Weight-balanced polygonal mirror, light scanning unit using the polygonal mirror, and image forming apparatus

An image forming apparatus comprising:

• a light scanning unit comprising a light source to emit a light beam;
• a polygonal mirror to deflect the light beam emitted from the light source, in a main scanning direction;
• and an imaging optical system to image the light beam deflected by the polygonal mirror, onto a scanning surface;
• a developing unit comprising a photoconductor that is disposed at an imaging point of the light beam emitted from the light scanning unit, wherein an electrostatic latent image is formed on the photoconductor, and a developing roller that develops the electrostatic latent image formed on the photoconductor;
• and
• a transfer unit onto which an image developed by the developing unit is transferred,
• wherein the polygonal mirror is formed of a plastic and comprises a plurality of reflection surfaces that are formed in an outer portion of the polygonal mirror and rotate around a rotational axis and an internal mirror surface that defines a hole, wherein a ratio of an of an internal diameter d to an outer diameter D satisfies 0.1≦d/D≦0.3,
• the polygonal mirror is assembled by being adhered to a motor unit that supports and rotates the polygonal mirror, using an adhesive,
• the internal mirror surface of the polygonal mirror defining the hole is point-bonded to the motor unit using the adhesive, and
• the point-bonding is conducted in a direction toward a corner of the reflection surfaces.