Image reading apparatus

An image reading apparatus accurately determines the positions of image forming mirrors formed with an off-axis reflecting surface, while enabling any thermal expansion caused by a rise in temperature due to a rise in the surrounding temperature to be absorbed. Each image forming mirror formed with an off-axis reflecting surface comprises respective and independent units for determining the positions in the longitudinal direction, in the lateral position, and in the direction orthogonal to the reflecting surface. Holes with which the longitudinal position determining units and the lateral position determining units engage have gaps in the directions orthogonal to the position determining directions to absorb the thermal expansion caused by a rise in the temperature of the image forming mirror when the position determining units engage with the holes. Determination of the position of the reflecting surfaces of the image forming mirrors is carried out by urging faces provided on the reflecting surface side against the housing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image reading apparatus that illuminates documents and reads the images of the documents by a photoelectric conversion unit, and particularly relates to an image forming unit that forms images on the photoelectric conversion unit.

2. Description of the Related Art

Hitherto, an image scanner for reading image data on documents has been known as an image reading apparatus, in Japanese Patent Laid-Open No. 3-113961, for example.

In such an image scanner, an image forming lens and a line sensor are fixed, and exposure scanning of a document is carried out by moving only reflecting mirrors, thus reading image data.

Recently, to simplify the structure of such an apparatus, carriage-integrated scanning systems that integrate mirrors, an image forming lens, and a line sensor, have been adopted to scan documents.

FIG. 5shows an image reading apparatus of a known carriage-integrated scanning system. A light beam emitted by a light source501illuminates a document503mounted on a document table glass502, then the reflected light beam from the document503gets bent along an optical path inside a carriage511through first to third mirrors504to506, and thus an image forming lens509forms an image onto a line sensor510as the light beam passes through the image forming lens509. The carriage511is moved by a driving motor (not shown) in the direction arrow A (feed direction) to read the image data of the document503. The image forming lens509is fixed in a lens barrel512, and the first to third mirrors504to506and the lens barrel512are fixed to the carriage511.

In an image reading apparatus such as a digital copy machine, however, since high resolution and high speed are required, the field angle must be narrow to improve the resolution of the image forming lens, but then the length of the optical path is extended and the light quantity is decreased. If the optical path length is shortened, the field angle becomes wider, which lowers the resolution and thus makes it difficult to employ a carriage-integrated scanning system.

An image reading apparatus of a carriage-integrated scanning system adopting an off-axis optical system that forms an image by the reflection of a light beam, as disclosed in Japanese Patent Laid-Open No. 8-292371 or the like, is presented in Japanese Patent Laid-Open No. 2002-335375 (US Patent Application No. 20030038228). With respect to a reference axis along a light beam going through the image center and the pupil center, an off-axis optical system is defined as an optical system that includes a curved surface (off-axis curved surface) whose surface normal at the intersection point of the surface and the reference axis is not on the reference axis. In Japanese Patent Laid-Open No. 2002-335375, a construction that avoids chromatic aberration, with air as the medium between the reflecting surfaces of an off-axis optical system, particularly for scanning color documents, is presented.

SUMMARY OF THE INVENTION

To solve the above described problem with a known image reading apparatus, the present invention presents a construction for an image reading apparatus as follows.

The invention presents an image reading apparatus, for reading an image of a document, including an image reading unit for reading the image of the document; an illumination unit for illuminating the document; an image forming unit for forming the image of the document on the image reading apparatus, the image forming unit being constructed with a plurality of image forming mirrors formed with an off-axis reflecting surface with which a reference-axis ray has a different incident direction and reflected direction, the off-axis reflecting surface having a curvature; a housing for supporting the image reading unit, the illumination unit, and the image forming unit; and a scanning unit that moves the housing to perform scanning of the image of the document, wherein each of the image forming mirrors is disposed on a reflecting surface side thereof with urging parts being urged against the housing to determine the position of the reflecting surface.

The invention presents another image reading apparatus, wherein the urging parts provided on the image forming mirrors have a flat part.

The invention presents still another image reading apparatus, wherein the off-axis reflecting surface and the urging parts of each image forming mirror are formed integrally.

