Index error estimating apparatus, index error calibrating apparatus, and index error estimatng method

摘要

An index error estimating apparatus used for an index error calibrating apparatus (1) that has a grating disk (2) supported by a rotation shaft (22) and four detectors (3) arranged on the grating disk. The index error estimating apparatus includes a detected value synthesizer (41) that calculates a linear sum by multiplying by a predetermined coefficient each of detected values obtained from each of the at least four detectors; and a Fourier component identifier that uses a Fourier component of the linear sum and identifies a Fourier component of the index error.