JP2001109224A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep the tone reproduction of each color constant regardless of the sensitivity difference of a photoreceptor drum provided corresponding to each color in a color image forming device. SOLUTION: This device is equipped with image stations 1a to 1d provided with developing means 4a to 4d corresponding to developing colors, exposure means 6a to 6d forming a latent image on the photoreceptor drums 2a to 2d, a transfer means 7 forming a synthesized image on an intermediate transfer belt 12 by superposing respective color toner images, a test pattern generating means 13 forming a test pattern having different density each other in every color on the belt 12, a toner density detection means 14 detecting the density of the test pattern, an exposure intensity correction means 15 individually correcting the exposure power of the exposure means 6a to 6d, and a developing bias correction means 16 individually correcting the developing bias value applied to the developing means 4a to 4d based on the detected result from the detection means 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus based on an electrophotographic technique, and more particularly to a technique which is effective when applied to maintaining gradation reproducibility of each color.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus employing an electrophotographic technique, the surface of a photosensitive member as an image carrier is uniformly charged by a charger, and the charged photosensitive member is exposed to light corresponding to image information. Irradiation is performed to form a latent image, the latent image is developed by a developing device, and the developed toner image is transferred to a sheet material or the like to form an image.

On the other hand, with the colorization of images, a plurality of image stations for executing the above-described image forming processes are provided, and each color image of a cyan image, a magenta image, a yellow image, and preferably a black image is carried on each image station. A tandem type color image forming apparatus that forms a full-color image by forming a full-color image by superposing and transferring each color image onto a sheet material at a transfer position of each image carrier is also proposed.

[0004] Such a tandem type color image forming apparatus has an image forming section for each color, which is advantageous for speeding up.

[0005]

However, in the above-described conventional color image forming apparatus, since different photoconductors are used for each color, the gradation reproducibility is determined by the difference in the sensitivity of the photoconductor between the colors. And the color reproducibility of the output image deteriorated.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a color image forming apparatus capable of maintaining a constant tone reproducibility of each color regardless of the sensitivity difference of a photosensitive member provided for each color. And

[0007]

In order to solve this problem, a color image forming apparatus according to the present invention develops a photosensitive member on which a latent image is formed and a latent image formed on the photosensitive member as a toner image. A plurality of image stations provided with developing means corresponding to the developing colors, a plurality of exposing means for irradiating light to each photoconductor to form a latent image, and a plurality of image stations for each color formed by the plurality of image stations. A transfer unit that sequentially superimposes and transfers the toner image onto the image carrier to form a composite image on the image carrier, and generates a test pattern on a plurality of exposure units, and develops the image carrier via a developing unit and a photoconductor. A test pattern generating means for forming test patterns having different densities for each color, a toner density detecting means for detecting the density of the test pattern, and a toner density detecting means for detecting the density of the test pattern. Exposure intensity correction means for individually correcting the exposure power irradiated by each exposure means, and development bias for individually correcting the development bias value applied to each development means based on the detection result from the toner density detection means And a correcting means.

[0008] This makes it possible to keep the gradation reproducibility of each color constant irrespective of the sensitivity difference of the photoconductor provided for each color.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to a first aspect of the present invention, there is provided a photosensitive member on which a latent image is formed and a developing means for developing the latent image formed on the photosensitive member as a toner image into a developing color. A plurality of image stations provided correspondingly, a plurality of exposure means for irradiating each photoconductor with light to form a latent image, and a toner image of each color formed by the plurality of image stations on an image carrier. A transfer unit that sequentially superimposes and transfers to form a composite image on the image carrier, and generates a test pattern on a plurality of exposure units. A test pattern generating means for forming test patterns having different densities; a toner density detecting means for detecting the density of the test pattern; A color image forming apparatus comprising: an exposure intensity correcting unit for individually correcting the developing bias; and a developing bias correcting unit for individually correcting a developing bias value applied to each developing unit based on a detection result from the toner density detecting unit. Since the exposure intensity and development bias of each color are individually corrected based on the toner density of each color, the gradation reproducibility of each color can be improved regardless of the sensitivity difference of the photoconductor provided for each color. It has the effect that it can be kept constant.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. In these drawings, the same members are denoted by the same reference numerals, and duplicate description is omitted.

FIG. 1 is a schematic diagram showing a configuration of a color image forming apparatus according to an embodiment of the present invention, and FIG. 2 is a flowchart showing operations of exposure intensity correction and developing bias correction in the color image forming apparatus of FIG. 3 is an explanatory view showing an exposure correction test pattern formed on the intermediate transfer belt of the color image forming apparatus of FIG. 1; FIG. 4 is a graph showing the result of detecting the exposure correction test pattern of FIG. FIG. 5 is an explanatory diagram showing a development correction test pattern formed on the intermediate transfer belt of the color image forming apparatus of FIG. 1, and FIG. 6 is a graph showing a result of detecting the development correction test pattern of FIG. It is.

First, a process for obtaining a color image will be described with reference to FIG.
This will be described with reference to FIG.

In FIG. 1, the color image forming apparatus
One image station 1a, 1b, 1c, 1d is arranged, and each image station 1a, 1b, 1c, 1d is a photosensitive drum (photosensitive member) 2a, 2b, 2 as an image carrier.
c, 2d, around which charging means 3a, 3b, 3c, 3d for uniformly charging the surfaces of the photosensitive drums 2a, 2b, 2c, 2d, and visualizing the electrostatic latent image Developing means 4a, 4b, 4c, 4d, cleaning means 5a, 5b, 5c, 5d for removing residual toner, and light corresponding to image information to the respective photosensitive drums 2a, 2b, 2c, 2
exposure means 6a, 6b, 6c,
6d, transfer units 8a, 8b, 8 for transferring a toner image to an intermediate transfer belt (image carrier) 12 constituting the transfer unit 7.
c and 8d are arranged respectively.

Here, the image stations 1a, 1b, 1
In c and 1d, a yellow image, a magenta image, a cyan image, and a black image are formed, respectively.
From b, 6c and 6d, a yellow image, a magenta image,
Exposure lights 9a, 9b, 9c and 9d, which are scanning lights corresponding to the cyan image and the black image, are output.

Each of the image stations 1a, 1b, 1c, 1
d, the photosensitive drums 2a, 2b, 2c,
An endless belt-shaped intermediate transfer belt 12 supported by rollers 10 and 11 is disposed below 2d, and rotates in the direction of arrow A.

Further, a toner density detecting means 14 for detecting the toner density of the test pattern from the test pattern generating means 13 is disposed facing the intermediate transfer belt 12. An exposure intensity correction unit 15 for correcting the exposure power of each color based on the result and a development bias correction unit 16 for correcting the development bias value of each color based on the detection result from the toner density detection unit 14 are provided. The exposure means 6
Reference numerals a, 6b, 6c, and 6d output the exposure intensity based on the correction value from the exposure intensity correction unit 15, and the developing units 4a, 4b, and 4d output the exposure intensity.
c and 4d apply a developing bias based on the correction value from the developing bias correcting means 16.

The sheet material 18 stored in the sheet cassette 17 is fed by a sheet feed roller 19, and is discharged to a sheet discharge tray (not shown) via a sheet material transfer roller 20 and a fixing unit 21.

In the color image forming apparatus having the above configuration, first, in the image station 1d, the charging means 3d
A latent image of a black component color, which is image data, is formed on the photosensitive drum 2d by a known electrophotographic process means using the exposure means 6d and the like. Thereafter, the developing means 4d
Is visualized as a black toner image by a developing material having a black toner in the intermediate transfer belt 1 by the transfer device 8d.
2, a black toner image is transferred.

On the other hand, while the black toner image is being transferred to the intermediate transfer belt 12, a latent image of a cyan component color is formed at the image station 1c, and the cyan toner image of the cyan toner is visualized by the developing means 4c. Then, the image is transferred by the transfer device 8 c and is superimposed on the black toner image previously transferred on the intermediate transfer belt 12.

Thereafter, image formation is performed in the same manner for the magenta toner image and the yellow toner image. When the superposition of the four color toner images on the intermediate transfer belt 12 is completed, the paper feed cassette The toner images of four colors are collectively transferred and conveyed by a sheet material transfer roller 20 onto a sheet material 18 such as paper fed from the fixing device 2.
1 to form a full-color image on the sheet material 18.

Each of the photosensitive drums 2a, 2b, 2c, and 2d, to which the transfer has been completed, is connected to a cleaning unit 5a,
At 5b, 5c, and 5d, the residual toner is removed, and the printing operation is completed in preparation for the subsequent image formation.

Although a color image can be obtained as described above, in a color image forming apparatus, between the photosensitive drums 2a, 2b, 2c, 2d in the image stations 1a, 1b, 1c, 1d. Has a sensitivity difference, which causes a difference in gradation reproducibility (hereinafter, referred to as “γ characteristic”) of each color. Therefore, when the power is turned on or each image station 1
The gamma correction operation by exposure intensity correction and development bias correction is performed at the time of replacement of a, 1b, 1c, 1d or every time the temperature / humidity changes in the apparatus.

Here, as shown in FIG. 2, the γ correction operation is executed in six steps, namely, an exposure correction test pattern generation step (first test pattern generation step) and an exposure correction test pattern density detection step ( First test pattern density detection step), exposure intensity correction step, development correction test pattern generation step (second test pattern generation step), development correction test pattern density detection step (second test pattern density detection step), development bias correction step And the six steps. Hereinafter, these steps will be sequentially described with reference to the drawings.

(Exposure Correction Test Pattern Generation Step) FIG.
3 shows an exposure correction test pattern formed on the intermediate transfer belt 12. Table 1 shows the image forming conditions of the exposure correction test pattern.

[0025]

[Table 1]

As shown in FIG. 3, the exposure correction test pattern generated from the test pattern generating means 13 is composed of four pattern groups for each image station.
Exposure correction test patterns 22, 23, 24 in image station 1d (black), image station 1c
(Cyan) exposure correction test patterns 25 and 2
6, 27, exposure correction test patterns 28, 29, 30 in the image station 1b (magenta) and exposure correction test patterns 31, 32, 33 in the image station 1a (yellow). Each of the exposure correction test patterns 22 to 33 includes three blocks 22a to 22c, 23a to 23c,.
3c.

Next, the image station 1d (black)
Will be described in more detail with reference to the exposure correction test pattern in FIG.

Exposure correction test patterns 22, 23, and 24 correspond to the image station 1d (black), and the exposure correction test patterns 22, 23, and 24 have exposure intensities of 0.9, 1.0,. It is 1 μJ / cm ² . Each exposure correction test pattern further includes a first pattern 22a, 23a, 24a, a second pattern 22b, 23b, 24b, and a third pattern 22c, 23c, 24c.
a, 23a and 24a are 30% image data, the second patterns 22b, 23b and 24b are 50% image data, and the third patterns 22c, 23c and 24c are 70% image data.

The process of generating the exposure correction test pattern in the above configuration will be described.

First, from the test pattern generating means 13 shown in FIG. 1, the three exposure correction test patterns 22, 23 and 24 shown in FIG. A latent image is formed on the photoreceptor 2d in the image station 1d, visualized by the developing unit 4d, and the black toner image is transferred to the intermediate transfer belt 12 in the transfer unit 7. At this time, the developing bias value applied to the developing unit 4d is constant.

On the other hand, while the black toner image is being transferred to the intermediate transfer belt 12, in the image station 1c, a cyan image is formed from the test pattern generating means 13 shown in FIG. 1 via the exposure means 6c. The latent images of the three exposure correction test patterns 25, 26, and 27 shown in FIG.
The toner image is formed on the photoreceptor 2c in the inside, is visualized by the developing means 4c, and the cyan toner image is transferred to the intermediate transfer belt 12.

Thereafter, image formation is similarly performed for the magenta toner image and the yellow toner image, and the exposure correction test patterns 22 to 3 shown in FIG.
3 is formed.

(Exposure Detection Test Pattern Density Detecting Step) The exposure correction test patterns 22 to 33 formed on the intermediate transfer belt 12 move in the direction of arrow A as the intermediate transfer belt 12 moves, as shown in FIG. Then, the toner density of each of the exposure correction test patterns 22 to 33 is detected by the toner density detecting means 14. Specifically, the toner adhesion amount per unit area is optically detected by the toner concentration detection unit 14.

(Exposure intensity correction step) The exposure intensity is corrected based on the toner density detection result of the toner density detection means 14. Here, the correction of the exposure intensity corresponding to black will be described.

FIG. 4 shows the exposure correction test patterns 22 and 2.
3 and 24 are the results of detection by the toner density detecting means 14.

As shown in FIG.
The increase rate (gradient) of the toner adhesion amount per unit area in the range of 0% can be understood. From this, an exposure intensity having a predetermined inclination is selected and used as an exposure intensity in a black image at the time of actual image formation. Here, when the predetermined inclination is not obtained in the range of the exposure intensity of 0.9 to 1.1, the range of the exposure intensity is widened, and the exposure correction test patterns 22 to 33 are again created, detected, and corrected. I do. Then, the same processing as the correction of the exposure intensity corresponding to black is performed for cyan, magenta, and yellow.

By correcting the exposure intensity as described above, it is possible to make the rate of increase in the amount of toner adhered per unit area of each color the same.

In the exposure intensity correction described above, the exposure intensity of the exposure correction test patterns 22 to 33 is 0.9 to 0.9.
The number of steps is not limited to the range of 1.1.
It is not limited to one. Further, the image data of the exposure correction test patterns 22 to 33 is not limited to the range of 30 to 70%. Further, the exposure intensity may be estimated from the detection result of one exposure correction test pattern so as to have a predetermined inclination.

(Development Correction Test Pattern Generation Step) FIG.
2 shows a development correction test pattern formed on the intermediate transfer belt. Table 2 shows the image forming conditions of the development correction test pattern.

[0040]

[Table 2]

As shown in FIG. 5, the development correction test pattern generated by the test pattern generation means 13 is composed of four pattern groups for each image station.
Development correction test pattern 34 in image station 1d (black), development correction test pattern 35 in image station 1c (cyan), and development correction test pattern 3 in image station 1b (magenta).
6, a development correction test pattern 37 in the image station 1a (yellow). Each of the development correction patterns 34 to 37 has three blocks 3 respectively.
4a to 34c, 35a to 35c, 36a to 3c, 37a
To 37c.

Next, the image station 1d (black)
This will be described in more detail with reference to the development correction test pattern in FIG.

The exposure correction test pattern 34 corresponding to the image station 1d (black) has an exposure intensity corrected by the above-described exposure correction, and has an image data of 100.
%. Furthermore, the development correction test pattern 34 includes a first pattern 34a and a second pattern 34a.
b, the third pattern 34c, the first pattern has a developing bias of -200V, and the second pattern has a developing bias of -250V.
V and the third pattern is -300V.

The process of generating a development correction test pattern in the above configuration will be described.

First, the latent image of the development correction test pattern 34 shown in FIG. 5 is applied from the test pattern generating means 13 shown in FIG. 1 to the image station 1d where a black image is formed via the exposure means 6d. Is formed on the photoreceptor 2d, and is visualized by the developing means 4d, and the black toner image is transferred to the intermediate transfer belt 12 in the transfer means 7. At this time, the exposure intensity is constant at the exposure intensity corrected by the above-described exposure correction.

On the other hand, while the black toner image is being transferred to the intermediate transfer belt 12, the image station 1c receives an image from the test pattern generating means 13 shown in FIG. The development correction test pattern 35 shown in FIG.
Is formed on the photoreceptor 2c in the image station 1c, and is visualized by the developing means 4c, so that the intermediate transfer belt 1
2, a cyan toner image is transferred.

Thereafter, image formation is performed in the same manner for the magenta toner image and the yellow toner image, and the exposure correction test patterns 34 to 3 shown in FIG.
7 is formed.

(Development Correction Test Pattern Density Detecting Step) The exposure correction test patterns 34 to 37 formed on the intermediate transfer belt 12 move along with the movement of the intermediate transfer belt 12 in the direction of arrow A as shown in FIG. Then, the toner density of each of the development correction test patterns 34 to 37 is detected by the toner density detecting means 14. Specifically, the toner adhesion amount per unit area is optically detected by the toner concentration detection unit 14.

(Development Bias Correction Step) Based on the toner density detection result of the toner density detection means 14, the development bias is corrected. Here, correction of the developing bias corresponding to black will be described.

FIG. 6 shows the result of detection of the development correction test pattern 34 by the toner density detecting means 14.

As shown in FIG. 6, the developing bias is -20.
The increase rate (slope) of the toner adhesion amount per unit area in the range of 0 to -300 V can be seen. From this, the developing bias value that can obtain the toner adhesion amount corresponding to the maximum density is calculated,
This is a developing bias value in a black image at the time of actual image formation. Here, the developing bias is -200 to -300.
If the predetermined maximum density cannot be obtained in the range of V, the range of the developing bias is expanded, and the creation, detection, and developing bias correction of the development correction test patterns 34 to 37 are performed again. Then, the same processing as the correction of the developing bias corresponding to black is performed for cyan, magenta, and yellow.

By correcting the developing bias as described above, the maximum density of each color can be made the same, and the gradation reproducibility of each color can be kept constant.

As described above, according to the color image forming apparatus of the present embodiment, since the exposure intensity and the developing bias of each color are individually corrected based on the toner density of each color, they are provided corresponding to each color. Irrespective of the difference in sensitivity of the photoconductors, the gradation reproducibility of each color can be kept constant. Thus, an image with good color reproducibility can be obtained.

In this embodiment, the color image forming apparatus in which the transfer and conveyance of the toner image is performed by the intermediate transfer belt has been described. It can also be applied to an image forming apparatus.

[0055]

As described above, according to the present invention, since the exposure intensity and the developing bias of each color are individually corrected based on the toner density of each color, the photoconductor provided for each color is corrected. There is an effective effect that the gradation reproducibility of each color can be kept constant irrespective of the sensitivity difference.

As a result, an effective effect that an image with good color reproducibility can be obtained can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration of a color image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a flowchart showing operations of exposure intensity correction and development bias correction in the color image forming apparatus of FIG.

3 is an explanatory diagram showing an exposure correction test pattern formed on an intermediate transfer belt of the color image forming apparatus of FIG.

4 is a graph showing a result of detecting the exposure correction test pattern of FIG. 3 by a toner density detecting unit.

5 is an explanatory diagram illustrating a development correction test pattern formed on an intermediate transfer belt of the color image forming apparatus of FIG. 1;

FIG. 6 is a graph showing a result of detecting the development correction test pattern of FIG. 5 by a toner density detection unit.

[Explanation of symbols]

 1a, 1b, 1c, 1d Image station 2a, 2b, 2c, 2d Photoconductor drum (photoconductor) 3a, 3b, 3c, 3d Charging means 4a, 4b, 4c, 4d Developing means 6a, 6b, 6c, 6d Exposure means 7 Transfer Means 12 Intermediate Transfer Belt (Image Carrier) 13 Test Pattern Generation Means 14 Toner Density Detection Means 15 Exposure Intensity Correction Means 16 Developing Bias Correction Means

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G03G 15/06 101 G03G 15/04 120 15/08 115 F term (reference) 2H027 DA10 EA02 EA05 EB04 EC04 EC06 2H030 AA03 AB02 BB13 BB34 BB36 BB42 2H073 BA28 CA22 2H076 DA07 EA01 2H077 DA05 DA47 DA63 DB08

Claims (1)

[Claims] A plurality of image stations provided with a photoreceptor on which a latent image is formed and a developing unit for developing the latent image formed on the photoreceptor as a toner image corresponding to a development color; A plurality of exposure means for irradiating each of the photoconductors with light to form a latent image; and transferring and transferring the toner images of each color formed by the plurality of image stations on an image carrier in order. Transfer means for forming a composite image on a body, test patterns generated on the plurality of exposure means, and test patterns having different densities for each color on the image carrier via the developing means and the photoreceptor. A test pattern generating means for forming the test pattern; a toner density detecting means for detecting the density of the test pattern; and each of the exposing means illuminating based on a detection result from the toner density detecting means. Exposure intensity correcting means for individually correcting the exposure power to be applied, and developing bias correcting means for individually correcting a developing bias value applied to each of the developing means based on a detection result from the toner density detecting means. A color image forming apparatus, comprising: