Patent ID: 7711508
Filing Date: 2010-05-04
Classification: G01D

Abstract:
1. A position detector for detecting a displacement of a target, comprising: a position sensor that outputs two signals that sinusoidally vary at a pitch of wavelength λ with respect to the displacement and have phases shifted from each other by 90 degrees; an offset memory that stores offset values regarding the two signals output from the position sensor; an offset elimination circuit that eliminates the offset values stored in the offset memory from the respective two signals output from the position sensor; an interpolation calculator that converts the two signals after the offset elimination into position data; a radius calculator that calculates a root-sum-square of the two signals after the offset elimination; and an offset value calculator that calculates offset values to be stored in the offset memory based on the position data and an output value from the radius calculator which are obtained when the measured displacement is changed by an integer multiple of wavelength λ; wherein the offset values stored in the offset memory are updated using the offset values obtained in the offset value calculator.