JP2003344956A - Image reader - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reader constituted of an off-axial reflection mirror, and realizing higher performance and the moderation of figure tolerance. <P>SOLUTION: In the image reader having an image-formation optical device consisting of a plurality of off-axial reflection surfaces, at least one of the off-axial reflection surfaces is turnably attached to a lens barrel. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus, and more particularly, to a line sensor for image scanners, digital copying machines, facsimiles, etc., which uses a small image-forming optical element having various resolutions in a well-balanced manner and having high resolution. It is suitable for reading a monochrome image or a color image used.

[0002]

2. Description of the Related Art Conventionally, as an image reading device (image scanner) for reading image information on a document surface, a flat bed type image scanner is disclosed in, for example, Japanese Unexamined Patent Publication No. Hei 3 (1999) -3.
It is proposed in Japanese Laid-Open Patent Application No. -113961. The flatbed type image scanner fixes the image forming lens and the line sensor, and moves only the reflecting mirror to perform slit exposure scanning of the document surface to read image information. In recent years, in order to simplify the structure of the apparatus, a carriage-integrated scanning method in which a mirror, an imaging lens, a line sensor, and the like are integrated to scan the document surface has been increasingly adopted.

FIG. 5 is a schematic view of the main part of a conventional image reading apparatus of the carriage-integrated scanning type. In the figure,
The light flux emitted from the illumination light source 1 directly illuminates the original document 8 placed on the original document table 2, and the reflected light flux from the original document 8 is sequentially passed through the first, second and third reflection mirrors 3a, 3b and 3c. The optical path is bent inside the carriage 6, and an image is formed on the surface of the line sensor 5 by the imaging lens (imaging optical system) 4. Then, the carriage 6 is moved in the direction of arrow A (sub-scanning direction) shown in FIG. 5 by the sub-scanning motor 7 to read the image information of the document 8. The line sensor 5 in the figure has a configuration in which a plurality of light receiving elements are arranged in a one-dimensional direction (main scanning direction).

FIG. 6 is an explanatory view of the basic configuration of the image reading optical system of FIG. In the figure, 4 is an imaging optical system, 5R, 5G,
5B is a line sensor for reading each color of R (red), G (green), and B (blue) of the line sensor 5, 8
R, 8G and 8B are reading ranges on the document surface corresponding to the line sensors 5R, 5G and 5B. In the image reading apparatus shown in FIG. 5, the carriage 6 scans the stationary document surface, but in scanning the carriage, the line sensor 5 and the imaging lens 4 are stationary and the document surface 8 moves as shown in FIG. Is equivalent to doing. By scanning the document surface, the same portion can be read in different colors at certain time intervals. In the above configuration, when the imaging lens 4 is composed of a normal refracting system, axial chromatic aberration and lateral chromatic aberration occur, so that the line image formed on the line sensors 5B and 5R is defocused or defocused with respect to the reference line sensor 5G. A position shift occurs. Therefore, when the images of the respective colors are superimposed and reproduced, the image becomes conspicuous with color fringing and deviation. That is, when high aperture and high resolution performance is required, the demand cannot be met.

On the other hand, recently, it has become clear that even in a non-coaxial optical system, an optical system with sufficiently corrected aberrations can be constructed by introducing the concept of a reference axis and making the constituent surfaces asymmetrical aspherical surfaces. Came. For example, Japanese Patent Application Laid-Open No. 9-5650 discloses its design method, Japanese Patent Application Laid-Open No. 8-292371,
Japanese Patent Application Laid-Open No. 8-292372 discloses an example of the design.

Such a non-coaxial optical system is an off-axial optical system (when the reference axis along the ray passing through the image center and the pupil center is considered, the surface normal at the intersection with the reference axis of the constituent surface is on the reference axis. An optical system defined as an optical system including a curved surface (off-axial curved surface), in which case the reference axis has a bent shape). In this off-axial optical system, the constituent surfaces are generally non-coaxial, and vignetting does not occur even on the reflecting surface, so it is easy to construct an optical system using the reflecting surface. In addition, it is characterized in that the optical path can be laid out relatively freely, and it is easy to form an integrated optical system by a method of integrally molding the constituent surfaces.

[0007]

On the other hand, since the image reading system of a digital copying machine or the like is required to have high resolution and high speed, it has not been constituted by an integrated optical system. Since the imaging lens required for the reading system needs to be bright and has high resolution, it is difficult to increase the angle of view in order to secure the optical performance. A narrow angle of view results in a long optical path length. On the other hand, when a color image is read, the optical performance is adversely affected by the difference in the image forming position for each color due to the chromatic aberration and the chromatic aberration such as the color shift in the screen as the resolution increases.

On the other hand, it is required to make the brightness (Fno and transmittance) of the image forming optical system brighter in accordance with the speeding up of image reading, and in particular, the reflectance of the mirror is a coated refraction system. Since the transmittance is worse than that of the lens, it is not possible to efficiently guide the light from the illuminated original to the line sensor when a large number of mirrors are used to fold a long optical path length.

