JP3465412B2 - Image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to image quality control of an image output from an image output device, and more particularly to an image forming device that always accurately detects the image quality of an output image.

[0002]

2. Description of the Related Art Conventionally, image quality control of image output devices has been widely performed. In particular, in the electrophotographic system in which an image is formed using a plurality of steps, various control methods have been proposed for each step. For example, Japanese Patent Laid-Open No. 3-0877
In Japanese Patent Publication No. 68, a reference developed image is formed on a photoconductor, the reference developed image is monitored, and a predetermined developed image is obtained.
A method of controlling each step is adopted, and in JP-A-4-193576, each step is controlled by monitoring the toner density after transfer.

However, in the above-mentioned method, since the control is performed in the intermediate stage of the image forming process, the quality of the image actually picked up by the user, that is, the fixed image itself is not guaranteed, and an error is likely to occur.

Further, Japanese Patent Laid-Open No. 4-077060,
In Japanese Patent Laid-Open No. 4-366165, a reference image is once output, the reference image is read by an image reading device provided in the device itself, and is used for actual control of an image forming process. In this way, since the control can be performed using the fixed image that the user actually holds, the control accuracy is improved.

However, in the above-mentioned method, the user has to perform the work of outputting the reference image once and reading the image by using the image reading device of the device itself, which is troublesome for the user and the daily operation. Image quality management cannot be performed. In addition, this method, like a copier,
It can be realized only when the image output device itself includes the image reading device. That is, it is a method that cannot be realized by an image output device that does not have an image reading device such as a printer.

Therefore, the image forming apparatus disclosed in Japanese Patent Laid-Open No. 4-055868 proposes a method of reading a print pattern on a sheet with an optical fiber. This saves the user the trouble of causing the image reading device of the device to read the output image one by one, and
It can be adopted even in an image output device having no image reading device such as a printer.

[0007]

As described above, the above-mentioned Japanese Patent Laid-Open Nos. 3-087768 and 4-19357.
In JP-A-6, since the control is performed in the intermediate stage of the image forming process, the quality of the fixed image itself is not guaranteed, and there is a problem that an error easily occurs.

Further, Japanese Patent Laid-Open No. 4-077060,
In Japanese Unexamined Patent Publication No. 4-376165, the control accuracy is improved, but the user's hand must be troubled for that. Further, it is a method that cannot be realized by an image output device that does not have an image reading device such as a printer.

As a solution to the above-mentioned problems of the prior art, there is Japanese Patent Laid-Open No. 4-055868.
In this method, an optical fiber is used to monitor only the amount of reflected light from the image. On the other hand, in a normal image reading apparatus, in order to quantitatively and accurately capture various image quality, various corrections such as white reference correction and shading correction are performed.
I am making full use of proofreading means. However, since the sensitivity of humans to image quality is extremely high, it is difficult to detect various image quality items with high accuracy in the above-described conventional technology, as compared with the method using an image reading apparatus that is calibrated with high accuracy, There was a problem that it was difficult to control with.

The present invention has been made in view of the above-mentioned circumstances, and the image of the final process held by the user can be quantitatively and accurately monitored without any trouble of the user, and the image can be controlled or managed. The image quality is not just a physical quantity such as the amount of reflected light of an image, but a color, gradation,
It is an object of the present invention to provide an image forming apparatus capable of monitoring the line reproducibility and further the state of resolution of the apparatus itself.

[0011]

In order to solve the above-mentioned problems, in the invention described in claim 1, the image pattern which is the standard of the image quality printed on the paper or the like is monitored to check the image quality of the output image. in the image forming apparatus which performs control, paper waste
It is installed in the vicinity of the discharge port to be output, and calibration target reference image pattern is recorded, the reference image pattern
And the paper to be ejected is
Is installed so as to pass through the serial gap, when the paper is not discharged, while that reading the reference image pattern of the calibration target, when the sheet is discharged,
An optical sensor for reading the real image pattern printed on a sheet, an output signal of the optical sensor at the time of reading the reference image pattern, an output signal of the optical sensor at the time of reading the real image pattern An image correction unit that controls the correction of the output image based on the difference is provided.

