JP4877718B2 - Reading lens, image reading lens unit, image reading apparatus, and image forming apparatus - Google Patents

Description

  The present invention relates to a reading lens, an image reading lens unit, an image reading apparatus, and an image forming apparatus. The reading lens and the image reading lens unit according to the present invention can be used for an image reading unit of a facsimile, a digital copying machine, and an image scanner. The image reading unit is an image forming apparatus such as a facsimile or a digital copying machine. Can be used.

  An image reading unit or an image scanner of an image forming apparatus such as a facsimile or a digital copying machine reduces image information to be read with a reading lens, forms an image on a solid-state imaging device such as a CCD, and outputs the image information as a signal. Turn into. In order to read image information of a document in color, for example, a so-called three-line CCD is used in which light receiving elements having red, green, and blue filters are arranged in three rows to form one light receiving element chip. . There is a reading lens optical system that separates the three primary colors by forming an original image on the light receiving surface and converts color image information into a signal.

  Such a reading lens is required to have a uniform and high contrast from the vicinity of the optical axis to the periphery in a high spatial frequency region. For this purpose, the reading lens needs to correct the field curvature well. Particularly, in order to make the contrast in the sub-scanning direction uniform, the field curvature in the sagittal direction is well corrected and the coma flare is corrected. It is necessary to keep it small. In addition, in order to read a color original satisfactorily, it is necessary to match the imaging positions of red, green, and blue colors with respect to the optical axis direction on the light receiving surface. The chromatic aberration of other wavelengths when correcting the axial chromatic aberration must be corrected very well. Furthermore, the aperture efficiency is required to be close to 100% up to the periphery of the angle of view.

  In general, the Petzval sum is reduced to some extent in order to correct the curvature of field to a small extent, and as a positive lens material for correcting axial chromatic aberration, it has a high refractive index and low dispersion (high Abbe number). As a material for the negative lens, it is necessary to use a material having a low refractive index and a high dispersion (small Abbe number). Further, in order to suppress the secondary spectrum of chromatic aberration to a small value, the deviation of the partial dispersion of each material from the reference line (the straight line connecting the partial dispersion θgd of the reference materials K7 and F2 and the Abbe number νd) is added to the positive lens. For negative lenses, negative. However, optical glasses that are currently in mass production and are frequently used as positive lenses, high refractive index, low dispersion lanthanum crown and tantalum crown glasses have negative partial dispersion deviations and negative lenses. The low-refractive-index, high-dispersion heavy flint glass, which is frequently used as a glass, has a positive partial dispersion deviation, and is excellent in three aberrations: Petzval sum, axial chromatic aberration, and axial chromatic aberration secondary spectrum It was difficult to correct.

  As a conventional reading lens, 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 suppressed even with a relatively large aperture, and the chromatic aberration correction capability is also high. There are six groups of Gaussian types (see, for example, Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, Patent Document 5, and Patent Document 6).

Japanese Patent No. 2729039 Japanese Patent No. 2790919 JP-A-9-304696 Japanese Patent Laid-Open No. 10-253881 JP 2001-166359 A Japanese Patent Laid-Open No. 2002-287022

  However, the lenses described in Patent Document 1, Patent Document 3, and Patent Document 5 have a property that the partial dispersion deviation is negative to the third and fourth lenses, which are negative lenses, for correcting the secondary spectrum of axial chromatic aberration. The so-called anomalous dispersion glass is used. The anomalous dispersion glass used in these inventions has a problem in terms of processing such as high unit price of glass material and easy burn. Therefore, when this glass material is used for two lenses, there is a problem that the cost becomes high. The lenses described in Patent Documents 2 and 4 have a large amount of absolute aberration and a large amount of sagittal image surface curvature, and therefore cannot have uniform and good performance from the vicinity of the optical axis to the outermost periphery.

  In recent years, as the pixel size of the light receiving element is reduced, the imaging magnification of the optical system is reduced. For example, when the temperature rises, the holding member holding the reading lens and the light receiving element expands. There is a problem that the distance between the reading lens and the light receiving element becomes long and the performance is greatly deteriorated, which is a problem for obtaining a highly accurate read image.

  In view of the above-mentioned problems of the prior art, the present invention uses a Gauss-type lens having a four-group, six-element structure, and has a relatively bright aperture ratio (F / NO.) Of about 4.5 to 5.0, and an aperture efficiency. Is close to 100% up to the periphery, and the field curvature is corrected very well and the coma flare is reduced, so that the high spatial frequency region has a high contrast from the vicinity of the axis to the outermost periphery. By suppressing the chromatic aberration and secondary spectrum of the image, the difference in image formation position between red (R), green (G), and blue (B) can be minimized, and the position of the light-receiving element fluctuates due to temperature changes. It is an object to provide a small, low-cost, high-performance reading lens, an image reading lens unit, and an image reading apparatus and an image forming apparatus using the same that have small performance deterioration and can be used for full-color reading. To do.

  The present invention also provides a small, low-cost reading lens, an image reading lens unit, an image reading apparatus and an image reading apparatus, and an image taking into consideration the global environment in which materials can be recycled and water quality is not contaminated by waste liquid during processing. An object is to provide a forming apparatus.

