JP5029947B2 - 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, and an image forming apparatus.

  An image reading unit or an image scanner in a digital copying machine or a facsimile apparatus reduces image information to be read from an original by an image reading lens and forms an image on an image pickup device such as a CCD, thereby converting the image information into a signal. In addition, for reading color image information, for example, a so-called three-line CCD in which line sensors each having red, green, and blue filters are arranged in three rows on one substrate is used to color the color image into three primary colors. Decomposing into signals is performed.

In general, an image reading lens used for such image reading requires “high contrast in a high spatial frequency region” on the light receiving surface of an image pickup device that is an image surface, and an aperture efficiency is around the angle of view. It is required to be close to 100%.
In addition, in order to read a color image satisfactorily, it is necessary to match the image forming positions of a plurality of colors used for color separation, for example, red, green, and blue light in the optical axis direction on the image plane. It is necessary to satisfactorily correct the chromatic aberration.

  Furthermore, in order to meet the demand for downsizing and cost reduction of the image reading apparatus, a “small image reading lens having a small number of lens components” is desired.

  As an image reading lens having a small number of constituting lenses and good performance suitable for reading, in order from the object side, a positive meniscus first lens having a convex surface facing the object side, a second lens having a biconcave surface, and a second lens having both convex surfaces. A telephoto type of a four-group four-lens configuration in which three lenses and a negative meniscus fourth lens with a concave surface facing the object side is arranged is known (Patent Documents 1 to 8, etc.).

  Among these image reading lenses described in Patent Documents, those described in Patent Documents 1, 2, 3, 6, 7, and 8 are preferable by taking a wide space between the third lens and the fourth lens. Although aberration correction is performed, in this configuration, the diameter of the fourth lens tends to be large, and it is difficult to reduce the size of the image reading lens.

  In addition, the image reading lenses described in Patent Documents 4 and 5 have “the interval between the third lens and the fourth lens is set to be narrow in order to shorten the entire length of the lens”, and the imaging position of each angle of view is set as light. It is difficult to achieve a sufficient alignment in the axial direction. In the image reading lens described in Patent Document 4, the “difference in Abbe number between the first lens and the fourth lens” is small, and it is difficult to sufficiently correct chromatic aberration.

  Further, Patent Documents 1 to 8 do not disclose “suppression of performance deterioration at the time of temperature rise due to temperature change in the image reading apparatus, for example, heat generation of an illumination light source”.

Japanese Patent Laid-Open No. 3-240010 Japanese Patent Application Laid-Open No. 9-101452 JP 2000-249913 JP2001-100096 JP 2004-294925 A Japanese Patent Publication No. 2-38925 Japanese Patent No. 3856258 Japanese Patent No. 3507287

The present invention has been made in view of the above, and it is an object of the present invention to realize a small-sized four-group / four-lens image reading lens having high image reading performance. Another object of the present invention is to realize an image reading lens that can satisfactorily match the “image plane position in the optical axis direction” between the sagittal light beam and the meridional light beam at each angle of view.
Another object of the present invention is to realize an image reading lens that can correct chromatic aberration well and realize high image reading performance for a color image, and can cope with a wide angle of view.
It is another object of the present invention to realize an image reading lens capable of reducing deterioration in performance due to a change in use environment due to temperature fluctuation.

  Another object is to realize an image reading apparatus and an image forming apparatus with good performance by using these image reading lenses.

The image reading lens according to claim 1, in order from the object side, a positive meniscus first lens having a convex surface facing the object side, a second lens having a biconcave surface, a diaphragm, a third lens having a biconvex surface, and a concave surface on the object side. A negative meniscus fourth lens is provided and has the following characteristics.
That is, the focal length of the entire image reading lens system: f, the thickness of the entire image reading lens system: Σd, and the distance on the optical axis between the third lens and the fourth lens: d ₇ are:
(1) 0.6f <Σd <0.8f
(2) 0.07 <d ₇ / Σd <0.15
Satisfied.
Furthermore, with conditions (1) and (2), the sum of the refractive index temperature coefficients of the d-line of the first lens and the third lens: Σdn / dt (convex), the refractive index of the d-line of the second lens and the fourth lens Sum of temperature coefficients: Σdn / dt (concave), condition:
(7) -8 <Σdn / dt (convex) -Σdn / dt (concave) <0
Satisfied.
The unit of the refractive index temperature coefficient: dn / dt is [10 ⁻⁶ / ° C.].

