JPH104488A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the image reader with high image quality where read distortion due to a floated original and image deterioration in a mirror processing error are not caused. SOLUTION: An original 2 placed on an original platen glass 1 is lighted by a lighting means in this reader, an image of a luminous flux from an original 2 is formed on a read means 8 by an image forming means 7 via a scanning mirror 6 having a plurality of planer mirrors and image information of the original 2 is read. In this case, a convex lens 5a longer than a read width of the original 2 in the main scanning direction is placed close to the original platen glass 1 and a main light of the image forming means 7 is emitted nearly perpendicularly to the original platen glass 1, and the convex lens 5a is formed integrally with a planer mirror closest optically to the original platen glass l among a plurality of the planer mirrors being components of the scanning mirror 6. Then the incident face of the integrated optical member 5 is set in parallel with the face of the original platen glass 1 and the angle of the reflecting face of the optical member 5 is set to 45 deg. with respect to the face of the original platen glass 1.

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 reading of image information of an original placed on an original platen glass (transparent flat glass) by a line sensor (CCD) or the like via an image forming means. The present invention relates to an image reading apparatus suitable for, for example, a copying machine or the like, in which an image is formed on a unit and the reading unit reads the image information with high accuracy.

[0002]

2. Description of the Related Art FIG. 7 is a schematic view of a main part of a conventional image reading apparatus such as a digital copying machine, and FIG. 8 is a schematic view of a main part of the optical system shown in FIG.

In FIG. 7, a reading area of a document 22 placed on a document table glass (transparent flat glass) 21 is provided with a light source 23 and a concave mirror 24 provided below the document table glass 21. The illumination light is illuminated in the form of a slit, and the light beam reflected from the document 22 is passed through a scanning mirror unit 26 having a plurality of plane mirrors (reflection mirrors) 26a, 26b, and 26c, and is formed by an imaging lens 27 as a solid-state image reading unit. An image is formed on the surface of the image sensor 28. Then, the original platen glass 21 or the light source 23, the concave mirror 24, the plane mirrors 26a, 26b, 26c and the like are moved in the sub-scanning direction as indicated by the arrows to read the original two-dimensionally.

In general, when an original is placed on an original platen glass in this type of image reading apparatus, a sponge plate having substantially the same size as the original platen glass is placed from above the original surface so that the original surface is not distorted. The pressure plate 29 is pressed down by a substantially flat pressure plate 29 composed of. In this way, the original surface is corrected to a substantially flat surface, using glass having some rigidity.

A plurality of plane mirrors (reflection mirrors) constituting a scanning mirror section used in this type of image reading apparatus.
The reflection surface is raised in reflectance by depositing aluminum or the like on the reflection surface by a float manufacturing method. Usually, the reflectance at a wavelength of 550 nm is 95% or more.

[0006] The reading means of this type of image reading apparatus includes, for example, 5000 pixels and a length of about 50 m.
m, a line sensor (CCD) 28 as a solid-state imaging device having a width of one pixel of 0.01 mm is used.
The size of the document to be read (image information) is, for example, A3 size, and its dimension in the short direction (main scanning direction) is 297 mm.
And a width of 49.5 on the line sensor 28 surface at a magnification of 1/6
mm. Assuming that the distance from the document 22 to the image forming surface is, for example, 400 mm, the focal length of the image forming lens 27 is about 48.98 mm. Also the imaging lens 27
If the optical axis 71 is arranged so as to be located at the center of the surface of the document 22, the object height becomes 148.5 mm on one side. In this case, the half angle of view of the imaging lens 27 is about 23.4 degrees.

[0007]

The conventional image reading apparatus constructed as described above has the following various problems.

(First Problem) H1 to H as shown in FIG.
If the original 22 on which a square of 5 has the same size is drawn, the original 22 is creased. In the document 22 or the like having a fold as shown in FIG. 10, even if the document 22 is pressed from above by, for example, a pressure plate, the fold portion (bent portion) 22a is inevitably formed as shown in FIG. Will emerge from That is, the bent portion 22a moves away from the imaging lens, and the magnification becomes smaller, and the imaging size (reading magnification) becomes smaller.

