JP2014035396A - Image reading lens, image reading device, and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reading lens configured to properly correct color aberration even when imaging magnification is small (0.1-0.2, for example), and to prevent deterioration in imaging performance due to changes of temperature environment.SOLUTION: An image reading lens includes, sequentially from an object side, a first lens L1 which is a positive meniscus lens with its convex surface facing the object side, a second lens L2 which is a negative lens with its concave surface facing an image side, a third lens L3 having both convex surfaces, a fourth lens L4 which is a negative lens with its concave surface facing the object side, and a fifth lens L5 which is a positive meniscus lens with its convex surface facing the image side. The image reading lens has a diaphragm S. When an average of deviation from a standard line of a partial dispersion ratio θgFi of the i-th lens from the object side is δθgFi, and a refractive index temperature coefficient is βi, the positive lens arranged opposite the third lens L3 with respect to the diaphragm S satisfies the following expressions (1) and (2):(1) 0.005<δθgFi<0.05, and (2)βi<0.

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.

  An image reading apparatus (image reading unit, image scanner, etc.) of a facsimile or a digital copying machine reduces document information to be read by an image reading lens and forms an image on an image pickup device such as a CCD (Charge Coupled Device). Document information is converted into a signal. In order to read document information in color, for example, a so-called three-line CCD in which imaging elements having red, green, and blue filters are arranged in three rows on one substrate is used. The three-line CCD image-forms document information on the image sensor surface to separate the colors into three primary colors and convert the color document information into a signal.

  In general, an image reading lens used in such an optical system is required to have high contrast in a high spatial frequency region on an image pickup element that is an image plane, and has an aperture efficiency close to 100% up to the periphery of the angle of view. It is requested. In addition, in order to read a color original satisfactorily, it is necessary to match the imaging positions of red, green, and blue colors on the image plane in the optical axis direction, and it is necessary to correct chromatic aberration correction of each color satisfactorily. .

  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, an image reading lens having a small size and a small number of lenses is required.

  Conventionally, a Gaussian reading lens has been used as an image reading lens that can provide high image quality. The Gaussian type reading lens can correct field curvature well up to a half field angle of about 20 ° and can suppress coma flare even with a relatively large aperture. Since the lens is configured, the lens diameter increases, and it is difficult to reduce the size and cost of an image reading apparatus using the lens.

  On the other hand, a lens having a five-group five-lens configuration in which the number of lenses is five has been proposed (see, for example, Patent Documents 1 to 3). The copying lens described in Patent Document 1 is a five-group five-lens lens having a front group and a rear group, each consisting of two symmetric lenses centered on a biconvex lens disposed in the center of the lens, etc. The configuration of a completely symmetric system is described on the assumption that it is used in a double system. On the other hand, as for the copying machine lens described in Patent Document 2 and the imaging lens described in Patent Document 3, an asymmetric lens has been proposed on the assumption of zooming.

  In recent years, with a reduction in the pixel size, use at a small imaging magnification is required. However, the lens described in Patent Document 1 has a problem in that, when it is intended to be used in a reduction system, each aberration increases and good imaging cannot be obtained. Furthermore, when used in a reduction system, the image-side depth becomes narrower in proportion to the square of the magnification, so in the case of the glass materials mentioned in the examples, it is possible to suppress degradation in imaging performance due to changes in the temperature environment. There is also a problem that it cannot be done.

  On the other hand, in the lenses described in Patent Document 2 and Patent Document 3, the assumed magnification is between 0.5 and 2 times, and the magnification in the reduction system of 0.1 to 0.2 times is It is not assumed. In addition, there is no description on how to cope with degradation of imaging performance due to changes in temperature environment.

  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 is used with a small imaging magnification (for example, 0.1 to 0.2 times). Even in such a case, an object is to provide an image reading lens that can satisfactorily correct chromatic aberration and can suppress deterioration in imaging performance due to a change in temperature environment.

