JP6048094B2 - Image reading lens, image reading apparatus, and image forming apparatus - Google Patents

Description

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

  In an image reading apparatus such as a facsimile or a digital copying machine, image information to be read is reduced by an imaging lens and imaged on a solid-state imaging device such as a CCD (Charge Coupled Device) to convert the image information into a signal. . As an optical system for reading image information of a document in color in the image reading apparatus, so-called three lines in which light receiving elements having, for example, red, green, and blue filters as image pickup elements are arranged in three rows on one chip. There is an optical system that uses a CCD and forms a document image on this light receiving surface to separate the three primary colors and convert color image information into a signal.

  As an image reading lens used as an imaging means for fixed focus in an image reading device, an image reading lens called a Gauss type having 6 elements in 4 groups is generally used, but a telephoto type with a reduced number of lenses. In recent years, however, they are increasingly used for the purpose of downsizing and cost reduction.

As a telephoto type image reading lens, an image reading lens having four elements in four groups of a positive lens, a negative lens, a positive lens, and a negative lens is generally used (for example, see Patent Documents 1 and 2).
As such an image reading lens, a wide-angle lens having a half angle of view of 30 ° or more described in Patent Document 1 to a lens having a half angle of view of approximately 18 ° described in Patent Document 2 is known.

  However, the above-mentioned image reading lens having four groups and four elements has realized a reduction in cost in terms of reduction in the number of sheets, but when trying to obtain the same performance as a six-element Gauss type image reading lens. There is an aspect that the effect of miniaturization cannot be obtained because approximately the same size is required.

In view of this, there has been proposed a configuration in which the performance equivalent to that of an image reading lens having a six-lens configuration is obtained with a configuration of four or less (see, for example, Patent Documents 3 and 4).
According to the image reading lenses of Patent Documents 3 and 4, the final negative lens is made aspherical to achieve miniaturization and high resolution, and the negative lens is made of a plastic material. It is said that both of these can be achieved.

  On the other hand, in a general image reading apparatus, it is known that the temperature in the image reading apparatus rises due to heat generated when a fluorescent lamp such as a xenon lamp emits light or heat generated by driving an image pickup device such as a line CCD. It has been. When the temperature in the image reading apparatus rises, the holding member that presses and holds the image reading lens is thermally expanded, and the image forming surface of the image reading lens is displaced from the light receiving surface of the image sensor, resulting in a decrease in resolution. There's a problem. In addition, since the plastic lens disposed in the vicinity of the image sensor is strongly affected by the heat generated by the image sensor, there is a possibility of further deterioration in performance.

  In order to solve this problem, it has been proposed to compensate for the deviation of the imaging plane by suppressing the change in the focal length extension when the temperature rises (see, for example, Patent Document 5). Patent Document 5 describes that the influence on the performance change due to the temperature fluctuation is compensated by canceling the change in the focal length of the positive lens and the negative lens.

  However, in the plastic lens, compensation can be performed by such means when the positive lens and the negative lens are arranged close to each other. When the positive lens and the negative lens are arranged apart from each other, the incident angle to the next plastic lens changes because the angle from the first plastic lens changes between normal and when the temperature rises. In particular, the ambient light has a problem that it is impossible to compensate for a change in imaging performance when the temperature rises.

  In view of the above problems, an object of the present invention is to provide an image reading lens that can obtain good image performance even when the temperature environment changes and can be downsized.

In order to solve the above problems, an image reading lens according to the present invention includes, in order from the object side to the image side, a first group including one or more lenses, and one plastic having negative power. A second group constituted by a lens, and a second group holding member that holds the plastic lens of the second group and defines an air gap between the first group and the second group, The focal length of the second group of plastic lenses is fB, the air gap between the first group and the second group is L12, the distance between the second group of plastic lenses and the image plane is LB , When the linear expansion coefficient of the group holding member is αB and the amount of change in the focal length when the temperature of the second group rises is ΔfB , the following conditional expression (1) 0.2 <−L12 / fB <1.0
(2) 0.1 <LB / L12 <0.3
(3) 0.02 <−L12 × αB / ΔfB <0.10
The image reading lens is configured to satisfy any of the above.