Here, for example, as shown in FIG. 12, when the end portion (bent portion) 22a of the A3 size document 22 rises by 2 mm from the platen glass 21, the reading magnification is reduced by about 0.6%. That is, a document 22 having a size of 148.5 mm
Approximately 0.9m
m. This is because the reading magnification locally changes, and in particular, a straight line near the end 22a is bent and read as shown in FIG.

In order to reduce the floating amount of the original, for example, when the pressure plate is strongly pressed, the supporting member supporting the original platen glass does not change much at an end position of the original platen glass. In this case, since the document is warped toward the image forming lens together with the platen glass, the central portion of the document is closer to the image forming lens than the end portion. Therefore, as shown in FIG. The reading magnification becomes large only at the center. That is, distortion occurs. In this case, the relationship between the dimensions of each side is H11 <H12 as shown in FIG.
<H13.

When only one end (lifting portion) B of the document 22 is raised above the platen glass 21 as shown in FIG. 8, as shown in FIG. Only the part B is read small. In this case, the relationship between the dimensions of each side is H6 <H7 <as shown in FIG.
H8.

(Second Problem) The reflecting surface (glass surface) of a plane mirror is processed by depositing a reflecting material such as aluminum by a procedure shown in FIGS. 16, 17, 18, and 19, for example. ing. However, before depositing the reflective material on the glass surface, for example, as shown in FIG. 16, fine dust and the like may inevitably remain on the surface, and may be deposited as shown in FIG. Then, as shown in FIG. 18, if dust or the like is not removed during cleaning later, a portion having no reflective surface, that is, a pinhole that transmits light is formed as shown in FIG. 19. If the diameter of the pinhole is large, the amount of light passing through this position increases, and conversely, the amount of reflected light decreases, causing a local decrease in the amount of light, resulting in image deterioration (loss).

According to the present invention, an elongated convex lens (elongated lens) longer than the reading width of the original in the main scanning direction is arranged between the original platen glass and the image forming means to provide a substantially telecentric reading optical system. By integrating the convex lens and a plane mirror that constitutes one element of the scanning mirror unit,
It is an object of the present invention to provide an image reading apparatus capable of preventing a magnification of a read image from being changed depending on a position of a document surface and eliminating image deterioration (image loss) due to a pinhole or the like on a reflection surface of the mirror.

[0014]

An image reading apparatus according to the present invention has the following features. (1) A document placed on a platen glass is illuminated by illumination means including a light source, and a light beam from the document has a plurality of plane mirrors. In an image reading apparatus that forms an image on a reading unit surface by an image forming unit via a scanning mirror unit and reads image information of the original, an elongated convex lens longer than a reading width of the original in a main scanning direction is provided on the original. It is arranged in close proximity to the platen glass between the platen glass and the image forming means, and the main lens of the image forming means is configured to be substantially perpendicular to the platen glass by the convex lens, The convex lens is optically integrated with a plane mirror closest to the platen glass among a plurality of plane mirrors constituting the scanning mirror unit, and the incident surface of the integrated optical member is set to the platen glass. The optical member being parallel to the surface and The angle of the reflecting surface is characterized by being configured so as to be 45 ° with respect to the platen glass surface.

(2) The original placed on the platen glass is illuminated by an illuminating unit including a light source, and a light beam from the original is read by an image forming unit via a scanning mirror unit having a plurality of plane mirrors. In an image reading apparatus for forming an image on the original and reading image information of the original, an elongated convex lens longer than a reading width of the original in a main scanning direction is provided between the original platen glass and the imaging means. The convex lens is arranged close to the base glass, and the chief ray of the imaging means is converged by the convex lens after passing through the platen glass. The convex lens is formed of a plurality of flat mirrors constituting the scanning mirror unit. Of these, optically integrated with a flat mirror closest to the platen glass, the incident surface of the integrated optical member is parallel to the platen glass surface, and the reflection surface of the optical member is Angle 4 degrees to the platen glass surface The angle is set to 5 °.

