JP2010028390A - Image reader and image forming apparatus provided with same - Google Patents

Abstract

An image reading apparatus and an image forming apparatus capable of preventing a document floating from a document table from being darkly read without increasing power consumption of a light source.
A CPU detects a gradation value of a background level of a background area included in a document based on an electric signal converted by a CCD during pre-scanning. Then, the CPU 201 calculates the amplification degree of the amplifier 301 in accordance with the detected gradation value of the background level, stores the calculated amplification degree in the RAM 203 in association with the relative distance in the sub-scanning direction, and performs the main scan. The amplifier 301 is made to update the amplification degree with the contents stored in the RAM 203.
[Selection] Figure 5

Description

  The present invention relates to an image reading apparatus that reads an image by irradiating light from a light source on a document, and an image forming apparatus including the image reading apparatus.

  There is an image reading apparatus that reads an image by irradiating a document placed on a document table with a straight tubular light source such as a xenon lamp. FIG. 13 is a longitudinal sectional view schematically showing the structure of a conventional image reading device 9. Below the substantially rectangular and horizontally long document table 92, a little closer to one side in the longitudinal direction of the document table 92 than just below the reading position B of the document A placed on the document table 92, the longitudinal direction A straight tubular xenon lamp 93 is provided horizontally so as to be perpendicular to both sides.

  The xenon lamp 93 has an emission window 93a having an opening angle of about 65 ° with respect to the tube axis, and light emitted from the emission window 93a irradiates the document A obliquely upward on the other side. A part of the light emitted from the emission window 93a is reflected by the reflector 94 disposed on the other side of the xenon lamp 93, and irradiates the document A obliquely upward on one side. Immediately below the reading position B, a first mirror 95 for reflecting light reflected downward from the original A further to one side is disposed with a normal inclined at 45 ° from vertically upward to one side. Yes.

  On one side of the first mirror 95, a second mirror 96 for relaying light reflected at a right angle by the first mirror 95 is arranged with a normal inclined at 45 ° from the vertically lower side to the other side, Further, below the second mirror 96, a third mirror 97 for returning the light relayed by the second mirror to the other side is provided with a normal inclined at 45 ° from the vertical upper side to the other side. .

  A lens 98 for condensing the light reflected by the third mirror 97 is disposed on the other side of the third mirror 97, and the light collected by the lens 98 is transmitted on the other side of the lens 98. The photoelectric conversion elements are imaged on the CCD 99 arranged in the tube axis direction of the xenon lamp 93.

  When the image reading device 9 reads the document A, the CCD 99 linearly scans the formed image to convert it into an electric signal, and an amplifier (not shown) amplifies the converted electric signal and outputs it. The xenon lamp 93, the reflector 94, and the first mirror 95 are moved relative to the document table 92 at a predetermined speed v in the sub-scanning direction orthogonal to the main scanning direction in the horizontal plane. The second mirror 96 and the third mirror 97 are moved relative to the document table 92 at a speed of v / 2 in the sub-scanning direction.

  As a result, the length of the optical path from the reading position B to the CCD 99 is always constant, and the CCD 99 can read the image of the original A that has been subjected to main scanning and sub scanning two-dimensionally and convert it into an electrical signal.

  By the way, when there is a step due to cutting and pasting on the document, when the step between the document and the document table is large, and when there is a binding portion on the document surface like a book document, the back of the document irradiated with light in the sub-scanning direction Therefore, the shadow of the step is generated, and the amount of reflected light from the document tends to decrease at the binding portion.

  In the conventional image reading apparatus 9 described above, the ratio between the illuminance at which the xenon lamp 93 irradiates the original A with direct light and the illuminance at which the reflector 94 irradiates the original A with the reflected light of the xenon lamp 93 is, for example, By using 6 to 4, even if the level difference is large, the occurrence of a shadow of the level difference is suppressed.

In Japanese Patent Laid-Open No. 2004-228688, a light source is arranged directly below a reading position, and a first mirror is disposed obliquely above or obliquely below the light source, thereby eliminating the shadow of the original step even if no reflector is provided. Is disclosed. Patent Document 2 discloses a technique for increasing the amount of reflected light by increasing the amount of light from a plurality of point light sources arranged in parallel to the main scanning direction when reading a binding portion of a book document.
JP-A-5-72641 JP 2002-314760 A

  However, in the technique used in the conventional image reading apparatus 9 and the technique disclosed in Patent Document 1, when reading a book document, the vicinity of the binding portion of the document is lifted from the document table, and thus the amount of light emitted. There is a problem that a part of the original is read as black. Further, the technique disclosed in Patent Document 2 has a problem that the power consumption of the light source increases when reading a book document.

  The present invention has been made in view of such circumstances, and the object of the present invention is to raise the power of the light source without increasing the power consumption of the light source by changing the amplification degree of the electrical signal read from the document. Another object of the present invention is to provide an image reading apparatus and an image forming apparatus capable of preventing the original from being read in black.

