| CPC G01D 5/2448 (2013.01) | 12 Claims |
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1. An automatic correction method for an encoder system for reading periodic signals on a scale as “SIN” and “COS” signals and converting the periodic signals into position signals, the automatic correction method comprising:
detecting an offset of the “SIN” or “COS” signal, and feeding back the offset to the “SIN” or “COS” signal to make the offset smaller so as to reduce an interpolation error after the conversion; and
correcting the encoder using the offset after the detecting the offset,
wherein a component synchronous with a sine or cosine wave is extracted from a radius variation waveform of a Lissajous waveform formed by the “SIN” and “COS” signals to obtain the offset of the “SIN” signal or the “COS” signal,
wherein for extracting the component synchronous with the sine or cosine wave from the radius variation waveform of the Lissajous waveform, results of multiplying the radius variation waveform of the Lissajous waveform by sin(2πn/N) or cos(2πn/N) are averaged over a most recent one period of the Lissajous waveform,
where N is an even natural number, and n is an integer from 0 to N−1 proportional to a phase of the Lissajous waveform in one period.
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