JP3341778B2 - 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 a method for setting parameters relating to color and density in an electrophotographic process for obtaining an appropriate image density in a digital color image output apparatus or the like using the electrophotographic process.

[0002]

2. Description of the Related Art Main parameters of an electrophotographic process for determining an image density are development potentials (dark potential _VH , bright potential _VL ,
Development bias potential V _BIAS ) and development characteristic γ. These parameters are controlled by process control so that the parameters are stably maintained. However, it is necessary to set initial values (control target values) of these parameters when the image output apparatus is shipped or maintained, or before copying. There is. Conventionally, when setting the control target value of each color, the image density output from the image output device was changed using a densitometer or a density limit sample, and the control target value was changed to set the target value. .

[0003] However, the densitometer has high accuracy but is expensive and has a problem that it must be carried at all times during maintenance of the image output apparatus. In addition, the density limit cannot set the image density with high accuracy. Was. further,
There is a problem that these setting operations are complicated.

In order to solve the above problem, Japanese Patent Laid-Open Publication No.
As disclosed in Japanese Patent Application Laid-Open No. 6760, there is known a method of outputting a built-in gray scale signal on a sheet of paper, reading this gray image, and correcting the tone of an image output device based on the result.

[0005]

However, in the above-mentioned conventional system, since the image is gray, the detection output of the reading device is low, and Y (yellow), M (magenta),
There is a disadvantage that the balance of C (cyan) cannot be accurately grasped, and the parameters of the electrophotographic process cannot be set. In addition, the present applicant has applied for a method of detecting the densities of a plurality of colors and correcting the conversion characteristics of the density conversion means of the reading device in a similar manner. Since the correction is performed here, there are disadvantages that the correction range becomes large, that the correction cannot be completed, and that the correction method is complicated.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image density setting method capable of setting a parameter of an electrophotographic process, that is, a control target value of image density with high accuracy, in a short time, and easily.

[0007]

In order to achieve the above object, an image density setting method according to the present invention outputs a density setting pattern, a toner consumption pattern, and a toner non-consumption pattern corresponding to a development color on a recording paper. An image output device, an image reading device that reads the image density of the density setting pattern output on the recording paper, a toner amount detecting unit that detects a toner amount of the developed density setting pattern, and an image density target value. Means for setting a toner amount target value corresponding to, a developing characteristic control device for controlling the amount of toner supplied to the developing device by comparing the toner amount target value with the detected toner amount, and the image reading device Means for correcting the toner amount target value based on the difference between the image density and the image density target value read according to the above. The calculated than this to calculate the density correction amount for each color, the average value of the density correction for each color density correction amount for each color
The value subtracted from the amount is used as the difference from the image density target value, and a toner consumption pattern is generated when the read image density is higher than the image density target value, and a toner non-consumption pattern is generated when the read image density is lower than the image density target value. Accordingly, the toner amount of the developed density setting pattern is set to the corrected toner amount target value.

[0008]

In the present invention, for example, an image of a density setting pattern output on recording paper is read by an image reading device, converted into an image density, and an image density target value of each color determined in advance based on the image density. Is calculated for each color, a control target value correction amount is calculated, and then the correction amount is added to the output value of the developing toner amount detection sensor of the developing patch when the correction pattern is output, to control the development characteristics. Set target values.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an example of a digital color copying machine, showing one embodiment of an image density setting method according to the present invention. The present invention is not limited to such a color copying machine, but can be applied to an image output device such as a facsimile or a printer.

A color original is placed on a platen glass 1, and an image reflected by an illumination lamp 2 is input to a color CCD 4 via a lens 3. Color CCD4
, Using a color filter and a CCD image sensor, the reflectance information of a color original is converted into B, which is the primary color of light.
(Blue), G (green), and R (red) signals are read and converted into digital image signals for each color by an image reading device (IIT) 5, and then the reflectance information is converted into density information. After the signal is subjected to various data processing in order to enhance the reproducibility of color, gradation, definition, etc. by an image processing device (IPS) 6, the primary colors Y (yellow) and M
(Magenta), C (Cyan), and K (Black) are converted into pixel signals, and the on-duty time of the laser is determined for each pixel according to this signal.
S) Output to 7.

