JPH02181772A - Developing device - Google Patents

Abstract

PURPOSE:To improve the accuracy in detecting a toner concentration by detecting the toner concentration by a magnetic sensor disposed near to a rotor for stirring developer while the rotor for stirring the developer rotates and a developing roller stops because of a bristle cutting. CONSTITUTION:Each developing roller 4Y, 4M and 4C stop except at the action time of developing and at the action time or cutting the bristle, on the other hand, a stirring paddle 11 always continues rotating and stirs the developer even when the developing roller stops. Each magnetic sensor 20 is disposed in an area near to the stirring paddle 11 where the developer is forcibly conveyed by the paddle 11, the toner concentration is detected while the bristle cutting is performed in the developing roller of each developing roller 4Y, 4M and 4C which is not in process of action of developing, and the developing roller stops. Because of this constitution, the speed and the flow quantity of the developer which flows on the magnetic sensor 20 are nearly fixed, and the toner concentration is detected by a plenty of stirred developer, so that the toner concentration of the developer in a developing tank can be detected with accuracy by the magnetic sensor 20.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a developing tank containing a two-component developer consisting of toner and a carrier, a rotating developing roller,
The roller is equipped with a magnet installed therein, a rotating body for stirring the developer that stirs the developer in the developing tank, and a magnetic sensor that detects the toner concentration of the developer in the developing tank. The electrostatic latent image formed on the latent image carrier is visualized by transporting the developer while being supported on the developing roller by the action of the magnetic force of the magnet, and the magnetic sensor detects insufficient toner concentration in the developer. The present invention relates to a developing device that replenishes toner to a developing tank when the developing tank is loaded.

[Conventional technology]

2. Description of the Related Art The above-mentioned type of developing device attached to an image forming apparatus such as an electronic copying machine, a printer, or a facsimile machine is well known. In this type of developing device that uses a two-component developer, as the image forming operation is performed, the toner in the developer is sequentially consumed and the toner concentration decreases, so a lack of toner concentration is detected by a magnetic sensor. At this time, toner is replenished into the developing tank to prevent a decrease in the density of the visible image.

A magnetic sensor detects changes in the magnetic permeability of a developer passing over it.1 For example, when a developer consisting of a magnetic carrier and a non-magnetic toner is used, development occurs when the ratio of the toner decreases. This detects changes in the magnetic permeability of the agent.

In order to accurately detect toner concentration using such a magnetic sensor, it is necessary that the flow rate and velocity of the developer flowing over the sensor be approximately constant during the detection time. For this reason, in the past, a magnetic sensor was provided in an area where the developer transported on the developing roller and subjected to development leaves the developing roller and flows downward. The concentration was being detected. This is done in consideration of the fact that the velocity of the developer that has flown down away from the developing roller is always approximately constant, and its flow rate is also relatively constant.

[Problem to be solved by the invention]

However, the developer immediately after being subjected to development contains a mixture of areas where toner has transferred to the electrostatic latent image and the toner density has become low, and areas where it has not.

Even if such a toner concentration of the developer is detected, it is not possible to accurately detect the average toner concentration of the developer present in the entire developing tank.

In addition to the two conditions mentioned above, the conditions for correctly detecting toner concentration with a magnetic sensor include the presence of a large amount of developer around the sensor, and the sufficient detection time required for the sensor. One example is that it is ensured. However, when placed in the position mentioned above,
In a conventional magnetic sensor that detects toner concentration when the developing roller rotates, a large amount of developer is carried on the developing roller at the time of detection, so the amount of developer present around the sensor is small. Furthermore, in a developing device in which the developing roller is stopped during non-developing operations, the rotating time of the developing roller is short, and therefore sufficient detection time cannot be secured. For these reasons, conventional magnetic sensors may not be able to accurately detect toner concentration.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a developing device of the type mentioned at the outset, which eliminates the above-mentioned conventional drawbacks with a simple construction and allows more accurate detection of toner concentration.

[Means to solve the problem]

In order to achieve the above object, the present invention provides the following steps after the development operation is completed:
The ears are cut so that there is no developer on the developing roller, and the magnetic sensor is located in an area near a rotating body for stirring the developer, where the developer is forcibly conveyed by the rotating body. The toner concentration is detected by a magnetic sensor.
We propose a configuration in which the developer stirring is carried out while the rotating body is rotating and the developing roller is stopped.

〔Example〕

Hereinafter, an embodiment in which the present invention is applied to a developing device of a full-color copying machine will be described with reference to the drawings.

In the figure, a yellow developing device 3Y is located below a drum-shaped photoreceptor 1, which is an example of the configuration of a latent image carrier.

A magenta developing device 3M and a cyan developing device 3C are provided. Developing tank 10Y of each developing device.