  According to the image reading lens of the present invention, it is possible to provide an image reading lens that can obtain a good image performance even when the temperature environment changes and can be downsized.

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 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 block diagram which shows the principal part of one Embodiment of an image reading apparatus. It is a schematic block diagram which shows the principal part of one Embodiment of an image reading apparatus. 1 is a schematic configuration diagram for explaining 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.

[First Embodiment (Example 1)]
An example of the configuration of the image reading lens according to the present invention is shown in FIG.
The image reading lens includes, in order from the object side to the image side, a first group G1 including one or more lenses (three lenses L1 to L3 in the present embodiment shown in FIG. 1), and a negative group And a second group G2 including a single plastic lens L4 having power.
The focal length of the plastic lens L4 of the second group G2 is fB, the air gap between the first group G1 and the second group G2 is L12, and the distance between the plastic lens L4 of the second group G2 and the image plane I is When LB, the following conditional expression (1) 0.2 <−L12 / fB <1.0
(2) 0.1 <LB / L12 <0.3
It is comprised so that all may be satisfied.

The meanings of the symbols in FIG. 1 are as follows.
ri (i = 1 to 9): radius of curvature of the i-th lens surface counted from the object side di (i = 1 to 8): i-th surface interval counted from the object side rc1: curvature of the contact glass on the object side 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

  In FIG. 1, the surface distance d7 between the lens L3 disposed closest to the image side of the lenses constituting the first group G1 and the plastic lens L4 of the second group G2 is the first group G1 and the second group G2. This corresponds to the air gap L12 between the group G2.

The conditional expression (1) represents the range of the ratio of the air gap L12 between the first group G1 and the second group G2 with respect to the focal length fB of the plastic lens L4 of the second group G2.
In general, the plastic lens has a greater change in focal length when the temperature changes than a glass lens. Therefore, if the air distance L12 is too short, the value of L12 does not change much, whereas only the value of fB changes greatly. Will do. For example, as the temperature rises, the second group of plastic lenses having negative power changes in the direction in which the focal length fB extends, so that the image formation position shifts in the direction in which the image formation position extends, resulting in defocus and good image formation. It can no longer be obtained.

  Conditional expression (1) is a conditional expression necessary for reducing the change amount of the focal length fB of the second group G2 constituted by one plastic lens to the same extent as the change amount of the glass lens. By satisfying this conditional expression (1), it is possible to achieve a satisfactory temperature with only one plastic lens without suppressing a change in the focal length of the image reading lens using a plurality of plastic lenses in the second lens group G2. It is possible to suppress the occurrence of focus shift due to the change.

  That is, even if the value of -L12 / fB exceeds the lower limit of 0.2 or exceeds the upper limit of 1.0, only one plastic lens constituting the second group can be used to degrade image formation due to temperature changes. Is difficult to suppress.

Conditional expression (2) represents the range of the ratio of the distance LB between the second group and the image plane I to the air distance L12 between the first group G1 and the second group G2.
When the value of LB / L12 is small, the magnification of the second group G2 is small because the elongation of the interval LB is small with respect to the elongation of the air interval L12. On the other hand, when the value of LB / L12 is large, the magnification formed by the second group G2 is large.

  As described above, both the value of the air gap L12 and the value of the focal length fB of the second group G2 change depending on the temperature and cause a focus shift. Furthermore, since a change in the magnification of the second group G2 also occurs, conditional expression (2) defines the conditions necessary to suppress these.

  Conditional expression (2) indicates that the second group G2 is arranged on the image plane side with respect to the first group G1, and with this arrangement, the lens surface of the second group G2 is arranged. The influence of surface accuracy on imaging performance can be minimized. That is, it is difficult to obtain the processing accuracy of the lens surface, and even a plastic lens having a large surface shape change due to a temperature change can reduce the influence due to the shape and obtain a good image.

  Furthermore, by arranging the second group G2 having negative power near the image plane I, a retrofocus type in which the rear principal point is arranged in front of the lens can be obtained, and the distance from the lens front end to the imaging surface Can be made shorter than the conventional Gaussian type, which is effective in realizing a reduction in size of the first group G1 composed of a plurality of lenses.