  An image reading apparatus and an image forming apparatus according to the present invention include a document table on which a document is placed, a light source that irradiates light to the document through the document table, and reflected light from the document as an electrical signal. In the image reading apparatus including the conversion unit for conversion, the conversion unit is configured to increase / decrease the conversion rate from light to electric signal according to the small / large amount of the reflected light. It is characterized by.

In the present invention, the conversion unit converts the reflected light from the document into an electric signal to calculate the amount of light on the background of the document, and amplifies the electric signal according to the small / large of the calculated amount of light. Increase / decrease amplification.
Thus, the conversion rate from light to electrical signal is increased / decreased according to the small / large amount of reflected light.

  In the image reading apparatus and the image forming apparatus according to the present invention, the conversion unit includes a photoelectric converter in which photoelectric conversion elements are linearly arranged, and an amplification variable amplifier that amplifies an electric signal converted by the photoelectric converter. The photoelectric converter is configured to convert the electric signal into an electric signal in the order of arrangement of the photoelectric conversion elements, and the original table and the light source are relatively moved in a direction perpendicular to the arrangement direction of the photoelectric conversion elements. And a means for updating the amplification degree according to the relative position of the relative movement.

In the present invention, the photoelectric converter of the conversion unit in which the photoelectric conversion elements are linearly arranged is main-scanned in the arrangement direction of the photoelectric conversion elements, converted into an electrical signal, and relatively moved. The light source is relatively moved in the sub-scanning direction orthogonal to the main scanning direction. Then, the variable amplification amplifier of the conversion unit amplifies the electric signal converted by the photoelectric converter with an amplification corresponding to the relative position of the relative movement.
Thus, for example, stable photoelectric conversion is performed without changing the conversion rate during main scanning, and the conversion rate is changed following the change in the amount of reflected light in the sub-scanning direction of the document.

  An image reading apparatus and an image forming apparatus according to the present invention are configured to detect a background level of a background area included in a document based on an electrical signal converted by the photoelectric converter, and to detect the background level. Means for calculating the amplification degree of the amplifier, and storage means for storing the calculated amplification degree in association with the relative position of the relative movement, wherein the amplifier is stored in the storage means in association with the relative position. The degree of amplification is updated with the contents that have been set.

In the present invention, the detecting means detects the background level of the background area included in the document based on the electrical signal converted by the photoelectric converter. Then, the calculating means calculates the amplification degree of the amplifier according to the detected background level, the storage means stores the calculated amplification degree in association with the relative position of the relative movement, and the amplifier The degree of amplification is updated with the contents stored in the storage means in association with.
Thereby, for example, when the background level is detected in the preliminary scan of the document, in the main scan, the electrical signal obtained by converting the reflected light from the document is amplified by the amplification degree corresponding to the background level detected in the preliminary scan. .

  In the image reading apparatus and the image forming apparatus according to the present invention, the light source is configured to irradiate light vertically to the document.

In the present invention, the light emitted from the light source enters the document vertically from directly below the document table.
Thereby, for example, the degree of reduction in the amount of reflected light at the binding portion of the book document is reduced. Furthermore, the generation of shadows on the steps of the original is suppressed.

  In the image reading apparatus and the image forming apparatus according to the present invention, the light source is a xenon lamp including a reflecting portion having a rectangular emission window for emitting light to the outside around a straight tube having a light emitting portion therein. And a crossing line between the plane including the tube axis of the xenon lamp and the center line of the exit window in the direction along the tube axis and the document table is an irradiation center of the light source. It is characterized by.

In the present invention, the light source is a straight tubular xenon lamp having a light emitting portion inside, and a reflection portion having a rectangular emission window for emitting light to the outside is provided around the xenon lamp. Further, a central portion where the light source irradiates the original is formed in a straight line portion where the plane including the center line in the direction along the tube axis of the xenon lamp and the tube axis of the exit window intersects the original table.
Thus, when the position at which the light passing through the center of the emission window from the light emission center illuminates the document table is set as the document reading position, the document can be read at a position where the amount of light irradiated becomes maximum.

  In the image reading apparatus and the image forming apparatus according to the present invention, the light source is disposed on one side in the relative movement direction, and the reflected light from the irradiation center is transmitted to the other side in the relative movement direction. And a mirror that reflects in the direction along the line.

In the present invention, the mirror disposed on one side in the direction of relative movement of the light source reflects the reflected light from the irradiation center to the other side in the direction of relative movement in a direction along the document table.
Thereby, the reading position of the original and the irradiation center of the original are made coincident with each other, and light is reflected in a direction along the original with a part of the optical path leading to the photoelectric converter.

According to the present invention, the degree of amplification of the electric signal is increased / decreased according to the small / large amount of light calculated from the electric signal obtained by converting the reflected light from the original.
Thus, the conversion rate from light to electrical signal is increased / decreased according to the small / large amount of reflected light. Therefore, it is possible to prevent the document that has been lifted from the document table from being darkly read without increasing the power consumption of the light source.

