JP2007057968A - Reading lens, reading lens unit, original reading apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new reading lens capable of reading a wide original whose size exceeds an A-column No.2 size with high density of 600dpi. <P>SOLUTION: The reading lens has four-group, six-lens constitution including, in order from an original side, a first group composed of a first positive lens L1, a second group of negative refractive power, wherein a second positive lens L2 and a third negative lens L3 are cemented, a third group of negative refractive power, wherein a fourth negative lens L4 and a fifth positive lens L5 are cemented, and a fourth group composed of a sixth positive lens L6, and also, a diaphragm S arranged between the second and third groups. The deviation of partial dispersion of at least one material of the second lens L2 and the fifth lens L5 from a reference line: δθgd is positive, and the deviation of the partial dispersion of at least one material of the third lens L3 and the fourth lens L4 from a reference line:δθgd is negative, and conditions: 9500<N<15000 and 4.5<P<7.0 are satisfied, provided that the number of necessary pixels of a line sensor is expressed by N and the pixel pitch (unit:μm) of the line sensor is expressed by P. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a reading lens, an image reading lens unit, a document reading device, and an image forming apparatus. The reading lens of the present invention can be suitably used for a document reading unit of a facsimile machine or a digital copying machine and various image scanners. In particular, it is suitable as a reading lens for a wide document having a size of row A 2 or more.

  In a document reading unit or an image scanner of a facsimile machine or a digital copying machine, generally, image information to be read is reduced by a reading lens and formed on a solid-state image pickup device such as a CCD to convert the image information into a signal. Since document information is generally read as color information, a so-called “3-line CCD” in which light receiving elements having, for example, red, green, and blue filters are arranged in three rows on one chip is used as a solid-state image sensor. A document image is formed on the light receiving surface to separate the three primary colors, and color image information is converted into a signal.

  Thus, the reading lens that reduces the document information and forms an image on the solid-state imaging device 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 reason, it is necessary for the reading lens to correct the curvature of field well, and in particular, to make the contrast in the sub-scanning direction uniform, it is necessary to favorably correct the curvature of field in the sagittal direction and to reduce coma flare. .

  In addition, in order to read document information as color information 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 the other wavelengths when correcting the chromatic aberration on the axes of the two wavelengths must be corrected very well. Furthermore, it is desired that the aperture efficiency is close to 100% up to the periphery of the field angle.

  In order to read a wide document with a size larger than A row 2 (short length: 420 mm to 18 inches: 457.2 mm) at a high density of 600 dpi, A row 3 (usually about 304.8 mm for 12 inches) ) Since the document information is about 1.5 times that of the reading lens for reading, it is necessary to correct the aberration to be 1 / 1.5 times smaller.

Conventionally, a Gauss type having four groups and six elements is widely used as a reading lens.
The Gaussian type is a type that can satisfactorily correct the curvature of field up to a half angle of view of about 19 degrees, can suppress the occurrence of coma flare even with a relatively large aperture, and has high chromatic aberration correction capability. Conventionally, Gauss-type reading lenses that can read an A-line No. 3 size document have been described in various patent documents such as Patent Document 1, Patent Document 2, and Patent Document 3. Yes.

  These “reading lenses for reading an A-line No. 3 original document”, when used for reading an A-line No. 2 original document having a larger size, have a large amount of absolute aberration and a high-density original with a high density of 600 dpi. Is difficult in terms of performance.

  As "reading lenses for reading a wide document of size A row No. 2", those described in Patent Documents 4 and 5 are known. Aberrations relating to specific examples shown in these patent publications From the figure, it can be considered that it is difficult to cope with a reading density larger than 400 dpi because the absolute aberration amount, particularly coma aberration is large.

Japanese Patent No. 2790919 Japanese Patent Laid-Open No. 06-342120 JP 08-146292 A Japanese Patent No. 2729039 JP 09-171136 A

  In view of the above-described circumstances, the present invention realizes a novel reading lens capable of reading a wide document exceeding the size of row A No. 2 (short length: 420 mm to 18 inches: 457.2 mm) at a high density of 600 dpi. Let it be an issue.

  Another object of the present invention is to realize a reading lens unit in which such a reading lens is unitized, a document reading apparatus using the reading lens, and an image forming apparatus.

