JP2008003507A - Image reader and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reader capable of reading a document by using the excellent feature of the optical characteristic of a lens even if the document is smaller than a readable area, and to provide an image forming apparatus having the image reader. <P>SOLUTION: The image reader equipped with an optical system is characterized in that an imaging characteristic varies according to image height. In the lens composing the optical system, its position perpendicular to its optical axis is determined according to the imaging characteristic of the lens. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image reading apparatus, and more particularly to an image reading apparatus that can read a document that is smaller than the size of a document table with high quality and an image forming apparatus that includes the image reading apparatus.

  Although a readable area is set in the image reading apparatus, when an optical system is designed, the image forming characteristic is designed to fall within a predetermined specification value in the entire readable area.

  However, a lens that is an optical component always has a plurality of types of aberration characteristics, and the greater the influence of aberration, the lower the imaging quality. An index representing the imaging characteristics of the lens is MTF characteristics.

  For this reason, when designing an optical system, it is necessary to design the aberration to be close to 0. However, if the aberration in the entire optical system is to be close to 0, the number of lenses increases, or an aspheric lens must be used. And the structure becomes complicated. Furthermore, in reality, it is impossible to completely eliminate aberrations even if it is intended to improve aberrations.

  Therefore, in designing an optical system, it is common to determine design values while balancing cost and optical characteristics. The optical system designed in this way has good optical characteristics near the central axis of the lens, but often exhibits the property that the optical characteristics deteriorate as the image height increases. The central axis of the lens here is optically called an “optical axis” and is an axis passing through the center on the optical layout.

  As conventional techniques related to the design of an optical system of an image forming apparatus, there are an “image reading apparatus” disclosed in Patent Document 1 and an “original reading apparatus and image forming apparatus” disclosed in Patent Document 2.

  The invention disclosed in Patent Document 1 changes the magnification by changing the positional relationship between the lens and the CCD in order to change the magnification.

The invention disclosed in Patent Document 2 is an image forming apparatus of a type in which a read image is directly written on a photosensitive drum, and a single abutting surface of a read original is used to improve the running stability of the paper on the drum. It is for raising.
JP-A-6-309493 JP-A-8-179439

  However, depending on how the lens is assembled, the optical characteristics are not necessarily the highest in the vicinity of the central axis of the lens. As shown in FIGS. 7 and 8, the portion with the best characteristic (MTF) is the lens. In some cases, it may deviate from the central axis.

There are various sizes of originals read by the image reading apparatus. The image reading apparatus has a reference of a document position reference portion (abutment portion). When the reference is at the end of the table on which the document is placed, a small document is read at a position where the image height is high. .
For example, in the case of an image reading apparatus capable of reading up to A3 size, if a document as large as an L size of a photograph is applied as it is to the optical system of A3 setting, almost the entire area of the scanned document is at the center of the lens for the above reasons. It is read by using a region having a characteristic inferior to that of the portion.

  The inventions disclosed in Patent Document 1 and Patent Document 2 do not take these problems into consideration, and solve the problem of reading using an area with inferior optical characteristics when the document is smaller than the readable area. I can't do it.

  The present invention has been made in view of such a problem, and an image reading apparatus capable of reading a document using a portion having excellent optical characteristics of a lens even when the document is smaller than a readable region, and an image including the image reading device. An object is to provide a forming apparatus.

  In order to achieve the above object, the present invention provides, as a first aspect, an image reading apparatus equipped with an optical system having different imaging characteristics depending on the image height, wherein the lens constituting the optical system has its optical axis. The image reading apparatus is characterized in that the position in the direction orthogonal to the direction is determined in accordance with the imaging characteristics of the lens.

  In the first aspect of the present invention, it is preferable that the optical axis of the lens is shifted from the center of the readable area. In addition, the optical axis of the lens is shifted from the center of the readable position to the center of the document. It is more preferable to shift to the side.

  In any of the above configurations of the first aspect of the present invention, it is preferable to provide a lens position adjusting mechanism for adjusting the position of the lens in a direction orthogonal to the optical axis of the lens.

  In any of the above configurations of the first aspect of the present invention, a sensor for detecting the size of the document placed on the document table is provided, and the optical axis of the lens is determined according to the detection result of the sensor. It is preferable to change the position in the orthogonal direction. Alternatively, it is preferable that the lens is shifted to a reference position side when placing the document.

  In order to achieve the above object, the present invention provides, as a second aspect, an image forming apparatus including the image reading apparatus according to any one of the first aspect of the present invention.

  According to the present invention, it is possible to provide an image reading apparatus and an image forming apparatus including the image reading apparatus that can read an original using a portion having excellent optical characteristics of a lens even when the original is smaller than the readable area.

[First Embodiment]
A first embodiment in which the present invention is suitably implemented will be described.
FIG. 1 shows a configuration of an image reading apparatus according to the present embodiment. In order to facilitate understanding of the structure, some components such as a mirror are omitted in the figure. 4 and 5 are enlarged views of the reading unit (lens 101, CCD 102, cradle 103, slide block 105, and substrate 106).

A receiving base 103 for positioning the lens 101 and the CCD 102 is installed in the image reading apparatus. The CCD 102 mounted on the cradle 103 is electrically connected to the substrate 106. The cradle 103 is mounted via a slide block 105 on a rail 104 extending in a direction orthogonal to the central axis. The slide block 105 on which the cradle 103 is placed is slidable along the rail 104 by driving means (not shown). In addition, as a drive means, well-known power sources and transmission mechanisms, such as a motor, a belt, an air cylinder, and a rod, are applicable. Furthermore, the drive means may be configured only by a transmission mechanism and may be configured to transmit manual power.
Document position reference portions 107a and 107b are provided around the document table as a reference when placing the document.

  As the slide block 105 slides on the rail 104, the lens 101 and the CCD 102 move in a direction perpendicular to the central axis.

  In a state where the central axis of the lens 101 is coincident with the reading range (the state shown in FIG. 7), the lens characteristics are as shown in FIG. 8 (the best point of the optical characteristics is shifted from the center). 9, the position of the lens 101 is moved in the minus direction of the image height, so that the characteristic on the apparatus is in a state where the best point of the optical characteristic coincides with the center of the reading range (FIG. 10). The state shown in FIG.

  As described above, by moving the lens 101 and the CCD 102 in the direction orthogonal to the optical axis, it is possible to read an image using a portion having excellent optical characteristics of the lens 101 even for a small document.

[Second Embodiment]
A second embodiment in which the present invention is suitably implemented will be described.
FIG. 2 shows the configuration of the image reading apparatus according to the present embodiment.
This image forming apparatus is substantially the same as that of the first embodiment, but in this embodiment, the image reading apparatus includes a plurality of document sensors (here, two of 108 and 109). It is configured so that the size of the document can be grasped by the sensor.
The cradle 103 is moved together with the slide block 105 according to the detection results of the document sensors 108 and 109.

  FIG. 3 shows a state in which the document is placed on the document table. Since the center of the document is deviated from the center of the readable area, when this is detected by the document sensors 108 and 109, it is determined that the document is close to the reading position reference side (upward in the figure) The cradle 103 (the center axis of the lens) is moved upward in the figure.

  Thereby, the position of the central axis of the lens 101 can be adjusted according to the size of the document.

Note that the amount of movement of the central axis of the lens 101 is approximately obtained by calculation. In the case of an image reading apparatus capable of reading up to A3 landscape (vertical 297 × 410 mm), assuming that the center of the document is 0 mm at the time of A3 landscape, if the document is A4 landscape (210 × 297 mm), the document Therefore, the amount of movement is 43.5 mm, which is half of the difference.
In the case of A5 landscape orientation (length 148 × width 210 mm), the width of the document is different by 149 mm (297 mm−148 mm = 149 mm), and the movement amount is half that of 74.5 mm.
For B-size originals and other standard originals, the approximate amount of movement can be calculated by the same calculation.

  As described above, the image reading apparatus according to the present embodiment can adjust the position of the central axis of the lens 101 according to the size of the document.

[Third Embodiment]
A third embodiment in which the present invention is preferably implemented will be described. FIG. 6 shows a main part of the image reading apparatus according to the present embodiment.
In the image reading apparatus according to the present embodiment, a receiving table 102 on which a lens 101 and a CCD 102 are mounted is offset from the center of a document readable area.

  The central axis of the lens 101 is offset by “x” from the center of the readable area toward the document position reference portion 107a.

In the state shown in the drawing, when reading a small document, the vicinity of the central axis of the lens 101 is used, so that the read image quality is good. On the other hand, when a large original is read, the image quality on the side opposite to the original position reference unit 107a is deteriorated.
However, in general, when a scanned image is viewed by printing, for example, an image read from a small document is often viewed closely, and an image read from a large document is often viewed remotely. . That is, when reading an image from a small document, it is necessary to read it with high image quality, but when reading an image from a large document, there is little need to read it with high image quality. Therefore, when reading a large document, the image quality on the side opposite to the document position reference unit 107a may be deteriorated.

  In the figure, the document position reference parts 107a and 107b (document abutting parts) are located at the upper part (horizontal reference) and the right part (vertical reference) of the figure, but this position is not particular. The horizontal reference may be at the center of the readable area or at the lower side of the figure. In this case, as described above, the center axis of the lens may be shifted in the direction where the document position reference portion is located.

[Fourth Embodiment]
A fourth embodiment in which the present invention is preferably implemented will be described.

  As shown in FIG. 11, the image forming apparatus 1 includes an apparatus main body 2, an automatic document feeder (ADF) 3, an image reading unit 4, a paper feeding unit 5, and a writing unit 6.

  The apparatus main body 2 is formed in a box shape, for example, and is installed on a floor or the like. The apparatus main body 2 accommodates an image reading unit 4, a paper feeding unit 5, and a writing unit 6.

  The automatic document feeder 3 is attached to the upper part of the apparatus body 2. The automatic document feeder 3 includes a document placing plate 7 and a belt feeder 8. The document placing plate 7 is formed in a flat plate shape, is attached to the upper part of the apparatus main body 2, and a plurality of documents 9 are placed on the surface. The belt feeding device 8 feeds the originals 9 on the original placing plate 7 one by one onto a contact glass 10 which will be described later, and the original 9 on which a reflection image has been read by a lens block 16 which will be described later from the contact glass 10. Drain out of the main body 2.

  The image reading unit 4 is provided above the apparatus main body 2 and below the automatic document feeder 3 described above, and includes a contact glass 10 on which a document is placed and an optical scanning system 11. The contact glass 10 is attached to the upper surface of the apparatus main body 2 with both surfaces parallel to the horizontal direction. The optical scanning system 11 includes an exposure lamp 12, a first mirror 13, a second mirror 14, a third mirror 15, a lens block 16, and the like.

  The exposure lamp 12 irradiates the document 9 on the contact glass 10 with light. The first mirror 13, the second mirror 14, and the third mirror 15 guide the reflected image from the document 9 to the lens block 16. The exposure lamp 12 and the first mirror 13 are fixed on a first carriage (not shown), and the second mirror 14 and the third mirror 15 are fixed on a second carriage (not shown). When reading a document, the first carriage and the second carriage are mechanically moved at a relative speed of 2: 1 so that the optical path length does not change. The first carriage and the second carriage of the optical scanning system 11 are moved by a scanner drive motor (not shown).

  The lens block 16 includes an imaging lens system 31, an image sensor 32, and the like. The lens block 16 reads the above-described reflection image of the original by the image sensor 32, converts the optical signal into an electric signal, and processes it. The converted electrical signal is output toward an image processing unit (not shown). When the imaging lens system 31 and the CCD image sensor 32 are moved in the left-right direction (horizontal direction) in FIG. 1, the image magnification can be changed. That is, the positions of the imaging lens system 31 and the CCD image sensor 32 in the left-right direction in FIG. 1 are set corresponding to the specified magnification.

  The paper feed unit 5 includes a plurality of transfer paper storage portions 19 provided at the lower part of the apparatus main body 2 and a transfer paper feed unit 20. The transfer paper storage unit 19 stores a plurality of transfer papers 21. The transfer paper feed unit 20 sends the transfer paper 21 in the transfer paper storage unit 19 between registration rollers 25 described later. The paper feeding unit 5 feeds the transfer paper 21 in the transfer paper storage unit 19 one by one toward the registration roller 25, that is, the writing unit 6.

  The writing unit 6 includes a laser output unit 22, an imaging lens 23, a mirror 24, a registration roller 25, a photosensitive drum 26, a developing device 27, a transfer member 28, and a fixing device 29. Yes.

  Inside the laser output unit 22, there is provided a polygon mirror that rotates at a high speed at a high speed by a laser diode as a laser light source and a motor. Laser light emitted from the laser output unit 22 is deflected by a polygon mirror that rotates at a constant speed, passes through an imaging lens 23, is folded back by a mirror 24, and is condensed on the outer peripheral surface of the photosensitive drum 26 to form an image. To do. The deflected laser light is exposed and scanned in a so-called main scanning direction orthogonal to the direction in which the photosensitive drum 26 rotates, and recording is performed in line units of an image signal output from an image processing unit (not shown). Then, the writing unit 6 forms an image, that is, an electrostatic latent image, on the outer peripheral surface of the photosensitive drum 26 by repeating main scanning at a predetermined cycle corresponding to the rotational speed and recording density of the photosensitive drum 26. .

  In this way, the laser light output from the writing unit 6 is applied to the photosensitive drum 26 of the image forming system, and a main scanning synchronization signal is generated at the irradiation position of the laser light near one end of the photosensitive drum 26. A beam sensor (not shown) is arranged. Based on the main scanning synchronization signal output from the beam sensor, control of image recording timing in the main scanning direction and generation of control signals for input / output of image signals, which will be described later, are performed.

  The registration roller 25 sends the transfer paper 21 sent from the transfer paper storage unit 19 by the transfer paper sending unit 20 between the transfer member 28 and the photosensitive drum 26. The photosensitive drum 26 is formed in a columnar shape or a cylindrical shape that is rotatable around an axis. The photosensitive drum 26 is developed by the toner attached to the electrostatic latent image formed and carried by the laser output unit 22, and the toner image thus obtained is transferred onto the transfer paper 21 positioned between the transfer member 28. Transcript.

  The developing device 27 causes toner to adhere to the outer peripheral surface of the photosensitive drum 26 and develops the electrostatic latent image on the outer peripheral surface of the photosensitive drum 26. The transfer member 28 presses the transfer paper 21 against the outer peripheral surface of the photosensitive drum 26 to transfer the toner on the outer peripheral surface of the photosensitive drum 26 to the transfer paper 21 and directs the transfer paper 21 toward the fixing device 29. Send it out. The fixing device 29 fixes the toner image formed on the photosensitive drum 26 and the like onto the transfer paper 21 and discharges the transfer paper 21 out of the apparatus main body 2.

  In the image forming apparatus 1 described above, the automatic document feeder 3 automatically feeds the document onto the contact glass 10 of the image reading unit 4 and automatically discharges the document after reading. In the image forming apparatus 1, the image reading unit 4 irradiates light on a document set on the contact glass 10, and a reflected image from the document is read by a line type photoelectric conversion element 42 as a photoelectric conversion element.

  In the image forming apparatus 1, the writing unit 6 forms an image on the photosensitive drum 26 in accordance with the image signal of the read original, and transfers the image onto the transfer paper 21 fed from the paper feeding unit 5. And fix. The image forming apparatus 1 discharges the transfer paper 21 that has been fixed to the outside of the apparatus main body 2.

  By applying the image reading apparatus according to the first, second, or third embodiment to the illustrated image forming apparatus, it is possible to read an image from a document with high image quality and form the image on a transfer sheet. It becomes.

  Each of the above embodiments is an example of a preferred embodiment of the present invention, and the present invention is not limited to this, and various modifications are possible.

1 is a diagram illustrating a configuration of an image reading apparatus according to a first embodiment in which the present invention is preferably implemented. It is a figure which shows the structure of the image reading apparatus concerning 2nd Embodiment which implemented this invention suitably. FIG. 3 is a diagram illustrating a state where a document is placed on a document table. It is a figure which shows the structure of a reading unit. It is a figure which shows the structure of a reading unit. It is a figure which shows the structure of the principal part of the image reading apparatus concerning 3rd Embodiment which implemented this invention suitably. It is a figure which shows an example of the MTF characteristic of a lens. It is a figure which shows an example of the MTF characteristic of a lens. It is a figure which shows the state which moved the position of the lens to the minus direction of image height. It is a figure which shows the state in which the best point of an optical characteristic corresponds with the center of the reading range. It is a figure which shows the structure of the image forming apparatus concerning 4th Embodiment which implemented this invention suitably.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Document reading unit 3 Automatic document feeder 4 Image reading unit 5 Paper feed unit 6 Writing unit 7 Document placing plate 8 Belt feeder 9 Document 10 Contact glass 11 Optical scanning system 12 Exposure lamp 13 First mirror 14 Second mirror 15 Third mirror 16 Lens block 19 Transfer paper storage unit 20 Transfer paper feed unit 21 Transfer paper 22 Laser output unit 23 Imaging lens 24 Mirror 25 Registration roller 26 Photosensitive drum 27 Developing device 28 Transfer member 29 Fixing device 31 Imaging lens system 32 CCD image sensor 101 Lens 102 CCD
103 Receiving base 104 Rail 105 Slide block 106 Substrate 107a, 107b Document position reference section 108, 109 Document sensor

Claims (7)

An image reading apparatus equipped with an optical system having different imaging characteristics depending on image height,
An image reading apparatus, wherein the lens constituting the optical system has a position in a direction perpendicular to the optical axis determined in accordance with an imaging characteristic of the lens.   The image reading apparatus according to claim 1, wherein the optical axis of the lens is arranged so as to be shifted from the center of the readable area.   3. The image reading apparatus according to claim 2, wherein the optical axis of the lens is shifted from the center of the readable position toward the center of the document.   4. The image reading apparatus according to claim 1, further comprising a lens position adjusting mechanism for adjusting the position of the lens in a direction orthogonal to the optical axis of the lens. 5.   A sensor for detecting the size of a document placed on a document table is provided, and a position in a direction perpendicular to the optical axis of the lens is changed according to a detection result of the sensor. 5. The image reading apparatus according to claim 4.   The image reading apparatus according to claim 1, wherein the lens is shifted to a reference position side when placing a document.   An image forming apparatus comprising the image reading apparatus according to claim 1.

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