Hereinafter, an embodiment in which an image reading apparatus and an image forming apparatus according to the present invention are applied to a digital multi-function peripheral will be described in detail.
FIG. 1 is a front sectional view schematically showing a digital multi-function peripheral according to an embodiment of the present invention. In the figure, reference numeral 100 denotes a digital multi-function peripheral, and the digital multi-function peripheral 100 includes a main body apparatus 110 having an image reading apparatus 9 according to the present invention provided thereon with a document table 92 made of transparent glass on the upper surface. Is provided with an automatic document processing device 120 that conveys the document on the document table 92. The automatic document processing device 120 is configured to be rotatable in the direction of an arrow M in the figure by a hinge (not shown) connected to the image reading device 9, and the upper side of the document table 92 is opened to manually place the document. Can be done.

  An exposure unit as an image forming unit that forms latent images of images corresponding to image data of black (K), cyan (C), magenta (M), and yellow (Y) is provided at a substantially central portion of the main body device 110, respectively. 1, a developing device 2, a photosensitive drum 3, a cleaner unit 4, and a charging device 5, each of which has four systems, and these constitute four image stations.

The exposure unit 1 is a laser scanning unit (LSU) having optical elements such as a laser emitting portion, a polygon mirror that scans laser light, and a reflection mirror that guides the laser light reflected by the polygon mirror to each photosensitive drum 3. It is.
As the exposure unit, an EL or LED writing head in which light emitting elements are arranged in an array may be used.

  The charger 5 uniformly charges the surface of the photosensitive drum 3 to a predetermined potential. In this embodiment, a charger-type charger is used. In addition to the charger type charger, a contact type roller type or brush type charger may be used.

  The exposure unit 1 emits laser light in accordance with image data, thereby exposing the charged photosensitive drum 3 to form an electrostatic latent image. The developing device 2 supplies toner of four colors (Y, M, C, K) to the electrostatic latent image formed on the photosensitive drum 3 to visualize the toner image. The cleaner unit 4 removes and collects toner remaining on the surface of the photosensitive drum 3 after development and image transfer.

  The intermediate transfer belt unit 6 disposed above the photosensitive drum 3 includes an intermediate transfer belt 61 provided at a position in contact with the photosensitive drum 3 and an intermediate medium that rotates the intermediate transfer belt 61 while stretching the intermediate transfer belt 61. The image forming apparatus includes a transfer belt driving roller 62, four (Y, M, C, K) intermediate transfer rollers 64, an intermediate transfer belt driven roller 63, and an intermediate transfer belt cleaning unit 65.

The intermediate transfer belt 61 is formed endlessly using a film having a thickness of about 100 μm to 150 μm, for example, and the intermediate transfer roller 64 as a transfer electrode is based on a metal (for example, stainless steel) shaft having a diameter of 8 to 10 mm. The surface is covered with a conductive elastic material (for example, EPDM, urethane foam, etc.).
In the present embodiment, the transfer electrode has a roller shape, but may have a brush shape.

  A high-voltage transfer bias having a polarity (+) opposite to the toner charging polarity (−) is applied to the intermediate transfer roller 64. Each intermediate transfer roller 64 applies an applied transfer bias to the intermediate transfer belt 61 in order to transfer the toner image on the corresponding photosensitive drum 3 to the intermediate transfer belt 61. As a result, the toner images of the respective colors formed on the respective photosensitive drums 3 are sequentially transferred and stacked on the intermediate transfer belt 61 to form a color toner image (multicolor toner image).

  The image forming unit further includes a transfer roller 10 that transfers the multicolor toner image on the intermediate transfer roller 64 to a recording sheet (sheet). A high voltage (+) opposite to the toner charging polarity (−) is applied to the transfer roller 10, and the intermediate transfer belt 61 is sandwiched between the transfer roller 10 and the intermediate transfer belt drive roller 62. . When the transfer roller 10 is made of a hard material such as metal, the intermediate transfer belt drive roller 62 is made of a soft material such as an elastic roller. Thereby, the transfer roller 10 and the intermediate transfer belt 61 are pressed against each other at a predetermined nip.

  A sheet fed from a sheet feeding cassette 8 to be described later is conveyed to the position of the transfer roller 10, and a high voltage applied to the transfer roller 10 is given as the intermediate transfer belt 61 rotates. As a result, the multicolor toner image on the intermediate transfer belt 61 is transferred to the sheet.

  On the other hand, toner adhering to the intermediate transfer belt 61 due to contact with the photosensitive drum 3 and toner remaining on the intermediate transfer belt 61 without being transferred to the sheet by the transfer roller 10 cause toner color mixing in the next step. For this reason, it is removed and collected by an intermediate transfer belt cleaning unit 65 provided in the vicinity of the intermediate transfer belt driven roller 63.