  The reading lens of the present invention is a “reading lens that is used in an original reading apparatus that reads an original image by forming an original image on a line sensor and forms an original image on the line sensor”, and is configured as shown in FIG. In order from the original side (left side of the drawing), the first group consisting of the positive first lens L1, the positive second lens L2, and the negative third lens L3 are cemented to form negative refractive power. A second group having a negative fourth lens L4 and a positive fifth lens L5 cemented to form a third group having a negative refractive power, and a fourth group consisting of a positive sixth lens L6. A four-group six-lens configuration having a diaphragm S between the group and the third group.

The reading lens according to claim 1 has the following characteristics.
First, partial dispersion: θgd is the refractive index of d line (587.56 nm): nd, the refractive index of c line (656.27 nm): nc, the refractive index of F line (486.13 nm): nF, g line ( 435.83 nm), with the following formula:
θgd = (ng−nd) / (nF−nc)
Defined by

Next, a two-dimensional coordinate plane is assumed in which the partial dispersion of the optical material: θgd and the Abbe number: νd are two orthogonal axes. Then, “the optical material in which the partial dispersion: θgd and the Abbe number: νd are specified” is expressed as “coordinate point (θgd, νd)” on this two-dimensional coordinate plane.
A straight line connecting the coordinate point of the reference material K7 and the coordinate point of the reference material F2 located on the two-dimensional coordinate plane is defined as a “reference line”.

  Partial deviation of the optical material: The deviation of θgd from the reference line on the two-dimensional coordinate plane is defined as δθgd. That is, the deviation: θgd is the distance in the “direction parallel to the partial dispersion axis” between the coordinate point on the two-dimensional coordinate plane of the optical material given the partial dispersion: θgd and the Abbe number: νd and the reference line. It is.

  The reading lens according to claim 1, wherein the deviation of at least one material of the second lens and the fifth lens: δθgd is positive, and the deviation of at least one material of the third lens and the fourth lens is δθgd. Is negative.

The necessary number of pixels of the line sensor on which the original image is formed: N, the pixel pitch of the line sensor (unit: μm): P is as follows:
(1) 9500 <N <15000
(2) 4.5 <P <7.0
Satisfied.

Deviation of second and fifth lenses: sum of δθgd, ie {δθgd (second lens) + δθgd (fifth lens)} is “δθgd25”, deviation of third and fourth lenses: sum of δθgd, ie , {Δθgd (third lens) + δθgd (fourth lens)} is defined as “δθgd34”. Further, the average refractive index of the first, second, fifth and sixth lenses with respect to the d-line is “n convex”, the average of the Abbe number is “ν convex”, and the third and fourth lenses are refracted with respect to the d line. If the average of the rate is “n-concave” and the average of the Abbe number is “ν-concave”, these δθgd25, δθgd34, n-convex, n-concave, ν-convex, and ν-concave are as follows:
(3) −0.03 <δθgd25−δθgd34 <0.03
(4) -0.003 <n convex -n concave <0.063
(5) 12.7 <ν convex−ν concave <18.6
Is preferably satisfied (claim 2).

  3. The reading lens according to claim 1, wherein the second group formed by joining the second lens and the third lens is a “meniscus shape with a convex surface facing the object side”, and the fourth lens and the fifth lens are joined. The third group is preferably a “meniscus shape with the convex surface facing the image surface” (Claim 3). In this case, it is preferable that 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”.

5. The reading lens according to claim 1, wherein the total focal length for the entire system e line is f, the focal length for the first group e line is f 1, and the second group and third group e lines. Is the following condition:
(6) 0.77 <f1 / f <0.96
(7) -1.06 <f25 / f <−0.63
Is preferably satisfied (Claim 5).

  The reading lens according to any one of claims 1 to 5, wherein all of the six lenses can be constituted by glass lenses. In that case, the glass material of each lens is "hazardous substances such as lead and arsenic". It is preferable not to contain (Claim 6). In this case, it is preferable that all six lenses are configured as “spherical lenses”.

  The reading lens unit according to the present invention is an optical element in which the reading lens according to any one of claims 1 to 7 is assembled and integrated in a lens barrel (claim 8).

The document reading apparatus according to claim 9 is an “apparatus for reading a document image in full color”, and includes document support means, illumination means, a document reading lens, color separation means, and imaging means.
“Document support means” is means for supporting an original.
“Illuminating means” is means for illuminating the original document supported by the original document supporting means.