The invention presents yet another image reading apparatus, wherein the image forming mirrors comprise longitudinal position determining parts and lateral position determining parts for respectively and independently determining a longitudinal direction position and a lateral direction position.

The invention also presents another image reading apparatus, wherein either the longitudinal position determining parts or the lateral position determining parts provided on the image forming mirrors are formed on flat parts.

The invention presents still another image reading apparatus, wherein the longitudinal position determining parts and the lateral position determining parts provided on each image forming mirror determine the position of a reference axis of the off-axis reflecting surface of the image forming mirror.

The invention presents yet another image reading apparatus, wherein the off-axis reflecting surface, and the longitudinal position determining parts and the lateral position determining parts are formed integrally for each of the image forming mirrors.

The invention presents still another image reading apparatus, wherein the housing comprises respective engaging parts with which the longitudinal position determining parts and the lateral position determining parts of the image forming mirrors engage, and when the engaging parts, and the longitudinal position determining parts and the lateral position determining parts engage with each other, each portion of the engaging parts can slide in a direction orthogonal to a position determining direction, thereby allowing thermal expansion of the image forming mirrors.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

FIG. 1is a cross-sectional view of an essential part of an image reading apparatus in a first embodiment according to the invention; the apparatus is applied to a system such as an image scanner and a copy machine.FIG. 2is a top view of a carriage12inFIG. 1.

In the figures, reference numeral1denotes a document table glass upon which a document S is mounted. Reference numeral2denotes a light source such as a xenon lamp, for example. Reference numerals3to5respectively denote first to third reflecting mirrors which bend the optical path of a light beam from the document S. Reference numerals6to9respectively denote first to fourth image forming mirrors formed with a single off-axis reflecting surface, wherein the image forming mirrors bend, with air as the medium, the light beam reflected from the image data of the document S and form an image on the surface of a reading unit10. The first to fourth image forming mirrors6to9are formed of a resin such as polycarbonate. Reference numeral10denotes a linear image sensor (CCD), as a reading unit, that is constructed in such a manner that a plurality of light receiving elements is arranged in a single dimensional direction (main scanning direction). Reference numeral11denotes a housing of the carriage12that houses the light source2, the first to third reflecting mirrors3to5, the first to fourth image forming mirrors6to9, and the CCD10. The housing11is integrally formed with lamp supporting parts11aand11b, reflecting mirror supporting parts11cand11d, and an image forming mirror supporting part11e. The light source2is positioned at the lamp supporting parts11aand11band directly fixed thereto; the first to third reflecting mirrors3to5are likewise fixed to the reflecting mirror supporting parts11cand11d; and the first to fourth image forming mirrors6to9are likewise fixed to the image forming mirror supporting part11e. Reference numeral15denotes a CCD mounting table which is directly fixed to CCD supporting portions11gand11h(inFIGS. 1 and 2, reference numerals11gand11hdenote different portions of the same part), which are integrally formed on the housing11. The CCD10is fixed on a CCD table16by blade springs17aand17b. The CCD mounting table15and the CCD table16are fixed to each other by a weld (X), where the position of the CCD10is adjusted such that the reading image quality (focus, geometric properties, etc.) of the image data read by the CCD10satisfies predetermined specifications. Reference numeral13denotes a driving motor which has a function to move the carriage12in the direction of arrow A in the figure through a driving belt14connected to the housing11and the driving motor13.

In the present embodiment, the document S is illuminated by the light beam emitted from the light source2; then, the reflecting light beam from the document S is bent along an optical path inside the carriage12by the first to third mirrors3to5, and is further bent by the first to fourth image forming mirrors to form an image on the surface of the CCD10. Then, the carriage12is moved by the driving motor13in the direction of arrow A (feed direction) to read the image data of the document S.