In particular, in the above (1) and (2), an antifouling cover is provided near the reflection surface of the optical member in which the convex lens and the flat mirror are integrated, and the convex lens and the flat mirror are integrated. The optical member is fixed to a holding member that holds the light source, and the reflection surface of the optical member is covered with the holding member.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of a main part of a first embodiment of the present invention, and FIG. 2 is a schematic view of a main part showing an extracted optical path of the optical system of FIG.

In FIGS. 1 and 2, reference numeral 1 denotes a platen glass, which is made of transparent flat glass. Reference numeral 2 denotes a document (image), which is placed on the document table glass 1. Reference numeral 3 denotes a light source, which is formed of, for example, a fluorescent lamp having a linear light-emitting surface extending in a direction perpendicular to the paper surface (main scanning direction). 4
Reference numeral a denotes a first concave mirror (concave reflecting mirror) which condenses a light beam emitted from the light source 3 in a direction opposite to the direction of the original 2, and
To improve the illumination efficiency on the two originals. Reference numeral 4b denotes a second concave mirror (concave reflecting mirror), which condenses the light beam emitted from the light source 3 and reflects it to the reading area side of the original 2 surface. The light source 3 and the first and second concave mirrors 4a and 4b each constitute one element of the illumination means.

Reference numeral 5 denotes a first plane mirror 6 which is optically closest to the platen glass 1 among a plurality of plane mirrors 6a, 6b, 6c constituting a scanning lens unit 6 and a convex lens 5a to be described later.
a is a prism lens (mirror with a long lens) as an optical member integrally formed with the prism lens 5.
Is PMMA (acrylic) whose material has a refractive index of 1.49
Made of resin.

As shown in FIG. 2, the convex lens 5a is disposed between the platen glass 1 and an image forming lens 7 which will be described later, in the vicinity of the platen glass 1, and has a reading width of the document 2 in the main scanning direction. A telecentric optical system (incident type telecentric optics) is provided on the image side where the main lens of the imaging lens 7 is substantially perpendicular to the platen glass 1 by the convex lens 5a. System).

The prism lens 5 in the present embodiment is
The incident surface 5a1 is parallel to one surface of the platen glass (two surfaces of the original), and the reflecting surface 5a of the prism lens 5
The angle of 2 with respect to one platen glass (two originals)
5 °, and the incident angle of the light beam incident on the reflection surface 5a2 is 45 °. Thus, in the present embodiment, even if a reflection film is not formed on the reflection surface 5a2 of the prism lens 5, the light flux reflected from the document 2 surface and totally downward directed substantially vertically is totally reflected by "Snell's law". , To the second plane mirror 6b. That is,
The first plane mirror 6a in the present embodiment functions as a total reflection mirror.

Reference numeral 6 denotes a scanning mirror unit, which has first, second, and third three plane mirrors 6a, 6b, and 6c for scanning. The light path is bent to guide the light to an imaging lens 7 described later. In the present embodiment, as described above, the first plane mirror 6a and the convex lens 5a are integrally formed.

Reference numeral 7 denotes an image forming lens (image forming optical system) as image forming means, which forms image by reducing image information of the document 2 on a surface of a solid-state image pickup device 8 as reading means to be described later.
The solid-state imaging device 8 has 5000 pixels and a length of about 50 pixels.
mm, a line sensor with a width of one pixel of 0.01 mm (C
CD), and the size of the original to be read is, for example, A
3 sizes and 29 mm in the short direction (main scanning direction)
7mm, width 4 on line sensor 8 at 1/6 magnification
It projects at 9.5 mm. Assuming that the distance from the two originals to the imaging plane is, for example, 400 mm, the focal length of the imaging lens 7 is about 48.98 mm.

