JPH06194917A - Image forming device - Google Patents

Abstract

(57) [Summary] [Object] To provide an image forming apparatus capable of preventing a friction coefficient between an image carrier and a blade from increasing when a pattern image is output and performing stable cleaning. An image forming apparatus that transfers a toner image developed on an image carrier to a recording medium and removes toner remaining on the image carrier with a cleaning blade, and means for forming a pattern image for gradation control. A unit for detecting the density of the pattern image, and a gradation control unit for performing gradation control according to the detection result of the density detection unit, wherein the toner forming the pattern image is the length of the cleaning blade. It is characterized in that the pattern image is formed so as to cover substantially the entire area in the direction.

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 copying machine or a printer for forming an image by an electrophotographic method.

In an image forming apparatus such as a copying machine, a toner image is formed on a photosensitive drum which is an image carrier, the toner image is transferred to a recording medium for recording, and the toner image is further transferred. A so-called electrophotographic method is generally used, which is configured so that the toner remaining on the photosensitive drum is removed by a cleaning unit later.

In such an image forming apparatus, in order to improve image stability, a special pattern image 50 is formed on the photosensitive drum 51 as shown in FIG. 10, and the pattern density is detected. Then, the gradation correction control is performed by feeding back to the toner supply amount and other image forming conditions.

From the viewpoint of toner consumption and prevention of toner scattering, it is preferable that the pattern image 50 be a small amount of pattern output at a fixed location in the longitudinal direction of the photosensitive drum 51. Therefore, as shown in FIG.
I try to make 50 as small as possible.

[0005]

The pattern image 50 is scraped off by the cleaning blade 52 after the density is detected, but if the photosensitive drum 51 is rotated many times for the detection, the blade and the drum are easily damaged. . This is because the performance of the cleaning blade 52 for scraping off the toner on the photoconductor drum 51 largely depends on the lubricity of the residual toner.

The edge portion of the rubber blade 52 is in contact with the photosensitive drum 51 at a predetermined pressure. However, since the friction coefficient between them is high, if the photosensitive drum 51 is rotated as it is, a stick slip or a blade edge is generated. The so-called blade turning is likely to occur. Therefore, the toner is continuously fed to the abutting portion between the photoconductor drum 51 and the cleaning blade 52 to some extent (about the amount of fog toner), and the toner acts as a lubricant to prevent the stick slip and the like.

However, as shown in FIG.
When the cleaning blade 52 scrapes off the pattern image 50 formed only at the center of the longitudinal direction of the 51, in the longitudinal direction of the cleaning blade 52, toner is supplied in the region where the pattern image 50 exists, but stick-slip does not easily occur. , The blade 52 in the area where other toner is not supplied.
The stick-slip becomes large in order to maintain a high friction coefficient between the photosensitive drum 51 and the photosensitive drum 51.

At the boundary between the portion where stick-slip does not occur and the portion where stick-slip occurs, the force applied to the blade 52 becomes very large, and cleaning failure, blade flipping, or blade chipping may occur.

The present invention has been made to solve the above-mentioned conventional problems, and an object thereof is to prevent the friction coefficient between the image carrier and the blade from increasing when the pattern image is output, and to stabilize the pattern. An object is to provide an image forming apparatus capable of performing cleaning.

[0010]

A typical configuration according to the present invention for achieving the above object is to form a pattern image for gradation control, and to detect the density of the pattern image. And a gradation control unit that performs gradation control according to the detection result of the density detection unit, and when the toner forming the pattern image is removed by the cleaning blade, the cleaning blade has a substantially longitudinal direction. It is characterized in that the pattern image is formed so as to cover the entire area.

[0011]

In the above construction, when the toner forming the pattern image is scraped off by the cleaning blade, it is present in substantially the entire area in the longitudinal direction of the blade, and this acts as a lubricant. The coefficient of friction between the carrier and the blade does not increase, and stable cleaning is performed.