FIG. 3is an enlarged perspective view of a part where one of the first to fourth image forming mirrors6to9is fixed to the image forming mirror supporting part11eprovided on the housing11. InFIG. 3, reference numerals6to9denote the first to fourth image forming mirrors; reference numeral19denotes flat urging faces that determine the position of the mirror surface provided on the mirror surface side of the image forming mirror; reference numerals20and21denote bosses that determine the positions of the image forming mirror in the longitudinal direction and the lateral direction; reference numerals22and23denote a circular hole and a long hole that are provided on the image forming mirror supporting part11eand engaged with the bosses of the image forming mirror; and reference numeral24denotes a blade spring to fix one of the image forming mirrors6to9to the image forming mirror supporting part11e.

The positions of the image forming mirrors6to9in the longitudinal direction and the lateral direction are determined by the engagement of the bosses20and21with the circular hole22and the long hole23, the position of the mirror surface is determined by urging the urging faces19against the mirror supporting part11e, and the image forming mirror is fixed by the pressure force of the blade spring24.

The method of determining the positions of the image forming mirrors in the longitudinal direction and the lateral direction is not limited to the construction shown in the present embodiment; for example, the side faces of the image forming mirrors may be engaged with the housing, or the image forming mirrors may be fixed after determining the positions with a position determining tool.

Further, in addition to the method using the pressure force of a blade spring, the image forming mirrors may be fixed by bonding or screwing, for example.

Second Embodiment

A second embodiment of the invention will be described below with reference toFIG. 4. The essential construction of an image reading apparatus in the second embodiment is the same as that described in the first embodiment.

FIG. 4is an enlarged perspective view of a part where one of the first to fourth image forming mirrors6to9inFIGS. 1 and 2is fixed to the image forming mirror supporting part11eprovided on the housing11. InFIG. 4, reference numerals6to9denote the first to fourth image forming mirrors; reference numeral25denotes flat urging faces that determine the position of the mirror surface provided on the mirror surface side of the image forming mirror; reference numerals26to29denote bosses and projecting parts (longitudinal position determining parts and lateral position determining parts) that determine the positions in the longitudinal direction and the lateral direction of the image forming mirror; reference numerals30to33denote long holes that are provided on the image forming mirror supporting part11eand engaged with the bosses and the projecting parts of the image forming mirror; and reference numeral34denotes a blade spring to fix one of the image forming mirrors6to9to the image forming mirror supporting part11e.

With respect to the positions of the image forming mirrors6to9, the position in the lateral direction is determined by engaging the bosses26and27with the long holes30and31; the position in the longitudinal direction is determined by the engagement of the projecting parts28and29with the long holes32and33; the position of the mirror surface is determined by urging the urging faces25against the mirror supporting part11e; and the image forming mirror is fixed by the pressure force of the blade spring34.

Even when the image forming mirror expands more compared to the mirror supporting part with a rise in temperature in the housing11, the long holes30to33and the projecting parts26to29slide along each other, and there are sufficient gaps in the position determination directions and the vertical direction; therefore, the expansion can be absorbed, thereby avoiding deformation of the reflecting surfaces of the image forming mirrors6to9.

The image forming mirrors are disposed such that the intersection point of a line defined by the bosses26and27and a line defined by the projecting parts28and29corresponds with the position, on the surface of the mirror, where rays along the reference axis are reflected. If the mirror is disposed at this position, even if the mirror expands more compared to the mirror supporting part due to a rise in temperature, the position where the rays along the reference axis are reflected does not move, and thus it is possible to reduce the deterioration of the image forming accuracy.

The bosses and projecting parts provided on the image forming mirrors are not limited to the construction shown in the present embodiment; for example, it is possible to use only bosses or only projecting parts.

In addition to the method using the pressure force of a blade spring, the method of fixing an image forming mirror can be implemented, for example, by bonding or screwing, which allows fixing of the mirror with high accuracy. However, a method like that described in the present embodiment is desirable in order to absorb the expansion of the image forming mirrors due to a rise in temperature.

As described above, according to the invention, image forming mirrors formed with an off-axis reflecting surface can be positioned with high accuracy; also, the image forming mirrors can be supported while absorbing the thermal expansion when the temperature in the carriage rises, and thus it is possible to read the images of documents with high resolution and at high speed even with a carriage-integrated scanning system.