JP2012253607A - Image reading device, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce density unevenness of read image data even when the fluctuation in the amount of light of a light source has low reproducibility.SOLUTION: In configuring a read line period, a timing clock generating unit 64 receives analog image data from an analog processing unit 60, detects fluctuation in the amount of light for each read line from the analog image data, calculates the maximum value, the minimum value, and the total average value of the average values of each level of the amount of light in the main scanning direction for each image data. If the difference value between the maximum value and the minimum value is not less than 5% of the total average value, the timing clock generating unit 64 performs controls including reconfiguring the amount of light of the light source that is in inverse proportion to the read line period, and reconfiguring the reading rate that is in inverse proportion to the read line period.

Description

  The present invention relates to an image reading apparatus that optically reads an image on a document and an image forming apparatus including the image reading apparatus.

An image reading device such as a scanner device irradiates light on a document and reads the image on the document by detecting the reflected light.
As the light source, a xenon lamp or a lamp including an LED (Light Emitting Diode) is used.
In particular, since the LED is more responsive than the xenon lamp, it is possible to control illuminance by lighting time control (PWM).

In such an image reading apparatus, the light amount of the light source that irradiates the light needs to be constant.
This is because if the amount of light emitted from the light source fluctuates during the reading of the image, the brightness of the reflected light partially varies, resulting in uneven density in the read image.
As a result, the quality of the image data read from the document is deteriorated.
Conventionally, the reference light quantity value of the light source is stored in advance, and when the light quantity of the light source changes during the image reading operation, the image reading is performed to control the light quantity of the light source so as to absorb the fluctuation amount based on the reference light quantity value. There was an apparatus (for example, refer to Patent Document 1).

However, the conventional image reading apparatus has a problem that it cannot cope with the density unevenness of the read image data when the reproducibility is low with respect to the fluctuation of the light amount of the light source.
The present invention has been made in view of the above points, and an object thereof is to reduce density unevenness of read image data even when reproducibility is low due to fluctuations in the amount of light of a light source.

  In order to achieve the above object, the present invention provides an image reading apparatus that irradiates a subject with light from a light source and reads an image on the subject based on reflected light from the subject. A light amount fluctuation detecting means for detecting a light quantity fluctuation for each reading line, and a reading line period changing means for changing the reading line period based on the light quantity fluctuation for each reading line detected by the light quantity fluctuation detecting means. An image reading apparatus is provided.

  The image reading apparatus and the image forming apparatus according to the present invention can reduce the density unevenness of the read image data even when the reproducibility is low due to the fluctuation of the light amount of the light source.

It is a block diagram which shows the structural example which concerns on the data processing of the control part of the reading unit shown in FIG. It is a wave form diagram which shows the example of a change of LED drive current at the time of using LED for the light source of the reading unit shown in FIG. It is a schematic block diagram of the mechanism part of the multifunctional machine which is one Embodiment of this invention. It is a flowchart figure which shows the process of the timing clock generation part shown in FIG.

Hereinafter, embodiments for carrying out the present invention will be specifically described with reference to the drawings.
FIG. 3 is a schematic configuration diagram of a mechanism unit of the multifunction peripheral 100 according to the embodiment of the present invention.
The multi-function device 100 is an image forming apparatus in which a plurality of functions including a data communication function, a copy function, and a printer function are integrated.
An automatic document feeder (hereinafter referred to as “ADF”) 10 is mounted on the upper part of the main body of the multifunction peripheral 100 constituting the reading unit (scanner) and the printer.
In addition, an operation display unit (not shown) is provided on the upper surface on the front side of the multifunction peripheral 100.

The data communication function including facsimile communication, local area network (LAN), and Internet communication of the multi-function device 100 is well known, and illustration and description thereof are omitted.
The ADF 10 is connected to the main body of the multi-function device 100 via a hinge (not shown) so as to open and close with respect to the contact glass 21 of the reading unit 20 provided on the upper surface of the main body of the multi-function device 100.

