JP2014013293A - Image reading lens, image reading device, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reading lens that can be used for reading of a full-color document image.SOLUTION: An image reading lens is configured of, from an object side to an image side, a first group G1 comprising a first lens L1 of a positive meniscus lens directing a convex surface to the object side, a second group G2 comprising a second lens L2 of a negative meniscus lens directing a convex surface to the object side, a third group G3 comprising a third lens L3, a fourth group G4 comprising a fourth lens L4 having a positive power, a fifth group G5 comprising a fifth lens L5 having a negative power, and a sixth group G6 comprising a sixth lens L6 of a negative meniscus lens directing a concave surface to the object side. The image reading lens has a diaphragm S between the second group G2 and the third group G3, has an aspherical surface at least on the second lens L2 and the sixth lens L6, and properly satisfies set conditions.

Description

  The present invention relates to an image reading lens, and an image reading apparatus and an image forming apparatus including the image reading lens.

  In an image reading apparatus such as a facsimile or a digital copying machine, a document image to be read is reduced by a reading lens and formed on a solid-state image pickup device such as a CCD (Charge Coupled Device) to convert image information into a signal. . An image reading lens is used as an optical system for forming such a document image.

  FIG. 13 shows a schematic configuration of an example of the image reading apparatus. In the image reading apparatus shown in FIG. 13, in order to read the image information of a document in color, for example, light receiving elements (16a, 16b, 16c) having red, green, and blue filters are arranged in three rows on one chip. A so-called 3-line CCD 16 is used. The three-line CCD is an optical system that separates the three primary colors by forming an original image on the light receiving surface by the image reading lens 15 and converts the color image information into a signal.

  In general, an image reading lens used in such an optical system is required to have a high contrast in a high spatial frequency region on the image plane and to have an aperture efficiency close to 100% up to the periphery of the angle of view. . In addition, in order to read a color original satisfactorily, it is necessary to match the image formation positions of red, green, and blue colors on the light receiving surface in the optical axis direction, and chromatic aberration correction for each color must be corrected very well. Don't be.

  Further, image reading apparatuses are required not only to improve performance but also to reduce size and cost. In order to achieve downsizing of the optical system, it is necessary to shorten the conjugate length. For this reason, a lens having a wide angle of view is required, and further, the number of lenses is reduced in order to realize cost reduction. It is demanded.

  As an image reading lens having a wide angle of view and a relatively small number of components, for example, a half angle of view of about 30 ° is achieved, and the number of components consists of 5 elements in 5 groups (see Patent Documents 1 and 2). A lens using an axisymmetric aspherical surface (see Patent Documents 3 and 4) has been proposed.

  An image reading lens having a small number of lenses suitable for miniaturization and cost reduction is difficult to meet various demands. Specifically, axial chromatic aberration is corrected well over a wide range from C line (656.27 nm) to g line (435.83 nm), and at a very wide angle (for example, the half angle of view exceeds 39 °). Despite the fact that the curvature of field is corrected well, a large aperture is achieved (for example, F-number is about 4.4), the aperture efficiency is close to 100% up to the periphery, and the aberration is also good It is required to be corrected and have high contrast in a high spatial frequency region.

Since the lenses described in Patent Documents 1 and 2 use so-called anamorphic lenses having different refractive powers in directions orthogonal to each other, there is a problem in the processing surface, and the lens becomes expensive, thereby realizing cost reduction. There is a problem that it is difficult.
On the other hand, the lenses described in Patent Documents 3 and 4 have a problem that since the half angle of view is as narrow as about 21.5 °, the conjugate length of the optical system becomes long and it is difficult to reduce the size.

  Therefore, in view of the above problems, the present invention responds to various demands required for an image reading lens in spite of a small number of lenses, and has a bright F number and a wide angle of view (for example, an F number of about 4.4, In addition, the image reading lens has a half angle of view of about 39 °), the aperture efficiency is substantially 100% up to the periphery, various aberrations are corrected well, and the contrast is high in the high spatial frequency region. An object of the present invention is to provide an image reading lens that can also be used for reading full-color original images.

