JP2012141464A - Image reading lens, image reading device and image forming device - Google Patents

Abstract

An image reading lens that is small in size, has chromatic aberration corrected, and obtains high image quality, and an apparatus using the image reading lens.
In order from the object side, a first group G1 composed of a meniscus first lens L1 having negative refractive power, a second group G2 composed of a meniscus second lens L2 having positive refractive power, negative A third lens unit G3 composed of a meniscus third lens L3 having a refractive power of 5%, a fourth lens unit G4 formed by cementing a fourth lens L4 having convex surfaces on both sides and a fifth lens L5 having negative refractive power, A fifth lens group G5 composed of a sixth lens L6 having a refractive power and a sixth lens group G6 composed of a seventh lens L7 having a negative refractive power, and a stop between the third lens group G3 and the fourth lens group G4 And an image reading lens satisfying the following conditional expression, and an apparatus using the image reading lens.
(1) 0.7 <d / f <1.0
(2) 0.5 <−f ₆ /f<1.6
(3) 1.8 <(f ₂ + f ₅ ) / f <5.2
[Selection] Figure 1

Description

  The present invention relates to an image reading lens and an apparatus including the image reading lens, and more specifically, image information of a document is reduced and formed on an image pickup element in which elements are arranged in a line shape, and the image information is read by the image pickup element. The present invention relates to an image reading lens used for an image reading unit such as a digital copying machine and a facsimile and various image scanners, an image reading apparatus including the image reading lens, and an image forming apparatus.

  An image reading unit or an image scanner of a facsimile or a digital copying machine reduces image information of a document to be read by an image reading lens and forms an image on an image sensor such as a CCD (Charge Coupled Device) to signal the image information. Turn into. A three-line CCD is often used as a CCD for reading image information of an original for color. The three-line CCD is composed of image sensors having red, green, and blue filters arranged in three rows on a single substrate, and images image information of an original on the image sensor surface, so that the three primary colors are colored. It is an optical system that decomposes and converts color image information into signals.

  In general, an image reading lens 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. Further, in order to read a color original satisfactorily, it is necessary to match the image forming positions of red, green, and blue colors on the image plane in the optical axis direction, and chromatic aberration must be corrected well for each color.

  Further, in order to reduce the size of the image reading apparatus, a downsized image reading lens corresponding to a wide angle of view is required. On the other hand, Patent Document 1 describes an image reading lens having a half angle of view exceeding 20 °.

  However, in the image reading lens described in Patent Document 1, the astigmatic difference is large, and the deviation of the imaging position of the image plane in the optical axis direction between the meridional ray and the sagittal ray is large. There is a problem that imaging performance cannot be obtained.

  On the other hand, an image reading lens is required to suppress performance deterioration when the temperature rises due to a temperature change in the image reading device, for example, heat generation of an illumination light source. Furthermore, from the viewpoint of resource saving in recent years, the recycling of the lens glass is required, and for the recycling of the lens glass, it is required that the lens material does not contain harmful substances.

  Therefore, in view of the above problems, the present invention is an image reading lens that is small in size, has an image plane position in the optical axis direction that is well matched for both sagittal rays and meridional rays, corrects chromatic aberration, and provides high image quality. An object is to provide an apparatus using an image reading lens.

  In addition, an image reading lens that can reduce performance degradation due to changes in the usage environment and temperature, and an image reading lens that takes into account the global environment that can be recycled, and that is free from water pollution due to waste liquid during processing. An object of the present invention is to provide an apparatus using the image reading lens.

In order to solve the above problems, an image reading lens, an image reading apparatus, and an image forming apparatus according to the present invention are as follows.
[1] In order from the object side, a first group of meniscus-shaped first lenses having a negative refractive power with a convex surface facing the object side, a meniscus-shaped first lens having a positive refractive power with a convex surface facing the object side. A second group consisting of two lenses, a third group consisting of a meniscus third lens having negative refractive power with the concave surface facing the object side, a fourth lens having convex surfaces on both sides, and a fifth lens having negative refractive power , A fifth group consisting of a sixth lens having a positive refractive power, and a sixth group consisting of a seventh lens having a negative refractive power. The third group and the fourth group Is an image reading lens having a six-group, seven-element configuration having a diaphragm between and satisfying the following conditional expressions (1) to (3).
(1) 0.7 <d / f <1.0
(2) 0.5 <−f ₆ /f<1.6
(3) 1.8 <(f ₂ + f ₅ ) / f <5.2
However,
d: Thickness of the entire image reading lens system f: Focal length of the entire image reading lens system f ₂ : Focal length of the second group f ₅ : Focal length of the fifth group f ₆ : Focal length of the sixth group
[2] The image reading lens according to [1], wherein the following conditional expressions (4) and (5) are satisfied.
(4) 0.6 <d _A /d<0.8
(5) 2.7 <−f _B / f _C <4.6
However,
d _A : Sum of thicknesses from the fourth group to the sixth group f _B : Composite focal length from the first group to the third group f _C : Composite focal length from the fourth group to the sixth group
[3] The image reading lens according to [1] or [2], wherein the second lens satisfies the following conditional expressions (6) and (7).
(6) 0.9 <f ₂ /f<2.3
(7) -7 <dn / dt (L2) <0
However,
dn / dt (L2): a refractive index temperature coefficient of the second lens.
[4] All of the seven lenses are glass lenses, and the glass material of the glass lens does not contain lead, arsenic, and similar harmful substances, [1] to [3] The image reading lens according to any one of the above.
[5] The image reading lens according to any one of [1] to [4], wherein at least one of the lenses has a non-circular outer shape.
[6] An illumination system that illuminates a document placed on a document placement surface, and an imaging lens that forms image information of the document illuminated by the illumination system on a line-shaped imaging device, An image reading apparatus using the image reading lens according to any one of [1] to [5] as a lens.
[7] An image reading unit that includes at least one mirror, and in which the illumination system, the image reading lens, the imaging element, and the mirror are integrally held, scans the image reading unit, and [6] The image reading apparatus according to [6], which reads image information of a document.
[8] An image forming apparatus that forms an image by writing an image corresponding to an image signal, and reads the image information of a document to convert it into an image signal. The image described in [6] or [7] An image forming apparatus using a reading device.

As an effect of the present invention, according to the first aspect of the present invention, in order from the object side, the first group of meniscus first lenses having negative refractive power with the convex surface facing the object side, the convex surface on the object side is provided. A second group of meniscus-shaped second lenses having a positive refractive power directed to the second lens, a third group of meniscus-shaped third lenses having a negative refractive power having a negative refractive power directed toward the object side, and a fourth lens having convex surfaces on both sides. A fourth group formed by joining a lens and a fifth lens having a negative refractive power, a fifth group including a sixth lens having a positive refractive power, and a sixth group including a seventh lens having a negative refractive power. An image reading lens having seven elements in six groups and having a diaphragm between the third group and the fourth group, and conditional expression (1) 0.7 <d / f <1.0, equation _{(2) 0.5 <-f 6 /f<1.6} , condition _{(3) 1.8 <(f 2} + f 5) / f <5.2 ( was And, d is the image reading lens system thickness, f is the focal length of the image reading lens system, f ₂ is the focal length of the second lens group, f ₅ is the focal length of the fifth group, f ₆ is group 6 The image reading lens satisfies the above-mentioned focal length), and is small in size and can suppress deterioration in imaging performance due to spherical aberration and coma aberration, and maintain good image quality.
According to the invention of claim 2, in the image reading lens of claim 1, the conditional expression (4) 0.6 <d _A /d<0.8 and the conditional expression (5) 2.7 <−f _B / f _C <4.6 (where d _A is the sum of the thicknesses from the fourth group to the sixth group, f _B is the combined focal length from the first group to the third group, and f _C is the fourth group) (The combined focal length from the first lens unit to the sixth lens unit)), the image formation position between the image heights is further suppressed, and good imaging performance on the image sensor surface is obtained. In addition, it is possible to suppress distortion errors between image heights by suppressing the occurrence of distortion.
According to the invention of claim 3, in the image reading lens of claim 1 or 2, the conditional expression (6) 0.9 <f ₂ /f<2.3 and the conditional expression (7) -7 <dn / dt Since the image reading lens satisfies (L2) <0 (where dn / dt (L2) is the refractive index temperature coefficient of the second lens), the distance from the image reading lens to the imaging position is increased as the temperature rises. Since it can be extended, it can follow the temperature increase of the lens holding portion satisfactorily, and high image quality can be obtained even in different temperature environments.
According to the invention of claim 4, in the image reading lens according to any one of claims 1 to 3, all of the seven lenses are glass lenses, and the glass material of the glass lens is lead, arsenic, and these Because it does not contain any toxic substances similar to the above, it is possible to recycle the material, and it is possible to make a great contribution to the preservation of the global environment without causing water pollution due to waste liquid during processing.
According to a fifth aspect of the present invention, in the image reading lens according to any one of the first to fourth aspects, at least one of the lenses has a non-circular outer shape, and is orthogonal to the pixel arrangement direction of the line CCD. The image reading lens in the direction can be thinned, and the size can be further reduced.
According to the invention of claim 6, an illumination system that illuminates the document placed on the document placement surface, and an imaging lens that forms image information of the document illuminated by the illumination system on a line-shaped image sensor. And an image reading apparatus using the image reading lens according to any one of claims 1 to 5 as the imaging lens. Therefore, the image reading apparatus can be downsized.
According to a seventh aspect of the present invention, in the image reading apparatus according to the sixth aspect, the image reading apparatus has at least one mirror, and the illumination system, the image reading lens, the imaging device, and the mirror are integrally held. Since the image reading unit is a device that scans the image reading unit and reads the image information of the original, the size can be reduced, and fluctuations in the image reading unit can be reduced. Image reading quality can be obtained.
According to an eighth aspect of the present invention, there is provided an image forming apparatus for forming an image by writing an image corresponding to an image signal, wherein the image information of a document is read and converted into an image signal. Since it is an image forming apparatus using the described image reading apparatus, it is possible to maintain high image quality in any use environment at the time of copying and to realize miniaturization.

