JP2013161019A - Image reading lens, image reading device, and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reading lens of a small diameter and a low cost that has a high contrast in a high spatial frequency area, enables a full color to be read, allows a light beam to be incident at a full stop even in a peripheral area, while a peripheral light amount is thereby secured.SOLUTION: The image reading lens comprises: a first positive meniscus lens 1 with a convex surface on the object side; a second negative lens 2 with a concave surface on an image side; a stop 6; a third positive lens 3 with the convex surface on the object side; a fourth positive lens 4 with the convex surface on the object side; and a fifth negative lens 5 with the convex surface on the image side; arranged in order from an object side. The image reading lens satisfies the following condition (1)νd3-νd4>25 and (2)0.3<f3/f4<3, where an Abbe number of the third lens 3 denotes νd3, an Abbe number of the fourth lens 4 denotes νd4, a focal length of the third lens 3 denotes f3, and a focal length of the fourth lens 4 denotes f4.

Description

  The present invention relates to an image reading lens, an image reading apparatus, and an image forming apparatus. More specifically, it is used for a digital copying machine or a facsimile machine that reads image information by reducing and forming an image of an original on imaging elements arranged in a line and forms an image based on the read image information. The present invention relates to an image reading lens.

  A digital copying machine, an image reading unit of a facsimile, an image scanner, and the like convert original image information to be read by an image reading lens and form an image on an image pickup device such as a CCD, thereby converting the original image information into a signal. When document image information is read in color, for example, a so-called three-line CCD in which three rows of image sensors having red, green, and blue filters are arranged on one substrate is used. By forming an image, color original image information separated into three primary colors is converted into a signal.

  On the other hand, in the image reading apparatus as described above, for the purpose of cost reduction, it is proposed to reduce the diameter of the image reading lens and reduce the number of images by reducing the number of pixels of the image sensor. Furthermore, in recent years, due to demands for space saving and resource saving, the image reading lens has been increased in angle of view, the diameter of the image reading lens has been further reduced, and the optical path length from the document to the image sensor has been shortened. By using a unit in which an image reading lens is integrated, downsizing of an image reading apparatus is being promoted.

  As a general image reading lens, a so-called Gauss type having 6 elements in 4 groups is known. Patent Document 1 describes this type of image reading lens. In this Gaussian type, the field curvature can be corrected well up to a half angle of view of about 20 °, and the occurrence of coma flare can be reduced. However, the number of constituent lenses is large and the outer diameter of the lens increases, making it difficult to reduce the size and cost of the lens and the apparatus using the lens.

  Patent Document 2 describes an image reading lens with a reduced number of lenses. The image reading lens includes a first lens having a positive meniscus having a convex surface facing the object side, a second lens having a biconcave surface, a third lens having a biconvex surface, a fourth lens having a positive meniscus having a convex surface facing the image side, This is a five-lens configuration composed of a negative meniscus fifth lens having a convex surface facing the image side. This lens can achieve the same aberration correction as the Gauss type at a half angle of view of around 20 °. However, if the half angle of view is increased to 25 ° or more, coma flare increases, and correction of chromatic aberration becomes difficult, and it is difficult to reduce the diameter of the image reading lens.

  The present invention corrects various aberrations satisfactorily even when the lens configuration is 5 and the half angle of view is 25 ° or more, has a high contrast in a high spatial frequency region, can support full color reading, and has a full aperture in the peripheral portion. An object of the present invention is to provide a small-diameter and low-cost image reading lens, and an image reading apparatus and an image forming apparatus using the same while ensuring the amount of peripheral light by making light incident on the lens.

The image reading lens according to the present invention includes, from the object side, a positive first meniscus lens having a convex surface on the object side, a second negative meniscus lens having a concave surface on the image side, and a third lens having a positive meniscus having a convex surface on the object side. An image reading lens in which a fourth lens having a positive meniscus having a convex surface on the object side and a fifth lens having a negative meniscus having a convex surface on the image side are arranged in this order, and the Abbe number of the third lens: νd3, the Abbe number of the fourth lens : Νd4, focal length of the third lens: f3 and focal length of the fourth lens: f4.
(1) νd3-νd4> 25
(2) 0.3 <f3 / f4 <3
The main feature is satisfying.

