JP6089716B2 - Photoelectric conversion apparatus, image reading apparatus, and image forming apparatus - Google Patents

Description

  The present invention relates to a photoelectric conversion device (photoelectric conversion device) that converts the intensity of incident light into an electrical signal and outputs it, an image reading device including the photoelectric conversion device, and an image forming apparatus including the image reading device. .

  In an image reading apparatus including a photoelectric conversion device in which a plurality of photoelectric conversion elements (light receiving elements) are arranged, each pixel is read at the time of image reading due to an individual difference of a signal reading circuit (pixel signal generation circuit) for each photoelectric conversion element in each pixel. Fixed pattern noise occurs. As a result, even if an image having a uniform density is read, image quality deterioration such as vertical streaks may occur.

  For this reason, black shading correction is performed by subtracting the black level, which is the read value in the dark state, from the read pixel value so as to suppress the occurrence of density fluctuation in units of pixels in the main scanning direction. When acquiring the black level used for the black shading correction, it is necessary to shield the light from entering the photoelectric conversion element. For this reason, when a plurality of documents are continuously read, if a black level is acquired every time one document is read, productivity decreases. There is also a problem that accurate black level acquisition may not be possible because light cannot be completely blocked.

  In order to solve this problem, the charge detection unit that converts the charge accumulated in the light receiving element into a voltage and detects it so that the black level can be updated every reading even in the lighted state of the light source. Is already known as a pseudo black level. For example, Patent Document 1 discloses that a black level is generated by reading a signal in a state where a potential detection unit connected to a light receiving element of a pixel for a black level generation circuit is reset.

However, in the conventional photoelectric conversion device, when the signal with the charge detection unit in the reset state as described above is acquired as a pseudo black level, there are the following problems.
When the photoelectric conversion device reads an image, the charge transfer gate is opened and closed in order to transfer the charge accumulated by the light receiving element of each pixel according to the intensity of incident light to the charge detection unit. Therefore, the read signal (voltage level) of each pixel includes a switching noise component due to gate opening and closing.
In the dark state, when the photoelectric conversion device operates in the same way as normal image reading to generate a black level, the charge transfer gate is opened and closed, so the generated black level signal also includes a switching noise component due to gate opening and closing. It is included.
Therefore, by reducing the black level from the read level of each pixel by the black shading correction, the switching noise component can be almost removed.

However, as described above, when the voltage obtained by resetting the charge detection unit is acquired as a pseudo black level, the charge transfer gate is kept open, so that the generated black level signal includes a switching noise component. Is not included.
Therefore, even if the black level is subtracted from the read level of each pixel by black shading correction, the switching noise component at the read level of each pixel cannot be removed. As a result, there has been a problem that variation in density in units of pixels in the main scanning direction cannot be accurately suppressed.

  The present invention has been made to solve such a problem, and it is possible to generate an appropriate black level for each pixel without blocking incident light to the light receiving element while the light source is turned on. Thus, an object is to realize highly accurate black shading correction.

In order to achieve the above object, in a photoelectric conversion device having a light receiving element that generates and accumulates charges according to the intensity of incident light, and a charge detection unit that converts charges accumulated in the light receiving elements into voltage,
A normal output mode for outputting a signal corresponding to the intensity of incident light for each pixel, and a dummy black level output mode for outputting a black level signal irrelevant to the incident light for each pixel;
In the normal output mode, the charge detection unit is reset, the charge accumulated in the light receiving element is transferred to the reset charge detection unit, and a signal converted into a voltage is output,
In the dummy black level output mode, and resets the charge detection part, a period corresponding to the charge transfer period in the normal output mode, not transferred to the charge detection part reset charges accumulated in the light receiving element In addition, a signal obtained by resetting the charge detection unit is output as a black level signal for each pixel .

According to the photoelectric conversion device of the present invention, in the dummy black level output mode, a black level signal unrelated to incident light can be generated, and the black level signal includes a switching noise component due to resetting again. .
Therefore, even when the light source is kept on during continuous reading, a black level that includes switching noise components can be generated for each pixel, thereby enabling high-accuracy black shading correction that cancels the influence of noise for each reading. Can be realized.

It is a block diagram which shows the outline of the signal system of one Embodiment of the image reading apparatus provided with the photoelectric conversion apparatus by this invention. FIG. 2 is a block diagram illustrating a configuration example of a photoelectric conversion device 3 in the image reading device illustrated in FIG. 1. FIG. 3 is a circuit diagram illustrating a configuration example of a pixel signal generation circuit illustrated in FIG. 2. It is a figure for demonstrating output mode switching in the pixel signal generation circuit shown in FIG. 6 is a timing chart showing gate signals and output waveforms when the pixel signal generation circuit is in a normal output mode operation.

It is a timing chart which shows each gate signal and output waveform in the case of outputting a pseudo black level in the conventional dummy black level output mode. It is a timing chart which shows the output waveform containing each gate signal and a noise component at the time of normal output mode operation | movement. It is explanatory drawing in the case of performing black shading correction | amendment with the black level acquired in the dark state of normal output mode. It is explanatory drawing in the case of performing black shading correction | amendment with the pseudo black level acquired in the conventional dummy black level output mode. 4 is a timing chart showing gate signals and output waveforms when a pseudo black level is output in a dummy black level output mode in the photoelectric conversion apparatus according to the present invention.

