Encoder for forming interference fringes by re-diffracted lights from an optical type scale and photoelectrically converting the interference fringes to thereby detect the displacement of the scale

摘要

An optical type encoder for projecting a light beam onto an optical type scale having a diffraction grating formed thereon, forming interference fringes by the use of the diffracted light from the scale, and photoelectrically converting such interference fringes to thereby detect the displacement of the scale. The first and second light beams are caused to obliquely enter substantially the same position on the scale from different first and second directions, first and second diffracted light beams emerging perpendicularly from the scale by the light beams being diffracted by the scale are received by a common reflecting element, the first and second diffracted light beams are directed to said position by the reflecting element, and interference fringes formed by diffracted light beams emerging from the scale in the first and second directions by the first and second diffracted light beams being diffracted by the scale are photoelectrically converted.