In order to solve the above-described problem, an image reading lens according to the present invention includes:
A first lens unit composed of a first lens of a positive meniscus lens arranged with a convex surface facing the object side in order from the object side to the image side, and a second lens of a negative meniscus lens arranged with the convex surface facing the object side A second group comprising: a third group comprising a third lens; a fourth group comprising a fourth lens having positive power; a fifth group comprising a fifth lens having negative power; and a concave surface directed toward the object side A six-group six-element configuration composed of a sixth group consisting of sixth negative meniscus lenses arranged
Having a diaphragm between the second group and the third group;
At least the second lens and the sixth lens have aspheric surfaces,
The total focal length of e-line of the entire system is f, the focal length of e-line of the first lens is f1, the focal length of e-line of the sixth lens is f6, and the average refractive index of d-line of the positive lens is n-convex, When the average refractive index of d-line of the negative lens is n-concave, the average of Abbe number of d-line of positive lens is ν-convex, and the average of Abbe number of d-line of negative lens is ν-concave, the following conditional expression (1 ) To (4) are satisfied.
(1) 0.9 <f1 / f <1.4
(2) -1.2 <f6 / f <-1.0
(3) 0.03 <(n convex-n concave) <0.09
(4) 10.0 <(ν convex−ν concave) <16.0

  According to the image reading lens of the present invention, the F number is bright and has a wide angle of view (for example, the F number is about 4.4) in response to various demands required for the image reading lens in spite of a small number of lenses. In addition, the image reading lens has a half field angle of about 39 °), the aperture efficiency is substantially 100% up to the periphery, various aberrations are corrected well, and high contrast is obtained in a high spatial frequency region. In addition, it is possible to provide an image reading lens that can be used for reading full-color original images.

It is a schematic sectional drawing which shows an example of a structure of an image reading lens. It is explanatory drawing which shows an example of the external shape of a 6th lens. It is a schematic sectional drawing which shows the lens structure which concerns on a 1st embodiment. FIG. 5 is an aberration curve diagram showing spherical aberration, astigmatism, distortion, and coma aberration in the lens configuration of the first embodiment. It is a schematic sectional drawing which shows the lens structure which concerns on a 2nd embodiment. It is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration in the lens configuration of the second embodiment. It is a schematic sectional drawing which shows the lens structure which concerns on a 3rd embodiment. It is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration in the lens configuration of the third embodiment. It is a schematic sectional drawing which shows the lens structure which concerns on a 4th embodiment. FIG. 9 is an aberration curve diagram showing spherical aberration, astigmatism, distortion, and coma aberration in the lens configuration of the fourth embodiment. It is a schematic sectional drawing which shows the lens structure which concerns on a 5th embodiment. FIG. 10 is an aberration curve diagram showing spherical aberration, astigmatism, distortion, and coma aberration in the lens configuration of the fifth embodiment. It is a schematic block diagram for demonstrating an example of embodiment of an image reading apparatus. 1 is a schematic configuration diagram for explaining an example of an embodiment of an image forming apparatus.

  Hereinafter, an image reading lens, an image reading apparatus, and an image forming apparatus according to the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments described below, and other embodiments, additions, modifications, deletions, and the like can be changed within a range that can be conceived by those skilled in the art, and any aspect is possible. As long as the functions and effects of the present invention are exhibited, the scope of the present invention is included.

An example of the configuration of the image reading lens according to the present invention is shown in FIG.
As shown in FIG. 1, the image reading lens includes, in order from the object side to the image side, a first group (G1) including a first lens L1 of a positive meniscus lens disposed with a convex surface facing the object side, A second group (G2) composed of a second lens L2 of a negative meniscus lens disposed with a convex surface facing the side, a third group (G3) composed of a third lens L3, and has positive power (positive refractive power). A fourth group (G4) composed of the fourth lens L4, a fifth group (G5) composed of the fifth lens L5 having negative power (negative refractive power), and a negative meniscus disposed with the concave surface facing the object side The sixth group (G6) is composed of the sixth lens L6 of the lens, and the sixth group (G6) has a six-element configuration, and has a diaphragm between the second group (G2) and the third group (G3). The second lens L2 and the sixth lens L6 have aspheric surfaces.
The positive or negative of the third lens L3 is not limited, and may take the form of a positive lens and a negative lens as appropriate according to the embodiment.
A contact glass CN is disposed on the object side of the first lens L1, and a CCD cover glass CV is disposed on the image side of the sixth lens L6. The image plane is indicated by IS.

In addition, the meaning of the code | symbol in FIG. 1 is as follows.
ri (i = 1 to 13): radius of curvature of the i-th lens surface counted from the object side di (i = 1 to 12): i-th surface interval counted from the object side Nj (j = 1 to 6): Refractive index of the lens material with the jth surface interval counted from the object side νj (j = 1 to 6): Abbe number of the lens material with the jth surface interval counted from the object side rc1: Curvature of the object side of the contact glass Radius rc2: Radius of curvature on the image side of the contact glass rc3: Radius of curvature on the object side of the CCD cover glass rc4: Radius of curvature on the image side of the CCD cover glass dc1: Thickness of the contact glass dc3: Thickness of the CCD cover glass Nc1: Refractive index of contact glass νc1: Abbe number of CCD cover glass Nc2: Refractive index of contact glass νc2: Abbe number of CCD cover glass

The total focal length of e-line of the entire system is f, the focal length of e-line of the first lens is f1, the focal length of e-line of the sixth lens is f6, and the average refractive index of d-line of the positive lens is n-convex, When the average refractive index of d-line of the negative lens is n-concave, the average of Abbe number of d-line of positive lens is ν-convex, and the average of Abbe number of d-line of negative lens is ν-concave, the following conditional expression (1 ) To (4) are satisfied.
(1) 0.9 <f1 / f <1.4
(2) -1.2 <f6 / f <-1.0
(3) 0.03 <(n convex-n concave) <0.09
(4) 10.0 <(ν convex−ν concave) <16.0
The first lens L1 and the fourth lens L4 are positive lenses, and the second lens L2, the fifth lens L5, and the sixth lens L6 are negative lenses. The third lens L3 is either a positive lens or a negative lens depending on the embodiment.

  Conditional expression (1) determines the power of the first lens L1, and if it exceeds the upper limit (1.4), the power of the first lens L1 becomes too weak. Become. If the lower limit (0.9) or less is reached, the power of the first lens L1 becomes too strong, so that negative spherical aberration occurs greatly and cannot be corrected by the lenses of other groups.

  Conditional expression (2) determines the power of the sixth lens L6. If the upper limit (−1.0) or more is reached, the power of the sixth lens L6 becomes too strong. It cannot be corrected. If it is below the lower limit (−1.2), the power of the sixth lens L6 becomes too weak, and the lens becomes large and the curvature of field increases.

  Conditional expression (3) defines the refractive index range of the convex lens and the concave lens constituting the image reading lens. When the upper limit (0.09) or more is reached, the Petzval sum becomes too small, and the image surface is on the positive side. And the field curvature increases. If the lower limit (−0.03) is not reached, conversely, the Petzval sum becomes too large, the image surface falls to the negative side, and the astigmatic difference becomes large. Outside the range of this conditional expression (3), it is impossible to obtain good imaging performance over the entire screen.

  Conditional expression (4) is a condition for satisfactorily correcting axial chromatic aberration. When the upper limit (16.0) is exceeded, axial chromatic aberration is overcorrected, and axial chromatic aberration increases toward the positive side at shorter wavelengths than the main wavelength. When the lower limit (10.0) or less is reached, the axial chromatic aberration becomes insufficiently corrected, and the axial chromatic aberration becomes larger on the negative side at a shorter wavelength than the main wavelength.

  By configuring the image reading lens to satisfy the above conditional expressions (1) to (4), even in the case of a 6-group 6-lens configuration, in response to various demands required for the image reading lens, An image reading lens that is bright and has a wide angle of view (for example, an F number of about 4.4 and a half angle of view of about 39 °), and the aperture efficiency is substantially 100% up to the periphery, and various aberrations Is corrected well, has a high contrast in a high spatial frequency region, and can also read full-color original images.