Around the photosensitive member 9 forming the image bearing member,
A scorotron 10 for uniformly charging the surface of the photoconductor 9; a potential sensor 11 for detecting the surface potential of the photoconductor 9; a developing unit 12 for developing the electrostatic latent image into a toner image; And a developing toner amount detection sensor 15 for transferring the photoreceptor 9 to the recording paper, and rotate the photoconductor 9 as shown by the arrow in the figure.

In the laser writing device 7, for example, yellow image signals from the image processing device 6 are converted into optical signals, and a laser beam is exposed on the photosensitive member 9 to form an electrostatic latent image corresponding to the original image. The yellow latent image is developed by a yellow developing unit Y of the developing unit 12. The multi-transfer device 13 is rotated in synchronization with the photoreceptor 9 as shown by an arrow in the drawing, carries the recording paper conveyed from the paper tray 16, and transfers the yellow toner image onto the recording paper.

As for the developing potential of the photosensitive member 9, a potential patch (not shown) is formed outside the image area, the surface potential is detected by a potential sensor 11, and the developing potential is controlled so as to reach a target developing potential which is an image density setting parameter. It is controlled by the device 21. The developing characteristic γ of the developing unit 12 is
Similarly, a development patch (not shown) is created outside the image area,
The developed toner amount is used as a developed toner amount detection sensor 1
5, and is controlled by the developing characteristic control 22 so that the target developing toner amount, which is an image density setting parameter, is obtained.

Subsequently, the residual toner on the photosensitive member 9 is removed,
After removing the residual charges, the photosensitive member 9 is again put into the scorotron 1
0, the laser writing device 7
Outputs a magenta optical signal, creates a magenta electrostatic latent image, develops the image, and multiple-transfers the magenta toner image onto recording paper in the multiple transfer device 13. Thereafter, the formation, development and transfer of cyan and black latent images are performed in the same manner. When the multi-transfer device 13 makes four rotations to complete the transfer of the four colors, the recording paper is sent to the fixing device 17 where the toner image is fused and fixed, and the image output ends.

Next, the configuration relating to the image density setting method of the present invention will be described. On the output side of the IIT 5, an image output of the density setting pattern 27 (FIG.
A control target value setting device 20 for reading at T5, comparing the image density with an image density target value and setting an image density setting parameter is connected, and outputs an output signal as the control target value and a detection signal of the potential sensor 11. In comparison, in the developing potential control device 21, the charging voltage V _G of the scorotron 10,
ROS7 of exposure LD, the developing bias voltage V _{BI AS} is controlled to a desired image density is controlled. Alternatively, an output signal as a control target value of the control target value setting device 20 is compared with a detection signal of the developing toner amount detection sensor 15 and output to the developing characteristic control device 22 and output to the toner supply device 23 to output the toner to the developing device. The developing characteristic γ is controlled by controlling the amount of toner supplied to the unit 12, and the desired image density is controlled. Here, in order to simplify the explanation, the control target value of the development potential control device 21 is always fixed, and a method of setting the control target value of the development characteristic control device 22 will be described.

A built-in pattern storage device 26 is connected to the ROS 7 via a changeover switch 25. FIG. 2 shows the density setting pattern 2 stored in the built-in pattern storage device 26.
7 is a pattern that can output a three-color superimposed patch of Y, M, C, K, and YMC colors. These patches form a latent image on the photoreceptor 9, develop, and transfer the latent image on the photoreceptor 9 by setting the output of the on-duty time ratio of the laser of the ROS 7 to, for example, 60%, and output the density setting pattern 27 on recording paper. . The built-in pattern storage device 26 has
As will be described later, in order to adjust the toner mixture ratio in the developing machine, a solid pattern of the entire image area in which the toner is consumed and a pattern without the entire image in which the toner is not consumed are included.

