JP2698095B2 - 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.

Particularly, in the conventional method of controlling the image density by controlling the toner density by detection by the photoelectric sensor, mechanical abnormalities such as toner scattering, filming, runaway of the sensor, and image abnormalities such as background dirt, carrier traces, carrier adhesion, etc. are caused. 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 controls the color balance of the halftone portion by controlling the exposure amount so that the detection value of the toner adhesion amount to the halftone portion original by the photoelectric sensor is adjusted to the reference density of each color. If the amount of toner adhered to the original in the high-density area fluctuates vertically with respect to the reference value depending on the color, adjust the toner density of the developing device to the reference value. When the toner density sensor fluctuates downward, the toner density sensor of each color has the same amount as the correction value of the output of the toner density sensor of the developing device within the allowable range of the toner density according to the detection value of the representative one color by the photoelectric sensor. Is corrected.

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 photoreceptor 8 as an image color-separated by an optical system 7 having a color separation filter 5 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 which is a complementary color of blue. A latent image of a separated color light image is formed on the body 8 by a green filter, visualized by a developer in a magenta developing unit 10b, a magenta toner image is superimposed on a yellow toner image, and further separated by a 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 toner 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 an important issue 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, that is, 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 magenta, 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), and the curve between A and B from the high density area to the low density area due to the original capacity and displacement of the photoconductor potential. Fluctuates in width. As a result, the copy density always fluctuates, and 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.

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

In the case of the gray balance control of the halftone portion, for example, the halftone pattern density of 0.
Those photoelectric sensor output V ₀ is 2V is for four, become as curve B image density due to fatigue of the photosensitive member is varied, the photoelectric sensor output V ₁ is made to 1.7.

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. Further, the developing conditions of the developing device are corrected as needed. 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, a reference characteristic for each color is shown by a curve D,
Characteristics of yellow curve E ₁ as an example that caused a reduction in density due to environmental fluctuation, the characteristics of cyan curve E _2, showing an example in which characteristics of magenta is changed to a curve E _3. Conversely, the density may increase, but the characteristic of one example of cyan color is a curve
Represented by E _4. The description of other colors is omitted. Curves E _{1 to} E ₃
As shown by, the respective color materials of yellow, magenta, and cyan are shifted in the same direction, that is, in a direction in which the density decreases, and the shift amount is often within an allowable range.
In this case, for example, the center curve of the three colors is taken, that is, the output of the photoelectric sensor of the center curve is selected, and the output of the photoelectric sensor is selected as a representative of the combination of the three colors. The density corrects the same amount of toner density. Figure 6 in the example chosen a characteristic curve E ₂ when the total concentration was reduced, those in the example of the original density of 1.0 the output of the photoelectric sensor at a reference characteristic curve D is V ₀ = 0.7 V, the characteristic curve E ₂ the change in the order of V ₁ = 1.2V. The curve E ₄ is when the concentration rises, V ₂ = 0.5 in the example of the original concentration 1.0
It changes to about V.

Looking at the black balance in the high density area, when the density decreases, the exposure amount is controlled to increase the photoelectric sensor output from 1.2V.
It is possible to perform the correction control so that the voltage becomes 0.7 V as in the case of the halftone. However, in this case, since the tendency of change is not the same for each color, the color balance cannot be kept constant by the exposure control. Then, the set values of the toner density sensors (eg, magnetic permeability sensors) 19a, 19b, 19c, and 19d provided for the toner supply control in the developing units 10a, 10b, 10c, and 10d of the respective colors of the developing device 10 are determined by the photoelectric sensor 18. Change correction is performed according to the output. This permeability sensor 19
FIG. 7 shows a control flow for the correction of.

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 1.5 V in FIG. . However, the toner adhesion amount is, for example, 0.6 m
if it becomes lower than the target, as the g / cm ^2, for example, characteristics are changed to the state shown by the curve J ₁ of Figure 8, the toner concentration sensor output is 1V. In this case, if the toner density of the developing device is changed from 4% of the reference case to 5.6%, the toner adhesion amount of the pattern becomes 0.8 mg / cm ² , and the predetermined density is maintained. Therefore, the output of the toner density sensor is corrected, and the correction is set to 1.5 V from the reference 1.5 V, so that the toner of the developing device is corrected from 4% to 5.6%. Since almost the same correction is performed for yellow and aagenta, color reproduction is sufficient. Yellow, magenta,
Compensation is easier and less erroneous than compensating by comparing all of cyan with the reference. Generally, this method makes it possible to perform correction at a practical level from the toner characteristics.

On the other hand, when the toner adhesion amount becomes darker than the target, for example, 0.9 mg / cm ² , for example, the characteristics have changed to the state shown by the curve J ₂ in FIG. 8, and the output of the toner density sensor is 1.
8V. Therefore, the output of the toner density sensor is corrected, and the correction is set to 1.5 V from the standard 1.5 V. At this time, the toner density of the corresponding developing device is 3.4%, and the toner adhesion amount is approximately the same as 0.8 mg / cm ² . Yellow and magenta are corrected in substantially the same manner.

Although the characteristics of color developers are not the same for each color,
Even if the amount of change in the characteristic of one representative color is detected as described above and each color, that is, yellow, magenta, and cyan are corrected by the same amount, a stable image that does not cause any problem in practical use has a black color. Color balance can be obtained.

When the density of each color varies up and down with respect to the above reference characteristics, the output of the toner density sensor is adjusted to the reference value.

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.

According to the present invention, the image density can be stabilized under all conditions, and an image with good color balance can be obtained.

[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 photoreceptor, 10 developing device, 18 photoelectric sensor, 19 magnetic permeability sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication location H04N 1/23 101 H04N 1/40 D 1/46 1/46 Z 1/60 (72) Inventor Yuji Sawai 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Hideo Yu 1-3-6, Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (56) References JP JP-A-61-248068 (JP, A) JP-A-1-281470 (JP, A) JP-A-63-95471 (JP, A) JP-A-62-35382 (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. In a multicolor image forming apparatus that forms a multicolor image by superimposing toner images of different colors, a color balance control of a halftone portion is performed by using a detection value of the toner adhesion amount to a halftone portion original by the photoelectric sensor as a reference density of each color. If the amount of toner adhered to the original in the high-density area fluctuates above and below the reference value depending on the color, the toner density of the developing device is adjusted to the reference value. When each color fluctuates above or below the reference value, the toner density allowable range corresponding to the value detected by the photoelectric sensor for one representative color. Color balance control method of the multi-color image forming apparatus and correcting by the correction value the same amount of output of the toner density sensor in the developing device the output of each color toner density sensor in.