JP2003140406A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of accurately correcting the gradation of an inputted image signal. SOLUTION: By adjusting the inclination of a gradation correction table correcting curve A by an angle α based on the density of a toner patch 20 actually measured by an ADC sensor 10 and the target density of the toner patch 20 by a table correction means 50, a gradation correction table correcting curve B is obtained, and a correction amount is obtained based on the curve B whose inclination is adjusted, and further the gradation of the image signal is corrected based on a gradation correction table LUT in a gradation correction means 41 based on the obtained correction amount.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus used in an electrophotographic copying machine or printer.

[0002]

2. Description of the Related Art Conventionally, an electrostatic latent image is formed on a photosensitive member by scanning the photosensitive member with an exposure beam modulated according to an image signal, and then the electrostatic latent image is developed with toner. There is known an image forming apparatus which forms a toner image on the photoconductor, and finally transfers and fixes the toner image on a recording medium to form an image of the fixed toner image on the recording medium. ing. In such an image forming apparatus, the density of an image formed on a recording medium is higher than a preset reference density due to environmental conditions such as temperature and humidity with respect to the apparatus and aging of members constituting the apparatus. It may shift in the dark or light direction. Therefore, a toner patch for image density detection is formed in a non-image area on the image carrier such as a photoconductor or an intermediate transfer belt, and the density of the toner patch is adjusted to ADC (Auto Density Con
control), the gradation of the image signal is corrected so that the density of the toner patch becomes the reference density by referring to the gradation correction table for correcting the gradation of the input image signal. Has been done.

[0003]

The gradation gradient (γ characteristic curve) represented by the gradation correction table by the toner patch of the reference density and the gradation by the toner patch deviated to the density other than the reference density. Gradient inclinations represented by the correction table are different from each other. However, in the conventional image forming apparatus,
Since the correction is performed by referring to the gradation correction table with the toner patch of the reference density, it is difficult to accurately perform the gradation correction of the input image signal.

In view of the above circumstances, it is an object of the present invention to provide an image forming apparatus capable of accurately correcting the gradation of an input image signal.

[0005]

SUMMARY OF THE INVENTION An image forming apparatus of the present invention that achieves the above object scans a photosensitive member with an exposure beam modulated according to an image signal, thereby forming an electrostatic latent image on the photosensitive member. Is formed, the electrostatic latent image is developed with toner to form a toner image on the photoconductor, and the toner image is finally transferred and fixed on the recording medium to be fixed on the recording medium. In an image forming apparatus for forming an image composed of a toner image, a gradation correction means for correcting the gradation of an input image signal based on a gradation correction table,
Based on the light source which emits the exposure beam modulated based on the image signal corrected by the gradation correction means and the image signal representing the patch having the predetermined area ratio corresponding to the predetermined target density, the predetermined From the target density of the toner patch of the density of the toner patch measured by the patch density measuring means and the patch density measuring means for measuring the density of the toner patch When the deviation is used as a variable, the above-mentioned gradation correction table correction curve representing the correction amount for correcting the gradation correction table for the image signal having the same area ratio as that of the toner patch When the toner patch formed by the patch forming means is actually measured by the patch density measuring means, the toner density of the toner patch A table correction for obtaining a correction amount for the deviation from the target density of the patch, obtaining the correction amount of the gradation correction table for the image signals of all area ratios based on the correction amount, and correcting the gradation correction table The table correction means adjusts the inclination of the gradation correction table correction curve by an angle based on the density of the toner patch actually measured by the patch density measuring means and the target density of the toner patch. Then, in obtaining the correction amount corresponding to the deviation from the deviation,
The correction amount is obtained based on a gradation correction table correction curve whose inclination is adjusted.

Here, the patch density measuring means also detects the density of the background where the patch is not formed, and the table correcting means detects the difference between the background density and the measured density of the toner patch. , The inclination of the gradation correction table is adjusted by rotating the gradation correction table correction curve by an angle based on the ratio between the background density and the target density of the toner patch. It is preferable.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus of the present invention.

The image forming apparatus 100 shown in FIG. 1 includes four photoconductors corresponding to four colors of yellow (Y), magenta (M), cyan (C), and black (K) from the right side of FIG. 1Y, 1M, 1C and 1K are arranged side by side in a straight line, and around these photoconductors 1Y, 1M, 1C and 1K, chargers 2Y, 2M, 2C and 2K and developing units 3Y and 3M,
3C and 3K and transfer devices 4Y, 4M, 4C and 4K are arranged. An electrostatic latent image is formed on the photoconductors 1Y, 1M, 1C, 1K by scanning with an exposure beam modulated according to an image signal. Developing devices 3Y, 3M, 3
C and 3K develop the electrostatic latent image with the toner in the developer in which the toner and the carrier are mixed.

