Patent ID: 7332708

Claim:
An optical encoder comprising: a scale having an optical grating; a plurality of photoreceptor units each having a same number of photoreceptor elements arranged in a relationship to a pitch of the optical grating to obtain two-phase signals by computing outputs of the photoreceptor units, the photoreceptor units being disposed in a row in a moving direction of the scale; a light source having a plurality of light emitting portions which irradiates the photoreceptor elements via the scale from at least two different directions; and a controller which changes the light emitting power balance by changing current-balance between the light emitting portions; wherein the controller obtains relative-position information between the scale and the photoreceptor units based on the light emitting power balance and on the plurality of two-phase signals obtained respectively in accordance with the changes of light emitting power balance of the light emitting portions.