JP3530733B2 - Image reading device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device, and more particularly, when an image is read using a solid-state image pickup device such as a CCD, the F-number (FNo) of the imaging optical system in the sub-scanning direction is brightened and read. The present invention relates to an image reading apparatus which is suitable for, for example, a facsimile, a digital copying machine, or the like, which is capable of reading an image with high accuracy by increasing the amount of light.

[0002]

2. Description of the Related Art Conventionally, image information of a document or a film on a platen glass illuminated by an illumination system is projected on a predetermined surface by a focusing optical system (imaging lens), for example, a reading means surface such as a CCD. However, various image reading apparatuses have been proposed in which the image information is digitally read by the image reading means.

As an image reading means, a one-dimensional CCD (line sensor) in which a plurality of light receiving elements are arranged one-dimensionally at a constant cycle is used in many cases because an image can be read relatively accurately.

FIG. 4 is a schematic view of a main part of a conventional image reading apparatus. In the figure, reference numeral 40 denotes a document table glass for supporting a document, on which a document 46 is placed. Reference numeral 48 denotes a light source, which is composed of, for example, a fluorescent lamp. Reference numeral 49 is a concave mirror, which efficiently collects the light flux emitted from the light source 48 on the surface of the original 46. Reference numeral 41 denotes a slit, which is arranged in the vicinity of the surface of the document 46 and limits the luminous flux (light amount) from the surface of the document 46. 43a, 43b and 43c are the first and
The second and third mirrors guide the light flux from the surface of the document 46 to the imaging optical system (imaging lens) 44. The image forming optical system 44 forms (projects) a light flux based on the image information on the surface of the document 46 on the surface of the image reading means 47 including a CCD (line sensor) or the like.

In the figure, the scanning unit comprising the light source 48, the concave mirror 49, the slit 41 and the first mirror 43a is moved at a speed v in the sub-scanning direction as indicated by an arrow H in the figure, and the second and third scanning units are moved. The mirror-shaped mirror unit is moved from the mirrors 43b and 43c in the sub-scanning direction at a speed v / 2 in conjunction with the scanning unit as indicated by an arrow H to scan the surface of the document 46. As a result, the image information on the surface of the document 46 is read two-dimensionally.

Then, the image information of the document 46 read by the image reading means 47 is sent to an output device (not shown), for example, when the image information is output as a print output, or sent to a storage device (not shown). However, the input image information may be stored and used as an image reading device.

[0007]

The above-mentioned conventional image reading apparatus has the following various problems.

First, the pixel size of CCD is generally 7
˜14 μm, read resolution is 400-60
If it is about 0 dpi, the imaging relationship will always be a reduction system,
A specific magnification is a value of -0.1 to -0.2x.

In such a reduction optical system, there is little substantial deterioration of FNo caused by the relationship between F∞ representing FNo at infinity and Fef representing effective FNo, but the image formation on the image plane is small. Since the size (= the size of one CCD pixel) is small, if the sensitivity (charge generation amount per unit area) of the CCD light receiving surface is constant, the smaller the reduction ratio β is, the more the CCD on the image plane is formed. Output becomes smaller. Therefore, there is a demand for a method capable of obtaining a desired CCD output on the image plane.

Second, in order to keep the height of the apparatus low, the FNo in the main scanning direction and the FNo in the sub scanning direction of the imaging lens are set to different values, and in particular, the FNo in the sub scanning direction is made dark, for example, When the image forming lens is used as a flat lens, it is necessary to set the FNo in the main scanning direction to be brighter by the amount corresponding to the darkening of the FNo in the sub scanning direction in order to obtain the same brightness as that of the round lens. Therefore, in order to obtain the same brightness as that of the round lens, a method of independently brightening the FNo in the sub-scanning direction is desired.

According to the present invention, the FNo in the sub-scanning direction is set to the effective FNo in the main-scanning direction by setting the power of the imaging optical system in the sub-scanning direction to be substantially smaller than the power in the main-scanning direction. An object of the present invention is to provide an image reading device that can be made brighter.

