JPS5930918Y2 - magnetic brush developing device - Google Patents

Description

[Detailed description of the invention] The present invention is a magnetic brush development method in which an electrostatic latent image formed on the surface of an image carrier such as an electrophotographic wedge electrostatic recording device is developed with a two-component developer consisting of toner and carrier. It is related to the device.

In a magnetic brush developing device using a two-component developer,
It is common to use a non-magnetic toner and a magnetic material such as iron powder as a carrier2.And when the developer is used repeatedly, the toner σ is unilaterally consumed and the toner mixing ratio decreases. 2. If the amount of toner in the developer decreases, it is not possible to improve the image quality of the copy, so new toner (reinforced by the amount of decrease) must be added.

Various toner concentration detection devices are known as devices for detecting such changes in toner.

In particular, a magnetic toner concentration detection method is widely adopted, taking advantage of the fact that the developer is a dynamic developer.

In method 2, which magnetically detects the toner concentration of the developer, the developer is placed in a certain volume within the sleeve, and as the toner mixing ratio changes, the amount of magnetic carrier in the volume also changes. There are two systems that use so-called bulk density, which detects the concentration using changes in the inductance of a coil wound around the coil, and one that allows the developer to drip down from an orifice of a predetermined size and flow down per unit time. There is a method that uses so-called fluidity, which uses the flow rate of the developer to change depending on the toner concentration and detects the toner concentration by detecting the magnetic permeability of the developer while it is flowing through a slight change in the inductance of the coil. It has been known.

If such a device that magnetically detects toner concentration is placed within the range of influence of the magnetic force of the magnets placed around it, it will have an adverse effect on the developer flowing down inside the toner concentration detection device, causing problems with development. Accurate toner density detection may become impossible due to poor toner flow or blockage, which may prevent the toner concentration from being accurately detected.In particular, as shown in Figure 1, if one of the developing rollers is overloaded, it may cause the toner to not flow. The above-mentioned problems are unavoidable in a device that performs the pumping of the agent and the developing action. In FIG. 1, the photoreceptor drum 1 is rotating counterclockwise, and the Developing roller 2 at the bottom
is located.

The developing loaf-2 includes a non-magnetic sleeve 3 that rotates clockwise, and magnets 4, 5, 6 fixedly installed inside the sleeve 3.
, 7.8.

The doctor plate 9 is moved to the developing container 10 by the developing roller 2.
It is also provided to remove excess developer that has been pumped up and to straighten the M brushes on the sleeve 3.

The developer removed by this doctor plate 9 is guided by a separator 11 and returned to the developer container 10 again.

A magnetic toner concentration detection device 12 is attached to this separator 11.
is installed.

The magnet inside the developing roller 2 must be placed in order to draw up the developer, and due to the magnetic force of the magnet 5, the developer flowing down inside the toner concentration detection device 12 can become clogged at the orifice 13. This phenomenon occurs.

Therefore, in order to shield the magnetic force of the magnet 5, the magnet 5 and the toner concentration detection device 12 are placed under the separator 11.
However, it was not possible to achieve a complete magnetic shielding effect, and the toner concentration could not be detected accurately.

In addition, when we conducted an experiment to create a magnetic shielding effect using a magnetic material such as iron, which is the separator 11, the magnetic shielding effect was indeed exhibited, and the flow of developer through the orifice was normal, but the separator 11 and the sleeve 3, the developer was clogged between the two, and it became impossible to sufficiently pump up and supply the developer to the developing section.

The present invention has been devised in view of the above-mentioned points, and an object of the present invention is to provide a magnetic brush developing device that allows a magnetic toner concentration detection device to function normally and can appropriately draw up and supply developer to a developing section. With the goal.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a diagram for explaining the principle of the present invention.

The position of the magnet 5 indicated by a solid line in the figure is the same as the position of the magnet in the developing device of FIG.

The surface of the magnet 5 facing the sleeve 3 is at approximately the same height as the orifice 13 of the toner concentration detection device 12.

The present inventor experimented by changing the position of the magnet 5, which greatly affects the toner concentration detection accuracy, to the upper and lower positions shown by imaginary lines A and B in the figure, respectively.

1. At the upper position of the magnet 5 indicated by the imaginary line A, that is, the magnet 5
If the lower corner of the toner concentration sensor 12 is positioned above the orifice 13, developer clogging in the toner concentration detection device 12 will occur.
It was found that the condition was worse than the case shown in Figure 1.

Next, the magnet 5 is placed at the lower position indicated by the imaginary line B, that is, the magnet 5
If the upper corner is positioned below the orifice 13, developer clogging in the toner concentration detection device 12 will occur.
No problems with developer flow were observed.