It is a schematic sectional drawing which shows an example of a structure of the image reading lens of this invention. It is a schematic sectional drawing which shows the lens structure which concerns on a 1st embodiment. FIG. 3 is an aberration curve diagram showing spherical aberration, astigmatism, distortion, and coma aberration in the lens configuration of FIG. 2. 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. It is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration and coma aberration in the fifth embodiment. It is a schematic sectional drawing which shows the lens structure which concerns on a 6th embodiment. FIG. 10 is an aberration curve diagram showing spherical aberration, astigmatism, distortion, and coma aberration in the lens configuration of the sixth embodiment. It is a schematic sectional drawing which shows the lens structure which concerns on a 7th embodiment. It is an aberration curve diagram showing spherical aberration, astigmatism, distortion, and coma aberration in the lens configuration of the seventh embodiment. It is a schematic sectional drawing which shows the lens structure which concerns on an 8th embodiment. It is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration and coma aberration in the eighth embodiment. It is a schematic sectional drawing which shows the lens structure which concerns on a 9th embodiment. It is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration in the ninth embodiment. It is a schematic sectional drawing which shows the lens structure which concerns on a 10th embodiment. It is an aberration curve figure which shows the spherical aberration, the astigmatism, the distortion aberration, and the coma aberration in the tenth embodiment. It is a schematic sectional drawing which shows the lens structure which concerns on an 11th embodiment. It is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration in the lens configuration of the eleventh embodiment. It is a schematic sectional drawing which shows the lens structure which concerns on a 12th embodiment. It is an aberration curve figure which shows the spherical aberration, astigmatism, distortion aberration, and coma aberration in the lens structure of the 12th embodiment. It is a schematic perspective view which shows the other example of a structure of the image reading lens of this invention. 1 is a schematic configuration diagram illustrating a main part of an example of an image reading apparatus of the present invention. It is a schematic block diagram which shows the principal part of the other example of the image reading apparatus of this invention. 1 is a schematic configuration diagram illustrating a main part of an example of an image forming apparatus of the present invention.

  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. It should be noted that the present invention is not limited to the embodiments of the examples shown 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. Any aspect is included in the scope of the present invention as long as the operations and effects of the present invention are exhibited.

An example of the image reading lens of the present invention is shown in FIG.
As shown in FIG. 1, the image reading lens of the present invention includes, in order from the object side, a first group including a first lens L1 having a negative refractive power and a second lens L2 having a positive refractive power. 2nd group G2, 3rd group G3 which consists of 3rd lens L3 with negative refractive power, 4th group G4 which joins 4th lens L4, and 5th lens L5 with negative refractive power, positive refraction The fifth lens group G5 is composed of a sixth lens L6 having power and the sixth lens group G6 is composed of a seventh lens L7 having negative refracting power, and a diaphragm is formed between the third lens group G3 and the fourth lens group G4. It is an image reading lens having a 6-group 7-element configuration.
A contact glass CG1 is disposed on the object side of the first group, and a CCD cover glass CG2 is disposed on the image side of the sixth group.