In the image reading lens according to claim 1, the lens thickness of the third lens: d ₆ and the thickness of the entire image reading lens system: Σd are:
(3) 0.3 <d ₆ / Σd <0.5
Is preferably satisfied (claim 2).

The image reading lens according to claim 1, wherein the focal length of the entire image reading lens system is f, the radius of curvature of the second surface of the third lens is r ₆ , and the radius of curvature of the first surface of the fourth lens is r _7. But the condition:
(4) 3.2 <(1 / r ₆ -1 / r ₇ ) f <3.7
Is preferably satisfied (Claim 3).

The image reading lens according to claim 1, wherein the first lens has a d-line refractive index: nd ₁ , a fourth lens has a d-line refractive index: nd ₄ , and the first lens has an Abbe number: νd ₁ , Abbe number of the fourth lens: νd ₄ , conditions:
(5) -0.4 <nd ₁ -nd ₄ <-0.08
(6) 20 <νd ₁ -νd ₄ <60
Is preferably satisfied (claim 4).

Of course, the image reading lens according to any one of claims 2 to 4 also satisfies the condition (7).

Any image reading lens according to one of claims 1 to 4, the first lens to the fourth lens are all glass lenses, arsenic, it is preferred that do not contain harmful substances such as lead (claim 5) .
In the image reading lens according to any one of claims 1 to 5 , it is preferable that at least one lens has a “non-circular outer shape” ( claim 6 ).
It is preferable that the image reading lens according to any one of claims 1 to 6 uses a “plastic barrel molded by an injection molding method” ( claim 7 ).

The image reading apparatus according to claim 8 is used with an illumination system that illuminates a document placed on a document placement surface, and an image reading lens that forms an image of document information illuminated by the illumination system on a line-shaped image sensor. An image reading apparatus for reading document information, wherein the image reading lens according to any one of claims 1 to 7 is used as an image reading lens .
The “line-shaped image sensor” is an image sensor in which minute photoelectric conversion elements are arranged in a line.

The image reading apparatus according to claim 8 is configured such that one or more mirrors, an illumination system, an image reading lens, and an image sensor for bending an optical path from the document placement surface to the image sensor are integrally formed as an image read unit. The image information of the document on the document placement surface can be read by scanning of the reading unit ( claim 9 ).
The image reading apparatus according to claims 8 and 9 can be used as a configuration of an image reading unit of a digital copying apparatus, a facsimile machine or the like.

An image forming apparatus according to a tenth aspect reads an image by using the image reading apparatus according to the eighth or ninth aspect . Specifically, the image forming apparatus includes image information of an original such as the digital copying apparatus or the facsimile apparatus. Is a device having a function of reading the signal into a signal and using it for image formation.

  To supplement the explanation, among the conditions (1) and (2) in claim 1, the condition (1) defines “the total length of the image reading lens”. When the lower limit of condition (1): 0.6 f is exceeded, it is difficult to correct the image plane satisfactorily because “the refractive power of each lens becomes too strong” in order to shorten the total length. On the other hand, if it exceeds the upper limit value of 0.8 f, the total length becomes large, and it is difficult to downsize the image reading lens. In order to reduce the size of the image reading lens and to obtain “high image reading performance”, it is necessary to satisfy the condition (1).

  Condition (2) defines “the distance between the third lens and the fourth lens”. If the lower limit value of the condition (2): 0.07 is exceeded, the distance between the lens surfaces of the third lens and the fourth lens becomes too narrow, and the light incident on the first surface of the fourth lens has a “steep angle”. It becomes difficult to correct the marginal ray well. On the other hand, when the value exceeds the upper limit value of 0.15, the “height of off-axis rays passing through the fourth lens” becomes high, and the diameter of the fourth lens tends to increase, making it difficult to reduce the size of the image reading lens. Become.

  By satisfying the conditions (1) and (2), it is possible to achieve downsizing of the image reading lens and high image reading performance. A “diaphragm” disposed between the second lens and the third lens enables good distortion correction.

In order to ensure “higher image reading performance”, the parameter (d ₇ / Σd) in the condition (2) is slightly narrower than the condition (2).
_{(2A) 0.09 <d 7 /} Σd <0.14
Is preferably satisfied.
The condition (3) in claim 2 defines “the thickness of the third lens with respect to the entire length of the image reading lens”. If the lower limit value of the conditional expression is less than 0.3, the thickness of the third lens is decreased, the positive refractive power of the third lens is decreased, and the astigmatic difference is increased due to insufficient correction of the meridional image plane. easy. If the upper limit value exceeds 0.5, the thickness of the third lens is increased, the positive refractive power is increased, the correction of the meridional image plane is excessive, and the field curvature is likely to increase. By satisfying the condition (3) together with the conditions (1) and (2), it becomes easy to match the image forming positions in the optical axis direction in the vicinity of the optical axis and in the peripheral portion, and the total image height of the image reading lens is increased. High image reading performance can be realized.

  The condition (4) of claim 3 regulates “the relationship between the radius of curvature of the second surface of the third lens of the image reading lens and the radius of curvature of the first surface of the fourth lens”. Since the third lens is a biconvex lens and the fourth lens is a negative meniscus lens with the concave surface facing the object side, both the second surface of the third lens and the first surface of the fourth lens are “surfaces convex to the image side”. And the radius of curvature is both negative.

In the range where the condition (4) is satisfied, the radius of curvature of the second surface of the third lens: r ₆ is larger in absolute value than the absolute value of the radius of curvature of the first surface of the fourth lens: r ₇ .

If the lower limit value of condition (4): less than 3.2, the absolute value of the curvature radius: r ₇ is relatively larger than the absolute value of the curvature radius: r ₆ , and the coma aberration tends to be undercorrected. upper limit: above 3.7, the curvature radius of curvature with respect to the absolute value of r ₆ radius absolute value to correct coma aberration becomes relatively small r ₇ tends to be excessive.
By satisfying the condition (4) together with the conditions (1) and (2) or together with the conditions (1) to (3), it becomes easy to realize “high image reading performance in the peripheral portion”.

  The condition (5) of claim 4 is a condition that prescribes "the difference between the refractive index of the first lens that is a convex lens and the refractive index of the fourth lens that is a concave lens". The Petzval sum becomes large, and it becomes difficult to match the “imaging position in the optical axis direction” between the vicinity of the optical axis and the peripheral portion. On the other hand, when the value exceeds the upper limit: −0.08, the Petzval sum becomes small, and it becomes difficult to match the “imaging position in the optical axis direction” between the vicinity of the optical axis and the peripheral portion.

  By satisfying Condition (5) together with Conditions (1) and (2) or these, Condition (3) and Condition (4), it is possible to obtain “high image reading performance at the entire image height of the image reading lens”. become.

  Condition (6) prescribes the “difference between the Abbe number of the first lens that is a convex lens and the Abbe number of the fourth lens that is a concave lens”. If the value exceeds 60, chromatic aberration tends to be overcorrected. Satisfying the condition (6) enables good reading of a color image.

In claim 1, the condition ( 7) that is satisfied together with the conditions (1) and (2) is “the sum of the refractive index temperature coefficients of the first lens and the third lens that are convex lenses, the second lens that is a concave lens and the second lens. The difference from the sum of the refractive index temperature coefficients of the four lenses is defined.