  The intermediate transfer belt cleaning unit 65 is provided with a cleaning blade as a cleaning member that comes into contact with the intermediate transfer belt 61, and the portion where the cleaning blade comes into contact with the intermediate transfer belt 61 starts from the back side of the intermediate transfer belt 61. A driven roller 43 is supported.

  A paper feed cassette 8 for accumulating and feeding sheets used for image formation is arranged at the inner bottom of the main unit 110 and below the exposure unit 1. In addition, a manual paper feed cassette 8b for placing a manual feed sheet projects from one side of the lower part of the main body device 110. Above the intermediate transfer belt unit 6, there is provided a paper discharge tray 14 on which a sheet on which an image has been formed and fixed is placed face down.

  The sheets accommodated in the paper feed cassette 8 are separated and fed one by one by a pickup roller 11 a provided at one end of the paper feed cassette 8. The exposure unit 1 and the intermediate transfer belt unit 6 The sheet is supplied to a substantially vertical sheet conveyance path S1 arranged on one side. Further, the sheet placed in the manual sheet feed cassette 8b is taken into the apparatus by the pickup roller 11b and supplied to the sheet transport path S1. The sheet supplied to the sheet conveyance path S1 reaches a registration roller 13 disposed below the transfer roller 10 via a conveyance roller 12a for promoting and assisting the conveyance of the sheet. The registration roller 13 conveys the sheet to the transfer roller 10 at a timing when the leading edge of the sheet and the leading edge of the multicolor toner image on the intermediate transfer belt 61 are aligned.

  The transferred sheet is further conveyed substantially vertically and reaches the fixing unit 7 provided on the upper side of the transfer roller 10. The fixing unit 7 includes a heating roller 71 and a pressure roller 72, and maintains the heating roller 71 at a predetermined fixing temperature by controlling heating means such as a heater lamp based on a detection value of a temperature detector (not shown). At the same time, the sheet on which the multicolor toner image is transferred is rotated between the heating roller 71 and the pressure roller 72, and the heat of the heating roller 71 fixes the multicolor toner image on the sheet. The heat-fixed sheet is discharged by a conveyance roller 12b provided near the exit of the fixing unit 7.

  The sheet that has passed through the fixing unit 7 is discharged face down onto the discharge tray 14 through the discharge roller 12b in the case of a single-sided printing request, and is discharged after chucking the sheet by the discharge roller 12b in the case of a double-sided printing request. The paper roller 12b is rotated in the reverse direction to be guided to the double-sided document conveyance path S3, and is conveyed again to the registration roller 13 by the conveyance rollers 12c and 12d. Then, after the multicolor toner image is transferred and thermally fixed on the back side of the sheet, it is discharged onto the discharge tray 14 by the discharge roller 12b.

  FIG. 2 is a longitudinal sectional view schematically showing the structure of the image reading apparatus 9 according to the present invention. A straight tubular xenon lamp 93 that irradiates light upward at an opening angle of 65 ° is provided horizontally below the substantially rectangular and horizontally long document table 92 so as to be perpendicular to the longitudinal direction of the document table 92. . A first mirror 95 that reflects the reflected light from the document A on the document table 92 irradiated to the xenon lamp 93 to the other side is disposed obliquely below one side of the xenon lamp 93. On the other side of the first mirror 95, a second mirror 96 for relaying the light reflected by the first mirror 95 is disposed with the normal inclined at 45 ° from the vertically lower side to the one side. Below the second mirror 96, a third mirror 97 for returning the light relayed by the second mirror to one side is provided with the normal inclined at 45 ° from the vertical upper side to the one side.

  In FIG. 2, the direction in which the luminous flux emitted from the xenon lamp 93 is maximum and the document table 92 are substantially perpendicular to each other. As a result, the amount of light becomes maximum at the position where the xenon lamp 93 irradiates the document table 92 substantially vertically. In this case, it is desirable to determine the inclination of the normal line of the first mirror 95 so that the CCD 99 can read the original at a position where the amount of light to be irradiated becomes maximum. In the present embodiment, the position where the light quantity is maximum is set as the reading position B, and the reflected light emitted obliquely downward on one side from the reading position B is reflected in the direction along the document table 92 on the other side. It is. For this reason, the normal line of the first mirror 95 is inclined at an angle larger than 45 ° from vertically above to the other side.

  FIG. 3 is a longitudinal sectional view showing the internal structure of a known xenon lamp 93. The main body of the xenon lamp 93 is a straight circular glass tube 931 in which xenon gas is sealed. A fluorescent material that emits visible light when excited by ultraviolet rays generated by discharge is applied to the inner wall of the glass tube 931. A fluorescent film 932 is formed. On the outer wall of the glass tube 931, a trigger electrode 933 for igniting discharge in the xenon lamp 93 is attached, and the outer periphery of the glass tube 931 and the trigger electrode 933 is a reflection protected by the tube 935. Covered with a membrane 934.