In this embodiment, an original 2 placed on an original table glass 1 is illuminated in a slit shape by an illuminating means, and a light beam based on image information from the original 2 is reflected by a prism lens 5, a second and a third plane. The image is reduced and formed on the surface of the line sensor 8 by the imaging lens 7 via the mirrors 6b and 6c. Then, the platen glass 1 or the light source 3, the first and second concave mirrors 4a and 4b, the lens prism 5, and the second and third mirrors
The original 2 is read two-dimensionally by moving the flat mirrors 6b, 6c, etc. in the sub-scanning direction as indicated by arrows.

In the present embodiment, as described above, the image forming lens 7 is configured to be a substantially telecentric optical system on the image side by the convex lens 5a, and the convex lens 5a and the first plane mirror 6a are integrated. And the incident surface 5a1 of the integrated prism lens 5 is made parallel to one surface of the original platen glass (two originals), and the angle of the reflecting surface 5a2 of the prism lens 5 is set to one surface of the original platen glass. Is set to 45 ° with respect to.

As described above, in the present embodiment, each element is appropriately configured, and a light beam is incident substantially perpendicularly to the surface of the original 2, so that the original 2
Of the read image can be reduced, that is, the reading magnification of the read image can be prevented from changing depending on the position of the original 2 surface.
Can be formed without performing a reflective film treatment on the reflective surface 5a2, so that there is no pinhole, high image quality and light weight can be achieved. Further, the reflective surface 5a2 of the prism lens 4 has a reflective film formed on the reflective surface 5a2. Since no treatment is required, production can be facilitated.

In this embodiment, the convex lens 5a and the first plane mirror 6a are integrally formed, but they may be formed independently.

FIG. 3 is a schematic view of a main part of the optical system according to the second embodiment of the present invention, in which the optical path is extracted and shown. In FIG.
The same elements as those shown in FIG.

This embodiment is different from the first embodiment in that a convex lens 35a having a shorter focal length than the convex lens 5a of the first embodiment is used, and the principal ray of the imaging lens 7 is transmitted through the platen glass 1 by the convex lens 35a. That is, it is configured to converge to an arbitrary position (H portion) later. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus the same effects are obtained.

That is, in the figure, reference numeral 35a denotes a convex lens (long lens) which has a long shape longer than the reading width of the document 2 in the main scanning direction. Is converged to an arbitrary position (H portion) after passing through.

The convex lens 35a in the present embodiment is integrated with the first flat mirror constituting one element of the scanning mirror unit similarly to the first embodiment, and the integrated prism lens Is made parallel to the surface of the platen glass, and the angle of the reflection surface of the prism lens is set to 45 ° with respect to the surface of the platen glass. As a result, as in the first embodiment, all the light beams incident on the prism lens are totally reflected by the "Snell's law" without providing a reflecting film on the reflecting surface.

As described above, in the present embodiment, the respective elements are appropriately configured as described above, and a light beam is incident substantially perpendicularly to the surface of the original 2 to correct the apparent distortion due to the warpage of the original 2. In addition, since it is possible to form the reflection surface of the prism lens without performing the reflection film treatment as in the first embodiment, there is no pinhole, high image quality, and light weight can be achieved. Further, since it is not necessary to treat the reflecting surface of the prism lens with a reflecting film, the manufacturing can be facilitated.

FIG. 4 is a schematic view of a main part of a third embodiment of the present invention,
FIG. 5 is an enlarged explanatory view of the prism lens (mirror with a long lens) shown in FIG. 4 and 5, the same elements as those shown in FIG. 1 are denoted by the same reference numerals.

In this embodiment, the first and second embodiments are described.
The difference is that a dirt prevention cover is provided near the reflection surface (outside the reflection surface) of the prism lens in which the convex lens and the first plane mirror are integrated. Other configurations and optical functions are substantially the same as those of the first and second embodiments, and thus, similar effects are obtained.