On the document tray (document placement table) 11 of the ADF 10, a bundle of a plurality of documents (document bundle) is placed with the image surface facing upward. Each document corresponds to a subject on which an image is described.
For example, when a print key on the operation display unit (not shown) of the multifunction peripheral 100 is pressed by the user, a controller (not shown) drives the paper feed motor (not shown) of the ADF 10 to rotate forward. The feed roller 12 is rotated clockwise relative to the front of the figure. Further, the controller rotates a conveyor belt motor (not shown) to rotate the feeding belt 13 in the counterclockwise direction (the direction of arrow B in the figure) with respect to the front of the figure.

In this way, the uppermost original is fed from the original bundle and conveyed toward the contact glass 21.
When the document set detection sensor 16 detects the leading edge of the document, the document set detection sensor 16 sends an output signal to the controller, and the controller reversely drives a paper feed motor (not shown) of the ADF 10 based on the output signal from the document set detection sensor 16.
Thus, the subsequent original is prevented from entering and is not separated.

Further, when the document set detection sensor 16 detects the trailing edge of the document, the controller counts the number of rotation pulses of the conveyance belt motor (not shown) from this detection time point. Then, the number of rotation pulses reaches a predetermined value. At this time, the document is stopped at the reading position of the contact glass 21 by stopping the driving of the conveying belt motor and stopping the feeding belt 13.
When the original is conveyed to the reading position on the contact glass 21 and stopped, the image of the original is read by the reading unit 20.
Thereafter, the document is discharged to a discharge port A (a discharge port when the document is reversed and discharged) by the feeding belt 13 and the discharge roller 14.

When the document set detection sensor 16 detects that the next document is on the document tray 11, the controller displays the ADF 10 when the document set detection sensor 16 detects the trailing edge of the previous document. Then, the paper feeding motor which omits is driven again, and the subsequent document is separated and conveyed toward the contact glass 21 as described above.
Thereafter, when the number of rotation pulses of the paper feed motor from the time when the original is detected by the original set detection sensor 16 reaches a predetermined number of pulses, the paper feed motor is stopped and the next original is put on standby.

Further, when the document stops at the reading position of the contact glass 21, the image of the document is read by the reading unit 20.
The reading unit 20 corresponds to an image reading device.
Thereafter, the document is discharged to a discharge port A (a discharge port when the document is reversed and discharged) by the feeding belt 13 and the discharge roller 14.

Next, an operation until the image of the original is read by the reading unit 20 and an electrostatic latent image corresponding to the read image data of the original is formed on the surface of the photosensitive drum 41 will be described.
The electrostatic latent image is a potential distribution generated by converting image data into optical information and writing the surface of the photosensitive drum 41 (the surface charged by the charger) with a laser beam.

The reading unit 20 includes a contact glass 21 on which a document is placed, a white reference plate 29 for correcting various distortions caused by a reading optical system, and an optical scanning system.
The white reference plate 29 corresponds to a subject together with a document to be read.
The optical scanning system includes a light source (exposure lamp) 1 for document exposure, a lens 24, a CCD linear image sensor (hereinafter abbreviated as "CCD") 25, a first mirror 26, a second mirror 27, and a third mirror 28. Etc.
In addition, a control unit 9 realized by a microcomputer including a CPU, a ROM, and a RAM that controls the entire reading unit 20 is also provided.

As the light source 1, various lamps including a xenon lamp, an organic electroluminescence (organic EL) lamp, and an LED can be applied.
The light source 1 and the first mirror 26 are fixed on the first carriage 22.
The second mirror 27 and the third mirror 28 are fixed on the second carriage 23.
When reading an image of a document, the first carriage 22 and the second carriage 23 are mechanically scanned in the sub-scanning direction indicated by an arrow C in the figure at a relative speed of 2: 1 so that the optical path length does not change. . The optical scanning system is driven by a drive unit such as a scanner drive motor (not shown).

Further, in document reading by sheet through, the first carriage 22 and the second carriage 23 move below the sheet through reading slit S.
After that, the document placed on the ADF 10 is read in the position of the sheet through reading slit S by being guided in the direction indicated by the arrow B in the drawing by the roller 15.
The reading unit 20 optically reads a document image and converts it into image data (also referred to as an image signal).

