A portable magnetic position and orientation tracker

This paper presents the design and testing of a portable magnetic system for human motion tracking. Three essential components comprise this system (1) 3D source, consisting of three orthogonal coils, placed on the body; (2) a compatible 3D sensor, which is fixed at a remote body segment and measures the fields generated by the source; (3) a processor whose function is to relate the signals from source and sensor. Given the signals from the source and sensor, the position and orientation of the sensor in 6 degrees of freedom (DOF) with respect to the position of the transmitter can be estimated. Coil parameters, such as the radius are optimized for tracking the distance between the lower back and the shoulder of a person. The electronics are designed to run on battery supply, making it suitable for body mounting and ambulatory measurements. The system is tested with functional body movements such as flexion of the back, arm movement and walking. The accuracy of measurements is approximately 8 mm in position and 5° in orientation with 6 DOF movements. Results are less accurate during relatively high velocities of the source or sensor due to under sampling. The magnetic tracker will be used as an aiding system for fusion with inertial sensors, therefore, the update rate requirements can be relatively low.