In order to solve the above-described problem, an image reading lens according to the present invention includes:
In order from the object side to the image side, a first lens that is a positive meniscus lens with a convex surface facing the object side, a second lens that is a negative lens with a concave surface facing the image side, and a third lens that is a biconvex lens A lens, a fourth lens that is a negative lens with the concave surface facing the object side, a fifth lens that is a positive meniscus lens with the convex surface facing the image side, between the second lens and the third lens, and A diaphragm is provided between the third lens and the fourth lens, the partial dispersion ratio θgF, the c-line refractive index nc, the F-line refractive index nF, and the g-line refractive index ng Is defined by θgF = (ng−nF) / (nF−nc), and a line segment connecting the coordinate points of the glass materials C2 and F2 on the coordinate plane having the partial dispersion ratio and the Abbe number as two orthogonal axes is defined. The part of the i-th lens from the object side to the image side as the standard line When the average deviation of the dispersion ratio θgFi from the standard line is δθgFi and the refractive index temperature coefficient of the i-th lens from the object side to the image side is βi, the aperture is opposite to the third lens. The positive lens disposed on the side satisfies the following conditional expressions (1) and (2).
(1) 0.005 <δθgFi <0.05
(2) βi <0

  According to the image reading lens according to the present invention, the image reading lens can be used at a small imaging magnification (for example, 0.1 to 0.2 times) in response to various demands required for the image reading lens in spite of a small number of lenses. In this case, it is possible to provide an image reading lens that can satisfactorily correct chromatic aberration and can suppress deterioration in imaging performance due to a change in temperature environment.

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. 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 block diagram for demonstrating one embodiment of an image reading apparatus. It is a schematic block diagram for demonstrating one embodiment of an image reading apparatus. 1 is a schematic configuration diagram illustrating 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 is shown in FIG.
As shown in FIG. 1, the image reading lens is a first lens L1 that is a positive meniscus lens having a convex surface directed toward the object side in order from the object side to the image side, and a negative lens having a concave surface directed toward the image side. A second lens L2, a third lens L3 that is a biconvex lens, a fourth lens L4 that is a negative lens with the concave surface facing the object side, and a fifth lens L5 that is a positive meniscus lens with the convex surface facing the image side. The diaphragm S is configured between the second lens L2 and the third lens L3. The diaphragm S may be disposed between the third lens L3 and the fourth lens L4.
A contact glass CG1 is disposed on the object side of the first lens L1, and a CCD cover glass CG2 is disposed on the image side of the fifth lens L5.

In addition, the meaning of the code | symbol in FIG. 1 is as follows.
ri (i = 1 to 12): radius of curvature of the i-th lens surface counted from the object side rc1: radius of curvature of the contact glass on the object side rc2: radius of curvature of the contact glass on the image side rc3: object side of the CCD cover glass Rc4: radius of curvature on the image side of the CCD cover glass di (i = 1 to 11): i-th surface distance counted from the object side dc1: thickness of the contact glass dc3: thickness of the CCD cover glass ndi ( i = 1 to 5): refractive index of d-line of i-th lens counted from object side νdi (i = 1 to 5): Abbe number of i-th lens counted from object side Ndc1: d-line of contact glass Νdc1: CCD cover glass Abbe number Ndc2: d-line refractive index of contact glass νdc2: CCD cover glass Abbe number

The image reading lens has θgF = (ng−nF) / (nF−) where the partial dispersion ratio θgF is nc, the refractive index of the c-line is nc, the refractive index of the F-line is nF, and the refractive index of the g-line is ng. nc), and a line segment connecting the coordinate points of the glass materials C2 and F2 on the coordinate plane having the partial dispersion ratio and the Abbe number as two orthogonal axes is defined as a standard line, and the i-th component from the object side to the image side. When the average deviation of the partial dispersion ratio θgFi of the lens from the standard line is δθgFi and the refractive index temperature coefficient of the i-th lens from the object side to the image side is βi,
A positive lens disposed on the opposite side of the stop S from the third lens L3 satisfies the following conditional expressions (1) and (2).
(1) 0.005 <δθgFi <0.05
(2) βi <0

  Here, “a positive lens disposed on the opposite side of the third lens L3 with respect to the diaphragm S” is an aspect in which the diaphragm S is disposed between the second lens L2 and the third lens L3 (third lens). In the aspect in which L3 is disposed on the image side of the diaphragm S, the first lens L1, and the aspect in which the diaphragm S is disposed between the third lens L3 and the fourth lens L4 (the third lens L3 is the diaphragm). In the embodiment in which the lens is disposed closer to the object than S, the fifth lens L5 is used.

  The glass material C2 and the glass material F2 are names of glass materials manufactured by HOYA Corporation, and their optical properties are as shown in Table 1 below.

