Development of magnetic motion capture system for multi-position detection

We developed and demonstrated a wireless multi-position detecting system using up to five LC resonant magnetic markers. The small size and light weight marker (4 mm in diameter, 10 mm long and 0.63-g in weight) uses a soft ferrite core with a coil, representing a minimal LC circuit with no battery, driven wirelessly by electromagnetic induction. The markers were given respective resonant frequencies range of 150 kHz to 450 kHz. The magnetic signal of the marker is detected by twenty-five matrix-designed search coils array. Generated flux density from the marker is considered as an ideal magnetic dipole field, the position and orientation of the marker is calculated using the nonlinear method of least squares, which effect an optimization using the Gauss-Newton method. According to the attitude angle of the markers, positional and orientational accuracies of the markers degrade as the markers distance from the search coils array increase due to decrease of S/N ratio. Cylinder axes of the markers are arranged with exciting field, however, the positional error of the markers was less than 2 mm within 100 mm and the maximum error was less than 5 mm at 150 mm of the search coils array. Approximately correct orientation of the markers was able to be acquired.