According to the first aspect of the present invention, in order from the object side, a first group including a positive first lens, a second group having a negative refractive power in which a positive second lens and a negative third lens are cemented, a negative The fourth lens group is composed of a fourth lens group having a negative refractive power and a fourth lens group consisting of a positive sixth lens, and a stop between the second lens group and the third lens group. A reading lens having
Partial dispersion (θgd) is defined as follows: d-line (587.56 nm) refractive index nd, c-line (656.27 nm) refractive index nc, F-line (486.13 nm) refractive index nF, g-line (435 .83 nm) where ng is the refractive index, defined by θgd = (ng−nd) / (nF−nc),
On the coordinate plane having the above partial dispersion: θgd and Abbe number: νd as two orthogonal axes, reference material: K7 coordinate point: K7 (θgd, νd) = (1.2343195, 60.5) and reference glass material: F2 A straight line connecting the coordinate points of F2 (θgd, νd) = (1.2892272, 36.30) is a reference line,
δθgd convex: average of deviations from the partial dispersion reference line of the positive lens (first, second, fifth, sixth lens) δθgd concave: from the partial dispersion reference line of the negative lens (third, fourth lens) Average of deviation n convex: average refractive index (d-line) of positive lenses (first, second, fifth and sixth lenses) n concave: refractive index of negative lenses (third and fourth lenses) (d Line) average ν convex: average of Abbe number of positive lenses (first, second, fifth, sixth lens) ν concave: average of Abbe number of negative lenses (third, fourth lens)
The Abbe number of at least one positive lens is 60 or more,
(1) −0.0075 <δθgd convex −δθgd concave <−0.001
(2) -0.02 <n convex-n concave <0.02.
(3) 19.5 <ν convex−ν concave <22.0
It satisfies the following conditions.

  In order to correct the curvature of field small, the Petzval sum is reduced to some extent, and in order to correct axial chromatic aberration, a material with a high refractive index and low dispersion (a large Abbe number) is used as a positive lens material. As a material for the negative lens, it is necessary to use a material having a low refractive index and a high dispersion (small Abbe number). In general, if a high refractive index glass material having a refractive index of 1.65 or more is used as the material of the positive lens, the Abbe number of currently available optical glass that satisfies this condition becomes smaller than 60. The refractive index coefficient with respect to the temperature of the glass material having a refractive index larger than 1.65 and an Abbe number smaller than 60 has a positive value. For this reason, when the temperature rises, the refractive index increases, and as a result, the focal length becomes shorter. On the other hand, the coefficient of linear expansion of the member that holds the lens and the light receiving element usually has a positive value. When the temperature rises, the member between the lens and the light receiving element expands, and the distance between the lens and the light receiving element increases. Become. Therefore, when a reading lens using a glass material having a positive temperature coefficient as a positive lens as described above is combined with the holding member, the focal length of the reading lens becomes short when the temperature rises, and the lens and the light receiving element The distance will become longer and the focus movement will increase, causing a significant performance degradation.

  Therefore, the reading lens according to the present invention uses a glass material having an Abbe number of 60 or more for at least one positive lens. Currently available optical glass with an Abbe number of 60 or more has a refractive index as low as 1.6 or less. For example, PCD4 and FC5 (both manufactured by Hoya Glass Co., Ltd. (HOYA)) are representative. Thus, the temperature coefficient of the refractive index is a negative value (the relative refractive index coefficient between + 20 ° C. and + 40 ° C. is −2.6 for PCD4 and −1.5 for FC5). By using such a glass material for the positive lens, it becomes possible to make the change in the focal length positive when the temperature rises, and it becomes possible to cancel the influence of the extension of the holding member having a positive linear expansion coefficient.

That is, in the lens according to the present invention, when the Abbe number of at least one positive lens is 60 or more, in other words, at least one temperature coefficient of the positive lens has a negative value. . In addition, when the extension of the holding member is large, it is desirable to use a glass material in which the Abbe number of two or more positive lenses is 60 or more, in other words, the temperature coefficient of two or more positive lenses is negative.
In the lens as described above, conditions for satisfactorily correcting the longitudinal chromatic aberration, the secondary spectrum, and the field curvature are conditional expressions (1) to (3). In order to suppress the secondary spectrum of chromatic aberration to a small value, the deviation of the partial dispersion of each material from the reference line (the straight line connecting the partial dispersion θgd of the reference materials K7 and F2 and the Abbe number νd) The lens should be negative.

  Conditional expression (1) is obtained by taking the average difference of deviations from the reference line of partial dispersion of each of the positive lens (first, second, fifth and sixth lenses) and the negative lens (third and fourth lenses). . If the lower limit is exceeded, the secondary spectrum in the range outside the wavelength for correcting chromatic aberration on the axis will be undercorrected and will be positive and large. On the other hand, if the upper limit is exceeded, the secondary spectrum between the wavelengths for correcting the axial chromatic aberration is minus and too large.

