Patent ID: 8517501

Claim:
An encoder sensor for reading a plurality of slits of an encoder scale, the encoder sensor comprising: a light emitting part configured to emit light; and a light receiving part configured to receive the light emitted from the light emitting part; wherein the light emitting part includes a plurality of light sources including first and second light sources positioned on a light emitting surface; wherein the light receiving part is positioned on a light receiving surface that receives light from the plural light sources; wherein the plural slits of the encoder scale include light blocking slits and transparent slits; wherein each of the transparent slits is configured to transmit the light from the plural light sources; wherein a distance between the first and the second light sources is more than a minimum distance between the first and the second light sources; wherein the minimum distance between the first and the second light sources is obtained by a formula of Xw=Xm×X 0 /Xs; wherein “Xw” indicates the minimum distance between the first and the second light sources, “Xm” indicates an anticipated width of a stain adhered to the encoder scale, “X 0 ” indicates a distance between the light emitting surface and the light receiving surface, and “Xs” indicates a distance between the encoder scale and the light receiving surface.