  The fluorescent film 932, the trigger electrode 933, and the reflective film 934 are formed with a substantially rectangular exit window 93 a with the direction along the tube axis of the glass tube 931 as the longitudinal direction. The light reflected by 934 is emitted from the emission window 93 at a predetermined opening angle.

  FIG. 4 is a schematic longitudinal sectional view showing the relative positions of the xenon lamp 93 and the document table 92. The opening angle α of the emission window 93a with respect to the tube axis C is 65 ° in the present embodiment. Assuming that a straight line intersecting the plane that bisects the opening angle α of the exit window 93a and the exit window 93a is D, D is a center line in the direction along the tube axis C of the exit window 93a. The luminous flux in the direction toward the line D is maximized. Thus, the intersection line between the plane including the tube axis C and the center line D and the document table 92 becomes the irradiation center of the xenon lamp 93.

  In the present embodiment, as described with reference to FIG. 2, the direction in which the luminous flux is maximized and the document table 92 are substantially perpendicular to each other. Therefore, the plane including the irradiation center and the tube axis C, the document table 92, Is almost vertical. Accordingly, the original can be read at a position where the irradiation center coincides with the reading position B and the amount of irradiated light is maximum.

  FIG. 5 is a block diagram mainly showing the configuration of the image reading device 9 in the digital multifunction peripheral 100. The digital multi-function peripheral 100 includes a control unit 20 having a CPU 201 that is the center of control, a ROM 202 that stores information such as programs, and a RAM 203 that stores temporarily generated information. The control unit 20 includes a conversion unit 30 that photoelectrically converts reflected light from the document into an electrical signal, a document scanning motor control unit 40 that subscans the document, a xenon lamp 93, and first to third mirrors 95 and 96, An optical unit motor controller 50 that moves the optical unit 97 in the sub-scanning direction and a lamp power source 93 b that lights the xenon lamp 93 are connected. The control unit 20 is also connected with an operation panel 60 for receiving operations and a display unit 61 for displaying information for operations (see FIG. 6).

The CPU 201, the ROM 202, and the RAM 203 are connected to each other via a bus, and the CPU 201 executes processes such as input / output and calculation according to a control program stored in advance in the ROM 202.
The conversion unit 30 includes a CCD 99, a variable amplification amplifier 301 that amplifies the electric signal photoelectrically converted by the CCD 99, and an A / D converter 302 that performs A / D conversion on the signal amplified by the amplifier 301. RGB digital signals are supplied to the image processing unit 70.

  The image processing unit 70 includes a shading correction circuit 701 that performs processing for removing various distortions generated in the optical unit and the conversion unit 30 on the RGB digital signal supplied from the A / D converter 302, and a shading correction circuit 701. A gamma correction circuit 702 for gamma correcting the corrected signal. The RGB digital signal after the gamma correction is written in an image memory (not shown).

  The document scanning motor control unit 40 causes the driver 401 to drive the document scanning drive motor of the automatic document processing apparatus 120 to move the document A relative to the document table 92 in the sub-scanning direction. When the document A is manually placed on the document table 92, the optical unit motor control unit 50 causes the driver 501 to drive the optical unit drive motor 503 so that the xenon lamp 93 and the first mirror 95 are moved in the sub scanning direction. The second mirror 96 and the third mirror 97 are moved at a speed of v / 2 in the sub-scanning direction.

  FIG. 6 is an explanatory diagram showing the appearance of the operation panel 60 of the digital multi-function peripheral 100, and FIG. 7 shows a document selection screen 611 for allowing the user to select a document type. The operation panel 60 includes a copy key 601 for selecting a copy mode, start keys 602a and 602b for starting black and white or color copying, and a display unit 61 having a touch panel and made of liquid crystal.

  FIG. 8 is a graph illustrating the ratio of the light amount at a position spaced from the reading position B in the sub-scanning direction (horizontal direction) to the light amount at the reading position B. In the figure, the horizontal axis represents the horizontal separation distance (mm) from the reading position B, and the vertical axis represents the light amount ratio (%). In the graph, square marks indicate the case of the present invention, and triangular marks indicate the case of the conventional example of FIG. 13 in which the ratio of illuminance by the xenon lamp 93 and the reflector 94 at the reading position B is approximately 6 to 4. When the horizontal separation distance is positive (or negative), in the conventional example of FIG. 13, it indicates that the horizontal separation distance is away from the reflector 94 (or the xenon lamp 93).

In the case of the conventional example, the decrease in the light amount ratio accompanying the separation toward the reflector 94 side (or the xenon lamp 93 side) in the plus direction (or the minus direction) is a decrease in the amount of light irradiated from the reflector 94 (or the xenon lamp 93). Due to is dominant. The decrease in the light amount ratio from the early stage in the positive direction is due to the fact that the ratio of the light amount irradiated from the reflector 94 is smaller than that of the xenon lamp 93.
On the other hand, in the case of the present invention, no decrease in the amount of light is observed even at positions separated by plus / minus 1 mm in the sub-scanning direction, and a stable target light amount ratio is obtained in the plus / minus direction.

