Abstract: A rotary encoder for detecting a rotation status of a rotary scale having a diffraction grating formed along a rotational direction comprises a directing device for directing a radiation beam to a first position on the rotary scale and directing a plurality of diffracted beams generated at the first position to a second position different from the first position. The direction device is constructed such that the plurality of diffracted beams gave a common light path between the first position and the second position. The encoder also includes a forming device for forming an interference beam from a plurality of rediffracted beams generated at the second position, and a convertor for converting the interference beam to a signal to produce the signal representing the rotation status.

Abstract: An encoder for measuring the displacement of a movable diffraction grating has means for applying a radiation beam to the diffraction grating, a reflecting optical system for causing first and second reflected and diffracted beams created on the diffraction grating by the application of the radiation beam to be reflected and diffracted at least twice by the diffraction grating, and means for receiving an interference beam formed by the first and second reflected and diffracted beams reflected and diffracted at least twice and converting it into a signal conforming to the displacement of the diffraction grating.

Abstract: An encoder for detecting the state of movement of a scale having a plurality of tracks consisting of arranged predetermined codes comprises first detecting device for reading the codes of the plurality of tracks and detecting data comprising a row of the codes, and second detecting device for detecting the state of movement of the codes of a particular track plurality of tracks to obtain more detailed data. The state of movement of the scale is detected on the basis of the signals from the first and second detecting devices.

Abstract: 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.

Abstract: An optical type encoder comprises a light source for supplying a light beam for illuminating a diffraction grating formed on a movable scale, photoelectric converting means for photoelectrically converting interference fringes formed by causing a plurality of diffracted lights created by the diffraction grating to interfere with one another to measure the displacement of the movable scale and outputting a predetermined signal, detecting means for receiving a predetermined diffracted light created by the diffraction grating and detecting any fluctuation of the intensity thereof, and control means for modulating the intensity of the light beam illuminating the diffraction grating, on the basis of a signal from the detecting means, so that the amplitude of the output signal from the photoelectric converting means may become substantially constant.