JP2013106309A - Image reading device, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformly reproduce colors of a read image in a document without increasing costs and a time for reading.SOLUTION: An image reading device includes: an LED light source 102 that has LEDs arranged in array for irradiating a document to be read with light; and a light source drive control unit 20 that controls drive of the LED light source 102 at a constant current. The image reading device further includes: a voltage detection unit 32 that detects a potential difference of the LEDs of the LED light source 102; and a CPU 33 that sets a reading gain for an image signal to a signal processing unit 34 in accordance with the detection result by the voltage detection unit 32.

Description

  The present invention relates to an image reading apparatus and an image forming apparatus equipped with the image reading apparatus.

In recent years, as a light source for irradiating light on a reading original of an image reading apparatus, there is a movement to mount a long-life and low power consumption LED light source instead of a conventional xenon (Xe) light source.
The LED light source can irradiate light on a reading document in a state where a plurality of LEDs (light emitting diodes) are arranged in an array (in series) on one surface in the main scanning direction.
In general, an LED used as an LED light source of an image reading apparatus is a pseudo white LED, and is realized by a combination of a blue LED and a yellow phosphor.

Since the amount of light of the LED changes with time as the temperature rises as the lighting state continues, when reading an image of a document, for example, during automatic adjustment at power-on or when returning from the energy saving mode, Control is performed to adjust the amount of light.
Further, even when image reading of a plurality of originals is performed continuously (hereinafter referred to as “original continuous reading”), the light amount of the LED changes with time, and color correction for this is already known. . The color tone refers to color shading, degree of shift, hue, or color adjustment.

  For example, Patent Document 1 discloses the following configuration in an image reading apparatus that includes an LED light source having a plurality of LEDs and the drive control unit drives the LED light source by current control. That is, as an improvement plan to shift the emission wavelength and change the chromaticity with the change of the drive current value flowing to the LED light source over time, the current value to the changed LED drive unit is retained in advance. A configuration is disclosed in which an image processing unit multiplies a coefficient on image data read by using the correction coefficient for correction processing. Also disclosed is a configuration in which when the chromaticity (the color of light excluding lightness) changes, the carriage is moved to the position where the reference white plate is arranged to perform gain adjustment and light amount adjustment. The carriage is mounted with an LED light source that irradiates light on the image surface of the document and a mirror that reflects reflected light from the image surface in order to read the image of the document.

However, the conventional correction as described above is a method of driving the LED light source using a plurality of drive current values in the drive control unit, and it is possible to set the drive current for each LED drive control unit. However, there is a problem that the circuit scale increases accordingly and the cost increases.
When correction is performed due to color change in the image caused by the chromaticity change of the LED light source, the carriage is moved to the position where the reference white plate is arranged in spite of continuous reading of the original, and gain adjustment and Since the LED light amount adjustment is performed, there is a problem that the reading time becomes long.

  The present invention has been made in view of the above points, and an object of the present invention is to make the color reproduction of a read image of an original uniform in an image reading apparatus without increasing the cost and lengthening the reading time. To do.

The present invention has light source means in which LEDs for irradiating light to a reading original are arranged in an array, and the reflected light from the original by the irradiation light from the light source means is converted into an image signal. An image reading apparatus that reads an image of the original document, and is characterized by the following in order to achieve the above object.
That is, a drive control means for driving and controlling the light source means with a constant current, a voltage detection means for detecting a potential difference between the LEDs of the light source means, and a gain for the image signal is set according to a detection result by the voltage detection means. And gain setting means.

  According to the light source driving device of the present invention, it is possible to perform color correction of image data without increasing the cost (although having a small circuit configuration) and without interrupting continuous document reading.

1 is a circuit diagram illustrating an example of a “light source driving device for correcting a color change of a read image of a document due to a change with time” mounted in an image reading apparatus according to a first embodiment of the present invention; FIG. It is a diagram which shows an example of the relationship between the ambient temperature of LED of the LED light source 102 of FIG. 1, and relative luminous intensity. It is a diagram which shows the relationship between the electric potential difference (Vf) of LED of the LED light source 102 and temperature which can be known with the light source drive device shown in FIG. FIG. 4 is a diagram showing an example of the relationship between the ambient temperature of the LED shown in FIG. 3 and the chromaticity of the light source for the general LED shown in FIG. 1. It is a block diagram which shows the structural example of the control system of the image reading apparatus carrying the light source drive device shown in FIG.

FIG. 6 is an overall configuration diagram illustrating a configuration example of a mechanism unit of the image reading apparatus illustrated in FIG. 5. It is a whole block diagram which shows the structural example of the mechanism part of the image forming apparatus which is 10th Embodiment of this invention. It is a diagram showing an example of a spectral spectrum of a general RGB color filter of a CCD and a spectral spectrum of an LED light source that irradiates a reading original with light. FIG. 9 is a diagram showing an example of a color change of a read document that occurs when the LED light source shown in FIG. 8 is turned on for a long time. FIG. 10 is a circuit diagram showing an example of a “light source driving device for correcting a color change of a document due to a change with time” proposed in the prior art.