FIG. 3 shows an embodiment of the magnetic brush developing device of the present invention in which the magnets 5 are arranged at appropriate positions as described above.

In the figure, parts having the same functions as the apparatus in FIG. 1 will be explained using the same reference numerals.

Magnets 4', 5', 6' fixed in the sleeve 3,
7' and 8' are the state 11ff in which the magnets shown in Figure 1 are rotated counterclockwise by an angle θ without changing the spacing between them.
i is determined.

Magnets 4' and 5' are magnets for drawing up developer, magnet 6' is a main developing pole, and magnets 7' and 8' are magnets for transporting developer.

The magnetic poles from the magnet 4' to the magnet 8'1 are arranged so that N poles and S poles alternate, and only adjacent magnets 4' and 8' have the same polarity.

In this portion, the developer adhering to the sleeve 3 after development is removed by the homopolar repulsion action of the magnet.

By the way, as mentioned above, the magnet 5' is attached so that its upper corner is located at the orifice 1 of the toner concentration detection device 12.
It is arranged below position 3.

The developer in the developing container 10 is drawn up by the sleeve 3, and the height of the magnetic brush is regulated by the doctor 9 along the way.

The electrostatic latent image formed on the arranged magnetic brush photosensitive drum 1 is visualized.

Excess developer removed by the doctor 9 is guided by a scraper 11 and returned to the developer container 10.

Two stirring members 15 and 16 are rotatably disposed within the developer container 10, and each stirs the developer laterally in the direction of its rotation axis to equalize the toner concentration.

A portion of the developer flowing down on the scraper 11 is separated so as to flow down the toner concentration detection device 12 .

This toner concentration detection device 12 is of a type that detects the toner concentration based on the fluidity of the developer, and therefore the orifice 1
It has 3.

When the toner concentration decreases, a control circuit (not shown)
The toner replenishing device 17 is operated to replenish a predetermined amount of toner into the developer container 10.

In this embodiment, as described above, the magnet 57 closest to the toner concentration detection device 12 is placed below the orifice 13, so that there is no possibility that the developer will get stuck inside the toner concentration detection device 12. Ta.

However, in this embodiment, the amount of developer pumped up by the sleeve 3 was slightly reduced.

Although this is not a fatal flaw, in order to obtain the normal amount of developer pumped up, the pumping magnet 4' was rotated clockwise by an angle θ as shown in Fig. 1 and placed in its original position. It had no effect.

Therefore, it was found that there is a limit to the ability of the magnets to be placed in order to improve the pumping of the developer, so experiments were carried out on the pumping performance of the developer by changing the surface condition of the sleeve 30 in various ways.

As a factor for the surface condition, experiments were conducted by varying the pitch of a plurality of grooves extending parallel to the axial direction formed on the surface of the sleeve 30.

Figure 4 shows the experimental data.

The horizontal axis represents the pitch (rra) of the grooves on the sleeve 3, and the vertical axis represents the amount of developer pumped up when the pitch is one row or less.
Each represents the relative value of the amount of developer pumped up when it is set to 0.

The developer is a two-component developer using a magnetic carrier with a particle size of approximately iooμ.

According to this, it was found that when the pitch is 3rIrIrL or less, there is almost no change in the pumping amount, and when the pitch exceeds this, the pumping amount decreases rapidly.

Experiments have shown that when the relative value is lower than 0.5, the effect of insufficient developer appears on the developed image.

Therefore, it has been found that the pitch must be kept below 4TIrIIL.

That is, the pitch must be less than 40 times the carrier particle size.

Further, in another experiment, it was found that even if a carrier having a particle size of 300 μm is used, it is still good to use a carrier particle size of 40 times or less.

On the other hand, in the above experiment, when an electrostatic latent image on the photosensitive drum 1 was actually developed using sleeves of various pitches, the results were as shown in FIG. 5.

The horizontal axis represents the pitch (rrrm), and the vertical axis represents the image characteristics.

The image characteristics are the developed image quality classified into four levels based on visual judgment.

The first stage is very bad, the second stage is bad, the third stage is somewhat good, and the fourth stage is good, and each stage is divided into upper, middle, and lower.

According to this, it was found that the image characteristics were good when the pitch was 1.5 m or more, but when the pitch was smaller than i, 577B, the image characteristics deteriorated rapidly.

The practical limit of image characteristics is the third stage 1.

That is, it was found that the pitch was required to be 0.8 m or more.

Even in this case, even when experimenting with different carrier particle diameters, it was found that a pitch of 8 times or more the carrier particle diameter is required.

In order to satisfy both conditions, it has been found that the pitch of the grooves on the sleeve is preferably within a range of 8 to 40 times the carrier particle size used.

