Correction value calculation method, correction value calculation program, correction value calculation apparatus, and encoder

A correction value calculation method for calculating correction values to correct the 2-phase sinusoidal signals (X, Y) output by the encoder, comprising:

• a polar coordinate calculation step for calculating, for N phase angles θi and the Lissajous radius Ri corresponding to each phase angle θi in the Lissajous waveform drawn by the 2-phase sinusoidal signals, a squared radius Ri2, which is the square of the Lissajous radius Ri corresponding to each phase angle θi;
• and
• a correction value calculation step for calculating, based on each phase angle θi and the squared radius Ri2 corresponding to the phase angle θi calculated in the polar coordinate calculation step, at least a correction residual ΔCx of an offset error Cx of the signal X, a correction residual ΔCy of an offset error Cy of the signal Y, a correction residual ΔKa of an amplitude ratio error Ka of the signals X and Y, and a correction residual ΔPy of a phase difference error Py between the signal X and the signal Y, and then calculating the correction values based on correction residuals,
• wherein the signals X and Y constitute the 2-phase sinusoidal signals, and in the correction value calculation step, and
• coefficients in an approximate expression model in which the squared radius R2 is expressed by a trigonometric function including the phase angle θ as an argument are obtained by the least-squares method using each phase angle θi and the squared radius Ri2 corresponding to each phase angle θi and the correction residual is obtained from the obtained coefficients.