Hereinafter, embodiments for carrying out the present invention will be specifically described with reference to the drawings. Note that “R” shown below represents red (Red), “G” represents green (Green), and “B” represents blue (Blue).
In the following embodiments, the image reading apparatus has the following characteristics (a) and (b) when driving an LED light source (LED array) which is a light source means (light source unit).

(A) The voltage (potential difference) Vf applied to LEDs arranged in an array of LED light sources can be known.
(B) Using a correction coefficient held in advance as a gain for spectral changes of the LED during continuous document reading due to the relationship between the changes in the “temperature and voltage Vf” and “voltage Vf and chromaticity” of the LED. Thus, the color change of the read image data (image signal) can be corrected.

In short, the LED of the LED light source is driven to turn on by pulse width modulation (PWM) control.
During continuous document reading, the LED is always lit, so the amount of heat generation increases, and the LED temperature (hereinafter also referred to as “ambient temperature” or “atmosphere temperature”) rises.
The LED is turned on with a constant current (If = constant).
Since the LED voltage Vf is a function of the ambient temperature, it decreases as the temperature rises.
Further, from the ambient temperature and chromaticity characteristics of the LED, the chromaticity (x, y) decreases as the temperature rises.

Here, it corresponds to x = R (Red) and y = G (Green).
As x and y become smaller, B (Blue) becomes larger (from the well-known CIE chromaticity diagram).
That is, when viewed as the output of a CCD image sensor (hereinafter abbreviated as “CCD”) that has passed through a color filter, the output of R and G decreases and the output of B increases due to the spectral change of the LED over time.

In this embodiment, the ambient temperature is discriminated from the LED voltage Vf using the feature that the value (level) of the LED voltage Vf arranged in an array is known.
Since the change in chromaticity is known from the ambient temperature, the amount of change in RGB can be known.
Therefore, the RGB RGB output change data in response to the LED temperature change is held in advance, and the voltage Vf is monitored (monitored), so that reading is performed in accordance with the color change of the read image of each original during continuous reading. The image data can be corrected without stopping the operation.

  Therefore, its features will be specifically described with reference to FIGS. 1 to 7. Before the description, for convenience of understanding, an image reading apparatus equipped with a general CCD and a conventional light source driving device will be described. These problems and the like will be described with reference to FIGS.

FIG. 8 is a diagram showing an example of a spectral spectrum of a general CCD RGB color filter and a spectral spectrum of an LED light source that irradiates light on a reading original (hereinafter also referred to as “reading original” or simply “original”). It is.
In FIG. 8, the vertical axis indicates the intensity, the horizontal axis indicates the wavelength, the spectral spectrum of a general CCD RGB color filter, and the spectral spectrum of an LED light source using a pseudo white LED that irradiates light on a document. It is shown. The pseudo white LED is a blue LED coated with a yellow phosphor.

FIG. 9 is a diagram showing an example of a color change of a read document that occurs when the LED light source shown in FIG. 8 is turned on for a long time.
The LED light source that irradiates light on the read original (illuminates the read original) increases the amount of heat generated when it is lit for a long time by continuous original reading. As the heat generation increases and the temperature of the LED (also referred to as “LED device”) rises, the emission chromaticity of the LED changes and the spectral spectrum (wavelength and intensity) changes. This spectral spectrum changes immediately after the LED is turned on (thick solid line → thick broken line indicates a change with time). When the spectral spectrum of the LED changes, the amount of light transmitted through the RGB color filter of the CCD changes, so the RGB output level of the CCD changes.

In the example of FIG. 9, the spectral spectrum (peak wavelength: 440 mm) of the blue LED portion of the LED shifts to the long wavelength side due to the change over time indicated by the thick broken line, with respect to the LED spectral spectrum immediately after lighting indicated by the thick solid line. The spectrum of the yellow phosphor part (peak wavelength: 550 nm) shifts to the short wavelength side and the peak intensity decreases.
That is, the blue output of the CCD is increased by shifting the wavelength of blue (Blue) to a wavelength with abundant CCD blue sensitivity due to the change in the spectral spectrum of the LED.

Green shifts to a wavelength with abundant green sensitivity of the CCD, but the green output of the CCD decreases as the peak intensity decreases.
Red (Red) shifts to a wavelength with less red sensitivity of the CCD, and the peak intensity is lowered, so that the red output becomes smaller than the green output of the CCD.
For the above reasons, when continuous document reading is performed, the color tone in color reproduction of the read image of the document changes with time due to a change in RGB output balance.

