JP5445090B2 - Reading lens, image reading apparatus, and image forming apparatus - Google Patents

Description

  The present invention relates to a reading lens for reading a document image, an image reading apparatus using the reading lens, and an image forming apparatus.

In a facsimile, a digital copying apparatus, or the like, an image reading apparatus that reads an image of a transmission original or a copy original reduces the image to be read with a reading lens and forms an image on a solid-state image pickup device such as a CCD to convert the image information into a signal. .
In order to read document information in color, for example, a so-called three-line CCD in which light receiving elements having red, green, and blue filters are arranged in three rows on one chip is used to form a document image on the light receiving surface. Thus, there is an optical system that performs color separation into three primary colors and converts a color image into a signal.

In general, a reading lens used for such image reading is required to have high contrast in a high spatial frequency region on the image plane and to have an aperture efficiency close to 100% up to the periphery of the angle of view. .
Further, in order to read a color original satisfactorily, it is necessary to match the image forming positions of red, green, and blue colors on the light receiving surface in the optical axis direction, and chromatic aberration of each color must be corrected extremely well.

  Further, there is a demand for downsizing of the image reading apparatus, particularly for reducing the conjugate distance between the original and the light receiving surface. For this purpose, it is necessary to widen the angle of view of the reading lens.

  In addition, speeding up of image reading is also demanded. For this purpose, a lens having a large aperture and a bright lens is required.

  Conventionally, as a reading lens realizing a large aperture, many Gauss type lenses having four groups and six elements are known. The Gauss-type lens system is a “lens type that can suppress the occurrence of coma flare to a small size” even with a large aperture, but the majority of currently known lenses have a half angle of view of about 18 degrees, which is a relatively large image. Even with a wide angle, the half angle of view remains at about 20 degrees.

  For this reason, a Gaussian reading lens is effective in terms of brightness, but is not necessarily sufficient to meet the demand for downsizing of an image forming apparatus.

  There is known a reading lens in which one lens is further added to a Gauss type lens configuration to form a five-group seven-lens configuration (Patent Document 1). This reading lens has a large aperture of F number: about 4.0, but has a half angle of view of about 20 degrees, and is not necessarily sufficient to sufficiently achieve downsizing of the image reading apparatus.

  The reading lens described in Patent Document 1 also employs an aspherical surface. The use of an aspherical surface not only makes it difficult to form an aspherical surface, but it is not only a factor in increasing the cost of the reading lens, but also a lens with a large outer diameter cannot maintain good surface accuracy, and the imaging performance of the reading lens. It also causes deterioration.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to realize a reading lens that can realize a wider angle of view and a good performance in addition to a large aperture comparable to that of the conventional one.

  The reading lens according to the present invention is used in an image reading apparatus for reading an image of a transmission original or a copy original in a facsimile or a digital copying apparatus, and the image to be read is reduced by the reading lens and connected to a solid-state imaging device such as a CCD. An image reading lens ”is configured as follows.

  That is, in order from the object side to the image side, a positive first group, a negative second group, a negative third group, a positive fourth group, a positive fifth group, and a negative sixth group are arranged. An aperture stop is provided between the second group and the third group.

  The first group is a positive first lens, the second group is “a cemented lens of a positive second lens and a negative third lens”, the third group is a negative fourth lens, and the fourth group is a positive fifth lens. The fifth group is a positive sixth lens, and the sixth group is a negative seventh lens. The above “positive / negative” is positive / negative of the refractive power of each group and each lens.

  The second group is formed by cementing a positive second lens and a negative third lens. The second group has a negative refractive power. Accordingly, the refractive power distribution of the first group to the sixth group is positive / negative / negative / positive / positive / negative, and the refractive power distribution of the first lens to the seventh lens is positive / positive / negative / negative.・ Positive / positive / negative.

  The reading lens described in claim 1 satisfies the following conditions (1) and (2).