The “original reading lens” is a lens that forms an image of an illuminated original, and the reading lens according to any one of claims 1 to 7 (the “reading lens unit” according to claim 8 as a usage form). Is used.
The “color separation unit” is a unit that is disposed on the imaging optical path of the document reading lens and performs color separation of the document image.
The “imaging means” is means for receiving an image of the original image formed by the original reading lens and converting it into an electric signal.

  In the document reading device according to claim 9, the document support means is “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. It is possible to employ a configuration in which a “scanning unit for scanning a document in a direction crossing the illumination unit” is provided and the imaging unit is a “line sensor”.

  The image forming apparatus according to claim 11 is an “apparatus for writing an image corresponding to an image signal to form an image”, and as means for reading a document image in full color to form an image signal. A document reading device. “Writing an image corresponding to an image signal” can be performed by various known methods such as an ink jet method, an ink ribbon method, and a thermal method. Configuration ”(claim 12).

  In this case, an electrostatic latent image corresponding to an image to be formed can be formed on the photoconductive photosensitive member by optical writing. “Optical writing” may be “optical scanning” or “method of forming an image of a light emitting point such as an LED array on a surface to be scanned by a lens array”.

  Supplementally, in general, in order to correct the curvature of field small, it is necessary to reduce the Petzval sum to some extent to ensure the flatness of the image surface. It is necessary to use an optical material having a low refractive index (low Abbe number) and a material having a low refractive index and high dispersion (low Abbe number) for the negative lens. Further, in order to keep the secondary spectrum of chromatic aberration small, it is preferable to set the deviation of partial dispersion of each optical material from the above-mentioned “reference line”: δθgd as “plus for positive lens” and “minus for negative lens”. .

  However, among optical glasses currently mass-produced, “high refractive index and low dispersion lanthanum crown and tantalum crown materials that are frequently used as positive lenses” have a partial dispersion deviation of δθgd of minus. In addition, “low refractive index and high dispersion heavy flint material that is frequently used as a negative lens” has a positive deviation of partial dispersion: Δθgd.

  In other words, in order to `` suppress Petzval sum '' and correct axial chromatic aberration well, use `` lanthanum crown and tantalum crown materials with high refractive index and low dispersion '' for the positive lens, and `` A high refractive index and low dispersion lanthanum crown or tantalum crown material can be used. However, with such an optical material combination, the sign of the partial dispersion deviation: δθgd is relative to that of the positive and negative lenses. Since it is opposite to the desired sign (“positive for positive lens”, “minus for negative lens”), it is difficult to keep the secondary spectrum of chromatic aberration small. For this reason, it has been difficult to satisfactorily correct the three aberrations of Petzval sum, axial chromatic aberration, and “secondary spectrum of axial chromatic aberration”.

  The reading lens according to the present invention is at least one of positive lenses of the cemented lens (second group, third group) in order to suppress the secondary spectrum of Petzval sum and axial chromatic aberration within the range of glass materials currently mass-produced. One of the negative lenses is an optical material having a partial dispersion deviation: δθgd and at least one of the negative lenses is an optical material having a partial dispersion deviation: δθgd.

  To read a wide document of size A or larger in row A with “high density of 600 dpi or more”, “the number of pixels required for the line sensor (= document surface length (mm) × {read density / 25.4 (mm)}” ) ", The number of pixels in the range of the condition (1) is required. In an actual optical system, a line sensor having “a margin of about 10%” with respect to the required number of pixels defined by the condition (1) is used.

  Condition (2) defines the condition of “line sensor pitch”. If the lower limit is exceeded, the evaluation spatial frequency on the surface of the line sensor becomes very high, so various aberrations must be corrected to be very small. The Gauss type with 4 groups and 6 elements makes it difficult to correct aberrations, increases the overall length of the lens to ensure performance, or requires the use of very expensive glass, leading to an increase in the cost of the reading lens. .

  If the upper limit of condition (2) is exceeded, the reduction magnification of the optical system increases, so when trying to make the entire reading optical system compact, the half angle of view of the reading lens becomes very large, and the entire area from off-axis to on-axis It is difficult to ensure good performance over a long period of time. On the other hand, if the half angle of view is to be set to about 19 degrees, it is necessary to make the focal length very long, and the total length of the lens and the outer diameter of the lens become long, making it difficult to make the reading lens compact, resulting in an increase in cost.

Condition (3) is that the sum of partial dispersion deviations of the positive lens (second lens and fifth lens) in the “positive and negative cemented lenses” constituting the second and third groups: δθgd25 and the negative lens in the cemented lens Sum of partial dispersion deviations of (third lens, fourth lens): difference from δθgd34:
δθgd25―δθgd34
Is used as a parameter, and an appropriate range of this parameter is determined.

  If the parameter: δθgd25−δθgd34 exceeds the lower limit of the condition (3), the secondary spectrum becomes insufficiently corrected in the region “outside the wavelength for correcting chromatic aberration on the axis” and becomes “positive and large”. Conversely, when the parameter: δθgd25−δθgd34 exceeds the upper limit of the condition (3), the secondary spectrum becomes “negative and large” in the region “between wavelengths for correcting axial chromatic aberration”.

  Condition (4) defines "the range of the refractive index of the four convex lenses and the two concave lenses constituting the reading lens". When the upper limit of the condition (4) is exceeded, the refractive index of the concave lens becomes small. The negative component in the Petzval sum is increased, the Petzval sum is likely to be reduced, and the image surface is inclined to the positive side and the curvature of field is likely to be increased. On the contrary, if the lower limit of condition (4) is exceeded, the refractive index of the convex lens tends to decrease, the positive component in the Petzval sum increases, the Petzval sum tends to increase, and the image plane falls to the negative side and is astigmatism. The gap is likely to increase. Therefore, it is difficult to “obtain good imaging performance over the entire screen” outside the range of condition (4).

  Condition (5) is “a condition to correct axial chromatic aberration satisfactorily”. When the upper limit is exceeded, axial chromatic aberration is overcorrected, and “axial chromatic aberration is larger on the shorter wavelength side than the main wavelength on the positive side” Become. On the other hand, if the lower limit is exceeded, the axial chromatic aberration is insufficiently corrected, and “the axial chromatic aberration becomes larger on the negative side on the shorter wavelength side than the main wavelength”.

  By making the “lenses close to the diaphragm (second group, third group)” into a meniscus shape as in the reading lens according to claim 3, the diaphragm disposed between the second group and the third group, It is possible to make the light beam “enter as concentric as possible”, and to suppress spherical aberration and curvature of field.

  5. The reading lens according to claim 4, 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”. In addition to the configuration described in claim 3, “all the lenses are meniscus-shaped”, so that all the lenses emit light “concentric as much as possible” with respect to the diaphragm arranged between the second group and the third group. It is possible to maintain the symmetry with respect to the stop, and to suppress the spherical aberration, the distortion aberration, and the chromatic aberration of magnification.

  The reading lens according to any one of the first to fourth aspects can satisfy each of the conditions (6) and (7) according to the fifth aspect, thereby making it possible to correct each aberration more satisfactorily. Cost reduction can be realized.

  Condition (6) is a condition for defining “relative power of the first group with respect to the power of the entire system”. When the parameter f1 / f exceeds the upper limit, the power of the first group is compared with the power of the entire system. It becomes relatively weak, and it is necessary to enlarge the entire lens to ensure performance, which tends to increase costs. On the contrary, if the parameter f1 / f exceeds the lower limit, it is advantageous for making the lens compact. However, since the power of the first unit relative to the power of the entire system becomes relatively strong, the coma flare tends to increase. The contrast at low frequencies tends to decrease.

  Condition (7) is a condition that regulates “the combined power of the second group and the third group having negative power” in the reading lens having a four-group configuration having positive, negative, negative, and positive power distributions. When the parameter: f25 / f exceeds the upper limit, the “negative power in the entire system” becomes too small, both the spherical aberration and the field curvature are overcorrected, and the coma around the periphery is deteriorated. On the other hand, if the parameter f25 / f exceeds the lower limit, the “negative power in the entire system” becomes too large, both the spherical aberration and the curvature of field become insufficiently corrected, and the astigmatism at the intermediate angle of view increases. The coma at the intermediate angle of view deteriorates. For this reason, it is extremely difficult to “obtain good imaging performance over the entire screen” outside the range of condition (7).

  When the first to sixth lenses are all made of a “glass material that does not contain harmful substances such as lead and arsenic” as in the reading lens according to claim 6, the material can be recycled and processed. There is no water pollution due to the waste liquid at the time, and a small and low-cost color image reading lens considering the global environment can be realized.

  In recent years, aspherical lenses have been widely used in various lens systems. However, since aspherical lenses are generally manufactured by resin molding, it takes time to mold and the processing cost increases as the lens outer diameter increases. To do. An aspherical lens configured as a resin lens is easily affected by temperature and humidity, and its surface shape is likely to change due to deformation due to temperature change. As in the reading lens according to claim 7, the first lens to the sixth lens are all composed of spherical lenses made of glass, and by not using an aspheric surface, the restriction on the size of the lens is greatly relaxed, and workability is improved. Further, by improving the surface shape accuracy, it is possible to realize a reading lens with high processing accuracy, and it is possible to read a document that is hardly affected by environmental fluctuations.

  A low-cost, high-performance “reading lens unit (claim 8)” can be obtained by “assembling and integrating the reading lens according to claims 1 to 7”.

  As described above, in the document reading device according to the tenth aspect, “a document placed in a plane on the contact glass is illuminated and scanned by the illuminating means” indicates that the positional relationship among the illumination device, the document reading lens, and the line sensor is The document to be scanned is illuminated in a slit shape on the contact glass placed at a position conjugate to the line sensor, and the document is moved in a direction crossing the slit-shaped illumination position to perform illumination scanning of the document. You may comprise. In this case, the contact glass has only to have “a narrow width necessary for illuminating the original”.

  Also, “a document to be read is placed flat on the document glass, the entire 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 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.

  As described above, according to the present invention, the line sensor satisfying the conditions (1) and (2) is used, and the performance necessary for reading a wide document having a size of column A No. 2 or larger at a high density of 600 dpi is provided. A Gauss-type reading lens can be realized with a four-group six-lens configuration.

  As shown in each embodiment described later, the reading lens according to the present invention has a bright F / NO of about 4.5, the aperture efficiency is close to 100% up to the periphery, the field curvature is corrected very well, and the coma flare is corrected. Is small and has high contrast from the vicinity of the axis to the outermost periphery in the high spatial frequency region, the axial chromatic aberration and the secondary spectrum are kept small, and the color-separated R (red), G (green), B ( The difference in the image forming position of blue) can be suppressed small, and a wide original having a size of row A No. 2 or larger can be satisfactorily read at a reading density of 600 dpi.

In the reading lens according to the sixth aspect, each constituent lens material can be recycled, and there is no water pollution due to waste liquid during processing.
An original reading apparatus using such a reading lens can read a color image of the original satisfactorily, and an image forming apparatus using such an original reading apparatus can obtain a good color image based on well read color image information. Can be formed.

One embodiment of the document reading apparatus is shown in FIG.
In FIG. 8, a document 2 to be read is placed flat on a contact glass 1 serving as a document support means, and an illumination optical system (not shown) disposed under the contact glass 1 (long in a direction perpendicular to the drawing). A known appropriate one composed of a tube lamp and a reflector can be used.) The “long slit-like portion in the direction orthogonal to the drawing” is illuminated.

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 third mirror 4B provided on the second traveling body 4. Are sequentially reflected and transmitted through the reading lens 5A assembled in the lens barrel of the reading lens unit 5 to form a reduced image of the original on the light receiving portion of the line sense 6 as the imaging means.
As the reading lens 5A, the one described in any one of claims 1 to 9, specifically, for example, any one of the document reading lenses of Examples 1 to 3 described later 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 illumination-scanned document portion to the document reading lens” is kept unchanged.

  The line sensor 6 is a so-called three-line CCD (three-line CCD) in which light-receiving elements having red (R), green (G), and blue (B) filters as color separation means are arranged in three rows on one chip. Line sensor) ”, and the original image is converted into an image signal as the original 2 is illuminated and scanned. In this way, reading of the document 2 is executed, and the color image of the document 2 is read by color separation into three primary colors of red, green, and blue.

  That is, the document reading apparatus shown in FIG. 8 is a device that reads a document image in full color, and includes a document support unit 1 that supports the document 2 and an illumination unit that illuminates the document 2 supported by the document support unit 1 ( An illumination optical system (not shown), the first traveling body 3, the second traveling body 4, the first to third mirrors 3A, 4A, 4B held by the traveling bodies 3, 4 and the traveling bodies 3, 4 A driving unit (not shown) that travels), a reading lens 5A that forms an image of the illuminated original 2 (attached to the barrel of the reading lens unit 5), and a reading lens 5A. 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 imaging optical path and the reading lens 5A is received and an electric signal is received. Imaging means 6 for converting to a reading lens As a those using a document reading lens according to any one of claims 1 to 7 (Claim 9).

  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 the line sensor 6 (claim 10).

  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 illuminated part 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.

  Further, the reading lens can be disposed in a document feeder (so-called ADF) and used as “for document back side reading” when reading both sides of a document.

  In “color separation”, a color separation prism or filter is selectively inserted between the document reading lens 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”.

  One embodiment of the “image forming apparatus” is shown in FIG.

  This image forming apparatus includes a document reading apparatus 200 positioned at the upper part of the apparatus and an “image forming unit” positioned at a lower position thereof. The portion of the document reading apparatus 200 is the same as that described with reference to FIG. 8, and the same reference numerals as those in FIG.

  The image signal output from the three-line line sensor (imaging means) 6 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, magenta, cyan, Signal for writing each color of black) ”.

  The image forming unit includes a photoconductive photosensitive member 110 formed in a cylindrical shape as a “latent image carrier”, and a charging roller 111 as a charging unit, a revolver type developing device 113, and a transfer belt around the photosensitive member 110. 114 and a cleaning device 115 are provided. As the charging means, a “corona charger” can be used instead of the charging roller 111.

  An optical scanning device 117 that receives a signal for writing from the signal processing unit 120 and writes on the photosensitive member 110 by optical scanning performs optical scanning of the photosensitive member 110 between the charging roller 111 and the developing device 113. ing.

  Reference numeral 116 denotes a fixing device, reference numeral 118 denotes a cassette, reference numeral 119 denotes a registration roller pair, reference numeral 122 denotes a paper feed roller, reference numeral 121 denotes a tray, and reference numeral S denotes a transfer sheet as a “recording medium”.

  When image formation is performed, the photoconductive photosensitive member 110 is rotated at a constant speed in the clockwise direction, the surface thereof is uniformly charged by the charging roller 111, and is subjected to exposure by optical writing of the laser beam of the optical scanning device 117. An electrostatic latent image is formed. The formed electrostatic latent image is a so-called “negative latent image”, and the image portion is exposed.

  “Image writing” is performed in the order of a yellow image, a magenta image, a cyan image, and a black image in accordance with the rotation of the photoconductor 110, and the formed electrostatic latent image is stored in each developing unit Y ( Development with yellow toner), M (development with magenta toner), C (development with cyan toner), K (development with black toner) are sequentially reversed and visualized as a positive image. The respective color toner images are sequentially transferred onto the transfer belt 114 by the transfer voltage application roller 114A, and the respective color toner images are superimposed on the transfer belt 114 to form a color image.

  The cassette 118 storing the transfer paper S is detachable from the main body of the image forming apparatus. When the cassette 118 is mounted as shown in the drawing, the uppermost sheet of the stored transfer paper S is fed by the paper feed roller 122. The leading edge of the fed transfer sheet S is caught by the registration roller pair 119.

  The registration roller pair 119 feeds the transfer sheet S to the transfer unit at the timing when the “color image by toner” on the transfer belt 114 moves to the transfer position. The transferred transfer paper S is superimposed on the color image at the transfer portion, and the color image is electrostatically transferred by the action of the transfer roller 114B. The transfer roller 114B presses the transfer sheet S against the color image during transfer.

  The transfer sheet S on which the color image has been transferred is sent to the fixing device 116, where the color image is fixed, passes through a conveyance path by a guide means (not shown), and is discharged onto the tray 121 by a pair of paper discharge rollers (not shown). The Each time each color toner image is transferred, the surface of the photoreceptor 110 is cleaned by the cleaning device 115 to remove residual toner, paper dust, and the like.

  That is, the image forming apparatus shown in the embodiment in FIG. 9 is an image forming apparatus that forms an image by writing an image corresponding to the image signal, and as means for converting a document image into an image signal. 10 to 10 (claim 11). The image corresponding to the image signal is written by optical writing (claim 12), and an electrostatic latent image corresponding to the image to be formed is formed on the photoconductive photosensitive member 110 by optical writing (claim). Item 13).

  Three specific examples of the reading lens will be described below.

The meanings of symbols in each embodiment are as follows.
DPI: Reading density f: Total focal length of e-line in the entire system F: F number m: Reduction magnification Y: Object height ω: Half angle of view (degrees)
N: Necessary number of pixels of the line sensor P: Pixel pitch of the line sensor r: Surface radius of curvature d: Surface spacing nd: Refractive index for d line (587.56 nm) ne: Refractive index ng for e line (546.07 nm) : Refractive index nF with respect to g-line (435.83 nm): Refractive index n with respect to F-line (486.13 nm) n: Refractive index with respect to C-line (656.27 nm) νd: Abbe number c1 with respect to d-line (587.56 nm): Contact Curvature radius c2 on the object side of the glass: Curvature radius c3 on the image side of the contact glass: Curvature radius c4 on the object side of the CCD cover glass: Curvature radius 1-11 on the image side of the CCD cover glass: Lens surfaces counted from the document side And diaphragm surface δθgdj (j = 2 to 5): Partial dispersion deviation δθgd (convex) of the material of the j-th lens counted from the object side: Average of partial dispersion deviation of lens having positive refractive power δθgd (concave): Average of partial dispersion deviation of lens having negative refractive power

DPI = 600 dpi, f = 77.128, F = 4.50, m = 0.1258,
Y = 228.6, ω = 18.3 °, N = 10800, P = 5.325
The data of Example 1 is shown in Table 1.

  Table 2 shows the values of the parameters in the condition (3).

  Table 3 shows the values of the parameters of the conditions (4) and (5).

  Table 4 shows the values of the parameters of the conditions (6) and (7).

DPI = 600 dpi, f = 76.399, F = 4.48, m = 0.1258,
Y = 228.6, ω = 18.5 °, N = 10800, P = 5.325
The data of Example 2 is shown in Table 5.

  Table 6 shows the values of the parameters in the condition (3).

  Table 7 shows the values of the parameters of the conditions (4) and (5).

Table 8 shows the values of the parameters of the conditions (6) and (7).

DPI = 600 dpi, f = 84.9, F = 4.40, m = 0.1417,
Y = 228.6, ω = 18.5 °, N = 10800, P = 6.0
The data of Example 3 is shown in Table 9.

  Table 10 shows the values of the parameters of the condition (3).

  Table 11 shows the values of the parameters of the conditions (4) and (5).

  Table 12 shows the values of the parameters of the conditions (6) and (7).

  In Examples 1 to 3, the glass materials used are all “made by HOYA glass”, and the glass material names are trade names.

  FIG. 2 shows a lens configuration diagram of the first embodiment. In the figure, reference numeral “CG is contact glass” and reference numeral CDG is “CCD cover glass”. Reference numerals I, II, III, and IV indicate first to fourth groups, respectively, and reference numeral S indicates a stop. The same applies to FIG. 4 showing the lens configuration diagram of Example 2 and FIG. 6 showing the lens configuration diagram of Example 3.

  FIG. 3 shows aberration diagrams related to Example 1. The wavy line in the spherical aberration diagram indicates the sine condition, the solid line in the astigmatism diagram indicates the sagittal ray, and the broken line indicates the meridional ray. The symbol e represents the e-line (546.07 nm), the symbol g represents the g-line (436.83 nm), the symbol c represents the c-line (656.27 nm), and the symbol F represents the F-line (486.13 nm). The same applies to FIG. 5 showing an aberration diagram related to Example 2 and FIG. 7 showing an aberration diagram related to Example 3.

  As is clear from the corresponding aberration diagrams, each example has very good performance, and a line sensor satisfying the conditions (1) and (2) is used, and a wide original having a size of column A, No. 2 or larger, has a high resolution of 600 dpi. It achieves the performance necessary to read with density.

It is a figure for demonstrating the reading lens of this invention. 1 is a lens configuration diagram of Example 1. FIG. FIG. 6 is an aberration diagram for Example 1. 6 is a lens configuration diagram of Example 2. FIG. FIG. 6 is an aberration diagram for Example 2. 6 is a lens configuration diagram of Example 3. FIG. FIG. 6 is an aberration diagram for Example 3. It is a figure for demonstrating one Embodiment of an original reading apparatus. It is a figure for demonstrating one Embodiment of an image forming apparatus.