  That is, even if the value of LB / L12 exceeds the lower limit of 0.1 or the upper limit of 0.3, the influence of the temperature change on the imaging performance is reduced by one plastic lens, and the first It becomes difficult to reduce the size of the first group G1.

The air gap L12 between the first group G1 and the second group G2 is defined by fixing the position of the plastic lens of the second group G2 by at least a holding member that holds the plastic lens of the second group G2. The
The image reading lens of the present embodiment includes a second group holding member that holds the plastic lens of the second group G2 and defines an air gap L12 between the first group G1 and the second group G2.
When the linear expansion coefficient of the second group holding member is αB and the change amount of the focal length when the temperature of the second group is increased is ΔfB, the following conditional expression (3) 0.02 <−L12 × αB / ΔfB < 0.10
Satisfied.

Conditional expression (3) indicates that the change amount L12 × αB of the air gap L12 between the first group G1 and the second group G2 due to the thermal expansion of the material of the second group holding member that is actually used, and the first change due to the temperature change. The amount of change ΔfB of the focal length fB of the second group G2 is regulated.
For example, as a material of the second group holding member, conditional expression (3) is expressed with respect to an amount that the air gap L12 between the first group G1 and the second group G2 and the focal length fB of the second group G2 extend due to temperature change. By selecting a material having a satisfactory linear expansion coefficient αB, it is possible to correct the shift of the imaging position. Further, based on the linear expansion coefficient αB of the material of the second group holding member used and the amount by which the focal length fB of the second group G2 extends due to the temperature change, the air interval L12 that satisfies the conditional expression (3) is defined. Thus, it is possible to correct the deviation of the imaging position.

Specifically, by forming the second holding member with a material having a linear expansion coefficient of 1.0 to 2.4 × 10 ⁻⁵ , it is possible to reduce the occurrence of focus deviation due to a temperature change. it can.

  Even if the value of −L12 × αB / ΔfB exceeds the lower limit value of 0.02 or exceeds the upper limit value of 0.10, it is difficult to correct the shift of the imaging position.

  The plastic lens of the second group G2 is preferably a meniscus lens arranged with the convex surface facing the image surface. By arranging the convex surface facing the image surface side, the change in the incident angle can be kept small at any image height even when the height of the light incident on the plastic lens changes during a temperature change. It becomes possible to suppress the performance deterioration at the time of temperature change.

  All of the one or more lenses constituting the first group G1 are preferably glass lenses. By configuring all the lenses of the first group G1 with glass lenses, it is possible to suppress a change in the focal length of the first group G1 due to a temperature change. As a result, in addition to the second group G2 that can suppress the deterioration of the imaging performance at the time of temperature change as described above, the influence of the temperature change can be reduced in the entire image reading lens system, and good imaging performance can be obtained. Can be obtained.

In addition, if all the lenses constituting the first group G1 are glass lenses and the second group G2 arranged away from the first group G1 is a plastic lens, the focal length of each group due to temperature change The amount of change in is about the same.
In the first group G1, compensation for temperature change is performed in the first group G1, and in the second group G2, the relationship between the distance from the first group G1 and the change in the focal length of the second group G2 is described above. By defining so as to satisfy the conditional expression, it is possible to easily control the amount of change in the focal length of the image reading lens, and it is possible to design as desired.

In the image reading lens of the present embodiment, it is preferable that the diaphragm S is disposed between the lenses constituting the first group G1.
By disposing the diaphragm S between the lenses constituting the first group G1, it is possible to obtain a small retrofocus type image reading lens in which curvature of field and distortion are satisfactorily suppressed.

The image reading lens of the present embodiment further includes a first group holding member that holds the first group G1 lens as a holding member. The first group holding member is a member different from the second group holding member, and is rotatable in the circumferential direction of a plastic lens of the second group G2 or a circle around the optical axis of the plastic lens.
The lenses constituting the first group can move together with the first holding member, and can rotate in the coaxial direction of the optical axis as described above independently of the second group G2, and also move in the optical axis direction. Is possible.

