Information reading device and method of adjusting information reading device

A method of adjusting an information reading device for optically reading information recorded on an information recording medium, the information reading device comprising:

• an imaging element;
• a transparent placing member on which the information recording medium is placed;
• a first illuminator configured to irradiate a back side of the information recording medium placed on the placing member, with light;
• a second illuminator configured to irradiate a top side of the information recording medium placed on the placing member, with light;
• a first optical system configured to read information recorded on the back side of the information recording medium placed on the placing member;
• a second optical system configured to read information recorded on the top side of the information recording medium placed on the placing member;
• and
• an image-forming optical system configured to cause light passing through the first optical system to form an image onto the imaging element and cause light passing through the second optical system to form an image on the imaging element, wherein
• the first optical system comprises a reflection mirror arranged below the placing member,
• the second optical system comprises a reflection mirror arranged above the information recording medium placed on the placing member,
• at least one of the reflection mirror comprised in the first optical system and the reflection mirror comprised in the second optical system is adjustable in position in an optical path length direction of light heading toward the imaging element after being reflected by the information recording medium placed on the placing member,
• the second optical system comprises, as the reflection mirror, a first reflection mirror configured to receive the light reflected by the top side of the information recording medium placed on the placing member, and a second reflection mirror configured to receive the light reflected by the first reflection mirror,
• the reflection mirror comprised in the first optical system is fixed in a first optical path length direction being an optical path length direction of light heading toward the imaging element after being reflected by the back side of the information recording medium placed on the placing member,
• at least one of the first reflection mirror and the second reflection mirror is adjustable in position in a second optical path length direction being an optical path length direction of light heading toward the imaging element after being reflected by the top side of the information recording medium placed on the placing member,
• a mirror holding member configured to hold the first reflection mirror and the second reflection mirror is provided,
• the mirror holding member is adjustable in position in the perpendicular direction,
• when the mirror holding member is adjusted in position in the perpendicular direction, the first reflection mirror and the second reflection mirror are adjusted in position in the second optical path length direction,
• the first reflection mirror is fixed to the mirror holding member while being inclined at a predetermined angle with respect to the perpendicular direction, and
• the second reflection mirror is attached to the mirror holding member so that an inclination angle of the second reflection mirror with respect to the perpendicular direction is adjustable, wherein the method comprises:
• a first adjustment step of adjusting the imaging element in position in a rotation direction where an optical axis of the image-forming optical system serves as a rotation axis, adjusting the image-forming optical system and the imaging element in position in the perpendicular direction, and adjusting a focal point wherein a focal position of the light passing through the first optical system and the image-forming optical system is adjusted by adjusting the image-forming optical system in position in the optical axial direction of the image-forming optical system;
• and
• a second adjustment step, after the first adjustment step, of adjusting the mirror holding member in position in the perpendicular direction to adjust the first reflection mirror and the second reflection mirror in position in the second optical path length direction, and adjusting the inclination angle of the second reflection mirror with respect to the perpendicular direction.