That is, in FIGS. 4 and 5, reference numeral 51 denotes a dirt-preventing cover (dust-proof cover or back cover), which covers the reflecting surface 5a2 of the prism lens 5 so as to cover it.
It is fixed to the tip of a convex part 52 formed in a part other than the effective part of No. 2. In addition, as this fixing method, for example, an adhesive or a double-sided tape may be used.

Numeral 53 denotes a flange portion, which is provided horizontally below the upper surface of the prism lens 5, and through which the prism lens 5 is connected to a mirror base stay (not shown) as a holding member. It is fixed to. The stain prevention cover 51 of the present embodiment may be formed of, for example, PET resin.

As described above, in this embodiment, as described above, the dirt prevention cover 51 is attached to the reflecting surface 5a of the prism lens 5.
2, it is possible to prevent the reflection surface 5a2 from being stained beforehand, thereby ensuring stable optical performance.

FIG. 6 is a schematic view of a main part of a main part of a fourth embodiment of the present invention. In this figure, the same elements as those shown in FIGS. 1 and 5 are denoted by the same reference numerals.

The present embodiment differs from the first embodiment in that the prism lens 5 is fixed to a mirror base stay 61 as a holding member for holding the light source 3 and the like, and the reflecting surface 5a2 of the prism lens 5 is a mirror. That is, it is configured to be covered by the pedestal stay 61. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus, similar effects are obtained.

That is, in the figure, reference numeral 61 denotes a mirror base stay as a holding member, which fixes the light source (including the first concave mirror 4a) 3 and the prism lens 5.

The prism lens 5 is provided with a convex portion 52 at an end of the reflecting surface 5a2 other than the effective portion.
Is fixed to the mirror base stay 61 so that the reflection surface 5a2 is covered by the mirror base stay 61 through the base.
In addition, as this fixing method, for example, an adhesive or a double-sided tape may be used.

As described above, in the present embodiment, the prism lens 5 is fixed to the mirror base stay 61 as described above, and the reflecting surface 5a2 of the prism lens 5 is fixed so as to be covered by the mirror base stay 61. The contamination of the reflection surface 5a2 is prevented beforehand, and stable optical performance can be secured for a long period of time. In the present embodiment, the reflection surface 5
It is not necessary to separately provide a member for preventing the contamination of a2, thereby making it possible to reduce the size and cost of the entire apparatus.

[0043]

According to the present invention, as described above, a long convex lens longer than the reading width of a document in the main scanning direction is disposed between the document table glass and the image forming means, close to the document table glass. In addition, by integrating the convex lens and the plane mirror that constitutes one element of the scanning mirror unit, without causing reading distortion due to floating of the original and image deterioration due to an error in mirror processing, It is possible to achieve an image reading device that is lightweight and can obtain high-quality images.

In particular, according to the first embodiment, the principal ray of the image forming means is configured to be substantially perpendicular to the platen glass by the long convex lens, and the convex lens and the flat mirror are integrated. By using a plane mirror as a total reflection mirror, image distortion due to floating of the original can be reduced, and image defects due to pinholes on the reflection surface can be eliminated. Is also unnecessary, and manufacturing can be facilitated.

According to the second embodiment, the principal ray of the image forming means is converged after passing through the platen glass by means of the long convex lens, and the convex lens and the plane mirror are integrated into one. By acting as a total reflection mirror, the same effect as in the first embodiment can be obtained, and image distortion due to the floating of the document can be further reduced to the limit as compared with the first embodiment.

According to the third embodiment, by providing a dirt prevention cover near the reflection surface of the optical member in which the convex lens and the flat mirror are integrated, it is possible to prevent a decrease in the reflectance due to the dirt on the reflection surface. Can be.

According to the fourth embodiment, the optical member in which the convex lens and the flat mirror are integrated is fixed to the holding member for holding the light source, and the reflecting surface of the optical member is covered by the holding member. Thus, it is possible to prevent the reflection surface from being stained beforehand, to secure stable optical performance for a long period of time, and it is not necessary to separately provide a member for preventing the stain, thereby providing the entire device. Can be made more compact.