  An image reading apparatus according to the present invention includes the image reading lens according to the present invention, and an image forming apparatus according to the present invention includes the image reading apparatus according to the present invention. And

  According to the present invention, it is possible to reduce the size and wide angle of the image reading lens, and it is also possible to reduce the size of the image reading apparatus or the image forming apparatus on which the image reading lens is mounted.

FIG. 2 is an optical arrangement diagram showing an embodiment of an image reading lens according to the present invention. 1 is an optical arrangement diagram of Embodiment 1 of an image reading lens according to the present invention. FIG. FIG. 3 is an aberration diagram of Example 1 of the image reading lens according to the present invention. FIG. 6 is an optical arrangement diagram of Embodiment 2 of the image reading lens according to the present invention. FIG. 6 is an aberration diagram of Example 2 of the image reading lens according to the present invention. FIG. 6 is an optical arrangement diagram of Embodiment 3 of the image reading lens according to the present invention. It is an aberration diagram of Example 3 of the image reading lens according to the present invention. FIG. 6 is an optical arrangement diagram of Embodiment 4 of the image reading lens according to the present invention. FIG. 6 is an aberration diagram of Example 4 of the image reading lens according to the present invention. FIG. 6 is an optical arrangement diagram of Embodiment 5 of the image reading lens according to the present invention. FIG. 10 is an aberration diagram of Example 5 of the image reading lens according to the present invention. FIG. 10 is an optical arrangement diagram of Embodiment 6 of the image reading lens according to the present invention. It is an aberration diagram of Example 6 of the image reading lens according to the present invention. FIG. 10 is an optical layout diagram of Embodiment 7 of the image reading lens according to the present invention. It is an aberration diagram of Example 7 of the image reading lens according to the present invention. 1 is a diagram showing an embodiment of an image reading apparatus according to the present invention. It is a figure which shows another embodiment of the image reading apparatus which concerns on this invention. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention.

  Hereinafter, embodiments of an image reading lens according to the present invention and an image reading apparatus and an image forming apparatus using the same will be described.

<Image reading lens>
As shown in FIG. 1, the image reading lens according to the present invention is configured by arranging the following optical elements in order from the object side to the image surface side. Note that the object side means the left side as viewed in FIG. 1, and the image plane side means the right side.

As shown in FIG. 1, the image reading lens according to the present invention includes a positive meniscus first lens 1 having a convex surface on the object side, a negative meniscus second lens 2 having a concave surface on the image side, an aperture 6, and an object side. A positive meniscus third lens 3 having a convex surface, a positive meniscus fourth lens 4 having a convex surface on the object side, and a negative meniscus fifth lens 5 having a convex surface on the image side are sequentially arranged. A parallel flat plate 7 disposed on the object side of the first lens 1 represents a document placing glass, and a parallel flat plate 8 disposed on the image side of the fifth lens 5 represents a cover glass. A diaphragm 6 is disposed between the third lens 3 and the fourth lens 4.
<First Embodiment>

  In order to widen the angle of the image reading lens, it is necessary to increase the power of each of the first to fifth lenses, particularly the positive meniscus lens. However, as the power of the positive meniscus lens increases, the chromatic aberration generated in the positive meniscus lens also increases. Then, a chromatic aberration cannot be suppressed satisfactorily with a small number of negative meniscus lenses. In order to balance the positive meniscus lens and the negative meniscus lens, the number of the negative meniscus lens may be increased. However, the cost increases and the size reduction becomes difficult.

<< Regarding Conditional Expression (1) >>
Therefore, in the first embodiment of the image reading lens according to the present invention, by using a glass material smaller than the Abbe number of the third lens for the fourth lens, various aberrations can be suppressed satisfactorily while suppressing the occurrence of chromatic aberration. It is possible.
By using a glass material having a small Abbe number for the fourth lens 4 that is a positive meniscus lens, on-axis chromatic aberration caused by a larger number of positive meniscus lenses in an image reading lens composed of five lenses is suppressed. Can do. Further, the fourth lens 4 is arranged at a position farther from the stop than the third lens 3. Thereby, the chromatic aberration of magnification in the off-axis light beam generated after the third lens 3 exits can be corrected by the convex shape of the lens surface when incident on the convex surface of the first surface of the fourth lens 4. If a glass material having a large Abbe number is used for the lens 4, chromatic aberration of magnification is overcorrected. By using a glass material smaller than the Abbe number of the third lens 3 for the fourth lens 4, lateral chromatic aberration can be suppressed.