The developing toner amount detecting sensor 15 is an optical density sensor comprising a light emitting element and a light receiving element. After developing a developing patch for controlling the developing toner amount (not shown), the light from the light emitting element is applied to the patch. Then, the reflected light is detected by a light receiving element, converted into an electric signal, and is converted into an electric signal.
Here, the amount of reflected light V _{clean in a clean} portion where no toner is _loaded on the photoconductor 9 and the photoconductor 9
Reflected light amount V at the portion where toner is on the upper patch
ratio to _patch , ie sensor output V = reflectance
V _patch / V _clean is calculated.

On the other hand, an image of the density setting pattern 27 output on the recording paper to be set to the target image density is placed on a platen and read by the IIT 5. Y color is B
Color, M color is G color, C color is R color, YMC 3 color overlap is BGR
Each of the three colors is read by the signal of the color CCD 4,
In IIT5, the single color is converted into image density D, and the YMC three-color superimposition is converted into chromaticity L ^* , a ^* , b ^* .

Average Developed Toner Amount Sensor Outputs V and II
The relationship with the image density D measured at T5 is a characteristic as shown in FIG. Target value V ₁ of the sensor output is the target value of the developing characteristic control device 22 with respect to the target value D _s of the image density. However, the characteristic curve a indicates the average characteristic of the sensor, and in practice, a variation occurs as shown in a characteristic curve b for each sensor for each copying machine. Without variation, can be the V ₁ and the target value, it is necessary to set a target value for each copying machine because there are variations. Therefore, the control target value setting device 20 compares, for each color, the single-color image density D _M read by the IIT 5 and the image density target value D _{S of} each color predetermined from the output V _M of the developing toner amount sensor at this time. Then, the control target value correction amount ΔV = V ₂ −V ₁ is calculated from the characteristic curve a in FIG. 3, and then the developing toner amount detection sensor of the developing patch when the correction pattern 27 is output from the characteristic curve b. correction amount of the output value V _M of the 15 delta
By adding the V, to set the control target value V _s.

FIG. 4 is a graph showing the development characteristics, and shows the relationship between the difference between the surface potential _{VP / R} of the photosensitive member 9 and the bias potential _VBIAS and the amount of toner to be developed. The image density can be set to a desired value by controlling the amount of toner supplied to the developing unit 12 in accordance with the control target value V _S and the output of the developing toner amount sensor, which changes according to the toner mixing ratio.

[0021] To quickly converge to the developing control target value V _S which is set for each color, if the image density is high, to generate a whole-area solid pattern to consume the toner from the internal pattern storage unit 26, and the toner supply The supply of the toner is stopped in the device 23, and the developing patch is controlled to the control target value V _S.
Perform until it becomes. When the control target value is reached, a pattern is generated from the built-in pattern storage device 26 which does not consume toner and has no entire image. The developing device is operated for a short time while the supply of toner is stopped, and then stopped.

Conversely, when the image density is low, a pattern that does not consume toner is generated from the built-in pattern storage device 26, toner is supplied, and the processing is performed until the development patch reaches the control target value. , Do the same as when the concentration is high.

As described above, when the control of the development characteristic γ is in the control state, the density setting pattern 27 is output again from the built-in pattern storage device 26, and if the image density has reached the target value, the image density is set. To complete. If the target value has not been reached, the same operation is repeated.

As another embodiment, a density setting pattern 2 output on recording paper to be set to a target image density
Place 7 image on the platen, the image density was measured in the same manner as described above, the density difference Δ by the measured value density D _M and a target density D _S
D is calculated, and the amount of toner in the developing device for correcting the calculated density difference ΔD is calculated from the relationship between the amount of developer in the developing device and the previously measured representative toner mixing ratio of the developer and the image density. If the amount of toner is large, the running time of the entire solid pattern is calculated as a target value of the indirect image density setting parameter in order to consume this amount of toner. When the amount of the toner is small, the toner is supplied without consuming the toner, and the traveling time when the vehicle travels is calculated as a target value of the indirect image density setting parameter. According to these running times, the vehicle is driven in each mode. After the running, the image density of the density setting pattern 27 output on the recording paper is measured again. If the image density is not the target image density, the same operation is performed again. The output V of the sensor 15 is stored as a control target value of the developing characteristic control device 22.

Therefore, compared with the conventional method, the operation can be simplified and the balance between the colors can be set with good precision and the image density can be set.

Next, another embodiment of the present invention will be described with reference to FIG. In the above embodiment, the control target value of the development characteristic γ is set. However, in the present embodiment, an image output apparatus that does not control the development characteristic γ and controls the toner mixture ratio of the developer to be constant. In this case, the image setting parameter is a development potential (contrast potential), and a target value of the development potential is set in the same manner as described above. The image parameters of the image processing device 6 and the laser writing device 7 can be set by other similar methods. Further, in the embodiment, one type of density setting pattern is used for each color. However, several types of tone patterns having different densities can be generated and the image density can be set over the entire tone range.

The output of the density setting pattern 27 on the recording paper in the embodiment of FIG. 1 is such that when the density is read by the IIT 5, the read value is saturated at a high density and the reading sensitivity is low, so that a halftone pattern is generally used. You. In many image output devices, pixels are formed by a dot image. In this case, when reading is performed by one pixel of the color CCD 4, the measured image density varies with and without dots. For this reason, when the patches of each color are read by the color CCD 4, pixels continuous in the main scanning direction are read as shown in FIG. 6A, and when the density of the patches is not uniform, as shown in FIG. The image density is calculated from the pixels at many places. Thus, since continuous pixels are read, it is possible to read image density with high accuracy.

Next, another embodiment of the present invention will be described. In the embodiment of FIG. 1, since the image density target value uses a predetermined value, even if the image density target value is set, the absolute image density variation can be accurately determined due to the characteristic variation of the CCD 4 and IIT5. occured. As a method for solving this problem, a color corresponding to the signal of the color CCD 4 and a reference chart having a predetermined density are previously stored in the CCD 4, II.
The method of measuring and calibrating at T5 is generally used, but it is necessary to control the color and density with high accuracy, and especially the color reference chart is expensive. A large number of reference charts are required for shipping image output elements and for maintenance. Therefore, an inexpensive one will be an achromatic gray, but if the density of each color is calibrated at the same density, the difference between the measured value of this density and the measured value at the target density of the image obtained from the image output element will be The calibration accuracy is high when they match, but the color with a large difference has low calibration accuracy.

According to the present invention, as shown in FIG. 7, the density of the reference chart 29 is 1.0 for the patch portion of three colors, 0.71 for the Y color portion, 0.91 for the M color portion, In the C color part:
13, a 1.19 gray patch is printed on the K color portion. This density corresponds to a value measured by an image reading device including CCD 4, IIT5 and the like when the density of each color of the output image of the density setting pattern 27 obtained from the average image output device is the target image density. It is a density that gives a value. Therefore, the same calibration accuracy can be obtained for each color.

Next, still another embodiment of the present invention will be described. In the embodiment shown in FIG. 1, the control target value is set. In the case of color, for example, it is a good color reproduction condition that three-color superposition of Y, M, and C is set to gray. To achieve this, it is necessary to set the Y, M, and C colors with high accuracy. However, if the density is set to a certain level, the gray balance of the three colors Y, M, C is important, and if the density can be set to a certain level in the embodiment of FIG. A control target value is set as a difference between the image density read again and the target image density, a value obtained by subtracting the difference between each color again from the average value of the differences between the Y, M, and C colors of the image density and the target image density.
As a result, each color is corrected on average, the amount of correction can be reduced, and gray balance can be quickly obtained.

As a modification, the target gray chromaticity L _S ^* , L _M ^* , a _M ^* , and b _M ^* measured from the three-color superimposed patches are used.
From the difference between a _S ^* and b _S ^* , ΔL ^* , Δa ^* , Δb ^* , Y, M, C
Approximate expression for calculating the amount of color correction

[0032]

(Equation 1)

It is also possible to obtain the difference from the target image density.

If only the gray balance is emphasized, it is possible to treat ΔL ^* = 0 in the above equation.
Further _{△ D Y, △ D M,} △ D the average value of _{C △ D Y, △ D M} ,
△ what was subtracted from the D _C, again _{△ D Y, △ D M,} △
It is also possible to D _C, thereby, similarly to the above correction amount is reduced, thereby shortening the setting time.

It should be noted that the present invention is not limited to the above embodiment, and various modifications can be made by those skilled in the art.
For example, in the above embodiment, the parameter setting for a color copying machine has been described, but the present invention is also applicable to a monochrome digital copying machine.

As is apparent from the above description, according to the present invention, the dispersion of the output characteristics of the toner amount detecting means is corrected, the operation is simple, the balance between the colors is good, and the accuracy is short, with high accuracy. The image density can be set.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of an image density setting method of the present invention.

FIG. 2 is a view for explaining a density setting pattern according to the present invention;

FIG. 3 is a diagram for explaining a method of setting a control target value from a value obtained when an image density is measured by a reading device according to the present invention.

FIG. 4 is a diagram for explaining control of development characteristics.

FIG. 5 is a view illustrating another embodiment of the present invention and illustrating a method of setting a development potential target value.

FIG. 6 is a diagram showing a read pixel portion of the reading device.

FIG. 7 is a diagram illustrating a reference chart for determining an image density target value of the reading device.

[Explanation of symbols]

1 ... platen glass, 2 ... lighting lamp, 3 ... lens,
4 ... Color CCD 5 ... Image reading device, 6 ... Image processing device, 7 ... Laser writing device 9 ... Photoconductor, 10 ... Scotron, 11 ... Electric potential sensor,
12: developing machine unit 13: multiple transfer device, 15: developing toner amount detection sensor
DESCRIPTION OF SYMBOLS 16 ... Paper tray 17 ... Fixing device, 20 ... Control target value setting device, 21 ... Development potential control device 22 ... Development characteristic control device, 23 ... Changeover switch, 26 ...
Built-in pattern storage device 27: density setting pattern, 29: reference chart

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI H04N 1/60 H04N 1/46 (72) Inventor Shunichiro Shishikura 2274 Hongo, Ebina-shi, Kanagawa Prefecture Fuji Xerox Co., Ltd. Ebina Office (72) Inventor Satoshi Tomita 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd.Ebina Office (72) Inventor Toru Yoshida 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd.Ebina Office (56) References JP-A-3-233576 (JP, A) JP-A-1-297682 (JP, A) JP-A-2-16874 (JP, A) JP-A-63-85661 (JP, A) JP-A-63-136064 (JP, A) JP-A 64-85762 (JP, A) JP-A-2-76760 (JP, A) JP-A 63-208369 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15 / 00 303 G03G 21/00 370-540 G03G 21/14 G03G 15/01-15/01 117 G03G 15/08-15/08 507 B41J 2/52-2/525 H04N 1/00-1/00 108 H04N 1/23-1/31 H04N 1/40- 1/409 H04N 1/46-1/64

Claims (1)

(57) [Claims] An image output device for outputting a density setting pattern, a toner consumption pattern, and a toner non-consumption pattern corresponding to a development color on a recording sheet, and an image for reading the image density of the density setting pattern output on the recording sheet A reading device, toner amount detecting means for detecting a toner amount of the developed density setting pattern, means for setting an image density target value and a corresponding toner amount target value, and detecting the toner amount target value. A developing characteristic control device that controls the amount of toner supplied to the developing device by comparing the
Means for correcting the toner amount target value based on the difference between the image density read by the image reading device and the image density target value, wherein the chromaticity is obtained from the gray of each color overlap except black, and the density of each color is obtained from this. Calculate the correction amount and determine the density of each color.
A value obtained by subtracting the average value of the correction amount from the density correction amount of each color is used as a difference from the image density target value, and a toner consumption pattern is generated when the read image density is higher than the image density target value. An image density setting method, wherein a toner non-consumption pattern is generated when the density is low, thereby setting the toner amount of the developed density setting pattern to a corrected toner amount target value.