JP2004193839A - Image read apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image read apparatus capable of easily and simply correcting the variations in the quantity of light made incident on an image sensor due to the light distribution characteristics of a light source or deficiency of the brightness at the edge of an image forming lens or the like without causing color slip. <P>SOLUTION: An image read apparatus 100 for reading an image by transmitting the light R3 reflected on an original through the image forming lens 50 and forming the image on the image sensor 51 is provided with an aperture mechanism 106 which limits the light made incident onto the image forming lens 50 in response to a read line of the image sensor 51 and which has a slit shaped in such a way that the width of the slit is the narrowest at the center of the mechanism 106 corresponding to nearly the center of the image forming lens 50 and becomes increasingly broader toward both ends of the mechanism 106. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image reading apparatus that reads an image by forming an image of reflected light from a document on an image sensor, and in particular, to make the amount of light incident on the image sensor uniform with respect to a decrease in the amount of light around the imaging lens. The present invention relates to an image reading apparatus capable of performing the following.
[0002]
[Prior art]
2. Description of the Related Art In a scanner, a facsimile, a copying machine, and the like, generally, a document such as paper placed on a platen glass is scanned by a light source and a reflection mirror below the platen glass, or an automatic document feeder (ADF) is used. ), The original is irradiated with light while the original is automatically conveyed, and reflected light from the original is focused on an image sensor such as a CCD to read an image.
[0003]
The light source has a variation in light distribution characteristics. For example, when the light source is a rod-shaped light source at the main scanning position (in the reading line direction), the light amount is not uniform in all the axial directions. Few. Such a bias in the amount of light causes a bias in the output distribution of the image formed on the image sensor, which is one of the causes of deteriorating the image reading accuracy. In addition, a decrease in the output signal level due to a shortage of light at the periphery of the imaging lens has conventionally been electrically amplified by a shading correction circuit.
[0004]
In order to adjust the variation of the light distribution characteristics of the light source as described above, a plurality of light amount adjusting plates are provided along the axial direction of the light source, and light incident on the document from the light source is partially blocked by each light amount adjusting plate. A lighting device has been devised (see Patent Document 1). According to this device, each light amount adjusting plate is made to protrude largely with respect to the center of the light source, and is made to protrude small at both ends, so that the amount of light incident on the document from the light source can be adjusted to be uniform. Also, a black print layer is partially formed at the center of the reflection surface of the reflector that reflects the light of the light source in the document direction to reduce the reflectance, or a notch is provided so that the light of the light source can be reflected on the back of the reflector. A document illuminating device that makes the amount of light incident on a document from a light source uniform by escaping the document has been devised (see Patent Document 2).
[0005]
[Patent Document 1]
JP-A-7-319081 [Patent Document 2]
JP-A-8-204906
[Problems to be solved by the invention]
In image reading by a scanner, a facsimile, a copying machine, or the like, reflected light from a document guided to an image sensor by a reflection mirror or the like is converged on a reading surface of the image sensor by an imaging lens. Even if the amount of light incident on the document by the illuminating device is uniform, the main scanning of the document may also be caused by a lack of light amount in the peripheral portion of the imaging lens due to the so-called cos4 law, a variation in the sensitivity of the image sensor between individual members, or the like. The level of the output signal varies at the position (read line).
[0007]
In addition, if the output of the image sensor is electrically amplified by a shading correction circuit in order to correct the variation in the amount of light incident on the image sensor due to the lack of the amount of light at the periphery of the coupling lens, the output signal of the image sensor may be reduced. Is also amplified, and the dynamic range of the amplified portion is reduced. In particular, in the case where reading is performed with, for example, 8 bits and 256 gradations for each of RGB in reading a color image, if the above-described shading correction by electrical amplification is performed, the dynamic range of a portion where light quantity is insufficient is reduced. For the same color of the same document, there is a problem that color shift occurs at the center and both ends of the document.
[0008]
The present invention has been made in view of these points, and the variation in the amount of light incident on the image sensor due to the light distribution characteristics of the light source and the lack of peripheral light amount of the imaging lens, etc., without causing color shift and the like. It is an object of the present invention to provide an image reading apparatus capable of performing correction easily and easily.
[0009]
[Means for Solving the Problems]
An image reading apparatus according to the present invention is an image reading apparatus for reading an image by transmitting reflected light from a document through an image forming lens and forming an image on an image sensor. And a diaphragm mechanism having a slit having a shape in which a slit width is narrowest at a central portion corresponding to substantially the center of the imaging lens and is widened to both ends at a central portion corresponding to substantially the center of the imaging lens. It is. Thereby, the slit most restricts the amount of light incident on the imaging lens in the central portion where the slit width is the narrowest, and the slit is widened toward both ends of the reading line of the image sensor from the central portion. By increasing the amount of incident light, the amount of light incident on the image sensor is made uniform over the entire image sensor.
[0010]
The slit is formed by at least two light shielding members movable in the slit width direction. Thereby, the light shielding member is moved in the slit width direction, so that the output level of the image sensor becomes constant in accordance with the degree of shortage of the peripheral light amount due to the individual difference between the light source, the imaging lens, and the image sensor. The slit width can be adjusted.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an image reading apparatus according to an embodiment of the present invention will be specifically described with reference to the drawings. Note that the image reading apparatus according to the present embodiment is merely an example of the present invention, and the configuration of the present invention is not limited to the image reading apparatus.
[0012]
FIG. 1 is a schematic perspective view showing an external appearance of an upper part of a multi-function facsimile machine 1 including an image reading apparatus 100 according to an embodiment of the present invention. As shown in the figure, the copy / facsimile multifunction peripheral 1 includes a reading table 3 on which a platen glass 2 on which a document to be read is placed is arranged, and a document for pressing the document onto the platen glass 2 and fixing the document. A press cover 4 and an operation panel 5 for inputting the start of reading of a document and the like are provided. The image reading device 100 described in detail below is provided in the housing of the reading table 3, and reads an image of a document from below the platen glass 2.
[0013]
Although not shown in the figure, the copy / facsimile multifunction peripheral 1 includes a paper feeding unit that supplies recording paper for recording a read image, an image recording unit that records an image on recording paper, and an image recording unit. The copy / facsimile multifunction peripheral 1 is also an example of a device including the image reading device according to the present invention, and the image recording unit and the like have an arbitrary configuration. Of course.
[0014]
FIG. 2 is a view showing a vertical cross section of the reading table 3 and the document holding cover 4. As shown in FIG. 2, the image reading apparatus 100 reads a document placed on the platen glass 2. It is configured as a bed scanner (FBS), and is configured to read a document automatically conveyed by the ADF 6 of the document pressing cover 4. The ADF 6 includes a paper feed tray 61 on which a bundle of documents to be read is placed, a pickup roller 62a, a separate roller 62b, and a retard roller 62c that take out and supply the topmost sheet from the bundle of documents, A conveyance path 64 that guides the sheet to the discharge tray 63 while inverting the sheet downward, a conveyance roller 65 that is appropriately disposed in the conveyance path 64 and conveys a document, and a sheet discharge tray 63 that is disposed at the most downstream of the conveyance path 64. Is provided. With the ADF 6 configured as described above, the document sequentially fed from the paper feed tray 61 to the transport path 64 passes through the reading position P of the platen glass 2, and after the image is read at the reading position P, the document is discharged. The paper is discharged to the paper tray 63.
[0015]
Under the platen glass 2, when using the FBS, the original on the platen glass 2 is scanned while moving below the platen glass 2 in the horizontal direction. When the ADF 6 is used, the original which is moved to the reading position P and sequentially conveyed is scanned. An image reading unit 101 for scanning is provided.
[0016]
FIG. 3 is a diagram showing a main configuration of the image reading unit 101. As shown in FIG. 3, below the platen glass 2, a full-rate carriage 102 and a half A rate carriage 103 is provided. The full-rate carriage 102 includes, on the carriage main body 20, a light source 21 for irradiating the original with light, and a reflecting mirror 22 for reflecting the reflected light R1 from the original in the scanning direction and guiding the reflected light R1 to the half-rate carriage 103. The half-rate carriage 103 includes two reflection mirrors 31 and 32 that guide the reflected light R2 from the full-rate carriage 102 to the scanner unit 104 in the carriage main body 30. The thus configured full rate carriage 102 and half rate carriage 103 are slidably supported by guide rails (not shown).