  Conditional expression (2) defines the range of the refractive index of the convex lens and the concave lens constituting the reading lens according to the present invention. If the upper limit is exceeded, the Petzval sum becomes too small, and the image plane falls to the positive side and the field curvature increases. If the lower limit is exceeded, the Petzval sum becomes too large, the image surface falls to the negative side, and the astigmatic difference increases.Under these conditions, good imaging performance can be obtained over the entire screen. Disappear.

  Conditional expression (3) is a condition for satisfactorily correcting axial chromatic aberration. If the upper limit is exceeded, the axial chromatic aberration will be overcorrected, and the axial chromatic aberration will become larger on the positive side at shorter wavelengths than the dominant wavelength. When the lower limit is exceeded, the axial chromatic aberration is insufficiently corrected, and the axial chromatic aberration becomes larger on the negative side at a shorter wavelength than the main wavelength.

According to a second aspect of the present invention, in the reading lens according to the first aspect, the following condition is satisfied.
(4) 0.86 <f1 / f <1.05
(5) -0.64 <f25 / f <-0.46
However,
f: total focal length of the e-line of the entire system f1: focal length of the e-line of the first group (first lens) f25: second group (second and third lenses) and third group (fourth and fifth) Lens) e-line composite focal length

  2. The reading lens according to claim 1, wherein when the conditional expressions (4) and (5) are satisfied, each aberration can be corrected satisfactorily, and a high-performance, compact and low-cost reading lens is obtained. be able to.

  Conditional expression (4) determines the power of the first lens group. If the upper limit is exceeded, the power of the first lens group becomes too weak, and it is necessary to enlarge the entire lens in order to ensure performance. It becomes. On the other hand, if the lower limit is exceeded, it is advantageous for making the lens compact, but the power of the first lens unit becomes too strong, so the coma flare becomes large and the contrast at a low frequency is lowered.

  Conditional expression (5) determines the combined power of the second group and the third group having negative power. If the upper limit is exceeded, both spherical aberration and field curvature will be overcorrected, and coma near the periphery will deteriorate. Resulting in. When the lower limit is exceeded, conversely, both spherical aberration and field curvature are insufficiently corrected, the astigmatic difference at the intermediate angle of view increases, and the coma aberration at the intermediate angle of view deteriorates. For this reason, outside the range of this conditional expression, it becomes impossible to obtain good imaging performance over the entire screen.

  According to a third aspect of the present invention, in the reading lens according to the first or second aspect, the shape of the cemented lens adjacent to the stop is determined in order to suppress spherical aberration, distortion, and chromatic aberration of magnification. The second group after joining the lens and the third lens has a meniscus shape with the convex surface facing the object side, and the third group after joining the fourth lens and the fifth lens has the convex surface facing the image surface. It is characterized by having a meniscus shape arranged.

  By making the lens close to the stop into a meniscus shape, the light beam can be made more concentrically incident on the stop disposed between the second group and the third group, and spherical aberration and field curvature Can be kept small.

  According to a fourth aspect of the present invention, in the reading lens according to the third aspect, the shapes of the first lens and the sixth lens are defined. The first lens has a meniscus shape with a convex surface facing the object side. The six lenses have a meniscus shape with a convex surface facing the image surface.

  In this way, by combining all the lenses with a meniscus shape together with the structure according to claim 3, as much light rays as possible can be obtained from all the lenses with respect to the diaphragm arranged between the second group and the third group. In addition to being incident on the lick, symmetry with respect to the stop is maintained. As a result, spherical aberration, distortion, and chromatic aberration of magnification can be reduced.

  According to a fifth aspect of the present invention, in the reading lens according to any of the first to fourth aspects, all six lenses are glass lenses, and the glass material does not contain harmful substances such as lead and arsenic. It is characterized by that.

All lenses are made of optical glass that is chemically stable and does not contain harmful substances such as lead and arsenic, so that materials can be recycled, and there is no water pollution caused by waste liquid during processing, saving resources, CO _{2 and the} like generated during processing can be reduced, and a small and low-cost reading lens can be obtained in consideration of the global environment.
According to a sixth aspect of the present invention, in the reading lens according to any one of the first to fifth aspects, all six lenses are formed of a spherical surface. Currently, aspherical lenses are used in digital cameras and other devices. However, when the outer diameter of the aspherical lens increases, it takes time during molding, resulting in high processing costs and maintaining a good surface shape. Can not be. Therefore, in the reading lens according to the sixth aspect, all the surfaces are formed of spherical surfaces, so that a lens with no size limitation and good workability and surface shape accuracy can be obtained.

  The invention according to claim 7 is an image reading lens that is low-cost, high-performance, and takes the global environment into consideration by assembling and integrating the reading lens according to any one of claims 1 to 6 into a lens barrel. You get a unit.

  According to an eighth aspect of the present invention, there is provided an apparatus for reading an image on an original, an original supporting means for supporting the original, an illuminating means for illuminating the original supported by the original supporting means, and an image of the illuminated original. And an image pickup means for receiving an image of the original image formed by the original reading lens and converting it into an electrical signal, wherein the original reading lens is any one of claims 1 to 7. The present invention relates to an image reading apparatus using the reading lens described above.