[0012]

【Example】

First Embodiment Next, an embodiment of the present invention will be described with reference to the drawings. 1 is an explanatory view of a pattern image, and FIG. 2 is a schematic cross-sectional view of an electrophotographic color image forming apparatus using a photosensitive drum which is an image carrier.

First, the overall structure of the apparatus will be described. As shown in FIG. 2, the primary charger 2, the developing device 3, the transfer drum 4, and the photosensitive drum 1 that rotate counterclockwise are provided around the photosensitive drum 1.
A cleaning device 5 is arranged. The above primary charger 2
Between the developing device 3 and the developing device 3, there is a portion where the laser beam from the laser scanner 6 is scanned on the photosensitive drum 1, that is, the exposure portion 7.

The developing device 3 is divided into equal parts around the circumference of the developing device 3a, 3 for yellow, magenta, cyan and black.
It supports b, 3c and 3d. And each developing device has a shaft 3
It can be rotated like a ferris wheel around e, is indexed to the developing position S corresponding to the electrostatic latent image of each color, and visualizes the latent image with toner.

The toner on the photosensitive drum 1 is transferred to the recording medium 7 supported on the transfer drum 4 at the transfer portion T by corona discharge of the transfer charger 8. The toner remaining on the photoconductor drum 1 by this transfer is cleaned by the cleaning blade 5 whose edge portion is brought into contact with the photoconductor drum 1 thereafter.
It is cleaned by the cleaning device 5 having a. This cleaning device 5 has a Young's modulus of the blade so that the cleaning is performed in a steady state in which the photosensitive drum 1 rotates at a constant speed during image formation, and the cleaning is performed without the blade making a noise.
The pressing force and the intrusion amount of the blade are set in consideration of the eigenvalue such as the dynamic friction coefficient of the photosensitive drum 1.

On the other hand, the recording medium 7 is sent out from the cassette 9, passes through the roller pair 10, and is abutted against the nip portion of the registration roller 11. Then, the recording medium 7 is sent out in synchronism with the rotation of the transfer drum 4, the tip of the recording medium 7 is abutted against the gripper 13 on the transfer drum 4 opened by the gripper cam 12, and the gripper 13 passes through the gripper cam 12. When it is closed, the tip is pinched.

After the transfer of the image of the required color, the recording medium 7 is separated from the gripper 13 opened by the separating cam 14 by the separating claw 15 and passes through the conveying unit 16 and the fixing unit 17 to the external tray 18
Is discharged to.

This image forming apparatus is capable of forming gradation images. The configuration will be described with reference to the block diagram of the gradation image reproduction process shown in FIG.

The image brightness signal is obtained at the CCD input 19,
The brightness signal is converted into a digital brightness signal by the A / D conversion circuit 20. The luminance signal passes through a shading circuit 21 that corrects sensitivity variations of individual CCD elements,
To convert the modified luminance signal to a density signal, LO
Pass through G converter 22.

The density signal obtained by the LOG converter 22 is converted by the LUT 23 in order to correct the γ characteristic of the printer at the initial setting so that the original image density and the output image density match. The LUT 23 is adapted to be corrected by the LUT correction table 24 formed by the calculation result described later.

The pulse width conversion circuit 25 converts the signal converted by the LUT 23 into a signal corresponding to the dot width, and sends the signal to the laser driver 26. With such digital signal processing, a latent image having a gradation characteristic due to a dot area change is formed on each photoconductor drum 1 by laser scanning, and a gradation image is obtained through processes of development, transfer, and fixing. I am trying.

The image forming apparatus has a built-in test pattern generator on the photoconductor drum 1 for changing the density signal level by several steps and outputting the density signal level.

The density signal level of this embodiment has 8 bits, that is, 256 gradations, and five levels of 00 ^H , 40 ^H , 80 ^H , CO ^H , and FF ^H are shown in FIG. 1 by the test pattern generator. Thus, the gradation pattern image 27 is formed on the photosensitive drum 1.

In the gradation pattern formed as described above, the output corresponding to each toner optical density of the gradation pattern is detected by the light emitting element 28 and the light receiving element 29 shown in FIG.

In this embodiment, the light emitting element 28 is approximately
An LED having a main wavelength of 950 nm is used, and the photosensitive drum 1 has an reflectance of about 20% at a wavelength of 950 nm.
The C photoconductor is used, and the toner is mainly composed of a styrene copolymer resin having a reflectance of 90% or more at 950 nm. FIG. 4 is a graph showing the relationship between the output image density of each color and the output of the light receiving element 29 in this embodiment.

Next, a configuration for processing the detection signal read by the light receiving element 29 to create the LUT correction table 24 will be described with reference to the block diagram of FIG. Light receiving element
The signal read in 29 is converted into a digital signal by the A / D converter 30, and converted into a density signal by the density conversion circuit 31.

The density for each density level of the gradation pattern image 27 is set by the LUT 23 so that the curve C shown in FIG. However, the sensitivity, the development characteristics, etc. of the photosensitive drum 1 change due to changes in the toner replenishment mode, changes in the environment, changes over time, etc., and the curve C in FIG. Changes from curve A to curve B.

Therefore, if the density detection result obtained from the light receiving element 29 is higher than the set value as shown by the curve A in FIG. 6, it becomes high as shown by the curve A'in FIG. The correction calculation is performed so as to lower the setting from the setting. On the contrary, when the detection result is lower than the set value as shown by the curve B in FIG. 6, a correction calculation is performed so as to raise the setting by a small amount as shown by the curve B ′ in FIG.

Therefore, the LUT correction table 24 for correcting the LUT 23 is created through the correction value calculation circuit 32 for calculating the correction value as described above from the density calculated by the density conversion circuit 31 shown in FIG.

LUT correction table obtained as described above
By correcting the LUT 23 by 24, it is possible to correct the changed printer gradation characteristics and always obtain a constant printer gradation characteristics. By performing the above correction for each color, an image with a good full-color color balance can be obtained.

The correction value is the RA of the control unit (not shown).
It is stored in M, and when it is judged that the gradation characteristics are abnormal,
It is used until the correction is performed again.

Next, the pattern image 27 for discriminating the gradation characteristic will be described. Pattern image 27 according to the present embodiment
1, is composed of a gradation pattern 27a for reading the density value, and a toner pattern 27b in which toner is formed before and after the pattern 27a in a length corresponding to the entire width in the longitudinal direction of the cleaning blade 5a. is doing.

Therefore, when the density is detected, the pattern image 27 is formed on the photosensitive drum 1 and the gradation pattern 27a is formed.
The density is detected through the light receiving element 29, and the above-described correction control is performed. Then, the pattern image 27 is scraped off the photosensitive drum 1 by the cleaning blade 5a. At this time, since the toner pattern 27b is formed over the entire width of the blade 5a, the toner is present over the entire width of the blade 5a. The toner acts as a lubricant. Thus, no matter how many rotations the photosensitive drum 1 makes in detecting the density, the blade 5a does not cause stick-slip or blade flipping, and stable cleaning is performed.

The density level of the toner pattern 27b is not necessarily unique, and the tone pattern 27a to be created is
Any value from 00 ^{H to} FF ^H equivalent to Experimentally, good results were obtained when the amount of transfer residual toner on the photosensitive drum 1 during image formation was about 00 ^H to 40 ^H.

[Second Embodiment] The pattern image 27 described above is composed of the gradation pattern 27a and the toner pattern 27b.
The pattern image 27 is shown in FIG. 8 in consideration of the time reduction and the memory reduction due to the time required to have the gradation correction sequence and the necessity of having a plurality of gradation patterns.
It may be configured as shown in.

The pattern image 27 of FIG. 8 is formed by forming a gradation pattern 27a for reading the density over the entire width in the longitudinal direction of the cleaning blade 5a, and the operation of the toner pattern 27b of the first embodiment described above is gradation. Pattern 27
The toner a is used.

By constructing the pattern image 27 as described above, a good cleaning state can be obtained even in the gradation correction sequence.