3 is a flowchart showing a flow of operations when a pressure plate is read by the image reading apparatus shown in FIG. 1. It is a flowchart which similarly shows the flow of operation | movement at the time of the DF reading. It is a block diagram which shows only the change part of the partial change example of the image reading apparatus shown in FIG. 14 is a flowchart showing a flow of operations at the time of document reading by the image reading apparatus shown in FIG. 13. 1 is a schematic cross-sectional view showing a schematic configuration of a mechanism unit of an embodiment of an image forming apparatus according to the present invention. FIG. 16 is a schematic enlarged cross-sectional view illustrating a schematic configuration of a mechanism unit of the image reading apparatus in FIG. 15.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
First, an outline of an embodiment of an image reading apparatus provided with a photoelectric conversion apparatus according to the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing an outline of a signal system of the image reading apparatus.
The image reading apparatus 200 includes a light source 1, a light source control unit 2 that controls turning on and off the light source 1, a photoelectric conversion device 3, a pressure plate opening / closing detection unit 5 that detects opening and closing of a pressure plate (not shown), And a black shading correction unit 7.

The photoelectric conversion device 3 receives reflected light from a reading target (original) illuminated by the light source 1, converts the light into an electric signal corresponding to the intensity, performs A / D conversion, and outputs the digital value. . As the light source 1, a xenon lamp, a fluorescent lamp, an LED array, or the like is used.
The photoelectric conversion device 3 includes a timing signal generation unit 4 that generates a timing signal.

The image reading apparatus 200 includes a pressure plate that can be opened and closed so as to cover the object to be read, and the pressure plate open / close detection unit 5 detects an open / closed state of the pressure plate. For example, a micro switch or a reflective photo sensor is used. is there.
The black shading correction unit 7 performs offset level correction by subtracting a dark pixel value (black level data) from a read pixel value that is a digital signal output from the photoelectric conversion device 3.

Next, a configuration example of the photoelectric conversion device 3 in the image reading apparatus 200 will be described with reference to FIG. FIG. 2 is a block diagram illustrating a configuration example of the photoelectric conversion device 3.
In the photoelectric conversion device 3, the light receiving elements 8 are linearly arranged by the number of main scanning pixels, which is the predetermined number of pixels. A light receiving element 8 corresponding to each pixel receives (receives) reflected light from a reading target (original) illuminated by the light source 1, and generates and accumulates charges corresponding to the intensity.

  A pixel signal generation circuit 9 is provided for each light receiving element 8. Then, the charges accumulated in each light receiving element 8 are transferred to each pixel signal generation circuit 9, converted into a voltage by an internal charge detection unit, and processed as a digital signal through processes such as gain adjustment and A / D conversion. The pixel value of each pixel is output. The operation timing of each pixel signal generation circuit 9 is controlled by a signal from the timing signal generation unit 4.

That is, the same number of pixel signal generation circuits 9 as the light receiving elements 8 are provided, and the pixel value of the pixel by the corresponding light receiving element 8 is output for each pixel signal generation circuit 9.
In this way, the photoelectric conversion device 3 sequentially outputs pixel values in which pixels for one line are arranged in the main scanning direction in the sub-scanning direction, whereby the photoelectric conversion device 3 that is a one-dimensional line sensor outputs Reading data can be acquired.

FIG. 3 is a circuit diagram showing a configuration example of the pixel signal generation circuit 9 shown in FIG.
The pixel signal generation circuit 9 includes a charge detection unit 10, an amplifier 11, and an A / D converter 12. The charge detection unit 10 includes an RS (reset) gate 13 and a capacitor 14 connected in series between a DC power source having a voltage VDD and the ground, and a connection point a between the cathode of the photodiode PD as the light receiving element 8. And a connected PT (charge transfer) gate 15. The anode of the photodiode PD is connected to the ground.
A switching transistor such as a MOSFET is used for the RS gate 13 and the PT gate 15.

  The charge detection unit 10 charges and resets the capacitor 14 to the voltage VDD while the PT gate 15 is off and the RS gate 13 is on, and the light receiving element 8 when the RS gate 13 is off and the PT gate 15 is on. The electric charge accumulated in is transferred to the capacitor 14. As a result, the capacitor 14 is discharged according to the amount of charge accumulated in the light receiving element 8, and the voltage at the point a is lowered. Therefore, the electric charge accumulated in the light receiving element 8 is converted into a voltage at point a.

The ON / OFF period of the RS gate 13 and the PT gate 15 is controlled by the RS gate signal and the PT gate signal from the timing signal generation unit 4 shown in FIG.
The voltage at point a of the charge detection unit 10 is amplified by the amplifier 11 to adjust the gain, converted to a digital value by the A / D converter 12, and a pixel value is output.
In addition, although the example which used the photodiode as the light receiving element 8 was shown, photoelectric conversion elements, such as CCD and CMOS, may be used.

FIG. 4 is a diagram for explaining output mode switching in the pixel signal generation circuit 9 shown in FIG.
The photoelectric conversion device 3 according to the present invention has “normal output mode” and “dummy black level output mode” as output modes in each pixel signal generation circuit 9.
The “normal output mode” is a mode in which a signal corresponding to the intensity of light incident on the photodiode which is the light receiving element 8 shown in FIG. 3 is output for each pixel. The “dummy black level output mode” is a mode in which a signal corresponding to a black level in a dark state unrelated to the light incident on the light receiving element 8 is output for each pixel.

