JPH02179659A - Corona charger for electric copying device - Google Patents

Abstract

PURPOSE:To prevent electrification unevenness due to the soiling of a corona charger by actuating a cleaning means in response to a detecting signal when the output voltage of a toner concentration sensor is lower than a fixed value. CONSTITUTION:The toner concentration sensor 13 scans in the axial direction of a photosensitive drum 5 by a reciprocatingly driving means. When an image on a reference density plate is developed and reaches the position of the sensor 13, the scanning is started: When an output voltage according to the density V1 is larger than a prescribed value V2, unevenness more than prescribed value does not exist and the cleaning pad 22 does not move. When the electrifying wire 21 is soiled, then V1<V2, and the pad 22 is driven by a motor 25 to clean the wire 21. The pad 22 is fixed to the moving body 23 sliding in the longitudinal direction of a case 20, and is reciprocated between sensors 26 and 27 by a screw shaft 24 connected to the motor 25. Under this constitution, when the corona charger is soiled, it is immediately cleaned, therefore, electrification unevenness is prevented and a stable image density can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a corona charging device for electronic copying machines, laser printers, etc.

[Conventional technology] Rona chargers are equipped with dust in the air, corona products caused by corona discharge, transfer paper powder, scattered toner, etc. that adhere to the charge wire and the inner surface of the shield case, and if the dirt is significant, abnormal discharge or uneven discharge may occur. In some cases, abnormal images may appear due to corona discharge, or the charger may lose its function.

Therefore, a corona charging device is already known which solves the above problem by providing a cleaning means for cleaning the charge wire of the corona charger and the inner surface of the shield case. In this case, the cleaning timing at which the cleaning means of the corona charging device is activated is determined by a signal based on turning on the main switch, opening/closing the front cover, or the like. Therefore, cleaning of the corona charger will not be performed until the main switch is turned ON and then turned ON again or the front cover is opened. Therefore, in the past, when the charge wire and the inside of the shield case of the corona charger became dirty, they were not cleaned.
There is a problem in that the stains are noticed only when the above-mentioned problems occur.

Problems to be Solved by the Invention The present invention solves the above-mentioned conventional problems, and provides an electronic copying apparatus that can detect uneven discharge of a corona charger and automatically operate a cleaning means. The purpose is to provide a corona charging device.

Means for Solving the Problems The structure of the present invention to achieve the above object is as follows.

At least the charge wire of the corona charger.

In a corona charging device for an electronic copying machine that is equipped with a cleaning means that uses a reciprocating cleaning body, a toner density sensor that forms a toner image of a reference density plate on the surface of a photoreceptor and outputs a voltage corresponding to the density of the toner image is provided. and a toner concentration control device that controls toner concentration based on a signal from the sensor, and when the output voltage of the toner concentration sensor of the toner concentration control device is below a predetermined value, the cleaning means is activated to move the cleaning body back and forth. The corona charging device is characterized in that it moves.

According to the above configuration, the discharge unevenness of the corona charger appears as image density unevenness, so the image density unevenness is detected when the output voltage of the toner density sensor of the toner density control device becomes less than a predetermined value. The cleaning means is activated based on the signal. The corona charger can be cleaned before it becomes dirty before it adversely affects the image quality of copies.

Example Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of an electrophotographic copying machine equipped with a corona charging device according to the present invention. In this copying machine, as shown in FIG. 2, a document 2 placed on a platen glass 1 is placed on a light source
The original 2 is scanned in the direction of the arrow a, and the reflected light of the original 2 is passed through an optical system such as a mirror and lens to a photosensitive material that is charged with high voltage in advance by a corona charging device 4 and rotates in the direction of the arrow in synchronization with the scanning. By guiding the photoreceptor to the photoreceptor drum 5, a latent image is formed on the photoreceptor drum 5. In the next process, the latent image is formed with toner by the developing unit 6, and the toner image is transferred by the transfer charger 7 onto a transfer sheet fed in the direction of arrow C. After the transfer, the transfer paper is separated from the photosensitive drum 5 by a separation charger 8, and is conveyed via a conveyor belt 9 to a fixing unit (not shown), where the toner image is fixed. Note that the reference numeral 1o indicates the photosensitive drum 5.
cleaning unit that removes residual toner.

Reference numeral 11 denotes an eraser for removing unnecessary charges from the surface of the photosensitive drum 5 charged by the corona charging device 4 to prevent wasteful toner consumption.

The electrophotographic copying machine configured as described above is equipped with a toner density control device which is known per se. The toner density control device controls the document leading edge position IA on the platen glass l as shown in FIG.
A reference density plate 12 is disposed upstream of the light source 3 in the scanning direction a, and the image on the density plate 12 is transferred to the photosensitive drum 5 which has been charged with a high voltage by the corona charging device 4 in advance due to the scanning of the light source 3. guided by. Then, a toner image is formed by the developing unit 6, and this toner image is a batch image whose toner density is detected. This batch image.

Transfer/separation charger 7.8 and cleaning unit 1
The toner concentration is detected by a toner concentration sensor 13 provided between the toner concentration sensor 13 and the toner concentration sensor 13 provided between the toner concentration sensor 13 and

The toner concentration sensor 13 is reciprocated in the direction of arrow d by a reciprocating drive device shown in FIG. 3, and is operated in the axial direction of the photosensitive drum 5. This reciprocating drive device has a bearing 1 on the side plate 14.
The toner concentration sensor 13 is rotatably mounted via the toner concentration sensor 5.
The toner concentration sensor has a screw shaft 16 that is screwed together, a stepping motor 17 that rotationally drives the screw shaft 16, and a guide shaft 18 that prevents the toner concentration sensor 13 from rotating about the screw shaft 16. 13 is normally held at a home position detected by a home position sensor 19.

In the corona charging device 4, as shown in FIGS. 4 and 4A, a cleaning body configured as a cleaning pad 22 is brought into contact with a charge wire 21 stretched in a shield case 2o. It is attached to a movable body 23 that is slidably attached to the shield case 2o in the longitudinal direction. The moving body 23 has a screw shaft 24
The screw shaft 24 is drivingly connected to a stepping motor 25.

The moving body 23 is rotated by the stepping motor 25.
is reciprocated between the positions detected by the home position sensor 26 and the return position sensor 27, and at this time, the charging wire 21 is cleaned by the cleaning pad 22. FIG. This will be explained according to the flowchart.

When the image on the reference density plate 12 is developed and reaches the position of the toner density sensor 13, the toner density sensor 13 is scanned in the axial direction of the photoreceptor drum 5. At this time, the toner concentration sensor 13 outputs a voltage according to the toner concentration, and the detected output voltage v0 is compared with a predetermined value v3. If the detected output voltage V is larger than the predetermined value v2, there is no unevenness in image density above the predetermined value, so the corona charging system is ready! The stepping motor 25 that reciprocates the No. 4 cleaning pad 22 does not rotate.

Here, if the charge wire 21 etc. of the corona charging device 4 become dirty and thereby cause uneven toner density, the detected output voltage v1 becomes smaller than the predetermined value v2, the stepping motor 25 is energized, and the cleaning pad 2
2 cleans the charge wire 21.

Thus, uneven corona discharge due to dirt on the charge wire 21 appears as uneven toner density, and the toner density sensor 13 detects this uneven toner density, and the cleaning pad 22 cleans the charge wire 21. Therefore, when dirt on the charge wire 21 is detected, the dirt can be immediately cleaned.
Charging unevenness caused by 1 dirt is eliminated, and copies with stable image density can be obtained.

Although preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and can be modified in various ways. For example, the cleaning body is not limited to just the charge wire.
It may be something that can also clean the inside of the shield case, or
The device that drives the cleaning body back and forth is not limited to screw shafts, but also wires,
Any suitable reciprocating means such as a rack may be used.

According to the above configuration, when the corona charger becomes dirty, it can be detected and immediately cleaned, so that uneven charging due to the corona charger is reliably prevented and stable image density is always obtained. .

[Brief explanation of the drawing]

Fig. 1 is an electrophotographic copying machine equipped with a corona charging device according to the present invention, Fig. 2 is an explanatory diagram showing a part of its document placement section, and Fig. 3 is an explanation of a device that reciprocates a toner concentration sensor. 4 and 4A are a plan view and a sectional view showing an embodiment of the present invention, and FIG. 5 is a diagram showing a control flow thereof. 4... Corona charging device 5... Photosensitive drum 13... Toner concentration sensor 20... Shield case 21... Charge wire 22... Cleaning pad 25... Stepping motor

Claims (1)

[Claims] In a corona charging device of an electronic copying machine, which is equipped with a cleaning means for cleaning at least the charge wire of the corona charging device with a cleaning body that moves back and forth, a toner image of a reference density plate is formed on the surface of a photoreceptor, and the toner image of the reference density plate is adjusted to that density. A toner concentration control device is provided which has a toner concentration sensor that outputs a corresponding voltage and controls the toner concentration based on a signal from the sensor, and when the output voltage of the toner concentration sensor of the toner concentration control device is below a predetermined value, the The corona charging device described above is characterized in that the cleaning body is reciprocated by operating a cleaning means.