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A New Precision 3D Motion Analysis System


 A new in vitro technique for measuring three-dimensional six-degree-of-freedom motion was developed. The system consists of twenty-four nylon lines activating digital rotary encoders which are mounted on six panels of a rigid frame that surround the testing space. The system is capable of tracking motion of up to four independent bodies in a space of approximately 0.5 × 0.5 × 0.5 meter. By knowing the coordinates of three non-collinear points on the frame and the straight line distances from these points to any point on the moving body, the spatial location of that point can be determined based on simple geometry. The location and orientation of a rigid body can be further calculated from the spatial coordinates of three non-collinear points on the rigid body or its extension. The system has an accuracy of 1% in the vertical direction and 0.7% in the horizontal plane. The system can be used in biomechanical analysis of multi-segment spinal motion and motion of other joints.