Patent ID: 8461790

Claim:
A rotary encoder comprising: a disk in a disk shape that is arranged rotatably about a rotation axis and that includes one or more tracks in a ring shape on which an optical rotating grating is formed on whole circumference and one or more origin detection areas serving as partial areas on which an optical rotating grating is formed and that are offset from the rotation axis; and a mask that is fixed and arranged in a manner facing the disk and on which two or more optical fixed gratings capable of constituting a diffraction interference optical system together with each of the rotating grating of the tracks and the rotating grating of the origin detection areas are formed, wherein a plurality of slits included in the rotating grating of the origin detection areas are inclined slits formed in a manner inclined in a circumferential direction with respect to radial lines about the rotation axis or curved slits curved in the circumferential direction with respect to the radial lines about the rotation axis.