  By rotating the first group G1 independently, it is possible to change the direction of variation in the eccentricity of the lens when the lens is assembled. Therefore, it is possible to search for a direction with less eccentricity with respect to the line CCD sensor arrangement direction. Further, since the second group G2 can be rotated separately from the second group G2, the second group that is large with respect to the sensor arrangement direction of the line CCD can be adjusted without moving, and the image reading lens can be reduced in size. it can.

  By moving the first group G1 independently, adjustment of the tilt of the image plane caused by deviation from the design values of the curvature, thickness, and lens interval of the lens, and the distance from the second group G2 to the image plane I It is possible to adjust the LB by the air interval L12 between the first group G1 and the second group G2. Thereby, good imaging performance can be obtained. Of course, the adjustment amount of the air gap L12 is defined within a range that satisfies the conditional expressions (1), (2), and (3).

Furthermore, the plastic lens of the second group G2 may be configured to be held integrally with the image sensor that forms the image plane I. It is possible to adjust the distance between the second group G2 and the image sensor for focus adjustment. However, if the image sensor is accurately adjusted in the direction perpendicular to the optical axis of the second group G2, the second group G2 can be adjusted. The adjustment process of G2 and an image sensor can be omitted.
Thereby, as an adjustment process, in order to perform rotation of the 1st group G1, adjustment of air space L12 of the 1st group G1 and 2nd group G2, and adjustment of an image plane, and adjustment of a focus, in the 1st group G1 Even if this adjustment is included, only the first group needs to be adjusted, and the adjustment process can be simplified and the adjustment time can be shortened.

In the image reading lens of this embodiment, the plastic lens of the second group G2 only needs to have a size corresponding to the alignment direction of the sensors of the line CCD, and there may be no lens surface in the orthogonal direction. Absent. That is, the plastic lens of the second group G2 can be a strip-shaped lens.
Regarding the orthogonal direction of the line CCD sensor arrangement, the diameter of the first group holding member of the first group G1 determines the size thereof, and an image reading lens capable of reducing the size in the height direction is obtained.
Therefore, by using the image reading lens of the present embodiment for an image reading apparatus, it is possible to obtain an image reading apparatus that is smaller in the height direction than the conventional one, while having the same image reading quality.

Further, by using the image reading apparatus, it is possible to obtain an image forming apparatus that is similarly miniaturized in the height direction.
From the viewpoint of workability, even if the height of the image forming apparatus is the same as before without reducing the height, it is usually placed on the side of the image forming apparatus in the area caused by the shortening in the height direction. Since a post-processing mechanism (for example, a staple mechanism, a hole punch mechanism, etc.) to be performed can be accommodated, space saving can be realized as a whole.

The various aberrations and specific numerical data of the image reading lens according to this embodiment are shown below. The meanings of symbols in each embodiment (example) shown in Table 1 are as follows. The same applies to Tables 2 to 12 showing data of image reading lenses according to other embodiments.
f: Total focal length of e-line in the entire system FNo: F number m: Reduction ratio j: Surface number r: Radius of curvature of lens surface d: Surface interval ne: Refractive index of e-line of each lens material

  In the surface number indicated by “j”, C1 represents the object-side surface of the contact glass, C2 represents the image-side surface of the contact glass, and numbers 1 to 13 represent the respective surfaces counted from the object side of the imaging lens ( C3 represents the object side surface of the CCD cover glass, and C4 represents the image side surface of the CCD cover glass. “*” Represents an aspherical surface.

The aspherical surface is expressed by the following formula.
X: distance from the tangent plane at the aspherical vertex of the aspheric surface at height Y from the optical axis Y: distance from the optical axis in the direction orthogonal to the optical axis (height from the optical axis)
k: conic coefficient Ai: an aspheric coefficient for the order i.

The aberration diagram of this embodiment is shown in FIG. In the aberration diagram of FIG. 2, “e” is e-line (546.07 nm), “g” is g-line (436.83 nm), “c” is C-line (656.27 nm), and “F” is 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 broken line indicates the meridional ray.
The same applies to the aberration diagrams shown in FIGS. 4, 6, 8, 10, and 12 according to other embodiments.

  Table 1 shows specific numerical data of the constituent lenses.

  Table 2 shows the aspherical conical constant k and the aspherical coefficients (A4, A6, A8, A10) of the first embodiment.