According to the invention described in claim 2,
The image forming apparatus described above is characterized by comprising a printing means for printing the same actual image pattern as the reference image pattern on a sheet in a predetermined situation.

In the invention according to claim 3, the invention according to claim 1
In the image forming apparatus described above, the reference image patterns are different reference colors arranged in the main scanning direction.

According to the invention described in claim 4,
In the image forming apparatus described above, the reference image patterns are different gradation images arranged in the main scanning direction.

According to the invention of claim 5, claim 1
In the image forming apparatus described above, the reference image pattern is a line array having different line widths arranged in the main scanning direction.

According to the invention of claim 6, claim 1
In the image forming apparatus described above, the reference image pattern is a line array arranged at different intervals in the main scanning direction.

[0017]

According to the present invention, a calibration target having a reference image pattern recorded thereon and an optical sensor opposed to the reference image pattern with a gap therebetween are disposed in the vicinity of the discharge port through which the paper is output. . At the time of calibration, first, the reference image pattern of the calibration target is read by the optical sensor installed near the discharge port when the paper is not discharged. Then, when the paper is ejected, the reference image
The paper passes through the gap between the pattern and the optical sensor, and the actual image pattern that is the same as the reference image pattern printed on the paper is read. Then, the optical sensor calibration unit performs correction control of the output image based on the difference between the output of the optical sensor when the reference image pattern is read and the output of the optical sensor when the actual image pattern is read.
Therefore, the image of the final process that the user holds is constantly monitored quantitatively and accurately without bothering the user, and the image quality to be controlled or managed is simply a physical quantity such as the reflected light quantity of the image. Instead, it becomes possible to monitor color, gradation, line reproducibility, and the state of resolution of the apparatus itself.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. The image forming apparatus according to this embodiment may be of any type. That is,
Any method such as an electrophotographic method, an inkjet method, or a thermal transfer method may be used.

A. First Embodiment FIG. 1 is a perspective view showing a part of an image forming apparatus according to a first embodiment of the present invention and a structure near an image output port. In the figure, reference numerals 1 and 2 denote rollers for finally discharging a sheet on which an image is printed, and a CCD or a contact color sensor near the rollers 1 and 2, that is, in the vicinity of an image output port. 3 are installed. Further, in the sensing area of the contact type color sensor 3, a gradation target 4 on which a gradation pattern 4a having five different gradations (density) is printed is provided along the contact type color sensor 3.

Next, FIG. 2 is a block diagram showing a configuration of a sensor circuit and an analog signal processing circuit when a CCD is used as the color sensor 3 described above. In the figure, a CCD board 10 is a CCD driver 11, a CCD
12, a DC cut circuit 13 and a buffer circuit 14. The CCD driver 11 supplies a drive signal to the CCD 12 based on the reference clock from the clock generation circuit 27. CCD 12 is the CCD driver 1
1 to read the gradation pattern 4a of the gradation target 4 described above, supply the image signal to the DC cut circuit 13 and correspond to the gradation target 4 output on the paper 5. The actual gradation pattern is read and the image signal is supplied to the DC cut circuit 13. The DC cut circuit 13 removes long-period noise such as temperature fluctuations of the output signal from the CCD 12 and supplies it to the buffer circuit 14. The buffer circuit 14 is a CCD
It is a circuit for transmitting a signal from the board 10 to the analog signal processing circuit 20.

