JPH0514602A - Picture reader - Google Patents

Abstract

PURPOSE:To realize the picture reader by compensating an astigmatism of an image forming system when a wide picture angle of a read picture is devised so as to attain picture read with high precision. CONSTITUTION:The image of picture information lighted by a lighting system 1a is formed on a picture read means 8 in which plural light receiving elements are arranged linearly via an image forming system 6 for the reading, and an optical member 11 is provided in an optical path between the image forming system 6 and the picture read means 8 so that the reflectance in the vertical direction is rotationally asymmetric with respect to the arrangement direction of the light emitting elements and the optical axis of the image forming system 6.

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, it accurately corrects astigmatism of an image forming system when an image is read by using a light receiving element (image pickup element) such as a CCD to obtain a highly accurate image. The present invention relates to an image reading device suitable for reading, such as a facsimile and a digital copying machine.

[0002]

2. Description of the Related Art Conventionally, image information of a document or a film on a document table illuminated by an illumination system is projected by an imaging system (photographing system) onto a predetermined surface, for example, an image pickup means surface such as a CCD, Various image reading apparatuses in which image information is digitally read by an image pickup means have been proposed, for example, in JP-A-63-26065 and JP-A-63-79470.

As the image pickup means, a one-dimensional CCD in which a plurality of light receiving elements are arranged one-dimensionally at a constant cycle can read an image with relatively high accuracy, and is therefore widely used.

FIG. 11 is a schematic view of a conventional image reading apparatus. In the figure, 1a is a light source, and 1b is a concave mirror, which efficiently collects the light from the light source 1a on the original 4 side. 3 is a platen glass for supporting a document, 6 is an image forming system (projection lens), and a line sensor such as a CCD arranged with the document 4 in a direction perpendicular to the paper surface (main scanning direction) via mirrors 7a, 7b and 7c. The image is read on the surface of the image reading means 8. Then, the platen glass 3 or the light source 1a, the concave mirror 1b, the mirrors 7a, 7
b, 7c, etc. are moved in the sub-scanning direction as indicated by arrow 7d,
The original 4 is read two-dimensionally.

[0005]

As a method for reducing the size of the image reading apparatus, there is a method of shortening the distance from the original 4 to the image forming system 6, and this method is used. The shooting angle of view increases.

Generally, when the photographing field angle increases in the image forming system, an image forming point (meridional image plane) in the meridional direction (arrangement direction of light receiving elements, main scanning direction) and a sagittal direction (arrangement direction of light receiving elements, sub-direction). So-called astigmatism in which the image forming point (sagittal image plane) in the scanning direction is displaced from each other increases.

12 and 13 are explanatory views schematically showing the astigmatism at this time. 12A and 12B are shown in FIG.
1 shows a part of the main scanning cross section and a part of the sub scanning cross section, and FIG. 13 shows the on-axis light flux and the off-axis light flux of the 12A cross section of FIG. Of these, the light beam 4A on the optical axis is symmetrical with respect to the optical axis. Therefore, the meridional image plane and the sagittal image plane of the light flux A coincide with each other and form an image at a point A on the surface of the image reading means 8.

However, since the off-axis light beam 4B has astigmatism, for example, when the meridional image plane is made to coincide with the point B on the image reading means 8, the sagittal image plane is in front of the point B (depending on the optical characteristics of the image forming system). Will form an image at a point B ′ that is behind the point B). As a result, there is a problem that the optical performance in the sagittal direction is deteriorated.

FIG. 14 shows the angle of view ω at each point on the optical axis at this time.
It is explanatory drawing which shows the imaging state of ₀ , (omega) ₁ , (omega) ₂ ,-(omega) ₁ ,-(omega) ₂ . In the figure, the horizontal axis represents the defocus amount, and the vertical axis represents the contrast indicating the degree of focus.

The solid line is the sagittal image plane, and the dotted line is the meridional image plane. As is clear from the figure, when the meridional image plane is aligned with the surface of the image reading means 8, an off-axis point B is obtained.
Then, there arises a problem that the image forming performance in the sagittal direction is deteriorated.

As described above, when the angle of view of the imaging system is widened and the size of the entire apparatus is reduced, a horizontal line of a part of the read image is blurred and the reading accuracy of the image information is deteriorated. There was a problem that came.

According to the present invention, an optical member, which is appropriately set to correct off-axis astigmatism when the angle of view of the image forming system is widened, is arranged in the optical path between the image forming system and the image reading means. It is an object of the present invention to provide an image reading apparatus which can perform good reading and can read the entire read image with high accuracy.

[0013]

In the image reading apparatus of the present invention, image information illuminated by an illumination system is formed on a surface of an image reading means in which a plurality of light receiving elements are arranged in a one-dimensional direction through an image forming system. When an image is read, the refractive power in the direction of arrangement of the light receiving elements and the direction perpendicular to the optical axis of the image forming system forms an image in the optical path between the image forming system and the image reading means. It is characterized in that an optical member which is rotationally asymmetric with respect to the optical axis of the system is provided.