10M, IOC is a two-component developer consisting of only toner particles or toner with additives and carrier.
(not shown), and the colors of toner particles in each of the developing devices 3Y, 3M, and 3C are yellow, magenta, and cyan, respectively.

Each developing device is provided with developing rollers 4Y, 4M, and 4C, which are arranged facing each other around the photoreceptor 1 with a predetermined gap therebetween.

Inside each of the developing rollers 4Y, 4M, and 4C, a magnet 5, a magnetic shield plate 6 made of a magnetic material, and the like are provided in the arrangement shown in the figure, and these are held in a non-rotating state. On the other hand, each developing roller 4Y, 4M, 4
C are individually driven by drive motors (not shown), and are rotationally driven in the direction of the solid line arrow during development.Hereinafter, rotation in this direction will be referred to as "normal rotation."

The developer contained in each of the developing tanks IOY, IOM, and 10G is stirred by a stirring paddle 11, which is an example of a rotating body for stirring the developer. Each stirring paddle 11 biases the outer screw 12, inner screw 13, and stirring blade 14, rotates clockwise and stirs the developer, and each developing roller 4Y, 4M.

Supply developer to 4C. The stirring paddle 11 is driven separately from each developing roller (the driving sources may be separate or the same driving source).

Here, an explanation will be given using the yellow developing device 3Y as an example.
The developer supplied to the developing roller 4Y is supported on the developing roller 4Y by the rotation (normal rotation) of the roller and the magnetic force of the internal magnet 5, and is regulated to a predetermined thickness by the doctor blade 15, and is then developed. It is conveyed in the same direction as the normal rotation direction of the roller 4Y (arrow A direction). This developer is
When it rotates clockwise, it reaches the developing area where the photoreceptor 1 and the developing roller 4Y face each other, where it comes into contact with the photoreceptor 1, and the yellow toner in the developer is electrostatically applied to the electrostatic latent image on the photoreceptor. As a result, the latent image becomes visible in yellow.

When the developer subjected to development reaches the position of the magnetic shield plate 6 in the developing roller 4Y, the magnetic force on the developing roller 4Y is substantially eliminated, so that the developing roller 4Y is moved as shown by arrow B.
and falls onto the stirring paddle 11.

The visible image formed on the photoreceptor 1 is transferred to a transfer paper on a transfer drum (not shown) that is in contact with the photoreceptor 1. Similarly, a visible image formed by magenta toner is formed on the photoreceptor 1 by the magenta developing device 3M, and a visible image is formed by the cyan developing device 3C.
Visible images are obtained using cyan toner, and these visible images are sequentially superimposed on transfer paper on a transfer drum. After all such transfer is completed, the transfer paper is removed from the transfer drum, fixed, and then discharged outside the machine as color copy paper or color recording paper.

Here, when the yellow developing bag U3Y is performing development, the developing rollers 4M and 4C of the other developing devices are subjected to panicle cutting. Further, when developing is performed using the magenta developing bag Wi3M, the developing rollers 4Y and 4C of the other developing devices are subjected to panicle cutting. Furthermore, the cyan developing device 3
When development is being performed by C, the developing rollers 4Y and 4M of other developing devices are subjected to panicle cutting.

The purpose of this is that if the developing rollers other than the developing roller during the developing operation are not trimmed, the visible image of the respective colors formed on the photoreceptor 1 may be disturbed or color mixing may occur. It is from.

Here, for example, assuming that ear cutting is performed at the developing roller 4Y, this is performed as follows.

As mentioned earlier, when the developing roller 4Y rotates normally in the direction of the solid arrow, the developer is magnetically drawn up and carried on the developing roller 4Y. , rotate it in the direction of the dashed arrow. That is,
It reverses it.

During such rotation, there is a magnetic shield plate 6 for the area where the developer is to be pumped up, and no magnet is provided in this opposing area.
The magnetic force is substantially eliminated, and the developer is no longer drawn up, resulting in a state where the developer is not substantially present on the developing roller.

The flow of the developer at this time is indicated by an arrow C. Normally, the ear cutting operation can be completed by reversing the developing roller 4Y once or several times. Such ear cutting is performed in exactly the same manner for the other developing rollers 4M and 4C.

Each of the developing rollers 4Y, 4M, and 4C is stopped at times other than the developing operation and the ear cutting operation.

On the other hand, the stirring paddle 11 continues to rotate and stirs the developer even when the developing roller is stopped.

As the developing operation is performed as described above, the toner concentration in the developer gradually decreases, and if this is left untreated, the visible image's concentration decreases and its image quality deteriorates.

Therefore, the developing tank 10Y of each developing device 3Y, 3M, 3C
, IOM, and IOC are each fixed with a magnetic sensor 20 that detects the toner concentration of the developer in the tank.

When these sensors 20 detect insufficient toner concentration of the developer in each developing tank, 1. From each toner container (not shown).

Toner of each color is replenished into each developing tank. Through such toner concentration control, the toner concentration of each developer is kept within a predetermined range.

As described above, the magnetic sensor 20 detects the toner concentration by detecting a change in magnetic permeability in accordance with a change in the ratio of toner in the developer flowing thereon.

In addition to using such a sensor, there is also a method of detecting the toner density by detecting the amount of toner adhering to the photoconductor 1 with a reflective photosensor, but in a full color copying machine like the one shown in the figure, Since a yellow, magenta, or cyan visible image is formed on each color, the light reflectance of each color is different.

For this reason, even if a reflective sensor is used, it is not possible to accurately detect the toner concentration.If a magnetic sensor 2° is used,
This kind of problem can be avoided.

By the way, in the conventional developing device, a magnetic sensor is arranged at a position indicated by a broken line in the figure and indicated by the reference numeral 200. The sensor 200 measures the toner concentration of the developer that has left the rotating developing roller and flowed downward.
This was detected during the developing operation, but this does not avoid the various drawbacks described above. In addition, in the developing device shown in the figure, in order to prevent color mixing on the photoreceptor, the developing roller is stopped except during the developing operation and the ear cutting operation. The development time is very short, and sufficient detection time cannot be secured.

Particularly in color copying machines, variations in the density of visible images of each color have a large effect on the color reproducibility of the final image, so if toner density detection is inaccurate, the quality of the image is significantly degraded.

Therefore, in the configuration according to the present invention shown in the figure, each magnetic sensor 20 is located near the stirring paddle 11, and
The developer is disposed in an area where the developer is forcibly conveyed as shown by arrow X. Therefore, the speed and flow rate of the developer flowing over the magnetic sensor 20 are almost constant, and the toner concentration of the developer that has been sufficiently stirred by the stirring paddle 11 away from the developing roller is detected. can accurately detect the toner concentration of the developer in the developer tank.

Further, the magnetic sensor 20 is configured to detect the toner concentration while the developing roller is stopped and the stirring paddle 11 is rotating. In other words, substantially no developer is present on the developing roller due to the tip breakage, which is detected while the roller is stopped. Therefore, a large amount of developer exists in the developer tanks IOM, IOY, and IOC, and a large amount of developer exists around the magnetic sensor 20, so that accurate detection can be performed. In the conventional configuration in which toner concentration is detected while the developing roller is rotating, since a large amount of developer exists on the developing roller, the amount of developer around the magnetic sensor 200 decreases, making it difficult to perform accurate detection.

Furthermore, since the present invention performs toner concentration detection during non-development, a sufficiently long detection time can be ensured and detection accuracy can be improved.

The developing devices 3Y, 3M, and 3C shown in the figure are installed and recessed by a removable bottom plate 21 and left and right covers 22, 23, and are pulled out integrally to the front side to remove the bottom plate 21.
Although the cover 22 and 23 can be removed,
In this case, if each sensor 20 is provided at the bottom of each developing tank as shown in the figure, each magnetic sensor 20 can be removed by removing the bottom plate 21 and cover 23 as described above.
0 can be easily replaced.

It is clear that the present invention can also be applied to image forming apparatuses provided with a number of developing devices other than three.

[Effects of the Invention] According to the present invention, toner density can be detected more accurately than before, and when applied to a color copying machine, it is possible to suppress variations in toner density of each color and obtain high-quality images. Can be done.

[Brief explanation of the drawing]

The drawing is a block diagram of a full-color copying machine equipped with a developing device according to the present invention. 3Y, 3M, 3C...Developing device 4Y, 4M, 4C...Developing roller 5...Magnet 20...Magnetic sensor representative Patent attorney Norio Hoshino

Claims (1)

[Scope of Claims] A developing tank containing a two-component developer consisting of toner and carrier, a rotationally driven developing roller, a magnet installed in the roller, and stirring the developer in the developing tank. Equipped with a rotating body for stirring the developer and a magnetic sensor that detects the toner concentration of the developer in the developer tank, the developer is transported while being supported on the developer roller by the rotation of the developer roller and the magnetic force of the magnet. In the developing device that visualizes the electrostatic latent image formed on the latent image carrier by the magnetic sensor and replenishes the toner to the developing tank when the insufficient toner concentration of the developer is detected by the magnetic sensor, after the developing operation is completed. , the ears are cut so that there is no developer on the developing roller, and the magnetic sensor is located in the vicinity of a rotating body for stirring the developer, in an area where the developer is forcibly conveyed by the rotating body. 1. A developing device, characterized in that toner concentration detection using a magnetic sensor is performed while a rotating body for stirring developer is rotating and a developing roller is stopped.