In the image forming apparatus 100, toners for replenishing the developing devices 3Y, 3M, 3C and 3K with yellow (Y), magenta (M), cyan (C) and black (K) toners. Cartridges 5Y, 5M, 5C, 5K and toner replenishment motors 6Y, 6M, 6C, 6K, and ATC (Auto Toner Concentr) for measuring the toner concentration of the developer in the developing units 3Y, 3M, 3C, 3K.
ation Control) Sensors 7Y, 7M, 7
C and 7K are provided.

Further, the image forming apparatus 100 has an arrow A
The intermediate transfer belt 8 that is driven in the direction, the drive roll 9,
ADC (Auto Density Control)
The sensor 10 is provided. The ADC sensor 10 is
It corresponds to an example of the patch density measuring means according to the present invention, and measures the density of the toner patch 20 formed on the intermediate transfer belt 8. In addition, this ADC sensor 10
When measuring the density of the toner patch 20, the density of the background on which the toner patch 20 is not formed is also measured.

The image forming apparatus 100 also includes a controller 40. This controller 40
Together with the developing units 3Y, 3M, 3C, 3K, etc., they play the role of the patch forming means in the present invention, and based on a signal representing a patch having a predetermined area ratio corresponding to a predetermined target density. The toner patch 20 having the predetermined target density is formed on the intermediate transfer belt 8. In addition, the controller 40
Is provided with gradation correction means 41 for correcting the gradation of the print image represented by the input image signal based on the gradation correction table (LUT).

Further, the image forming apparatus 100 is provided with a table correction means 50. The table correction unit 50 has the same area ratio as the area ratio of the toner patch 20 when the deviation of the density of the toner patch 20 measured by the ADC sensor 10 from the target density of the toner patch 20 is used as a variable. The toner patch 20 is converted by the ADC sensor 10 based on a gradation correction table correction curve, which will be described later, that represents a correction amount for correcting the gradation correction table (LUT) provided in the gradation correction unit 41 for the image signal of. A correction amount for the deviation of the density of the toner patch 20 when actually measured from the target density of the toner patch 20 is obtained. Further, based on the correction amount, the correction amount of the gradation correction table (LUT) is calculated for the image signals of all area ratios, and the gradation correction table (L
UT) is corrected.

Further, the image forming apparatus 100 corresponds to an example of a light source according to the present invention, which emits an exposure beam modulated based on image data representing the image signal corrected by the gradation correcting means 41. Raster scanning device (hereinafter,
30). This ROS
By 30, an electrostatic latent image is written on the photoconductors 1Y, 1M, 1C, 1K charged by the chargers 2Y, 2M, 2C, 2K.

Further, the image forming apparatus 100 includes a ROS.
An LD light amount control unit 60 for controlling the light amount of the exposure beam from 30 is provided.

In the image forming apparatus 100, the transfer amount of each color toner to each electrostatic latent image by each developing device 3Y, 3M, 3C, 3K is adjusted according to the measurement result by the ADC sensor 10. A TC control unit 70 that controls the toner stacking amount is provided.

The image forming apparatus 100 configured as described above.
Scans the photoconductors 1Y, 1M, 1C, 1K with an exposure beam that is modulated according to the print image represented by the image signal to form an electrostatic latent image on the photoconductors 1Y, 1M, 1C, 1K. And then form those electrostatic latent images with yellow (Y), magenta (M), cyan (C), black (K)
To develop a color toner image on the photoconductors 1Y, 1M, 1C, and 1K, and finally transfer and fix the color toner image on the recording medium to fix the toner image on the recording medium. Is used to form a color image. In this image forming apparatus 100, gradation correction of an image signal is performed as follows.

The table correction means 50 is an ADC sensor 1.
The density of the toner patch 20 actually measured by 0,
To adjust the inclination of the gradation correction table correction curve by an angle based on the target density of the toner patch 20 and obtain the correction amount corresponding to the deviation from the deviation, the gradation correction table correction curve with the adjusted inclination is used. The correction amount is calculated based on.

Further, the table correction means 50 provides an angle based on the ratio between the difference between the background density and the measured density of the toner patch and the difference between the background density and the target density of the toner patch 20. By rotating the gradation correction table correction curve, the inclination of the gradation correction curve is adjusted. Hereinafter, a specific description will be given with reference to FIGS.