This condition (7) regulates “temperature dependence of the imaging position” in the image reading lens. If the lower limit of condition (7) is less than −8 [10 ⁻⁶ / ° C.] , the focal length of the image reading lens is too “extended when the temperature rises”, and if the upper limit is greater than 0 [10 ⁻⁶ / ° C.]. The focal length of the image reading lens becomes too short when the temperature rises.

  By satisfying the condition (7), “when the temperature in the image reading device rises, the member holding the line CCD as the image reading lens and the image sensor extends, whereas the image in the optical axis direction is extended. It is possible to obtain high image reading performance regardless of the use environment. Although the above-mentioned “refractive index temperature coefficient” is defined by the d-line, an equivalent effect can be obtained by using the “refractive index temperature coefficient of the same wavelength”. Even if expressed, it is possible to obtain the same effect.

The image reading lens according to any one of claims 1 to 4 has a focal length of the i-th lens (i = 1 to 4): f _i (i = The ratio of 1-4) is as follows:
(8) 0.6 <f ₁ / f <0.9
(9) -0.7 <f ₂ / f <-0.4
(10) 0.3 <f ₃ / f <0.5
(11) -0.9 <f ₄ / f <-0.6
Is preferably satisfied.

If the first lens to the fourth lens are all glass lenses and glass materials not containing harmful substances such as arsenic and lead are used as in the image reading lens of claim 5 , the lenses can be safely recycled. it can. In addition, it can greatly contribute to global environmental conservation without causing "water pollution due to waste liquid" during lens processing. Further, the “temperature dependency of the focal length of the image reading lens” can be effectively reduced by using all the lenses as glass materials.

In the image reading lens of the present invention, the lens diameter tends to increase in order to obtain high image quality, and this tendency is particularly remarkable in the fourth lens. When a line sensor such as a CCD in which photoelectric conversion units (small light receiving elements) are arranged in one direction is used as an image sensor, it is only necessary to secure a “width through which light rays pass” only in the arrangement direction of the photoelectric conversion units. In the direction orthogonal to the arrangement of “the lens diameter of the image reading lens can be reduced”. Therefore, as in claim 6 , it is preferable that “at least one lens (preferably the fourth lens) is a non-circular outer shape”.

Further, as in the case of the image reading lens of claim 7 , “using a plastic lens barrel using an injection molding method”, plastic molding using an injection molding method can accurately position an arbitrary position. Since it is softer than the glass material of the lens to be inserted into the lens, it is possible to satisfactorily suppress the eccentricity of the lens by press-fitting and holding the lens (glass lens) in the plastic barrel.
In general, the clearance between each lens and the lens barrel causes the center of each lens to shift from the optical axis, making it difficult to obtain a good image. However, an image reading lens usually has a “performance in one line direction”. For this reason, in the image reading lens production process, the entire image reading lens is usually rotated to find a position with good performance. However, by using a plastic lens barrel, a metal lens barrel can be used. it is possible to also Crossed image reading lens even with a small clearance, since it is possible to satisfactorily suppress the eccentricity of the lens by retaining further press-fitting the lens, in particular, a "non-circular contour of claim 6 When the rotation adjustment of the image reading lens is difficult, such as “a lens having a shape”, this is an effective means in the image reading lens manufacturing process.

By using an integrally configured unit as in the image reading unit of claim 9 , it is possible to further reduce the size of the image reading apparatus, and the image reading unit moves integrally as a unit. It is possible to suppress the “performance deterioration when the unit moves”.

As described above, according to the present invention, while maintaining a high image reading performance, can compact image reading lens (Claim 1) in an implementation, the image reading lens "variation of the focal distance at the time of temperature rise" Can be satisfactorily corrected, and high image reading performance can be realized over a wide range of environmental conditions. Further, in the image reading lens according to claim 2, it is possible to obtain “high image reading performance” by matching the imaging positions in the optical axis direction in the vicinity of the optical axis and in the peripheral portion. Further, the image reading lens can achieve high image reading performance by good correction of the coma at the peripheral portion.