[Second Embodiment (Example 2)]
The lens configuration of the second embodiment is shown in FIG. 3, and the aberration diagram is shown in FIG.
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.

[Third Embodiment (Example 3)]
FIG. 5 shows the lens configuration of the third embodiment, and FIG. 6 shows aberration diagrams.
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.

[Fourth Embodiment (Example 4)]
FIG. 7 shows the lens configuration of the fourth embodiment, and FIG. 8 shows aberration diagrams.
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.

[Fifth Embodiment (Example 5)]
FIG. 9 shows a lens configuration of the fifth embodiment, and FIG. 10 shows aberration diagrams.
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.

[Sixth Embodiment (Example 6)]
FIG. 11 shows the lens configuration of the sixth embodiment, and FIG. 12 shows aberration diagrams.
As shown in FIG. 11, in the image reading lens of the present embodiment, the first group G1 is composed of five lenses L1 to L5, and the second group G2 is composed of one plastic lens L6 having negative power. Is done.
Table 11 shows specific numerical data of the constituent lenses.

  Table 12 shows the aspherical conical constant K and the aspherical coefficients (A4, A6, A8, A10) of the sixth embodiment.

  Table 13 shows the calculation results of the value of −L12 / fB, the value of LB / L12, and the value of −L12 × αB / ΔfB in each example.

As shown in Table 13, in the image reading lens of any of the embodiments, the following conditional expression (1) 0.2 <−L12 / fB <1.0
(2) 0.1 <LB / L12 <0.3
(3) 0.02 <−L12 × αB / ΔfB <0.10
Satisfied.

  Further, as is apparent from the respective aberration diagrams shown in FIGS. 2, 4, 6, 8, 10, and 12, in the imaging lens of any embodiment, from the C line (656.27 nm) to g It is possible to satisfactorily correct axial chromatic aberration and satisfactorily correct aberrations in a wide range of lines (435.83 nm).

[Image reading device]
An image reading apparatus according to the present invention includes: an illumination system that illuminates a document; and a fixed-focus imaging unit that reduces and forms image information of the document illuminated by the illumination system on an image sensor. The image reading lens of the present invention is used.
The image reading unit includes a reflection optical system, and the illumination system, the image reading lens, the imaging element, and the reflection optical system are integrally held, and scans the image reading unit. Thus, the image information of the original can be read.

FIG. 13 is a cross-sectional view for explaining the image reading apparatus according to the first embodiment.
In FIG. 13, reference numeral 31 denotes a document placing glass, reference numeral 33 denotes a first traveling body, reference numeral 34 denotes a second traveling body, reference numeral 35 denotes an image reading lens (hereinafter also referred to as “imaging lens”), and reference numeral 36 denotes imaging. The element is shown.

  A document 32 from which a document image is to be read is placed flat on the upper surface of the document placement glass 31. 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 45 degrees with respect to the document placement surface of the document placement glass 31, and is denoted by reference numeral 33 in FIG. It moves at a constant speed: V from the position to the position indicated by the broken line.

  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 rightward in FIG. 13 and illuminates the document 32 on the document placement glass 31. Accordingly, the document 32 is illuminated and scanned while the first traveling body 33 is displaced to the position indicated by the broken line.

  As the fluorescent lamp, a tube lamp such as a halogen lamp, a xenon lamp, or a cold cathode tube may be used. The lamps are arranged in a line using a point light source such as an LED, or a light guide for converting the point light source into a line light source. It is also possible to use a linear light source using a body, and it is also possible to use a surface light source represented by organic EL.

  The second traveling body 34 holds a pair of mirrors 34 a and 34 b that are long in a direction orthogonal to the drawing and whose mirror surfaces are inclined perpendicularly to each other, and are moved to a position indicated by a broken line in synchronization with the displacement of the first traveling body 33. Constant speed: Displacement at V / 2.

  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 imaging lens 35. At this time, since the speed ratio of the first traveling body 33 and the second traveling body 34 is 2: 1, the optical path length from the original illumination part to the imaging lens 35 is kept constant.