  The operations in these two modes are switched by changing the RS gate signal and the PT gate signal by the timing signal generator 4. This is shown as mode switching means 16 such as a kind of changeover switch in FIG.

FIG. 5 is a timing chart showing an ideal output waveform when the pixel signal generation circuit 9 operates in the normal output mode. The operation shown in this timing chart will be described with reference to FIGS.
The RS gate signal output from the timing signal generator 4 is at a high level H only during the reset period Tr in a predetermined cycle, and the RS gate 13 shown in FIG. Charged to voltage VDD.

  On the other hand, the PT gate signal is also at the high level H only during the charge transfer period Tt during the period when the RS gate signal is at the low level L in the same cycle as the RS gate signal. Accordingly, the PT gate 15 shown in FIG. 3 is turned on only during this period, and the charge accumulated in the light receiving element 8 is transferred to the capacitor 14 of the charge detection unit 10.

Since the polarity of the charge charged in the capacitor 14 and the charge transferred from the light receiving element 8 are opposite to each other, the capacitor 14 is charged to the opposite polarity according to the amount of accumulated charge in the transferred light receiving element 8, and the point a The voltage decreases as shown in FIG.
Therefore, the level of the RS output, which is the output (voltage at point a) of the charge detection unit 10 at reset, is VDD, and the level of the output after charge transfer (referred to as PT output) is the reduced voltage due to the transferred charge. If VS is VS, VDD-VS is obtained.

  As the amount of charge stored in the light receiving element 8 increases, the reduced voltage VS increases and approaches the white level. As the amount of charge stored in the light receiving element 8 decreases, the decreased voltage VS decreases and approaches the black level. The signal having the output waveform shown on the upper side of FIG. 5 is inverted and amplified by the amplifier 11 shown in FIG. The corresponding pixel values are sequentially output.

The output level after inversion amplification by the amplifier 11 is such that the voltage VDD is 0 level, and the PT output level is a level corresponding to the drop voltage VS.
In this way, by repeatedly setting the RS gate signal and the PT gate signal to the high level H for a predetermined period alternately, the read pixel values in the sub-scanning direction orthogonal to the arrangement direction of the light receiving elements (main scanning direction) are successively obtained. Will be output.

  Further, in the dark state where no light is incident on the light receiving element 8 shown in FIG. 3, since no charge is accumulated in the light receiving element 8, ideally, the charge of the capacitor 14 does not change after charge transfer, The level of the PT output should remain VDD when the drop voltage VS = 0. Therefore, the output waveform of the charge detection unit 10 should be as shown on the lower side of FIG.

Therefore, the output level in the dark state (the output level after inversion amplification is approximately 0 level) is output as a black level pixel value. This is obtained by smoothing random noise by using black level pixel value data acquired before reading a document and averaged over a plurality of lines.
Then, in the black shading correction unit 7 shown in FIG. 1, by performing black shading correction by subtracting this black level pixel value from the read pixel value at the time of document reading, the occurrence of density fluctuation in the pixel unit in the main scanning direction. Can be suppressed.

As described above with reference to FIG. 5, the pixel value of the black level is obtained by the output level in the dark state on the precondition that no light is incident on the photodiode as the light receiving element 8 and no charge is accumulated. .
For this reason, for example, when the light source is turned on at the time of document reading or when a little external light enters the light receiving portion of the light receiving element 8, a dark state cannot be secured, and the black level is set as described above. There is a problem that it cannot be generated.

Therefore, in the dummy black level output mode, by forcibly controlling the PT gate signal for charge transfer so as not to rise during the charge transfer period, the PT output level becomes the same voltage VDD as the RS output level. A black level can be output. However, the output waveform does not become an ideal output waveform as shown in the lower part of FIG. 5 due to the influence of fixed pattern noise (FPN) generated due to gain variation or the like, as shown in FIG. In addition, an error of ± ΔFPN occurs in the black level (VDD).
However, the error of ± ΔFPN due to the fixed pattern noise also occurs during document reading, and is canceled by performing black shading correction by subtracting the black pixel value from the read pixel value.

Next, switching noise will be described with reference to FIG.
The dummy black level output mode described above enables pseudo black level output. However, as a problem in that case, there is an influence by switching noise (SN). Switching noise is noise generated at the rise and fall of a signal. Here, attention is focused on noise caused by a PT gate signal.

  The output waveform of the black level in the dark state shown in the lower side of FIG. 5 actually generates fixed pattern noise (FPN) and switching noise (SN) for each pixel signal generation circuit 9 as shown in FIG. . Therefore, the black level output value is ideally VDD (0 after inversion amplification), but the output level includes an error ± ΔFPN due to fixed pattern noise and an error ± ΔSN due to switching noise.

  Among these noise components, the error ± ΔSN due to switching noise is controlled by forcibly controlling the PT gate signal so that it does not rise during the charge transfer period, as described with reference to FIG. Not included when output. However, when reading a document in the normal output mode, switching noise is generated due to on / off of the PT gate 15, and an error ± ΔSN due to the noise is included in the PT output level.

Therefore, even if black shading correction is performed by subtracting this black level pixel value from the read pixel value, the error component due to switching noise is not canceled out.
Therefore, in a photoelectric conversion apparatus having an individual pixel signal generation circuit for each pixel in the main scanning direction, even when a document having a uniform density is read, the reading level varies among pixels in the main scanning direction.

