of impact events. An appropriate low-pass digital filter cutoff frequency for differentiating the angular rate sensor data into angular accelerations was sought via residual analysis in accordance with current SAE J211 guidelines to find appropriate cutoff frequencies which would best match the angular acceleration data measured by the 3-2-2-2 array, which is the present gold standard. It was found that there was no specific cutoff frequency that consistently matched the angular accelerations measured by the 3-2-2-2 array, and the combination of a triaxial linear accelerometer and a triaxial rate sensor could not simultaneously match the 3-2-2-2 RMS and peak angular accelerations regardless of cutoff frequency. The differentiation step to convert angular velocity data into angular acceleration data was found to insert frequency dependent noise which low-pass filtering could not adequately eliminate. This may be overcome in the future, if the noise floor for angular rate sensors can be sufficiently lowered, although for comparable results, these rate sensors would need to exhibit less noise than contemporary linear accelerometers . While angular rate sensors are essential for long-duration accelerometer recording and are effective for analyses requiring integration, care must be taken when they are used for impact acceleration analyses. For impact data analysis, a 3-2-2-2 array or a 3-2-2-2 array paired with an angular rate sensor will generate results with lower noise, and should be used wherever possible.
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