The partial dispersion ratio θgFi of the i-th lens from the object side to the image side can be expressed by the following formula based on the partial dispersion ratio θgF of the glass material C2 and the glass material F2.
θgFi = a × νd + b + δθgFi
Here, a and b are the slope and intercept of a straight line connecting the partial dispersion ratio θgF of the glass material C2 and the glass material F2 on the orthogonal coordinate plane with the partial dispersion ratio as the vertical axis and the Abbe number as the horizontal axis.

  The conditional expression (1) is a condition necessary for obtaining good imaging performance, and is a positive lens (the first lens L1 or the fifth lens) disposed on the opposite side of the third lens L3 with respect to the stop S. When the average δθgFi of the deviation from the standard line of the partial dispersion ratio θgFi of L5) is below the lower limit (0.005), the axial chromatic aberration is corrected well in the visible light region (430 nm to 650 nm) to be used. When red, green, and blue signals are read by an image sensor (for example, a three-line CCD), the best image plane for each color shifts, resulting in a difference in imaging performance such as resolving power. On the other hand, when the value exceeds the upper limit (0.05), the chromatic aberration of magnification in the visible light region to be used increases, resulting in a difference in magnification for each color and a defect such as color shift.

The conditional expression (2) defines the temperature dependence of the refractive index of the glass material of the positive lens (the first lens L1 or the fifth lens L5) disposed on the opposite side of the third lens L3 with respect to the stop S. It is.
The temperature characteristic of the glass material is expressed by a linear expansion coefficient and a temperature coefficient of refractive index. Since most glass materials have a positive linear expansion coefficient, the shape of the lens increases proportionally as the temperature rises. If the lens is a positive lens, the focal length becomes longer and the lens becomes shorter for a negative lens. Further, since there are many glass materials having a positive refractive index temperature coefficient of the glass material, the refractive index increases as the temperature rises, so that the focal length is shortened in the positive lens and is long in the negative lens. Therefore, in the positive lens, even if the focal length increases due to the change due to the linear expansion coefficient, the focal length may be shortened when the temperature rises if the temperature coefficient of the refractive index is also positive.

As a holding member for an optical member such as a general lens barrel, lens, or CCD, a metal or resin member is used. For this reason, the linear expansion coefficient of a holding member expands similarly to a glass lens with a temperature rise. In other words, the distance between the lens and the image sensor increases as the temperature rises. However, as described above, the focal length of the lens also increases, so that the distance from the lens to the best image plane increases and the imaging performance is maintained. I can do it.
When the value of the refractive index temperature coefficient βi of the positive lens satisfies the conditional expression (2), the positive lens exhibits the effect of extending the focal length of the entire lens when the temperature rises, and the deterioration of the imaging performance is suppressed. it can.

  The positive lens (the first lens L1 or the fifth lens L5) disposed on the opposite side of the third lens L3 with respect to the stop S is configured to satisfy the conditional expressions (1) and (2). It is possible to provide an image reading lens that can satisfactorily correct chromatic aberration as a lens and is resistant to temperature environment fluctuations.

In the image reading lens, the radius of curvature of the object-side lens surface of the i-th lens from the object side to the image side is rip, the radius of curvature of the image-side lens surface is iq, and the entire system e-line The third lens L3 satisfies the following conditional expressions (3) and (4), where f is the combined focal length and fi is the combined focal length of the e-line of the i-th lens from the object side to the image side.
(3) rip + riq <0
(4) 0.2f <fi <0.5f

  Conditional expression (3) defines the coma aberration of the third lens L3. In the image reading lens, the third lens L3 has an effect of correcting coma. In a reduction optical system with an imaging magnification of about 0.1 to 0.2 times, the object-side lens surface shape (curvature radius r3p) of the third lens L3 is larger than the image-side lens surface shape (curvature radius r3q). If the value of r3p + r3q is less than 0, it appears as outward coma, and good imaging performance cannot be obtained.

  Conditional expression (4) defines the range of the focal length f3 of the third lens L3. When f3 is less than the lower limit (0.2f), high-order spherical aberration occurs, and the resolving power cannot be obtained, so that a good increase performance cannot be obtained. On the other hand, if f3 exceeds the upper limit (1.0f), the curvature of field at the periphery changes greatly, and the depth in the optical axis direction at which the resolving power is obtained becomes shallow. There arises a problem that a margin at the time of position adjustment between the lens and the image sensor is reduced.