(1) 0.0 <φ4 / ν5 + φ5 / ν6 <0.04
(2) 0.0 <| f4-f5 | / f <0.1
In the condition (1), ν5 is “the Abbe number of the material of the fifth lens (fourth group)”, and ν6 is “the Abbe number of the material of the sixth lens (fifth group)”.

φ4 and φ5 are quantities defined as follows.
That is, the combined focal length for the e-line of the entire system: f (> 0), the focal length of the fourth group (fifth lens) for the e-line: f4, and the focal length of the fifth group (sixth lens) for the e-line: By f5, φ4 = f4 / f and φ5 = f5 / f are defined.

The first to seventh lenses constituting the reading lens according to claim 1 can be as follows (claim 2).
First lens: “convex meniscus lens having a convex surface facing the object”.
Second lens: “Positive lens with a convex surface on the object side”
Third lens: “Negative lens with concave surface on image side”
Fourth lens: “Concave meniscus lens with concave surface facing the object”
Fifth lens: “Positive lens with a convex surface on the image side”
6th lens: “Biconvex lens”
Seventh lens: “biconcave lens”.

The second lens, the third lens, and the fifth lens in the reading lens according to claim 2 can be as follows.
That is, the second lens can be a “positive meniscus lens with a convex surface facing the object side”, the third lens can be a “negative meniscus lens with a concave surface facing the image side”, and the fifth lens can be a “biconvex lens” ( Claim 3).

  The second lens is a “positive meniscus lens having a convex surface facing the object side”, the third lens is a “negative meniscus lens having a concave surface facing the image side”, and the fifth lens is “a positive meniscus lens having a convex surface facing the image side”. Lens "(claim 4).

  Further, the second lens can be a “biconvex lens”, the third lens can be a “biconcave lens”, and the fifth lens can be a “positive meniscus lens having a convex surface facing the image side”.

  In the reading lenses according to the first to fifth aspects, it is preferable that all of the first to seventh lenses are glass lenses made of glass containing no harmful substances such as lead and arsenic.

  An image reading apparatus of the present invention is an image reading apparatus that reads an image of a transmission original or a copy original in a facsimile, a digital copying apparatus, or the like, and includes an illumination system, an imaging lens, and a line sensor. ).

The “illumination system” illuminates the document.
The “imaging lens” forms a reduced image of the reflected light of the document illuminated by the illumination system.
A “line sensor” receives and photoelectrically converts a document image formed by an imaging lens.

  The reading lens according to any one of claims 1 to 6 is used as the imaging lens.

  The image forming apparatus according to the present invention uses the image reading device according to claim 7 and forms an image using the read image information.

Supplement the explanation.
The reading lens of the present invention has a 6-group 7-element configuration and 13 lens surfaces, and has more design parameters than a conventionally known Gauss type, so the degree of freedom in design is high. Various aberrations can be corrected satisfactorily.

  Further, since all the lens surfaces are formed as spherical surfaces, it is easy to form the lens surfaces, and the reading lens can be realized at low cost.

Condition (1) is a condition for ensuring an achromatic function by the lenses of the fourth group and the fifth group (the fifth lens and the sixth lens).
When the upper limit of the condition (1) is exceeded, a sufficient achromatic effect cannot be obtained and the chromatic aberration of the entire system becomes large.

  Condition (2) is a condition that regulates the “power distribution difference” between the lenses in the fourth group and the fifth group (the fifth lens and the sixth lens). If the upper limit is exceeded, the difference in power distribution between the two lenses And the “difference in lens outer diameter” between the fifth and sixth lenses increases, which is disadvantageous for making the reading lens compact.

As described above, in the reading lens of the present invention, the first to seventh lenses constituting the reading lens are all “spherical lenses” and do not use aspherical surfaces. Accordingly, these first to seventh lenses can be easily “all composed of glass lenses”.
If all the lenses are glass lenses, the reading lens has high environmental resistance, and even if the temperature in the image reading apparatus fluctuates due to the movement of the illumination system, the change in optical characteristics can be suppressed to a small level.

When all the lenses are glass lenses, the first to seventh lenses are all made of “glass that does not contain harmful substances such as lead and arsenic” as in the reading lens of claim 6. The material can be easily recycled, and there is no water pollution due to waste liquid during lens processing, so that resources can be saved and CO ₂ generated during processing can be reduced.

As described above, according to the present invention, a novel reading lens can be realized.
The reading lens according to the present invention has the above-described configuration. As shown in the examples described later, the reading lens has a large aperture of about 4.0 and a wide angle of view of about 24 degrees. It has a high contrast in the frequency domain ”, an aperture efficiency close to 100% up to the periphery of the angle of view, chromatic aberration is well corrected, and can be realized compactly.
Therefore, by using such a “wide viewing angle reading lens”, the conjugate length from the document surface to the line sensor can be set short, and a compact image reading apparatus and image forming apparatus can be realized.

It is a figure for demonstrating a reading lens. FIG. 3 is a diagram illustrating a lens configuration of a reading lens of Example 1. FIG. 6 is an aberration diagram for Example 1. FIG. 6 is a diagram illustrating a lens configuration of a reading lens of Example 2. FIG. 6 is an aberration diagram for Example 2. 6 is a diagram illustrating a lens configuration of a reading lens according to Example 3. FIG. FIG. 6 is an aberration diagram for Example 3. 6 is a diagram illustrating a lens configuration of a reading lens of Example 4. FIG. FIG. 6 is an aberration diagram for Example 4. 6 is a diagram illustrating a lens configuration of a reading lens according to Example 5. FIG. FIG. 9 is an aberration diagram for Example 5. It is a figure for demonstrating one Embodiment of an image reading apparatus. It is a figure for demonstrating one Embodiment of an image forming apparatus.

  FIG. 1 is a diagram for explaining a lens configuration of a reading lens.

  The left side in FIG. 1 is the object side, that is, the side of the original to be read, and the original is placed with the original surface in close contact with the left side in the figure of the contact glass CT.

  The reading lens sequentially includes a positive first group, a negative second group, a negative third group, a positive fourth group, a positive fifth group, and a negative sixth group from the object side to the image side. And an aperture stop ST is provided between the second group and the third group.

  The first group is a positive first lens L1, the second group is a cemented lens of a positive second lens L2 and a negative third lens L3, the third group is a negative fourth lens L4, and the fourth group is a positive first lens L1. The fifth lens L5, the fifth group has a positive sixth lens L6, and the sixth group has a six-group seven-lens configuration that is a negative seventh lens L7.

  As shown in the figure, the first lens L1 is “a convex meniscus lens having a convex surface facing the object side”, the second lens L2 is “a positive lens having a convex surface on the object side”, and the third lens L3 is “a concave surface on the image side surface”. Negative lens ", fourth lens L4 is" concave meniscus lens with concave surface facing the object side ", fifth lens L6ha" positive lens having convex surface on the image side ", sixth lens L6 is" biconvex lens ", seventh lens L7 is a “biconcave lens”.

  The Abbe number of the material of the fifth lens L5: ν5, the Abbe number of the material of the sixth lens L6: ν6, the combined focal length with respect to the e-line of the entire system: f, with respect to the e-line of the fifth lens L5 forming the fourth group Focal length: f4, the focal length for the e-line of the sixth lens L6 in the fifth group: f5 and the amount defined by φ4 = f4 / f and φ5 = f5 / f: φ4, φ5 is the condition (1) Satisfactory, the focal lengths f, f4, and f5 satisfy the condition (2).

A transparent parallel plate CG is disposed on the image side of the seventh lens L7. This transparent parallel plate CG is
A cover glass and various filters of a solid-state imaging device such as a CCD are simply depicted as transparent parallel plates having optical characteristics equivalent to these.

  In the examples described later, the transparent parallel flat plate CG is denoted as “CCD cover glass”.

  Although the contact glass CT and the first lens L1 are actually separated, they are drawn in close contact for the convenience of illustration.