FIG. 10 is a circuit diagram showing an example of a “light source driving apparatus for correcting a color change of a document due to a change with time” proposed in the prior art.
This light source driving device includes an LED light source 102 (LED array) in which LEDs are arranged in an array in order to irradiate light on a read document, and the LED light source 102 is provided to a plurality of light source blocks 102a, 102b,. It is divided. And the light source drive control part 10a, 10b, ... 10n is provided for every divided light source block 102a, 102b, ... 102n.

In such a light source driving device, the following control is performed for the problem that the light quantity and chromaticity of the LED change with time.
That is, in response to changes in the LEDs, the current control units 11a, 11b,... 11n in the light source drive control units 10a, 10b,. The amount of current to flow is changed. A correction coefficient corresponding to the change is selected from a look-up table (LUT: Look Up Table), and the coefficient is added to the image data by an image processing unit (not shown).
When the chromaticity change occurs, the continuous reading of the original is stopped, and the carriage is moved to the position where the reference white plate is arranged to adjust the light amount and the gain of the LED.

However, since the drive current is set for each light source drive control unit (LED drive control unit), the circuit scale increases correspondingly and the cost increases.
When correction is performed due to chromaticity change, the reading time is long because the carriage is moved to the position of the reference white plate and the LED light amount adjustment and gain adjustment are performed even during continuous reading of the document. turn into.

An embodiment for solving these problems will be described below.
[First Embodiment]
First, a first embodiment of the present invention will be described.
FIG. 1 is a circuit diagram showing an example of a “light source driving device for correcting a color change of a read image of a document due to a change with time” mounted in an image reading apparatus according to a first embodiment of the present invention. The parts corresponding to those in FIG. 10 are denoted by the same reference numerals.

This light source driving device is provided with an LED light source 102 (LED array) as light source means in which LEDs as point light sources are arranged in an array in order to irradiate light on a read original. not going. And the light source drive control part (LED driver) 20 which controls the drive of the LED light source 102 is provided.
The light source drive control unit 20 performs lighting of each LED of the LED light source 102 by PWM control. The current flowing through each LED, that is, the current flowing out from the terminal I_led of the light source lighting control unit 21 (I_LED) is constant. Therefore, the light source drive control unit 20 corresponds to a drive control unit that drives and controls the LED light source 102 with a constant current.

  In the prior art, as shown in FIG. 10, light source blocks 102a, 102b,... 102n are respectively provided in current control units 11a, 11b,. Since the amount of current flowing through the LEDs in the LED is adjusted to adjust the amount of light, it is necessary to provide a light source drive control unit depending on the number of LEDs arranged, and there is a problem that the circuit scale increases.

In the case of this embodiment, the amount of current flowing through each LED of the LED light source 102 is constant (I_LED = const), and the PWM signal input from the terminal V_pwm of the light source lighting control unit 21 by the light source drive control unit 20 to adjust the light amount. Therefore, it is not necessary to set a current value for each light source block, and the drive control circuit can be configured on a minimum scale.
Further, the light source drive control unit 20 supplies a voltage (V_LED) boosted from the terminal V_led of the light source lighting control unit 21 to the LED light source 102, and the voltage of the terminal Vf_mon of the light source lighting control unit 21 is V_LED (= LED (Potential difference × number of LEDs + V_CH) is divided. V_CH is a constant voltage supplied to the terminal V_ch of the light source lighting control unit 21 in order to operate the light source drive control unit 20.

In this embodiment, unlike the prior art, the potential difference (Vf) of the LED can be known from the voltage level of Vf_mon.
Moreover, since the change in the amount of light of the LED appears in the change in the potential difference (Vf) of the LED, it can be known by monitoring the potential difference (Vf).

FIG. 2 is a diagram showing an example of the relationship between the ambient temperature of the LED of the LED light source 102 and the relative luminous intensity.
In FIG. 2, the relative luminous intensity corresponds to the green output of the CCD when it passes through the RGB color filter of the CCD.
FIG. 2 shows how the relative luminous intensity decreases as the temperature of the LED increases.

FIG. 3 is a diagram showing the relationship between the potential difference (Vf) of the LED of the LED light source 102 and the temperature, which can be known by the light source driving device of this embodiment shown in FIG.
As can be seen from FIG. 3, as the ambient temperature of the LED increases, the potential difference (Vf) applied to the LED decreases.
Therefore, a decrease in the potential difference (Vf) of the LED monitored in this embodiment is a change in the light amount of the LED (from FIG. 2).

FIG. 4 is a diagram showing an example of the relationship between the ambient temperature of the LED shown in FIG. 3 and the chromaticity of the light source for the general LED shown in FIG.
As can be seen from FIG. 4, the chromaticity (x, y) decreases as the ambient temperature of the LED increases.
Here, x = red (Red) and y = green (Green). As chromaticity (x, y) decreases, blue increases (from the well-known CIE chromaticity diagram).
That is, as the CCD output after passing through the color filter, the spectral spectrum changes due to the change with time (temperature rise) of the LED, the output of red (Red) and green (Green) decreases, and the blue (Blue) It shows that the output rises.

FIG. 5 is a block diagram illustrating a configuration example of a control system of the image reading apparatus in which the light source driving device illustrated in FIG. 1 is mounted.
This image reading apparatus is a scanner apparatus or a single scanner apparatus mounted on an image forming apparatus such as a digital copying machine, a digital multifunction peripheral, or a facsimile machine, and includes an LED light source 102 and a light source driving apparatus shown in FIG. A light source drive control unit 20 is provided. Further, a drive signal control unit 31, a voltage detection unit 32 that is a voltage detection unit, a CPU 33, and a signal processing unit 34 are also provided.

The LED light source 102 is an LED array in which LEDs, which are point light sources, are arranged in an array to irradiate a read original with light.
The light source drive control unit 20 is an LED driver that performs lighting of each LED of the LED light source 102 by PWM control.
The drive signal control unit 31 supplies a PWM signal to the light source drive control unit 20 and supplies a clock to the signal processing unit 34 that integrates a gain (to be described later) (hereinafter also referred to as “read gain”) before reading an image of the document. It is a timing generator (TG).

The voltage detection unit 32 is a voltage detection sensor that monitors from the terminal of the light source drive control unit 20 and detects the potential difference (Vf) of the LED of the LED light source 102.
The CPU 33 is a microcomputer that comprehensively controls the image reading apparatus, and includes a central processing unit, a ROM that stores a program executed by the central processing unit, a RAM that temporarily stores data, and a correction coefficient holding unit 33a. And a non-volatile memory that is a storage means used as a storage device. The CPU 33 acquires a chromaticity correction coefficient corresponding to a change in the spectral spectrum of the LED light source 102 from the correction coefficient holding unit 33a based on the detection result of the LED potential difference (Vf) by the voltage detection unit 32, and outputs a signal as a reading gain. Set for the processing unit 34. Therefore, the CPU 33 functions as a gain setting unit.

Here, the chromaticity correction coefficient is a coefficient for determining the reading gain in accordance with the relationship between the LED potential difference, the temperature, and the chromaticity of the LED light source 102.
The correction coefficient holding unit 33a is a lookup table (LUT) that holds chromaticity correction coefficients.
The signal processing unit 34 is an analog signal processing unit (AFE: Analog Front End) that reflects the chromaticity correction coefficient obtained from the correction coefficient holding unit 33a as a reading gain when reading an image of a document.

This signal processing unit 34 is configured as follows, for example. That is, a clamp circuit, a sample hold circuit, an amplifier circuit (PGA: Programmable Gain Amplifier), and an A / D converter are provided.
The clamp circuit clamps the black offset level of the image signal (analog signal) from the CCD to a predetermined potential at the input timing of the clamp signal from the drive signal control unit 31.
The sample hold circuit samples the analog signal output from the clamp circuit at the input timing of the sample hold signal from the drive signal control unit 31, and holds (holds) the level of the analog signal for a certain time. This is called “sample hold”.

The sample hold signal is input to the switch element that turns on / off the signal to the capacitor in the sample hold circuit that holds the sample value. The sample starts when the sample hold signal is asserted and ends when the assert ends. (Hold).
The amplifier circuit amplifies the analog signal from the sample hold circuit with the set read gain. Note that when the gain is set, the dynamic range of the signal increases.
The A / D converter quantizes the analog signal amplified by the amplifier circuit and converts it into a digital signal (image data) at the input timing of the conversion signal from the drive signal control unit 31. That is, the image signal from the amplifier circuit is converted from an analog signal to a digital signal.
Therefore, the digital signal output from the A / D converter is subjected to chromaticity correction by the reading gain (chromaticity correction coefficient).

Here, for example, when the LEDs are continuously lit (lit for a long time) at the time of continuous reading of the document or the like, the spectral spectrum of the LEDs changes as the ambient temperature of the LEDs increases, and the amount of light and chromaticity change.
As shown in FIG. 9, since the change in the spectral spectrum of the LED changes independently as RGB as the output of the CCD, there is a problem that the read image data leads to a change in color (abnormal image). .

As a measure against color change, it is possible to adjust the light amount of the LED during image reading of the document and to adjust the gain. However, since the document continuous reading operation is stopped, image reading throughput (productivity), etc. May cause new problems (prior art).
Further, when the LED is turned on by current control (prior art), it is necessary to adjust each light source drive control unit that drives the LED, which may increase the circuit scale.

