JP2000162834A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid unevenness in color due to unevenness in sensitivity of a photoreceptor by measuring unevenness in sensitivity of the photoreceptor at the time of non-image formation and compensating exposure at each position during rotation of the photoreceptor, according to the measured result. SOLUTION: In this color image forming device, 4 units of image-forming parts are placed side by side in the direction of a paper that is carried, and a full color image is formed by having the toner images of 4 colors superimposed on stransfer paper. The transfer paper is separated from a transfer belt 20 by a separating mechanism, and then the toner is fixed at a fixing device. Since each color image is formed by different photoreceptor 1, unevenness in density due to the unevenness in the sensitivity of each photoreceptor 1 becomes the unevenness in color. Therefore, marks for position detection and position detection holes are provided independently at the edge part of each photoreceptor 1, the rotated position of the photoreceptor 1 is detected by utilizing a reflection type sensor or transmission type sensor, and the unevenness in sensitivity of one rotation of the photoreceptor 1 at the time of non-image formation is measured. Compensation is carried out independently for each color concerning exposure of a laser diode by a controller 4 so as to correct to the rotated position of the photoreceptor.

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 such as a printer, a facsimile, a copying machine or the like, and particularly to a color image forming apparatus using an electrophotographic system. The present invention relates to a configuration for correcting a process condition.

[0002]

2. Description of the Related Art In an image forming apparatus for forming an image using toner, there is a possibility that the image quality is deteriorated due to deterioration of an image forming body (photoreceptor or intermediate transfer body), an exposing device, a charging device, a developer and the like. Therefore, the image density is corrected to prevent this. The deteriorated state of the image forming body or the like is determined by forming a toner image on the image forming body and comparing the density of the toner image with the density in the initial state. Generally, the toner image density is detected by an optical sensor. However, the optical sensor has a problem that the sensor output is affected by the base image forming body when detecting the toner image density. Therefore, conventionally, the light output of the image forming body is detected to correct the sensor output at the time of detecting the toner image density.

However, in a conventional manner,
If the image forming body has the same light reflectance as the toner, it becomes difficult to detect the toner image. In particular, in the case of a color toner as compared with a black toner, the toner itself reflects the light of the color, so that if the light reflectance of the image forming body is low, the S / N ratio of the reflection type optical sensor is low. In some cases, the correction became difficult.

When the light reflectance of the image forming body is high, it is necessary to adjust the gain of the reflection type optical sensor at the time of maintenance in order to prevent the limit from being exceeded. .

In Japanese Patent Application Laid-Open No. Hei 7-104540, the light reflectance of the entire circumference of the image forming body is detected, and the area where the detected light reflectance is the maximum value is defined as the toner density at the time of process condition correction. It discloses that the gain is adjusted for a reflection-type optical sensor based on a maximum value of a detected light reflectance set as a detection area.

[0006]

The disclosed technique focuses on the fact that the light reflectance of an image forming body is uneven during one round, and measures the light reflectance over the entire circumference to improve the accuracy of process control. Is to do so. However, the sensitivity unevenness of the photoconductor is not considered. If there is uneven sensitivity in the photoreceptor, this is not a problem in a relatively low-density image forming apparatus or an image forming apparatus for binary writing, but in a so-called full-color image forming apparatus in which three or four color toner images are superimposed, Density unevenness due to sensitivity unevenness of the body is located at a different position on the synthesized image where the image is to be formed, and if an image is formed in that state, color unevenness occurs. The human eye is more sensitive to color unevenness than density unevenness, so color unevenness is more noticeable than density unevenness for the same sensitivity unevenness.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a color image forming apparatus for forming a color image by superimposing different colors so that color unevenness due to sensitivity unevenness of a photoreceptor does not occur.

[0008]

According to the present invention, there is provided an image forming apparatus capable of forming a color image by superimposing different colors according to the present invention. A mechanism for measuring the sensitivity unevenness of one round of the body, measuring the sensitivity unevenness of the photoconductor at the time of non-image formation, and performing exposure amount correction for each rotational position of the photoconductor according to the measurement result, Will be resolved.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described with reference to the drawings. FIG. 1 shows a conceptual configuration of an example of an image forming or image forming unit of an image forming apparatus according to the present invention. Belt-shaped photoconductor 1
Is charged to a uniform negative potential by the charging charger 2. After the charging, the latent image is formed by exposure by the exposure optical system 3 using a laser diode (LD). The exposure optical system 3 is controlled by a controller 4 by multi-level writing using pulse width modulation and power modulation. After the exposure, the developing unit 6 develops the first color.

In this embodiment, the developing section 6 is a one-component developing apparatus, and an image is formed by the developing roller 7 and a supply roller 8 for supplying toner to the developing roller. However, the developing system may be a two-component developing method. . Further, in this example, the development of four colors is performed by a revolver type developing device, but a configuration in which four developing devices are juxtaposed may be used if there is sufficient space.

The developed first color is primary-transferred onto the intermediate transfer belt 10 by the transfer bias applying means 9, and the untransferred residual toner on the photosensitive belt 1 is cleaned by a cleaning means (not shown).

Further, at the timing when the images of the respective colors match on the intermediate transfer belt 10, the charging, exposure, development, primary transfer, and cleaning of the second and subsequent colors are repeated to form a full-color image of four colors on the intermediate transfer belt. I do. Then, the toner image on the intermediate transfer belt is transferred to transfer paper conveyed from a paper supply unit (not shown) by the bias applying member 11, and further fixed by a fixing unit (not shown).

FIG. 2 is a conceptual diagram showing an example of a potential measurement result when a belt-shaped photosensitive member having uneven sensitivity is charged and then uniformly exposed at an exposure amount for forming a halftone image. (Unit omitted). Even when exposure is performed with a uniform exposure amount, the potential after exposure may be uneven. The measurement results show that the difference between the maximum and the minimum potential is 1
It was 0 V or more. Even if the potential after charging is uneven,
Such potential non-uniformity can occur, but such potential non-uniformity is unlikely to occur with charging by the charging charger. Such potential unevenness largely depends on the unevenness of the sensitivity of the photoreceptor, and high and low potentials tend to have the same potential in the width direction of the belt. Therefore, when a halftone image is formed in a single color, a dark portion and a light portion are formed in a band shape in a direction perpendicular to the transfer paper conveyance direction.

FIG. 3 shows a sequence in the image forming apparatus using the intermediate transfer belt (intermediate transfer member) shown in FIG. 1 when the peripheral length of the intermediate transfer belt is not an integral multiple of the peripheral length of the OPC belt. In both the intermediate transfer belt and the OPC belt, the interval between the vertical lines indicates the length of one circumference. A single color toner image is formed on the intermediate transfer belt by one rotation of the intermediate transfer belt, and a full color image of four colors is formed by four rotations.

As can be seen from the drawing, assuming that a certain position of the intermediate transfer belt and the OPC belt coincide at the position of the leading end of the sequence, the positions of the second color, the third color, and the fourth color on the OPC belt are different from each other. Therefore, different positions come into contact with each other on the intermediate transfer belt. When the final image is formed because the position distribution that causes the density unevenness due to the sensitivity unevenness of the photoreceptor differs between the images for each color, the color unevenness occurs. Therefore, the color unevenness occurs in the above state.

If the peripheral length of the intermediate transfer belt is an integral multiple of the peripheral length of the OPC belt, density unevenness due to sensitivity unevenness of the photoreceptor does not differ on images of each color, so that color unevenness does not occur. However, at present, it is common practice to reduce costs by using an OPC belt (photoreceptor) in common with many other models, and the peripheral length of the intermediate transfer belt is always an integer of the peripheral length of the OPC belt. Sometimes it is not possible to double. In such a case, in the present invention,
A mark for position detection and a position detection hole are provided at the end of the OPC belt, and a reflection type sensor or a transmission type sensor is used.
The rotational position of the PC belt is detected.

At the time of non-image formation, the sensitivity unevenness of one round of the OPC belt is measured. In order to measure sensitivity unevenness, for example, charge and image exposure with a constant light amount are performed, and a value for one round is sampled from the timing of detection of a detection mark by a potential sensor installed on the rotation upstream side of the developing unit. I do.
This makes it possible to make the position of the OPC belt correspond to the potential.

Based on the sampling value, the LD with respect to the rotational position of the OPC belt is corrected so as to correct the density difference.
Is calculated. Using this, the rotational position of the OPC belt is always detected during image formation, and writing is performed with the rotational position corrected.

As another example, the density correction can be performed only by the density sensor without using the potential sensor. At this time, a halftone pattern image is formed on the entire circumference of the photoconductor during non-image formation, and the density sensor measures the density unevenness on the entire circumference of the photoconductor. To make the pattern image halftone,
This is because the higher the image density, the smaller the density difference with respect to the potential difference. The pattern image need only be created at a position where the density sensor is located. The sensitivity unevenness of the photoreceptor is more accurate when the potential is measured, but the sensitivity unevenness can be grasped depending on the density unevenness. From the density measurement values for the entire circumference and the data of the image density difference with respect to the LD output, a correction coefficient for multi-level writing of the LD with respect to the rotational position of the photoconductor is determined so as to correct the density difference.

FIG. 4 shows an example of an image forming section having another configuration according to the present invention. In this example, four imaging units are juxtaposed,
The four color toner images are superimposed on the transfer paper. In this example, one image forming unit has the following configuration. The photoconductor 1 is charged to a uniform negative potential by the charging charger 2. After the charging, the latent image is formed by exposure by the exposure optical system 3 using the LD. Exposure optical system 3
Is controlled by the controller 4 by multi-level writing by pulse width modulation and power modulation. After the exposure, the developing unit 6 develops the first color. The developing unit 6 is formed by a developing roller 7 and the like. The toner developed on the photoreceptor is transferred to the transfer paper on the transfer belt 20 by applying a bias by the transfer bias applying unit 11. The unfixed residual toner is cleaned on the photoconductor by a cleaning unit (not shown). Reference numeral 15 denotes a density sensor for performing process control.

Four such image forming units are arranged side by side in the paper transport direction, and a full-color image is formed by superimposing four color toner images on transfer paper. The transfer paper is separated from the transfer belt 20 by a separation mechanism (not shown), and further the toner is fixed by a fixing device (not shown).

In this image forming apparatus, since each color is formed by a different photoconductor, density unevenness due to sensitivity unevenness of each photoconductor becomes color unevenness. Therefore, in the present invention,
In each color image forming unit, a mark for position detection or a position detection hole is provided at the end of the photoconductor independently, and the rotational position of the photoconductor is detected using a reflection type sensor or a transmission type sensor. Then, at the time of non-image formation, the sensitivity unevenness of one round of the photoconductor is measured.
The method of measuring the sensitivity unevenness may be a method of measuring a potential or a method of forming a pattern image on a photoconductor and measuring the density. The controller 4 independently corrects the exposure amount of the LD according to the rotational position of the photoconductor for each color.

[0023]

According to the present invention, in an image forming apparatus capable of forming a color image by superimposing different colors, a mechanism for detecting a rotational position of a photoreceptor, and sensitivity unevenness in one rotation of the photoreceptor are provided. And a mechanism for measuring the sensitivity of the photoconductor during non-image formation, and corrects the exposure amount for each rotation position of the photoconductor according to the measurement result. Color unevenness can be avoided.

In an image forming apparatus that forms a color image by superimposing a color image formed on a photoreceptor on an intermediate transfer member, if the exposure amount correction is performed as described above, the peripheral length of the photoreceptor becomes intermediate transfer. Color unevenness does not occur even when the density unevenness due to the unevenness in sensitivity of the photoreceptor may be at a different position on the superimposed image instead of being an integral multiple of the perimeter of the body. In an image forming apparatus that arranges a plurality of image forming units of different colors and sequentially forms images of different colors on a recording material to form a color image, the above-described exposure amount correction is performed independently for each image forming unit. By doing so, it is possible to prevent the occurrence of color unevenness.

[Brief description of the drawings]

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

FIG. 2 is a conceptual graph of a measurement result of a potential when a photosensitive member having uneven sensitivity is uniformly exposed.

FIG. 3 is a sequence diagram when the peripheral length of the intermediate transfer member is not an integral multiple of the peripheral length of the photosensitive belt.

FIG. 4 is a schematic diagram of an image forming unit showing another configuration.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 3 Exposure optical system 4 Controller 9 Transfer bias application means 10 Intermediate transfer belt 11 Bias application means

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 DA02 DA10 DA22 DE09 DE10 EA02 EC03 EC06 EC10 EC11 ED01 ED03 ED06 ED24 FA28 HA03 HA08 HA12 HB05 HB06 HB14 2H030 AD12 AD16 BB24 BB42 2H076 DA06 DA07 EA01 EA24

Claims (3)

[Claims] In an image forming apparatus capable of forming a color image by superimposing different colors, a mechanism for detecting a rotational position of a photoconductor and a mechanism for measuring sensitivity unevenness of one round of the photoconductor are provided. A color image forming apparatus, comprising: measuring non-uniformity of sensitivity of a photoconductor at the time of non-image formation; and performing exposure correction for each rotation position of the photoconductor according to the measurement result. 2. An image forming apparatus for forming a color image by superimposing a color image formed on a photoreceptor on an intermediate transfer member, comprising: a mechanism for detecting a rotational position of the photoreceptor; A color image forming apparatus having a mechanism for measuring sensitivity unevenness, measuring sensitivity unevenness of the photoconductor during non-image formation, and performing exposure correction for each rotational position of the photoconductor according to the measurement result. apparatus. 3. An image forming apparatus for arranging a plurality of image forming units of different colors and sequentially superimposing images of different colors on a recording material to form a color image, wherein each image forming unit includes a rotating photosensitive member. It has a mechanism to detect the position and a mechanism to measure the sensitivity unevenness of one round of the photoconductor, and measures the sensitivity unevenness of the photoconductor during non-image formation independently for each image forming unit. A color image forming apparatus that performs exposure amount correction for each rotation position of each photoconductor independently of each other in response to the rotation amount.