JPS59174873A - Magnetic brush cleaning device - Google Patents

Abstract

PURPOSE:To carry out excellent cleaning stably for a long period by forming a standard density part for test development on the surface of an image carrier, detecting its density by a detecting means, and impressing a bias to a conductive sleeve and a toner recovering means according to the detected density. CONSTITUTION:A standard chart is provided to the front end part of the reverse surface of a platen except in a picture formation area and the standard density part 19 for the test development is formed right in front of an electrostatic latent image part 18 formed on a photosensitive body 1. This standard density part 19 is painted solid in, for example, black. A bias voltage controller 9 varies the bias voltage to a specific level corresponding to the density detected by the density sensor 8 and impresses it to the conductive sleeve 14 and reproducing roll 16. Consequently, the reverse sticking of toner and the stain of the photosensitive body are minimized to obtain excellent cleaning effect.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a cleaning device for an image transfer type electrophotographic copying machine, and more particularly to a magnetic brush cleaning device.

(2) Prior Art Image transfer type electrophotographic copying machines are currently widely used because they can use plain paper.

In such a copying machine, 1' copying process is completed by charging, exposing, developing, transferring, and cleaning, and the copying process is repeated to make continuous copies. However, since the same photoreceptor is used repeatedly, after the visible image on the photoreceptor is transferred to paper, the residual toner on the photoreceptor must be cleaned and removed before a new copying process begins. However, the image transfer type electrophotographic copying machine is provided with a cleaning device for this purpose.

Various cleaning methods are known, and a typical one is a magnetic brush cleaning method. In this method, a magnetic carrier is held on a cleaning roll placed close to the photoconductor to form a so-called magnetic brush, and the tip of the brush is rubbed on the photoconductor surface, mainly by electrostatic force. This is to clean and remove the remaining toner on the top.

In this method, the bias voltage applied between the photoreceptor and the magnetic brush is an important factor for improving the cleaning ability, and the higher the bias voltage, the better the cleaning ability, and the more thoroughly the photoreceptor is cleaned. However, as this bias voltage is increased, the following drawbacks become more noticeable. In other words, if the bias voltage becomes too high, a reverse charge is injected into the toner through the magnetic brush, and the toner re-adheres to the photoconductor, resulting in a so-called reverse adhesion phenomenon of toner to the photoconductor, resulting in poor cleaning. do. Therefore, it is necessary to set the bias voltage to an optimal value taking into account both the cleaning performance and toner back-adhesion phenomenon. However, due to changes in various conditions such as carrier deterioration, the optimal value is not necessarily constant, and the bias voltage setting must be adjusted accordingly. The current situation is making this even more difficult. Various means have been proposed to solve this problem.

For example, Japanese Patent Publication No. 55-42392 proposes a method in which the bias voltage applied to the magnetic brush is set to 0 to 150 pol 1, which is a range in which the reverse adhesion phenomenon of toner does not occur. Japanese Patent Application No. 53-33153 proposes a method in which a predetermined bias voltage is applied to a magnetic brush device via an impedance element, and the magnetic brush device is made to follow a changing optimum bias voltage.

Further, Japanese Patent Application Laid-Open No. 57-79979 proposes a method in which two magnetic brush rolls are provided and bias voltages applied to each magnetic brush roll are made different.

(3) Problems with the Prior Art However, with any of the methods described in the above-mentioned publications, it is likely that the cleaning ability is initially sufficient, or as the number of copies increases, the cleaning ability decreases, resulting in poor cleaning. become. That is, it has the disadvantage that sufficient and stable cleaning ability cannot be obtained over a long period of time. Furthermore, using multiple magnetic brush rolls necessitates an increase in the size of the device, which is not appropriate from the viewpoint of production costs.

(4) Purpose of the Invention In view of the above-mentioned drawbacks of the conventional art, the present invention has been developed by minimizing back-adhesion of toner and providing high cleaning ability, thereby stabilizing good cleaning and cleaning for an image carrier such as a photoreceptor for a long period of time. An object of the present invention is to provide a magnetic brush cleaning device that can perform the following operations.

(5) The main points and objects of the invention are, in a magnetic brush cleaning device for cleaning the surface of an image carrier, comprising means for forming a standard density area for test development on the surface of the image carrier; A detection means for detecting the density of the standard density area for test development; a bias applied to the conductive sleeve on the outer periphery of the cleaning roll according to the detected density detected by the detection means; and/or formed on the conductive sleeve. This is achieved by providing a magnetic brush cleaning device characterized by comprising: means for varying the bias applied to a toner collecting means for collecting toner from the magnetic brush.

(6) Examples of the invention Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram of an electrophotographic copying machine for explaining an embodiment of the present invention. In Figure 1, ■ is a photoreceptor, 2 is a charging electrode, 3 is an image exposure device, 4 is a developing device, 5 is a transfer paper, 6 is a transfer pole, 7 is a separation pole, 9 is a bias voltage control device, and 10 is a electrode, 11 is a cleaning device, 12
indicates the static electricity removal light.

