JPH0377508B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic brush developing device for an electronic copying machine.

A magnetic brush developing device has a roller provided to rotate and one or more permanent magnets provided inside the roller, and magnetically attracts toner particles or carriers and toner particles to the outer peripheral surface of the roller to form a brush. Form. The latent image is developed by bringing the toner particles or carrier and the magnetic brush of the toner particles or developer into contact with a latent image carrier carrying the electrostatic latent image on its surface.

The roller of such a magnetic brush device, that is, the developing roller, has the function of capturing the developer, the function of making the thickness of the adsorbed developer layer uniform, that is, the cutting function, the function of development, and the function of facilitating the removal of residual developer after development. It must be constructed in such a way that it can effectively release the

Here, in the magnetic brush developing device, a magnet provided inside a developing roller disposed opposite to the latent image carrier is used to form a magnetic brush that brings the developer on the developing roller into contact with the latent image carrier. A main pole, for example, an N pole, and a plurality of magnetic poles for attracting and transporting the developer to the developing roller are formed. The plurality of magnetic poles are alternately arranged magnetic poles of opposite polarity.
Further, the magnetic brush in the developing roller comes into contact with or comes close to the electrostatic latent image carrier, and the developer after passing through a development area where the latent image is visualized is further attracted to the electrostatic latent image carrier. In order to prevent fog from occurring or adhesion of carrier in the two-component developer, a complementary pole having a polarity opposite to that of the main pole is disposed adjacent to the main pole.

In order to downsize the developing device, it is necessary to downsize the developing roller. Moreover, if the magnetic force on the developing roller is not impaired, the size of the magnet cannot be made very small. If you make the developing roll smaller, there is a limit to how small the magnet can be.
A problem arises in that unnecessary magnetic poles of the magnet act on the magnetic field on the developing roller. For example, the N pole, which is the opposite pole of the magnet that forms the complementary pole of the S pole, is not located near the center of the developing roller, but is close to the developing roller, as if there were only one N pole facing the roller surface of the developing roller. As a result, detachment of the developer, which is one of the functions required of the developing roller, is hindered.

An object of the present invention is to provide a magnetic developing device that solves the above problems.

In a magnetic brush developing device, a magnet is used inside the developing roller that is magnetized uniformly in the axial direction of the developing roller, but the magnetic field is not uniform on the developing roller, and fringing occurs at the end of the developing roller. The effect weakens the magnetic field. Furthermore, the force with which the magnetic developer is attracted to the developing roller is affected not only by the strength of the magnetic field but also by the condensation force due to the magnetic charge of the developer itself.

The force Fr in the normal direction of the developing roller that acts on the developer attracted to the developing roller magnetized in a sinusoidal waveform (σ = σ _p cos mθ) is expressed as Fr = k{cos( 2mθ)+μ ² −1/μ ² +1}. Here, k is a constant determined by the shape of the developing roller and the thickness of the adsorbed developer.

Therefore, depending on the location of the developer, there are places where the developer receives an attractive force from the developing roller and places where it receives a force that repulses and pulls it away, but overall, the attractive force prevails, and moreover, the developer mutually interacts with each other due to cohesive force. This prevents the developer from coming off the developing roller.

At the end of the developing roller, the magnetic force is weakened and at the same time there is no developer next to it, so the balance of developer adsorption is lost and the developer is likely to separate. Therefore, the developer does not come off the developing roller uniformly, but comes off from the end first. If such a location is near the opening of the developing device, the developer will spill out of the developing device and contaminate the machine.

As mentioned above, even if the unnecessary magnetic poles in the developing roller act on the surface of the developing roller and weaken the strength of the magnetic field, the developer will similarly be detached, causing the problem of contaminating the inside of the machine with spilled developer. .

The present invention solves the above-mentioned conventional problem, which is due to the fact that the diameter of the developing roller has become smaller due to miniaturization of the device, and the opposite pole of the auxiliary magnet adjacent to the main magnet is closer to the surface of the developing roller. The magnetic flux formed between the opposite pole and the adjacent conveying magnet has the negative effect of preventing the developer from leaving the developing roller, and the magnetic force of the magnet weakens at the end of the developing roller, causing the developer to attract It is an object of the present invention to provide a developing device that solves the problem of unbalanced development and uneven separation of the developer from the developing roller.

The present invention solves the above problems by including a rotatable non-magnetic developing roller disposed facing an electrostatic latent image carrier at a predetermined interval, and a main pole disposed within the developing roller at a position facing the developing area. a main magnet disposed on the upstream side in the rotational direction of the developing roller in the developing area; The magnetic flux formed between the opposite pole of the auxiliary magnet on the opposite side of the auxiliary magnet and the conveying magnet is applied to the developer on the surface of the developing roller. In a magnetic brush developing device in which the auxiliary magnet is arranged at a position where it exerts an influence, a magnetic adjustment member made of a ferromagnetic material is provided that connects the opposite pole of the auxiliary magnet and the transport magnet so as to create a magnetic short circuit, The problem was solved by a magnetic brush device characterized in that the length of the magnetic adjustment member in the axial direction of the developing roller is shorter than the length of the auxiliary magnet at both ends.