Further, the imaging magnification in the sub-scanning direction and the imaging magnification in the main scanning direction of the imaging optical system are set to different values, and the imaging magnification in the sub-scanning direction is set to the imaging magnification in the main scanning direction. It is an object of the present invention to provide an image reading device that can increase the substantial reading light amount by setting the reading light amount to be smaller.

[0013]

The image reading apparatus of the present invention comprises: (1) Image information of a document illuminated by an illumination system is imaged at a predetermined magnification on the surface of the image reading means via an imaging optical system. In the image reading apparatus that reads the image, the imaging optical system includes a lens A having power in the main scanning direction and the sub-scanning direction, a first lens group B having power in the sub-scanning direction, and a power in the sub-scanning direction. And a second lens group C including the lens A, and the combined power of the first and second two lens groups B and C in the sub-scanning direction is Sub-scanning by setting it to be smaller than the power of
Direction effective F number to main scanning direction effective F number
The feature is that it is smaller than the above.

In particular, (1-1) the image forming magnification of the image forming optical system in the main scanning direction and the image forming magnification of the sub scanning direction are matched, and (1-2) the image forming optical system has an auxiliary image forming magnification. The image forming magnification in the scanning direction is set to be smaller than the image forming magnification in the main scanning direction, and (1-3) the first lens group B is arranged so that the incident light flux is substantially parallel light flux in the sub-scan section. Or (1-4) the lens A is a spherical lens, (1-5) the lens A is a toric lens, (1-6) The first lens group B has a cylindrical lens having a positive power in the sub-scanning direction, and (1-7) the second lens group C has a negative power in the sub-scanning direction. Cylindrical lens of
It is characterized in that it has a second cylindrical lens having a positive power in the sub-scanning direction.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1A and 1B are schematic views of a main portion showing a power arrangement in a main scanning direction and a sub scanning direction according to a first embodiment of the present invention.

In the figure, reference numeral 1 is a document on which an image is formed. 2 is a solid-state image sensor as an image reading means,
For example, it is composed of a CCD (line sensor).

A positive lens A is a spherical lens having a positive power (refractive power) φ ₁ in the main scanning direction and the sub scanning direction.

Reference numeral B denotes a first lens group having a positive power φ ₂ in the sub-scanning direction, which has a cylindrical lens, and a light beam based on image information from the original 1 in the sub-scanning section is a substantially parallel light beam. Has been converted to.

Reference numeral C denotes a second lens group having a positive power φ ₃ in the sub-scanning direction, and the lens A and a first cylindrical lens c having a negative power φ ₄ in the sub-scanning direction.
1 and a second cylindrical lens c2 having a positive power φ ₅ in the sub-scanning direction.

Each element of the positive lens A, the first lens group B, and the second lens group C constitutes one element of the image forming optical system.

In the present embodiment, the power in the sub-scanning direction of the imaging optical system is divided into the first and second lens groups B and C,
The powers φ ₂ and φ _{3 of the} first and second lens groups B and C maintain the imaging relationship in the sub-scanning direction, and the first and second
The combined power φ _s of the lens groups B and C in the sub-scanning direction is set to be smaller than the power φ ₁ of the positive lens A in the main scanning direction.

In this embodiment, a light flux based on image information from the original 1 illuminated by an illumination system (not shown) is imaged on the CCD 2 surface by the positive lens A in the main scanning section, and the image information is displayed. Reading with CCD2. The imaging magnification in the main scanning direction at this time is β _m .

Illumination system (not shown) in the sub-scan section
The first luminous flux based on the image information from the original 1 illuminated by
Is converted into a substantially parallel light flux by the second lens group B and is imaged on the surface of the CCD 2 through the second lens group C, and the image information is converted into C
I am reading it on CD2. The imaging magnification in the sub-scanning direction at this time is β _S.

Combined power φ _{s of the} imaging optical system in the sub-scanning direction
Can be expressed as φ _s = φ ₂ + φ ₃ −e′φ ₂ φ ₃ where e ′ is the principal point distance between the first lens group B and the second lens group C.