  FIG. 9 is a graph illustrating the illuminance at a position spaced vertically upward from the reading position B. In the figure, the horizontal axis represents the vertical separation distance (mm) from the document table 92, and the vertical axis represents the illuminance (lx). In the graph, square marks indicate the case of the present invention, and triangular marks indicate the case of the conventional example of FIG. 13 in which the ratio of illuminance by the xenon lamp 93 and the reflector 94 at the reading position B is approximately 6 to 4.

  In the case of the present invention, since the original is irradiated only by the direct light from the xenon lamp 93, the illuminance at the reading position is 3000 lux or more higher than that in the conventional example. Furthermore, in the case of the present invention, as described with reference to FIG. 2, since the light is radiated substantially perpendicularly to the document A, the rate at which the illuminance decreases with the separation from the document table 92 vertically upward is It is shown that it is much smaller than in the case of the conventional example. As a result, when reading a book document, the reduction in the amount of reflected light at the binding portion is alleviated, and the degree to which a portion of the document is read in black is reduced.

Next, a specific operation in which the digital multifunction peripheral 100 reads a document will be described. In the present embodiment, the background level of the book document A is detected by preliminary scanning (pre-scan), and in the main scanning (main scan), the amplification degree of the amplifier 301 is increased according to the background level detected by pre-scanning. The book document A is read while updating.
When the user places the book document A on the document table 92 so that the binding portion is substantially parallel to the main scanning direction and presses the copy key 601, a document selection screen 611 is displayed on the display unit 61. Next, when the user selects “book” on the touch panel of the display unit 61 and presses the start key 602a or 602b, the CPU 201 of the control unit 20 performs pre-scanning in order to read the background area of the book document A. Let

  In the pre-scan, the xenon lamp 93 irradiates the book original A with light, and the reflected light from the book original A forms an image on the CCD 99 via the first to third mirrors 95, 96, 97 and the lens 98. . Further, the optical unit motor control unit 50 moves the above-described optical unit in the sub-scanning direction. The CCD 99 linearly scans the formed image linearly and converts it into an electric signal. The converted electric signal is amplified by the amplifier 301 with a constant amplification factor (1 in this embodiment), and A The / D converter 302 converts the gray level from 256 to 256 with white as the maximum gradation. The CPU 201 detects the gradation value of the background level of the background area included in the book document A based on the A / D converted digital signal. In this case, the detected gradation value of the background level corresponds to the light amount of the background.

  FIG. 10 is an explanatory view schematically showing how the gradation value of the background level of the book document A changes in the sub-scanning direction. In the figure, the horizontal axis represents the relative distance in the sub-scanning direction, and the vertical axis represents the gradation value (0 to 255). The gradation values of the background level in the portion of the book document A that is in close contact with the document platen 92 and the binding portion are 220 and 100 in the present embodiment, respectively, and in the portion that is raised from the document platen 92 in the meantime, The value changes gradually.

  The CPU 201 stores the detected background level gradation value in the RAM 203 in association with the relative distance in the sub-scanning direction, and sets the amplification degree to be set in the amplifier 301 in the main scan according to the relative distance in the sub-scanning direction. And stored in the RAM 203 in association with the relative distance. In this case, the amplification degree is set to a value that cancels the change in the gradation value of the stored background level.

In the main scan, the amplification degree stored in the pre-scan is read according to the relative distance in the sub-scanning direction, and the amplification degree of the amplifier 301 is updated with the read content.
FIG. 11 is an explanatory diagram schematically showing how the amplification degree of the amplifier 301 is changed in the sub-scanning direction. In the figure, the horizontal axis represents the relative distance in the sub-scanning direction, and the vertical axis represents the amplification degree. The amplification degree at the portion of the book document A that is in close contact with the document table 92 is calculated as 1.16 (= 1.00 × 255/222) from the ratio with the gradation value of the white level, The amplification degree is calculated as 2.55 (= 1.00 × 255/100). Further, in the portion that is lifted from the document table 92 in the meantime, the amplification degree is gradually changed according to the change of the gradation value in FIG.

FIG. 12 is a flowchart showing the processing procedure of the CPU 201 in the digital multi-function peripheral 100 according to the embodiment of the present invention. The following processing is executed by the CPU 201 in accordance with a control program stored in the ROM 202 in advance. When the user manually places the book document A on the document table 92 and presses the copy key 601 on the operation panel 60, the CPU 201 starts the following processing when the selection of “book” is received on the screen 611. .
It is assumed that the optical unit is in the initial position of sub-scanning and the amplification degree of the amplifier 301 is set to 1.00.