In this embodiment, chromaticity correction is performed using a feature that the potential difference (Vf) of the LED is known by making the current flowing through the LED constant and lighting the LED by PWM control.
From the relationship between the LED potential difference (Vf) and the ambient temperature, and the relationship between the LED ambient temperature and the chromaticity change, it can be seen how much RGB changes as the output of the CCD depending on the change in the LED potential difference (Vf).

Regarding the relationship between the change amount of the LED potential difference (Vf) and the change amount of the CCD output in advance, the correction coefficient holding unit 33a in the CPU 33 holds the chromaticity correction coefficient, and the chromaticity correction coefficient is set every time an image of the document is read. By reflecting it in the reading gain, it is possible to perform color reproduction without any color change even during continuous document reading.
In this embodiment, the reading gain handled as the chromaticity correction coefficient is the gain of the signal processing unit 34.

  In general, the shading gain after reading an image of a document and the gray balance gain for adjusting the color are generally accumulated in an image processing unit at a later stage after the image is read. The image data at the time of image processing is read image data. Therefore, the chromaticity correction is performed on the read image data of 10 bits. Actually, chromaticity correction is performed by an amplification circuit (PGA) on the analog signal immediately before being converted into the 10-bit read image data.

Further, as in this embodiment, a method of detecting the potential difference (Vf) of the LED and detecting the level change due to the image data instead of the correction process using the correction coefficient holding unit 33a is also conceivable.
In this method, a white background member (corresponding to a reference white plate) for conveying a read document is read before reading the image of the document, and RGB chromaticity correction coefficients (read gain) are calculated from the level change.

However, the white background member for document conveyance may become dirty as the document is conveyed.
In that case, since the image data read from the document becomes dark data due to contamination, it may be determined that the light quantity of the LED has decreased. For example, when the chromaticity correction coefficient is calculated with a dirty white background member even though the blue CCD output has risen over time, the gain may be reduced when the gain should be reduced. Can make it bigger. That is, there is a possibility that the RGB balance is worsened due to an erroneous chromaticity correction coefficient. Therefore, correction coefficient calculation using image data is not appropriate.

In the image reading apparatus according to this embodiment, the change in color of the image data can be corrected by the change in chromaticity of the LED as the temperature rises, but the user may allow the change in color.
For example, when the reading operation is finished at a level that does not cause a problem due to color change, there is a case where the color correction need not be executed.
In such a case, in accordance with an instruction from the user in advance (instruction from an operation unit or the like not shown in the figure) to perform chromaticity correction when the potential difference (Vf) of the LED exceeds a certain threshold value, FIG. The CPU 33 can hold the chromaticity correction coefficient in the internal correction coefficient holding unit 33a and set the timing of chromaticity correction (gain setting).
As a result, it is possible to reduce processing for color correction.

In addition, when performing continuous document scanning, a scanned document is set in an ADF, which will be described later. This is because the image of the original is read until there is no set original.
When the number of originals set is small and the user can tolerate color change, the following processing is performed to obtain the image data as soon as possible by reducing the processing required for correction without performing color correction. It is also possible to do so. That is, the CPU 33 in FIG. 5 holds the chromaticity correction coefficient in the internal correction coefficient holding unit 33a in accordance with an instruction from the user in advance so that the correction is started when a certain number of original images are read. Set the chromaticity correction timing.

6 is an overall configuration diagram illustrating a configuration example of a mechanism unit of the image reading apparatus illustrated in FIG.
The image reading apparatus 100 illuminates a document, which is a subject, with light emitted from an LED light source 102, receives reflected light from the document with a CCD 109, converts the light into an image signal, and performs image processing. Image data can be read. Since the image signal converted by the CCD 109 is an analog signal, it is converted into a digital signal (image data).

  As shown in FIG. 6, the image reading apparatus 100 includes a contact glass 101 that is a document glass on which a document is placed, a first carriage 106 including a document exposure LED light source 102 and a first reflection mirror 103, and a first carriage 106. And a second carriage 107 including a second reflecting mirror 104 and a third reflecting mirror 105. Further, a CCD 109, a lens unit 108 for forming an image on the CCD 109, a reference white plate 110 for correcting various distortions caused by a reading optical system, and a sheet-through reading slit 111 are also provided.

An automatic document feeder (hereinafter abbreviated as “ADF”) 200 as an automatic document feeder is mounted on the upper part of the image reading apparatus 100 so that the ADF 200 can be opened and closed with respect to the contact glass 101. Are connected via a hinge or the like (not shown).
The ADF 200 includes a document tray 201 as a document placing table on which a document bundle composed of a plurality of documents can be placed. In addition, separation / feeding means including a feeding roller 202 that separates documents one by one from a bundle of documents placed on the document tray 201 and automatically feeds them toward the sheet-through reading slit 111 is also provided.

