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

摘要

A light scanning unit includes a light source to emit a light beam; a polygonal mirror to deflect the light beam in a main scanning direction; and an imaging optical system to image the light beam onto a scanning surface. The polygonal mirror includes 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. A ratio of an internal diameter d to an outer diameter D satisfies 0.1≦d/D≦0.3. The polygonal mirror is 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.