Therefore, in order to satisfactorily correct the chromatic aberration generated in the third lens 3, it is important to satisfy the relational expression (1) of the Abbe number of the fourth lens 4 with respect to the third lens 3.
Conditional expression (1) νd3-νd4> 25

<< Regarding Conditional Expression (2) >>
Conditional expression (2) limits the ratio of the focal lengths of the third lens 3 and the fourth lens 4. When the lower limit value of the conditional expression is exceeded, the power of the third lens 3 becomes larger than the power of the fourth lens 4. As a result, the balance of correction of the chromatic aberration of magnification of the third lens 3 and the fourth lens 4 is lost in the fourth lens 4, and the correction of the chromatic aberration of magnification becomes insufficient. That is, in the peripheral portion, a magnification error is generated in which the magnification is larger on the long wavelength side than on the short wavelength side. On the other hand, when the upper limit value of the conditional expression is exceeded, overcorrection occurs, and in the peripheral portion, the magnification becomes larger on the short wavelength side than on the long wavelength side, resulting in a magnification error.
Conditional expression (2) 0.3 <f3 / f4 <3

  According to the embodiment of the image reading lens described above, the relationship satisfying the conditional expressions (1) and (2) is satisfied when an image reading lens having a five-sheet configuration with a half field angle of 25 ° or more, which is a wide field angle, is used. Therefore, it is possible to satisfactorily suppress chromatic aberration in the visible light region, and there is an effect of realizing a wide angle of view, downsizing, and cost reduction of the image reading lens.

<Second Embodiment>
Another embodiment of the image reading lens according to the present invention is characterized in that, in the first embodiment, the third lens and the fourth lens satisfy the following conditional expression (3).

<< Regarding Conditional Expression (3) >>
Conditional expression (3) limits the ratio of the combined focal length of the third lens 3 and the fourth lens 4 to the combined focal length of the entire system.
Conditional expression (3) 0.3 <f34 / f <0.7

  When the lower limit value of conditional expression (3) is exceeded, the balance between the positive power and the negative power after the stop is lost, and Petzval falls negatively, causing curvature of field. Therefore, a focus shift occurs at every image height, and the resolving power becomes non-uniform so that a good image quality cannot be obtained.

  On the other hand, when the upper limit value of conditional expression (3) is exceeded, coma aberration deteriorates. By reducing the power of the third lens 3 and the fourth lens 4 relative to the power of the entire system, if the chromatic aberration is corrected by the power of the convex lens of the third lens 3 and the fourth lens 4, the power for the entire system becomes smaller. . As a result, correction becomes insufficient, resulting in a difference in resolving power for each color.

  According to the invention described above, since the third lens and the fourth lens have a relationship satisfying the conditional expression (3), it is possible to satisfactorily suppress field curvature and to maintain a good balance of resolution between image height differences. It becomes. Therefore, it is possible to obtain a full color reading having a high contrast in a high spatial frequency region, and to realize a cost reduction of a five-group five-element configuration that allows a light beam to enter the aperture to the peripheral portion and suppresses a decrease in peripheral light amount. Play.

<Third Embodiment>
Still another embodiment of the image reading lens according to the present invention relates to the distance of the entire system from the first surface of the first lens to the second surface of the fifth lens in the first and second embodiments. The ratio of the distance from the stop to the first surface of the fourth lens satisfies the conditional expression (4).

<< Condition (4) >>
Conditional expression (4) represents the ratio of the distance from the stop to the first surface of the fourth lens 4 with respect to the total distance from the first surface of the first lens to the second surface of the fifth lens.
Conditional expression (4) 0.2 <Ds4 / D <0.4

<< Definition of the first and second surfaces >>
Here, when the image reading lens is actually used, a surface facing the object side is referred to as a first surface, and a surface facing the image side is referred to as a second surface.

  When the lower limit of conditional expression (4) is exceeded, the off-axis light beam passes through the vicinity of the optical axis of the first surface of the fourth lens 4 and the chromatic aberration of magnification cannot be suppressed well. On the other hand, if the upper limit is exceeded, off-axis light flux passes far away from the optical axis of the fourth lens 4 and it becomes difficult to reduce the size.

  Therefore, satisfying conditional expression (4) makes it possible to reduce the size of the image reading lens while correcting chromatic aberration.

