Rotary disk eccentricity measurement method, rotary encoder, and image forming apparatus including the rotary encoder

An eccentricity measurement method of measuring eccentricity between a center of a radial scale of a rotary disk formed along a peripheral portion of the rotary disk and a center of a connection portion of the rotary disk for connecting the rotary disk to a rotary shaft of a measured object,

• the eccentricity measurement method comprising:
• forming, on the rotary disk, a plurality of equally spaced first circle patterns concentric with the radial scale from a base point a predetermined distance away from the center of the radial scale;
• forming, on a table comprising a projection that engages the connection portion of the rotary disk, the same number of second circle patterns as that of the first circle patterns, concentric with the first circle patterns at a pitch different from the pitch of the first circle patterns from a base point the predetermined distance away from the center of an outer diameter of the projection;
• placing the rotary disk on the table;
• and
• measuring an amount and direction of the eccentricity of the rotary disk using the position of the first circle pattern that coincides with the second circle pattern,
• wherein a central portion of the rotary disk includes the connection portion.

An eccentricity measurement method of measuring an eccentricity between a center of a radial scale of a rotary disk formed at a peripheral portion of the rotary disk and a center of a connection portion of the rotary disk for connecting the rotary disk to a rotary shaft of a measured object,

• the eccentricity measurement method comprising:
• forming, on the rotary disk, at least one first arc-shape pattern group in different radial directions, the first arc-shape pattern group including a plurality of arc-shape patterns equally spaced radially and extending in a normal line direction from a base point a predetermined distance away from the center of the radial scale;
• forming, on a table comprising a projection that engages the connection portion of the rotary disk, at least one second arc-shape pattern group, the second arc-shape pattern group including the same number of the plurality of the arc-shape patterns as that of the first arc-shape pattern group in the same radial direction as that of the arc-shape patterns of the first arc-shape pattern group at a pitch different from the pitch of the arc-shape patterns of the first pattern group from a base point the predetermined distance away from the center of an outer diameter of the projection;
• placing the rotary disk on the table such that the base point of the first arc-shape pattern group coincides with the base point of the second arc-shape pattern group;
• and
• measuring an amount and direction of the eccentricity of the rotary disk using the position of the arc-shape pattern of the first arc-shape pattern group in the radial direction that corresponds to the arc-shape pattern of the second arc-shape pattern group,
• wherein a central portion of the rotary disk includes the connection portion.