This reading variation due to pixels in the main scanning direction will be described with reference to FIGS. FIG. 8 is an explanatory diagram in the case of performing black shading correction based on the black level acquired in the dark state of the normal output mode.
In this case, similarly to the original reading value and the black level reading value acquired in the normal output mode, components of error ΔFPN due to fixed pattern noise and error ΔSN due to switching noise are included. Therefore, the original reading level after the black shading correction when reading a document having a uniform density, that is, the level obtained by subtracting the black level reading value from the original reading value is shown in FIG. Uniform in pixels.

  However, as described with reference to FIG. 6, in the pseudo black level generation method obtained by forcibly controlling the PT gate signal so as not to rise during the charge transfer period in the dummy black level output mode, the RS gate The black level is generated without performing the switching operation. Therefore, switching noise does not occur, and as shown in FIG. 9, the black level read value does not include a component of error ΔSN due to switching noise (only error ΔFPN is included). Therefore, even if black shading correction for subtracting the black level reading value from the original reading value is performed, the error ΔSN component cannot be canceled out and the reading level in the main scanning direction is made uniform as shown by the solid line b in FIG. Can not.

Therefore, in the dummy black level output mode in the photoelectric conversion device 3 according to the present invention, the following is performed in order to solve this problem.
FIG. 10 is a timing chart showing each gate signal and output waveform in the dummy black level output mode in the photoelectric conversion device 3 according to the present invention.

In this example, in the dummy black level output mode, the period corresponding to the charge transfer period Tt in the normal output mode is also set as the reset period Tr, and the RS gate signal is raised in this period instead of the PT gate signal, as shown in FIG. After the RS gate 13 is turned on, it is turned off. The RS gate 13 and the PT gate 15 are equivalently located when viewed from the point a which is a charge detection point by the capacitor 14, and the influence of the switching noise is generated in the RS gate 13 and the PT gate 15 to the same extent.

Therefore, as shown in FIG. 10, the RS gate 13 is turned on during the period corresponding to the charge transfer period in the normal output mode, and the capacitor 14 of the charge detection unit 10 is reset again. Thus, by performing the switching operation in a pseudo manner, it is possible to obtain a black level output including the switching noise ΔSN for each pixel .
As a result, even in a situation where a complete dark state cannot be secured, dummy black level data including a switching noise component equivalent to the black level pixel value acquired in the dark state in the normal output mode is obtained for each pixel. Can do.

Therefore, even when the light source is always on during continuous reading of the document, the black level similar to that in the dark state in the normal output mode with respect to a change in the amount of light over time, etc. by performing the operation in the dummy black level output mode. Can be updated.
Thereby, highly accurate black shading correction can be performed without the influence of switching noise.

In summary, the photoelectric conversion device 3 according to the present invention can generate the black level data for black shading correction by selecting the following (1) and (2).
(1) Normal output mode: When no light is incident on the light receiving element 8, a read value read by a normal reading operation is generated as black level data.
(2) Dummy black level output mode: When light is incident on the light receiving element 8, the charge detection unit 10 performs an operation of raising the RS gate signal instead of the PT gate signal during a period corresponding to the charge transfer period. The capacitor 14 is reset again. Thereby, dummy black level data that is equivalent to a dark state is generated.

Thus, the photoelectric conversion device 3 according to the invention, depending on whether light is incident on the light receiving element 8, the normal output mode if not incident, if incident the dummy black level output mode And an output mode switching means for switching the output mode.
Therefore, the image reading apparatus 200 shown in FIG. 1 is provided with a pressure plate that can be opened and closed to cover and hold a document to be read, and the detection signal of the pressure plate open / close detection unit 5 that detects the open / closed state of the pressure plate is sent to the photoelectric conversion device. 3 is input to the timing signal generator 4.
Further, the light source control unit 2 that controls turning on and off of the light source 1 is provided, and a signal that controls turning on and off of the light source 1 from the light source control unit 2 is sent to the timing signal generation unit 4 of the photoelectric conversion device 3. Also let me input.

The timing signal generation unit 4 also has a function of an output mode switching unit that switches an output mode depending on whether light is incident on the light receiving element 8 or not.
Therefore, the timing signal generator 4 can determine whether light is incident on the light receiving element 8 based on the open / close state of the pressure plate based on the detection signal from the pressure plate open / close detector 5. In that case, the timing signal generator 4 determines that light is incident on the light receiving element 8 if the pressure plate is open, and determines that light is not incident on the light receiving element 8 if it is closed.

  Alternatively, the timing signal generation unit 4 can determine whether or not light is incident on the light receiving element 8 based on a signal for controlling turning on and off of the light source 1 from the light source control unit 2. In that case, the timing signal generator 4 determines that light is incident on the light receiving element 8 if the light source 1 is turned on, and determines that light is not incident on the light receiving element 8 if it is turned off. .

Furthermore, if the timing signal generator 4 combines these and determines whether or not light is incident on the light receiving element 8 based on the open / close state of the pressure plate and the signal for controlling turning on and off of the light source 1. , Can make more reliable judgment.
In that case, if the pressure plate is closed and the light source 1 is turned off, the timing signal generation unit 4 determines that light is not incident on the light receiving element 8 of the photoelectric conversion device 3, and otherwise, the light receiving element 8 determines that light is incident.