  In the image reading apparatus 100 configured as described above, in the scan mode in which the image surface of the document is scanned (scanned) to read the image of the document, the first carriage 106 and the second carriage 107 are indicated by arrows by a stepping motor (not shown). The document is scanned in the A direction (sub-scanning direction). At this time, the second carriage 107 moves at a half speed of the first carriage 106 in order to keep the optical path length from the contact glass 101 to the CCD 109 constant.

  At the same time, an image surface which is the lower surface of the document set on the contact glass 101 is illuminated (exposed) by the LED light source 102 of the first carriage 106. Then, the reflected light image from the image plane is sequentially sent to the CCD 109 via the first reflecting mirror 103 of the first carriage 106, the second reflecting mirror 104 and the third reflecting mirror 105 of the second carriage 107, and the lens unit 108. To form an image. Then, an analog signal is output by photoelectric conversion of the CCD 109, and converted into a digital signal by a signal processing unit at the subsequent stage. Thereby, the image of the original is read and digital image data is obtained.

  On the other hand, in the sheet through mode in which the original is automatically fed and the image of the original is read, the first carriage 106 and the second carriage 107 move to the lower side of the sheet through reading slit 111. Thereafter, the document placed on the document tray 201 is automatically fed in the arrow B direction (sub-scanning direction) by the feeding roller 202, and the document is scanned at the position of the sheet through reading slit 111.

  At this time, the lower surface (image surface) of the automatically fed document is illuminated by the light source 102 of the first carriage 106. Therefore, the reflected light image from the image plane is sequentially sent to the CCD 109 via the first reflecting mirror 103 of the first carriage 106, the second reflecting mirror 104 and the third reflecting mirror 105 of the second carriage 107, and the lens unit 108. To form an image. Then, an analog signal is output by photoelectric conversion of the CCD 109, and converted into a digital signal by a signal processing unit at the subsequent stage. Thereby, the image of the original is read and digital image data is obtained. The document whose image has been read in this way is discharged to a discharge port (not shown).

  The reflected light from the reference white plate 110 is converted into an analog signal by the CCD 109 by illumination by the LED light source 102 started before reading an image in the scan mode or the sheet through mode, and converted into a digital signal by a signal processing unit in the subsequent stage. Converted. Thereby, the reference white plate 110 is read, and shading correction at the time of reading the image of the document is performed based on the reading result (digital signal). Since this shading correction is a well-known technique, a detailed description thereof will be omitted.

  Further, when the ADF 200 is provided with a conveyance belt, the document can be automatically fed to the reading position on the contact glass 101 by the ADF 200 and the image of the document can be read even in the scan mode.

According to the image forming apparatus of the first embodiment, the following effects (1) to (6) can be obtained.
(1) A light source drive control unit that drives and controls an LED light source (LED array), which is a light source unit in which LEDs for irradiating a read original with light arranged in an array are detected with a constant current, and detects a potential difference between the LEDs of the LED light source. The CPU sets a reading gain for the image signal in the signal processing unit according to the detection result by the voltage detection unit. That is, by detecting a change in the potential difference of the LED, it is possible to detect a change in chromaticity (amount of light) of the LED, and thus it is possible to set a reading gain for the image signal. The color correction can be performed on the image signal by the reading gain.

  Therefore, there is no need to set a drive current for each light source drive control unit, and the circuit scale does not increase. Further, when correction is performed due to a change in chromaticity, there is no need to move the carriage to the white plate position and perform gain adjustment and LED light amount adjustment even during continuous reading of the document. Therefore, it is possible to make the color reproduction uniform for the read image of the document without increasing the cost and lengthening the reading time.

(2) A lookup table (storage means) that holds a chromaticity correction coefficient for determining a reading gain in accordance with the relationship between the LED potential difference, temperature, and chromaticity, and the CPU responds to the detection result by the voltage detection unit. The reading gain is set for the signal processing unit from the chromaticity correction coefficient. This facilitates setting of the reading gain.

(3) The light source drive control unit is an LED driver, the voltage detection unit is a voltage detection (also referred to as “electric detection”) sensor, and the voltage detected by the voltage detection unit is the potential difference of the LED, thereby reducing the cost. Connected.
(4) Since the CPU sets a reading gain each time an image of a read original is read, it is not necessary to stop the color correction and continuously perform color correction at the time of continuous original reading, leading to an improvement in the throughput of reading the original image.

(5) By setting the reading gain when the potential difference of the LED detected by the voltage detection unit exceeds a preset threshold, it is possible to reduce the color correction before reading the document image.
(6) The CPU sets the reading gain when the number of originals subjected to image reading exceeds a preset number (for example, when continuous original reading takes a long time when there is a possibility of color change). As a result, it is possible to reduce the color correction before reading the document image.