That is, the image surface of the document is illuminated by the light source 1 of the optical scanning system, and the reflected light image from the image surface is received by the CCD 25 via the first mirror 26, the second mirror 27, the third mirror 28, and the lens 24. Form an image on the surface.
Then, it is converted into image data by the CCD 25.
At this time, the magnification of the image to be copied is changed by moving the lens 24 and the CCD 25 in the left-right direction with respect to the front in the drawing.
That is, the lens 24 and the CCD 25 are set so as to correspond to the designated magnification in the left-right direction position.

Next, the writing unit 30 includes a laser output unit 31, an imaging lens 32, a mirror 33, and the like.
The laser output unit 31 includes a laser diode that is a laser light source and a polygon mirror (rotating polygonal mirror) (not shown) that rotates at a constant high speed by a motor.
When a laser beam is emitted from the laser output unit 31, it is deflected by a polygon mirror that rotates at a constant speed, passes through an imaging lens 32, is folded back by a mirror 33, and is condensed on a charged surface of the photosensitive drum 41. Imaged.

The deflected laser beam is exposed and scanned in a direction (main scanning direction) orthogonal to the direction in which the photosensitive drum 41 rotates, and image data output by a selector of an image processing unit (not shown) is written in line units. Recording is performed for main scanning.
By repeating this main scanning at a predetermined cycle corresponding to the rotational speed of the photosensitive drum 41 and the scanning density (recording density), an electrostatic latent image is formed on the charged surface of the photosensitive drum 41.

Although not shown, a beam sensor is disposed at a position where a laser beam near one end of the photosensitive drum 41 is irradiated.
This beam sensor generates a main scanning synchronization signal. Based on the main scanning synchronization signal, a control signal for controlling image recording timing in the main scanning direction and inputting / outputting the image signal is generated.
As the electrostatic latent image on the photosensitive drum 41 passes through the developing unit 40, a toner image is formed on the photosensitive drum 41.

On the other hand, transfer paper (paper) for forming an image is stacked on the first paper feed tray 51, the second paper feed tray 52, or the third paper feed tray 53, and the first paper feed device 54, The paper is fed by the second paper feeding device 55 and the third paper feeding device 56 and is transported by the vertical transport unit 50 to a position where it abuts on the photosensitive drum 41.
Actually, any one of the paper feed trays 51 to 53 is selected, and the transfer paper is fed therefrom.
Then, the toner image on the photosensitive drum 41 is transferred to one of the first surfaces while the fed transfer paper is conveyed by the conveying belt (transfer belt) 42 at the same speed as the rotation of the photosensitive drum 41, and The toner image is fixed by the fixing unit 43 and discharged to a paper discharge tray 57 outside the apparatus.

In addition, when forming toner images on both sides of the transfer paper, the transfer paper with the toner image formed on the first side is not transported to the discharge tray 57 side, and the path is switched by a branching claw not shown in the figure. Once transported to the duplex transport path 45.
Thereafter, the transfer paper is fed again, the toner image formed on the photosensitive drum 41 is transferred to the other second surface, the toner image is fixed by the fixing unit 43, and then the paper discharge tray 57. To discharge.
The paper discharge unit 44 discharges the transfer paper to the paper discharge tray 57 when the staple mode is not performed.
In this way, the multifunction peripheral 100 operates the duplex conveyance path 45 when images are formed on both sides of the transfer paper.

FIG. 1 is a block diagram illustrating a configuration example relating to data processing of the control unit 9 of the reading unit 20 illustrated in FIG. 3.
The control unit 9 of the reading unit 20 outputs analog image data photoelectrically converted by the CCD 25 to the analog processing unit 60.
The analog processing unit 60 performs various image processing such as sample hold processing and black level correction on the analog image data, and then outputs the analog image data to the analog / digital (A / D) conversion unit 61. Further, analog image data is output to the timing clock generator 64 when the reading line cycle is set.

