Patent attributes
Two position sensors provide, as outputs, two signals that vary sinusoidally at a pitch of wavelength λ with respect to a displacement of a target and have phases shifted from each other by 90°. A memory unit has stored therein offset values for the two signals, and two subtractors eliminate the offset values from the two signals, respectively. The two signals after offset elimination are converted into position data in an interpolation calculator. A radius calculator calculates a radius value of the two signals after offset elimination. An FFT calculates offset values based on the position data and the radius values, and the calculated offset values are used to update the values stored in the memory unit. An amplitude ratio correction value and a phase difference correction value for the two signals are updated similarly. By performing elimination of the components that degrade interpolation accuracy at every rotational position, interpolation accuracy is improved.