On the other hand, in the case where an integrated optical system is constructed by integrally molding the off-axial constituent surface with glass or plastic, in order to prevent the performance deterioration due to the manufacturing error of each off-axial constituent surface, the accuracy of the surfaces and the surface-to-surface relationship are prevented. The tolerance of the interval must be made very strict, which causes an increase in manufacturing price.

In view of the above problems, the present invention provides an image reading and imaging optical system in which asymmetric aberrations are less likely to occur even when the imaging optical system is constructed with an off-axial reflecting surface, and the optical performance is not significantly deteriorated. It is an object of the present invention to provide an image reading apparatus using the image reading apparatus, such as a digital copying machine or an image scanner, which requires high speed and high resolution.

[0011]

According to another aspect of the present invention, there is provided an image reading apparatus, wherein image information on a document surface is formed on a line sensor by an image forming optical element including a plurality of off-axial reflecting surfaces, and the line sensor is formed. In the image reading apparatus for reading by (1), at least one off-axial reflection surface is rotatably attached to the lens barrel.

According to a second aspect of the present invention, in the first aspect of the present invention, the rotational direction of the rotatable off-axial reflecting surface is defined by the Z-axis and the surface normal at the point where the reference axis ray is incident on the surface. X in the direction parallel to the main scanning direction on the plane perpendicular to
It is characterized in that at least one of the six directions of parallel movement in the X, Y, and Z-axis directions and rotation movement around the X, Y, and Z-axes as the center of rotation is defined as the Y-axis that is perpendicular to the axes. .

The invention of claim 3 is characterized in that, in the invention of claim 1, the rotatable off-axial reflecting surface is in the vicinity of a diaphragm.

According to a fourth aspect of the present invention, in the first aspect, the line sensor is rotatably attached.

According to a fifth aspect of the invention, in the first aspect of the invention, the rotatable off-axial reflecting surface is adjusted by rotating with reference to the output from the line sensor.

The invention of claim 6 is characterized in that, in the invention of claim 5, the rotatable off-axial reflecting surface is fixed at the end of the adjustment by the rotation.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIGS. 1 and 2 show a first embodiment of the present invention. FIG. 1 is a schematic sectional view of the image reading apparatus of this embodiment. In the figure, 1 is a light source, 2 is a platen glass, 3a, 3b and 3c are first, second and third reflecting mirrors, 4a is an image forming optical element, and 5 is a CCD.
And the like, a line sensor, and 6 is a carriage (housing).

The original 8 placed on the original table glass 2 is imaged through the reflecting mirrors 3a, 3b and 3c to form an image forming optical element 4a.
Thus, one line of the original 8 can be read by forming an image on the line sensor 5. In order to make the document reading device compact, the first and second reflection mirrors 3a, 3b,
The optical path is folded by 3c. The imaging optical element 4a also contributes to folding the optical path. By using the imaging optical element 4a, the image reading device of the carriage-integrated optical system can be configured with a small number of parts including the three plane folding mirrors and the imaging optical element, which enables miniaturization. As a result, high-speed reading is possible.

The carriage-integrated optical system scans the document 8 and the carriage 6 relatively in a direction perpendicular to the line direction (X direction) of the line sensor, that is, in the sub-scanning direction (Y direction, A direction). The surface 8 is read two-dimensionally.

FIG. 2 shows a perspective view of the imaging optical element 4a and the line sensor 5 of this embodiment. In FIG. 2, 4a and 5
Are shown upside down, but this does not affect the gist of the present invention. Here, the image information is input to the imaging optical element 4a, the output from the line sensor 5 is read, and the off-axial reflection surface Sa is SX, SY, SZ so as to obtain a predetermined performance.
Adjust in the RX, RY, and RZ directions. The off-axial reflecting surface Sa used for adjustment is preferably a surface near the diaphragm. This is because the surface near the diaphragm is relatively more sensitive to changes in MTF performance, and adjustment can be performed with a small amount of movement. This is because it does not have a bad influence on other distortions. At this time, the off-axial reflection surface Sa is adjusted with respect to another off-axial reflection as an imaging optical element unit on the adjustment tool and fixed by using a photo-curing resin, a screw lock agent, an epoxy resin or the like, and then the carriage. 6 may be attached as an imaging optical element unit. Alternatively, a method may be used in which the off-axial reflection surface S is adjusted and fixed in a state where the off-axis reflection surface S is attached to the carriage 6, that is, a state in which the folding mirror is included.

(Second Embodiment) FIGS. 3 and 4 show a second embodiment of the present invention. FIG. 3 is a schematic sectional view of the image reading device of the second embodiment. The symbols and their roles in the figure are the same as those in FIG. 1, and therefore their explanation is omitted. Figure 1
The difference is that there are two folding mirrors 3 and five off-axial reflecting surfaces of the imaging optical element 4.

FIG. 4 shows an image forming optical element 4b according to the second embodiment.
And a perspective view of the line sensor 5. In this embodiment, two off-axial reflection surfaces (Sb1, Sb) used for adjustment are used.
2). This facilitates the adjustment by separately setting the surface for correcting the deviation between the MTF in the main scanning direction and the MTF in the sub scanning direction and the surface for correcting the distortion. Further, the line sensor 5 is also rotatably attached and used for adjustment. In this way, by using the line sensor for adjustment, it becomes possible to correct the focus position shift in the main scanning direction, that is, the one-sided blur.