FIG. 2 is a graph showing the deviation value between the target density and the actually measured current density in the image forming apparatus shown in FIG.

The horizontal axis of FIG. 2 represents image data Cin representing the densities from 0% to 100% represented by the values 0 to 255, and the vertical axis represents the density value RADC measured by the ADC sensor 10. Indicates. The value P is 40%
Shows the image data Cin representing the toner patch 20 having an area ratio corresponding to the density of, and the value Q represents the image data Cin representing the density of 0% (the density of the background of the intermediate transfer belt 8).

The graph K1 shown in FIG. 2 shows the value RA corresponding to the image data Cin (value P) at the target density of 40%.
It is a graph obtained by connecting a point of DC (target density value: 1023-a) and a point of value RADC (ground density value: 1023) corresponding to image data Cin in the ground density. On the other hand, the graph K2 connects the point of the current value RADC (current density value: 1023-b) actually measured by the ADC sensor 10 and the point of the density value of the ground. It is the obtained graph. Table correction means 50
Then, the ratio between the target density value RADC (1023-a) and the current density value RADC (1023-b), that is, the ratio between the slope of the graph K1 and the slope of the graph K2 is defined as the deviation α (gamma correction rate), Based on this deviation α, the gradation correction table L
A gradation correction table correction curve representing a correction amount for correcting the UT is calculated.

FIG. 3 is a diagram showing a gradation correction table correction curve at a density of 40%.

FIG. 3 shows a gradation correction table correction curve A at a target density of 40% and a gradation correction table correction curve B calculated based on the deviation α. Here, the horizontal axis of FIG. 3 represents the difference value ΔRADC obtained by subtracting the target density value RADC from the current density value RADC by the ADC sensor 10. This difference value ΔRA
If DC is on the + side (right side of origin 0, 0), the current density of toner patch 20 is lower than the target density, and if difference value ΔRADC is on the − side (left side of origin 0, 0), it is current. It means that the toner patch 20 has a higher density than the target density. The vertical axis represents the correction amount (ΔLUT) for correcting the gradation correction table LUT 41, which corresponds to the difference value ΔRADC. In the gradation correction table correction curve A at the target density, it is sufficient to correct each value ΔLUTA0, A1 for each difference value ΔRADC in the − side range, and each correction value ΔRADC for each difference value ΔRADC in the + side range. Only the values ΔLUTA2 and A3 need to be corrected.

On the other hand, in the tone correction table correction curve B, each value ΔLUTB0, B1 is corrected in each difference value ΔRADC in the minus side range, and each difference value ΔRADC in each + side range is corrected. Value ΔLUTB2
Only B3 is corrected. The table correction means 50 is an ADC
The inclination of the gradation correction table correction curve A is adjusted by an angle (deviation) α based on the density of the toner patch 20 actually measured by the sensor 10 and the target density of the toner patch 20, and the deviation is changed to the deviation. In obtaining the corresponding correction amount, the correction amount is obtained based on the gradation correction table correction curve B whose inclination is adjusted. Specifically, the tone correction table correction is performed by an angle α based on the ratio between the difference between the background density and the measured density of the toner patch 20 and the difference between the background density and the target density of the toner patch 20. By rotating the curve A, the gradation correction curve A
Adjust the tilt of. When the value of the density (current density) measured by the ADC sensor 10 is larger than the value of the target density (the density is high), the above inclination is also large. Therefore, FIG.
The gradation correction curve B is obtained by making adjustments so that the inclination of the gradation correction curve A becomes smaller as shown in FIG. On the other hand, when the density value measured by the ADC sensor 10 is smaller than the target density value (the density is light), the inclination is small. In this case, contrary to the case shown in FIG. 3, the gradient of the gradation correction curve A is adjusted to be large.

FIG. 4 is a graph of an ideal gradation correction table and a graph of a corrected gradation correction table.

The horizontal axis of FIG. 4 represents the image data Cin representing the densities from 0% to 100% represented by the values 0 to 2550, and the vertical axis corresponds to the image data Cin of the ADC sensor 10. Image output level Cout from the value 0 to the value 255 for the toner patch 20 formed by
Indicates. Graph C shown in FIG. 4 is a graph of an ideal gradation correction table at the target density. On the other hand, graph D
Is an ideal gradation correction table for the image data Cin representing the image signal of all the area ratios including the value P at the area ratio of 40% for which the correction amount is obtained by the gradation correction table correction curve B. It is a graph.