Here, the power of the imaging optical system in the main scanning direction is φ ₁ , the magnification is β (β _m ), the front side distance of the positive lens A (distance from the document 1 to the positive lens A) is t ₁ , the positive lens The rear side distance of A (the distance from the positive lens A to the CCD ₂ ) is t ₂ ,
Considering the case where the optical path length is TC and the values shown in Table 1 are set (reading resolution 400 dpi, CCD pixel size 10 μm), the power φ _{2 of} the first and second lens groups B and C in the sub-scanning direction, Magnification β and optical path length TC for φ ₃
It is possible to obtain various combinations in which and have the same value as the main scanning direction.

[0026]

[Table 1] Here, the first in becomes smaller range than the front distance t ₁ of the focal length f ₂ obtained from the power phi ₂ of the value of the first lens group B is positive lens A, the second lens group B, the power of C phi ₂ , Φ
The combination of _{3 and} the combined power φ _{s in the} sub-scanning direction are obtained. At this time, as shown in Table-1, it can be seen that the value of all combined power φ _s in the sub-scanning direction is smaller than the value of power φ _{1 in} the main scanning direction.

Since the focal length f ₂ of the first lens unit B is set to be smaller than the front side distance t ₁ of the positive lens A, the pupil diameter is constant in the main scanning direction and the sub scanning direction. If kept, the effective FNo in the sub-scanning direction will be the effective FNo in the main-scanning direction.
Can be brighter than.

As described above, in the present embodiment, as described above, the image forming optical system is a system in which the image forming magnification β _{m in} the main scanning direction and the image forming magnification β _{S in the} sub scanning direction are matched. The effective power FNo in the sub-scanning direction is brighter than the effective power FNo in the main-scanning direction by setting the combined power φ _s in the sub-scanning direction to be substantially smaller than the power φ ₁ in the main-scanning direction.
(That is, the valid FNo value in the sub-scanning direction is set to the valid in the main scanning direction.
The value can be made smaller than the value of FNo) , which enables highly accurate image reading.

In the present embodiment, the positive lens A is composed of a spherical lens, but the present invention is not limited to this, and the present invention may be composed of a toric lens having different powers in the main scanning direction and the sub scanning direction. It can be applied in the same manner as in the first embodiment.

2 (A) and 2 (B) are schematic views of a main portion showing the power arrangement in the main scanning direction and the sub scanning direction according to the second embodiment of the present invention. In the figure, the same elements as those shown in FIG. 1 are designated by the same reference numerals. In the figure, the second lens group C shows the power φ ₃ of the entire group.

The present embodiment differs from the first embodiment described above in that the state of the light beam converted by the first lens group B in the sub-scan section is converted into a divergent light beam. Other configurations and optical actions are substantially the same as those of the first embodiment, and similar effects are obtained.

That is, in the figure, B is the first lens group having a positive power φ ₂ in the sub-scanning direction, and diverges the light flux based on the image information from the document 1 illuminated by the illumination system (not shown). It is converted into light flux.

In this embodiment, even with this configuration, there is a system in which the image forming magnification β _{m in the} main scanning direction and the image forming magnification β _{s in the} sub scanning direction are equal to each other. Similar to the first embodiment, the FNo in the sub-scanning direction can be made brighter than the effective FNo in the main-scanning direction, which enables highly accurate image reading.

FIGS. 3A and 3B are schematic views of the main parts showing the power arrangements in the main scanning direction and the sub scanning direction according to the third embodiment of the present invention. In the figure, the same elements as those shown in FIG. 1 are designated by the same reference numerals. In the figure, the second lens group C shows the power φ ₃ of the entire group.

This embodiment differs from the first embodiment in that the imaging magnification β _{m in} the main scanning direction and the imaging magnification β _{s in the} sub scanning direction of the imaging optical system are set to different values, respectively. The imaging magnification β _s in the sub-scanning direction is smaller than the imaging magnification β _{m in the main} scanning direction (β _s <β _m ), first,
That is, the powers φ ₂ and φ ₃ of the second two lens groups are set. Other configurations and optical actions are substantially the same as those of the first embodiment, and similar effects are obtained.

In the present embodiment, the relationship between the image forming magnifications β _m and β _s in the main scanning direction and the sub scanning direction of the image forming optical system is expressed by β _s <
Setting β _m assumes that the image forming magnifications β _m and β _{s of both} are a reduction optical system (β ≧ −1), and the image forming magnification β _s in the sub-scanning direction approaches the same magnification. Is equivalent to In the present embodiment, this imaging magnification β in the sub-scanning direction
By bringing _s closer to the same magnification direction, the light amount level on the CCD 2 surface is increased so that highly accurate image reading can be performed.

