JPH06273694A - Image reader - Google Patents

Abstract

PURPOSE:To provide the image reader capable of image reading of high precision by reducing the change of the spectral characteristic due to the angle of incidence to equalize the color reproducibility between the center part and the peripheral part of the image. CONSTITUTION:In the image reader where a document 2 placed on a platen is illuminated by an illuminating means 1 and the image of the document is formed on the surface of an image carrier means 8 by an image forming optical system 6 to record or read the document, colored optical materials having a light absorption characteristic are used as materials of at least a part of lenses constituting the image forming optical system 6, and a multilayered film interference filter having a wavelength selectivity is applied to at least one face of the lens using the colored optical materials.

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 in particular, a colored optical material having a light absorbing property is used as a material of a part of lenses forming an imaging optical system, and at least one of the colored optical materials is used. By applying a multilayer interference filter with wavelength selectivity to the surface (lens surface),
The change of the spectral transmittance due to the difference of the incident angle to the image forming optical system is reduced, the desired spectral characteristics are obtained, and the image information on the original surface is read with high accuracy. For example, a copying machine or a facsimile. Image reading apparatus suitable for the above apparatus.

[0002]

2. Description of the Related Art Conventionally, in an image reading apparatus such as a copying machine, an original (image) surface is illuminated by an illuminating means, and a light flux reflected from the original surface is imaged by an imaging optical system (imaging lens). An image is formed on the surface of an image carrier such as a line sensor) and then the image reading line (original surface) is moved in the sub-scanning direction to record or read image information on the original surface.

FIG. 11 is a schematic view of a main part of an optical system of a conventional image reading apparatus.

In FIG. 1, a document (image) 12 placed on a document table glass 13 is illuminated by a light source 11 to
The reflected light flux from 2 is limited by the slit member 14 and the optical path is bent through the folding mirrors 15a, 15b and 15c for scanning, and the imaging optical system 16 including a zoom lens passes the optical path bending mirrors 17a, 17b and 17c. An image is formed on the surface of the photoconductor (photoconductor drum) 18 at a predetermined magnification.

An electrostatic latent image is formed on the surface of the photosensitive drum 18 according to the lightness and darkness of the image, and image information (copy image) of the original is obtained by a known electrophotographic process.

In such an image reading apparatus, a halogen lamp, a fluorescent lamp or the like is generally used as a light source used as an illumination means, and an organic semiconductor (OPC) or amorphous silicon (A-Si) is used as a photoconductor. ) Etc. are often used.

Since the light source and the photoconductor have wavelength dependence such as specific spectral energy and spectral sensitivity, a specific color may not be accurately reproduced when the image information of the original is read.

For example, when a photosensitive drum having sensitivity to the red wavelength is used, if a red color (for example, a vermilion color of a seal stamp) is used for the original, the red color reproducibility is deteriorated, or the blue wavelength is changed. In the case of using a photosensitive drum having a sensitivity, if a blue color (for example, blue of section paper) is used for the original, the blue color reproducibility may be deteriorated.

Therefore, in the conventional image reading apparatus, a multilayer film interference filter having wavelength selectivity is arranged at an arbitrary position in the optical path from the surface of the original to the surface of the photosensitive drum, and for example, the color of the original to be reproduced can be selected. The above problem is solved by transmitting only the light flux of a specific wavelength band corresponding thereto by the multilayer interference filter to adjust the color.

[0010]

However, in the conventional image reading apparatus, since the multilayer interference filter is arranged in an arbitrary optical path between the original surface and the photosensitive drum surface as described above, the following will occur. There was a problem to show.

Generally, a multilayer interference filter has a problem that its spectral transmittance changes depending on the incident angle of a light beam (light ray).

For example, as shown in FIG. 12, the spectral transmittance of a light beam passing through the multilayer interference filter at an incident angle of 0 ° (solid line a) and the spectral transmittance of a light beam passing through the multilayer interference filter at an incident angle of 20 °. The spectral characteristics differ from the rate (dotted line b), especially on the long wavelength side. In the figure, the horizontal axis represents wavelength (λ) and the vertical axis represents transmittance.

As is clear from the figure, as the incident angle of the light beam increases, its spectral transmittance shifts to the shorter wavelength side.

That is, since the spectral transmittance of the multilayer interference filter changes according to the angle of view of the light beam incident on the imaging optical system, the central portion (corresponding to the vicinity of the axis) and the peripheral portion (corresponding to the vicinity of the axis) of the copied image are changed. There is a problem that the spectral reproducibility is different between the light fluxes corresponding to the maximum angle of view) and the color reproducibility changes.

Further, a supporting member for supporting the multilayer interference filter is also required, and there is a problem that the whole apparatus becomes complicated and the cost becomes high.