  According to the embodiment of the image reading lens described above, the relationship satisfying the conditional expression (4) is satisfied with respect to the fourth lens. Therefore, it is possible to satisfactorily suppress the chromatic aberration of magnification and to obtain a small image reading lens. Play.

<Fourth Embodiment>
Still another embodiment of the image reading lens according to the present invention is characterized in that, in the first, second, or third embodiment, at least the object-side surface of the fifth lens is an aspherical surface. And

  The fifth lens of the concave lens as the final lens kicks up the incident light beam to cope with a wide angle. However, the aberration of the fifth lens 5 itself tends to increase, and in order to suppress the aberration and cope with a wide angle, the fifth lens is used. The lens 5 itself tends to be large. Therefore, various aberrations can be satisfactorily reduced by making the object-side concave surface of the fifth lens 5 an aspherical surface.

  According to the embodiment of the image reading lens described above, it is possible to reduce the amount of aberration generated in the fifth lens by making the object side surface of the fifth lens an aspherical surface, and the small diameter of the fifth lens. In addition, the image reading lens can be reduced in size and cost.

<Fifth Embodiment>
According to still another embodiment of the image reading lens of the present invention, in the first, second, third, or fourth embodiment, an image surface side surface of the first lens is an aspheric surface, The shape of the spherical surface is characterized in that the curvature decreases toward the periphery with respect to the radius of curvature near the optical axis.

  By making the concave surface on the image plane side of the first lens 1 an aspherical surface, it becomes possible to satisfactorily correct the coma aberration of the marginal ray near the peripheral image height. If this lens surface is not aspherical, coma flare is reduced, and the diameter of the lens must be increased, in particular, the size of the positive meniscus lens of the third lens 3 must be increased. Therefore, it is difficult to reduce the size and cost.

  According to the embodiment of the image reading lens described above, the aspherical surface having a predetermined shape on the image plane side of the first lens contributes to correction of coma aberration, and the diameter of the third lens 3 is reduced. In addition, the image reading lens can be reduced in size.

<Sixth Embodiment>
In still another embodiment of the image reading lens according to the present invention, in the first, second, third, fourth, or fifth embodiment, the image side surface of the fifth lens is an aspheric surface, The shape of the aspherical surface satisfies that the curvature decreases toward the periphery with respect to the radius of curvature near the optical axis.

  By making the convex surface on the image side of the fifth lens 5 aspherical, in addition to the aspherical effect on the image side of the first lens 1, all image heights from the vicinity of the optical axis to the vicinity of the peripheral image height are obtained. It becomes possible to satisfactorily correct the coma aberration of the marginal ray. That is, even if the diameter of the fifth lens 5 is reduced, it is possible to obtain high contrast up to the high frequency region over the entire region.

  Since the aspherical shapes on the image plane side of the first lens 1 and the image plane side of the fifth lens 5 are in a direction in which the curvature becomes severe from the optical axis toward the periphery, the coma flare can be satisfactorily obtained even for light rays in the vicinity of the peripheral image height. Thus, the image reading lens can be reduced in size.

  According to the embodiment of the image reading lens described above, the image surface side of the fifth lens is an aspheric surface having a predetermined shape, so that it can be used at all image heights from the vicinity of the optical axis to the vicinity of the peripheral image height. Since the coma aberration of the marginal ray can be corrected satisfactorily, there is an effect of realizing high contrast up to a high frequency region over the entire region.

<Example of Image Reading Lens According to the Present Invention>
Next, specific examples of the image reading lens according to the present invention will be described. The meanings of symbols in each embodiment are as follows.
f: Total focal length of the entire system FNo: F number m: Reduction ratio ω: Half angle of view (degrees)
Y: object height r: radius of curvature of optical element surface such as lens or glass d: surface interval nd: refractive index of optical material such as lens νd: Abbe number of optical material such as lens

An aspherical surface is expressed by the following equation.

  When Y is a distance from the optical axis in a direction orthogonal to the optical axis, the surface shape of the aspheric surface can be expressed by a distance X from the surface vertex intersecting the optical axis in the optical axis direction at an arbitrary distance Y. k is a conical coefficient, and Ai is an aspheric coefficient for the degree i. The surface number j of each optical element is given in order from the object side. C1 and C2 indicate the first and second surfaces of the contact glass 7 on which the document is placed, and C3 and C4 indicate the first and second surfaces of the cover glass 8 of the image sensor.