In order to clarify the meaning of the constitution of the embodiment of the imaging optical element of the present invention, the off-axial optical system used in the present specification and the reference axis which is the framework thereof are defined as follows. To do. Definition of Reference Axis In general, the optical path of a light beam having a reference wavelength from an object to an image plane is defined as a reference axis in the optical system. Since this alone leaves some ambiguity in how to select the reference light beam, the reference light beam, that is, the reference axis is usually set according to one of the following two principles.

When the optical system has an axis having symmetry even partially, and aberrations can be put together with good symmetry, a ray passing through the axis having the symmetry is used as a reference ray. When the optical system generally does not have a symmetry axis, or when the symmetry axis is partially present and aberrations can be summarized with good symmetry, the center of the object plane (the center of the imaged or observed range) Among the light rays emitted from the optical system, a light ray passing through the optical system in the order of the designated surface of the optical system and passing through the stop center defined in the optical system is set as a reference light ray. The reference axis defined in this way generally has a bent shape.

Definition of Off-axial Optical System A curved surface whose surface normal does not coincide with the reference axis at the point where the reference axis defined as described above intersects the curved surface is defined as an off-axial curved surface, and an optical system including the off-axial curved surface is defined. It is defined as an off-axial optical system. (However, even if the reference axis is simply bent by the flat reflecting surface, the surface normal does not match the reference axis, but since the flat reflecting surface does not impair the symmetry of aberrations, it is excluded from the targets of off-axial optical systems. In the embodiment of the present invention, the reference axis that serves as the reference of the optical system is set as described above. However, how to determine the axis that serves as the reference of the optical system is based on the optical design, the collection of aberrations, or the optical system. It is only necessary to adopt an axis convenient for expressing each surface shape that constitutes

However, in general, the optical system is designed so that the path of a light ray passing through either the center of the image plane or the observation plane and the center of the stop or the entrance pupil or the exit pupil or the first surface or the final surface of the optical system. It is set as the reference axis that serves as the reference. The order of each surface is set to the order in which the reference axis ray is reflected.

Therefore, the reference axis finally reaches the center of the image plane while changing its direction according to the law of reflection along the set order of the respective surfaces.

[0028]

According to the present invention, in reading a digital color image, there is no chromatic aberration, and a compact carriage-integrated scanning system can be easily realized, and an original reading image forming optical system and an image reading using the same. It is possible to achieve an apparatus, in particular, an image reading apparatus such as a digital copying machine or an image scanner which requires high speed and high resolution.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an image reading apparatus according to a second embodiment of the present invention.

FIG. 2 is a perspective view of an image forming optical element and a line sensor according to a second embodiment of the present invention.

FIG. 3 is a schematic sectional view of an image reading apparatus according to a second embodiment of the present invention.

FIG. 4 is a perspective view of an image forming optical element and a line sensor according to a second embodiment of the present invention.

FIG. 5 is a view showing an arrangement example of a conventional scanning optical system integrated with a carriage.

FIG. 6 is a schematic view of main parts for explaining a conventional color image reading device.

[Explanation of symbols]

1 Illumination light source 2 Platen glass 3a, 3b, 3c Reflective mirror 4 Imaging optical system 4a, 4b Imaging optical element 5 Reading means (line sensor) 6 carriage 7 Sub-scanning motor 8 manuscript

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/19 F term (reference) 2H108 AA02 CB01 HA01 HA05 2H109 AA02 AA58 AA69 5C051 AA01 BA03 DB24 DC04 DE24 5C072 AA01 BA01 BA19 DA04 DA21 DA23 EA05 FB06 MA10

Claims (6)

[Claims] 1. An image reading apparatus for forming image information on a document surface on a line sensor by an imaging optical element comprising a plurality of off-axial reflecting surfaces, and reading the image on the line sensor, wherein at least one of the off-axial reflecting surfaces. Is an image reading device which is rotatably attached to a lens barrel. 2. The turning direction of the rotatable off-axial reflecting surface is parallel to the main scanning direction on a plane perpendicular to the Z axis and the surface normal at the point where the reference axis ray is incident on the surface. The direction is the X axis, and the direction perpendicular to the X axis is the Y axis. X, Y, Z
2. The image reading device according to claim 1, wherein the image reading device is at least one of six directions of parallel movement in the axial direction and rotational movement about the X, Y, and Z axes. 3. The image reading apparatus according to claim 1, wherein the rotatable off-axial reflecting surface is near a diaphragm. 4. The image reading device according to claim 1, wherein the line sensor is rotatably attached. 5. The image reading apparatus according to claim 1, wherein the rotatable off-axial reflecting surface is adjusted by rotating with reference to an output from the line sensor. 6. The image reading apparatus according to claim 5, wherein the rotatable off-axial reflection surface is fixed at the end of adjustment by rotation.