5. The image reading lens according to claim 4, wherein a high contrast is obtained in the vicinity of the optical axis, the image forming positions in the optical axis direction in the vicinity of the optical axis and in the peripheral portion thereof are matched, and color images are corrected satisfactorily to correct color images. High image reading performance can be realized .
Then, by using the image reading lens of the invention, it is possible to realize a compact image reading apparatus and an image forming apparatus excellent in image reading characteristics.

FIG. 1 shows an embodiment of an image reading lens according to the present invention.
In FIG. 1, the left side of the figure is the object side, and the parallel plate CN positioned closest to the object side indicates “original placement glass (contact glass)”. The first lens 1 is a “positive meniscus lens with a convex surface facing the object side”, the second lens 2 following this is a “biconcave lens”, and the third lens 3 provided through the stop is “biconvex surface”. The fourth lens 4 disposed on the image side of the “lens” is “a negative meniscus lens having a concave surface facing the object side”.

FIG. 9 is a view showing an embodiment of the image reading lens according to the sixth aspect. In order to avoid complication, the lenses are given the same reference numerals as in FIG.
In FIG. 9, the left side of the figure is the object side, and the first lens 1, the second lens 2, the third lens 3, and the fourth lens 4 are arranged in order from the object side. In this drawing, the “diaphragm” disposed between the second lens 2 and the third lens 3 is not shown.

  In this embodiment, the fourth lens 4 has a “non-circular outer shape”. That is, the fourth lens is formed in a rectangular shape (non-circular outer shape) that is long in the arrangement direction by cutting away the lens periphery on both sides orthogonal to the arrangement direction of the photoelectric conversion elements. Thus, by forming the fourth lens having the largest lens outer diameter in a “strip shape”, the image reading lens can be effectively downsized.

FIG. 10 is a diagram for explaining an example of a plastic lens barrel. The plastic lens barrel 21 is manufactured by injection molding.
FIG. 10A is a view of the lens barrel 21 as seen from the image plane side, and FIG. 9B is a view as seen from the direction orthogonal to the optical axis. Reference numerals 21a to 21i in the figure indicate "projections formed on the inner wall surface of the lens barrel". By manufacturing the lens barrel 21 having the projections 21a to 21i by the injection molding method as shown in the figure, the projections 21a to 21i can be accurately positioned and molded. Further, by assembling and holding the lenses so as to press fit into these protrusions, the optical axis positions of the lenses can be accurately aligned.

FIG. 11 shows an embodiment of the image reading apparatus.
In FIG. 11, 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 an image is to be read is placed on the upper surface of the document placing glass 31 in a planar manner.

  The first traveling body 33 holds a mirror 33c whose longitudinal direction is a direction orthogonal to the drawing and whose mirror surface is inclined 45 degrees with respect to the document placement surface of the document placement glass 31. In FIG. It moves at a constant speed: V from “position” to “position indicated by reference numeral 33 ′ (position where“ dash ”is added to each reference numeral)”.

  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. 11 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, or “a light source that converts point light sources such as LEDs in a line” or “a light source that converts a point light source into a linear light source” It is also possible to use a "linear light source using", 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 whose mirror surfaces are inclined perpendicularly to each other” long in a direction orthogonal to the drawing, and is denoted by reference numeral 34 ′ in synchronization with the displacement of the first traveling body 33. Displacement at a constant speed: V / 2 to the indicated 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 illuminated portion to the image reading lens 35” is kept constant.

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

The image sensor 36 can color-separate the formed image into three colors (red, green, and blue) to read color information, and synthesizes the electrical signals converted by the respective photoelectric conversion units to produce a color document. Can be read.
The image reading lens 35 shown in FIG. 11 can be miniaturized by using the image reading lens of the present invention (specifically, any one of the embodiments described later).

FIG. 12 shows another 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 an image is to be read is placed flat on the upper surface of the document placing 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 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 43e, 43f, and 43g 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 always constant during illumination scanning of the original 42. It is.