[0017]
Further, a pair of belt driving mechanisms 104 are provided along both ends of the full rate carriage 102 and the half rate carriage 103. As shown in the figure, the belt driving mechanism 104 is configured such that belts 44 and 45 wound around the driving pulleys 40 and 41 and the driven pulleys 42 and 43 respectively move circumferentially by the rotation of the driving shaft 46. The full-rate carriage 102 is fixed to the belt 44, and the half-rate carriage 103 is fixed to the belt 45. The drive pulleys 40 and 41 are both fixed to the drive shaft 46, and the scanning range of the full rate carriage 102 and the half rate carriage 103 is set by the gear ratio of the drive pulleys 40 and 41. That is, the full-rate carriage 102 and the half-rate carriage 103 that are scanned by the belts 44 and 45 wound around the drive pulleys 40 and 41, respectively, are moved at a speed approximately half the scanning speed of the full-rate carriage 102. 103 is scanned, and as shown in the figure, while the full-rate carriage 102 is scanned by the scanning distance L1, the half-rate carriage 103 is scanned by approximately half the scanning distance L2.
[0018]
The full-rate carriage 102 and the half-rate carriage 103 configured as described above move below the platen glass 2 in parallel with the original to scan the image of the original, and the light source 21 of the full-rate carriage 102 irradiates the original with light. The reflected light R1 from the document is reflected by the reflecting mirror 22 as reflected light R2 in the horizontal direction, further reflected vertically downward by the reflecting mirror 31 of the half-rate carriage 103, and then reflected by the reflecting mirror 32 in the horizontal direction. As a result, the light is guided to the scanner unit 105.
[0019]
FIG. 4 is a schematic perspective view showing a detailed configuration of the scanner unit 105 and the aperture mechanism 106. The scanner unit 105 is a so-called reduction optical system CCD reading unit, and as shown in FIG. And an image sensor 51 for converting the converged light into an electric signal. The image sensor 51 has a reading surface of the image forming lens 50. It is fixed to the back of the scanner frame 53 via an adjustment frame 52 that adjusts the position so as to be orthogonal to the optical axis. The reflected light R3 is read by the image sensor 51 and output as an electric signal by the scanner unit 105 configured as described above.
[0020]
As shown in the figure, a stop mechanism 106 for limiting the amount of light incident on the imaging lens 50 is provided in front of the imaging lens 50. As shown in FIGS. 4 and 5, the aperture mechanism 106 is configured such that an upper light shielding member 61 and a lower light shielding member 62 are fixed to a substrate 60 erected on the scanner frame 54 by screws 63. Only light passing through a slit formed by the member 61 and the lower light blocking member 62 is incident on the imaging lens 50.
[0021]
As will be described in more detail, the substrate 60 is fitted to a fitting portion 530 provided on the scanner frame 53 and is appropriately screwed to the scanner frame 53 so that the substrate 60 stands upright in front of the imaging lens 50. Fixed. A circular opening 601 having substantially the same diameter as the imaging lens 50 is formed substantially at the center of the substrate 60, and reflected light R <b> 3 from a document enters the imaging lens 50 through the opening 601. Screw holes 602 are formed on both sides of the opening 601, and the screws 63 are screwed together so that the upper light-shielding member 61 and the lower light-shielding member 62 can be tightened to the substrate 60. Further, positioning pins 603 are respectively provided outside the screw holes 602, and the upper light-shielding member 61 and the lower light-shielding member 62 fixed to the substrate 60 in the horizontal direction are sandwiched between the positioning pins 603. Is regulated. Also, positioning holes 604 for adjusting the mounting positions of the upper light shielding member 61 and the lower light shielding member 62 are vertically arranged on the upper and lower sides of each screw hole 602, respectively. The positioning holes 604 are holes into which claws 611 and 621 protruding from the upper light shielding member 61 and the lower light shielding member 62 are respectively fitted, and a position adjustment range of the upper light shielding member 61 and the lower light shielding member 62 is taken into consideration. A plurality of left and right positioning holes 604 are vertically arranged at a predetermined pitch. Therefore, by inserting the claws 611 and 621 into a pair of left and right positioning holes 604 respectively, the upper light-shielding member 61 and the lower light-shielding member 62 can be at desired heights with respect to the opening 601 of the substrate 60 respectively. Can be positioned.
[0022]
In the present embodiment, the plurality of positioning holes 604 are formed in two rows in a step shape, but this is for the purpose of enabling a finer position adjustment than the thickness of the claws 611 and 621. It is obvious that the arrangement of the positioning holes 604 can be changed by the thickness of the 611 and 621, the size of the positioning holes 604, the adjustment pitch of the upper light shielding member 61 and the lower light shielding member 62, and the like.