  The imaging light beam incident on the imaging lens 35 forms a reduced image of the document 32 on the light receiving surface of the image sensor 36 by the imaging action of the imaging 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 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. 14 is a sectional view for explaining an image reading apparatus according to the second embodiment.
In FIG. 14, reference numeral 41 denotes a document placing glass, reference numeral 43 denotes an image reading unit, reference numeral 44 denotes an image reading lens (imaging 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 the broken line.

  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 rightward in FIG. 14 and illuminate the document 42 on the document placement glass 41. Accordingly, the document 42 is illuminated and scanned while the image reading unit 43 is displaced to the position indicated by the broken line.

  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 imaging 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 illumination portion to the imaging lens 44 is constant during the illumination scanning of the original 42.

  The imaging light beam incident on the imaging lens 44 forms a reduced image on the original 42 on the light receiving surface of the image sensor 45 by the imaging action of the imaging lens. Thereafter, the document information can be read after being converted into an electric signal by the same method as in the first embodiment of the image reading apparatus.

[Image forming apparatus]
The image forming apparatus of the present invention uses the image reading apparatus.
FIG. 15 is a sectional view for explaining the image forming apparatus of the present invention.
The image forming apparatus illustrated in FIG. 15 includes 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 part of 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 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.

Of course, it goes without saying that the image forming apparatus can be “configured to perform monochrome image formation”.
Further, in a space-saving image forming apparatus of in-body discharge type in which paper output is formed between an image reading unit and an image forming unit, an image reading device using the imaging lens can be used to obtain an image. Since the reading device becomes thinner and the space between the image forming apparatus and the image forming apparatus increases, the visibility of the output paper to the worker is enhanced, and there is an effect of facilitating the work.

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 I Image surface 35 Image reading lens 44 Image reading lens 200 Image reading device

Japanese Patent No. 3856258 Japanese Patent Application Laid-Open No. 09-101542 Japanese Patent No. 3507287 Japanese Patent No. 3939908 JP-A-5-119255

Claims (11)

In order from the object side to the image side, a first group composed of one or more lenses, a second group composed of one plastic lens having negative power, and the second group of plastic lenses And a second group holding member for defining an air gap between the first group and the second group ,
The focal length of the second group of plastic lenses is fB, the air distance between the first group and the second group is L12, the distance between the second group of plastic lenses and the image plane is LB , When the linear expansion coefficient of the second group holding member is αB and the amount of change in the focal length when the temperature of the second group rises is ΔfB , the following conditional expression (1) 0.2 <−L12 / fB <1.0
(2) 0.1 <LB / L12 <0.3
(3) 0.02 <−L12 × αB / ΔfB <0.10
An image reading lens configured to satisfy any of the above. A first group holding member for holding the first group of lenses;
The first group holding member is a member different from the second group holding member, and is rotatable in a circumferential direction of a circle around the optical axis of the plastic lens of the second group or the plastic lens. The image reading lens according to claim 1 . The image reading lens according to claim 2 , wherein the lens constituting the first group is movable in the optical axis direction together with the first group holding member. The plastic lens of the second group, the image reading lens according to any one of claims 1 to 3, characterized in that the arranged meniscus lens with its convex surface facing the image plane. The image reading lens according to any one of claims 1 to 4 , wherein each of the one or more lenses constituting the first group is a glass lens. In order from the object side toward the image side, a first group including one or more lenses, and a second group including one plastic lens having negative power,
One or more lenses constituting the first group are all glass lenses,
The focal length of the second group of plastic lenses is fB, the air gap between the first group and the second group is L12, and the distance between the second group of plastic lenses and the image plane is LB. When the following conditional expression
(1) 0.2 <−L12 / fB <1.0
(2) 0.1 <LB / L12 <0.3
An image reading lens configured to satisfy any of the above. The image reading lens according to claim 6, wherein the second group of plastic lenses is a meniscus lens disposed with a convex surface facing the image surface. Image reading lens according to any one of claims 1 to 7, characterized in that the stop is arranged between the lenses constituting the first group. The plastic lens of the second group, the image reading lens according to any one of claims 1 to 8, characterized in that it is held together with the imaging elements constituting the image plane. Image reading apparatus characterized by using the image reading lens according to any one of claims 1 to 9. An image forming apparatus using the image reading apparatus according to claim 10 .