According to the present invention, a colored optical material having a light absorbing property is used as a material of at least a part of lenses forming the imaging optical system, and at least one surface (lens surface) of the lens using the colored optical material. By applying a multi-layer interference filter with wavelength selectivity to the film, changes in spectral transmittance due to incident angle dependence are reduced, and changes in color reproducibility between the central part and peripheral parts of the image are effectively prevented. It is an object of the present invention to provide an image reading device as described above.

[0017]

An image reading apparatus of the present invention illuminates an original placed on an original surface with an illumination unit,
In an image reading apparatus for recording or reading the original by forming an image of the original on the surface of an image carrier by an imaging optical system, at least a part of lenses constituting the imaging optical system has a light absorption characteristic. The present invention is characterized in that a colored optical material is used, and a multilayer interference filter having wavelength selectivity is applied to at least one surface of a lens using the colored optical material.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of a main part of the first embodiment when the present invention is applied to a copying machine, FIG. 2 is a sectional view of a lens of the image forming optical system shown in FIG. 1, and FIG. 3 is shown in FIG. 3 is a lens cross-sectional view of a convex lens 6b made of a colored optical material described later.

In FIG. 1, reference numeral 1 denotes an illuminating means, which comprises, for example, a halogen lamp or a fluorescent lamp. A document (image) 2 is placed on the document table glass 3. Reference numeral 4 denotes a slit member, which is arranged near the original platen glass 3 and limits the light flux reflected from the original 2 to expose the surface of the photosensitive drum 8 in a slit shape. 5 is a reflection means for scanning,
It is composed of three reflection mirrors, that is, first, second, and third reflection mirrors 5a, 5b, and 5c, and reflects the light flux that has passed through the slit member 4 and bends the optical path to form an image-forming optical system (connection). It is incident on the image lens) 6.

The image forming optical system 6 transmits a light beam based on image information from the original 2 onto a surface of a photosensitive drum 8 as an image carrying means via bending mirrors 7a, 7b and 7c constituting an optical path bending means 7. Imaged at magnification.

The image forming optical system 6 according to the present embodiment is composed of a so-called symmetrical lens in which lenses having a similar shape to each other with a diaphragm 6e interposed therebetween are arranged substantially symmetrically. That is, the imaging optical system 6 is concave (negative) in order from the document surface side as shown in FIG.
Lens 6a, convex (positive) lens 6b, concave (negative) lens 6
c, and a convex (positive) lens 6d is composed of 8 elements in 8 groups arranged symmetrically with the diaphragm 6e in between, and moves to the position of the dotted line as shown by the arrow in FIG. ing.

Here, the material of the convex lens 6b forming a part of the imaging optical system 6 is a colored optical material having the spectral transmittance shown in FIG. 4, and the original of the convex lens 6b using the colored optical material. A multilayer interference filter having a spectral transmittance shown in FIG. 5 is applied to the lens surface R3 on the second surface side.
The convex lens 6b has a meniscus shape as shown in FIG.

In this embodiment, the image (copy image) on the surface of the original document 2 illuminated by the luminous flux emitted from the illumination means 1 is slit member 4, and the first, second, and third reflection mirrors 5a for scanning, An image is formed on the surface of the photosensitive drum 8 at a predetermined magnification by the image forming optical system 6 via the folding mirrors 7a, 7b and 7c via 5b and 5c.

Further, in this embodiment, at the same magnification, the photosensitive drum 8 rotates in the direction of the arrow A in the drawing at the peripheral speed V, and the light source 1 and the first reflecting mirror 5a are united at the speed V and the second speed. , The third reflecting mirrors 5b and 5c are integrated into one, and the speed V
By scanning the original 2 in the direction of the arrow B with / 2, the original 2 is imaged in a slit shape at the same magnification while keeping the optical path length from the surface of the original 2 to the surface of the photosensitive drum 8 constant. .

On the other hand, at the time of zooming, the image forming optical system 6 moves to the position indicated by the dotted line in the figure according to the magnification (β), and the light source 1 and the first reflecting mirror 5a are united to form the velocity V / β.
In addition, the second and third reflection mirrors 5b and 5c are united to scan the document 2 at a speed V / 2β, so that an image (projection image) of a predetermined magnification is formed on the surface of the photosensitive drum 8. is doing.

An electrostatic latent image is formed on the surface of the photosensitive drum 8 according to the shade of the original 2, and a copy image is obtained by a known electrophotographic process.

Next, the optical function of the convex lens 6b using the colored optical material of the imaging optical system 6 according to the present invention will be described.

In this embodiment, the axial light flux (corresponding to the central portion of the image) is incident on the image forming optical system 6 and then a specific wavelength is obtained by the multilayer interference filter provided on the lens surface R3 of the convex lens 6b on the second side of the original. Only the light flux of a specific wavelength band is transmitted by the absorption effect of the colored optical material.
The light beam is absorbed by an amount corresponding to the thickness of the light beam passing through and is emitted from the imaging optical system 6 so that only the light beam in the wavelength band corresponding to the spectral sensitivity of the photoconductor is imaged on the surface of the photoconductor drum 8. ing.

In the case of this embodiment, the photosensitive drum 8 has amorphous silicon (A-Si) having a sensitivity on the long wavelength side.
In order to improve the color reproducibility of red when using, the filtering is performed to block the light flux on the long wavelength side.

On the other hand, the off-axis light flux (corresponding to the peripheral portion of the image) enters the image forming optical system 6 and then undergoes the following optical action.

That is, the convex lens 6b using a colored optical material
3 has a meniscus shape as shown in FIG. 3, the lens thickness in the peripheral portion of the convex lens 6b is smaller than the lens thickness in the central portion, and the absorption characteristics (absorption amount) in the central portion and the peripheral portion are smaller than this. Different from each other.

That is, as shown in FIG. 3, since the light flux D passing through the peripheral portion of the convex lens 6b has a shorter optical path length than the light flux C passing through the central portion, the light absorption by the convex lens 6b is small, The spectral transmittances of the on-axis light beam C and the off-axis light beam D are as shown in FIG.

In the same figure, the solid line a shows the spectral transmittance of the light beam C passing through the central portion of the convex lens 6b, and the dotted line b shows the spectral transmittance of the light beam D passing through the peripheral portion. The spectral transmittance shifts to the longer wavelength side as it goes to the periphery.

On the other hand, the spectral characteristic of the multilayer interference filter provided on the lens surface R3 of the convex lens 6b shifts its spectral transmittance to the shorter wavelength side as the incident angle of the light beam increases as shown in FIG. .

Therefore, the light flux (off-axis light flux) D at the position corresponding to the peripheral portion of the image due to the mutual optical action described above.
Is blocked (cut) more than the luminous flux (axial luminous flux) C at the position corresponding to the central portion of the image on the long wavelength side by the multilayer interference filter, but due to the absorbing action of the colored optical material, the central portion of the image is The amount of absorption is smaller than that of the luminous flux C.

As a result, the on-axis light flux and the off-axis light flux emitted from the imaging optical system 6 have substantially the same spectral transmittance irrespective of the incident angle.

That is, substantially the same spectral characteristics are obtained in the central portion and the peripheral portion of the image (original), and thus the change in the color reproducibility caused by the difference in the spectral characteristics, which has been a problem in the past, is effectively prevented. is doing.

As described above, in the present embodiment, the combination of the multilayer interference filter and the colored optical material as described above blocks the light beam on the long wavelength side to improve the color reproducibility of red (red original). The color reproducibility of red in the central portion of the image and the peripheral portion of the image is made uniform to obtain a high quality image.

Further, in this embodiment, the multilayer interference filter is applied to a part of the lenses constituting the image forming optical system, so that a supporting member for supporting the multilayer interference filter as compared with the conventional image reading apparatus. Can be simplified, thereby reducing the size and cost of the entire device.

In this embodiment, the colored optical material is used as the material of the part of the convex lens 6b constituting the imaging optical system 6, but the colored optical material may be used for the other lenses, and a multilayer structure is also used. The film interference filter may be provided not only on one lens surface but also on a plurality of lens surfaces, whereby the color reproducibility can be further made uniform.

FIG. 7 is a lens sectional view of the image forming optical system of the second embodiment when the present invention is applied to a copying machine.

In this embodiment, for example, the color reproducibility of a blue original such as section paper is improved and the blue color reproducibility is made uniform in the central portion and the peripheral portion of the original (image).

Generally, in order to improve the color reproducibility of a blue original, it is necessary to block the light beam on the short wavelength side.

Therefore, in this embodiment, the image forming optical system 76 is provided with a convex (positive) lens 76a and a concave (negative) lens 7 in order from the document surface side.
6b and 4b are symmetrically arranged with a diaphragm 76c sandwiched therebetween, and are composed of so-called cellar type four-group four-element symmetrical lenses.
A multilayer film having a spectral transmittance shown in FIG. 9 is used for the concave lens 76b and a lens surface R4 on the image side of the concave lens 76b using the colored optical material has a spectral transmittance shown in FIG. An interference filter is applied to block the light flux on the short wavelength side.

In FIG. 9, the solid line a indicates that the incident angle is 0 °.
The spectral transmittance of the light flux passing through the concave lens 76b at the dotted line b
Indicates the spectral transmittance of the light flux passing through the concave lens 76b at an incident angle of 20 °.

Since the peripheral lens thickness of the concave lens 76b made of the colored optical material in this embodiment is thicker than the central lens thickness, the light flux passing through the peripheral portion (off-axis light flux) passes through the central portion. It is absorbed more than (axial light flux).

On the other hand, in the multilayer interference filter provided on the image plane side of the concave lens 76b, its spectral transmittance shifts to the short wavelength side as the incident angle increases, as shown in FIG.

From this fact, the optical effects of the colored optical material and the multilayer interference filter mutually cause the luminous flux passing through the central portion of the imaging optical system 76 (axial luminous flux) and the luminous flux passing through the peripheral portion (off-axial luminous flux). ) And the spectral characteristics are substantially uniform, which makes it possible to uniformize the blue color reproducibility in the central portion of the image and the peripheral portion of the image.

FIG. 10 shows a CCD according to the present invention as a light receiving means.
9 is a lens cross-sectional view of the image forming optical system according to the third embodiment when a document (image) is read using a solid-state image sensor such as the above, and when applied to, for example, a facsimile apparatus, an image reader, or the like.

In the present embodiment, as in the first embodiment, the combination of the multilayer interference filter and the colored optical material blocks the light beam on the long wavelength side to improve the color reproducibility of the original document having a red color, and to improve the image quality. High-quality images are obtained by reducing the change in red color reproducibility between the central part and the peripheral part of the.

That is, in this embodiment, as shown in FIG. 10, the image forming optical system 106 includes a convex (positive) lens 10 in order from the document surface side.
6a, a concave (negative) lens 106b, and a convex (positive) lens 106c, which is a so-called triplet type lens. Of these, the convex lens 106a is formed of a colored optical material having the spectral transmittance shown in FIG. 4, and the lens surface R1 on the original side of the convex lens 106a using the colored optical material is a multilayer having the spectral transmittance shown in FIG. It has a membrane interference filter.

As a result, similar to the optical operation of the above-described first embodiment, the light beam on the long wavelength side is shielded to improve the color reproducibility of red, and at the same time, the central portion of the image (corresponding to the axial luminous flux) and the peripheral portion of the image ( High-quality images are obtained by eliminating the change in red color reproducibility (corresponding to off-axis light flux).

[0053]

According to the present invention, as described above, a colored optical material having a light absorbing property is used for at least a part of the lenses constituting the imaging optical system, and at least one of the lenses using the colored optical material is used. By applying a multilayer interference filter having wavelength selectivity to the surface (lens surface), the desired spectral characteristics are obtained and the change in the spectral characteristics due to the dependence of the incident angle of the light beam (light ray) is reduced, and It is possible to achieve an image reading apparatus which can make color reproducibility uniform in the peripheral portion of an image and can read an image with extremely high accuracy.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of a first embodiment when the present invention is applied to a copying machine.

FIG. 2 is a lens cross-sectional view of the image forming optical system shown in FIG.

3 is an explanatory view of a convex lens 6b made of a colored optical material shown in FIG.

FIG. 4 is an explanatory diagram showing spectral characteristics of the colored optical material of Example 1 of the present invention.

FIG. 5 is an explanatory diagram showing spectral characteristics of the multilayer interference filter according to the first embodiment of the present invention.

FIG. 6 is an explanatory diagram showing the spectral characteristics of the colored optical material of Example 1 of the present invention.

FIG. 7 is a lens cross-sectional view of an image forming optical system according to a second embodiment of the present invention.

FIG. 8 is an explanatory diagram showing the spectral characteristics of the colored optical material of Example 2 of the present invention.

FIG. 9 is an explanatory diagram showing the spectral characteristics of the multilayer interference filter according to the second embodiment of the present invention.

FIG. 10 is a lens cross-sectional view of an image forming optical system according to a third embodiment of the present invention.

FIG. 11 is a schematic view of a main part of a conventional image reading device.

FIG. 12 is an explanatory diagram showing spectral characteristics of a multilayer interference filter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Illumination means 2 Original (image) 3 Original stage glass 4 Slit member 5 Reflecting means 6,76,106 Imaging optical system 7 Optical path bending means 8 Image carrying means (photosensitive drum)

Claims (2)

[Claims] 1. An image reading apparatus for recording or reading an original placed on the original surface by illuminating the original by an illuminating means and forming an image of the original on the surface of the image carrying means by an image forming optical system. A multilayer interference filter using a colored optical material having a light absorbing property as a material of at least a part of lenses forming an imaging optical system and having wavelength selectivity on at least one surface of a lens using the colored optical material. An image reading device characterized by being subjected to. 2. The color reproducibility in the central portion and the peripheral portion of the original is made uniform by the mutual optical action of the colored optical material and the multilayer interference filter. Image reading device.