  When the third lens L3 is configured to satisfy the conditional expressions (3) and (4), the coma aberration of the image reading lens is effectively corrected, and good imaging performance is maintained while maintaining the best image plane balance. Is obtained.

In the image reading lens, the focal length of the e-line of the convex lens arranged on the opposite side of the third lens L3 with respect to the stop S satisfies the following conditional expression (5).
(5) 0.6f <fi <1.0f

  Here, “a convex lens arranged on the opposite side of the third lens L3 with respect to the diaphragm S” means that the diaphragm S is arranged between the second lens L2 and the third lens L3 (the third lens L3). Is the first lens L1 and the diaphragm S is disposed between the third lens L3 and the fourth lens L4 (the third lens L3 is the diaphragm S). The fifth lens L5 is a fifth lens L5.

The conditional expression (5) defines the range of the focal length fi of the e-line of the convex lens (the first lens L1 or the fifth lens L5) disposed on the side opposite to the third lens L3, and corrects the temperature of the positive lens. It defines the conditions for obtaining a sufficient effect.
If fi is below the lower limit (0.6 f), the power of the convex lens becomes strong, while the change in the focal length of the convex lens due to temperature change becomes small, and the best image plane can be moved effectively when the temperature rises. It becomes difficult. On the other hand, if fi exceeds the upper limit (1.0 f), the power of the convex lens becomes weak, and the inward coma tends to increase in the peripheral portion, so that good imaging performance cannot be obtained.

Further, the image reading lens includes a convex lens disposed on the opposite side of the stop S from the third lens L3 when the refractive index of the d-line of the i-th lens from the object side to the image side is ndi. The following conditional expression (6) is satisfied.
(6) 1.55 <ndi

The conditional expression (6) defines the range of the refractive index ndi of the d-line of the convex lens (the first lens L1 or the fifth lens L5) disposed on the side opposite to the third lens L3. The conditions for realizing the conversion are predetermined.
If ndi falls below the lower limit (1.55), the thickness of the convex lens tends to increase, leading to an increase in the diameter of the lens, making it difficult to reduce the size of the lens.

  By satisfying the above conditional expressions (1) to (5), in a five-lens configuration, in response to various demands required for an image reading lens, the reduction magnification is 0.1 to 0.2 times. Even when it is used, it is possible to correct chromatic aberration satisfactorily, and to suppress deterioration in imaging performance due to changes in temperature environment.

Hereinafter, various aberrations and specific numerical data of the lens according to the embodiment of the image reading lens will be described. The meanings of symbols in the respective embodiments (examples) shown in Tables 2 to 5 are as follows.
f: Composite focal length of the entire system of e-line FNo: 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 lens material d-line (587.56 nm) ng: refractive index of lens material g-line (435.83 nm) nF: F-line of lens material (486) .24 nm) refractive index nC: lens material C-line (656.27 nm) refractive index νd: lens material Abbe number β: lens material refractive index temperature coefficient (20 ° C. to 40 ° C. relative refractive index of wavelength e-line) Temperature coefficient at ℃)

The j column at the left end represents the jth surface counted from the object side. C1 and C2 represent the first and second surfaces of the contact glass on which the document is placed, and C3 and C4 represent the first and second surfaces of the cover glass of the image sensor.
The glass material column at the right end shows the lens type and manufacturer name of the lens.

  In addition, aberration diagrams are shown in FIGS. 3, 5, 7 and 9. In the astigmatism in the aberration diagram, the solid line indicates a sagittal ray, and the dotted line indicates a meridional ray. The e-line shows 546.07 nm, the g-line shows 436.83 nm, the c-line shows 656.27 nm, and the F-line shows 486.13 nm.

[First Embodiment (Example 1)]
FIG. 2 shows the lens configuration of the first embodiment, and FIG. 3 shows aberration diagrams.
Table 2 shows specific numerical data of the constituent lenses.

[Second Embodiment (Example 2)]
The lens configuration of the second embodiment is shown in FIG. 4, and the aberration diagram is shown in FIG.
Table 3 shows specific numerical data of the constituent lenses.

[Third Embodiment (Example 3)]
FIG. 6 shows the lens configuration of the third embodiment, and FIG. 7 shows aberration diagrams.
Table 4 shows specific numerical data of the constituent lenses.

