Automatic correction method

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 amplitude difference or a phase difference between the “SIN” and “COS” signals, and feeding back the amplitude difference or the phase difference to the “SIN” or “COS” signal to make the amplitude difference closer to 0 or make the phase difference closer to 90 degrees so as to reduce an interpolation error after the conversion,

• wherein a component synchronous with a sine or cosine wave with a period of ½ the period of the “SIN” or “COS” signal is extracted from a radius variation waveform of a Lissajous waveform formed by the “SIN” and “COS” signals to obtain the amplitude difference or the phase difference between the “SIN” signal and the “COS” signal.

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 a second order distortion of the “SIN” or “COS” signal, and feeding back the second order distortion to the “SIN” or “COS” signal to make the second order distortion smaller so as to reduce an interpolation error after the conversion,

• wherein a component synchronous with a sine or cosine wave with a period of ⅓ the period of the “SIN” or “COS” signal is extracted from a radius variation waveform of a Lissajous waveform formed by the “SIN” and “COS” signals to obtain the second order distortion of the “SIN” signal or the “COS” signal.

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 a third order distortion of the “SIN” or “COS” signal, and feeding back the third order distortion to the “SIN” or “COS” signal to make the third order distortion smaller so as to reduce an interpolation error after the conversion,

• wherein a component synchronous with a sine or cosine wave with a period of ¼ the period of the “SIN” or “COS” signal is extracted from a radius variation waveform of a Lissajous waveform formed by the “SIN” and “COS” signals to obtain the third order distortion of the “SIN” signal or the “COS” signal.