  The embodiment in which the present invention is applied to an image reading device (scanner or the like) that reads an image of a document with a CCD has been described above. However, the present invention is not limited to this, and the image reading device that reads an image of a document with another image sensor. Of course, the present invention can also be applied to various image forming apparatuses such as a digital multifunction machine, a digital copying machine, a facsimile machine, and a printer equipped with the image reading device. The image forming apparatus main body can print the image data from the image reading apparatus on a sheet such as paper as a visible image. Accordingly, it is possible to provide an image forming apparatus that can efficiently acquire a high-quality image.

[Second Embodiment]
Next, a second embodiment of the present invention will be specifically described with reference to FIG.
FIG. 7 is an overall configuration diagram showing a configuration example of a mechanism portion of the image forming apparatus according to the tenth embodiment of the present invention. The same reference numerals are given to the same portions as those in FIG.
The image forming apparatus 300 is a digital copying machine equipped with the image reading apparatus 100 shown in FIG. 6 (including a light source driving unit corresponding to the light source driving apparatus shown in FIG. 1).

As shown in FIG. 7, the image forming apparatus 300 is provided with an ADF 400 on an upper part of a contact glass 101 on which an original is placed. A hinge or the like (not shown) is provided so that the ADF 400 can be opened and closed with respect to the contact glass 101. It is connected through.
The ADF 400 includes a document tray 401 as a document placement table on which a document bundle composed of a plurality of documents can be placed. Further, when a print key on an operation unit (not shown) is pressed, the originals are separated one by one from the original bundle placed on the original tray 401 with the image surface facing upward, and automatically fed, and the sheet through reading slit 111 is provided. Alternatively, separation / feeding means including a feeding roller 402 and a conveying belt 403 that are conveyed toward the contact glass 101 is also provided.

The document fed by the feeding roller 402 or the conveying belt 403 is read out as described with reference to FIG. 6 and then discharged onto the upper surface of the ADF 400 by the conveying belt 403 and the discharging roller 404.
Here, the operation of the controller (not shown) and the ADF 400 when the document is conveyed to the reading position of the contact glass 101 by the ADF 400 will be described.

  The feed motor of the ADF 400 is driven by an output signal from the controller. When the feed start signal generated by pressing the print key on the operation unit is input, the controller corrects the feed motor.・ Reverse drive. When the feeding motor is driven to rotate in the forward direction, the feeding roller 402 rotates clockwise to automatically feed the document located at the highest position from the bundle of documents toward the sheet-through reading slit 111 or the contact glass 101. Be transported. When the leading edge of the document is detected by the document set detection sensor 405, the controller drives the feed motor in reverse based on the output signal from the document set detection sensor 405. This prevents subsequent documents from entering and prevents separation.

  When the document set detection sensor 405 detects the trailing edge of the document, the controller also counts a rotation pulse of a conveyance belt motor (not shown) from this detection point, and when the rotation pulse reaches a predetermined value, the conveyance belt 403. Is stopped and the conveying belt 403 is stopped, whereby the document is stopped at the reading position on the contact glass 101. Further, when the trailing edge of the document is detected by the document set detection sensor 405, the feeding motor is driven again, and the subsequent document is separated and automatically fed as described above. Then, the sheet is conveyed toward the contact glass 101, and when the pulse of the feeding motor from the time when the document is detected by the document set detection sensor 405 reaches a predetermined pulse, the feeding motor is stopped and the next document is detected. To wait first.

  When the document stops at the reading position on the contact glass 101, the image of the document is read. When this image reading is completed, a signal indicating that is input to the controller, so that the controller drives the conveyance belt motor in the normal direction by this signal, and the document is discharged from the contact glass 101 by the conveyance belt 403 to the discharge roller. Unload to 404.

As described above, the original bundle placed on the original tray 401 in the ADF 400 with the image side of the original facing upward is automatically fed from the uppermost original by pressing the print key. For example, the reading position on the contact glass 101 is read. It is conveyed to.
The original that has been conveyed to the reading position and stopped is discharged from the discharge port by the conveying belt 403 or the like after the image is read. Further, when it is detected that there is a next document on the document tray 401, the next document is automatically fed and conveyed onto the contact glass 101 like the previous document.

  The transfer sheets (paper sheets) stacked on the first tray 301, the second tray 302, and the third tray 303, which are sheet feeding trays, are a first sheet feeding unit 311, a second sheet feeding unit 312, and a third sheet feeding unit, respectively. The sheet is fed by 313 and conveyed by the vertical conveyance unit 314 to a position where it abuts on a drum-shaped photosensitive member (photosensitive drum) 315 as an image carrier. Actually, any one of the trays 301 to 303 is selected, and the transfer paper is fed therefrom. Also, a recording medium other than transfer paper can be used.

