Patent ID: 8056250

Claim:
An eccentricity measurement method of measuring the eccentricity between a center of a connection portion of a rotary disk of a rotary encoder connected to a rotary shaft of a rotary member and a center of a scale formed at the peripheral portion of the rotary disk, the eccentricity measurement method comprising: forming, on the rotary disk, a circle pattern concentric with the scale and at least three straight-line patterns intersecting or contacting the circle pattern and the connection portion; and measuring an amount and direction of eccentricity of the rotary disk by comparing a coordinate of the center of the connection portion, which is calculated from coordinates of intersections of the straight-line patterns and the connection portion, with a coordinate of the center of the scale, which is calculated from the coordinates of intersections of the straight-line patterns and the circle pattern, wherein a central portion of the rotary disk includes the connection portion and the scale including one of a combination of a light-transmitting portion and a light-blocking portion or a combination of a light-reflecting portion and a light-absorbing portion.