An example of the external shape of the sixth lens L6 is shown in FIG. 2A is a perspective view, and FIG. 2B is a front sectional view.
As shown in FIG. 2, the sixth lens L6 preferably has a strip shape whose outer shape is long in the main scanning direction. Furthermore, it is preferable that the sixth lens L6 is a plastic lens for cost reduction.
Here, the “main scanning direction” refers to the arrangement direction of the line sensors in the line sensor array combined with the document reading lens.

As shown in FIG. 1, since the sixth lens L6 is disposed in the vicinity of the image forming surface, the sixth lens L6 needs to have a diameter substantially equal to the longitudinal direction of the line sensor. For this reason, in the case of a circular shape, the outer shape of the lens becomes very large, the height of the image reading apparatus becomes very high, and the cost of the lens itself is greatly increased.
In the image reading apparatus, since the document information is imaged on the line sensor as lines, the outer shape of the image reading lens may not be “rotationally symmetric with respect to the optical axis”. Therefore, the outer shape of the sixth lens L6 is a “strip shape that is long in the main scanning direction” as shown in FIG. 2, thereby reducing the thickness and size of the image reading apparatus and reducing the cost of the rear lens group. be able to.

Hereinafter, various aberrations and specific numerical data of the lens according to the embodiment of the image reading lens of the present invention will be shown. The meanings of symbols in the embodiments (Examples) shown in Tables 1 to 10 are as follows.
f: Composite focal length of e-line of the entire system F: F number m: Reduction ratio Y: Object height ω: Half angle of view (degrees)
r: radius of curvature of lens surface d: surface spacing nd: refractive index of d-line of each lens material νd: Abbe number of d-line of each lens material ne: refractive index of e-line of each lens material

The meanings of symbols in Table 11 are as follows.
f1: Focal length of e-line of the first lens f6: Focal length of e-line of the sixth lens n-convex: positive lens (lens having positive power (positive refractive power)) n-th average n-concave: negative lens Nd average ν convex of (a lens having negative power (negative refractive power)): νd average ν concave of a positive lens (lens having positive power (positive refractive power)): negative lens (negative power) Νd average of (a lens having negative refractive power)

  In Table 1, Table 3, Table 5, Table 7, and Table 9 showing data of each example, the “leftmost column” is an index representing each surface, c1 is an object side surface of contact glass, and c2 is a contact. The surface on the image side of the glass is represented. Numbers 1 to 12 represent the surfaces (the lens surface and the surface of the diaphragm) counted from the object side of the image reading lens, c3 represents the surface on the object side of the CCD cover glass, and c4. Represents the image side surface of the CCD cover glass.

ここで、上記式において
Ｘ：光軸から高さＹにおける非球面の非球面頂点における接平面からの距離
Ｙ：光軸からの高さ
Ｒ：非球面の近軸曲率半径
Ｋ：円錐定数
Ａ４,Ａ６,Ａ８,Ａ１０：非球面係数
ＳＱＲＴ：平方根の意味
である。
また、表２、表４、表６、表８及び表１０に示す数値例の中で、「Ｅ−ＸＹ」は、１０^−ＸＹの意味であり、例えば「Ｅ−１２」は１０^−１２を意味する。 An aspherical surface is expressed by the following formula.

Here, in the above formula, X: distance from the tangent plane at the aspherical vertex of the aspherical surface at height Y from the optical axis Y: height from the optical axis R: paraxial radius of curvature of the aspherical surface K: conic constant A4, A6, A8, A10: aspheric coefficient SQRT: means square root.
Further, Table 2, Table 4, Table 6, among the numerical examples shown in Tables 8 and 10, ^"E-XY" means an ^{10 -XY,} for example, "E-12" ^{10 -12} means.

In the aberration diagrams shown in FIGS. 4, 6, 8, 10, and 12, “e” is e-line (546.07 nm), “g” is g-line (436.83 nm), and “C” is C line (656.27 nm), “F” indicates F line (486.13 nm).
In the spherical aberration diagram, the wavy line indicates the sine condition, and in the astigmatism diagram, the solid line indicates the sagittal ray and the dotted line indicates the meridional ray.

[First Embodiment (Example 1)]
FIG. 3 shows the lens configuration of the first embodiment.
The image reading lens shown in FIG. 3 has, in order from the object side to the image side, a first lens unit L1 of positive meniscus lenses arranged with a convex surface facing the object side, with the convex surface facing the object side. The second group consisting of the second lens L2 of the arranged negative meniscus lens, the third group consisting of the third lens L3 having positive power, the fourth group consisting of the fourth lens L4 having positive power, the negative power The sixth lens group includes a fifth lens unit L5 and a sixth lens unit including a sixth lens unit L6 that is a negative meniscus lens having a concave surface facing the object side.
Table 1 shows specific numerical data of the constituent lenses.

  Table 2 shows the conic constant K and aspheric coefficients (A4, A6, A8, A10) of the aspherical surface of the first embodiment.

FIG. 4 is an aberration diagram showing aberration curves of spherical aberration, astigmatism, distortion aberration, and coma aberration according to the lens configuration of the first embodiment.
As shown in FIG. 4, in this embodiment, it is understood that the aberration is sufficiently corrected and has high imaging performance.
The values of f1 / f, f6 / f, n convex-n concave, and v convex-nu concave are shown in Table 11 below.

[Second Embodiment (Example 2)]
The lens configuration of the second embodiment is shown in FIG.
The image reading lens shown in FIG. 5 has, in order from the object side to the image side, a first lens unit L1 of positive meniscus lenses arranged with a convex surface facing the object side, with the convex surface facing the object side. The second group consisting of the second lens L2 of the arranged negative meniscus lens, the third group consisting of the third lens L3 having positive power, the fourth group consisting of the fourth lens L4 having positive power, the negative power The sixth lens group includes a fifth lens unit L5 and a sixth lens unit including a sixth lens unit L6 that is a negative meniscus lens having a concave surface facing the object side.
Table 3 shows specific numerical data of the constituent lenses.

  Table 4 shows the aspherical conical constant K and the aspherical coefficients (A4, A6, A8, A10) of the second embodiment.

FIG. 6 is an aberration diagram showing aberration curves of spherical aberration, astigmatism, distortion and coma aberration according to the lens configuration of the second embodiment.
As shown in FIG. 6, it can be seen that also in this embodiment, the aberration is sufficiently corrected and has high imaging performance.
The values of f1 / f, f6 / f, n convex-n concave, and v convex-nu concave are shown in Table 11 below.

[Third Embodiment (Example 3)]
FIG. 7 shows the lens configuration of the third embodiment.
The image reading lens shown in FIG. 7 has, in order from the object side to the image side, a first lens unit L1 of positive meniscus lenses arranged with a convex surface facing the object side, with the convex surface facing the object side. The second group consisting of the second lens L2 of the arranged negative meniscus lens, the third group consisting of the third lens L3 having negative power, the fourth group consisting of the fourth lens L4 having positive power, the negative power The sixth lens group includes a fifth lens unit L5 and a sixth lens unit including a sixth lens unit L6 that is a negative meniscus lens having a concave surface facing the object side.
In addition, Table 5 shows specific numerical data of the constituent lenses.

  Table 6 shows the conic constant K and the aspheric coefficients (A4, A6, A8, A10) of the aspheric surface of the third embodiment.

FIG. 8 is an aberration diagram showing aberration curves of spherical aberration, astigmatism, distortion and coma aberration according to the lens configuration of the third embodiment.
As shown in FIG. 8, it can be seen that, in this embodiment as well, the aberration is sufficiently corrected and has high imaging performance.
The values of f1 / f, f6 / f, n convex-n concave, and v convex-nu concave are shown in Table 11 below.