In the image forming apparatus 100 of this embodiment, A
When the density of the toner patch 20 is detected by the DC sensor 10 and the gradation of the image signal is corrected based on the detection result, the density of the toner patch 20 actually measured by the ADC sensor 10 and the toner patch 20 The inclination of the gradation correction table correction curve A is adjusted by the angle α based on the target density to obtain the gradation correction table correction curve B, and the correction amount is calculated based on the gradation correction table correction curve B whose inclination is adjusted. Further, since the gradation of the image signal is corrected based on the gradation correction table represented by the graph D based on the correction amount, the gradation correction table based on the actually measured density of the toner patch 20. Since the gradation correction is performed based on the above, the gradation correction of the input image signal can be accurately performed.

[0029]

As described above, according to the image forming apparatus of the present invention, the gradation correction of the input image signal can be accurately performed.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a graph showing a deviation value between a target density and an actually measured current density in the image forming apparatus shown in FIG.

FIG. 3 is a diagram showing a gradation correction table correction curve at a density of 40%.

FIG. 4 is a graph of an ideal gradation correction table and a graph of a corrected gradation correction table.

[Explanation of symbols]

1Y, 1M, 1C, 1K photoconductor 2Y, 2M, 2C, 2K charger 3Y, 3M, 3C, 3K developing device 4Y, 4M, 4C, 4K transfer device 5Y, 5M, 5C, 5K toner cartridges 6Y, 6M, 6C, 6K Toner supply motor 7Y, 7M, 7C, 7K ATC sensor 8 Intermediate transfer belt 9 drive roll 10 ADC sensor 20 toner patch 30 ROS (raster scanning device) 40 controller 41 gradation correction means 50 table correction means 60 LD light quantity control unit 70 TC control unit 100 image forming apparatus

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yama ▲ Saki ▼ Naoya             Fuji Zero, 2274 Hongo, Ebina City, Kanagawa Prefecture             Co., Ltd. Ebina Office (72) Inventor Masahiro Gazuma             Fuji Zero, 2274 Hongo, Ebina City, Kanagawa Prefecture             Co., Ltd. Ebina Office F term (reference) 2C262 AA05 AA24 AB07 BB01 BB14                       BB36 BC01 BC13 EA11 FA13                       GA02                 2H027 DA09 DE02 DE07 EA02 EB04                       EC03 EC06 EC07 EC19                 5C074 AA05 BB02 BB17 BB26 DD03                       DD16 EE02 HH02

Claims (2)

[Claims] 1. An electrostatic latent image is formed on the photoconductor by scanning the photoconductor with an exposure beam that is modulated according to an image signal, and the electrostatic latent image is developed with toner. An image input by an image forming apparatus that forms a toner image on a photoconductor, and finally transfers and fixes the toner image on a recording medium to form an image composed of a fixed toner image on the recording medium. A gradation correction unit that corrects the gradation of the signal based on a gradation correction table, a light source that emits an exposure beam that is modulated based on the image signal corrected by the gradation correction unit, and a predetermined target Patch forming means for forming a toner patch having a predetermined target density based on an image signal representing a patch having a predetermined area ratio corresponding to the density; patch density measuring means for measuring the density of the toner patch; When the deviation of the density of the toner patch measured by the density measuring means from the target density of the toner patch is used as a variable, the gradation for the image signal having the same area ratio as the area ratio of the toner patch is set. Based on the gradation correction table correction curve representing the correction amount for correcting the correction table, the density of the toner patch when the toner patch formed by the patch forming unit is actually measured by the patch density measuring unit , A correction amount for deviation from the target density of the toner patch is obtained, and based on the correction amount,
Table correction means for calculating the correction amount of the gradation correction table for image signals of all area ratios and correcting the gradation correction table, wherein the table correction means is actually measured by the patch density measuring means. The inclination of the gradation correction table correction curve is adjusted by an angle based on the density of the toner patch and the target density of the toner patch, and the inclination is adjusted when the correction amount corresponding to the deviation is calculated from the deviation. An image forming apparatus, wherein the correction amount is obtained based on the corrected gradation correction table correction curve. 2. The patch density measuring means also detects the density of the background on which the patch is not formed, and the table correction means, the difference between the density of the background and the measured density of the toner patch, The inclination of the gradation correction curve is adjusted by rotating the gradation correction table correction curve by an angle based on the ratio between the background density and the target density of the toner patch. The image forming apparatus according to claim 1, wherein: