JPS63143572A - Developing device - Google Patents

Abstract

PURPOSE:To stabilize the feeding of a developer and to prevent image omission such as void from being caused by rotating a developing sleeve in the opposite direction from a developer conveyance direction only for a prescribed time except when developing operation is performed. CONSTITUTION:A motor driver 21 for the driving motor 17 of the developing sleeve 7 is set in forward rotation mode by a CPU in a normal stand-by state; when printing operation is accepted, the sleeve 7 rotates forward and when the driver 21 is set in reversing mode, the sleeve reverses for the prescribed time. When the developing sleeve 7 rotates in the opposite direction from the developer conveyance direction, an aggregate of part of a developer caught by the front end of a doctor blade 10 falls on the surface of the developing sleeve 7 from a space formed nearby the doctor blade 10 by gravitation or magnetic attractive force to contact the developing sleeve 7 and is collapsed by the doctor blade 10 by the rotation in the developer conveyance direction, so that it is removed as fine particles.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a developing device used in a recording device such as a copying machine, a printer, or a facsimile. especially.

A developer transport means, such as a so-called developing sleeve, which is disposed facing a latent image carrier such as a photoreceptor and rotates in a fixed direction to transport the developer toward the latent image carrier, and the developer transport means. A type of developer equipped with a developer layer thickness regulating member, such as a so-called doctor blade, which is arranged with a predetermined gap from the developer layer and regulates the developer conveyed toward the latent image carrier to a constant layer thickness as described above. Regarding equipment.

The above-mentioned type of developing device is a so-called dry developing device, and the developer used is a two-component developer consisting of a mixture of triboelectric charging fine particles (so-called carrier) and magnetic toner. There are also one-component developers made of only magnetic toner.

This developer is conveyed toward the photoconductor by a developing sleeve while its layer thickness is regulated to a constant level by a doctor blade, and develops the electrostatic latent images corresponding to the JM manuscript images formed on the photoconductor. Visualize.

In this case, the reason why the layer thickness of the developer is regulated to a constant level by the doctor blade is to ensure that the developer is supplied to the photoreceptor in just the right amount and in sufficient quantity, so that a uniform visible image is always created. However, the gap between the doctor blade and the developing sleeve is generally very small, and depending on atmospheric conditions such as heat, moisture, and magnetism, the developer may aggregate and stick at the tip of the doctor blade.

When such aggregation and sticking of the developer occurs, the developer with a predetermined thickness is not delivered to the downstream side of the doctor blade, and as a result, the electrostatic latent image on the photoreceptor is not visualized sufficiently. , so-called white spots may occur in the final recorded product.

In view of the above points, it is an object of the present invention to provide a developing device that does not cause image defects such as white spots.

SUMMARY OF THE INVENTION The present invention, which achieves the above-mentioned object, comprises: a developer conveying means disposed opposite to a latent image carrier and configured to rotate in a fixed direction to convey developer toward the latent image carrier; A developing device including a developer layer thickness regulating member disposed at a predetermined gap with respect to the developer conveying means and regulating the developer conveyed toward the latent image carrier to a constant layer thickness as described above. There it is,
This developing device rotates the developer conveying means in a direction opposite to the fixed direction for a predetermined period of time when a developing operation is not performed.

Hereinafter, the present invention will be explained based on Examples.

FIG. 1 is an overall side sectional view of a recording apparatus, particularly a laser printer, using a developing device according to an embodiment of the present invention. In the figure, an endless belt-shaped photoreceptor 1 serving as a latent image carrier is supported by two rollers 2 and 3, and further rotates in a clockwise direction as shown by an arrow. The circumferential surface of the rotating photoreceptor 1 is first uniformly charged by the charging charger 4, and then subjected to an image exposure operation by the laser exposure device 5, so that an electrostatic latent image corresponding to the image is formed on the circumferential surface. be done.

This electrostatic latent image is carried to the front of the developing device 6 as the photoreceptor 1 rotates.

As shown in FIG. 2, the developing device 6 includes a developing sleeve 7 as a developer conveying means arranged opposite to the photoreceptor 1;
A developing tank 9 containing a developer 8 (in the case of the embodiment, a two-component developer consisting of carrier and toner), and a doctor blade 1.0 as a developer layer thickness regulating member attached to the developing tank 9. and a toner tank 11 containing replenishment toner. During normal recording operations, the developing sleeve 7 rotates counterclockwise, and the developer in the developing tank 9 is conveyed toward the photoreceptor 1 due to this rotation and the influence of the magnetic field from the magnets 17a and 17b. or,
The layer thickness of the developer being transported is controlled to be constant by the doctor blade 10.

The electrostatic latent image on the photoreceptor 1 is developed into a developed image by the developer carried to the photoreceptor 1 by the developing sleeve 7. Thereafter, this developed image is conveyed to the front of the transfer charger 12 according to the circumferential movement of the photoreceptor 1.

While the above work is being carried out, the paper feed cassette 13a,
The transfer paper fed from one of the transfer paper sheets 13b is carried to the front of the transfer charger 12, where it is superimposed on the developed image on the photoreceptor 1. Then, due to the discharge of the transfer charger 12, the developed image is transferred onto the transfer paper.

The transfer paper carrying the developed image as a result of this transfer is carried to the fixing device 14 where it undergoes a fixing operation, and is then discharged to the paper discharge tray 15.

By repeating the above printing process, a plurality of printed products are obtained on the paper discharge tray 15. However, in some cases, the following inconvenience may occur in the developing device 6.

As shown in FIG. 4, part of the developer coagulates and sticks to the tip of the doctor blade due to atmospheric conditions such as heat, moisture, and magnetism, forming an aggregate 16.

Since the aggregate 16 is generally larger than the distance between the doctor blade 10 and the developing sleeve 7, the so-called doctor gap, it is caught at the tip of the doctor blade 1°. The caught aggregate 16 grows into a stronger aggregate at the tip of the doctor blade 10 due to powdered ash of the developer 8 sent by the developing sleeve 7 rotating in the direction of arrow A (counterclockwise). Doctor gap narrows.

As a result, the developer passing through the doctor blade 10 is interrupted or the amount thereof is decreased, resulting in a decrease in the density of one image or white spots in the image. This aggregate 1
The cohesive force of No. 6 is such that when only the aggregates 16 are placed on the developing sleeve 7 and the developing sleeve is rotated and the aggregates 16 collide with the doctor blade 10, the aggregates 16 are destroyed by the doctor blade 10. This is to the extent that it is possible. Therefore, it is considered that the reason why the aggregates 16 are formed as described above is because the developer 8 remains in a place where the conveying force of the developing sleeve 7 cannot reach. Therefore, even if such aggregates 16 are generated or mixed,
Growth of the aggregates 16 can be prevented if the aggregates 16 are always in contact with the developing sleeve 7 and the conveying force is exerted thereon.

In this embodiment, in view of the above facts, the rotation of the motor for driving the developing sleeve 7 is controlled as shown in FIG.
6 is prevented from occurring. Reference numeral 17 in FIG. 3 is a drive motor. The control system shown in FIG. 3 employs a quartz lock system using a direct drive (D-D) control element 17. This DD element is a speed control system (AFC)
) and an 8-bit D/A converter system for the phase control system (APC).

The motor control system is connected to a CPU with a built-in microcomputer via a lock output line, a start/stop line, and a CW/CCV line. The lock output is the rotary encoder 1 attached to the motor 17.
8 and the output of the internal oscillator in the DD element 17, the rotation speed of the motor 17 is within the lock range (specified rotation).
This is a signal that is output to the CPU when the While this signal is being output, it indicates that the motor is rotating at a constant rate, and the LED 19 lights up. Further, if this signal is not output, it means that the motor is not rotating normally, and the display unit 20 can notify the operator of this fact.

The CPU connects the motor 17 through the start/stop line.
Outputs a start or stop signal. Based on this, the motor 17 is started or stopped. Also, CPU
Instructs the motor 17 to rotate forward (CW) or CCW (reverse rotation) through the CW/CCW line. FIG. 7 shows an example of a CW and CCW time chart of the rotation of the motor 17. The driver 21 of the motor 17 is set to CW by the CPU during normal standby. When a printing operation by the laser printer is accepted, the motor 17 rotates in the forward direction, and when the printing operation is completed, the motor 17 stops.

After the motor 17 stops, the driver 21 is set to CCW by the CPU.
This causes the motor 17 to rotate in reverse for a predetermined period of time. When this reverse rotation is completed, the driver 21 is set to CW again. The above cw-ccw process is repeated every time the laser printer performs a printing operation.

As described above, in this embodiment, the developing sleeve 7 rotates counterclockwise for a predetermined period of time, that is, rotates in the opposite direction to the developer conveying direction, following the clockwise rotation for conveying the developer. Due to this reverse rotation, even if aggregates 16 are generated as shown in FIG. 4, a space is first created near the doctor blade 10, and then the aggregates 16 are moved to the developing sleeve by their own weight or magnetic attraction force. 7 and comes into contact with the sleeve. The smaller the amount of developer passing through the developing sleeve 7, the better this contact condition will be. When the aggregate 16 comes into contact with the developing sleeve 7 , the conveying force of the developing sleeve 7 is sufficiently applied to the aggregate 16 .

Therefore, when the developing sleeve 7 rotates again in the normal developer conveying direction A as shown in FIG. pass through. In this way, the developer 8 is stably supplied to the photoreceptor 1.

Using the laser printer shown in Figure 1, 10
After printing 10,000 print products, 2 dots in black area,
When we investigated the defects caused to the image by the aggregate 16 using a test pattern of 2 white dots (1 dot = 80μ), we found that if the developing sleeve is not reversed after printing, more than 80% of the prints will have some kind of problem on the image. A omission occurred.

On the other hand, if the reverse rotation is performed after printing,
More than 90% of the prints had no abnormalities, and the remaining 10% of the prints had very slight damage, and there were no printed products with one image missing.

Although the present invention has been described above with reference to one embodiment, the present invention is not limited to that embodiment and can be modified in various ways. For example, the timing for reversing the developing sleeve 7 may be any time other than when a printing operation is being performed, and therefore it may be before the printing operation.

Effects According to the present invention, since an appropriate amount of developer can be constantly fed to the photoreceptor, image defects such as white spots can be prevented from occurring.

[Brief explanation of the drawing]

FIG. 1 is an overall side sectional view of a laser printer using a developing device according to an embodiment of the present invention, FIG. 2 is a side sectional view of the developing device, and FIG. 3 is a diagram of a rotation control circuit for a developer conveying means. FIG. 4 is a block diagram showing an example. Figures 5 and 6 are diagrams showing how the developer moves, and Figure 7 is a diagram showing how the developer moves.
The figure is a timing chart of the rotation of the developer conveying means. 1...Latent image carrier (photoreceptor)

Claims (1)

[Claims] a developer conveying means arranged to face the latent image carrier and conveying the developer toward the latent image carrier by rotating in a fixed direction; and a developer conveying means disposed at a predetermined gap with respect to the developer conveying means. In a developing device having a developer layer thickness regulating member that regulates the developer conveyed toward the latent image carrier to a constant layer thickness as described above, the developer is A developing device characterized in that the conveyance means is rotated in a direction opposite to the above-mentioned fixed direction for a predetermined period of time.