  The CPU 201 determines whether or not the start key 601a or 601b of the operation panel 60 has been pressed (step S11). If it is determined that the button has not been pressed (step S11: NO), the CPU 201 waits until the button is pressed. When it is determined that the button has been pressed (step S11: YES), the CPU 201 turns on the lamp power supply 93b (step S12) and lights the xenon lamp 93. Thereafter, the CPU 201 causes the optical unit motor control unit 50 to start sub scanning of the optical unit (step S13).

  Next, the CPU 201 reads the output of the A / D converter 302 and includes the output from the output in the book document A by an algorithm known per se (for example, the maximum value level in the read signal is set as the background level). The gradation value of the background level of the existing background area is detected (step S14). Then, the CPU 201 stores the detected background level gradation value in the RAM 203 in association with the relative distance in the sub-scanning direction at that time (step S15).

  The CPU 201 calculates the amplification factor from the ratio of the white level gradation value (= 255) to the background level gradation value stored in the RAM 203 (step S16), and associates the calculated amplification degree with the relative distance. It memorize | stores in RAM203 (step S17). Thereafter, the CPU 201 determines whether or not the optical unit has reached the end position in the sub-scanning direction (step S18). If it is determined that the end position has not been reached (step S18: NO), the CPU 201 returns the process to step S14.

  If it is determined that the end position has been reached (step S18: YES), the CPU 201 turns off the lamp power supply 93b (step S19), turns off the xenon lamp 93, and sets the optical unit to the optical unit motor controller 50. Driving in the direction opposite to the sub-scanning direction (step S20). Thereafter, the CPU 201 determines whether or not the optical unit has returned to the initial position of sub-scanning (step S21). If it is determined that the optical unit has not returned to the initial position (step S21: NO), the CPU 201 waits until the optical unit returns to the initial position.

  When it is determined that the optical unit has returned to the initial position (step S21: YES), the CPU 201 turns on the lamp power source 93b again (step S22) and turns on the xenon lamp 93. Sub scanning of the optical unit is started (step S23). Thereafter, the CPU 201 reads the amplification degree from the RAM 203 according to the relative distance in the sub-scanning direction at that time (step S24), and updates the amplification degree of the amplifier 301 with the read content (step S25).

  Next, the CPU 201 determines whether or not the optical unit has reached the end position in the sub-scanning direction (step S26). If it is determined that the end position has not been reached (step S26: NO), the CPU 201 returns the process to step S24. If it is determined that the end position has been reached (step S26: YES), the CPU 201 turns off the lamp power supply 93b (step S27), turns off the xenon lamp 93, and instructs the optical unit motor control unit 50 of the optical unit. Sub-scanning is stopped (step S28), and the process is terminated.

As described above, according to the present embodiment, the conversion unit converts the reflected light from the document into an electrical signal, and converts the converted electrical signal into an A / D converted digital signal. Calculated as corresponding to the amount of light. Then, the conversion unit increases / decreases the amplification degree of the amplifier according to the calculated background level small / large.
Thus, the conversion rate from light to electrical signal is increased / decreased according to the small / large amount of reflected light. Therefore, it is possible to prevent the document that has been lifted from the document table from being darkly read without increasing the power consumption of the light source.

In addition, a CCD in which photoelectric conversion elements are linearly arranged is main-scanned in the photoelectric conversion element arrangement direction to convert it into an electrical signal, and the CPU and the optical unit motor control unit use the optical unit including the xenon lamp on the document table. On the other hand, it is moved in the sub-scanning direction orthogonal to the main scanning direction. Then, the variable amplification amplifier of the conversion unit amplifies the electrical signal converted by the CCD with the amplification calculated and stored in accordance with the relative distance in the sub-scanning direction.
Accordingly, an electric signal amplified with a stable amplification degree can be obtained during main scanning, and an electric signal with an amplification degree adjusted following the change in the amount of reflected light in the sub-scanning direction of the document can be obtained.

Further, the CPU detects the gradation value of the background level of the background area included in the document by a known algorithm based on the electrical signal converted by the CCD during the prescan. Then, the CPU calculates the amplification degree of the amplifier according to the detected background level gradation value, and stores the calculated amplification degree in the RAM in association with the relative distance in the sub-scanning direction. The amplifier is made to update the amplification degree with the contents stored in the above.
Therefore, by amplifying the electrical signal obtained by converting the reflected light from the document with an amplification factor corresponding to the ground level accurately detected by, for example, pre-scanning, an electrical signal having a uniform amplitude that does not depend on the level of the ground level. Can be obtained.

Furthermore, the light emitted from the xenon lamp enters the document substantially vertically from directly below the document table.
Accordingly, it is possible to reduce the degree to which the binding portion of the book document is read in black, and to read the document without the shadow of the step.

