Position measuring apparatus

Abstract

A position measuring apparatus for obtaining position information by processing a first and second sinusoidal signals with the phase difference of 90.degree. obtained by a detecting device in accordance with change of a position, comprises an adding and subtracting device for generating a third sinusoidal signal by subtracting the second sinusoidal signal from the first sinusoidal signal and a fourth sinusoidal signal by adding the first and second sinusoidal signals, a maximum and minimum measuring device for measuring respective maximum and minimum values of the first to fourth sinusoidal signals, a processing device for calculating amplitudes and offsets of the respective first and second sinusoidal signals based on the maximum and minimum values of the first and second sinusoidal signals measured by the maximum and minimum measuring device, obtaining fifth and sixth sunusoidal signals by standardizing the first and second sinusoidal signals based on the obtained amplitudes and offsets, forming a seventh sinusoidal signal by subtracting the sixth sinusoidal signal from the fifth sinusoidal signal and an eighth sinusoidal signal by adding the fifth and sixth sinusoidal signals, correcting the ratio of the seventh sinusoidal signal to the eighth sinusoidal signal based on the ratio between respective amplitudes of the seventh and eighth sinusoidal signals obtained by the use of the maximum and minimum values of the third and fourth sinusoidal signals measured by the maximum and minimum measuring device, and obtaining the position information from the corrected value.