Next, the analog signal processing board 20 has a buffer circuit 21, a sample hold circuit 22, an AGC circuit 23, a synchronous ground / DC regenerating circuit 24, and an AOC circuit 25.
And an A / D converter 26. The buffer circuit 21, like the buffer circuit 14, is a circuit for transmitting a signal. The buffer circuit 14 and the buffer circuit 21 perform impedance matching between the input and output circuits. The sample-hold circuit 22 also samples and holds the signal period of each pixel in the output signal of the CCD 12 based on the reference clock from the clock generation circuit 27, thereby removing the harmonic noise component and outputting it. Shape the waveform. Next, AG
The C circuit 23 adjusts the gain of the output signal of the CCD 12. Further, the synchronous ground / DC regenerating circuit 24 regenerates the signal DC level cut by the DC cutting circuit 13 based on the reference clock from the clock generating circuit 27. A
The OC circuit 25 adjusts the offset of the video output signal. The A / D converter 26 converts the analog video signal from the AOC circuit 25 into a digital video signal VD based on the reference clock from the clock generation circuit 27, and outputs the digital video signal VD.

The above is an example of the most general circuit configuration. For the present invention, any other circuit can be used as long as the image information read by the color sensor can be accurately extracted as a video signal. Good. Note that similar video signal detection can be performed with a similar circuit configuration in other embodiments described later.

In the above-mentioned image forming apparatus, first, the gradation pattern 4a of the gradation target 4 is set to the contact type color sensor 3.
Then, the image 5a corresponding to the gradation target 4 is printed on the actual paper 5, and the image 5a on the paper 5 is read by the contact color sensor 3. Here, FIG. 3 is a conceptual diagram showing how the video signal obtained as described above is used in this embodiment. The video signal VD is read in time series, but before the paper 5 passes through the contact type color sensor 3, the contact type color sensor 3 faces the gradation target 4. Upper gradation pattern 4a
Outputs the read value of. Next, when the sheet 5 on which the image 5a is printed passes, the margin on the sheet 5 first crosses the contact type color sensor 3, so that the read value is output. Next, the image (calibration patch) 5 a created on the paper 5 and corresponding to the gradation target 4 passes through the contact color sensor 3. Therefore, the contact color sensor 3 outputs the read value. In this way, the reading signal of the gradation target 4 and the corresponding reading signal of the image 5a on the sheet 5 are sequentially
It is output as time series data.

Here, a comparison between the read signal of the gradation target 4 and the read signal of the image 5a of the paper 5 is as shown in FIG. In the figure, the read signal of the gradation target 4 is shown by a solid line, and the read signal of the image 5a of the paper 5 is shown by a broken line. When a sufficiently accurate image is output, the video signal output values of the two are the same, but if not, there is a difference between the two and this is the amount to be corrected and controlled. In the example shown in FIG. 4, it is the difference between the solid line and the broken line. Then, according to the difference between the read signal of the gradation target 4 and the read signal of the image 5a on the paper, each color (YMCK, RGB) in the image forming process.
Rewrite the gradation correction table for each. Here, an example of the gradation correction table used in the first embodiment is shown in FIG.

In FIG. 5, the horizontal axis represents the input image signal and the vertical axis represents the output image signal. The actual gradation curve L1 shown by the thin solid line, the ideal gradation curve L2, and the corrected gradation curve shown by the thick solid line. Curve L3 is shown. This gradation correction table shows at what level the output image signal of the input image signal is output, and the actual gradation curve L1
Is the image 5a printed on the actual paper 5 described above.
The ideal gradation curve L2 corresponds to the read signal of the gradation pattern 4a of the gradation target 4. In the illustrated example, the actual gradation curve L1 has a lower output level in the central portion than the ideal gradation curve L2. Therefore, the actual gradation curve L1 is corrected, and the corrected curve L3 is rewritten so that the output level approaches the ideal gradation curve L2NI. By thus rewriting the gradation correction table, an optimum output image signal can be obtained. In the first embodiment, since the amount to be corrected is the density, the reflected light amount may be controlled so that the video signal corresponding to the density is output.