Here, an operation flow at the time of pressure plate reading and DF reading by the image reading apparatus 200 shown in FIG. 1 will be described with reference to FIGS.
The “pressure plate reading” is a reading method in which a user manually sets a document at a predetermined position on a contact glass, which will be described later, and reads the document while pressing it with the pressure plate.
“DF scanning” refers to an automatic document feeder (ADF) mounted on an image reading device that sequentially feeds documents one by one onto a contact glass for reading, or automatically fed documents are sheet-through. This is a reading method for reading when passing the reading position.

FIG. 11 is a flowchart showing a flow of operations when the image reading apparatus 200 reads a pressure plate.
When a reading start button not shown in FIG. 1 is pressed, the image reading apparatus 200 starts this processing. First, in step S <b> 1, the timing signal generator 4 determines whether or not the pressure plate is closed based on a detection signal from the pressure plate open / close detection unit 5. When the platen is read, the platen is normally closed, but this determination is made because the platen may not be completely closed as in the case where a thick original such as a book original is set.

If it is determined in step S1 that the pressure plate is closed, in step S2, the photoelectric conversion device 3 is set to the normal output mode described above (this mode is set in the initial state), and in step S3, the document is read in the dark state before reading the document. Take action and get black level. Thereafter, the process proceeds to step S7, where document reading is started.
If it is determined in step S1 that the pressure plate is not closed, the photoelectric conversion device 3 is switched to the above-described dummy black level output mode in step S4, and a black level is obtained by performing pseudo black level generation processing in step S5. Thereafter, in step S6, the photoelectric conversion device 3 is switched to the normal output mode, and then the process proceeds to step S7 to start reading a document.

When document reading is started in step S7, the light source is turned on to read the document in step S8. After reading the document in step S9, the light source is turned off in step S10 and the process is terminated.
In this manner, the black shading correction is performed on the pixel output value obtained by reading the document using the black level data acquired in step S3 or S5.
According to this embodiment, even when reading a pressure plate in a state where the pressure plate is not completely closed, such as when reading a book document or the like on a contact glass , the accuracy can be improved regardless of the incidence of external light. High black shading correction can be maintained.

FIG. 12 is a flowchart showing a flow of operations during DF reading by the image reading apparatus 200.
When an original is set on an automatic document feeder not shown in FIG. 1 and the reading start button is pressed, the image reading apparatus 200 starts this processing.
First, in step S11, the timing signal generation unit 4 determines whether or not the light source is turned off based on a signal for controlling turning on and off the light source 1 from the light source control unit 2. Since it is before starting the document reading, the light source should normally be turned off, but this determination is made because there is a possibility that the light source is turned on for some reason.

If it is determined in step S11 that the light source is turned off, in step S12, the photoelectric conversion device 3 is set to the normal output mode described above (this mode is set in the initial state), and in step S13, the dark state is set before reading the document. A reading operation is performed to obtain a black level. Thereafter, the process proceeds to step S17 to start reading a document.
If it is determined in step S11 that the light source is not turned off (turned on), the photoelectric conversion device 3 is switched to the above-described dummy black level output mode in step S14, and a pseudo black level generation process is performed in step S15. Get black level. Thereafter, in step S16, the photoelectric conversion device 3 is switched to the normal output mode, and the process proceeds to step S17 to start document reading.

  When document reading is started in step S17, the light source is turned on in step S18, and the first document is automatically fed and read. When the document reading is completed in step S19, it is determined in step S20 whether there is no next document in the automatic document feeder. This determination is made based on the presence or absence of a detection signal from a document set detection sensor provided in the automatic document feeder.

  If it is determined that there is a next document, the process returns to step S11 to determine whether or not the light source is turned off. In this case, since the light source is not turned off, the process proceeds to step S14. Then, the photoelectric conversion device 3 is switched to the dummy black level output mode, and a pseudo black level generation process is performed in step S15 to acquire a black level. Thereafter, in step S16, the photoelectric conversion device 3 is switched to the normal output mode, and the process proceeds to step S17 to start document reading. Then, the second original is automatically fed and read.

In this way, after the black level is acquired in the dummy black level output mode with the light source turned on until it is determined in step S20 that there is no next original, the original is sequentially automatically fed and read.
If it is determined in step S20 that there is no next original, the light source is turned off in step S21, and the process ends.
In this manner, black shading correction is performed on the pixel output value obtained by reading each document using the black level data acquired in step S13 or S15 for each page.

As a result, accurate black level values can be generated even when light from the outside is incident on the light receiving element of the photoelectric conversion device, or even when the light source is constantly lit during continuous reading. It is possible to perform highly accurate black shading correction without dropping the image.
The processing described with reference to FIGS. 11 and 12 may be executed under centralized control by a microcomputer that controls each unit of the image reading apparatus 200.

Next, an example of partial modification of the image reading apparatus shown in FIG. 1 will be described with reference to FIGS.
FIG. 13 is a block diagram showing only a changed portion of the image reading apparatus, and parts corresponding to those in FIG. This image reading apparatus is provided with light incident detection means 17 instead of the pressure plate opening / closing detection unit 5 in FIG.

The light incident detection means 17 has a memory 18 that stores data of a preset threshold value for the upper limit of the black level. The light incident detection means 17 detects a detection signal as to whether or not the pixel output value (read value) output when the photoelectric conversion device 3 generates the black level in the normal output mode is within the threshold range stored in the memory 18. , Input to the timing signal generator 4.
Based on the detection signal, the timing signal generation unit 4 determines that no light is incident on the light receiving element if the read value is within the threshold range, and if the read value exceeds the threshold range, the light is received on the light receiving element. Judge that it is incident.