[Fourth Embodiment (Example 4)]
The lens configuration of the fourth embodiment is shown in FIG.
The image reading lens shown in FIG. 9 has, in order from the object side to the image side, a first lens unit L1 of positive meniscus lenses arranged with a convex surface facing the object side, and a convex surface facing the object side. The second group consisting of the second lens L2 of the arranged negative meniscus lens, the third group consisting of the third lens L3 having positive power, the fourth group consisting of the fourth lens L4 having positive power, the negative power The sixth lens group includes a fifth lens unit L5 and a sixth lens unit including a sixth lens unit L6 that is a negative meniscus lens having a concave surface facing the object side.
Table 7 shows specific numerical data of the constituent lenses.

  Table 8 shows the aspherical conical constant K and the aspherical coefficients (A4, A6, A8, A10) of the fourth embodiment.

FIG. 10 is an aberration diagram showing aberration curves of spherical aberration, astigmatism, distortion and coma aberration according to the lens configuration of the fourth embodiment.
As shown in FIG. 10, it can be seen that also in this embodiment, the aberration is sufficiently corrected, and the imaging performance is high.
The values of f1 / f, f6 / f, n convex-n concave, and v convex-nu concave are shown in Table 11 below.

[Fifth Embodiment (Example 5)]
FIG. 11 shows the lens configuration of the fifth embodiment.
The image reading lens shown in FIG. 11 includes, in order from the object side to the image side, a first lens unit L1 of positive meniscus lenses arranged with a convex surface facing the object side, and a convex surface facing the object side. The second group consisting of the second lens L2 of the arranged negative meniscus lens, the third group consisting of the third lens L3 having positive power, the fourth group consisting of the fourth lens L4 having positive power, the negative power The sixth lens group includes a fifth lens unit L5 and a sixth lens unit including a sixth lens unit L6 that is a negative meniscus lens having a concave surface facing the object side.
Table 9 shows specific numerical data of the constituting lenses.

  Table 10 shows the aspherical conical constant K and the aspherical coefficients (A4, A6, A8, A10) of the fifth embodiment.

FIG. 12 is an aberration diagram showing aberration curves of spherical aberration, astigmatism, distortion and coma aberration according to the lens configuration of the fifth embodiment.
As shown in FIG. 12, it can be seen that in this embodiment as well, the aberration is sufficiently corrected and has high imaging performance.
The values of f1 / f, f6 / f, n convex-n concave, and v convex-nu concave are shown in Table 11 below.

  Table 11 shows the parameter values of the conditions in each embodiment.

As shown in Table 11, the image reading lens of any embodiment satisfies the following conditional expressions (1) to (4).
(1) 0.9 <f1 / f <1.4
(2) -1.2 <f6 / f <-1.0
(3) 0.03 <(n convex-n concave) <0.09
(4) 10.0 <(ν convex−ν concave) <16.0
Further, as is apparent from the respective aberration diagrams shown in FIGS. 4, 6, 8, 10, and 12, in any of the image reading lenses of any of the embodiments, the F number is bright and the wide angle of view (for example, F The number is about 4.4 and the half angle of view is about 39 °), the aperture efficiency is substantially 100% up to the periphery, various aberrations are also corrected well, and high contrast is achieved in a high spatial frequency region. And full-color original image reading is also supported.

[Image reading device]
An image reading apparatus includes: an illumination system that illuminates a document; an imaging lens that reduces and images reflected light of the document illuminated by the illumination system; and an image of the document image formed by the imaging lens The image reading lens according to the present invention is used as the imaging lens.
FIG. 13 shows an embodiment of the image reading apparatus.

As shown in FIG. 13, a document 12 having an image to be read is placed in a plane on a contact glass 11 serving as a document table. Illumination means 13 is disposed below the document table (contact glass) 11. The illuminating means 13 is composed of a tube lamp that is long in the direction orthogonal to the drawing as a light source and a reflector, and illuminates the “slit-like portion that is long in the direction orthogonal to the drawing”.
As the light source, for example, a xenon lamp, a halogen lamp, an LED light source or the like can be used, but it is preferable to use an LED light source. By using the LED light source, the power consumption of the reading optical system can be reduced, and energy saving can be achieved.

