Evaluating spatial orientation and position of an ATD head using accelerometers and angular rate sensors in dynamic impact testing

Abstract

Using three linear accelerometers and three angular rate sensors arranged to measure local acceleration in the X, Y, and Z directions and angular velocity about those axes, it is possible to calculate spatial orientation and position in a global coordinate system. The intent of this thesis is to use this calculation to provide the head trajectory of an Anthropomorphic Test Device (ATD) to supplement or replace photometric analysis. This thesis examines the various parameters of the calculations of the spatial orientation and position to determine the most accurate and efficient method. Using the local angular velocity as an input, this method determines spatial orientation as a function of a unit quaternion by numerically solving a system of ordinary differential equation. The parameters of the numerical integration examined are the numerical integration methods, time step, and order of rotation. These functions are examined through simulation data generated by various MADYMO models. The MADYMO three-dimensional multi-body simulations output the linear accelerations and angular velocity of selected bodies in simulations similar to the data provided from accelerometers and angular rate sensors during dynamic impact testing. Simulation data is useful in the examination and validation of the different parameters used in the method due to the lack of noise and gravitational effects incurred during physical dynamic impact testing. The method is evaluated for dynamic impact testing through a comparison between the calculated spatial orientation and position using the algorithm and photometric analysis as well as physical limitations in the test setup, i.e. rigid bulkhead. The method is demonstrated to be successfully implemented into the NIAR Crash Dynamics Laboratory at Wichita State University.