  The imaging light beam incident on the image reading lens 44 forms a reduced image of the original 42 on the light receiving surface of the image sensor 45 by the imaging action of the image reading lens. Then, it is converted into an electric signal by a method similar to that of the embodiment shown in FIG. 10, and the document information is read.

FIG. 13 shows an embodiment of the image forming apparatus.
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 part of the image reading apparatus 200 is the same as that described with reference to FIG. 11, 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 the color toner images are transferred, the surface of the photoconductor 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”.

Hereinafter, seven specific examples of the image reading lens will be described.
As shown in FIG. 1, the image reading lenses of Examples 1 to 6 are telephoto type lens systems having four elements in four groups and a diaphragm between the second and third lenses.

Symbols in each example are as follows.
f: Total focal length of the entire system
FNo: F number
m: Reduction rate
ω: Half angle of view (degrees)
Y: Object height
r: radius of curvature of lens surface
d: Surface spacing
nd: Refractive index of the lens material
νd: Abbe number of the lens material
dn / dt: d-line refractive index temperature change coefficient
Σdn / dt (convex): Refractive index temperature change coefficient of d-line of lens having positive refractive power
Σdn / dt (concave): Refractive index temperature change coefficient of d-line of lens having negative refractive power
"Example 1"
f: 38.6, FNo = 6.0, m = 0.124, Y = 108, ω = 17.1 degrees
The data of Example 1 is shown in Table 1.

In Table 1, j = C1 and C2 are the object side surface and image side surface of the document placement glass (contact glass), and j = C4 and C5 are the object side surface and image side surface of the cover glass of the image sensor. J = 5 indicates the surface of the “aperture”. Therefore, with respect to the lens surface: r, j = 6 is the object side surface of the third lens, j = 7 is the image side surface of the third lens, j = 8 is the object side surface of the fourth lens, and j = 9 is the image of the fourth lens. In the condition (4), r ₆ is a plane with j = 7, and r ₇ is a plane with j = 8. The same applies to Examples 2 to 6 below.

  Aberration diagrams relating to Example 1 are shown in FIG. The broken line in the spherical aberration diagram indicates the sine condition. Moreover, in the figure of astigmatism, a solid line shows a sagittal ray and a broken line shows a meridional ray. The same applies to the aberration diagrams of Example 2 and subsequent examples.

"Example 2"
f: 23.9, FNo = 6.0, m = 0.124, Y = 108, ω = 26.5 degrees
The data of Example 2 is shown in Table 2.

  Aberration diagrams relating to Example 2 are shown in FIG.

"Example 3"
f: 17.2, FNo = 6.0, m = 0.124, Y = 108, ω = 34.7 degrees
The data of Example 3 is shown in Table 3.

  Aberration diagrams relating to Example 3 are shown in FIG.

Example 4
f: 38.7, FNo = 6.0, m = 0.124, Y = 108, ω = 17.1 degrees
The data of Example 4 is shown in Table 4.

  Aberration diagrams relating to Example 4 are shown in FIG.

"Example 5"
f: 23.9, FNo = 6.0, m = 0.124, Y = 108, ω = 26.6 degrees
The data of Example 5 is shown in Table 5.

  Aberration diagrams relating to Example 5 are shown in FIG.

"Example 6"
f: 17.2, FNo = 6.0, m = 0.124, Y = 108, ω = 34.7 degrees
The data of Example 6 is shown in Table 6.

  Aberration diagrams relating to Example 6 are shown in FIG.

"Example 7"
f: 17.4, FNo = 6.0, m = 0.124, Y = 108, ω = 34.5 degrees
The data of Example 7 is shown in Table 7.

  The aberration diagram of Example 7 is shown in FIG.

  Table 8 shows values of the conditions (1) to (7) of the respective examples.

Table 9 shows the ratio of the focal lengths f _{1 to} f ₄ from the first lens to the fourth lens in each example to the focal length f of the entire system.