  Reflected light (reflected light by an image) reflected by the illuminated original 12 is sequentially reflected by a folding mirror (in FIG. 13, five mirrors M1 to M5 are arranged), guided to the image reading lens 15, and an image. The reading lens 15 forms a reduced image of the original image on the imaging surface of the line sensor 16 as a photoelectric conversion element. In the present embodiment, the number of folding mirrors is five, but the number is not limited to five.

  The illumination means 13, the folding mirrors M1 to M5, the image reading lens 15 and the photoelectric conversion element 16 are integrally held as an image reading unit 17, and run in the direction of the arrow (right side in the figure) by a driving means (not shown). Is displaced to the image reading unit 17 at the position indicated by, and the information of the entire document is read.

The image reading apparatus has color separation means on the optical path of the optical system, and reads a document image in full color.
In the present embodiment, the line sensor 16 serving as an imaging unit has three light receiving elements (16a, 16b, 16c) having R (red), G (green), and B (blue) color separation filters in one chip. It is a “3-line CCD” arranged in a row, and color separation is performed on the three primary colors by forming a color image on its light receiving surface. Therefore, a color original can be read in full color.

Along with the illumination scanning of the document 12, the document image is converted into an image signal, and the color image of the document 12 is read by color separation into three primary colors of red, green, and blue. As a method of performing color separation, separately from the above, a color separation prism or filter is selectively inserted between the image reading lens 15 and the line sensor (CCD) 16, and R (red), G (green), A method of color separation into B (blue), a method of illuminating a document by sequentially turning on R, G, and B light sources can be used.
It is also possible to read the document information as monochrome without having a color separation element in the imaging optical path.

  Since the image reading lens 15 is a lens in which the axial chromatic aberration is well corrected, by using the image reading lens, it is possible to read a full color with good performance, and the multifunction of the image reading device is improved. High performance can be achieved.

[Image forming apparatus]
An image forming apparatus includes the image reading apparatus including the image reading lens according to the present invention.
FIG. 14 shows an embodiment of the image forming apparatus of the present invention.

As shown in FIG. 14, the image forming apparatus includes an image reading apparatus 200 positioned at the upper part of the apparatus and an image forming unit positioned at a lower position. The image reading apparatus 200 is the same as that described with reference to FIG. 13, and the same reference numerals as those in FIG.
An image signal output from the three-line line sensor (imaging means) 16 of the image reading unit 17 is sent to the image processing unit 120 and processed by the image processing unit 120 to generate a “writing signal (yellow, magenta, cyan, Signal for writing each color of black) ”.

The image forming unit includes a photoconductive photosensitive member 110 formed in a cylindrical shape as a “latent image carrier”, and a charging roller 111 as a charging unit, a revolver type developing device 113, and a transfer belt around the photosensitive member 110. 114 and a cleaning device 115 are provided. As the charging means, a “corona charger” can be used instead of the charging roller 111.
An optical scanning device 117 that receives a writing signal from the signal processing unit 120 and writes on the photosensitive member 110 by optical scanning performs optical scanning of the photosensitive member 110 between the charging roller 111 and the developing device 113. Yes.

Reference numeral 116 denotes a fixing device, reference numeral 118 denotes a cassette, reference numeral 119 denotes a registration roller pair, reference numeral 122 denotes a paper feed roller, reference numeral 121 denotes a tray, and reference numeral 130 denotes a transfer sheet as a “recording medium”.
When image formation is performed, the photoconductive photosensitive member 110 is rotated at a constant speed in the clockwise direction, the surface thereof is uniformly charged by the charging roller 111, and is subjected to exposure by optical writing of the laser beam of the optical scanning device 117. An electrostatic latent image is formed. The formed electrostatic latent image is a so-called “negative latent image”, and the image portion is exposed.

  “Image writing” is performed in the order of a yellow image, a magenta image, a cyan image, and a black image in accordance with the rotation of the photoconductor 110, and the formed electrostatic latent image is stored in each developing unit Y ( Development with yellow toner), M (development with magenta toner), C (development with cyan toner), K (development with black toner) are sequentially reversed and visualized as a positive image. The respective color toner images are sequentially transferred onto the transfer belt 114 by the transfer voltage application roller 114A, and the respective color toner images are superimposed on the transfer belt 114 to form a color image.