The A / D converter 61 converts the input analog image data into digital image data, and outputs the digital image data to a subsequent stage (image processing unit or the like) via an LVDS interface (abbreviated as “LVDS” in the figure) 62. .
The analog processing unit 60 and the A / D conversion unit 61 may be realized by circuits.
In that case, they are called an analog processing circuit and an A / D conversion circuit, respectively.

The CCD 25, the analog processing unit 60, the A / D conversion unit 61, the stepping motor (not shown), the image processing unit, the light source driving unit, and various timing clocks of the light source in the control unit 9 are generated from the oscillation unit 63. Based on the clock signal, it is generated and supplied by the timing clock generator 64.
The timing clock generation unit 64 is a drive signal that emits light from the light source 1, a PWM signal that drives the constant current source, and a motor drive unit that controls the rotation speed of the motor that drives each unit in the reading unit 20 including the first carriage 22. The drive signal is also generated.

Further, the timing clock generation unit 64 controls the change of the reading line cycle based on the fluctuation of the light amount for each reading line and the reading line cycle based on the analog image data from the analog processing unit 60 when the reading line cycle is set. Control including resetting of the light amount of the light source inversely proportional to and resetting of the reading speed inversely proportional to the reading line cycle is performed.
That is, the reading unit 20 corresponds to an image reading apparatus that irradiates light from a light source onto a subject and reads an image on the subject based on reflected light from the subject.

In addition, the timing clock generation unit 64 detects a light amount variation for each reading line when the subject is read, and a reading line based on the light amount variation for each reading line detected by the light amount variation detecting unit. It functions as a reading line cycle changing means for changing the cycle.
Further, the timing clock generation unit 64 adjusts the light amount of the light source based on the reading line cycle changed by the reading line cycle changing unit, and the subject's object based on the reading line cycle changed by the reading line cycle changing unit. Each function includes a reading speed adjusting unit that adjusts the reading speed and a unit that changes the reading line cycle until the variation in the light amount detected by the light amount variation detecting unit becomes equal to or less than a set value.

Further, the timing clock generator 64 changes the light amount at an execution timing every certain time immediately after the image reading apparatus is turned on, immediately before reading the original image, after the reading of the original image, or after the image reading apparatus is turned on. The functions of the detecting means and the reading line cycle changing means are operated.
Further, the timing clock generation unit 64 detects the fluctuation in the amount of light for each reading line when reading the white reference plate, and the rotational speed of the motor that drives the carriage that moves the light source in the sub-scanning direction relative to the subject. It has each function of the means to adjust.

FIG. 2 is a waveform diagram showing a change example of the LED drive current when an LED is used as the light source 1 of the reading unit 20 shown in FIG.
In the waveform diagram of FIG. 2, the horizontal axis represents a change in time from the start of LED lighting, and the vertical axis represents a change in LED drive current from the start of LED lighting.
The scale h on the horizontal axis in FIG. 2A indicates the reading line cycle.

The waveform diagram of FIG. 2A shows a case where the drive current for causing the LED to emit light (hereinafter referred to as “LED drive current”) varies with the passage of time. Since the fluctuation range is small in this waveform, it can be considered that the LED drive current does not fluctuate substantially for each read line by averaging all LED drive currents within the read line period h.
Therefore, when the image is read, the density unevenness of the read image data has almost no influence on the image quality even if the light quantity of the LED varies.

On the other hand, the waveform diagram of FIG. 2B shows a state in which the LED drive current varies greatly for each reading line in the reading line cycle h before the change based on the default setting value.
In such a case, by changing the default read line period h to be longer and smoothing the LED drive current within the changed period, fluctuations in the LED drive current for each read line can be reduced. Can do.

The waveform diagram of FIG. 2B shows a changed read line period H corresponding to a period three times the default read line period h, and the LED drive current is averaged within the read line period H. In this case, fluctuations in the LED drive current for each reading line are reduced, and even when the amount of light from the LEDs fluctuates during image reading, the density unevenness of the read image data can be reduced to a level that hardly affects the image quality. .
Therefore, the timing clock generation unit 64 of the control unit 9 performs control to change the reading line cycle based on the fluctuation of the light amount for each reading line, so that the density unevenness of the read image data even if the light amount of the LED varies. To a level that has little effect on image quality.

Further, it is conceivable that the amount of accumulated light in the CCD 25 changes with the change in the reading line cycle, and the accumulated amount of light is saturated.
Therefore, in order to ensure the dynamic range of the CCD 25, the timing clock generator 64 also performs control to reset the light amount of the light source in inverse proportion to the reading line cycle.
Further, if the scanning line cycle is changed while the scanning speed remains unchanged, the aspect ratio of the scanned image changes. Therefore, the timing clock generator 64 also performs control to reset the scanning speed that is inversely proportional to the scanning line cycle.

Next, processing of the timing clock generator 64 shown in FIG. 1 will be described.
FIG. 4 is a flowchart showing the processing of the timing clock generator shown in FIG.
Step (indicated by “S” in the figure) 1: Initialization is performed by substituting 1 into a variable n (loop counter / line cycle setting coefficient), and the process proceeds to Step 2.
Step 2: The light source 1 of the reading unit 20 is turned on to read the white reference plate 29 of FIG.

  Step 3: The first carriage 22 is moved and stopped under the white reference plate 29 in FIG. 3, and an image of the white reference plate 29 is read for a certain period of time while the light from the light source 1 is irradiated on the white reference plate 29. Go to step 4. By reading for a certain period of time, it is possible to obtain an amount of image data corresponding to the image data for a plurality of reading lines while moving the light of the light source 1 with respect to the subject in the sub-scanning direction.

  Step 4: In order to detect fluctuations in the amount of light for each reading line of the image data read in Step 3, the reading value of the image data obtained every unit time at the time of reading for a predetermined time is used as the image data for each reading line. Then, an average value of each light amount level in the main scanning direction is obtained for each image data, and the process proceeds to Step 5. In the case of the color mode, an average value of each light amount level in the main scanning direction is obtained for each RGB image data.

Step 5: The maximum value, the minimum value, and the total average value of the respective light intensity levels in the main scanning direction for each image data calculated in Step 4 (the average value of the respective light intensity levels in the main scanning direction of all the image data). And proceed to Step 6.
Step 6: A difference value between the maximum value and the minimum value calculated in Step 4 is calculated, and it is determined whether the difference value is less than 5% of the total average value. If it is less than 5% (in the case of “Y” in the figure), the reading line cycle setting procedure is terminated, and the process proceeds to Step 12. If it is not less than 5% (in the case of “N” in the figure), the process proceeds to step 7 for changing the reading line cycle.

Step 7: The variable n is incremented by 1 to change the reading line cycle, and the process proceeds to Step 8.
Step 8: Change the reading line cycle to n times the initial value, and go to Step 9. However, the reading line cycle is not necessarily an integer multiple of the initial value.
Step 9: The light quantity of the light source 1 is changed to 1 / n times the initial value in accordance with the change of the reading line cycle, and the process proceeds to Step 10. When the light source 1 is an LED, the LED drive current value is increased by 1 / n.
In this way, the light amount of the light source that is inversely proportional to the reading line cycle can be set, and the dynamic range of the CCD 25 can be secured.

Step 10: It is determined whether or not the variable n is larger than 5. If it is not greater than 5 (in the case of “N” in the figure), the process returns to step 3. If it is larger than 5 (in the case of “Y” in the figure), the process proceeds to Step 11.
Step 11: The reading line cycle is set to 1 to 5 times the initial value, and the reading line cycle having the smallest difference between the maximum value and the minimum value is adopted and set.
As described above, the optimum reading line period is set while changing the reading line period until the fluctuation of the light amount detected by the processing in steps 3 to 10 becomes the set value 5 or less.

