Calibration methods of voltage-to-distance function for an electromagnetic articulometer (EMA) system

In electromagnetic articulometer (EMA) systems, the relationship between the voltage of the received signal and the distance between the transmitter and receiver coils is represented by a voltage-to-distance (VD) function. This paper describes an adaptive calibration method for determining unknown parameters in the VD function in which the parameters are determined using automatically selected local calibration data. This method is compared with the conventional fixed method in which the parameters are computed from calibration data covering the entire measurement area. Experimental results show that the measurement error of the adaptive method is 0.106 mm for a 14 x 14-cm measurement area and is less than half of that in the fixed method. In addition, this error is the same as that when the region of the receiver position is restricted to a 4x4-cm local area in the fixed method.