FIG. 14 is a flowchart showing a flow of operations at the time of document reading by the image reading apparatus. This process can be applied to both the above-described platen reading and DF reading.
The processes in steps S12 to S21 in FIG. 14 are the same as the processes in the corresponding steps in FIG. 12, and thus the same step numbers are given.

  The process of FIG. 14 differs from the process of FIG. 12 only in step S11 ′. In step S11 ′, the timing signal generator 4 shown in FIG. 13 determines whether or not the read value by the photoelectric conversion device 3 is within the threshold value range, based on the detection signal from the light incident detection means 17. As a result, if the read value is within the threshold value range, it is determined that no light is incident on the light receiving element, the photoelectric conversion device 3 is left in the normal output mode in step S12, and in the dark state in step S13. Get the black level. Thereafter, document reading is started in step S17.

If the read value exceeds the threshold range, it is determined that light is incident on the light receiving element 8, the photoelectric conversion device 3 is switched to the dummy black level output mode in step S14, and a pseudo operation is performed in step S15. Get black level. Thereafter, the normal output mode is restored in step S16, and document reading is started in step S17.
In the case of DF reading, the processing of steps S11 ′ to S20 is repeated while the light source is turned on until a determination is made in step S20 that there is no next original, thereby sequentially reading a plurality of originals. In the case of pressure plate reading, since it is determined in step S20 that there is no next original, the light source is turned off in step S21, and the process ends.

In this way, the black level generation mode can be selected without increasing the circuit scale by the same processing both when reading the pressure plate and when reading the DF. Further, it can be reliably determined whether or not light is incident on the light receiving element.
The processing described with reference to FIG. 14 may also be executed under overall control by a microcomputer that controls each unit of the image reading apparatus.

[Embodiment of Image Forming Apparatus]
Next, an embodiment of an image forming apparatus according to the present invention will be described with reference to FIGS. FIG. 15 is a schematic cross-sectional view showing a schematic configuration of the mechanism unit of the image forming apparatus, and FIG. 16 is a schematic enlarged view showing a schematic configuration of the mechanism unit of the image reading apparatus included in the image forming apparatus. It is sectional drawing.

The image forming apparatus shown in FIG. 15 has an image reading apparatus 200 according to the present invention mounted on the upper part of the image forming apparatus main body 100 and an automatic document feeder (hereinafter referred to as “ADF”) 300 mounted thereon. ing.
In FIG. 15 of the image forming apparatus main body 100, a large-capacity paper feeding device 400 is provided on the right side, and a paper post-processing device 500 is provided on the left side. The large-capacity paper feeding device 400 and the paper post-processing device 500 are optional, and one or both of them may not be equipped.
The image forming apparatus main body 100 includes an image writing unit 110, an image forming unit 120, a fixing unit 130, a duplex conveying unit 140, a sheet feeding unit 150, a vertical conveying unit 160, a manual feeding unit 170, and the like.

The image writing unit 110 modulates light emission of a laser diode (LD) as a light emission source based on image data of a document read by the image reading device 200, and scans an optical system such as a polygon mirror and an fθ lens (not shown). Thus, laser writing is performed on the photosensitive drum 121.
The image forming unit 120 includes a known electrophotographic system such as a photosensitive drum 121, a charging roller 122 disposed along the outer periphery thereof, a developing unit 123, a transfer unit 124, a cleaning unit and a charge eliminating unit not shown. Consists of image elements.

As the photosensitive drum 121 rotates clockwise in FIG. 15, the surface thereof is uniformly charged by the charging roller 122, and then scanned with laser light from the image writing unit 110 to form an electrostatic latent image. The electrostatic latent image on the surface of the photosensitive drum 121 is developed with toner when passing through the developing unit 123, and a toner image is formed.
The toner image on the surface of the photosensitive drum 121 is transferred to a sheet that is a transfer sheet sent to and from the transfer unit 124.
The fixing unit 130 fixes the toner image transferred onto the sheet by the transfer unit 124 to the sheet by applying heat and pressure with the fixing roller and the pressure roller.

The double-sided conveyance unit 140 is provided on the downstream side of the fixing unit 130 in the paper conveyance direction, and includes a first switching claw 141 that switches the paper conveyance direction to the paper post-processing device 500 side or the double-sided conveyance unit 140 side. In addition, the double-sided conveyance unit 140 includes a reverse conveyance path 142 guided by the first switching claw 141 and an image forming side conveyance path 143 that conveys the sheet reversed by the reverse conveyance path 142 to the transfer unit 124 again. Have. Further, the double-sided conveyance unit 140 includes a post-processing side conveyance path 144 that conveys the reversed paper to the sheet post-processing apparatus 500 side, and a branch portion between the image forming side conveyance path 143 and the post-processing side conveyance path 144 The 2nd switching claw 145 is arranged.

The paper feeding unit 150 is composed of four paper feeding stages 151 to 154 that can store papers of different sizes, and pulls out the paper stored in the selected paper feeding stage by the pickup roller 155 and the paper feeding roller 156, respectively. Then, it is sent to the vertical conveyance unit 160.
In the vertical conveyance unit 160, the paper fed from each paper feed stage is conveyed to a positioning roller (registration roller) 161 located immediately before the upstream of the transfer unit 124 in the paper conveyance direction. The positioning roller 161 feeds the paper to the transfer unit 124 in time with the leading edge of the toner image formed on the photosensitive drum 121. Thereby, the toner image on the photosensitive drum 121 is transferred to a predetermined position on the paper.

