Image reading apparatus with a mirror having a curved surface to reduce defocusing during image scanning

An image reading apparatus, comprising:

• a first running device configured to move to scan a document in a scanning direction at a predetermined speed and includes:
• an illumination unit configured to illuminate the document from direction different from the scanning direction, and
• a first mirror configured to reflect light reflected from the document illuminated by light from the illumination unit;
• a second running device configured to move in the scanning direction parallel to the first running device at half the predetermined speed of the first running device and includes:
• a second mirror configured to reflect the light reflected by the first mirror, and
• a third mirror configured to reflect the light reflected by the second mirror parallel to the scanning direction;
• an imaging lens configured to produce a reduced image by receiving the reflected light from the third mirror;
• and
• a line sensor configured to convert the reduced image to an electrical signal,
• wherein at least one of the second and third mirrors comprises a curved surface, and
• wherein a curvature radius of the curved surface of such mirror is such that a distance deviation between the imaging lens and an imaging surface remains within a usable range for actual operation regardless of movements of the first and second running devices, and
• wherein curvature radii of the first mirror, second mirror, and third mirror are greater than one fifth of a length of the mirror in a longitudinal direction of the mirror.

An image reading apparatus, comprising:

• a first running device configured to move to scan a document in a scanning direction at a predetermined speed and includes:
• an illumination unit configured to illuminate the document from direction different from the scanning direction, and
• a first mirror configured to reflect light reflected from the document illuminated by light from the illumination unit;
• a second running device configured to move in the scanning direction parallel to the first running device at half the predetermined speed of the first running device and includes:
• a second mirror configured to reflect the light reflected by the first mirror, and
• a third mirror configured to reflect the light reflected by the second mirror parallel to the scanning direction;
• an imaging lens configured to produce a reduced image by receiving the reflected light from the third mirror;
• and
• a line sensor configured to convert the reduced image to an electrical signal,
• wherein at least one of the second and third mirrors comprises a curved surface, and
• wherein a curvature radius of the curved surface of such mirror is such that a distance deviation between the imaging lens and an imaging surface remains within a usable range for actual operation regardless of movements of the first and second running devices, and
• wherein a polarity of the curvature radius of the second mirror is opposite from a polarity of the curvature radius of the third mirror.

An image reading apparatus, comprising:

• a first running device configured to move to scan a document in a scanning direction at a predetermined speed and includes:
• an illumination unit configured to illuminate the document from direction different from the scanning direction, and
• a first mirror configured to reflect light reflected from the document illuminated by light from the illumination unit;
• a second running device configured to move in the scanning direction parallel to the first running device at half the predetermined speed of the first running device and includes:
• a second mirror configured to reflect the light reflected by the first mirror, and
• a third mirror configured to reflect the light reflected by the second mirror parallel to the scanning direction;
• an imaging lens configured to produce a reduced image by receiving the reflected light from the third mirror;
• and
• a line sensor configured to convert the reduced image to an electrical signal,
• wherein at least one of the second and third mirrors comprises a curved surface, and
• wherein a curvature radius of the curved surface of such mirror is such that a distance deviation between the imaging lens and an imaging surface remains within a usable range for actual operation regardless of movements of the first and second running devices, and
• further comprising vibration-proof material provided in the mirror to protect the mirror from vibration,
• wherein the curvature radius of the mirror is a total length of the mirror including the vibration-proof material.