The photoreceptor is shaped like a tram that rotates clockwise at a constant speed, and various devices are provided along the outer periphery of the photoreceptor 1 . An electrostatic latent image is formed on the surface of the photoreceptor 1, that is, the image carrier, by charging by the charging electrode 2 and image exposure 3, and the electrostatic latent image is made visible by the developing device 4, and the visible image is transferred to the transfer paper 5. One copying process of cleaning the photoreceptor 1 with the cleaning device 11 after the image is transferred is performed while the photoreceptor 1 rotates once.

The cleaning device 11 includes a conductive sleeve 14, a regeneration roll 16, and a scraping plate 17, and a bias voltage is applied to the conductive sleeve 14 and the regeneration roll 16 by a bias voltage control device 9. The conductive sleeve 14 is formed in a cylindrical shape around the outer periphery of the cleaning roll 15, and is provided so as to be rotatable in a clockwise direction.

The carrier 1 is attached to the conductive sleeve 14 by magnetic attraction.
3 is held to form a so-called magnetic brush, and its tip is configured to rub the surface of the photoreceptor 1 to clean and remove residual toner on the photoreceptor 1 after transfer mainly by electrostatic force. There is. The toner adhering to the magnetic brush is attracted to the surface of a regeneration roll 16 that is rotatable in a clockwise direction, and is scraped off by a scraping plate 17 and collected.
The image density detection sensor 8 is for detecting the density of the standard density area 19 for test development on the photoreceptor 1 after development.

According to various experiments conducted by the present inventors, it has been found that there is a close relationship between the amount of toner adhering to the photoreceptor 1 after development and the cleaning performance.

That is, the amount of toner adhering to the photoreceptor 1 after development is determined by (1) the image density of the original, (2) the toner concentration in the developer, (3) the surface potential of the photoreceptor 1, (4) the transfer efficiency, and (5) the exposure lamp. If the cleaning bias voltage is set to a certain constant value, complete cleaning will be achieved when the amount of toner adhesion is small, but conversely, complete cleaning will not be achieved when the amount of toner adhesion is large. If this is not achieved, cleaning defects will occur. Furthermore, if a bias voltage is applied that is sufficient to achieve cleaning with respect to the expected maximum amount of toner adhesion, the original cleaning ability will be improved; It has been found that an adhesion phenomenon occurs, causing poor cleaning, and furthermore, the back adhesion of toner causes contamination of the photoreceptor, which greatly affects the life of the photoreceptor.

Based on the above facts, it is possible to apply a low bias voltage when the amount of toner adhesion is small, and apply a high bias voltage according to the amount of toner adhesion when there is a large amount of toner adhesion, that is, apply the minimum bias voltage necessary for cleaning. was found to be sufficient.

Therefore, in this embodiment, a standard chart is provided at the tip of the back surface of the document table (not shown) outside the image forming area.As shown in FIG.
Test development mark 41i just before 8? IM degree part 19 is formed. This test development target fS density area 19 is formed, for example, in black. After uniform charging, image exposure, and development according to the copying process, the image density detection sensor 8 detects the toner density in the standard density area 19 for test development. The bias voltage control device 9 varies a predetermined bias voltage according to the detected density detected by the image density detection sensor 8 and applies it to the conductive sleeve 14 and the reproduction roll 16. The density of the standard density area 19 for test development corresponds to the amount of toner attached. Therefore, when the toner concentration is high, a high bias voltage is applied, and when the toner concentration is low, a low bias voltage is applied, and the minimum bias voltage necessary for cleaning is applied according to the toner concentration.

Note that the bias voltage value applied to the reproducing roll 16 is
Although it is set to a value higher than the bias voltage value applied to the conductive sleeve 14, it is changed as the bias voltage value applied to the conductive sleeve 14 changes.

(7) Effects of the Invention As explained in detail above, according to the present invention, it is possible to apply a cleaning bias voltage according to the amount of toner adhering to the photoreceptor, so that a good cleaning effect can be obtained and This has the effect that the frequency with which high bias voltage is applied is reduced, and toner back-adhesion and photoconductor contamination are minimized.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an electrophotographic copying machine for explaining an embodiment of the present invention, and FIG. 2 is a schematic diagram for explaining a standard density area for test development formed on a photoreceptor. be. ■...Photoreceptor 4...Developing device 8...
Image density detection sensor 9...Bias voltage control device 11...Cleaning device 19...
Yoshiyuki Osuga, Patent Attorney, Standard Density Department for Test Development

Claims (1)

[Claims] A magnetic brush cleaning device for cleaning the surface of an image carrier, comprising means for forming a standard density area for test development on the surface of the image carrier, and a detection unit for detecting the density of the standard density area for test development. A bias is applied to a conductive sleeve on the outer periphery of the cleaning roll and/or a bias is applied to a toner collection means for collecting toner from a magnetic brush formed on the conductive sleeve in accordance with the detected concentration detected by the detection means. 1. A magnetic brush cleaning device comprising: means for varying a bias of the cleaning device.