  As shown in FIG. 1, the first lens L1 has a meniscus shape having a negative refractive power with a convex surface facing the object side, and the second lens L2 is a positive lens with a convex surface facing the object side. The third lens L3 has a negative meniscus shape with a concave surface facing the object side, and the fourth lens L4 has a convex shape on both sides.

The meanings of the symbols in FIG. 1 are as follows.
r _j (j = 1 to 14): radius of curvature of the j-th lens surface counted from the object side d _j (j = 1 to 13): j-th surface interval counted from the object side nd _j (j = 1, 1) 3, 5, 8, 9, 11, 13): Refractive index of the lens material with the j-th surface interval counted from the object side νd _j (j = 1, 3, 5, 8, 9, 11, 13): Object Abbe number of the lens material with the j-th surface interval counted from the side r _c1 : radius of curvature on the object side of the contact glass r _c2 : radius of curvature on the image side of the contact glass r _c3 : radius of curvature on the object side of the CCD cover glass r _c4 : radius of curvature of image side of CCD cover glass d _c1 : thickness of contact glass d _c3 : thickness of CCD cover glass n _c1 : refractive index of contact glass n _c3 : refractive index of CCD cover glass νd _c1 : contact glass Abbe number νd of _3: Abbe number of the CCD cover glass

The image reading lens of the present invention satisfies the following conditional expressions (1) to (3).
(1) 0.7 <d / f <1.0
(2) 0.5 <−f ₆ /f<1.6
(3) 1.8 <(f ₂ + f ₅ ) / f <5.2
Where d is the thickness of the entire image reading lens system, f is the focal length of the entire image reading lens system, f ₂ is the focal length of the second group, f ₅ is the focal length of the fifth group, and f ₆ is the sixth group. Is the focal length.

  Conditional expression (1) defines the total length of the image reading lens. If the value of d / f is less than the lower limit of 0.7, the refractive power of each lens group becomes strong and high-order spherical aberration occurs, making it difficult to match the image surfaces of the on-axis light beam and off-axis light beam. . On the other hand, if the value of d / f exceeds the upper limit value 1.0, the entire length of the image reading lens becomes long and the lens diameter of the sixth group G6 becomes large, so that it is difficult to reduce the size of the image reading lens. . Thus, satisfying conditional expression (1) is a necessary condition for downsizing the image reading lens and obtaining high image quality.

Conditional expression (2) defines the ratio of the focal length of the sixth group G6 to the entire image reading lens system. Decreasing the value of −f ₆ / f is advantageous for reducing the size of the lens, but if the value is below the lower limit of 0.5, coma increases and off-axis resolving power decreases. On the other hand, if the upper limit value of 1.6 is exceeded, the lens diameter of the sixth group G6 becomes too large, making it difficult to reduce the size. Thus, satisfying conditional expression (2) is also a necessary condition for downsizing the image reading lens and obtaining high image quality.

Conditional expression (3) defines the ratio of the sum of the focal lengths of the second group G2 and the fifth group G5 with respect to the entire image reading lens system. Reducing the value of (f ₂ + f ₅ ) / f is advantageous for reducing the size of the lens. However, when the value is below the lower limit of 1.8, the spherical aberration falls to the negative side and a good resolving power cannot be obtained. . On the other hand, if the upper limit value 5.2 is exceeded, the positive refractive power of the fifth group G5 becomes weak, so that the lens diameter of the fifth group G5 increases, and accordingly, the lens diameter of the sixth group G6 also increases. End up. Thus, satisfying conditional expression (3) is also a necessary condition for downsizing the image reading lens and obtaining high image quality.

The image reading lens of the present invention preferably satisfies the following conditional expressions (4) and (5).
(4) 0.6 <d _A /d<0.8
(5) 2.7 <−f _B / f _C <4.6
Where d _A is the sum of the thicknesses from the fourth group to the sixth group, f _B is the combined focal length from the first group to the third group, and f _C is the combined focal length from the fourth group to the sixth group. It is.