Step 12: Since reading of the white reference plate 29 is completed, the light source 1 of the reading unit 20 is turned off, and the process proceeds to Step 13.
Step 13: As the reading line cycle is changed, the reading speed is changed to 1 / n times in order to keep the read image aspect ratio constant. Specifically, the rotational speed of the motor that drives the first carriage 22 that moves the light source 1 is set to 1 / n times the initial value.

In this way, it is possible to set the reading speed inversely proportional to the reading line cycle and keep the aspect ratio of the read image constant.
The execution timing of this processing can be considered when the multifunction device 100 is turned on, every time immediately before the image reading of the document is performed, every time after the image reading of the document is completed, or every certain time after the power of the multifunction device 100 is turned on. .

In the reading unit 20 of this embodiment, the white reference plate is illuminated, and the reflected light from the white reference plate is accumulated in the CCD for a certain time, and then the accumulated amount is detected. Even if the light amount fluctuates during this accumulation time, the light amount is averaged over the entire accumulation time.
Therefore, the variation in the amount of light is detected, and the variation in the amount of light is averaged within the reading line cycle to change the reading line cycle so as to reduce the variation for each reading line, thereby accumulating the CCD within one reading line cycle. The influence of the light amount fluctuation on the light amount can be reduced, and the density unevenness of the read image can be reduced.

1: Light source 2, 3: LED 4: Light guide 5: Diffusing member 6: Light source adjusting unit 7: Reading control unit 8: Light source driving unit 9: Control unit 10: ADF 11: Document tray 12: Feeding roller 13: Feed belt 14: Discharge roller 15: Roller 16: Document set detection sensor 20: Reading unit 21: Contact glass 22: First carriage 23: Second carriage 24: Lens 25: CCD linear image sensor 26: First mirror 27 : Second mirror 28: Third mirror 29: White reference plate 30: Writing unit 31: Laser output unit 32: Imaging lens 33: Mirror 40: Development unit 41: Photosensitive drum 42: Conveyor belt (transfer belt) 43 : Fixing unit 44: Paper discharge unit 45: Both Surface transport path 50: Vertical transport unit 51: First paper feed tray 52: Second paper feed tray 53: Third paper feed tray 54: First paper feed device 55: Second paper feed device 56: Third paper feed device 57: Paper discharge tray 60: Analog processing unit 61: A / D conversion unit 62: LVDS interface 63: Oscillation unit 64: Timing clock generation unit 100: Multi-function device A: Ejection port S: Sheet through reading slit

JP 2003-338904 A

Claims (8)

An image reading device that irradiates a subject with light from a light source and reads an image on the subject based on reflected light from the subject,
A light amount variation detecting means for detecting a variation in light amount for each reading line when the subject is read;
An image reading apparatus comprising: a reading line cycle changing unit that changes a reading line cycle based on a change in light amount for each reading line detected by the light amount fluctuation detecting unit.   The image reading apparatus according to claim 1, further comprising a light amount adjusting unit that adjusts a light amount of the light source based on a reading line cycle changed by the reading line cycle changing unit.   3. The image reading apparatus according to claim 1, further comprising a reading speed adjusting unit that adjusts the reading speed of the subject based on the reading line cycle changed by the reading line cycle changing unit.   4. The reading line cycle changing unit includes a unit that changes a reading line cycle until a variation in light amount detected by the light amount variation detecting unit becomes a set value or less. The image reading apparatus described.   The light quantity fluctuation detecting means and the reading line cycle changing means are set at regular intervals immediately after the image reading apparatus is turned on, immediately before reading an image of a document, after reading an image of a document, or after turning on the power of the image reading apparatus. The image reading apparatus according to claim 1, wherein the image reading apparatus is operated at an execution timing.   6. The image reading apparatus according to claim 1, wherein the light quantity fluctuation detecting unit includes a unit that detects a fluctuation of a light quantity for each reading line when the white reference plate is read.   4. The image reading apparatus according to claim 3, wherein the reading speed adjusting means includes means for adjusting a rotational speed of a motor that drives a carriage that moves the light source in the sub-scanning direction with respect to the subject.   An image forming apparatus comprising the image reading apparatus according to claim 1.