Encoder, servomotor, and motor unit

A servomotor comprising:

• a motor configured to rotate a rotary shaft;
• and
• an encoder configured to measure an absolute position of the rotary shaft;
• the encoder comprising:
• a disk disposed rotatably about a rotating axis of the rotary shaft and including a first track and a second track in which a first rotating grating and a second rotating grating are formed, respectively;
• and
• a first detector and a second detector disposed so as to face the first track and the second track, including a first fixed grating constructing a first diffraction interference optical system together with the first rotating grating and a second fixed grating constructing a second diffraction interference optical system together with the second rotating grating, respectively, and configured to detect a first detection signal and a second detection signal from the first diffraction interference optical system and the second diffraction interference optical system, respectively,
• at least one of the first rotating grating and the second rotating grating includes a plurality of curved slits in a curved shape, and
• an absolute value of the disk is obtained based on a difference in the number of slits between the first rotating grating and the second rotating grating,
• the encoder further comprising a position data generating portion configured to generate first position data representing an absolute position of the disk during one rotation and second position data having a resolution higher than that of the first position data based on the first detection signal and the second detection signal, and to specify the absolute position of the disk with a resolution higher than that of the first position data based on the first position data and the second position data, wherein:
• the first rotating grating and the second rotating grating includes a first curved slit a second curved slit, respectively, and curve degrees of the first curved slit and the second curved slit are set respectively in the manner that pitches of the first curved slit and the second curved slit are substantially equal.

A motor unit comprising:

• a motor configured to rotate a rotary shaft;
• an encoder configured to measure a position of the rotary shaft;
• and
• a controller configured to control rotation of the motor based on the position detected by the encoder;
• the encoder comprising:
• a disk disposed rotatable about a rotating axis of the rotary shaft and including a first track and a second track in which a first rotating grating and a second rotating grating are formed, respectively;
• and
• a first detector and a second detector disposed so as to face the first track and the second track, including a first fixed grating constructing a first diffraction interference optical system together with the first rotating grating and a second fixed grating constructing a second diffraction interference optical system together with the second rotating grating, respectively, and configured to detect a first detection signal and a second detection signal from the first diffraction interference optical system and the second diffraction interference optical system, respectively,
• at least one of the first rotating grating and the second rotating grating includes a plurality of curved slits in a curved shape, and
• an absolute value of the disk is obtained based on a difference in the number of slits between the first rotating grating and the second rotating grating,
• the encoder further comprising a position data generating portion configured to generate first position data representing an absolute position of the disk during one rotation and second position data having a resolution higher than that of the first position data based on the first detection signal and the second detection signal, and to specify the absolute position of the disk with a resolution higher than that of the first position data based on the first position data and the second position data, wherein:
• the first rotating grating and the second rotating grating includes a first curved slit and a second curved slit, respectively, and curve degrees of the first curved slit and the second curved slit are set respectively in the manner that pitches of the first curved slit and the second curved slit are substantially equal.

An encoder comprising:

• a disk disposed rotatably about a rotating axis and including a first track and a second track in which a first rotating grating and a second rotating grating are formed, respectively;
• and
• a first detector and a second detector disposed so as to face the first track and the second track, including a first fixed grating constructing a first diffraction interference optical system together with the first rotating grating and a second fixed grating constructing a second diffraction interference optical system together with the second rotating grating, respectively, and configured to detect a first detection signal and a second detection signal from the first diffraction interference optical system and the second diffraction interference optical system, respectively,
• at least one of the first rotating grating and the second rotating grating includes a plurality of curved slits in a shape being along curved lines formed by curving a plurality of radial lines extending from the rotating axis in radial directions of the disk toward circumferential directions at curve degrees, C, determined based on a following equation:
• C=tan(sin−1{p×n/(2πr0)}),
• where n is a number of the curved slits in a respective track, p is a pitch of the curved slits in the respective track, and r is a radius of the respective track about the rotating axis, and
• an absolute value of the disk is obtained based on a difference in the number of slits between the first rotating grating and the second rotating grating.