The details of the present invention will be explained with reference to embodiments shown in the figures.

In FIG. 1, a developing roller 2 is rotatably supported at a predetermined distance from an electrostatic latent image carrier 1, such as a photosensitive drum.

Inside the developing roller 2, there is a main magnet 3 as a magnet forming a main pole at a position facing the electrostatic latent image carrier 1.
is fixed. For example, the N pole of the main magnet 3 faces the developing roller 2, and forms a magnetic brush of developer on the developing roller. In the range where the main magnet 3 faces, the magnetic brush forms a development region in contact with or close to the electrostatic latent image carrier 1, and develops the latent image into a visible image.

A supplementary magnet 4 is arranged adjacent to the main magnet 3 on the downstream side of the developing roller 2 in the rotational direction. The auxiliary magnet 4 is arranged such that the auxiliary pole of the opposite polarity (for example, the S pole) to the main pole (for example, the N pole) of the main magnet 3 faces the developing roller 2 . The auxiliary magnet 4 rapidly draws in the lines of magnetic force coming from the main pole, and the gradient of the magnetic field near the exit of the developing area becomes large. For this reason, the developer brush at the exit of the developing area becomes hard, which acts to prevent fog and carrier adhesion. The main magnet 3 is relatively large because it requires strong magnetic force, and the auxiliary magnet 4 is arranged adjacent to the main magnet 3, so it is arranged so that the central axis connecting the N and S poles faces in the radial direction of the developing roller 2. Therefore, the complementary pole (S pole) of the auxiliary magnet 4
The opposite pole, which is the opposite pole (for example, N pole), is also quite close to the developing roller 2, and the surface of the developing roller 2 is likely to be influenced by the magnetic field.

A transport magnet 5 is fixed on the upstream side of the main magnet 3 in the developing roller 2 in the rotational direction so that the opposite poles thereof face the developing roller 2 from the main pole.

The conveyance magnets 5 can be small magnets that can be arranged with an appropriate spacing between the adjacent magnets 3, 4, or 5, so they can be arranged so that their central axes face in the radial direction of the developing roller. can.

In order to eliminate the influence of the opposite pole N of the auxiliary magnet 4, the opposite pole N and the S pole of the adjacent transport magnet 5 are connected by a plate member 6 made of a ferromagnetic material for magnetic shorting.
In particular, it is preferable that the magnetic field created by the pole (S pole) and the opposite pole (N pole) of the auxiliary magnet 4 be 200 GAUSS or less on the surface of the developing roller 2. This eliminates the influence of the north pole of the auxiliary magnet 4 on the magnetic field on the surface of the developing roller 2.

A conveying magnetic roller 7 adjacent to the developing roller 2
is rotatably arranged, and the casing 1 of the developing device
It is formed so as to come into contact with the developer 14 contained in the container 3 . The developer 14 is in the casing 13
A developer reservoir 12 formed by the guide plate 8 and the guide plate 8.
From there, it passes through the gate between the guide plate 8 and the casing 13 and enters around the conveyance magnetic roller 7 .
The present developer is supplied to the developer reservoir 12 from the developer supply port 11 .

Due to the rotation of the conveyance magnetic roller 7, the roller 7
Under the action of the magnet 15 disposed at , the developer is attracted and conveyed clockwise in the figure, and is transferred to and from the developing roller 2 at a location close to the developing roller 2 by the action of the magnetic force.

The adhesion thickness of the developer conveyed by the developing roller 2 is regulated to a predetermined thickness by a doctor 9 made of a non-magnetic material. Excess developer is returned to the developer reservoir 12 along the guide plate 8.

The developer having passed through the doctor 9 and having a uniform thickness forms a magnetic brush at the active position of the main magnet 3, and develops the latent image on the electrostatic latent image carrier 1. After development, the developer that is transported while being prevented from being excessively attracted to the electrostatic latent image carrier 1 under the action of the auxiliary magnet 4 leaves the developing roller 2 at a position where it leaves the influence of the magnetic field of the auxiliary magnet 4 . By selecting the arrangement of the developing roller 2 and the conveying magnetic roller and the arrangement of their respective magnets, the developer that has left the developing roller 2 can be transferred to the conveying magnetic roller 7. The developer transferred to the magnetic conveying roller 7 is conveyed toward the gate through the lower part of the magnetic conveying roller 7, that is, the bottom of the casing 13, and is mixed with new developer supplied from the gate. Ru. In other words, it can be refreshed and transported to the development area in a state where it can be properly developed.

A ferromagnetic plate 6 that connects the opposite pole of the auxiliary magnet 4 and the adjacent transport magnet, that is, a magnetic field adjustment member 6
If the length of the auxiliary magnet is the same as the length of the roller 2 in the axial direction, the developer near both ends of the developing roller in the axial direction will be near the inner inner part of the developing roller 2 due to the strength of the magnetic field and the cohesive force of the developer. It will fall faster than that.
Therefore, even though the developer at the center is transferred to the magnetic transport roller 7, the developer near both ends often falls into the casing 13 as shown in FIG. In this case, as shown in FIG. 2A, the flow initially flows toward the conveying magnetic roller 7, and the effect is essentially the same as that of being passed to the conveying magnetic roller 7, but gradually as shown in FIG. 2 B, Casing 13
When the amount of developer stagnates near the falling position in the casing 13 and the amount of stagnation increases, it becomes blocked between the developing roller 2 and the latent image carrier 1, as shown in FIG. A portion of the developer will spill from the contact area with the body 1. At this point, the length of the magnetic field adjustment member 6 in the axial direction is made shorter than the length of the auxiliary magnet 4, for example, as shown in FIG.

By making the length of the magnetic field adjustment member 6 shorter than the length of the auxiliary magnet 4 and providing portions at both ends of the auxiliary magnet 4 where the magnetic field adjustment member 6 does not act, the strength of the magnetic field on the roller surface at both ends of the developing roller 2 can be reduced. The strength of the magnetic field is made larger than the strength of the magnetic field at the surface of the center of the roller, which eliminates the tendency for the developer to separate from the roller at both ends, and increases the tendency for the developer to adhere to the developing roller and be transported due to entanglement due to magnetic force. In the end, the developer at both ends of the roller also comes off from the developing roller at approximately the same location as the center of the roller.

When using a two-component developer, the carrier tends to adhere to both ends of the roller, but this can be resolved by making the strength of the magnetic field at both ends of the developing roller larger than at the center of the roller, as described above. .

According to the present invention, by providing the ferromagnetic field adjusting member between the auxiliary magnet and the conveying magnet, the influence of the opposite polarity of the auxiliary magnet can be prevented and developer removal can be improved. Moreover, the magnetic field on the roller surface due to the opposite polarity of the auxiliary magnet is
By reducing the 300 to 500 GAUSS to 200 GAUSS or less, it is possible to prevent the developer from moving around with the developer, and the detachment of the developer is almost complete.
The old developer and new developer that have passed through the development area can be mixed well, and a proper development function can always be obtained.

With the above configuration that improves the desorption of the developer,
Problems caused by accelerated detachment at both ends of the developing roller, where developer is easily detached even under normal circumstances, can be solved by increasing the strength of the magnetic field at both ends of the developing roller than at the center, and in particular by increasing the length of the magnetic field adjustment member. This problem was solved by making the auxiliary magnet shorter and providing a portion at both ends of the auxiliary magnet where the magnetic field adjustment member does not act.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of the magnetic brush developing device according to the present invention, Fig. 2 is a cross-sectional view illustrating the development that occurs due to early separation of the developer at both ends of the developing roller, and A, B, and C are changes over time. Diagrams sequentially explaining
FIG. 3 is a schematic diagram illustrating the relationship between the magnetic field adjusting member and the auxiliary magnet. 1... Electrostatic latent image carrier, 2... Developing roller, 3
...Main magnet, 4...Auxiliary magnet, 5...Transportation magnet, 6
...Magnetic field adjustment member.

Claims (1)

[Claims] 1. A rotatable non-magnetic developing roller disposed facing the electrostatic latent image carrier at a predetermined interval, a main magnet disposed within the developing roller and having a main pole at a position facing the developing area, and a developing area. a conveying magnet disposed on the upstream side in the rotational direction of the developing roller; and a copolarity pole having a polarity opposite to the main pole, disposed on the downstream side in the rotational direction of the developing roller in the developing area and close to the main pole. the auxiliary magnet is located at a position where the magnetic flux formed between the opposite pole on the opposite side of the auxiliary pole of the auxiliary magnet and the conveying magnet affects the developer on the surface of the developing roller. In the magnetic brush developing device in which a magnetic brush is disposed, a magnetic adjustment member made of a ferromagnetic material is provided which connects the opposite pole of the auxiliary magnet and the transport magnet so as to create a magnetic short circuit, and the developing roller shaft of the magnetic adjustment member is A magnetic brush device characterized in that the length in the direction is shorter than the length of the auxiliary magnet at both ends.