Conditional expression (4) defines the ratio of the thickness of the lens groups G4 to G6 after the diaphragm to the total length of the image reading lens. Conditional expression (5) is a combination of the lens groups G1 to G3 before the diaphragm. This is an equation that defines the ratio between the focal length and the combined focal length of the lens groups G4 to G6 after the stop.
When the value of -f _B / f _{C in} conditional expression (5) approaches the lower limit value 2.7, the image plane falls to the negative side, and when the value approaches the upper limit value 4.6, the image plane falls to the positive side. End up. For this reason, by satisfying conditional expression (5), variation in imaging performance between image heights can be suppressed.
Conditional expression (4) defines the positional relationship of the refractive powers from the lens groups G4 to G6 after the aperture stop. When the value of d _A / d exceeds the upper limit of 0.8, distortion becomes large. Cheap.
If d _A / d exceeds the upper limit of 0.8 and −f _B / f _C is less than 2.7, the lens diameter of the entire image reading lens becomes large, and it is difficult to reduce the size.
By satisfying conditional expressions (4) and (5), it is possible to suppress degradation in imaging performance due to curvature of field between image heights, and to suppress a change in magnification between image heights due to distortion. Therefore, good image quality can be obtained.

Furthermore, it is preferable that the image reading lens of the present invention satisfies the following conditional expressions (6) and (7).
(6) 0.9 <f ₂ /f<2.3
(7) -7 <dn / dt (L2) <0
However, dn / dt (L2) is the refractive index temperature coefficient of the second lens.

Conditional expression (6) is an expression that defines the range of the refractive power of the second meniscus second lens L2 of the second group G2. Conditional expression (7) is an expression defining the range of the refractive index temperature coefficient of the glass material used for the second lens L2.
In the image reading lens of the present invention, when the second lens L2 satisfies the conditional expressions (6) and (7), the temperature dependence of the imaging position of the entire image reading lens system can be effectively corrected. .
When the value of dn / dt (L2) is less than the lower limit value −7 of the conditional expression (7), the focal length is reduced, so that the change in focal length due to temperature is also reduced, and a satisfactory temperature compensation effect is obtained. Disappear. On the other hand, if the value of dn / dt (L2) exceeds 0, aberration correction due to the positive refractive power of the lens unit before the diaphragm cannot be obtained satisfactorily, and good imaging performance cannot be obtained. In order to obtain good imaging performance and temperature compensation in the entire image reading lens system, it is preferable that the second lens L2 satisfies the range of the conditional expression (6), and further satisfies the range of the conditional expression (7). By using a material (glass material) having a refractive index temperature coefficient of 0 or less, it is possible to effectively reduce the focal length from being shortened due to the influence of the glass material used in other lens groups. Temperature compensation can be performed.

In the image reading lens of the present invention, it is preferable that the seven lenses are all glass lenses, and the glass material of the glass lens does not contain lead, arsenic, and similar harmful substances.
All lenses are made of optical glass that is chemically stable and does not contain harmful substances such as lead and arsenic, so that materials can be recycled, and there is no water pollution caused by waste liquid during processing. The reading lens can be obtained.

Hereinafter, various aberrations and specific numerical data of the image reading lens according to the embodiment of the present invention will be described. The meanings of the symbols in each embodiment are as follows.
f: Composite focal length of e-line in the entire system FNo: F number m: Reduction ratio ω: Half angle of view Y: Object height nd: Refractive index of d line νd: Abbe number of d line ne: Refractive index of e line

[First Embodiment (Example 1)]
FIG. 2 shows a configuration diagram of a lens according to the first embodiment of the present invention. The lens configuration table is shown below.

FIG. 3 shows aberration diagrams in the lens configuration shown in FIG.
In the aberration diagrams, the e-line indicates 546.07 nm, the g-line indicates 436.83 nm, the C-line indicates 656.27 nm, and the F-line indicates 486.13 nm. In the spherical aberration diagram, the wavy line represents the sine condition, and in the astigmatism diagram, the solid line represents the sagittal ray, and the dotted line represents the meridional ray. The same applies to aberration diagrams of other embodiments (examples) described below.

[Second Embodiment (Example 2)]
FIG. 4 shows a configuration diagram of a lens according to the second embodiment of the present invention. The lens configuration table is shown below.

  FIG. 5 shows aberration diagrams in the lens configuration shown in FIG.

