JP5059326B2 - Illumination device for image reading apparatus - Google Patents

Description

The present invention relates to lighting equipment of the image reading apparatus for illuminating an original is read object.

  Conventionally, a document which is transported on or placed on a platen made of a transparent member such as glass is illuminated with light from an illumination device, and this is optically scanned and reflected from the document. An image reading device that forms an image of light on a photoelectric conversion element such as a CCD, outputs an accumulated charge amount corresponding to the amount of received light as an electrical analog signal, converts it into a digital signal, and acquires it as read image data Is known.

  In the conventional image reading apparatus as described above, it is possible to image the reflected light of the light irradiated onto the document surface, and to arrange the light source on the optical path where the reflected light from the document goes to the photoelectric conversion element. difficult. Therefore, the conventional image reading apparatus is configured to illuminate the document surface from an oblique direction by the illumination device and form an image of light reflected from the document surface on the photoelectric conversion element.

  When the surface of the document is illuminated obliquely as in the conventional image reading apparatus, if the surface of the document or the like to be read has unevenness, a shadow caused by the unevenness is generated. The shadow generated in this way appears as a shadow in the read image.

  Therefore, by installing the same light source at a symmetrical position with respect to the normal of the document surface, it is possible to suppress the occurrence of a shadow (an image that appears black) on the read image even in a portion where the document surface is uneven. Technology is provided.

  In the conventional image reading apparatus described above, in order to suppress the occurrence of document shadow on the read image, the area to be read is illuminated with the same light source from two directions contrasting with the normal of the document surface; It has become. However, the light source used for illuminating the document in the image reading apparatus is a relatively expensive light source such as a xenon lamp, and an increase in the number of such expensive light sources installed is not preferable from the viewpoint of cost reduction. .

The present invention has been made to solve the above-described problems. In an image reading apparatus that reads an image of a document, a low-cost and simple configuration enables shadows on a scanned image due to unevenness on the document surface. It aims at providing the technique which can suppress generation | occurrence | production.

In order to solve the above-described problem, an illumination device of an image reading apparatus according to the present invention has a document table on which a document is placed, and is disposed on the document table and below the document table, In the document reading apparatus that reads the reading area of the document while relatively moving an image reading sensor including an imaging unit that reads the image of the document in the sub-scanning direction, the image reading sensor includes the reading area of the document. A light source of red, green, and blue LEDs that illuminates a reading area of the document placed on the document table and that reflects light from the document surface to the imaging unit A first illuminating unit configured of a white type light guide tube provided with a light source and a reading area of the document placed on the document table, and reflected light from the document surface is directed to the imaging unit a light source of yellow-green LED array guided Is the have different spectral characteristics from the first illumination unit, and a second illuminating section which is disposed opposite in the sub-scanning direction with respect to the first illuminating portion across the imaging unit, The illumination light from the first illumination unit and the illumination light from the second illumination unit are mixed in the reading region where the illumination light is irradiated, so that the illumination light in the reading region has spectral characteristics of a white light source. The light emission control part which light-emits each light source of a said 1st illumination part and a 2nd illumination part by the light emission ratio which becomes is characterized by the above-mentioned.

  As described above in detail, according to the present invention, in an image reading apparatus that reads an image of a document, a technique for suppressing the occurrence of a shadow on a read image due to unevenness on the surface of the document with a low-cost and simple configuration. Can be provided.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is an overall configuration diagram for explaining an illumination device of an image reading apparatus and an image reading apparatus including the same according to the present embodiment. The image reading apparatus 1 according to the present embodiment is installed in an image processing apparatus (MFP: Multi Function Peripheral) M as shown in FIG.

  An image processing apparatus M shown in FIG. 1 includes an image reading apparatus 1 and an image forming apparatus 2. The image forming apparatus 2 can perform image forming processing (print processing, copy processing, etc.) based on image data received from an external device or image data read from a document by the image reading device 1.

The image reading apparatus 1 is an image reading sensor including an illuminating device that illuminates a document, an optical system for imaging reflected light from a document surface illuminated by the illuminating device, and an imaging unit ( CIS: Contact Image Sensor). ) By moving 120 in the sub-scanning direction R, manual reading for reading the image of the document placed on the platen glass 109 and automatic document reader (ADF (Auto Document Feeder) ) moving in the F direction an automatic document reading read by CIS120 stationary images more transported RuHara draft at a predetermined position P is possible.