[Third Embodiment] Further, the pattern image 27 does not necessarily have to be formed so as to extend over the entire width of the cleaning blade 5a in the longitudinal direction. For example, as shown in FIG. 9, a gradation pattern 27a for density reading may be formed in the central portion of the photosensitive drum 1 in the longitudinal direction and in the vicinity of the blade end portion where blade flipping or cleaning failure is likely to occur. In this case, when the toner of the gradation pattern 27a is scraped by the cleaning blade 5a, the scraped toner is laterally fed along the blade 5a, and as a result, the toner intervenes in the entire width in the longitudinal direction of the blade 5a. become. Therefore, as in the above-described embodiment, toner acting as a lubricant is present on the entire blade 5a, and the occurrence of stick-slip is prevented.

If the pattern image is constructed as shown in FIG. 9, it is possible to suppress the toner consumption and the toner scattering.

As shown in FIG. 9, in addition to providing the gradation patterns 27a at three locations in the longitudinal direction of the photosensitive drum 1,
For example, the same applies to the case where the toner amount is reduced from the central portion in the longitudinal direction of the photosensitive drum 1 toward both ends to form a thin pattern and the pattern image in which the toner amount is increased only at both ends.

[0044]

As described above, according to the present invention, when the toner forming the pattern image is scraped off by the cleaning blade, the toner is present in substantially the entire area of the blade in the longitudinal direction. As a result, the coefficient of friction between the image carrier and the blade does not increase, and stable cleaning can be performed.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a pattern image according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating the overall configuration of an image forming apparatus.

FIG. 3 is a block diagram of gradation control.

FIG. 4 is a graph showing an output image density of each color and an output relationship of a light receiving element.

FIG. 5 is a configuration block diagram for creating an LUT correction table.

FIG. 6 is a graph showing the relationship between the density and the density level of a gradation pattern image.

FIG. 7 is a graph showing the relationship between the input density level and the output density level.

FIG. 8 is an explanatory diagram of another embodiment of the pattern image.

FIG. 9 is an explanatory diagram of another embodiment of the pattern image.

FIG. 10 is an explanatory diagram of a conventional technique of a pattern image.

[Explanation of symbols]

1 ... Photosensitive drum, 2 ... Primary charger, 3 ... Developing device, 3
a ... Yellow developing device, 3b ... Magenta developing device, 3c ... Cyan developing device, 3d ... Black developing device, 3e ... Shaft, 4 ... Transfer drum, 5 ... Cleaning device, 5a ... Cleaning blade, 6 ... Laser scanner, 7 ... Recording medium, 8 ...
Transfer charger, 9 ... Cassette, 10 ... Roller pair, 11 ... Registration roller, 12 ... Gripper cam, 13 ... Gripper, 14 ...
Separation cam, 15 ... Separation claw, 16 ... Transport section, 17 ... Fixing section, 18 ...
External tray, 19 ... CCD input, 20 ... A / D conversion circuit, 21
... Shading circuit, 22 ... LOG converter, 23 ... LU
T, 24 ... LUT correction table, 25 ... Pulse width conversion circuit,
26 ... Laser driver, 27 ... Gradation pattern image, 27a ... Gradation pattern, 27b ... Toner pattern, 28 ... Light emitting element, 29
... light receiving element, 30 ... A / D conversion circuit, 31 ... concentration conversion circuit,
32 ... Correction value calculation circuit

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Nobuatsu Sasana 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Takashi Hasegawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (72) Inventor Takao Ogata 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (2)

[Claims] 1. An image forming apparatus in which a toner image developed on an image carrier is transferred to a recording medium and the toner remaining on the image carrier is removed by a cleaning blade to form a pattern image for gradation control. Means for detecting the density of the pattern image, and gradation control means for performing gradation control according to the detection result of the density detection means, wherein the toner forming the pattern image is the cleaning blade. The image forming apparatus is configured to form the pattern image so as to cover substantially the entire area in the longitudinal direction of the cleaning blade when removed by. 2. The image forming apparatus according to claim 1, wherein the pattern image is formed outside the image forming area of the image carrier.