When such a sleeve was used in an experiment using the magnetic brush developing device shown in FIG. 3, the ability to draw up the developer was greatly improved.

Phenomena of spike marks and decrease in image density that occur in solid images due to insufficient pumping of developer do not occur at all.

FIG. 6 shows an example of such a sleeve.

The sleeve 3 is made of aluminum or a material whose surface is hard alumite processed, and a plurality of grooves 18 are formed on the surface thereof in parallel to the direction of the rotation axis of the sleeve 30.

The groove 18 has a V-shaped cross section, its depth d is 2 to 3 times the carrier particle diameter used, and the opening width W is also 2 times the carrier particle diameter.
~3 times as much.

As described above, the pitch p between the grooves 18 is 8 to 40 times the carrier particle diameter.

In the above-described embodiments, an example in which an electrostatic latent image on a photoreceptor is developed with a magnetic brush has been described, but the present invention is not limited to this, and the electrostatic latent image on a dielectric material or an electrostatic recording material may be developed. It is also possible to apply the same method to objects.

FIG. 7 shows another embodiment of the invention.

Components having the same functions as those of the magnetic brush developing device shown in FIG. 3 will be designated by the same reference numerals, and detailed description thereof will be omitted.

The developing roller 19 is composed of a non-magnetic cylindrical sleeve 20 that rotates counterclockwise, and magnets 21, 22, and 23 fixedly installed within the sleeve 20.

The magnets 21 and 22 are magnets for drawing up developer, and the magnet 23 is a developing main pole magnet facing the photosensitive drum 1.

The scraper 24 has its tip disposed close to the surface of the sleeve 200 in order to remove the developer after development on the sleeve 20, and is obliquely disposed as a whole.

This scraper 24 includes a magnetic toner concentration detection device 1.
2 is installed.

A doctor 25 attached to the wall of the developer container 10 is disposed between the magnets 22 and 23, and regulates the amount of developer on the sleeve 20.

By the way, the magnet 21 closest to the toner concentration detection device 12
As shown in the figure, since the magnetic force of the magnet 21 is located below the orifice 13 of the toner concentration detection device 12, the magnetic force of the magnet 21 does not adversely affect the toner concentration detection device 12.

Therefore, in a magnetic brush developing device that is not of the type in which the developer passes through the sleeve portion facing the toner concentration detection device 12, the developer can be drawn up and the toner concentration accurately detected.

In particular, since the doctor 25 is not located in the upper part of the sleeve, the ability to draw up the developer will not deteriorate as explained in connection with the above-mentioned embodiments.

As described above, according to the present invention, even if the magnetic toner concentration detection device is placed close to the developing roller that has a built-in magnetic field generating means such as a magnet, it is possible to prevent the magnetic developer from clogging the toner concentration detection device. , the toner concentration of the developer can always be accurately detected without causing poor flow.

Further, the developer can be pumped up by the sleeve to the extent that it does not cause any practical problems.

Furthermore, as a result of this, the entire magnetic brush developing device can be kept compact, and the structure is extremely simple and inexpensive.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conventional magnetic brush developing device, FIG. 2 is a diagram for explaining the principle of the present invention, and FIG. 3 is a sectional view of a magnetic brush developing device showing an embodiment of the present invention. Figure 4 is a graph showing the relationship between the pitch of the grooves on the sleeve and the amount of developer pumped up, Figure 5 is a graph showing the relationship between the pitch of the grooves on the sleeve and image characteristics, and Figure 6 is the sleeve used in the present invention. FIG. 7 is a sectional view of a magnetic brush developing device showing another embodiment of the present invention. 1.--Photosensitive drum, 2,19...Developing roller 3
．． 20...Sleeve, 4-8.4', 8', 21-2
3... Magnet, 10... Developer container, 11.24...
Separator 12...-toner concentration detection device, 13...
...orifice, 18...groove.

Claims (1)

[Claims for Utility Model Registration] ■ A rotatable non-magnetic cylindrical sleeve that forms a magnetic brush of a two-component developer consisting of toner and carrier on its surface, and a plurality of magnets fixed within the sleeve. a separator for removing excess developer or developed developer on the developing roller; and a part of the developer flowing down on the separator is collected and passed through an orifice to detect the toner concentration. A magnetic brush developing device comprising a magnetic toner concentration detection device, characterized in that the magnet closest to the toner concentration detection device among the magnets is arranged below the position of the orifice. Magnetic brush developing device. 2. A utility model characterized in that the surface of the sleeve is sealed with a large number of grooves provided in its axial direction, and the interval between the grooves is 40 times or less the carrier particle diameter of the developer. A magnetic brush developing device according to claim 1.