Explanation of symbols

L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens L5 5th lens L6 6th lens S Aperture

Claims (13)

A reading lens that is used in a document reading device that forms a document image on a line sensor and reads document information, and that forms a document image on the line sensor,
In order from the document side, a first group consisting of a positive first lens, a second group having a negative refractive power by joining a positive second lens and a negative third lens, a negative fourth lens and a positive first lens A four-group six-lens configuration in which a third group having a negative refracting power and a fourth group consisting of a positive sixth lens are arranged with five lenses joined, and a stop is provided between the second group and the third group And
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) refractive index: ng gives the following formula:
θgd = (ng−nd) / (nF−nc)
Defines partial dispersion: θgd,
The reference line is defined as a straight line connecting the coordinate point of the reference material: K7 and the coordinate point of the reference material: F2 on the two-dimensional coordinate plane having the partial dispersion: θgd and the Abbe number: νd as two orthogonal axes.
Partial dispersion of optical material: θgd, when the deviation from the reference line on the two-dimensional coordinate plane is δθgd,
The deviation of at least one material of the second lens and the fifth lens: δθgd is positive,
The deviation of the material of at least one of the third lens and the fourth lens: δθgd is negative,
Necessary number of pixels of line sensor: N, pixel pitch of line sensor (unit: μm): P is as follows:
(1) 9500 <N <15000
(2) 4.5 <P <7.0
A reading lens characterized by satisfying The reading lens according to claim 1.
Deviation of second and fifth lenses: Sum of δθgd: δθgd25, Deviation of third and fourth lenses: Sum of δθgd: δθgd34,
Average refractive index for the d-line of the first, second, fifth and sixth lenses: n-convex, average Abbe number: v-convex, average of refractive index for the d-line of the third and fourth lenses: n-concave, Abbe number average: ν concave but under the following conditions:
(3) −0.03 <δθgd25−δθgd34 <0.03
(4) -0.003 <n convex -n concave <0.063
(5) 12.7 <ν convex−ν concave <18.6
A reading lens characterized by satisfying The reading lens according to claim 1 or 2,
The second group formed by bonding the second lens and the third lens has a meniscus shape arranged with the convex surface facing the object side, and the third group formed by bonding the fourth lens and the fifth lens has the convex surface directed toward the image plane. A reading lens having a meniscus shape arranged in the manner described above. The reading lens according to claim 3.
A reading lens, 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. The reading lens according to any one of claims 1 to 4,
The combined focal length for the entire system e-line: f, the focal length for the first group e-line: f1, the combined focal length for the second group and the third group e-line: f25, the following conditions:
(6) 0.77 <f1 / f <0.96
(7) -1.06 <f25 / f <−0.63
A reading lens characterized by satisfying The reading lens according to any one of claims 1 to 5,
A reading lens characterized in that all six lenses are glass lenses, and the glass materials do not contain harmful substances such as lead and arsenic. The reading lens according to claim 6.
A reading lens characterized in that all six lenses are composed of spherical lenses.   A reading lens unit in which the reading lens according to claim 1 is assembled and integrated with a lens barrel. A device for reading a document image in full color,
Document support means for supporting the document;
Illuminating means for illuminating the original document supported by the original document supporting means;
A document reading lens that forms an image of the illuminated document, and color separation means disposed on an imaging optical path of the document reading lens;
An image pickup unit that receives an image of the original image formed by the original reading lens and converts it into an electric signal, and the reading lens according to any one of claims 1 to 7 is used as the original reading lens. An original reading apparatus characterized by the above. The document reading device according to claim 9, wherein
The document support means is a contact glass for placing the document in a plane,
The illumination means has means for illuminating the document placed on the contact glass in a slit shape, and scanning the document in a direction intersecting the slit-shaped illumination unit,
An original reading apparatus, wherein the imaging means is a line sensor. An image forming apparatus for forming an image by writing an image corresponding to an image signal,
11. An image forming apparatus comprising the document reading device according to claim 9 or 10 as means for reading a document image in full color to form an image signal. The image forming apparatus according to claim 11.
An image forming apparatus, wherein an image corresponding to an image signal is written by optical writing. The image forming apparatus according to claim 12.
An image forming apparatus, wherein an electrostatic latent image corresponding to an image to be formed is formed on a photoconductive photosensitive member by optical writing.

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