Patent ID: 8188421

Claim:
An optical encoder comprising: an encoder head secured to one of a fixed member and a movable member which move relative to each other; and a scale secured to the other of the fixed member and movable member, facing the encoder head and having a second grating that has an optical pattern of a predetermined pitch, wherein: the encoder head has a light emission unit configured to emit specific light to the scale, a light transmission member configured to transmit the light emitted from the light emission unit and a light detection unit having light detection elements arranged at a predetermined pitch; the light transmission member has a first grating having an optical pattern of a predetermined pitch and an aperture configured to narrow the light emitted from the light emission unit and impinging on the second grating of the scale; and a motion of an image on the light detection elements of the light detection unit is detected, the image being formed by the light reflected or diffracted by the second grating of the scale after the light emitted from the light emission unit impinges on the scale through the light transmission member.