Since the image-forming magnification β _{m in} the main scanning direction and the image-forming magnification β _{s in the} sub-scanning direction are different from each other, it is desirable that the pixel size of the CCD 2 be a size corresponding to the magnification (for example, at a resolution of 400 dpi). β _m = -0.15748, β
_{When s} = -0.31496, the pixel size of the CCD is 10 μm in the main scanning direction and 20 μm in the sub scanning direction. Since image data integrated by scanning the original is obtained in the sub scanning direction, imaging in the sub scanning direction is performed. CCD2 for size
If the pixel size is small, no problem occurs.

If the imaging magnification β _{s in the} sub-scanning direction is β _s > β _m with respect to the imaging magnification β _{m in} the main scanning direction, the CCD 2
Since the imaging size in the sub-scanning direction becomes smaller than the pixel size of, the reading resolution is deteriorated, but when β _s <β _m is set as in the present embodiment, there is no problem.

In this embodiment, the state of the light beam between the first lens group B and the second lens group C in the sub-scan section may be a substantially parallel light beam (parallel light beam) or a divergent light beam. .

[0040]

According to the present invention, as described above, the FNo in the sub-scanning direction is set by setting the power of the imaging optical system in the sub-scanning direction to be substantially smaller than the power in the main scanning direction. The image can be made brighter than the effective FNo in the main scanning direction, and thus an image reading device capable of reading an image with high accuracy can be achieved.

Further, the image forming magnification in the sub-scanning direction and the image forming magnification in the main scanning direction of the image forming optical system are set to different values, and the image forming magnification in the sub scanning direction is set with respect to the image forming magnification in the main scanning direction. By setting so as to be small, it is possible to increase the substantial reading light amount, and thereby it is possible to achieve an image reading apparatus that can read an image with high accuracy.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part showing a power arrangement according to a first embodiment of the present invention.

FIG. 2 is a schematic view of a main part showing a power arrangement according to a second embodiment of the present invention.

FIG. 3 is a schematic view of a main part showing a power arrangement according to a third embodiment of the present invention.

FIG. 4 is a schematic view of a main part of a conventional image reading device.

[Explanation of symbols]

1 manuscript 2 Image reading means (CCD) A positive lens B First lens group C Second lens group D First cylindrical lens E Second cylindrical lens

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Claims (8)

(57) [Claims] 1. An image reading apparatus for forming an image of image information of a document illuminated by an illumination system on a surface of an image reading means through an image forming optical system at a predetermined magnification and reading the image information. A lens A having power in the scanning direction and the sub-scanning direction, a first lens group B having power in the sub-scanning direction, and a lens A having power in the sub-scanning direction
And a second lens group C including the second lens group C, and the combined power of the first and second two lens groups B and C in the sub-scanning direction is smaller than the power of the lens A in the main scanning direction. By setting so that the
Compare the effective F number to the effective F number in the main scanning direction
An image reading device characterized by being made smaller . 2. The image reading apparatus according to claim 1, wherein an image forming magnification of the image forming optical system in the main scanning direction and an image forming magnification in the sub scanning direction are matched. 3. The image reading apparatus according to claim 1, wherein the image forming magnification of the image forming optical system in the sub scanning direction is set to be smaller than the image forming magnification in the main scanning direction. 4. The image reading apparatus according to claim 1, wherein the first lens group B converts an incident light flux into a substantially parallel light flux or a divergent light flux within a sub-scan section. 5. The image reading apparatus according to claim 1, wherein the lens A is a spherical lens. 6. The image reading apparatus according to claim 1, wherein the lens A is a toric lens. 7. The image reading apparatus according to claim 1, wherein the first lens group B includes a cylindrical lens having a positive power in the sub-scanning direction. 8. The second lens group C has a first cylindrical lens having a negative power in the sub-scanning direction and a second cylindrical lens having a positive power in the sub-scanning direction. 4. The method according to claim 1, 2 or 3
Image reading device.