B. Second Embodiment Next, FIG. 6 is a perspective view showing a part of an image forming apparatus according to a second embodiment of the present invention and a structure near an image output port. The parts corresponding to those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In the figure, a contact type color sensor 29 is installed near the image output port as a sensor, and in the sensing area of the contact type color sensor 29, instead of the gradation target 4 described above, a reference color of YMCK is used. A reference color target 30 on which 30a is printed is provided. As the contact type color sensor 29, a CCD sensor unit using a reading optical system or a monocular color sensor having the same number as the reference number of colors may be used, and in any case, the same effect is exhibited. it can. In particular, in this embodiment, the reference color is always arranged at the same position, so that it is effective to use a monocular color sensor.

In the above-mentioned image forming apparatus, first, the reference color target 30 is read by the contact color sensor 29, and then the actual image 31a corresponding to the reference color target 30 is output on the paper 5, and the paper is printed. 5 is discharged, the image 31a on the paper is read by the contact color sensor 29, and based on the difference between the read value of the reference color target 30 and the read value on the paper 5, YMCK (or, Each reference color (RGB) is corrected. That is, when the color reproducibility of the monitored image 31a is different from that of the reference color target 4,
As in the prior art, feedback control is performed for each color formation process to perform correction control.

For example, in the case of the electrophotographic system, the difference in color is fed back to the actuators such as the charging potential, the exposure amount, and the developing bypass to perform the correction control. That is, the correspondence between the correction amount of the actuator and the color change amount is collected in advance as data, and the set value of the actuator is corrected by multiplying this by the amount to be corrected. However, the present invention is effective for any correction means regardless of such feedback correction means.

When managing not only YMCK but also RGB, a reference color target is provided for each color of YMCK and RGB, an image corresponding to this is printed on the paper 5, and In addition to the correction control of the actuator and the rewriting of the gradation table, it may be realized by executing the correction of the color correction coefficient. At this time, the effect on the appearance of the user is further enhanced by adding a gray balance to the target in which color differences are noticeable in color reproduction. It is also possible to combine the gradation target shown in FIG. 1 and the reference color target shown in FIG. 6 together to detect gradation and color reproducibility at the same time.

C. Third Embodiment Next, FIG. 7 is a perspective view showing a part of an image forming apparatus according to a third embodiment of the present invention and a structure near an image output port. The parts corresponding to those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In the figure, an image sensor 32 is installed as a sensor in the vicinity of the image output port, and the sensing area of the image sensor 32 is lined up in the horizontal direction and the vertical direction with respect to the discharge direction of the paper 5. A line target 33 having a line pattern 33a whose width is changed stepwise is provided. Needless to say, the resolution of the image sensor 32 itself is set sufficiently higher than the line width to be controlled or managed. Further, instead of the image sensor 32, a CCD using a reading optical system may be used,
More simply, a reflected light amount sensor with an aperture (aperture) may be used. In short, it is sufficient that the line width can be monitored with necessary and sufficient accuracy.

In the above-described image forming apparatus, first, the line target 33 is read by the image sensor 32, then the actual image 34a corresponding to the line target 33 is output on the paper 5, and the paper 5 is discharged. At this time, the image 34a on the paper is read by the image sensor 32, and is fed back to each image forming process based on the difference between the line width of the line target 33 and the line width on the paper 5 to perform correction control.

For example, FIG. 8 is a conceptual diagram showing an example of the read signal of the line target 33 and the corresponding read signal of the image 34a on the paper 5 when the line width reproducibility is targeted. In the illustrated example, it can be detected that the image 34a on the paper 5 has an excessively high density and a thick line width. In such a case, feedback correction control is performed in the direction of lowering the developing bias so that the line image is reproduced finely as a whole.

Since the line width usually has a high correlation with the image density, the method used as the density control means in the prior art is adopted in this embodiment. That is, in the case of the electrophotographic method, the difference in line width is fed back to the actuator such as the charging potential, the exposure amount, and the developing bias for correction control. Specifically, the correspondence between the correction amount of the actuator and the change amount of the line width is collected in advance as data, and this is used as a correction gain to actually print on the line width of the line target 33 and the paper 5. The set value of the actuator is corrected by multiplying the difference between the line width of the image 34a and the correction gain. However, the present invention is effective for any correction means regardless of such feedback correction means.

