Patent ID: 7405392

Claim:
An optical rotary encoder, comprising: a rotary slit plate having a rotation angle detection track including an optical slit; a light source for applying light to said optical slit; light receiving elements for rotation angle detection arranged in corresponding relationship with positions to which light emitted from said light source is applied to said optical slit, thereby receiving the light emitted from said light source and passing through said optical slit; and first and second light receiving elements for light amount monitoring arranged at respective locations on a circumference in corresponding relationship with positions at which light emitted from said light source is applied to said optical slit, and receiving the light emitted from said light source and passing through said optical slit, wherein each of said first and second light receiving elements for light amount monitoring has an angular width that is an integer multiple of an angular interval of light intensity distribution, on surfaces of said first and second light receiving elements for light amount monitoring, of the light emitted from said light source and that has passed through said optical slit, and said first and second light receiving elements for light amount monitoring are arranged on a circumference in corresponding relationship with positions at which the light emitted from said light source is applied to said optical slit, and said first and second light receiving elements for light amount monitoring are located 180 degrees from each other with respect to a center point of the circumference, thereby reducing variations of signals from said first and second light receiving elements for light amount monitoring that are caused by deviations of the light intensity distribution and deviations of said first and second light receiving elements for light amount monitoring in a radial direction with respect to a center of said rotary slit plate.