On the other hand, the image data read by the image reading apparatus 100 is written on the surface of the photoreceptor 315 charged in advance by a charging unit (not shown) by a laser beam from a writing unit 350 in the printer as an image forming unit (there is When the surface is exposed), the portion passes through the developing unit 327, and a toner image is formed there. The developing unit 327 that performs the image formation, the charging unit, and the like constitute image forming means.
The transfer sheet fed from the selected paper feed tray is transferred by the transfer belt 316 at the same speed as the rotation of the photoconductor 315, and the toner image on the photoconductor 315 is transferred. Further, the toner image is fixed by the fixing unit 317, and is discharged by a paper discharge unit 318 to a paper discharge tray 319 outside the apparatus.

  At this time, for example, in order to reverse the transfer paper on which the toner image is formed on one side in order to discharge face-down (the image surface faces downward in order to align the transfer paper in the page order), the transfer paper is discharged. The paper is conveyed to the double-sided paper conveyance path 320 by the unit 318, switched reverse by the reversing unit 321, and then discharged to the paper discharge tray 319 through the reverse paper conveyance path 322.

When images are formed on both sides of the transfer paper, the transfer paper on which the image is formed on one side is conveyed to the double-sided input conveyance path 320 by the paper discharge unit 318 and is switched back by the reverse unit 321. After that, it is sent to the duplex conveying unit 323.
The transfer paper sent to the double-sided conveyance unit 323 is fed again from the double-sided conveyance unit 323 to transfer the toner image formed on the photoconductor 315 again, and is again applied to the photoconductor 315 by the vertical conveyance unit 314. It is transported to the contact position. Then, after the toner image is transferred to the other surface, the toner image is fixed by the fixing unit 317 and discharged to the paper discharge tray 319 by the paper discharge unit 318.

  The photoconductor 315, the conveyance belt 316, the fixing unit 317, the paper discharge unit 318, and the development unit 327 are driven by a main motor (not shown), and the driving force of the main motor is transmitted to each of the paper feed units 311 to 313 by a paper feed clutch. Driven. The vertical conveyance unit 314 is driven by the driving force of its main motor being transmitted via an intermediate clutch.

  The writing unit 350 includes a laser output unit 351, an imaging lens 352, and a mirror 353. Inside the laser output unit 351, a laser diode that is a laser light source and a rotating polygon mirror (polygon mirror) that scans the laser light. Or it has a vibrating mirror. The laser light emitted from the laser output unit 351 is deflected by a polygon mirror or a vibrating mirror, passes through an imaging lens 352, is folded by a mirror 353, and is focused on the surface of the photoreceptor 315.

  According to the image forming apparatus (digital copying machine) of the second embodiment, the image reading apparatus of the first embodiment is provided, and an image is formed on a recording medium based on image data read by the image reading apparatus. Therefore, it is possible to avoid the deterioration of the image quality of the formed image. That is, it is possible to achieve high image quality of the formed image.

  In addition, this invention is not limited to each embodiment mentioned above, It cannot be overemphasized that all the technical matters contained in the technical idea described in the claim are object.

20: Light source drive control unit (LED driver) 21: Light source lighting control unit 31: Drive signal control unit (TG) 32: Voltage detection unit (voltage detection sensor)
33: CPU 33a: correction coefficient holding unit (look-up table)
34: Signal processing unit (AEF) 100: Image reading apparatus 102: LED light source (LED array) 109: CCD image sensor 200, 400: ADF 300: Image forming apparatus 315: Photoconductor 317: Fixing unit 327: Developing unit 350: Writing unit

JP 2010-252043 A

Claims (7)

Light source means in which LEDs for irradiating light to a reading original are arranged in an array, and the reflected light from the original by the light emitted from the light source means is converted into an image signal, whereby the original An image reading apparatus for reading an image,
Drive control means for driving and controlling the light source means with a constant current;
Voltage detection means for detecting a potential difference between the LEDs of the light source means;
An image reading apparatus comprising: gain setting means for setting a gain for the image signal in accordance with a detection result by the voltage detection means. The image reading apparatus according to claim 1,
A storage means for storing a chromaticity correction coefficient for determining the gain according to the relationship between the potential difference of the LED and the temperature and chromaticity is provided,
The image reading apparatus, wherein the gain setting means sets the reading gain from the chromaticity correction coefficient according to a detection result by the voltage detecting means. The drive control means is an LED driver,
The voltage detection means is a voltage detection sensor,
The image reading apparatus according to claim 1, wherein the voltage detected by the voltage detection unit is a potential difference between the LEDs.   The image reading apparatus according to claim 1, wherein the gain setting unit sets the gain every time an image of the document is read.   The gain setting unit sets the gain when the potential difference of the LED detected by the voltage detection unit exceeds a preset threshold value. The image reading apparatus described in 1.   4. The gain setting unit according to claim 1, wherein the gain setting unit sets the gain when the number of originals from which the image has been read exceeds a preset number. 5. Image reading device.   An image forming apparatus comprising the image reading apparatus according to claim 1.

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