Estimation of WorldSID thorax kinematics using multiple 3-axis accelerometers

It is essential to analyze the kinematics of anthropometry dummy in vehicle's crash test. In general, it is required to measure the linear and angular components in the three orthogonal directions, respectively, in order to calculate the 3D kinematics of a rigid body. The WorldSID is originally designed to measure the tri-axis linear accelerations at the first (T1), fourth (T4), and twelfth (T12) thoracic vertebrae segments and the angular accelerations in the x and z directions. However, only three tri-axis linear accelerations are often measured for the sake of convenience. The lack of the required information results in the inaccurate calculation of the 3D torso kinematics. In this study, we propose an algorithm to accurately estimate the 3D torso kinematics when only three tri-axis linear accelerations at T1, T4, and T12 are available. Given the fact that the three tri-axis accelerometers are fixed in the torso segment, the mathematical algorithm is developed to estimate the linear acceleration at the location of the center of mass for the torso and the angular acceleration of the torso. The accuracy of the proposed algorithm is validated against the results from a rigid-body model that models the WorldSID's spine block and tri-axis accelerometers attached to T1, T4, and T12. According to the comparison against the rigid-body model, the estimated values are calculated to be within 1.7 % of the target values. After the validation is achieved, the 3D kinematics of WorldSID's torso is estimated using a set of actual side impact test data. In conclusion, the proposed algorithm accurately estimates the 3D WorldSID kinematics when at least three sets of tri-axis linear accelerations are available without any measurements of angular components.