2007 Volume 43 Issue 9 Pages 821-828
This paper proposes a new calibration method of magnetic sensors for measurement of human finger tapping movements. The magnetic sensors consist of two coils; the detection coil and the oscillation coil. A voltage of the detection coil induced by the electromagnetic induction law changes depending on a distance between two coils. Therefore, by modeling relations between the measured voltages and the distances, we can estimate the distance between two fingertips in wearing two coils from the measured voltage.
In this paper, first, the relation between the output voltage and the distance is derived as a set of highly nonlinear equations. Then, using first-order approximations, it is shown that the nonlinear calibration equations can be reduced to a linear one, so that the unknown parameters included in the calibration equation can be estimated with the linear least-squares technique using a data set of measured output voltages and corresponding distances. Experimental results show that the relation between the output voltages and the distances can be identified by using only three calibration points (0.02, 0.03, 0.09 [m]) measured from each subject, and that the estimation accuracy is confirmed by comparing with the results using a camera. Finally, the differences of finger tapping movements among patients with Parkinson's disease, old healthy subjects and young healthy subjects are explored using the magnetic sensors with the proposed calibration method.