[Brief description of the drawings]

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

FIG. 2 is a schematic diagram of a main part of the optical system of FIG.

FIG. 3 is a schematic diagram of a main part, showing extracted optical paths of an optical system according to a second embodiment of the present invention;

FIG. 4 is a schematic diagram of a main part of a third embodiment of the present invention.

FIG. 5 is an enlarged explanatory view of a part of FIG. 4;

FIG. 6 is a schematic diagram of a main part of a main part of a fourth embodiment of the present invention

FIG. 7 is a schematic diagram of a main part of a conventional image reading apparatus.

FIG. 8 is a schematic diagram of a main part of an optical path of a conventional image reading apparatus extracted and shown.

FIG. 9 is an explanatory diagram showing an example in which an image is distorted when a document floats in a conventional example.

FIG. 10 is an explanatory view showing an example in which an image is distorted when a document floats in a conventional example.

FIG. 11 is an explanatory diagram showing an example in which an image is distorted when a document floats in a conventional example.

FIG. 12 is an explanatory diagram showing an example in which an image is distorted when a document floats in a conventional example.

FIG. 13 is an explanatory diagram showing an example in which an image is distorted when a document floats in a conventional example.

FIG. 14 is an explanatory diagram showing an example in which an image is distorted when a document floats in a conventional example.

FIG. 15 is an explanatory diagram showing an example in which an image is distorted when a document floats in a conventional example.

FIG. 16 is an explanatory diagram showing a process of forming a reflection surface of a plane mirror.

FIG. 17 is an explanatory diagram showing a process of forming a reflecting surface of a plane mirror.

FIG. 18 is an explanatory diagram showing a process of forming a reflection surface of a plane mirror.

FIG. 19 is an explanatory diagram showing a process of forming a reflection surface of a plane mirror.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Original platen glass 2 Original 3 Light source 5 Optical member (prism lens) 5a, 35a Convex lens (Long lens 6 Scanning mirror part 7 Image forming means (Image forming lens) 8 Reading means (Line sensor) 51 Dirt prevention cover 61 Mirror stand Stay

Claims (4)

[Claims] An original placed on a platen glass is illuminated by an illuminating unit including a light source, and a light beam from the original is passed through a scanning mirror unit having a plurality of plane mirrors and is focused on a reading unit surface by an image forming unit. An image reading device for reading image information of the document, wherein a long convex lens longer than a reading width of the document in the main scanning direction is provided between the platen glass and the image forming means. A plurality of plane mirrors arranged close to the glass so that the chief ray of the imaging means is substantially perpendicular to the platen glass by the convex lens; And an optical member which is optically closest to the platen glass and is integrated with the surface of the platen glass. Angle to the platen glass surface Image reading apparatus characterized by being configured to be 5 °. 2. A document placed on a platen glass is illuminated by an illuminating means including a light source, and a light beam from the document is illuminated on a reading means surface by an image forming means via a scanning mirror section having a plurality of plane mirrors. An image reading device for reading image information of the document, wherein a long convex lens longer than a reading width of the document in the main scanning direction is provided between the platen glass and the image forming means. The convex lens converges after passing through the platen glass by the convex lens, and the convex lens is formed of a plurality of plane mirrors constituting the scanning mirror unit. Optically integrated with a flat mirror closest to the platen glass, the incident surface of the integrated optical member is parallel to the platen glass surface, and the angle of the reflection surface of the optical member To the platen glass surface ° image reading apparatus characterized by being configured such that. 3. The image reading apparatus according to claim 1, wherein a dirt prevention cover is provided near a reflection surface of an optical member in which the convex lens and the flat mirror are integrated. 4. An optical member in which the convex lens and the plane mirror are integrated with each other is fixed to a holding member for holding the light source, and a reflection surface of the optical member is covered by the holding member. 3. The image reading device according to claim 1, wherein: