JP2698094B2 - Color balance control method for multicolor image forming apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a color balance control method for a multicolor image forming apparatus such as a color electrophotographic copying machine and a printer.

2. Description of the Related Art In a multi-color image forming apparatus such as an electrophotographic copying machine and a printer, that is, a multi-color image forming apparatus that forms a full-color image, image stabilization, for example, the balance of three-color images of yellow, magenta, and cyan is stabilized. A color balance is required. In order to achieve this image stabilization task, a photovoltaic surface voltmeter is provided to stabilize the image by stabilizing the surface potential if necessary. And irradiate the toner layer with light to detect the reflected light,
There is known a method of controlling the toner concentration so that the developing ability is constant.

In such a conventional method, since the stabilization of the latent image of the photoconductor and the stabilization of the developing ability are performed separately, there has been a problem in that the color balance is shifted in multi-color image formation and the gray balance is lost.

Also, in the conventional method, since the photovoltaic surface electrometer is used in combination with the photoelectric detecting device, the device becomes complicated, and the cost increases accordingly.In addition, both the electrometer and the photoelectric detecting device are located near the developing device. Because of the arrangement, there is a problem that it is weak against dirt, and a large number of detection abnormalities are likely to occur.

In particular, the conventional method of controlling the image density by controlling the toner density based on the detection by the photoelectric sensor causes mechanical abnormalities such as toner scattering, filming, runaway of the sensor, and image abnormalities such as background contamination, carrier traces, and carrier adhesion. There was a disadvantage.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a color balance control method which solves the above-mentioned conventional problems, provides a good color balance even when the environment fluctuates, and does not cause a mechanical abnormality or the like.

In order to achieve the above object, the present invention corrects a toner density sensor output set value of a developing device for a high-density portion original, and sets a toner density tolerance preset in the developing device for at least one color toner. For variations outside the range, the amount of toner adhered to the other color is corrected based on the amount of toner adhered to that color as a reference.

The configuration and operation of the present invention will be described in detail based on an embodiment shown in the drawings.

In a multicolor electrophotographic copying machine 1 as an example of a multicolor image forming apparatus shown in FIG. 1, a document on a contact glass 2 is illuminated by an illumination device 3, and reflected light from the document is reflected by a mirror 4 and a lens. The image is projected on a photoconductor 8 as an image color-separated by an optical system 7 having a color separation filter 6 and a color separation filter 6.

The photoreceptor 8 is charged by the de-electrification device 9, the separated color image is formed by the optical system 7 to form an electrostatic latent image, and the image is developed by the developing device 10, and the toner image is transferred around the transfer drum 11. It is transferred to paper under the action of the transfer charger 12. For example, a light image of a blue component is projected on the photoconductor 8 by a color separation filter blue, and the latent image is visualized by a developer of a yellow developing unit 10a that is a complementary color of blue. A latent image of the separated color light image is formed on the body 8 by the green filter, visualized by the developer of the magenta developing unit 10b, the magenta toner image is superimposed on the yellow toner image, and further separated by the red filter. A latent image of the image is formed, visualized by the developer of the cyan developing section 10c, and is overlaid and transferred on the transfer paper. If necessary, a visual image formed by black toner development by the black developing unit 10d is overlaid and transferred.

The toner image is superimposed and transferred onto the transfer paper by three or four rotations of the transfer drum 8.

The transfer paper after the transfer is separated from the transfer drum 11 by the action of the separation charger 13 and the separation claw 14, is fixed by the fixing device 15, and is discharged to the discharge tray 16.

The photoreceptor 8 after the transfer is cleaned by the cleaning device 17 and is subjected to static elimination and charging by the static eliminator 9 to repeat the above-described image forming process.

If necessary, an editor may be provided on the contact glass to specify a region to enable partial copy, color conversion copy, color black composite copy, composite copy with another document, and the like.

In multi-color image formation, it is important that the balance of the separated color images, for example, the balance of the three color images of yellow, magenta, and cyan is stable and the color balance or the gray balance of the multi-color image, that is, the full-color image, is achieved. Becomes

When a multi-color image is formed by three-color images of yellow, magenta, and cyan, it is preferable to select the density ratio of each color as shown in FIG.

In FIG. 2, the horizontal axis represents the density of the document, and the vertical axis represents the image density. Curve A is the optimal image density curve for yellow, B is the aagenta, and C is the optimal image density curve for cyan.

FIG. 3 shows a quaternary chart of image formation using toner of an arbitrary color. The first quadrant shows the relationship between the document density (horizontal axis) and the copy density CD (vertical axis). Fluctuates in width. As a result, the copy density always fluctuates, so that yellow, magenta,
When the cyan colors change at the same ratio, the whole becomes darker or lighter. If the balance of each color is lost, the color tone will change. When the color tone change is a multi-color image, the copy quality is greatly deteriorated.

The second quadrant shows the relationship between copy density (vertical axis) and photoconductor potential SV (horizontal axis), and curves C, D, and E show fluctuations in developing ability. The fourth quadrant is photoconductor potential SV (vertical axis) and original density OD.
(Horizontal axis), and curves F, G, and H show fluctuations in the photoconductor potential.

A standard pattern, for example, a halftone pattern 19a and a high-density pattern 19b are provided at positions outside the image area of the contact glass as shown in FIG. 4, for example. A pattern image is formed on the photoconductor 8 by the optical device 7 under the conditions, and a toner image is formed by the developing device 10. The density of the toner image is detected by a photoelectric sensor 18 disposed downstream of the transfer position in an unfixed state, and the density is determined according to the density. Voltage output.

For the halftone pattern, for example, the original density OD (horizontal axis) and the toner adhesion amount mg as shown in FIG.
The relationship between / cm ² (vertical axis), toner adhesion amount (vertical axis), and photoelectric sensor output V (horizontal axis) is obtained. Curves A and B are characteristic curves showing the relationship between the original density and the toner adhesion amount, respectively.
Curve C is a characteristic curve showing the relationship between the toner adhesion amount and the photoelectric sensor output. Since all the characteristic curves are almost the same without any difference between the yellow, magenta, and cyan colors, any one curve can be used. The color is also explained.

FIG. 6 similarly shows the relationship for the high density pattern.

The change in the amount of toner adhered to the original density, that is, the change in image density occurs when the photoconductor deteriorates due to fatigue of the photoconductor or the like.

For example, as shown in curve A, the halftone pattern density
When the photoelectric sensor output V ₀ is 2 V with respect to 0.4, the variation becomes as shown by a curve B due to the fluctuation, and the photoelectric sensor output V ₁ becomes 1.7 V.
become.

When there is such a density fluctuation, the exposure control circuit shown in FIG. 4 controls the exposure amount to be large so that the output of 1.7 V of the photoelectric sensor becomes a predetermined value of 2 V, and the curve B
Is corrected to become the curve A. This correction is performed for each of yellow, magenta, and cyan. As a result, it is possible to control the density of the halftone to a certain color balance.

In the high-density part, the color developer whose color developer is different from yellow, magenta, and cyan has different characteristics due to aging and environmental change. In the case of full color, when a change in the amount of charge occurs, the color changes unless each color has the same tendency.

In FIG. 6, when the characteristic changes from the curve D to the curve E for a certain color, the output of the photoelectric sensor changes from V ₀ = 0.7 V to V ₁ = 1.5 V in the example of the original density of 1.0. It is possible to control the amount of exposure to correct the photoelectric sensor output from 1.5 V to 0.7 V in the same way as in the case of halftone, but in this case, the tendency of change is not the same for each color. Control cannot keep the color balance constant. Therefore, the developing units 10a, 10b of the respective colors of the developing device 10,
Toner density sensors (for example, magnetic permeability sensors) 19a, 19b, 19c, 1 provided for toner replenishment control in 10c and 10d.
The set value of 9d is changed and corrected according to the output from the photoelectric sensor 18. The control flow for correcting the magnetic permeability sensor 19 is as shown in FIG.

As shown in FIG. 8, there is a relationship between the toner concentration (horizontal axis), the toner adhesion amount mg / cm ² (vertical axis lower part), and the magnetic permeability (toner density) sensor output V (horizontal axis). The toner adhesion amount can be corrected by correcting the output of the magnetic permeability sensor by the output of the photoelectric sensor based on the above. That is, there is a relationship as shown by a curve G between the toner density of the developing device and the output of the toner density sensor, and a relationship between the toner density and the toner adhesion amount is shown by a curve H. There is an allowable range of the toner density determined in consideration of toner scattering or the like in the developing device, and toner is supplied in the developing device so that the density is within the range.

As shown in FIG. 6, when the toner adhesion amount is 0.8 mg / cm ² with respect to the original density of 1.0, the output of the toner density sensor corresponding to the toner adhesion amount is about 1.25 V in FIG. . However, when the characteristic of the toner adhesion amount is changed to the state shown by the curve J in FIG. 8, the toner adhesion amount is 6.
In order to obtain the target toner adhesion amount of 7 mg / cm ² , it is necessary to use the toner in a state where the toner concentration exceeds a predetermined range, otherwise the necessary toner adhesion amount cannot be secured.

If one of the yellow, magenta, and cyan colors is in the state shown by the curve J in FIG. 8, and the remaining colors are in the state where the target toner adhesion amount can be obtained within the toner density allowable range, the toner The balance of the amount of adhesion is lost depending on the color. In order to eliminate this loss of balance, if the toner adhesion amount of yellow, magenta, and cyan fluctuates until the correction of one or more colors exceeds the allowable range of toner density, the color that has shifted the most within the allowable range of toner density Is corrected so that the color balance can be obtained based on. That is, for example, the adhesion amount of yellow toner changes to curve J, and magenta and cyan
When the value remains, the set value of the toner density sensor is corrected so that the toner density of the developing device is increased by a signal indicating that the density of the yellow image is lower than the output of the photoelectric sensor. However, even when the toner concentration reaches the allowable range of 7%, the toner concentration does not rise to 0.7 mg / cm ² or more. For example, if yellow, magenta, and cyan have the same adhesion amount, in the case of a toner having a color balance with a good color balance, the toner adhesion amount is 0.7 mg / cm in a magenta and cyan developing device.
^The toner concentration is corrected to about 3.3 wt% by the curve H so that the value becomes ² . For this purpose, the output of the toner density sensor (magnetic permeability sensor) shown in FIG. 8 is corrected and set to the value of B, for example, 1.5V. In this case, the output of the magnetic permeability sensor of the yellow developing device is corrected and set to the value of A, for example, 0.3V. In the case of a toner having a degree of coloring that achieves color balance with a different ratio of the amount of adhesion of each color, the correction value may be changed according to the ratio,
The above idea is the same.

The output of the magnetic permeability sensor can be corrected in exactly the same way in the case where the density of any of the above-mentioned colors becomes darker, as opposed to the case where the density becomes darker. In this case, the darkest toner density may be set to the lower limit of the toner density allowable range.

The color balance of the high-density portion can be kept constant as described above by always adjusting it to one reference amount of adhesion, that is, the image density or the output of the photoelectric sensor. If the amount of toner cannot be fixed to the reference amount due to toner concentration fluctuations due to toner fluctuations or photoconductor potential fluctuations, use a toner concentration range that does not cause abnormal phenomena such as toner scattering, filming, carrier streaks at low concentration, and carrier adhesion. When one of the colors becomes too light, the color balance is adjusted in a place where the whole color is light. If either of them becomes too dark, a color image can be obtained under the best conditions as an image or a machine by adjusting the color balance at a dark level as a whole.

Effects The present invention enables prevention of mechanical abnormalities that cannot be obtained only by toner concentration control using a photoelectric sensor, such as abnormal conditions such as toner scattering, filming, and sensor runaway, and image abnormalities such as background contamination, carrier ear marks, and carrier adhesion. became.

The present invention makes it possible to stabilize the color balance under all conditions.

[Brief description of the drawings]

1 is a schematic explanatory view of a color electrophotographic copying machine, FIG. 2 is an optimum density characteristic curve, FIG. 3 is a quaternary chart for image formation, and FIG. 4 is a block diagram showing a control system of the copying apparatus of FIG. FIG. 5, FIG. 5 and FIG. 6 are characteristic curves showing the relationship between the original density and the photoelectric sensor output, and FIG.
FIG. 6 is a diagram relating to the high density portion, FIG. 7 is a control flowchart, and FIG. 8 is a diagram showing the relationship between the toner adhesion amount and the output of the toner density sensor. 8 Photoconductor, 10 Developing device 18 Photoelectric sensor, 19 Magnetic permeability sensor

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yuji Sawai 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company, Ltd. (72) Inventor Hideo Yu 1-3-6, Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (56) References JP-A-63-95471 (JP, A) JP-A-62-35382 (JP, A) JP-A-61-248068 (JP, A) JP-A-1-281471 ( JP, A)

Claims (1)

(57) [Claims] A plurality of photosensors each having a light emitting element and a light receiving element for detecting a toner adhesion amount of an unfixed toner image on a photoconductor, and a toner density sensor for detecting an agent density in a developing device. A multi-color image forming apparatus that forms a multi-color image by superimposing toner images of different colors, a toner density sensor output setting value of a developing device according to a change in a detection value of the amount of toner attached to a high density portion original by the photoelectric sensor. And at least one
For a variation of the toner of one color that deviates from a preset toner density allowable range in the developing device, the adhesion amount of the toner of the other color is also corrected based on the adhesion amount of the toner of that color. A color balance control method for a multicolor image forming apparatus.