[0023]
As described above, the upper light-shielding member 61 has the claws 611 protruding from the upper end thereof on the front and back sides, respectively. The claws 611 are fitted into the positioning holes 604 of the substrate 60, and a desired front part of the substrate 60 is provided. Is positioned at the height of Each of the claws 611 on the front and back sides corresponds to one row of the positioning holes 604 formed in two rows, and the front and back sides of the upper light shielding member 61 are changed so that the claws are formed in the positioning holes 604 of any row. The height position can be adjusted by fitting 611. Near the center from the lower end of the upper light shielding member 61, a cutout portion 612 having a width substantially equal to the diameter of the opening 601 of the substrate 60 is formed, and when the upper light shielding member 61 is fixed to the substrate 60, The upper light-shielding member 61 shields a part of the upper side of the opening 601 of the substrate 60 and allows light to pass only from the cutout 612, thereby limiting light incident on the imaging lens 50. Further, vertically long holes 613 are formed on both sides of the cutout portion 612, and even if the claw 611 of the upper light shielding member 61 is fitted into any of the positioning holes 604, the screw 63 is inserted into the long hole 613. And the screw hole 602 of the substrate 60 can be communicated.
[0024]
On the other hand, similarly to the upper light shielding member 61, the lower light shielding member 62 also has a claw 621 projecting from the lower end thereof on each of the front and back sides, and the claw 621 is inserted into the positioning holes 604 in any row of the substrate 60. The height position can be adjusted by fitting. A cutout portion 622 having a size substantially equal to the diameter of the opening 601 of the substrate 60 is formed substantially in the vicinity of the center from the upper end of the lower light shielding member 62, and the lower light shielding member 62 is fixed when the lower light shielding member 62 is fixed to the substrate 60. The member 62 shields a portion of the substrate 60 below the opening 601 and allows light to pass only from the notch 622, thereby limiting light incident on the imaging lens 50. Further, vertically long holes 623 are formed on both sides of the cutout portion 622, and even if the claw 621 of the lower light shielding member 62 is fitted into any of the positioning holes 604, the screw 63 is inserted into the long hole 623. And the screw hole 602 of the substrate 60 can be communicated. The upper light-shielding member 61 and the lower light-shielding member 62 thus configured are positioned at desired heights of the substrate 60, respectively, and tightened by screws 63 communicating with the long holes 613, 623 and the screw hole 603, and FIG. And as shown in FIG. 6, it is fixed to the substrate 60.
[0025]
Thereby, as shown in the figure, a horizontally long slit is formed in front of the imaging lens 50 by the gap between the notch 612 and the notch 622 to limit the amount of light incident on the imaging lens 50. The horizontal slit is used because the reading line (main scanning direction) of the image sensor 51 is in a horizontal direction with respect to the imaging lens 50. The horizontal direction of the slit can be appropriately changed.
[0026]
The shape of the slit is such that the slit width (vertical direction) is the narrowest at a central portion corresponding to substantially the center of the imaging lens 50, and is widened to both ends. That is, as shown in the drawing, the notch 612 and the notch 622 have an upper light shielding member 61 or a lower light shielding member toward the center of the imaging lens 50 at a portion corresponding to the center of the imaging lens 50. The bulging portions 614 and 624 each having a bulging shape 62 are formed. The shape of the bulging portions 614 and 624 is such that the output signal level of the image sensor 51 is reduced at both ends of the image sensor 51 as shown in FIG. And the slit most restricts the amount of light incident on the imaging lens 50 in the central portion where the slit width is the narrowest, and in both ends, the width is larger than that in the central portion. Incident light amount increases. Thus, the amount of light incident on the image sensor 51 can be made uniform over the entire image sensor 51.
[0027]
The shapes of the bulging portions 614 and 624 can be set, for example, as follows. As shown in FIG. 7, the output level decrease rate at the end portion (1−Ve / Vc) is obtained from the output level at the end portion based on the output Ve at the end portion of the image sensor 51 and the output Vc at the central portion. Next, a dimension is calculated by multiplying the lens diameter of the imaging lens 50 by the reduction rate. By forming the bulges 614 and 624 with this bulge dimension, the slit formed by the bulges 614 and 624 controls the amount of light incident on the imaging lens 50 from the end in the center. It is limited by the decrease rate.