<Example 1>

f: 27.4, FNo = 5.6, m = 0.111, Y = 152.4, ω = 27 °

The basic configuration in Example 1 is shown in FIG. 2, and the aberration diagram is shown in FIG.

<Example 2>
f: 27.8, FNo = 5.0, m = 0.111, Y = 152.4, ω = 26 °

FIG. 4 shows a basic configuration in Example 2, and FIG. 5 shows aberration diagrams.

<Example 3>


f: 27.5, FNo = 5.6, m = 0.111, Y = 152.4, ω = 27 °

FIG. 6 shows a basic configuration in Example 3, and FIG. 7 shows aberration diagrams.

<Example 4>


f: 27.6, FNo = 5.6, m = 0.111, Y = 152.4, ω = 27 °

FIG. 8 shows a basic configuration in Example 4, and FIG. 9 shows aberration diagrams.

<Example 5>


f: 27.5, FNo = 5.6, m = 0.111, Y = 152.4, ω = 27 °

FIG. 10 shows a basic configuration in Example 5, and FIG. 11 shows aberration diagrams.

<Example 6>


f: 27.6, FNo = 5.6, m = 0.111, Y = 152.4, ω = 26 °

FIG. 12 shows a basic configuration in Example 6, and FIG. 13 shows aberration diagrams.

<Example 7>

f: 27.6, FNo = 5.0, m = 0.111, Y = 152.4, ω = 26 °

FIG. 14 shows a basic configuration in Example 7, and FIG. 15 shows aberration diagrams.

Table 15 shows the calculation results of the conditional formulas 1 to 4 parameters of Examples 1 to 7.

<Embodiment of Image Reading Apparatus>
An embodiment of the image reading apparatus according to the present invention is characterized by including the first, second, third, fourth, fifth, or sixth image reading lens.

  Hereinafter, a description will be given based on FIG. FIG. 16 is a diagram for explaining the image reading apparatus. In FIG. 16, 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. It moves at a constant speed V from the position indicated by the first traveling body 33 to the position indicated by reference numeral 33 ′.

  In addition, the first traveling body 33 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. 16 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 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. It is also possible to use a line light source that uses a point light source such as an LED arranged in a line, or a linear light source that uses a light guide that converts the point light source into a linear light source, and further, a surface emission represented by organic EL. It is also possible to use a light source.

  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 to the position at a constant speed 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 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 electric signal is subjected to 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.

  According to the embodiments of the image reading apparatus described above, the advantages described above can be obtained by using the image reading lenses of the first to sixth embodiments for the image reading lens. This has the effect of realizing reduction in weight, weight and cost.

<Another Embodiment of Image Reading Apparatus>
Still another embodiment of the image reading apparatus according to the present invention is characterized by including the image reading lens according to the first, second, third, fourth, fifth, or sixth embodiment.

  Hereinafter, a description will be given with reference to FIG. FIG. 17 shows a second embodiment 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 mirror surface inclined with respect to the document placement surface of the document placement glass 41 with the direction orthogonal to the drawing as the longitudinal direction. It moves at a constant speed V from the position indicated by the image reading unit 43 to the position indicated by reference numeral 43 '.

  Further, the image reading unit 43 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. 17 and illuminate the original 42 on the original 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 on the original 42 on the light receiving surface of the image sensor 45 by the imaging action of the image reading lens. After this, it is possible to read the original image information by converting it into an electrical signal in the same manner as in the first embodiment of the image reading apparatus.

  According to the embodiment of the image reading apparatus described above, each of the advantages described above can be obtained by using the image reading lens according to any one of the first to sixth embodiments as an image reading lens. The reading apparatus can be reduced in size, weight, and cost.

<Embodiment of Image Forming Apparatus>
An embodiment of the image forming apparatus according to the present invention includes the image reading device.

An embodiment of the image forming apparatus according to the present invention is shown in FIG. Hereinafter, a description will be given based on 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 image reading apparatus 200 is the same as that described with reference to FIG. 16, and the same reference numerals as those in FIG.

  An image signal output from a line sensor (imaging device) 36 that 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 ( Signals for writing yellow, magenta, cyan, and black colors).

  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 (electrostatic latent image) of the photosensitive member 110 between the charging roller 111 and the developing device 113. Write).

  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 performing image formation, the photoconductive photoconductor 110 rotates at a constant speed clockwise as viewed from the paper surface, the surface of the photoconductor is uniformly charged by the charging roller 111, and the laser beam of the optical scanning device 117 is An electrostatic latent image is formed upon exposure by optical writing. In the case of the reversal development method, the formed electrostatic latent image is a so-called “negative latent image”, and the image portion is exposed.