[Third Embodiment (Example 3)]
FIG. 6 shows a configuration diagram of a lens according to the third embodiment of the present invention. The lens configuration table is shown below.

  FIG. 7 shows aberration diagrams in the lens configuration shown in FIG.

[Fourth Embodiment (Example 4)]
FIG. 8 shows a configuration diagram of a lens according to the fourth embodiment of the present invention. The lens configuration table is shown below.

  FIG. 9 shows aberration diagrams of the lens configuration shown in FIG.

[Fifth Embodiment (Example 5)]
FIG. 10 is a structural diagram of a lens according to the fifth embodiment of the present invention. The lens configuration table is shown below.

  FIG. 11 shows aberration diagrams in the lens configuration shown in FIG.

[Sixth Embodiment (Example 6)]
FIG. 12 shows a configuration diagram of a lens according to the sixth embodiment of the present invention. The lens configuration table is shown below.

  FIG. 13 shows aberration diagrams in the lens configuration shown in FIG.

[Seventh Embodiment (Example 7)]
FIG. 14 shows a configuration diagram of a lens according to the seventh embodiment of the present invention. The lens configuration table is shown below.

  FIG. 15 shows aberration diagrams in the lens configuration shown in FIG.

[Eighth Embodiment (Example 8)]
FIG. 16 shows a configuration diagram of a lens according to the eighth embodiment of the present invention. The lens configuration table is shown below.

  FIG. 17 shows aberration diagrams in the lens configuration shown in FIG.

[Ninth Embodiment (Example 9)]
FIG. 18 shows a configuration diagram of a lens according to the ninth embodiment of the present invention. The lens configuration table is shown below.

  FIG. 19 shows aberration diagrams in the lens configuration shown in FIG.

[Tenth Embodiment (Example 10)]
FIG. 20 shows a configuration diagram of a lens according to the tenth embodiment of the present invention. The lens configuration table is shown below.

  FIG. 21 shows aberration diagrams in the lens configuration shown in FIG.

[Eleventh Embodiment (Example 11)]
FIG. 22 shows a configuration diagram of a lens according to the eleventh embodiment of the present invention. The lens configuration table is shown below.

  FIG. 23 shows aberration diagrams in the lens configuration shown in FIG.

[Twelfth Embodiment (Example 12)]
FIG. 24 shows a lens block diagram according to the twelfth embodiment of the present invention. The lens configuration table is shown below.

  FIG. 25 shows aberration diagrams in the lens configuration shown in FIG.

  The values of conditional expressions in the above-described embodiments (examples) are shown below.

In the image reading lens of the present invention, it is preferable that at least one of the lenses has a non-circular outer shape.
FIG. 26 shows an example of an image reading lens in which the sixth lens L6 of the sixth group G6 has a non-circular outer shape. From the object side, a first group G1 including a negative meniscus first lens L1 having a convex surface facing the object side, a second group G2 including a positive meniscus second lens L2 having a convex surface facing the object side, object side A third lens unit G3 composed of a negative meniscus third lens L3 with a concave surface facing to the fourth lens L4, a biconvex positive lens, and a fifth lens L5, which is a negative meniscus lens with a convex surface facing the image side. A fourth group G4 that is cemented, a fifth group G5 that is composed of a sixth lens L6 that has a positive refractive power, and a sixth group G6 that is composed of a seventh lens L7 that has a negative refractive power, are not shown. However, it has a stop between the third group G3 and the fourth group G4.

In the sixth group G6, the light beam height tends to be high in the image height direction and the lens diameter tends to be large, but in the direction orthogonal to the photoelectric conversion element array of the CCD line sensor, the luminous flux is comparable to that of other lenses. It is only necessary to have a size that passes through. Therefore, as shown in FIG. 26, it is possible to cut off the top and bottom to form a non-circular lens. By using such a lens, it is possible to reduce the size of the image reading apparatus in the height direction.
In the example of FIG. 26, only the seventh lens L7 of the sixth group G6 has a non-circular outer shape, but the other lens groups similarly have a non-circular outer shape by eliminating the outside of the light beam effective range. It is possible.