Furthermore, the light source is a straight tube xenon lamp, and a reflection film having a substantially rectangular exit window for emitting light to the outside is provided around the xenon lamp. Further, an irradiation center where the light source irradiates the document is formed in a straight line portion where the plane including the center line in the direction along the tube axis of the xenon lamp and the tube axis of the exit window intersects the document table.
Accordingly, when the irradiation center is set as the reading position of the document, the document can be read at a position where the amount of irradiated light is maximized.

Furthermore, the first mirror disposed on one side in the direction of relative movement of the optical unit reflects the reflected light from the irradiation center in the direction along the document table to the other side in the direction of relative movement.
Therefore, the reflected light from the original at the irradiation center can be guided to the CCD through the first mirror.

  In the present embodiment, when reading a book document, the document table on which the document is placed is fixed to the main unit, and the optical unit including the xenon lamp is moved in the sub-scanning direction. The document table on which the book document is placed may be moved in the sub-scanning direction.

  Further, the amplification degree of the amplifier is calculated from the ratio of the gradation level of the white level (255) to the gradation level of the detected background level, but the document is in close contact with the document table with respect to the detected gradation level of the background level. Alternatively, it may be calculated from the ratio of the gradation values of the background level of the portion that is present.

  Furthermore, although the background level is detected by pre-scanning, an amplifier with a fixed amplification used when detecting the background level, a buffer memory for storing a digital signal generated during the detection of the background level, and digital A signal switch may be further provided to eliminate the prescan.

1 is a front sectional view schematically showing a digital multi-function peripheral according to an embodiment of the present invention. 1 is a longitudinal sectional view schematically showing the structure of an image reading apparatus according to the present invention. It is a longitudinal cross-sectional view showing the internal structure of a known xenon lamp. It is a typical longitudinal cross-sectional view which shows the relative position of a xenon lamp and an original stand. FIG. 2 is a block diagram mainly illustrating a configuration of an image reading apparatus in a digital multi-function peripheral. It is explanatory drawing which shows the external appearance of the operation panel of a digital multifunctional device. 6 is a document selection screen for allowing a user to select a document type. It is a graph which illustrates ratio of the light quantity in the position spaced apart from the reading position to the subscanning direction (horizontal direction) with respect to the light quantity in a reading position. It is a graph which illustrates the illumination intensity in the position spaced apart from the reading position vertically upwards. FIG. 6 is an explanatory diagram schematically showing how the gradation value of the background level of a book document changes in the sub-scanning direction. It is explanatory drawing which shows typically a mode that the amplification degree of an amplifier is changed to a subscanning direction. 4 is a flowchart showing a processing procedure of a CPU in the digital multi-function peripheral according to the embodiment of the present invention. It is a longitudinal cross-sectional view which shows the structure of the conventional image reading apparatus typically.

Explanation of symbols

9 Image Reading Device 20 Control Unit 30 Conversion Unit 92 Document Stand 93 Xenon Lamp (Light Source)
95 First mirror (mirror)
99 CCD (photoelectric converter)
100 Digital MFP 110 Main Body Device 120 Automatic Document Processing Device 202 ROM
203 RAM
301 Amplifier

Claims (7)

An image reading apparatus comprising: a document table on which a document is placed; a light source that emits light to the document through the document table; and a conversion unit that photoelectrically converts reflected light from the document into an electrical signal.
The image reading apparatus, wherein the conversion unit is configured to increase / decrease a conversion rate from light to an electric signal according to a small / large amount of the reflected light. The conversion unit includes a photoelectric converter in which photoelectric conversion elements are linearly arranged, and an amplification variable amplifier that amplifies an electric signal converted by the photoelectric converter,
The photoelectric converter is configured to convert into an electric signal in the order of arrangement of the photoelectric conversion elements,
Means for relatively moving the document table and the light source in a direction orthogonal to the arrangement direction of the photoelectric conversion elements;
The image reading apparatus according to claim 1, wherein the amplifier is configured to update an amplification degree according to a relative position of the relative movement. Means for detecting a background level of a background area included in the document based on the electrical signal converted by the photoelectric converter;
Means for calculating the amplification degree of the amplifier according to the detected background level;
Storage means for storing the calculated amplification degree in association with the relative position of the relative movement,
The image reading apparatus according to claim 2, wherein the amplifier is configured to update the amplification degree with the content stored in the storage unit in association with the relative position.   4. The image reading apparatus according to claim 1, wherein the light source is configured to irradiate light vertically to the document. 5. The light source is a xenon lamp including a reflecting portion having a rectangular emission window for emitting light to the outside around a straight tube having a light emitting portion therein,
A crossing line between the plane of the xenon lamp and the center line of the exit window in the direction along the tube axis and the original table is configured to be an irradiation center of the light source. The image reading apparatus according to any one of claims 1 to 4.   The light source is disposed on one side in the direction of relative movement, and includes a mirror that reflects reflected light from the irradiation center to the other side in the direction of relative movement in a direction along the document table. The image reading apparatus according to claim 5.   An image forming apparatus configured to form an image based on an electric signal read by the image reading apparatus according to claim 1.

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