FIG. 2 is a configuration diagram showing details of the CIS 120 in the image reading apparatus 1 according to the present embodiment. As shown in the figure, the CIS 120 includes a first illumination unit 121, a second illumination unit 122, an optical system 125, and an imaging unit 126, and the CIS 120 is disposed below the document table glass 109. The image processing apparatus M includes a central processing unit ( CPU ) 105 and a memory ( MEMORY) 106 that are used in the image reading apparatus 1 and the image forming apparatus 2.

The first illumination unit 121 includes a white type light guide tube having three light emitting elements ( LED ) , green light emitting elements ( LED ), and blue light emitting elements ( LEDs ) as light sources. The original surface is illuminated from a direction inclined by a predetermined angle.

The second illumination unit 122 includes a light emitting element ( LED ) array including a yellow-green light emitting element ( LED ) as a light source, has a spectral characteristic different from that of the first illumination unit, and is normal to the document surface. On the other hand, the document surface is illuminated from a direction substantially symmetrical to the first illumination unit. In this way, by illuminating from two positions that are line-symmetric with respect to the document surface, it is possible to obtain a read image without a shadow regardless of the presence or absence of unevenness on the document surface.

The optical system 125 is composed of a SELFOC lens (registered trademark) or the like, and is irradiated from the first illumination unit 121 and the second illumination unit 122 and reflected by the document surface (see the downward arrow in FIG. 2). ) To a predetermined imaging position. Here, an example in which the entire optical system 125 is arranged on the CIS 120 is shown.

The imaging unit 126 is configured by a photoelectric conversion element or the like, and images the light guided to a predetermined imaging position by the optical system 125. The image of the document imaged by the imaging unit 126 is stored in the memory 106 and transmitted to an external device that can communicate with the image forming apparatus 2 or the image processing apparatus M as necessary.

The light emission ratio setting unit 123 mixes the irradiation light from the first illumination unit 121 and the irradiation light from the second illumination unit 122 so that the spectral characteristic (wavelength distribution) of the irradiation light on the document surface is increased. The first illumination unit and the second illumination are substantially the same as the spectral characteristics of a white light source composed of any one of xenon lamp, halogen lamp, LED, fluorescent lamp, and electroluminescence ( EL ) The light emission ratio of each light source constituting each part is set.
That is, since the LED has a characteristic that the maximum light emission intensity can be obtained at the peak value of the wavelength distribution (see FIG. 3), in order to obtain the desired spectral characteristic, the first illumination unit 121, which will be described later, is configured. The light emission intensity of each LED and the light emission intensity of the LED which will be described later constituting the second illumination unit 122 are adjusted. Moreover, even if the same voltage is applied to the LED due to the difference in structure or the like, the emission intensity is different. For this reason, as shown in FIG. 3 (relative emission intensity (non-dimensional) on the vertical axis and wavelength on the horizontal axis), the other LEDs are shown as relative emission intensity with respect to the emission intensity of one LED, and the same emission In order to obtain the intensity, the ratio of the output value of the drive output to the LED is used for drive control of each LED as a light emission ratio.

In the present embodiment, the light emission ratio setting unit 123 is a light source having the highest output value among the light sources constituting the first illumination unit 121 and the second illumination unit 122 (in the present embodiment, the first illumination unit). The drive output value to the green LED) 121 is fixed to a predetermined value, and the drive output value to the other light source is adjusted by a digital / analog ( D / A ) converter which is a drive output adjuster, thereby The light emission ratio of each light source constituting each of the illumination section and the second illumination section (referred to as a spectral characteristic setting light emission ratio) is set. Details of the setting process in the light emission ratio setting unit 123 will be described later. The D / A converter converts the digital signal into a voltage value that is an analog signal and adjusts the light emission intensity of the LED . The adjustment amount input as the digital signal is S103, S107, As shown in S112 and S117, 97 to 107, 24 to 30, 20 to 26, and 100 to 110 are set for 256 gradations (0 to 255).

In FIG. 3, the vertical axis represents relative emission intensity (dimensionless), and the horizontal axis represents wavelength, and the red (Red) LED, the green (Green) LED, the blue (Blue) LED, and the second LED constituting the first illumination unit 121. It is a figure which shows the spectral characteristic of yellowish green (YG) LED which comprises the illumination part 122, and the target spectral characteristic ( ideal spectral characteristic of a white xenon lamp). As described above, in this embodiment, the red LED, the green LED, and the blue LED (three-wavelength white type) constituting the first illumination unit 121 and the yellow-green LED constituting the second illumination unit 122 are two types. The illumination light having the ideal spectral characteristics is realized by combining the illumination lights of the illumination units having different spectral characteristics.

The light emission control unit 124 causes each light source constituting each of the first illumination unit 121 and the second illumination unit 122 to emit light based on the light emission ratio for spectral characteristic setting set by the light emission ratio setting unit 123. In addition, the light emission control unit 124 knows in advance in what spectral ratio setting light emission ratio each light source constituting each of the first illumination unit 121 and the second illumination unit 122 should emit light. In this case, regardless of the spectral characteristic setting light emission ratio set by the light emission ratio setting unit 123, each of the light sources can be caused to emit light at a predetermined spectral characteristic setting light emission ratio. In this case, information regarding the predetermined light emission ratio for setting the spectral characteristic of each light source described above is held in the light emission control unit 124 or the memory 106.

Further, the light emission control unit 124 receives the light received by the imaging unit 126 of the light emitted from the first illumination unit 121 and reflected by the document surface, and the light received from the second illumination unit 122 on the document surface. Each light source constituting each of the first illuminating unit 121 and the second illuminating unit 122 at a light emission ratio (light emission ratio for irradiating light intensity setting) at which the amount of reflected light received by the imaging unit 126 is substantially the same. Can also be made to emit light. As described above, the first illumination unit 121 and the first illumination unit 121 and the second illumination unit 122 are caused to emit light by causing the light sources constituting the first illumination unit 121 and the second illumination unit 122 to emit light so that the amounts of light received by the imaging unit 126 are substantially the same. Each of the two illumination units 122 is prevented from being biased in brightness for illuminating the document image placed on the document table 109, and it is effective that shadows due to unevenness of the document surface appear in the read image. Can be suppressed. Here, as an example, the light emission control unit 124 calculates the ratio of the light emission amounts (light emission intensity) of the first illumination unit 121 and the second illumination unit 122.
Light quantity of first illumination unit 121: Light quantity of second illumination unit 122 = 3: 2
It is said.

The CPU 105 has a role of performing various processes in the image processing apparatus M, and also has a role of realizing various functions by executing a program stored in the memory 106. The memory 106 includes, for example, ROM ( ROM ) , RAM ( RAM ), and the like, and has a role of storing various information and programs used in the image processing apparatus M.

  The illumination device of the image reading apparatus according to the present embodiment is configured to include a first illumination unit 121, a second illumination unit 122, a light emission ratio setting unit 123, and a light emission control unit 124.

  FIG. 4 is a flowchart for explaining the details of the light emission ratio setting process in the light emission ratio setting unit 123.

First, the light emission ratio setting unit 123 turns on the green LED in the first illumination unit 121 (S101), and executes peak detection processing based on the amount of received light (light reception intensity) in the imaging unit 126 (S102). That is, the received light amount is detected while changing the drive output to the green LED that is the reference of the relative light emission intensity, and the desired spectral characteristic (wavelength distribution) is obtained when the received light amount reaches a peak. The drive output at this time obtains a desired spectral characteristic. As described above, in order to set the color mixture due to illumination of the first illumination unit 121 and the second illumination unit 122 to a predetermined spectral characteristic, It is necessary to adjust the drive output of the first illumination unit 121 and the second illumination unit 122 to the LEDs. However, if the drive output to each LED can be changed in a large range for color mixing adjustment, a predetermined spectral characteristic cannot be obtained, and therefore it falls within a predetermined drive output value within a range where the predetermined spectral characteristic can be obtained. The gain adjustment is performed so that the light is turned off when the adjustment is completed (S103 to S105).
That is, in S102, for the drive output to the green LED, the digital signal input to the D / A converter is set in a range of 97 to 107 with respect to 256 gradations (0 to 255), and gain adjustment within this range is performed. If this is not possible (S103), error processing is performed (S104). That is, the range in which the peak value is obtained is within the above range.

The light emission ratio setting unit 123 turns on the red LED in the first illumination unit 121 (S106), and executes output adjustment based on the amount of received light (light reception intensity) in the imaging unit 126 (S107). Then, gain adjustment is performed so as to be within a predetermined drive output value, and the light is turned off when the adjustment is completed (S108 to S110).
That is, the drive output to the red LED so that the received light intensity is the same as the received light intensity indicating the peak value of the green LED, which is the basic emitted light intensity, based on the relationship between the spectral characteristics (wavelength distribution) and the relative emitted light intensity shown in FIG. In S107, the digital signal input to the D / A converter is set in a range of 24 to 30 with respect to 256 gradations (0 to 255), and the red LED emits light by adjusting the gain within this range. If the intensity is not the same as the basic emission intensity (S108), error processing is performed (S109).