D. Fourth Embodiment Next, FIG. 9 is a perspective view showing a part of an image forming apparatus according to a fourth embodiment of the present invention and a structure near an image output port. The parts corresponding to those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In the figure, a CCD sensor unit 35 is installed as a sensor in the vicinity of the image output port, and a plurality of ladder patterns at different intervals are arranged in the sensing area of the CCD sensor unit 35 along the paper discharge direction. (Eg 5 line pairs per millimeter)
A resolution target 36 is provided on which 36a is accurately recorded.

In the above-mentioned image forming apparatus, first, the resolution target 36 is read by the CCD sensor unit 35, then the actual image 37a corresponding to the resolution target 36 is output on the paper 5, and the paper 5 is discharged. In doing so, the image 37a on the paper 5 is read by the CCD sensor unit 35, and each resolution (MTF) is calculated from the resolution target 36 and the read signal of the paper 5. For example, FIG. 10 shows a ladder pattern (MTF:
Resolution) Resolution target 3 for reproducibility
6 is a conceptual diagram showing an example of the read signal of No. 6 and the read signal of the image 37a of the paper 5 corresponding to this. Figure 10
In the above example, the read signal of the image 37a of the sheet 5 is
The overall density is too high, the line width is thick, and the resolution (MT
It can be detected that F) is lowered.

In such a case, feedback correction control is performed in the direction of lowering the developing bias so that the line image is reproduced finely as a whole, as in the third embodiment. In this way, when the two are different, the digital filter coefficient in the image forming apparatus is changed by an amount corresponding to the difference. More specifically, when the resolution is lowered, the high frequency component of the digital filter is emphasized. On the other hand, when the resolution is increased, the high frequency component of the digital filter is reduced. However, in reality, the resolution tends to decrease in most cases.

As described above, according to the above-described first to fourth embodiments, the important image quality items such as color, gradation, line width, and resolution can always be corrected or controlled by the absolute value with the target as a reference. Like

In each of the above embodiments, the gradation target 4, the reference color target 30, and the line target 33 are used.
As a method of creating and outputting an image corresponding to the resolution target 36 on the paper 5, a method using a calibration button (not shown) and a method using a banner sheet are used together. That is, when the user wants to calibrate, by pressing the calibration button equipped on the device,
In addition to normal image formation, a reference image signal stored in the apparatus may be used to create an actual image corresponding to each target on the paper 5. Also,
In the case of a printer or fax, an actual image corresponding to the target may be written on the banner sheet by using the reference image signal when outputting the banner sheet. When the banner sheet is used, it can be automatically calibrated by automatically performing it at a predetermined time interval when the image forming apparatus is powered on, so that the user does not have to bother.

On the paper 5 or the banner sheet,
When an actual image corresponding to the gradation target 4 or the reference color target 30 is created using the reference image signal,
As shown in FIG. 11, 100%, 50%, 30%, ...
In this way, if images with different densities are printed and calibration is performed at each density, control can be performed with higher accuracy.

[0040]

As described above, according to the present invention, the image of the final step that the user holds can be monitored quantitatively and accurately without the user's hand, and the image forming step can be performed. The advantage is that it can be controlled with high precision. In addition, the image quality to be controlled or managed is not limited to the physical quantity such as the reflected light quantity of the image, but there is an advantage that it is possible to monitor the color, gradation, line reproducibility, and the state of resolution of the device itself. To be Further, the output of the sensor that detects the image quality is always subjected to absolute value calibration by the target, so even if the sensor is cheap and unstable,
The advantage is that sufficient accuracy can be guaranteed. That is, even if the sensor itself causes a phenomenon such as an output drift due to a change in the ambient temperature or the like, there is an advantage that the calibration can be automatically performed by reading the target.