  Image formation is performed in the order of a yellow image, a magenta image, a cyan image, and a black image as the photoconductor 110 rotates. The formed electrostatic latent image is developed by each developing unit Y (developing with yellow toner), M (developing with magenta toner), C (developing with cyan toner), K (developing with cyan toner) of the revolver type developing device 113. Development with black toner is carried out in order to reversely develop and visualize as a positive image. The obtained color toner images are sequentially transferred onto the transfer belt 114 by the transfer voltage application roller 114A, and the color toner images are superimposed on the transfer belt 114 to form a color image.

  The cassette 118 containing the transfer paper S is detachable from the image forming apparatus main body. In the loaded state as shown in the figure, the uppermost sheet of the stored transfer sheet S is fed by the sheet feeding roller 122, and 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 is not limited to the so-called revolver type color image forming apparatus described above, and a tandem type color image in which an image is formed on an individual photoconductor for each color component and the respective images are overlaid. It may be an image forming apparatus. Also, an image based on digital data such as a so-called monochromatic monochrome type image forming apparatus, a four-cycle type color image forming apparatus, a so-called ink jet type image forming apparatus that forms an image by ejecting liquid droplets, or a thermal transfer type image forming apparatus. Any device that performs the formation may be used.

  According to the invention described above, since the respective advantages described above can be obtained by using the image reading apparatus of the seventh or eighth invention, the image forming apparatus can be reduced in size, weight, and cost. There is an effect of realization.

DESCRIPTION OF SYMBOLS 1 1st lens 2 2nd lens 3 3rd lens 4 4th lens 5 5th lens 6 Aperture 7 Contact is lath 8 Cover glass 31, 41 Document placement glass 32, 42 Document 33 First traveling body 34 Second traveling body 35, 44 Image reading lens 36, 45 Image sensor 43 Image reading unit 100 Image forming unit 111 Charging roller 113 Developing device 114 Transfer belt 115 Cleaning device 117 Optical scanning device 118 Cassette 119 Register roller pair 120 Signal processing unit 121 Tray 122 Paper feed Kolo

Japanese Patent No. 3934197 JP 2011-008007 A

Claims (8)

From the object side, a positive first meniscus lens having a convex surface on the object side, a second negative meniscus lens having a concave surface on the image side, a stop, a third lens having a positive meniscus having a convex surface on the object side, and a positive meniscus having a convex surface on the object side. An image reading lens in which a fourth lens and a negative meniscus fifth lens having a convex surface on the image side are sequentially arranged,
Abbe number of the third lens: νd3, Abbe number of the fourth lens: νd4, focal length of the third lens: f3, and focal length of the fourth lens: f4.
(1) νd3-νd4> 25
(2) 0.3 <f3 / f4 <3
An image reading lens characterized by satisfying The focal length of the entire system: f and the combined focal length of the third lens and the fourth lens: f34 are the conditions:
(3) 0.3 <f34 / f <0.7
The image reading lens according to claim 1, wherein: The distance between the stop and the object side surface of the fourth lens: Ds4 and the distance D of the entire system from the first surface of the first lens to the image side surface of the fifth lens are:
(4) 0.2 <Ds4 / D <0.4
The image reading lens according to claim 1, wherein: At least the object-side surface of the fifth lens is an aspherical surface;
The image reading lens according to claim 1, wherein: A surface on the image plane side of the first lens is an aspheric surface, and the shape of the aspheric surface has a smaller curvature toward a peripheral portion with respect to a radius of curvature near the optical axis;
The image reading lens according to claim 1, wherein: The image-side surface of the fifth lens is an aspheric surface, and the shape of the aspheric surface is such that the curvature decreases toward the periphery with respect to the radius of curvature near the optical axis.
The image reading lens according to claim 1, wherein: The image reading lens according to claim 1, an illumination system that illuminates a document placement surface, a line-shaped imaging device, and at least one disposed between the document placement surface and the image reading lens. An image reading apparatus comprising: at least one reflection mirror 8. An image forming apparatus that forms an image by exposing the surface of an image carrier in accordance with document information read by an image reading apparatus, wherein the image reading apparatus according to claim 7 is used as the image reading apparatus. Image forming apparatus.