  As described above, the image reading lenses of Examples 1 to 7 also satisfy the conditions (1) to (9). In each example, the performance is good as shown in the aberration diagrams.

It is a figure which shows a lens structure as embodiment of an image reading lens. FIG. 6 is an aberration diagram for Example 1. FIG. 6 is an aberration diagram for Example 2. FIG. 6 is an aberration diagram for Example 3. FIG. 6 is an aberration diagram for Example 4. FIG. 9 is an aberration diagram for Example 5. FIG. 10 is an aberration diagram for Example 6. FIG. 10 is an aberration diagram for Example 7. It is a figure for demonstrating the embodiment of the image reading lens of Claim 6 . It is a figure for demonstrating the plastic lens tubes manufactured by injection molding. It is a figure for demonstrating one Embodiment of an image reading apparatus. It is a figure for demonstrating another form of implementation of an image reading apparatus. It is a figure for demonstrating one Embodiment of an image reading apparatus.

Explanation of symbols

1 First lens
2 Second lens
3 Third lens
4 Fourth lens

Claims (10)

In order from the object side, a first lens with a positive meniscus with the convex surface facing the object side, a second lens with a biconcave surface, a stop, a third lens with a biconvex surface, and a fourth lens with a negative meniscus with the concave surface facing the object side are arranged. An image reading lens comprising:
Focal length of the entire image reading lens system: f, thickness of the entire image reading lens system: Σd, distance on the optical axis between the third lens and the fourth lens: d ₇ , d line between the first lens and the third lens Sum of refractive index temperature coefficients: Σdn / dt (convex) [10 ^-6 / ° C], Sum of refractive index temperature coefficients of d-line of second lens and fourth lens: Σdn / dt (concave) [10 ^-6 / ° C] is the condition:
(1) 0.6f <Σd <0.8f
(2) 0.07 <d ₇ / Σd <0.15
(7) -8 <Σdn / dt (convex) -Σdn / dt (concave) <0
An image reading lens characterized by satisfying The image reading lens according to claim 1,
The lens thickness of the third lens: d ₆ , the thickness of the entire image reading lens system: Σd, the condition:
(3) 0.3 <d ₆ / Σd <0.5
An image reading lens characterized by satisfying The image reading lens according to claim 1 or 2,
The focal length of the entire image reading lens system is f, the radius of curvature of the second surface of the third lens is r ₆ , and the radius of curvature of the first surface of the fourth lens is r _7.
(4) 3.2 <(1 / r ₆ -1 / r ₇ ) f <3.7
An image reading lens characterized by satisfying The image reading lens according to any one of claims 1 to 3,
The refractive index of the d-line of the first lens: nd ₁ , the refractive index of the d-line of the fourth lens: nd ₄ , the Abbe number of the first lens: νd ₁ , and the Abbe number of the fourth lens: νd ₄ :
(5) -0.4 <nd ₁ -nd ₄ <-0.08
(6) 20 <νd ₁ -νd ₄ <60
An image reading lens characterized by satisfying The image reading lens according to any one of claims 1 to 4,
An image reading lens, wherein the first lens to the fourth lens are all glass lenses and do not contain harmful substances such as arsenic and lead. The image reading lens according to any one of claims 1 to 5,
An image reading lens, wherein at least one lens has a non-circular outer shape. The image reading lens according to any one of claims 1 to 6,
An image reading lens comprising a plastic lens barrel molded by an injection molding method. An image for reading image information of a document using an illumination system that illuminates a document placed on a document placement surface and an image reading lens that forms an image of document information illuminated by the illumination system on a line-shaped image sensor. A reading device,
An image reading apparatus using the image reading lens according to claim 1 as an image reading lens. The image reading apparatus according to claim 8.
One or more mirrors, an illumination system, an image reading lens, and an image sensor for bending an optical path from the document placement surface to the image sensor are integrally configured as an image read unit. An image reading apparatus for reading image information of a document on a surface . An image forming apparatus that performs image reading using the image reading apparatus according to claim 8 .

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