The manual feed unit 170 includes an openable and closable manual feed tray 171, and opens the manual feed tray 171 as necessary to supply paper manually. In this case as well, the sheet is conveyed by the positioning roller 161 and conveyed to the transfer unit 124.
The large-capacity paper feeder 400 stacks and supplies a large amount of paper of the same size. The bottom plate 402 rises as the paper is consumed, and the paper can be picked up from the pickup roller 401 at all times. Yes. The sheet fed by the pickup roller 401 is transported to the nip of the positioning roller 161 by the vertical transport unit 160.

The sheet post-processing apparatus 500 performs predetermined processing such as punching, alignment, stapling, and sorting. In this embodiment, for those functions, a punch 501, a staple tray (alignment tray) 502, a stapler 503, and A shift tray 504 is provided.
The paper carried from the image forming apparatus main body 100 to the paper post-processing device 500 is punched one by one with the punch 501 when punching, and then proofed unless particularly processed. It is sent to the tray 505. When sorting, stacking, and sorting, the sheets are discharged to the shift tray 504, respectively.

In this embodiment, the sorting is performed by the reciprocating movement of the shift tray 504 by a predetermined amount in a direction orthogonal to the sheet conveyance direction. In addition, sorting can be performed by moving the paper in a direction orthogonal to the paper transport direction on the paper transport path.
In the case of alignment, the paper that has been perforated as necessary is guided to the lower conveyance path 506, and in the staple tray 502, the direction perpendicular to the paper conveyance direction is aligned by the trailing edge fence, and the paper is aligned by the jogger fence. Alignment in the direction parallel to the transport direction is performed. When binding is performed, a predetermined position of the aligned sheet bundle, for example, a predetermined position such as a corner portion or two central positions is bound by the stapler 503 and discharged onto the shift tray 504 by the discharge belt.

  The image reading apparatus 200 reads an image on the lower surface of the document that has been conveyed onto the contact glass 201 by the ADF 300 and stopped, and temporarily stores the read image data in a storage device. Then, when the image is formed by the image forming apparatus main body 100, the image writing unit 110 reads the image data from the storage device, modulates the light emission of the laser diode in accordance with the image data, and charges the charged photosensitive drum 121. Optical writing is performed on the surface.

The ADF 300 is attached to an installation surface of a contact glass, which will be described later, of the image reading apparatus 200 so as to be openable and closable, and also serves as a pressure plate that covers and holds a document to be read. When the ADF is not installed, the pressure plate is attached to the contact glass installation surface so that it can be opened and closed.
The ADF 300 sequentially feeds one sheet at a time from the uppermost document in the document bundle 20S set on the document table 301 by the feed roller 302, and reads it on the contact glass by the transport roller 303 and the transport belt 304. Transport to position. The document after reading is discharged to the upper discharge tray or the side discharge tray 307 by the conveyance belt 304 and the discharge roller pair 305.

  As shown in FIG. 16, the image reading apparatus 200 includes a contact glass 201 on which an original 20 is placed. On the lower side, a first carriage 205 on which the document exposure light source 1 and the first reflection mirror 202 are mounted, and a second carriage 206 on which the second reflection mirror 203 and the third reflection mirror 204 are mounted are provided. In this embodiment, a xenon lamp or a fluorescent lamp is used as the light source 1.

The image reading device 200 further includes a lens unit 207 for forming an image of the light reflected by the third reflecting mirror 204 on the light receiving element 8 of the photoelectric conversion device 3 described above.
Image data composed of pixel output values for each line read by the photoelectric conversion device 3 is sent to the processing storage unit 210 through the signal line 209 and subjected to black shading correction, shading correction, and the like, and then the storage device (image Memory).

In this image reading apparatus 200, a reference member 208 having a reference density such as a reference white plate used for generating shading correction data is provided adjacent to the end of the contact glass 201. Based on the data obtained when the reference member 208 is read, shading correction adjusts the gain of each pixel data so that the white level of each pixel for each line at the time of document reading is uniform. Since this is a known technique and is not directly related to the present invention, a detailed description thereof will be omitted.
Although not shown, a sheet-through reading slit can also be provided adjacent to the end of the contact glass 201.

In the image reading apparatus 200 configured as described above, when the original 20 is set on the contact glass 201 or by the ADF 300 and a reading start button (not shown) is pressed, the black level is acquired as described above. After that, the document reading is started.
At that time, the first carriage 205 and the second carriage 206 are moved in the arrow A direction (sub-scanning direction) by a stepping motor (not shown) to scan the document 20. At this time, the second carriage 206 moves at a speed half that of the first carriage 205 in order to keep the optical path length from the contact glass 201 to the light receiving surface of the light receiving element 8 constant.

  At the same time, the image surface that is the lower surface of the document 20 set on the contact glass 201 is illuminated (exposed) by the light source 1 of the first carriage 205. The reflected light from the image plane is sequentially reflected by the first reflecting mirror 202 of the first carriage 205, the second reflecting mirror 203 of the second carriage 206, and the third reflecting mirror 204. Then, the light flux reflected by the third reflecting mirror 204 is focused by the lens unit 207 and imaged on each light receiving element 8 for one line of the photoelectric conversion device 3.