[Image reading device]
An image reading apparatus according to the present invention includes: an illumination system that illuminates a document placed on a document placement surface; and an imaging lens that forms image information of the document illuminated by the illumination system on a line-shaped image sensor. The image reading lens of the present invention is used as the imaging lens.
The image reading apparatus of the present invention further includes an image reading unit that includes at least one mirror, and the illumination system, the image reading lens, the imaging element, and the mirror are integrally held. The image information of the original can be read by scanning the reading unit.
FIG. 27 shows an example of the image reading apparatus of the present invention.

As shown in FIG. 27, a document 32 from which a document image is to be read is placed on a top surface of a document placement glass 31 in a planar manner. The first traveling body 33 holds a mirror 33c whose longitudinal direction is a direction orthogonal to the drawing and whose mirror surface is inclined by 45 degrees with respect to the document placement surface of the document placement glass 31. Move at a constant speed: V to the position indicated by '.
The first traveling body 33 also holds a fluorescent lamp 33a and a reflecting mirror 33b that are long in the direction orthogonal to the drawing as illumination means. The fluorescent lamp 33 a emits light when the first traveling body 33 is displaced to the right in the drawing, and illuminates the document 32 on the document placement glass 31. Accordingly, the original 32 is illuminated and scanned while the first traveling body 33 is displaced to the position indicated by reference numeral 33 ′.

  As the fluorescent lamp 33a, a halogen lamp, a xenon lamp, a tube lamp such as a cold cathode tube, a line source using a point light source such as an LED, or a line using a light guide that converts the point light source into a line light source. A surface light source represented by organic EL can be used.

The second traveling body 34 holds a pair of mirrors 34a and 34b that are long in the direction orthogonal to the drawing and whose mirror surfaces are inclined perpendicularly to each other, and are denoted by reference numeral 34 'in synchronization with the displacement of the first traveling body 33. Displace at a constant speed: V / 2 to the position.
When the document 32 is illuminated and scanned, the reflected light from the illuminated portion of the document 32 is reflected by the mirror 33c of the first traveling body 33, and sequentially reflected by the mirrors 34a and 34b of the second traveling body 34, thereby forming an imaging light beam. Is incident on the image reading lens 35. At this time, since the speed ratio between the first traveling body 33 and the second traveling body 34 is 2: 1, the optical path length from the original illumination portion to the image reading lens 35 is kept constant.

  The imaging light beam incident on the image reading lens 35 forms a reduced image of the original 32 on the light receiving surface of the image sensor 36 by the imaging action of the image reading lens 35. The image sensor 36 is a CCD line sensor, and minute photoelectric conversion units are closely arranged in a direction orthogonal to the drawing, and outputs an original image as an electric signal in pixel units as the original 32 is illuminated and scanned. This electrical signal undergoes signal processing such as A / D conversion to become an image signal, and is stored in a memory (not shown) as necessary. The image reading lens 35 can be downsized by using the image reading lens of the present invention.

  The image sensor 36 can color-separate the formed image into three colors (red, green, and blue) to read color information, and synthesizes the electrical signal converted by each photoelectric conversion unit to produce a color document. Can be read.

FIG. 28 shows another example of the image reading apparatus of the present invention.
Reference numeral 41 denotes a document placing glass, reference numeral 43 denotes an image reading unit, reference numeral 44 denotes an image reading lens, and reference numeral 45 denotes an image sensor.
A document 42 from which a document image is to be read is placed in a planar manner on the upper surface of the document placement glass 41. The image reading unit 43 holds mirrors 43e, 43f, and 43g that are arranged with the direction perpendicular to the drawing as the longitudinal direction and the mirror surface inclined with respect to the document placement surface of the document placement glass 41. In FIG. It moves at a constant speed: V from the position indicated by reference numeral 43 to the position indicated by reference numeral 43 '.

  The image reading unit 43 also holds fluorescent lamps 43a and 43c and reflecting mirrors 43b and 43d that are long in the direction orthogonal to the drawing as illumination means. The fluorescent lamps 43 a and 43 c emit light when the image reading unit 43 is displaced to the right in FIG. 9 and illuminate the document 42 on the document placement glass 41. Accordingly, the original 42 is illuminated and scanned while the image reading unit 43 is displaced to the position indicated by reference numeral 43 '.

  When the document 42 is illuminated and scanned, the reflected light from the illuminated portion of the document 42 is sequentially reflected by the mirrors 43e, 43f, and 43g, and enters the image reading lens 44 as an imaging light beam. At this time, since all the mirrors are integrally held by the image reading unit 43, the optical path length from the original illuminated portion to the image reading lens 44 is constant during the illumination scanning of the original 42.

