Reading module having reflection mirror array, image reading device comprising same, and image forming apparatus therewith

A reading module comprising:

• light source which irradiates a document with light;
• an optical system which images, as image light, reflected light of the light with which the document is irradiated by the light source;
• sensor in which a plurality of image regions where the image light imaged by the optical system is converted into an electrical signal are arranged next to each other in a main scanning direction;
• and
• a housing which houses the light source, the optical system, and the sensor,
• wherein
• the optical system includes:
• a mirror array in which a plurality of reflection mirrors whose reflection surfaces are aspherical concave surfaces are coupled together in an array in the main scanning direction;
• and
• a plurality of aperture stop portions which are provided respectively between the reflection mirrors and the image regions of the sensor and which adjust an amount of image light reflected from the reflection mirrors,
• the optical system is fixed on the housing at one point in the main in scanning direction,
• an imaging magnification of the reflection mirrors with respective to the image regions is set at a reduction magnification,
• a plurality of light shielding walls are provided which extend from the sensor toward the aperture stop portion, the light shielding walls being arranged at positions deviated by a predetermined amount from the boundaries between the image regions in a direction opposite to a fixed side of the optical system the light shielding walls shielding stray light striking the image regions,
• an amount of deviation of the light shielding walls from the boundaries between the image regions are determined based on an amount of expansion and contraction of the optical system in the main scanning direction due to change in temperature, and
• the light shielding walls are arranged at positions deviated from the boundaries between the image regions in the direction opposite to the fixed side of the optical system by a difference z2−z1 between an amount of contraction z1 of the optical system toward the fixed side and an amount of expansion z2 of the optical system toward a non-fixed side calculated by formula (1) below:
• z=x×Δt×a (1)
• where
• x represents a distance from a fixed position of the optical system to a light shielding wall;
• Δt represents a variation in ambient temperature from 25° C.;
• and
• a represents a linear expansion coefficient of a resin material forming the optical system.