Light beam scanner unit and image forming apparatus with adjustment for contamination

A light beam scanner unit comprising:

• plural generating means for generating light beams at a fixed power, respectively;
• a polygon mirror for reflecting the light beam from the generating means toward a scanning surface to scan the scanning surface;
• power sensor means for sensing power of the light beam while the polygon mirror scans the scanning surface;
• and
• contamination detecting means for detecting contamination of the polygon mirror by comparing a sensing result obtained by the power sensor means with a pre-set reference value.

A light beam scanner unit comprising:

• generating means for generating a light beam at a fixed power, wherein the generating means have been pre-adjusted initially with an initial value so as to generate the light beam at a desired power;
• a polygon mirror for reflecting the light beam from the generating means toward a scanning surface to scan the scanning surface;
• power sensor means for sensing power of the light beam while the polygon mirror scans the scanning surface;
• and
• contamination detecting means for detecting contamination of the polygon mirror by comparing a sensing result obtained by the power sensor means with a pre-set reference value.

A method of detecting contamination of a polygon mirror which reflects a light beam generated by light beam generating means toward a scanning surface to scan the scanning surface in a light beam scanner unit, comprising the steps of:

• sensing power of the light beam while the polygon mirror scans the scanning surface;
• detecting contamination of the polygon mirror by comparing a sensing result obtained in the sensing step with a pre-set reference value;
• and
• displaying whether the contamination of the polygon mirror is permissible or not when the detecting step detects the contamination of the polygon mirror.