  The imaging light beam incident on the image reading lens 44 reduces and forms an image of the document 42 on the light receiving surface of the image sensor 45 by the imaging action of the image reading lens. Thereafter, the document information can be read after being converted into an electric signal by a method similar to the example of the image reading apparatus shown in FIG.

[Image forming apparatus]
The configuration of an example of the image forming apparatus of the present invention is shown in FIG.
This image forming apparatus has an image reading apparatus 200 positioned at the upper part of the apparatus and an image forming unit 100 positioned at the lower part thereof. The portion of the image reading apparatus 200 is the same as that described with reference to FIG. 27, and the same reference numerals as those in FIG.

  An image signal output from a line sensor (imaging device) 36, which is a three-line CCD line sensor in the document reading apparatus 200, is sent to the signal processing unit 120 and processed by the signal processing unit 120 to generate a “writing signal (yellow). -Signal for writing each color of magenta, cyan, and 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 signal for writing 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. ing.

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 S 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 S is detachable from the main body of the image forming apparatus. When the cassette 118 is mounted as shown in the drawing, the uppermost sheet of the stored transfer paper S is fed by the paper feed roller 122. The leading edge of the fed transfer sheet S is caught by the registration roller pair 119.
The registration roller pair 119 feeds the transfer sheet S 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 S 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 sheet S against the color image during transfer.

  The transfer sheet S on 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.

  The image forming apparatus according to the present invention 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 perform monochrome image formation”.

L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens L5 5th lens L6 6th lens L7 7th lens CG1 Contact glass CG2 CCD cover glass

Japanese Patent Laying-Open No. 2005-266771

Claims (8)

In order from the object side, a first lens unit having a meniscus first lens having a negative refractive power with a convex surface facing the object side, and a meniscus second lens having a positive refractive power with a convex surface facing the object side. A second lens unit, a third lens unit composed of a third lens having a meniscus shape having negative refractive power with a concave surface facing the object side, and a fourth lens having convex surfaces on both sides and a fifth lens having negative power. A fourth group consisting of a sixth lens having a positive refractive power and a sixth group consisting of a seventh lens having a negative refractive power, and between the third group and the fourth group. An image reading lens having a six-group, seven-element configuration having a diaphragm at the above, satisfying the following conditional expressions (1) to (3).
(1) 0.7 <d / f <1.0
(2) 0.5 <−f ₆ /f<1.6
(3) 1.8 <(f ₂ + f ₅ ) / f <5.2
However,
d: Thickness of the entire image reading lens system f: Focal length of the entire image reading lens system f ₂ : Focal length of the second group f ₅ : Focal length of the fifth group f ₆ : Focal length of the sixth group The image reading lens according to claim 1, wherein the following conditional expressions (4) and (5) are satisfied.
(4) 0.6 <d _A /d<0.8
(5) 2.7 <−f _B / f _C <4.6
However,
d _A : Sum of thicknesses from the fourth group to the sixth group f _B : Composite focal length from the first group to the third group f _C : Composite focal length from the fourth group to the sixth group The image reading lens according to claim 1 or 2, wherein the second lens satisfies the following conditional expressions (6) and (7).
(6) 0.9 <f ₂ /f<2.3
(7) -7 <dn / dt (L2) <0
However,
dn / dt (L2): a refractive index temperature coefficient of the second lens.   The seven lenses are all glass lenses, and the glass material of the glass lenses does not contain lead, arsenic, and similar harmful substances. Image reading lens.   The image reading lens according to claim 1, wherein at least one of the lenses has a non-circular outer shape.   An illumination system that illuminates a document placed on a document placement surface, and an imaging lens that forms an image of image information of the document illuminated by the illumination system on a line-shaped image sensor, and is claimed as the imaging lens An image reading apparatus using the image reading lens according to any one of Items 1 to 5.   An image reading unit having at least one mirror, wherein the illumination system, the image reading lens, the image sensor, and the mirror are held together; and scanning the image reading unit to image the original The image reading apparatus according to claim 6, wherein information is read.   8. An image forming apparatus for forming an image by writing an image corresponding to an image signal, wherein the image reading apparatus according to claim 6 or 7 is used as means for reading image information of a document to convert it into an image signal. An image forming apparatus.

Images