  The invention according to claim 9 is the invention according to claim 8, wherein the document support means is a contact glass for placing the document in a plane, and the illumination means illuminates the document placed on the contact glass in a slit shape. And a means for scanning the document in a direction crossing the slit-shaped illumination section, and the imaging means is a line sensor.

  The invention according to claim 10 is an apparatus for reading a color image on a document in full color, the document supporting means for supporting the document, the illumination means for illuminating the document supported by the document supporting means, and the illumination A document reading lens that forms an image of a document, color separation means disposed on an imaging optical path of the document reading lens, and a document image formed by the document reading lens is received and converted into an electrical signal. The present invention relates to an image reading apparatus characterized in that the reading lens according to claim 1 is used as the document reading lens.

  According to the eleventh aspect of the present invention, in the document reading device according to the tenth aspect, the document supporting means is a contact glass for placing the document in a plane, and the illumination means is a slit-shaped document placed on the contact glass. And a means for scanning the document in a direction intersecting with the slit-shaped illumination section, and the imaging means is a line sensor.

  In the inventions according to claims 8 and 10, the “document support means” is means for supporting the document in order to read a color image or the like. “Illuminating means” is means for illuminating the original document supported by the original document supporting means. The “document reading lens” is a lens that forms an image of an illuminated document, and is a reading lens according to claim 1. The “color separation means” is arranged on the imaging optical path of the document reading lens and performs color separation. The “imaging means” receives an image of the original image formed by the original reading lens (color-separated by the color separation means) and converts it into an electrical signal.

  The document reading device according to claim 8 or 10, wherein the document support means is a contact glass for placing the document in a plane, and the illumination means illuminates the document placed on the contact glass in a slit shape, And a scanning unit for scanning the document in a direction intersecting with the illumination unit, and the imaging unit is a line sensor.

  In the document reading device according to claims 9 and 11, “the document placed in a plane on the contact glass is illuminated and scanned by the illumination means” is fixed, “the positional relationship among the illumination device, the document reading lens, and the line sensor is fixed. Then, while illuminating the original to be read in a slit shape on the contact glass placed at a position conjugate to the line sensor, the original is moved in a direction crossing the slit-like illumination position to perform illumination scanning of the original. It may be configured. In this case, the contact glass has only to have “a narrow width necessary for illuminating the original”. Also, “The document to be read is placed flat on the document glass, the entire surface of the document is illuminated with a predetermined illuminance distribution, and a reduced image of the entire document is imaged on the light receiving surface of the area sensor by the document reading lens. It is also possible to configure so that the entire surface of the image is read simultaneously. Further, as the color separation means, it is possible to use one that switches the illumination light of the document at a high speed in the order of red, green, and blue.

  According to a twelfth aspect of the present invention, there is provided an image forming apparatus for forming an image by writing an image corresponding to an image signal, the image reading apparatus according to the ninth aspect as means for reading a document image into an image signal. It is characterized by that.

  According to a thirteenth aspect of the present invention, there is provided an image forming apparatus for forming an image by writing an image corresponding to an image signal, and as a means for reading an original image in full color to form an image signal. It has the apparatus.

  According to a fourteenth aspect of the present invention, in the image forming apparatus according to the twelfth or thirteenth aspect, the image corresponding to the image signal is written by optical writing.

  According to a fifteenth aspect of the present invention, in the image forming apparatus according to the fourteenth aspect, an electrostatic latent image corresponding to an image to be formed is formed on a photoconductive photoreceptor by optical writing.

  In the image forming apparatus according to any one of claims 12 to 15, the image signal can be written by various known methods such as an ink jet method, an ink ribbon method, and a heat sensitive method. As described above, it is possible to “write the image corresponding to the image signal by optical writing”. In this case, writing by optical writing, silver salt film or the like may be performed. However, as in the invention of claim 15, “corresponding to an image to be formed by optical writing on a photoconductive photoconductor. Forming an electrostatic latent image.

  The invention according to claim 1 is a four-group six-lens configuration, wherein the second group and the third group are cemented lenses, the stop is disposed between the second group and the third group, and at least one lens of a positive lens By setting the Abbe number to 60 or more, at least one temperature coefficient of the positive lens can be a negative value, and the change in the focal length of the reading lens can be positive when the temperature rises. The influence of the increase in the distance between the reading lens and the light receiving element due to the temperature rise can be canceled, and a highly accurate read image can always be obtained even if the usage environment changes. When the temperature decreases, the focal length change of the reading lens becomes negative, and the influence due to the shortening of the distance between the reading lens and the light receiving element is canceled.

  Furthermore, by setting the glass material of each lens within the range of conditional expressions (1), (2), and (3), while using an inexpensive glass material, the axial chromatic aberration and the curvature of field are very small. The secondary spectrum of chromatic aberration can be kept small, for example, the focus surfaces of each color when separated into R, G, and B can be matched, and a high frequency can be obtained over the entire field angle of about 18 °. Even in the region, it is possible to obtain a reading lens that can read document information satisfactorily in full color with uniform high contrast. The reading lens according to the first aspect of the invention is not limited to full-color reading only, and has good reading performance even when used as a monochrome reading lens.

