MEASUREPIENT OF 3-D MOTION

The general three-din~nsional (3-D) motion of a rigid body (R.B.), described by its six degrees of freedom, rcay be determined by means of ni9e linear (translational) accele-rometers which are properly mounted on the R.B. in three clusters. The nine accelerations are mathematically nanipu-lated to produce the angular acceleration and velocity vectors of the R.E., its orientation in 3-0 inertial (laboratory) space, the absolute translational acceleration, velocity and position vectors of an arbitrary point on the rigid body. Each one of the three clusters is a triaxial accele-rometer (or triax) which measures 3 orthogonal components of the acceleration vector of its "center. " In general, these orhogonal instrumentation axes are arbitrarily chosen for convenience, and threfore, do not coincide with the "anatomical " reference frame in which the motion is to be described. It is assumed that the transformation matrix between the instrumentation and anztomical frames is known, so that the analysis is conducted on the anatomical compo-nents of the three acceleration vectors. Furthermore, it is assumed that the position vector of each triax center is known relative to an arbitrary point, which is taken as the origin of the anatomical reference frame. In the following sections, the kinematic equations of motion will be developed, their solution will be presented, then validated with actual and hypothetical motions