Hereinafter, embodiments of the image reading apparatus and the image forming apparatus will be described.
FIG. 12 is a diagram showing an embodiment of the image reading apparatus.
In FIG. 12, a document 112 having an image to be read is placed flat on a contact glass 111, and an illumination unit 113A using an “Xe lamp, LED light source, etc.” is disposed below the contact glass 111, and the illumination is performed. Light illuminates a “slit-like portion long in a direction perpendicular to the drawing” of the document surface of the placed document.
Reflected light from the illuminated portion of the document 112 (reflected light from the image) is reflected by the first mirror 113B provided on the first traveling body 113, and then provided on the second traveling body 114. 114A and the third mirror 114B are sequentially reflected, pass through the reading lens 115, and form a reduced image of the original image on the imaging surface of the line sensor 116 as a solid-state imaging device that performs photoelectric conversion.

The first to third mirrors 113B, 114A, and 114B constitute a “reflective optical system”, and the first traveling body 113 and the second traveling body 114 are each moved in the direction of the arrow (to the right in the figure) by driving means (not shown). Can be run.
The traveling speed of the first traveling body 113 is “V”, the traveling speed of the second traveling body 114 is “V / 2”, and the first traveling body 113 and the second traveling body 114 are indicated by “broken lines” shown in the drawings. Displacement to “shown position”.
The illumination unit 113 </ b> A and the first mirror 113 </ b> B move integrally with the first traveling body 113 to “illuminate and scan” the entire document 112 on the contact glass 1. Since the moving speed ratio of the first and second traveling bodies is “V: V / 2”, “the optical path length from the original scanned portion to the reading lens” is kept unchanged.

  The line sensor 116 indicates that “photoelectric conversion elements (116A, 116B, 116C) having filters of red (R), green (G), and blue (B) as color separation means are arranged in three rows on one chip. Line CCD (3-line sensor) ”, which converts the document image into an image signal as the document 112 is illuminated and scanned. In this way, reading of the original 112 is executed, and the color image of the original 112 is read by color separation into three primary colors of red, green, and blue.

  The image reading apparatus according to this embodiment is an apparatus that reads an image in full color, and includes “color separation means (red, green, red, green, etc. provided in the three-line CCD” provided in the imaging optical path of the image reading lens 115. Blue filter) ”.

  As another form of the image reading apparatus, “illuminating means for illuminating the original on the contact glass in a slit shape, a line sensor, and a plurality of mirrors forming an imaging optical path from the illuminated part of the original to the line sensor; The image reading lens arranged on the image forming optical path and the reading unit integrated with each other are moved relative to the document by the driving means so as to read and scan the document. You can also.

  In the “color separation”, a color separation prism or filter is selectively inserted between the reading lens 115 and the line sensor (CCD) separately from the above, and R (red), G (green), and B (blue). Or a “method of illuminating a document by sequentially turning on R, G, and B light sources”.

FIG. 13 is a diagram illustrating one embodiment of an image forming apparatus.
The image forming apparatus of FIG. 13 includes an image reading apparatus 200 located at the upper part of the apparatus and an “image forming part” located at the lower part thereof. The parts of the image reading apparatus 200 are the same as those described with reference to FIG. 12, and the same reference numerals as those shown in FIG.

  The image signal output from the three-line line sensor 116 of the image reading apparatus 200 is sent to the image processing unit 1200 and processed by the image processing unit 1200 to “write signals (yellow, magenta, cyan, and black colors). Signal for writing) ”.

  The image forming unit has a photoconductive photosensitive member 1100 formed in a cylindrical shape as a “latent image carrier”, and around it, a charging roller 1110 as a charging unit, a revolver type developing device 1130, a transfer belt. 1140 and a cleaning device 1150 are provided. As the charging means, a “corona charger” can be used instead of the charging roller 1110.

