Optical encoder and control apparatus

An optical encoder comprising:

• a light source;
• a scale;
• a light receiving unit configured to receive light from the scale;
• and
• a processing unit configured to process a signal from the light receiving unit,
• wherein the scale includes a diffraction grating configured to condense diffracted light in a periodic direction of the diffraction grating in order to detect a reference position,
• wherein the light receiving unit includes a light receiving element array configured to receive light from the diffraction grating,
• wherein the light receiving element array includes a first light receiving element, a second light receiving element, a third light receiving element, and a fourth light receiving element configured to output signals having phases different from each other,
• wherein the first light receiving element and the second light receiving element are adjacent to each other and are arranged between the third light receiving element and the fourth light receiving element,
• wherein the processing unit obtains a first differential signal between a signal from the first light receiving element and a signal from the third light receiving element and obtains a second differential signal between a signal from the second light receiving element and a signal from the fourth light receiving element, and
• wherein the processing unit adds the first differential signal and the second differential signal and subtracts the first differential signal and the second differential signal to output a reference voltage as a reference.