  Thereby, as described above, each light receiving element 8 generates and accumulates charges according to the intensity of incident light, converts the accumulated charges into a voltage in the photoelectric conversion device 3, and further converts it into a digital value. Then, it is sent to the processing storage unit 210 as image data for each line.

When the sheet-through reading slit is provided, the original can be automatically fed by the ADF 300, and the image can be read when the original passes through the sheet-through reading slit. This reading mode is called a sheet through mode.
In the sheet-through mode, the first carriage 205 and the second carriage 206 move to the lower side of the sheet-through reading slit and stop.
The light source 1 illuminates the image surface of the document that is automatically fed by the ADF 300 and passes through the sheet-through reading slit. The reflected light from the image plane is sequentially reflected by the first reflecting mirror 202, the second reflecting mirror 203 and the third reflecting mirror 204, and imaged on the light receiving element 8 by the lens unit 207 .

  The image forming apparatus configured as described above includes the above-described image reading apparatus according to the embodiment of the present invention. Therefore, when forming a copy image of a document, the image forming device is suitable for each document reading without reducing productivity. Black level data can be generated. Therefore, it is possible to cancel the influence of noise and always perform highly accurate black shading correction to form a high-quality image in which the occurrence of vertical stripes is suppressed.

The embodiments of the photoelectric conversion device, the image reading device, and the image forming device according to the present invention have been described above. The specific configuration of each unit, the contents of processing, the data format, and the like have been described in the embodiments. It is not limited to.
In addition, the configuration of each embodiment described above can be added, changed, or partially omitted as appropriate, and can be implemented in any combination as long as there is no contradiction.

1: Light source 2: Light source control unit 3: Photoelectric conversion device 4: Timing signal generation unit 5: Pressure plate open / close detection unit 7: Black shading correction unit
8: Light receiving element (photodiode) 9: Pixel signal generation circuit 10: Charge detection unit 11: Amplifier 12: A / D converter 13: RS (reset) gate 14: Capacitor (for charge detection) 15: PT (charge transfer) ) Gate 16: Mode switching means 17: Light incident detecting means 18: Memory
20: Document 20S: Document bundle

100: Image forming apparatus main body 110: Image writing unit 120: Image forming unit
121: Photosensitive drum 130: Fixing unit 140: Double-sided conveyance unit
150: paper feeding unit 160: vertical conveying unit 170: manual feeding unit 200: image reading device 201: contact glass 202: first reflecting mirror 203: second reflecting mirror 204: third reflecting mirror 205: first carriage 206: second Carriage 207: Lens unit 208: Reference member 209: Signal line 210: Processing storage unit 300: Automatic document feeder (ADF) 400: Large capacity feeder 500: Paper post-processing device

JP 2001-339643 A

Claims (10)

In a photoelectric conversion device having a light receiving element that generates and accumulates charge according to the intensity of incident light, and a charge detection unit that converts the charge accumulated in the light receiving element into a voltage,
A normal output mode for outputting a signal corresponding to the intensity of incident light for each pixel, and a dummy black level output mode for outputting a black level signal irrelevant to the incident light for each pixel;
In the normal output mode, the charge detection unit is reset, the charge accumulated in the light receiving element is transferred to the reset charge detection unit, and a signal converted into a voltage is output,
In the dummy black level output mode, and resets the charge detection part, a period corresponding to the charge transfer period in the normal output mode, not forward the accumulated in the light receiving element charges to the charge detection part, which is the reset And a signal obtained by resetting the charge detection unit again is output as a black level signal for each pixel .   2. The photoelectric conversion apparatus according to claim 1, wherein the light receiving elements are linearly arranged by a predetermined number of pixels, and each of the light receiving elements has the charge detection unit. In the photoelectric conversion device according to claim 1 or 2,
A photoelectric conversion device comprising: a timing signal generation unit configured to generate a signal for controlling a timing for resetting the charge detection unit and a timing for transferring the charge accumulated in the light receiving element to the charge detection unit. apparatus.   The photoelectric conversion device according to any one of claims 1 to 3, a light source that illuminates a reading target, and an optical system that causes reflected light from the reading target illuminated by the light source to enter the light receiving element. An image reading apparatus comprising:   Output that switches the output mode of the photoelectric conversion device to the normal output mode when it is incident, or to the dummy black level output mode when it is not incident, depending on whether or not light is incident on the light receiving element The image reading apparatus according to claim 4, further comprising a mode switching unit. The image reading apparatus according to claim 5.
A pressure plate that covers and holds the object to be read can be opened and closed.
The image reading apparatus according to claim 1, wherein the output mode switching unit determines whether light is incident on the light receiving element based on an open / closed state of the pressure plate. The image reading apparatus according to claim 5.
A light source control unit for controlling turning on and off of the light source;
The image reading apparatus according to claim 1, wherein the output mode switching means determines whether light is incident on the light receiving element based on a signal from the light source control unit that controls turning on and off of the light source. The image reading apparatus according to claim 5.
A pressure plate that can be opened and closed to cover the reading object, and a light source control unit that controls turning on and off of the light source,
The output mode switching means determines whether light is incident on the light receiving element based on an open / closed state of the pressure plate and a signal for controlling turning on and off of the light source from the light source control unit. A characteristic image reading apparatus.   The output mode switching means determines whether light is incident on the light receiving element, and whether the level of a signal output from the photoelectric conversion device in the normal output mode is within a preset threshold range. The image reading apparatus according to claim 5, wherein the determination is made.   An image forming apparatus comprising the image reading apparatus according to claim 4.

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