The light emission ratio setting unit 123 turns on the blue LED in the first illumination unit 121 (S111), and performs output adjustment based on the amount of received light (light reception intensity) in the imaging unit 126 (S112). Then, the gain is adjusted so as to be within a predetermined drive output value, and the light is turned off when the adjustment is completed (S113 to S115).
That is, the drive output to the blue LED so that the received light intensity is the same as the received light intensity indicating the peak value of the green LED, which is the basic emitted light intensity, based on the relationship between the spectral characteristics (wavelength distribution) and the relative emitted light intensity shown in FIG. In step S112, the digital signal input to the D / A converter is set to a range of 20 to 26 with respect to 256 gradations (0 to 255), and the blue LED emits light by adjusting the gain within this range. If the intensity is not the same as the basic emission intensity (S113), error processing is performed (S114).

The light emission ratio setting unit 123 turns on the yellow-green LED in the second illumination unit 122 (S116), and executes output adjustment based on the amount of received light (light reception intensity) in the imaging unit 126 (S117). Then, gain adjustment is performed so as to be within a predetermined drive output value, and the light is turned off when the adjustment is completed (S118 to S120).
That is, driving to the yellow-green LED so that the received light intensity is the same as the received light intensity indicating the peak value of the green LED, which is the basic emitted light intensity, based on the relationship between the spectral characteristics (wavelength distribution) and the relative emitted light intensity shown in FIG. The output is adjusted. In S117, the digital signal input to the D / A converter is set in the range of 100 to 110 with respect to 256 gradations (0 to 255), and the yellow green LED is adjusted by the gain adjustment within this range. If the emission intensity is not the same as the basic emission intensity (S118), error processing is performed (S119).

The light emission control unit 124 stores the drive output value of each LED adjusted as described above in the memory 106 (S121), and the drive is performed every time the image processing apparatus M is turned on ( ON ). Each LED is lit (output) at the drive output value until the output value is read and readjustment is executed (S122 to 123). After all lighting is performed with the drive output value of each LED, peak detection processing for reading an image is performed (S124), and gain adjustment of preprocessing for determining an optimum signal amplification factor of the analog signal is performed.

Thus, in this embodiment, the drive output value of the green LED is fixed (only gain adjustment in the peak detection process), and the other LEDs (red / blue / yellowish green) are red from the D / A converter. The illumination light having ideal spectral characteristics is obtained by adjusting the driving output to the / blue / yellow-green LED .

Each step in the processing in the image processing apparatus M described above is realized by causing the CPU 105 to execute a program stored in the memory 106.

  In this embodiment, the function for implementing the invention is recorded in advance in the apparatus. However, the present invention is not limited to this, and the same function may be downloaded from the network to the apparatus, and the same function is recorded. What is stored in the medium may be installed in the apparatus. The recording medium may be any form as long as the recording medium can store the program and can be read by the apparatus, such as a CD-ROM. Further, the function obtained by installing or downloading in advance may be realized in cooperation with an OS (operating system) or the like inside the apparatus.

  In the present embodiment, the example in which the optical system 125 and the imaging unit 126 are arranged on the CIS 120 has been described. However, the present invention is not limited to this. For example, a part of the optical system and the imaging unit are connected to the CIS 120. Are separated from each other, and the reflected light of the light irradiated by the CIS 120 that scans the document surface according to the document reading process in the image reading apparatus 1 is fixed in the image reading unit 1 by an optical system provided separately from the CIS 120. It can also be set as the structure guided with respect to the imaging part arrange | positioned automatically.

  In the present embodiment, the example in which the light emission ratio setting unit 123 and the light emission control unit 124 are arranged in the image processing apparatus M as a separate body from the CIS 120 has been described. For example, at least one of the light emission ratio setting unit 123 and the light emission control unit 124 may be arranged on the CIS 120.

  In the present embodiment, an example in which the second illumination unit 122 is configured by a yellow-green LED array has been described. However, the present invention is not limited thereto, and for example, a yellow LED array and a green LED array are used. The yellow-green irradiation light may be realized by mixing the irradiation light from the LED arrays.

  As described above, according to the present embodiment, the occurrence of shadows on the read image due to unevenness on the surface of the original is caused by a light source such as a light guide tube normally used in a reading optical system and a light guide tube. By using a configuration that uses a light source such as an LED array that is less expensive than the light source for suppression, it is possible to provide an illumination device that can realize high-quality image reading at low cost. The illumination device of the image reading apparatus according to the present embodiment is particularly effective when illuminating the document surface from a position close to the document as in CIS.

Also, as in this embodiment, once the output of the LED with the highest output value (green LED in this embodiment ) is set once, this is fixed and used as a reference, and the outputs of other LEDs are adjusted. By configuring
(1) Although an output port for driving output to the red LED, blue LED, and yellow-green LED is required by one D / A converter, the driving output by the D / A is changed for the green LED to obtain spectral characteristics ( unnecessary der because adjusting the wavelength distribution), it is possible to reduce that amount D / a output port, which can contribute to low cost of the apparatus,
(2) D / A converter adjusts light emission intensity by driving output to red LED, blue LED, and yellow-green LED. Adjustment with D / A drive output confirms the received light intensity and sets the gain. Since it takes time to control with the drive output within the adjustment range, the total adjustment time can be shortened by reducing such an adjustment process for the green LED .
There are effects such as.

  Although the present invention has been described in detail according to particular embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall configuration diagram for explaining an illumination device of an image reading device according to an embodiment and an image reading device including the same. It is a block diagram which shows the detail of CIS120 in the image reading apparatus 1 by this Embodiment. It is a figure which shows the spectral characteristic of the yellow LED which comprises red LED, green LED, blue LED, and the 2nd illumination part 122 which comprises the 1st illumination part 121, and the target spectral characteristic. 5 is a flowchart for explaining details of a light emission ratio setting process in a light emission ratio setting unit 123;

120 CIS, 121 1st illumination part, 122 2nd illumination part, 123 Light emission ratio setting part, 124 Light emission control part, 125 Optical system, 126 imaging part, 105 CPU, 106 memory .

Claims (4)

An original table on which an original is placed is placed, and an original on the original table and an image reading sensor disposed below the original table and including an imaging unit for reading an image of the original are relative to each other in the sub-scanning direction. In the document reading apparatus that reads the reading area of the document while being moved, the illumination apparatus is provided in the image reading sensor and illuminates the reading area of the document,
A white-type light guide tube provided with red, green, and blue LED light sources that illuminates a reading area of the document placed on the document table and that reflects light from the document surface to the imaging unit. the first illumination unit illuminates the reading area of the document placed on the document table, yellow-green LED array light source light reflected from the document surface is guided to the image pickup unit composed of And a second illumination unit that has a spectral characteristic different from that of the first illumination unit and is disposed opposite to the first illumination unit in the sub-scanning direction with the imaging unit interposed therebetween. And
The illumination light from the first illumination unit and the illumination light from the second illumination unit are mixed in the reading region where the illumination light is irradiated, so that the illumination light in the reading region has spectral characteristics of a white light source. An illuminating device for an image reading apparatus, comprising: a light emission control unit that emits light from each of the light sources of the first illumination unit and the second illumination unit at a light emission ratio of The illumination device of the image reading device according to claim 1,
Relative emission intensity of another light source is determined based on one light source selected from among the light sources of the first illumination unit and the second illumination unit, and the other light source is determined according to the determined relative emission intensity. A light emission ratio setting unit for setting the light emission ratio of the light source of
The light emission control unit is an illuminating device of an image reading apparatus that causes each light source of the first illumination unit and the second illumination unit to emit light according to the light emission ratio set by the light emission ratio setting unit. The illumination device of the image reading device according to claim 1 or 2 ,
The light emission ratio setting unit fixes a drive output to a predetermined value using the light source having the highest output value among the light sources of the first illumination unit and the second illumination unit as the selected one light source, An illuminating device of an image reading device that sets a light emission ratio of each light source constituting each of the first illuminating unit and the second illuminating unit by adjusting a drive output value to the light source. The illumination device of the image reading device according to claim 2 or 3,
The light emission ratio setting unit fixes the output of the green LED to a predetermined value, and adjusts the output values of the light sources of the red LED , blue LED , and yellow-green LED , whereby the first illumination unit and the second illumination unit An illuminating device of an image reading device that sets a light emission ratio of each light source constituting each illuminating unit.

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