In addition to the above, according to the present invention, the optical member comprises a lens member whose curvature in the vertical direction continuously changes as the distance from the optical axis increases, or the optical member has an arrangement direction of the light receiving elements. And the curvature in the direction perpendicular thereto are substantially constant on the optical axis, and are made up of lens members that differ from each other with increasing distance from the optical axis, or the optical member is relative to the optical axis of the imaging system. It is characterized by being made of a transparent member having a rotationally asymmetric refractive index distribution.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of the essential portions of a first embodiment of the present invention, and FIG.
1A and 1B are enlarged schematic views of a part of FIG. 1, in which FIG. 1A shows a main scanning cross section, and FIG. 1B shows a sub scanning cross section.

In this embodiment, an image is read by arranging an optical member having a structure described later in the optical path between the image forming system and the image reading means as compared with the conventional image reading apparatus shown in FIG. Is characterized by.

Next, each component of this embodiment will be described.

Reference numeral 4 is an original, on which an image is formed,
It is placed on the surface of the platen glass 3. 1a is a light source such as a fluorescent lamp or a halogen lamp. 1b is a concave mirror,
A light beam emitted from the light source 1a in a direction opposite to the original table glass 3 is condensed and guided to the original 4. An image forming system 6 guides the light flux from the original 4 onto the surface of an image reading means 8 in which a plurality of light receiving elements are arranged in a one-dimensional direction (main scanning direction) via mirrors 7a to 7c and an optical member 11. Then, the image of the original 4 is formed on the surface.

The optical member 11 has a refractive power with respect to the optical axis 6a in a direction (main scanning direction, meridional direction) of the light receiving elements and a direction (sub scanning direction, sagittal direction) perpendicular to the optical axis of the image forming system 6. The lens member and the transparent member are rotationally asymmetrical. Thereby, the astigmatism of the image forming system 6 is corrected.

In this embodiment, a light beam from one area of the original 4 on the surface of the original glass 3 illuminated by the light source 1a in the main scanning direction is condensed by the image forming system 6 via the mirrors 7a, 7b and 7c, Astigmatism is corrected through the optical member 11 to form an image of the original 4 on the surface of the image reading unit 8. Then, the platen glass 3 or the light source 1a, the concave mirror 1b, the mirrors 7a, 7
b, 7c, etc. are integrally moved in the sub-scanning direction of the arrow 7d to read the image on the surface of the original 4 in two dimensions.

Next, the structure of the optical member 11 of this embodiment will be described.

FIG. 3 is an explanatory view showing the optical action of the optical member 11. The optical member 11 shown in the figure is composed of a lens member in which the refractive power in the meridional direction (LM direction) is 0 and the refractive power in the sagittal direction (LS direction) is rotationally asymmetric with respect to the optical axis 6a.

That is, in the present embodiment, the refractive power is rotationally symmetric on the optical axis 6a, and the negative refractive power in the sagittal direction (LS direction) gradually increases toward the off-axis (LM direction). It is composed of a lens member that becomes weak and becomes zero in the periphery. Therefore, the light flux A on the optical axis that has passed through the optical member 11 forms an image at a point A on the surface of the image reading means 8.

On the other hand, the image forming point (meridional image plane) formed by the light beam in the meridional direction (LM direction) out of the light beam 4B passing through the optical member 11 has no refracting power in the meridional direction. Like the light flux of, the image can be formed at a point B on the surface of the image reading means 8.

At this time, the image forming point (sagittal image plane) formed by the light beam in the sagittal direction (LS direction) generally forms an image at a point B'before the point B due to the nature of the image forming system.

Therefore, in this embodiment, a negative refracting power is imparted to the optical member 11 only in the sagittal direction independently of the meridional direction, and the sagittal image plane is displaced from the point B'and a point on the image reading means 8 surface. The image is focused on B.

The method of giving the negative refractive power in the sagittal direction at this time is given according to the astigmatism curve of the image forming system. As a result, in the present embodiment, as shown in FIG. 4, the meridional image plane and the sagittal image plane are set at the total read field angles (ω ₀ , ω ₁ , ω ₂ ...
・) The optical system with a wide focus margin has been obtained.

In this embodiment, the optical member may be composed of a reflecting mirror whose refractive power in the sagittal direction is rotationally asymmetric with respect to the optical axis.

5A and 5B are main scanning cross sections (meridional cross sections) of the optical member 51 according to the second embodiment of the present invention.
FIG. 3 is a schematic diagram in a sub-scan section (sagittal section).

In this embodiment, the optical member 51 is composed of a toric lens having different curvatures in the meridional direction 51M and the sagittal direction 51S. Both curvatures of the toric lens 51 at this time correspond to astigmatism of the image forming system.

FIG. 6 shows each reading angle of view (ω ₀ , ω ₁ , ω _2, ... When the toric lens 51 in this embodiment is used.
The focus state in *) is shown using contrast.

When astigmatism on the optical axis becomes a problem in this embodiment, as shown in FIG. 7, the curvatures in the meridional direction (LM direction) and the sagittal direction (LS direction) are the same on the optical axis 6a. However, it is preferable to use a toric lens having a shape in which the curvature of only one side (sagittal direction) is changed as the distance from the optical axis increases.

FIG. 8 is a perspective view of the essential parts of Embodiment 3 of the optical member according to the present invention. The optical member 81 of this embodiment is composed of a flat plate-shaped transparent member having a refractive index distribution inside.
In the figure, an arc-shaped curve 81a indicates an isorefractive index line showing a refractive index distribution.

By using the optical member 81 of this embodiment instead of the optical member 11 of FIG. 1, the same effect as described above is obtained. In the optical member 81 of the present embodiment, the refractive index distribution in the sagittal direction (LS direction) gradually changes as it goes from the optical axis 6a in the meridional direction (LM direction), and then returns to the original value, and in the periphery, the same refractive index as the optical axis 6a. It is distributed.

FIG. 9 shows a method of manufacturing the optical member 81 of FIG. 8, and FIG. 10 is an explanatory view showing an optical path in each section of FIG. 9 (C).

In FIG. 9A, a mask 92 having slit openings 92a and 92b is formed on the front and back surfaces of the transparent member 91. Then, as shown in FIG. 9B, known ion exchange is performed on the transparent member 91 through the slit openings 92a and 92b to form a refractive index distribution inside the transparent member 91. Figure 9
(C) shows the refractive index distribution formed in the transparent member 91 at this time by the isoptric index line. In the figure, the cross section A has a uniform refractive index distribution as shown in FIG. 10 (A), so the light beam incident on this cross section passes through without being refracted. Since a refractive index distribution is formed in the front and back directions of the transparent member 91 in the B cross section of FIG. 9C, the light flux incident on this cross section is condensed as shown in FIG. 10B. Since the refractive index distribution is uniform in the C cross section of FIG. 9C as in the A cross section, the light flux incident on this cross section passes through as it is as shown in FIG. 10C.

As described above, in this embodiment, the same effect as described above is obtained by using the refractive index distribution type transparent member having different refractive index distributions in the meridional direction and the sagittal direction as the optical member.

In the present embodiment, the transparent member 91 may be formed of a curved surface having the same or different curvatures in the meridional direction and the sagittal direction on the light incident surface side and / or the light emitting surface side. good.

[0039]

According to the present invention, an optical member for which the correction of off-axis astigmatism when the angle of view of the imaging system for image reading is widened is appropriately set as described above is used as the imaging system. By arranging it in the optical path between the image reading unit and the image reading unit, it is possible to achieve an image reading apparatus which can satisfactorily perform highly accurate reading over the entire read image.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

FIG. 2 is an explanatory view of a part of FIG.

FIG. 3 is an enlarged explanatory view of a part of FIG.

FIG. 4 is an explanatory diagram showing an image formation state according to each angle of view of FIG.

FIG. 5 is an explanatory diagram of an optical member according to a second embodiment of the present invention.

FIG. 6 is an explanatory diagram showing an image formation state according to each angle of view of FIG. 5;

7 is an explanatory view of a modification of the optical member of FIG.

FIG. 8 is an explanatory diagram of an optical member according to a second embodiment of the present invention.

9 is an explanatory view of a method of manufacturing the optical member of FIG.

10 is an explanatory diagram of an optical path in each cross section of FIG.

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

FIG. 12 is an explanatory diagram of a part of FIG. 11.

FIG. 13 is an enlarged explanatory view of a part of FIG.

FIG. 14 is an explanatory diagram showing an image formation state at each angle of view in FIG.

[Explanation of symbols]

1a light source 1b concave mirror 3 Platen glass 4 manuscripts 6 Imaging system 7a, 7b, 7c Mirror 8 Image reading means 11,51,81 Optical member LM meridional image plane LS sagittal image plane

Claims (4)

[Claims] 1. When the image information illuminated by an illumination system is imaged and read through an imaging system on an image reading means surface in which a plurality of light receiving elements are arranged in a one-dimensional direction, the imaging system and the imaging system are read. In the optical path between the image reading means and the arrangement direction of the light receiving elements and the refractive power in the direction perpendicular to the optical axis of the imaging system, the refractive power is rotationally asymmetric with respect to the optical axis of the imaging system. An image reading apparatus provided with an optical member. 2. The image reading apparatus according to claim 1, wherein the optical member comprises a lens member whose curvature in the vertical direction continuously changes as the distance from the optical axis increases. 3. The optical member comprises a lens member having a curvature in an array direction of the light receiving elements and a curvature in a direction perpendicular to the curvature that are substantially constant on the optical axis and differ from each other as the distance from the optical axis increases. The image reading apparatus according to claim 1, which is characterized in that. 4. The image reading apparatus according to claim 1, wherein the optical member comprises a transparent member having a refractive index distribution that is rotationally asymmetric with respect to the optical axis of the image forming system.