[0028]
The bulging portions 614 and 624 have a shape bulging in an arc shape, but may have other shapes. For example, as shown in FIG. 8 (a), a pointed shape having a sharp central portion may be used. Further, in a case where the portion that mainly affects the output level of the image sensor 51 is not the entire area of the imaging lens 50 but a part near the center, or the like, as shown in FIGS. The bulges 614 and 624 may be formed in a part near the center of the notch 612 and the notch 622.
[0029]
As described above, the upper light-shielding member 61 and the lower light-shielding member 62 can be easily moved in the vertical direction (slit width direction) by changing the positioning holes 604 of the substrate 60 into which the claws 611 and 621 are fitted. Therefore, the slit width formed by the upper light shielding member 61 and the lower light shielding member 62 can be easily adjusted. Therefore, for example, by adjusting the slit width so that the output level of the image sensor 51 is constant during shipping, installation, and maintenance of the image reading apparatus 100, the light distribution characteristics of the light source 21 and the imaging lens 50 can be adjusted. It is possible to correct differences between individuals, such as insufficient peripheral light quantity and sensitivity of the image sensor 51.
[0030]
In the present embodiment, it is assumed that claws 611 and 621 protruding from the upper light-shielding member 61 and the lower light-shielding member 62 are fitted into any of the plurality of positioning holes 604 of the substrate 60, so that the upper light-shielding member 61 and the lower Although the light shielding member 62 can be moved in the slit width direction, other known moving mechanisms such as moving the upper light shielding member 61 and the lower light shielding member 62 in the vertical direction by a rack-pinion mechanism can of course be used. is there.
[0031]
In the above-described embodiment, the copy / facsimile multifunction peripheral 1 equipped with the image reading apparatus 100 has been described as an example. However, the image reading apparatus according to the present invention can be applied to other apparatuses such as a scanner. The configuration of the reading unit 101 of the image reading apparatus 100 described in the present embodiment is also an example, and it is obvious that the configuration can be changed without departing from the gist of the present invention.
[0032]
【The invention's effect】
As described above, according to the image reading apparatus of the present invention, the light incident on the imaging lens is limited corresponding to the reading line of the image sensor, and the slit width is set at the center corresponding to substantially the center of the imaging lens. Is provided with a diaphragm mechanism having a slit having a shape widened to both end portions, so that the amount of light incident on the image sensor can be made uniform over the entire image sensor. As a result, it is possible to easily and easily correct a decrease in the output signal level of the image sensor due to a light distribution characteristic of the light source or a shortage of the peripheral light of the imaging lens without causing a color shift or the like.
[0033]
Further, since the slit is formed by at least two light shielding members movable in the slit width direction, the slit width can be adjusted so that the output level of the image sensor is constant, and the light source, the imaging lens, and the image The difference between the sensors can be easily and simply corrected.
[Brief description of the drawings]
FIG. 1 is a schematic perspective view showing an external appearance of a multi-function facsimile machine 1;
FIG. 2 is a schematic sectional view showing a configuration of the image reading apparatus 100.
FIG. 3 is a side view illustrating a main configuration of the image reading unit 101.
FIG. 4 is a perspective view showing a configuration of a scanner unit 105 and an aperture mechanism 106.
FIG. 5 is an exploded perspective view showing the configuration of the aperture mechanism 106.
FIG. 6 is a front view showing the configuration of the aperture mechanism 106.
FIG. 7 is a diagram showing an output level of the image sensor 51.
FIG. 8 is a view showing a modification of the slit shape.
[Explanation of symbols]
REFERENCE SIGNS LIST 100 image reading device 106 aperture mechanism 50 imaging lens 51 image sensor 61 upper light shielding member 62 lower light shielding member

Claims (2)

In an image reading apparatus that reads an image by transmitting reflected light from a document through an imaging lens and forming an image on an image sensor,
The light incident on the imaging lens is restricted corresponding to the reading line of the image sensor, and the slit width is the narrowest at the center corresponding to the substantially center of the imaging lens, and the width is increased to both ends. An image reading apparatus comprising an aperture mechanism having a slit. The image reading apparatus according to claim 1, wherein the slit is formed by at least two light shielding members movable in a slit width direction.

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