  An optical scanning device 1170 that receives a writing signal from the signal processing unit 1200 and writes on the photosensitive member 1100 by optical scanning performs optical scanning of the photosensitive member 1100 between the charging roller 1110 and the developing device 1130. ing.

  Reference numeral 1160 denotes a fixing device, reference numeral 1180 denotes a cassette, reference numeral 1190 denotes a registration roller pair, reference numeral 1220 denotes a paper feed roller, reference numeral 1210 denotes a tray, and reference numeral S denotes a transfer sheet as a “recording medium”.

  When image formation is performed, the photoconductive photoreceptor 1100 is rotated at a constant speed in the clockwise direction, the surface thereof is uniformly charged by the charging roller 1110, and is subjected to exposure by optical writing of the laser beam of the optical scanning device 1170. 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 1100, 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 1140 by the transfer voltage application roller 114A, and the respective color toner images are superimposed on the transfer belt 1140 to form a color image.

  The cassette 1180 containing the transfer paper S is detachable from the main body of the image forming apparatus, and the uppermost sheet of the stored transfer paper S is fed by the paper feed roller 1220 when mounted as shown in the figure. The leading edge of the fed transfer paper S is caught by the registration roller pair 1190.

  The registration roller pair 1190 feeds the transfer sheet S to the transfer unit at the timing when the “color image by toner” on the transfer belt 1140 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 is transferred is sent to the fixing device 1160, where the color image is fixed in the fixing device 1160, passes through a conveyance path by a guide means (not shown), and is discharged onto the tray 1210 by a pair of paper discharge rollers (not shown). The Each time each color toner image is transferred, the surface of the photoreceptor 1100 is cleaned by a cleaning device 1150 to remove residual toner, paper dust, and the like.

  Hereinafter, five specific examples regarding the reading lens will be described. The meanings of the symbols in each example are as follows (see FIG. 1).

f: Composite focal length of e-line of the entire system FNo: F number m: Reduction ratio ω: Half angle of view Y: Object height ri (i = 1 to 14): Curvature radius of i-th surface counted from the object side di (I = 1 to 13): i-th surface interval counted from the object side nj (j = 1 to 7): Refractive index of the material of the j-th lens counted from the object side νj (j = 1 to 7): Abbe number of the material of the j-th lens 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: radius of curvature of the CCD cover glass on the object side rc4: CCD cover glass Radius of curvature on the image side dc1: contact glass thickness dc3: CCD cover glass thickness nc1: contact glass refractive index nc3: CCD cover glass refractive index νc1: contact glass Abbe number νc3: Abbe number of CCD cover glass nd: d-line refractive index νd: d-line Abbe number ne: e-line refractive index
Unless otherwise specified, the unit of the quantity having the length element is “mm”. .

"Example 1"
FIG. 2 shows the lens configuration of Example 1. In order to avoid complications, the same reference numerals as in FIG. 1 are used. The same applies to the drawings showing other embodiments described later.

f = 65.054, FNo = 3.99, m = 0.36222, Y = 152.4, ω = 24.1 °
Table 1 shows data of the reading lens of Example 1.

  FIG. 3 shows aberration diagrams related to Example 1.

  In the aberration diagrams, “e” is e-line (546.07 nm), “g” is g-line (436.83 nm), “c” is c-line (656.27 nm), “F” is F-line (486) .13 nm).

  In the spherical aberration diagram, the wavy line indicates the “sine condition”, and in the astigmatism diagram, the solid line indicates the sagittal ray and the dotted line indicates the meridional ray. The same applies to aberration diagrams relating to other examples described later.

"Example 2"
FIG. 4 shows the lens configuration of Example 2.

f = 66.523, FNo = 4.06, m = 0.36222, Y = 152.4, ω = 23.6 °
The data of Example 2 is shown in Table 2.

FIG. 5 is an aberration diagram for Example 2.
"Example 3"
FIG. 6 shows the lens configuration of Example 3.

f = 66.414, FNo = 4.02, m = 0.36222, Y = 152.4, ω = 23.7 °
The data of Example 3 is shown in Table 3.

