JPH01172881A - Developing device - Google Patents

Abstract

PURPOSE:To prevent the generation of uneven density on an image by providing additionally a magnet for forming a repulsion magnetic field so that a developer is carried toward a developer stirring, carrying and drawing member, in a magnet roller. CONSTITUTION:With respect to a magnet P8 for drawing magnetically a developer from a developer stirring, carrying and drawing member 6 and drawing it up, among each magnet in a magnet roller 20, a magnet P10 for forming a repulsion magnetic field so that the developer carried on the magnet roller 20 after having passed through a part 29 for supplying the developer to a developing sleeve is carried toward the developer stirring, carrying and drawing member 6 is provided additionally in the magnet roller 20. Accordingly, the developer carried through the lower part of the roller 20 by a magnetic field by the P10 pole is led positively toward the developer stirring, carrying and drawing member 6. In such a way, the generation of uneven density on an image is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing device used in an image forming apparatus such as an electrophotographic copying apparatus.

Some types of image forming devices, such as electrophotographic copying machines, form an electrostatic latent image on a latent image carrier such as a photoreceptor, and then process this electrostatic latent image with a powder developer. It is becoming visible. FIG. 3 shows an example of a dry type developing device that achieves this function.

In the developing device of this example, a two-component developer containing carrier in addition to toner is stored in the developer container 1, and a toner concentration detection sensor 2 detects a decrease in the toner concentration of the developer. At this time, toner is supplied from the toner replenishing section 3 to the developer in the container 1 via the toner replenishing roller 4. At least a portion of the developer, for example only the carrier or both the carrier and the toner, is made of a magnetic material.

A developer agitation conveyance pumping member 6 is provided in the developer container 1, and the developer agitation conveyance pumping member 6 is shown as an example in FIG.
is return auger 8. It consists of a 9° paddle, 10 supply augers, etc. Of these, the return auger 8 and paddle 9 rotate in the direction of the arrow as a pair, with the return auger 8 transporting the developer from the back side to the front side in the figure, and the paddle 9 transporting the developer around the circumference. Pump up and transport in the direction.

On the other hand, the supply auger 10 at the center rotates in the direction of the arrow to convey the developer from the front side to the back side.

In this way, the developer agitation conveyance pumping member 6 agitates the developer while conveying it in this axial direction, and also agitates the developer in a direction perpendicular to the axial direction while pumping up the developer with the paddle 9. During this bidirectional stirring, the carrier and toner are triboelectrically charged to opposite polarities. The developer stirring and conveying pumping member 6 stirs the developer in two directions, the vertical direction (axial direction) and the horizontal direction (direction orthogonal to the axial direction), and is also called a dual cross mixer. It also achieves the developer dispersion function of crushing the toner and mixing it into the developer.

Similarly, a developing sleeve 12 is provided within the developing container 1.
This consists of five fixed magnets p, , p, , p in the internal circumferential direction.
,, p4. The magnetic poles S and N on the side facing the sleeve 12 of these magnets are set as illustrated in the figure. Further, a magnetic shield plate 13 made of a magnetic material such as iron is provided inside the developing sleeve 12, and this can be moved between the solid line and the imaginary line position, and when the developing device performs development, it is moved to the solid line position It is located in The magnets P□~5 are hereinafter referred to as P□~5 poles.

A magnet roller 20 made of a non-magnetic material is provided between the developing sleeve 12 and the developer agitating conveyance pumping member 6. Like the developing sleeve 12, this magnetic roller 20 is immediately rotated in the counterclockwise direction, and the inner circle is rotated immediately in the counterclockwise direction. Four fixed magnets p in the circumferential direction,
p7. It is an array of p,, p,. The magnetic poles of these magnets facing the magnet roller 20 are also set as illustrated in the figure. Below, magnet P,
~P3 is called P6~P, a pole.

In order to perform development using the developing device, the developing sleeve 1
When supplying developer to P2, the magnetic shield plate 13
Both poles P are connected to the etched part (corner) of the pole and P3 pole.
,, p, are placed so as to cover them. Note that this etched portion is where lines of magnetic force enter and exit.

The developer on the magnet roller 20 is supplied with the developer from the developer agitation conveyance pumping member 6.

The circumferential surface portion where the P, pole, and P9 poles are located is magnetically conveyed and transported toward the developing sleeve 12 . .

In order for this transfer to take place, the P and PG poles have different polarities.

Next, this transported developer is transported on the circumferential surface of the sleeve in the order of P3 pole, P4 pole, P, and pole.

During this conveyance, the developer on the sleeve 12 moves between the P4 pole and the P4 pole.
, at the doctor blade 14 located between the poles,
The excess material is scraped off and the thickness is set to a value suitable for development.

In this state, the developer on the sleeve 12 is transferred to the latent image carrier,
For example, a drum-shaped photoreceptor 15 rotating in the direction of the arrow as shown in the figure
The electrostatic latent image formed on the surface of the photoreceptor is developed by the toner in the developer.

Next, when the developer on the developing sleeve 12 reaches the P2 pole, the developer on the sleeve reaches the magnetic shield plate 1.
Since the magnetic field of the P2 pole is shielded by the action of No. 3, it is released from the magnetic field, moves away from the sleeve, and is carried toward the magnet roller 20.

Note that when the developing device does not perform development, the magnetic shield plate 13 is displaced to the imaginary line position, thereby cutting off the supply of developer to the sleeve 12. At this time, the developer is magnetically attracted to the magnet roller 20, and adhesion of the developer to the developing sleeve 12 is more reliably prevented. That is, the developer is held on the roller 20 by magnetic force. In addition, the magnetic shield plate is
After a predetermined period of time has elapsed after it was brought to the position indicated by the chain line in the figure.

The developing sleeve 12, roller 20, and pumping member 6 may be stopped, or they may be kept rotating.

In addition, what is indicated by the reference numeral 26 is a doctor blade that forms a wedge-shaped space 27 with the magnet roller 20.
This is to squeeze the developer on the roller, apply stress and triboelectrically charge the developer more strongly, and also regulate the amount of developer when the developer supply to the developing sleeve 12 is cut off.

That is, a large amount of developer is retained on the magnet roller 20 and the developer is prevented from adhering to the developing sleeve 12.

The developing sleeve 12 is an example of a developer carrying member that develops an electrostatic latent image on a latent image carrier with a carried developer.

Here, the developer carried from the lower part of the developing sleeve 12 toward the magnetic roller 20 and the developer still carried on the roller are conveyed toward the lower part of the roller 20 by the P7 pole of this roller. , After that, the developer is conveyed toward the developer agitation conveyance pumping member 6. Next, the developer is pumped up counterclockwise from the lower part of the developer stirring, conveying and pumping member 6, and is magnetically attracted toward the P1 pole of the magnet roller 20.

Here, in the conventional example shown in FIG. 3, when the fluidity of the developer deteriorates due to high ambient humidity, the developer is transferred from the lower part of the magnetic roller 20 to the developer stirring conveyance pumping member 6. The developer gradually accumulates in the area indicated by the reference numeral 28.

In this case, the accumulated developer is circulated along with the row 520 due to the magnetic field of the P pole of the magnet roller 20. This is because such a developer has a low toner concentration.

If this is incorporated into the developer on the circumferential surface of the roller 20, this developer with a low toner concentration will be transferred to the developing sleeve 12.
There is a large possibility that the toner particles will be used for development via the wafer, which may cause density unevenness on one image.

■ The object of the present invention is to eliminate the above-mentioned conventional drawbacks by guiding the developer on the magnetic roller toward the developer agitation conveyance pumping member so that the developer is not taken directly onto the magnetic roller. It's about doing.

In order to achieve the above-mentioned object, the present invention includes a developer container that accommodates a developer, a developer agitation conveyance pumping member that agitates and pumps up the developer in the developer container, and a developer agitation conveyance pumping member that agitates and pumps up the developer in the developer container; A developer carrying member that develops the electrostatic latent image formed on the latent image carrier with the carried developer, and an internal circumference provided between the developer carrying member and the developer stirring conveyance pumping member. a magnet roller having a plurality of fixed magnets arranged in a direction, magnetically transporting the developer from the developer stirring conveyance pumping member and supplying it to the developer carrying member; In contrast to the magnet that magnetically attracts and pumps up the developer from the developer stirring and conveying pumping member, the developer carried on the magnetic roller after passing through the part that supplies the developer to the developer carrying member is developed. This device is characterized in that a magnet that forms a repulsive magnetic field is additionally provided within the magnet roller so that the agent is conveyed toward the stirring, conveying, and pumping member.

The present invention will be explained below based on one embodiment. In this description, the same reference numerals are used for the members that achieve the same functions as those in the conventional example for convenience.

FIG. 1 shows an embodiment of the present invention, and the feature of this embodiment is that one of the magnets in the magnet roller 20 magnetically attracts the developer from the developer agitation conveyance pumping member 6. The developing sleeve 12 is
The developer carried on the magnet roller 20 after passing through the part 29 that supplies developer to The magnets P1 . is additionally provided within the magnet roller 20. That is, in this example, five magnets are installed inside the roller 20.

Now, magnet P1° is Pl. This Pl is called a pole.

The pole faces the developer stirring, conveying and pumping member 6 together with the P pole, and is adjacent to the P pole. and,
Pl. The pole is p with respect to the rotation direction of the magnet roller 20.
It is provided upstream of the H pole.

P as shown in the figure, and Pl when the pole is a north pole.

The pole is the same north pole as the north pole, and the two magnetically repel each other.By this repulsive magnetic field, the developer conveyed under the magnet roller 20 is guided in the direction of arrow a, and the developer It is reliably conveyed to the stirring conveyance pumping member 6.

On the other hand, Pl forms a repulsive magnetic field with respect to the P pole.

Without the pole, if developer accumulates in the area 28 (FIG. 3), this developer will not be mixed with the toner being replenished and will be incorporated into the developer on the circumferential surface of the roller 20. It ends up.

On the other hand, if a Pll and a pole are provided, this P-work. The developer conveyed under the roller 20 by the magnetic field generated by the poles is actively guided toward the developer agitation conveyance pumping member 6, so that the above-mentioned accumulation does not occur.

Problems caused by this, ie, occurrence of density unevenness on the image, can be prevented.

In the embodiment shown in FIG. 1, the magnetic pole structure in the magnet roller 20 is a five-pole structure, but as shown in FIG. You may also do so.

The P pole and the P1□ pole are in a pair configuration and have different poles.

Also, Pl. Pole and P. In the same way as poles, they are opposite poles in a paired configuration. Since the P pole and the P□2 pole have the same polarity, they magnetically repel each other, and the developer carried under the lower part of the magnet roller 20 is Po. At the pole, the developer leaves the roller and is guided toward the developer agitation, conveyance, and pumping member 6 (FIG. 1). Even with such a magnetic pole configuration, it is possible to achieve the same function as the above-described embodiment.

As described above, according to the present invention, developer having a low toner concentration is prevented from being taken into the magnet roller and circulated, so it is possible to avoid the occurrence of density unevenness on an image, and to minimize this. This can be realized with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of one embodiment of the present invention, FIG. 2 is a schematic diagram of another configuration example of the magnet roller, and FIG. 3 is a sectional view of a conventional example. 1...Developing container 6...Developer stirring conveyance pumping member 12...Developing sleeve 20 as a developer carrying member.
...Magnetic roller ps, p□. ···magnet

Claims (1)

[Claims] A latent image carrier is formed by a developer container containing a developer, a developer agitation conveyance pumping member that transports, stirs and pumps up the developer in the developer container, and a supported developer carried on the peripheral surface. A developer carrying member for developing an electrostatic latent image, and a developer stirring member having a plurality of fixed magnets arranged in the circumferential direction between the developer carrying member and a developer stirring conveyance pumping member. and a magnet roller that magnetically transports the developer from the transporting and pumping member and supplies it to the developer carrying member, and among the magnets in the magnetic roller, the developer is transported from the developer stirring and transporting and pumping member. In contrast to the magnet that magnetically attracts and pumps up the developer, the developer carried on the magnetic roller after passing through the part that supplies the developer to the developer carrying member is conveyed towards the developer agitation conveyance pumping member. A developing device characterized in that a magnet for forming a repulsive magnetic field is additionally provided within a magnet roller.