[Fourth Embodiment (Example 4)]
The lens configuration of the fourth embodiment is shown in FIG. 8, and the aberration diagram is shown in FIG.
In addition, Table 5 shows specific numerical data of the constituent lenses.

  Table 6 shows the calculation results of conditional expressions (1) to (5) in each example.

[Image reading device]
An image reading apparatus according to the present invention includes an illumination system that illuminates a document, an imaging lens that forms an image of the document illuminated by the illumination system, and an image of the document that is imaged by the imaging lens. The image reading lens is used as the imaging lens.

FIG. 10 shows an embodiment of the image reading apparatus.
As shown in FIG. 10, 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, and reference numeral 36 denotes an image sensor.

  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 reference numeral 33 '.

  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. 10 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 reference numeral 33 '.

  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 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 electrical signal in units of pixels 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.

  By using the image reading lens according to the present invention as the image reading lens 35 shown in FIG. 10, it is possible to achieve downsizing and cost reduction of the image reading apparatus while maintaining good image quality.

FIG. 11 shows a second embodiment of the image reading apparatus.
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 being 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. 11 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 forms a reduced 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 the same method as the image reading apparatus shown in FIG.

[Image forming apparatus]
An image forming apparatus according to the present invention includes the image reading device.
FIG. 12 shows an embodiment of the image forming apparatus.
As shown in FIG. 12, the image forming apparatus 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. 10, 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.

  It goes without saying that the image forming apparatus can be “configured to perform monochrome image formation”.

  By using the image reading apparatus according to the present invention, it is possible to form a high-quality image and to obtain a small and low-cost image forming apparatus.

L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens L5 5th lens CN Contact glass CV CCD cover glass 41 Document table (contact glass)
42 Document 44 Image reading lens 45 Image sensor (line sensor, CCD)
43 Image Reading Unit 200 Image Reading Device

Japanese Examined Patent Publication No. 56-049332 JP 05-093857 A Japanese Patent Laid-Open No. 08-129131

Claims (6)

In order from the object side to the image side, a first lens that is a positive meniscus lens with a convex surface facing the object side, a second lens that is a negative lens with a concave surface facing the image side, and a third lens that is a biconvex lens A lens, a fourth lens that is a negative lens with the concave surface facing the object side, and a fifth lens that is a positive meniscus lens with the convex surface facing the image side,
Having a diaphragm either between the second lens and the third lens and between the third lens and the fourth lens;
The partial dispersion ratio θgF is defined by θgF = (ng−nF) / (nF−nc), where c-line refractive index is nc, F-line refractive index is nF, and g-line refractive index is ng.
A line segment connecting the coordinate points of the glass materials C2 and F2 on the coordinate plane having the partial dispersion ratio and the Abbe number as two orthogonal axes is defined as a standard line.
The average deviation from the standard line of the partial dispersion ratio θgFi of the i-th lens from the object side to the image side is δθgFi,
When the refractive index temperature coefficient of the i-th lens from the object side to the image side is βi,
An image reading lens, wherein a positive lens disposed on the side opposite to the third lens with respect to the stop satisfies the following conditional expressions (1) and (2).
(1) 0.005 <δθgFi <0.05
(2) βi <0 The radius of curvature of the lens surface on the object side of the i-th lens from the object side to the image side is rip, the radius of curvature of the lens surface on the image side is riq,
The total focal length of the e-line of the entire system is f,
When the combined focal length of the e-line of the i-th lens from the object side to the image side is fi,
The image reading lens according to claim 1, wherein the third lens satisfies the following conditional expressions (3) and (4).
(3) rip + riq <0
(4) 0.2f <fi <0.5f 3. The image reading lens according to claim 1, wherein a focal length of an e-line of a convex lens disposed on the opposite side of the third lens with respect to the stop satisfies the following conditional expression (5).
(5) 0.6f <fi <1.0f When the refractive index of the d-line of the i-th lens from the object side to the image side is ndi,
3. The image reading lens according to claim 1, wherein a convex lens disposed on the opposite side of the third lens with respect to the stop satisfies the following conditional expression (6): 3.
(6) 1.55 <ndi   An illumination system that illuminates the document, an imaging lens that forms an image of the document illuminated by the illumination system, and an image of the document imaged by the imaging lens is received and converted into an electrical signal An image reading apparatus comprising at least an image sensor and using the image reading lens according to claim 1 as the imaging lens.   An image forming apparatus comprising the image reading apparatus according to claim 5.