  FIG. 7 is an aberration diagram for Example 3.

Example 4
FIG. 8 shows the lens configuration of Example 4.

f = 67.047, FNo = 4.00, m = 0.36222, Y = 152.4, ω = 23.5 °
The data of Example 4 is shown in Table 4.

  FIG. 9 is an aberration diagram for Example 4.

"Example 5"
FIG. 10 shows the lens configuration of Example 5.
f = 65.541, FNo = 4.00, m = 0.36222, Y = 152.4, ω = 24.0 °
The data of Example 5 is shown in Table 5.

  FIG. 11 is an aberration diagram for Example 5.

  Table 6 shows parameter values of the condition (1) in Examples 1 to 5.

  Table 7 shows parameter values of the condition (2) in Examples 1 to 5.

  In each of Examples 1 to 5, FNo: about 4.0, a large aperture, and a half angle of view: about 24 degrees, a wide angle. As shown in each aberration diagram, the performance is also good.

L1 first lens
L2 second lens
L3 3rd lens
S Aperture stop
L4 4th lens
L5 5th lens
L6 6th lens
L7 7th lens

JP 2005-351973 A

Claims (8)

In order from the object side to the image side, a positive first group, a negative second group, a negative third group, a positive fourth group, a positive fifth group, and a negative sixth group are arranged, Having an aperture stop between the second group and the third group;
The first group is a positive first lens, the second group is a cemented lens of a positive second lens and a negative third lens, the third group is a negative fourth lens, the fourth group is a positive fifth lens, The 5th group is a positive sixth lens and the sixth group is a negative 7th lens.
The total focal length of the entire system for the e-line: f (> 0), the focal length of the fifth lens in the fourth group for the e-line: f4, the focal length of the sixth lens in the fifth group for the e-line: f5, When the Abbe number of the material of the fifth lens is ν5 and the Abbe number of the material of the sixth lens is ν6, φ4 and φ5 defined by φ4 = f4 / f and φ5 = f5 / f, and the Abbe number: ν5, ν6 and the composite focal length: f is the condition:
(1) 0.0 <φ4 / ν5 + φ5 / ν6 <0.04
(2) 0.0 <| f4-f5 | / f <0.1
A reading lens characterized by satisfying The reading lens according to claim 1.
A convex meniscus lens having a convex surface facing the object side;
A positive lens in which the second lens has a convex surface on the object side;
A third lens, a negative lens having a concave surface on the image side surface;
A concave meniscus lens having a concave surface facing the object side,
A fifth lens having a convex surface on the image side;
The sixth lens is a biconvex lens,
A reading lens, wherein the seventh lens is a biconcave lens. The reading lens according to claim 2, wherein
The second lens is a positive meniscus lens having a convex surface facing the object side;
The third lens is a negative meniscus lens having a concave surface facing the image side;
The reading lens, wherein the fifth lens is a biconvex lens. The reading lens according to claim 2, wherein
The second lens is a positive meniscus lens having a convex surface facing the object side;
The third lens is a negative meniscus lens having a concave surface facing the image side;
A reading lens, wherein the fifth lens is a positive meniscus lens having a convex surface directed toward the image side. The reading lens according to claim 2, wherein
The second lens is a biconvex lens;
The third lens is a biconcave lens;
A reading lens, wherein the fifth lens is a positive meniscus lens having a convex surface directed toward the image side. The reading lens according to claim 1,
A reading lens, wherein all of the first to seventh lenses are glass lenses made of glass containing no harmful substances such as lead and arsenic. An illumination system that illuminates the document; an imaging lens that reduces and images the reflected light of the document illuminated by the illumination system; a line sensor that receives and photoelectrically converts the document image formed by the imaging lens; An image reading apparatus comprising:
An image reading apparatus using the reading lens according to any one of claims 1 to 6 as an imaging lens.   An image forming apparatus that forms an image using the read image information using the image reading apparatus according to claim 7.

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