[Brief description of drawings]

FIG. 1 is a perspective view showing a part of an image forming apparatus according to a first embodiment of the present invention and a structure near an image output port.

FIG. 2 is a block diagram showing a configuration of a sensor circuit and an analog signal processing circuit when a CCD is used.

FIG. 3 is a conceptual diagram showing how a video signal is used in the first embodiment.

FIG. 4 is a conceptual diagram in which a read signal of a gradation target and a read signal of a gradation pattern of a sheet are compared in the first embodiment.

FIG. 5 is a conceptual diagram showing an example of a gradation correction table used in the first embodiment.

FIG. 6 is a perspective view showing a part of an image forming apparatus according to a second embodiment of the present invention and a structure near an image output port.

FIG. 7 is a perspective view showing a part of an image forming apparatus according to a third embodiment of the present invention and a structure near an image output port.

FIG. 8 is a conceptual diagram showing an example of a line target read signal and an image read signal corresponding to the line target read signal in the third embodiment.

FIG. 9 is a perspective view showing a part of an image forming apparatus according to a fourth embodiment of the present invention and a structure near an image output port.

FIG. 10 is a conceptual diagram showing an example of a read signal of a resolution target and a read signal of an image on paper corresponding to the read signal of a resolution target in the fourth embodiment.

FIG. 11 is a conceptual diagram showing another example in which an actual image corresponding to a gradation target or a reference color target is created on paper or a banner sheet.

[Explanation of symbols]

1, 2 rollers 3 Contact color sensor (optical sensor) 4 gradation target (calibration target) 4a gradation pattern (reference image pattern) 5 sheets 5a image (actual image pattern) 10 CCD board 11 CCD driver 12 CCD 13 DC cut circuit 14 Buffer circuit 20 Analog signal processing board 21 Buffer circuit 22 Sample and hold circuit 23 AGC circuit 24 Synchronous grounding / DC regeneration circuit 25 AOC circuit 26 A / D converter 27 Clock generation circuit 29 Contact color sensor (optical sensor) 30 Standard color target (calibration target) 30a Reference color (reference image pattern) 31a image (actual image pattern) 32 image sensor (optical sensor) 33 line target (calibration target) 33a line pattern (reference image pattern) 34a image (actual image pattern) 35 CCD sensor unit (optical sensor) 36 resolution target (calibration target) 36a ladder pattern (reference image pattern) 37a image (actual image pattern)

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15/00 303 G03G 21/00 370-540 G03G 15/01-15/01 117 B41J 29/00-29 / 70 H04N 1/00-1/00 108

Claims (6)

(57) [Claims] 1. An image forming apparatus for controlling an image quality of an output image by monitoring an image pattern which is a standard of image quality printed on a sheet or the like, is installed near a discharge port from which a sheet is discharged, and is a standard. When the calibration target on which the image pattern is recorded and the reference image pattern are opposed to each other through a gap,
Is installed so that the ejected paper passes through the gap.
Is, when the paper is not discharged, while that reading the reference image pattern of the calibration target, when the sheet is discharged, and an optical sensor for reading the real image pattern printed on paper, the reference Image correction means for correcting and controlling the output image based on the difference between the output signal of the optical sensor when the image pattern is read and the output signal of the optical sensor when the actual image pattern is read. An image forming apparatus characterized by. 2. The image forming apparatus according to claim 1, further comprising a printing unit that prints the same actual image pattern as the reference image pattern on a sheet in a predetermined situation. 3. The image forming apparatus according to claim 1, wherein the reference image patterns are different reference colors arranged in the main scanning direction. 4. The image forming apparatus according to claim 1, wherein the reference image patterns are different gradation images arranged in the main scanning direction. 5. The image forming apparatus according to claim 1, wherein the reference image pattern is a line array having different line widths arranged in the main scanning direction. 6. The image forming apparatus according to claim 1, wherein the reference image pattern is a line array arranged in the main scanning direction and arranged at different intervals.