  According to the second aspect of the present invention, by setting the combined focal length of the first group, the second group, and the third group within the range of the conditional expressions (4) and (5), the image plane is not increased. Since the curvature can be suppressed to a very low level and the coma flare can be reduced, a high-contrast reading lens can be obtained that is uniform in the main scanning direction and the sub-scanning direction over the entire reading range. .

  According to the third and fourth aspects of the present invention, all the lenses are formed in a meniscus shape so that the light beam is incident as concentrically as possible on the diaphragm arranged between the second group and the third group. Since the symmetry with respect to the stop can be maintained, spherical aberration, distortion, and chromatic aberration of magnification can be kept small, and there is no distortion or color blur, which is uniform and good over the entire reading range. Performance can be obtained.

  The invention according to claim 5 is a glass material that does not contain harmful substances such as lead and arsenic for all lenses, so that it is easy to recycle and does not cause water pollution due to waste liquid during processing. Can contribute.

  According to the sixth aspect of the present invention, since all the lenses are formed of spherical surfaces, no special processing equipment is required, and processing can be performed without restriction of the lens outer diameter. Furthermore, by using a glass material that is relatively inexpensive and is excellent in workability among currently mass-produced, it is possible to obtain a reading lens that is low in both material cost and processing cost.

According to the seventh aspect of the present invention, by using the reading lens according to any one of the first to sixth aspects, as is apparent from the aberration diagrams of each example described later, a four-group six-element configuration is provided. By using a Gaussian type, despite using a cheap glass material, the F number is about 4.5-5.0, while having a relatively large aperture ratio, the aperture efficiency is nearly 100%. Thus, an image reading lens unit capable of satisfactorily correcting chromatic aberration with a reduction ratio of 0.11102 can be obtained. Furthermore, it can be seen that the on-axis and off-axis aberrations are well balanced, and, as is apparent from the coma aberration curve, has a high contrast in the high spatial frequency region. By using this lens, it goes without saying that original information is read in monochrome, and as full-color reading, an image reading lens that can perform good reading with small variations in the SN ratio of each color of red, green, and blue. You can get a unit.
According to the invention described in claims 8 to 11, by providing the compact and low-cost reading lens, it is possible to obtain a low-cost and compact image reading apparatus that can read document information satisfactorily. .

  According to the invention of claims 12 to 15, by using the image reading apparatus provided with the reading lens, a high-quality image forming apparatus can be obtained at low cost.

  Embodiments of a reading lens, an image reading lens unit, an image reading apparatus, and an image forming apparatus according to the present invention will be described below with reference to the drawings.

First, embodiments of the reading lens according to the present invention will be described. FIG. 1 shows a configuration example of a reading lens according to the present invention, and the meanings of symbols attached to FIG. 1 and symbols attached to the respective embodiments are as follows.
f: Total focal length of e-line of the entire system F: F number m: Reduction ratio ω: Half angle of view (degrees)
Y: object height ri (i = 1 to 11): radius of curvature of i-th lens surface counted from the object side di (i = 1 to 10): i-th surface interval nj (j = 1) counted from the object side 6): Refractive index vj of the j-th lens material counted from the object side (j = 1 to 6): Abbe number rc1 of the material of the j-th lens counted from the object side: Curvature of the object side of the contact glass Radius rc2: Curvature radius rc3 on the image side of the contact glass: Curvature radius rc4 on the object side of the CCD cover glass: Curvature radius dc1 on the image side of the CCD cover glass: Thickness dc3 of the contact glass: Thickness nc1 of the CCD cover glass: Refractive index nc3 of CCD cover glass: Refractive index vc1 of contact glass: Abbe number of contact glass vc3: Abbe number of CCD cover glass nd: Refractive index ne of d-line (587.56 nm): Refractive index of line (546.07 nm) ng: Refractive index of g line (435.83 nm) nF: Refractive index of F line (486.13 nm) nC: Refractive index of C line (656.27 nm) δθgdj (j = 1) ˜6): Partial dispersion deviation δθgd (convex) of the material of the j-th lens counted from the object side: Average partial dispersion deviation δθgd (concave) of the lens having positive refractive power: Lens of the negative refractive power Average of partial variance deviation

  Also, in the aberration diagrams, the e-line shows 546.07 nm, the g-line shows 436.83 nm, the c-line shows 656.27 nm, and the F-line shows 486.13 nm. Also, in the spherical aberration diagram, the wavy line represents the sine condition, the astigmatism diagram, the solid line represents the sagittal ray, and the dotted line represents the meridional ray.

  The reading lens shown in FIG. 1 is a negative lens in which a first group consisting of a positive first lens 11, a positive second lens 12 and a negative third lens 13 are joined in order from the object side (left side in FIG. 1). The second group having refractive power, the fourth group consisting of a third group having negative refractive power in which the negative fourth lens 14 and the positive fifth lens 15 are cemented, and the positive sixth lens 16 are configured. Yes. A diaphragm 17 is disposed between the second group and the third group. Reference numeral 1 denotes a contact glass on which an original is placed in an image forming apparatus such as a copying machine. Reference numeral 19 denotes a cover glass of a CCD that is an image sensor.

  The second group after the second lens 12 and the third lens 13 are joined has a meniscus shape with the convex surface facing the object side. The third group after the fourth lens 14 and the fifth lens 15 are joined has a meniscus shape arranged with the convex surface facing the image plane. The first lens 11 has a meniscus shape arranged with the convex surface facing the object side, and the sixth lens 16 has a meniscus shape arranged with the convex surface facing the image surface. As described above, the entire reading lens constitutes a Gauss type lens system.

  The six lenses are all glass lenses, and all the lenses are made of a glass material that does not contain harmful substances such as lead and arsenic. In addition, the six lenses constituting the reading lens are all constituted by spherical surfaces. The reading lens system composed of the six lenses constitutes an image reading lens unit by being assembled and integrated with a lens barrel.

  Hereinafter, numerical examples of the reading lens according to the present invention will be described.

図２は、実施例１にかかる読取レンズの収差図である。

FIG. 2 is an aberration diagram of the reading lens according to the first example.

図３は、実施例２にかかる読取レンズの収差図である。

FIG. 3 is an aberration diagram of the reading lens according to the second example.

図４は、実施例３にかかる読取レンズの収差図である。

FIG. 4 is an aberration diagram of the reading lens according to the third example.

図５は、実施例４にかかる読取レンズの収差図である。

FIG. 5 is an aberration diagram of the reading lens according to the fourth example.

図６は、実施例５にかかる読取レンズの収差図である。

FIG. 6 is an aberration diagram of the reading lens according to the fifth example.

図７は、実施例６にかかる読取レンズの収差図である。

FIG. 7 is an aberration diagram of the reading lens according to the sixth example.

The table shown below shows the values of parameters used in the conditional expressions (1) to (5) in each example.

The table shown below shows the values of the conditional expressions (1) to (5) in each example.

  FIG. 8 shows a specific example of an image reading apparatus using the reading lens according to the present invention. In FIG. 8, a document 2 to be read is placed flat on a contact glass 1 as a document supporting means, and is “long in a direction perpendicular to the drawing” by an illumination optical system (not shown) disposed under the contact glass 1. The “slit-like part” is illuminated. The illumination optical system is provided in the first traveling body 3 described below. The reflected light from the illuminated portion of the document 1 is reflected by the first mirror 3A provided on the first traveling body 3, and then the second mirror 4A and the second mirror provided on the second traveling body 4. The light is sequentially reflected by 4B, passes through the original reading lens assembled in the lens barrel of the original reading lens unit 5, and forms a reduced image of the original on the light receiving portion of the line sense 6 as the imaging means. As the “document reading lens”, the reading lens described so far, specifically, any one of the document reading lenses in the first to sixth embodiments is used.

  The first traveling body 3 and the second traveling body 4 are caused to travel in the direction of the arrow (to the right in the figure) by driving means (not shown). The traveling speed of the first traveling body 3 is “V”, and the traveling speed of the second traveling body 4 is “V / 2”. By this traveling, the first traveling body 3 and the second traveling body 4 are displaced to positions indicated by broken lines, respectively. An illumination optical system (not shown) moves integrally with the first traveling body 3 and “illuminates and scans” the entire document 2 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 original reading lens is kept unchanged.

  The line sensor 6 is a so-called three-line CCD (three-line line sensor) in which light receiving elements having red, green, and blue filters as color separation means are arranged in three rows on one chip. Along with the illumination scanning, the document image is converted into an image signal. In this way, the original 2 is read, and the color image of the original 2 is read by color separation into the three primary colors of red, green, and blue. That is, the document reading device shown in FIG. 8 is a device that reads a color image on a document in full color, and illuminates the contact glass 1 that is a supporting means for the document 2 and the document 2 supported by the contact glass 1. Illuminating means (illumination optical system not shown, first and second traveling bodies 3 and 4, first to third mirrors 3A, 4A and 4B held by these traveling bodies, and the traveling body is not illustrated. A drive unit), a document reading lens for forming an image of the illuminated document 2 (attached to the barrel of the document reading lens unit 5), and the document reading lens unit 5. An image of the original image formed by the “color separation means (red, green and blue filters provided on the three-line CCD)” provided in the image optical path and the original reading lens is received and converted into an electrical signal. Shooting to convert And it means 6, as an original reading lens, wherein is obtained by using any one of such reading lens to the embodiments.

  Further, the “document supporting means” is the contact glass 1 for placing the document 2 in a plane, and the illumination means illuminates the document 2 placed on the contact glass 1 in a slit shape, and the slit-shaped illumination section. It has means for scanning the document in the intersecting direction, and the “imaging means” is composed of the line sensor 6.

  As another form of the document reading device, “illumination means for illuminating the document on the contact glass in a slit shape, a line sensor, a plurality of mirrors forming an imaging optical path from the non-illuminated portion of the document to the line sensor, It is also possible to adopt a configuration in which a reading unit in which a document reading lens arranged on the imaging optical path is integrated with each other is read and scanned relative to the document by driving means. it can. In addition, the document reading lens can be used in “document back side reading” when reading both sides of a document by placing it in a document feeder (so-called ADF).

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

  Next, an example of an image forming apparatus provided with the document reading apparatus will be described with reference to FIG. The image forming apparatus shown in FIG. 9 has a document reading apparatus 200 positioned at the upper part of the apparatus and an “image forming part” positioned at the lower part thereof. The portion of the document reading apparatus 200 is the same as that shown in FIG. 8, and the same components are denoted by the same reference numerals. In FIG. 9, an image signal output from the three-line line sensor (imaging means) 6 in the image reading apparatus 200 is sent to the signal processing unit 120 and processed by the signal processing unit 120. Magenta / cyan / black signals).

  The image forming unit includes a photoconductive photosensitive member 110 formed in a cylindrical shape as a “latent image carrier”, and around it, a charging roller 111 as a charging unit, a developing device 113, a transfer belt 114, and a cleaning device. A device 115 is 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 paper feeding cassette, reference numeral 119 denotes a registration roller pair, reference numeral 120 denotes a paper feeding roller, reference numeral 121 denotes a paper discharge path, reference numeral 122 denotes a paper discharge roller pair, and reference numeral 123 denotes a paper discharge tray. Show.

  When performing image formation, the photoconductive photosensitive member 110 is driven to rotate at a constant speed in the clockwise direction, the surface thereof is uniformly charged by the charging roller 111, and optical writing is performed with a laser beam by the optical scanning device 117. To expose an electrostatic latent image. The formed electrostatic latent image is a so-called “negative latent image”, and the image portion is exposed. The “negative latent image” is reversely developed with toner by the developing device 113 and visualized as a positive image, and the obtained toner image is transferred to the transfer paper supplied one by one from the paper feed tray 118 by the transfer pressure roller 114. Transcript. The transfer sheet is fixed by a fixing device 116 having a pair of fixing rollers, and is discharged from a pair of discharge rollers 122 to a discharge tray 123. The surface of the photoconductor 110 after the transfer is discharged and cleaned by a cleaning device 115 to prepare for image formation again.

  The example shown in FIG. 9 is an example of a monochrome image forming apparatus, but a full-color image forming apparatus can be obtained by using a known revolver as the developing device and providing an intermediate transfer belt. Examples thereof will be described below. According to the rotation of the photoconductor 110, “image writing” is performed in the order of yellow image, magenta image, cyan image, and black image, and electrostatic latent images corresponding to the written images are stored in the revolver-type developing device 113. A positive image is developed by reversal development in sequence by each development unit Y (development with yellow toner), M (development with magenta toner), C (development with cyan toner), and K (development with black toner). Each of the obtained color toner images is sequentially superimposed and transferred onto the transfer belt by the transfer voltage marking roller 114. The color toner images are superimposed on the transfer belt to form a full color image.

  The cassette 118 storing the transfer paper 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 is pulled out by the paper supply roller 120 and fed. Is done. The leading edge of the fed transfer paper is caught by the registration roller pair 119. The registration roller pair 119 feeds the transfer paper to the transfer unit at the timing when the color image by the toner on the transfer belt moves to the transfer position. The transferred transfer paper is superimposed with the color image at the transfer portion, and the color image is electrostatically transferred by the action of the transfer roller. The transfer paper onto which the color image has been transferred is sent to the fixing device 116, where the color image is fixed on the transfer paper, passes through a conveyance path 121 by a guide means (not shown), and is placed on the tray 123 by a pair of paper discharge rollers 122. Discharged. 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.

  That is, the embodiment of the image forming apparatus shown in FIG. 9 is an image forming apparatus that forms an image by writing an image corresponding to an image signal, and includes one of the reading lenses according to each of the embodiments. An image reading lens unit. Also, the image corresponding to the image signal is written by optical writing, and an electrostatic latent image corresponding to the image to be formed is formed on the photoconductive photoreceptor 110 by optical writing.

  Although the revolver type has been described as the full-color image forming apparatus, the image forming apparatus according to the present invention may be a so-called tandem type image forming apparatus in which a plurality of photoconductors are arranged corresponding to each color. Since the tandem image forming apparatus is well known, illustration is omitted.