The cassette 118 storing the transfer paper 130 is detachable from the main body of the image forming apparatus. When the cassette 118 is mounted as shown in the figure, the uppermost sheet of the stored transfer paper 130 is fed by the paper feed roller 122. The leading edge of the fed transfer paper 130 is caught by the registration roller pair 119.
The registration roller pair 119 feeds the transfer sheet 130 to the transfer unit at the timing when the “color image by toner” on the transfer belt 114 moves to the transfer position. The transferred transfer paper 130 is superimposed on the color image at the transfer portion, and the color image is electrostatically transferred by the action of the transfer roller 114B. The transfer roller 114B presses the transfer paper 130 against the color image during transfer.

  The transfer paper 130 onto which the color image has been transferred is sent to the fixing device 116, where the color image is fixed, passes through a conveyance path by a guide means (not shown), and is discharged onto the tray 121 by a pair of paper discharge rollers (not shown). The Each time each color toner image is transferred, the surface of the photoreceptor 110 is cleaned by the cleaning device 115 to remove residual toner, paper dust, and the like.

Since the image forming apparatus includes the image reading apparatus using the image reading lens according to the present invention, an image forming apparatus capable of forming a high-quality image based on good read image quality can be obtained at low cost.
The image forming apparatus may be a so-called tandem type image forming apparatus in which a plurality of photoconductors are arranged corresponding to respective colors. Of course, it goes without saying that the image forming apparatus can be “configured to form a monochrome image”.

L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens L5 5th lens L6 6th lens CN Contact glass CV CCD cover glass IS Image surface 11 Document table (contact glass)
12 Document 15 Image reading lens 16 Line sensor (CCD)
17 Image reading unit 200 Image reading device

Japanese Patent No. 3862446 JP 2002-244033 A Japanese Patent No. 3939908 Japanese Patent No. 4496231

Claims (6)

A first lens unit composed of a first lens of a positive meniscus lens arranged with a convex surface facing the object side in order from the object side to the image side, and a second lens of a negative meniscus lens arranged with the convex surface facing the object side A second group comprising: a third group comprising a third lens; a fourth group comprising a fourth lens having positive power; a fifth group comprising a fifth lens having negative power; and a concave surface directed toward the object side A six-group six-element configuration composed of a sixth group consisting of sixth negative meniscus lenses arranged
Having a diaphragm between the second group and the third group;
At least the second lens and the sixth lens have aspheric surfaces,
The total focal length of e-line of the entire system is f, the focal length of e-line of the first lens is f1, the focal length of e-line of the sixth lens is f6, and the average refractive index of d-line of the positive lens is n-convex, When the average refractive index of d-line of the negative lens is n-concave, the average of Abbe number of d-line of positive lens is ν-convex, and the average of Abbe number of d-line of negative lens is ν-concave, the following conditional expression (1 ) To (4) are satisfied.
(1) 0.9 <f1 / f <1.4
(2) -1.2 <f6 / f <-1.0
(3) 0.03 <(n convex-n concave) <0.09
(4) 10.0 <(ν convex−ν concave) <16.0   The image reading lens according to claim 1, wherein the sixth lens is made of plastic and has an outer shape that is a strip shape that is long in the main scanning direction. An illumination system for illuminating the original, an imaging lens for reducing and imaging the reflected light of the original illuminated by the illumination system, and a line for photoelectrically converting an image of the original image formed by the imaging lens In an image reading device comprising a sensor,
An image reading apparatus using the image reading lens according to claim 1 or 2 as the imaging lens.   4. The image reading apparatus according to claim 3, further comprising color separation means on an arbitrary optical path of the optical system, and reading a document image in full color.   The image reading apparatus according to claim 3, wherein the light source of the illumination system is an LED.   An image forming apparatus comprising the image reading apparatus according to claim 3.

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