Measurement of dynamic joint motion using magnetohydrodynamic angular rate sensors

Abstract

A method to measure rotary motion during dynamic loading of a complex human joint has been developed. Magnetohydrodynamic angular rate sensors are mounted to rigid links on either side of the joint and are employed to measure angular velocities about three orthogonal sensor axes. During post-processing, the angular velocity vector of each sensor is transformed to local axes and integrated to obtain the incremental change in angular position for each time step. Using the angular position time histories, a transformation matrix between the reference frame of each link is calculated. Incremental Eulerian rotations from the transformation matrix are calculated using an axis system defined for the joint. Summation of the incremental Eulerian rotations produces the angular position of the joint in terms of the standard axes.