FIG. 3 is an optical arrangement diagram illustrating an example of a reading lens according to the present invention. It is an aberration curve figure of Example 1 of the reading lens concerning this invention. It is an aberration curve figure of Example 2 of the reading lens concerning this invention. It is an aberration curve figure of Example 3 of the reading lens concerning this invention. It is an aberration curve figure of Example 4 of the reading lens concerning this invention. It is an aberration curve figure of Example 5 of the reading lens concerning this invention. It is an aberration curve figure of Example 6 of the reading lens concerning this invention. 1 is an optical layout diagram showing an embodiment of an image reading apparatus according to the present invention. 1 is an optical layout diagram showing an embodiment of an image forming apparatus according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Contact glass 5 Reading lens 11 1st lens 12 2nd lens 13 3rd lens 14 4th lens 15 5th lens 16 6th lens 110 Photoconductor

Claims (15)

In order from the object side, a first group including a positive first lens, a second group having a negative refractive power in which a positive second lens and a negative third lens are cemented, a negative fourth lens and a positive first lens A reading lens having a third lens group having a negative refractive power, and a fourth lens group having a positive sixth lens, and having a diaphragm between the second lens group and the third lens group;
Partial dispersion (θgd) is defined as follows: d-line (587.56 nm) refractive index nd, c-line (656.27 nm) refractive index nc, F-line (486.13 nm) refractive index nF, g-line (435 .83 nm) where ng is the refractive index, defined by θgd = (ng−nd) / (nF−nc),
On the coordinate plane having the above partial dispersion: θgd and Abbe number: νd as two orthogonal axes, reference material: K7 coordinate point: K7 (θgd, νd) = (1.2343195, 60.5) and reference glass material: F2 A straight line connecting the coordinate points of F2 (θgd, νd) = (1.2892272, 36.30) is a reference line,
δθgd convex: average of deviations from the partial dispersion reference line of the positive lens (first, second, fifth, sixth lens) δθgd concave: from the partial dispersion reference line of the negative lens (third, fourth lens) Average of deviation n convex: average refractive index (d-line) of positive lenses (first, second, fifth and sixth lenses) n concave: refractive index of negative lenses (third and fourth lenses) (d Line) average ν convex: average of Abbe number of positive lenses (first, second, fifth, sixth lens) ν concave: average of Abbe number of negative lenses (third, fourth lens)
The Abbe number of at least one positive lens is 60 or more,
(1) −0.0075 <δθgd convex −δθgd concave <−0.001
(2) -0.02 <n convex-n concave <0.02.
(3) 19.5 <ν convex−ν concave <22.0
A reading lens satisfying the following conditions.
The reading lens according to claim 1.
f: Composite focal length of e-line of the entire system f1: Focal length of e-line of the first group (first lens) f25: Second group (second and third lenses) and third group (fourth and fifth) Lens) and the combined focal length of the e-line,
(4) 0.86 <f1 / f <1.05
(5) -0.64 <f25 / f <-0.46
A reading lens satisfying the following conditions.   3. The reading lens according to claim 1, wherein the second group after the second lens and the third lens are joined has a meniscus shape with a convex surface facing the object side, and the fourth lens and the fifth lens. The third lens unit after cementing has a meniscus shape arranged with a convex surface facing the image surface.   4. The reading lens according to claim 3, wherein the first lens has a meniscus shape with a convex surface facing the object side, and the sixth lens has a meniscus shape with a convex surface facing the image surface. A characteristic reading lens.   5. The reading lens according to claim 1, wherein all of the six lenses are glass lenses, and the glass material does not contain harmful substances such as lead and arsenic.   6. A reading lens according to claim 1, wherein all of the six lenses are spherical.   An image reading lens unit in which the reading lens according to claim 1 is assembled and integrated with a lens barrel.   An apparatus for reading an image on an original, an original supporting means for supporting the original, an illuminating means for illuminating the original supported by the original supporting means, and an original reading lens for forming an image of the illuminated original And an image pickup means for receiving an image of the original image formed by the original reading lens and converting it into an electric signal, and the reading lens according to claim 1 is used as the original reading lens. An image reading apparatus.   9. The document reading apparatus according to claim 8, wherein the document support means is a contact glass for placing the document in a plane, and the illumination means illuminates the document placed on the contact glass in a slit shape, and slit-shaped illumination. An image reading apparatus having means for scanning a document in a direction intersecting with a section, and the image pickup means is a line sensor.   An apparatus for reading a color image on a document in full color, a document support unit that supports the document, an illumination unit that illuminates the document supported by the document support unit, and a document that forms an image of the illuminated document A reading lens, color separation means disposed on the imaging optical path of the document reading lens, and an imaging means for receiving an image of the document imaged by the document reading lens and converting it into an electrical signal, An image reading apparatus using the reading lens according to claim 1 as the document reading lens.   11. The document reading apparatus according to claim 10, wherein the document support means is a contact glass for placing the document in a plane, and the illumination means illuminates the document placed on the contact glass in a slit shape, and slit-shaped illumination. An image reading apparatus having means for scanning a document in a direction intersecting with a section, and the image pickup means is a line sensor.   An image forming apparatus for forming an image by writing an image corresponding to an image signal, the image forming apparatus having the image reading apparatus according to claim 9 as means for reading an original image into an image signal. .   An image forming apparatus for forming an image by writing an image corresponding to an image signal, the image forming apparatus having the image reading apparatus according to claim 11 as means for reading a document image in full color and converting it into an image signal. Image forming apparatus.   14. The image forming apparatus according to claim 12, wherein the image corresponding to the image signal is written by optical writing. 15. The image forming apparatus according to claim 14, wherein an electrostatic latent image corresponding to an image to be formed is formed on a photoconductive photoreceptor by optical writing.

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