JP2878322B2 - Developing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device in which a plurality of developing sleeves are provided around a latent image carrier.

[Conventional technology]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a facsimile, and a printer, a dry developing device is widely used in a type in which an electrostatic latent image is formed on a latent image carrier and is visualized with toner. . Among such developing devices,
In a magnetic brush type developing device, the developer is magnetically carried on the peripheral surface of the developing sleeve and transported.A developing sleeve that achieves such a developer transporting function is provided around the latent image carrier. 2. Description of the Related Art A plurality of developing devices are known.

FIG. 3 shows a conventional example of such a developing device.

Two developing sleeves 102, 103 are provided adjacent to and adjacent to the drum-shaped photoconductor 101, and these sleeves 102, 103 are made of a non-magnetic material. Developing sleeve 102
Inside, there are several magnets P along its circumferential direction.
₁₁ , P ₁₂ , P ₁₃ , P ₁₄ , P ₁₅ are fixedly arranged, and the developing sleeve
Inside of 103, a plurality of magnets P ₁₁ ′, P ₁₂ ′, P ₁₃ ′,
P ₁₄ ′ is fixedly arranged. Each magnet is arranged with one magnetic pole facing the inner peripheral surface of the developing sleeve 102, 103 and the other magnetic pole is oriented toward the center side of the developing sleeve. The polarities of the magnetic poles facing the peripheral surface and the magnetic poles facing the center of the developing sleeve are set as shown by adding S and N in FIG. Of these magnets, the magnets P ₁₁ and P ₁₁ ′ facing the photoreceptor are the main poles.

The developing sleeves 102 and 103 are driven to rotate in the same direction, that is, clockwise as shown by arrows in the example in the figure, and a powdery developer (not shown) at least partially made of a magnetic material is interposed between the two. While being delivered, the electrostatic latent image formed on the surface of the photoconductor 101 at the main poles P ₁₁ and P ₁₁ ′ is developed at the main poles P ₁₁ and P ₁₁ ′, and is visualized as a toner image. A developing device using a plurality of such developing sleeves can reduce the rotation speed of each developing sleeve, and when a two-component developer is used as a developer,
Even if the toner density is reduced to some extent, an image having a predetermined density can be obtained.

Here, a magnet is placed between the two developing sleeves.
The magnetic field from P ₁₃ ′ to magnet P _13
The magnetic field from ₁₄ ′ to magnet P ₁₂
A magnetic field or the like from P ₁₃ ′ to the magnet P ₁₂ is formed.

Among such magnetic fields, the magnetic field from the magnet P ₁₃ ′ toward the magnet P ₁₂ is lying sideways and along the circumferential direction of the developing sleeve 103, and is affected by this magnetic field to A part of the developer on 103 is carried between the two developing sleeves 102 and 103 while being carried, and the amount of the developer on the lower developing sleeve 103 (the amount of developer per unit area) is changed to the upper developing amount. As a result, a situation in which the amount of developer carried on the sleeve 102 is significantly increased occurs. That is, the magnetic field from the magnet P ₁₃ ′ toward the magnet P ₁₂ acts to increase the amount of developer carried on the developing sleeve 103.

If there is a difference in the amount of developer carried on each of the upper and lower developing sleeves, a load fluctuates in the rotation of the photoconductor 101, and the rotation speed of the photoconductor 101 becomes uneven. I do.

[Problems to be solved by the invention]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a developing device which has a magnet arrangement configuration in which there is little difference in the amount of developer carried on a plurality of developing sleeves so as to suppress the occurrence of striped image density unevenness.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a plurality of developing sleeves, in which a plurality of magnets are fixedly arranged along the inner circumferential direction, arranged around the latent image carrier so as to be adjacent to each other, and A developing device for rotating adjacent developing sleeves in the same direction, wherein each magnet has one magnetic pole facing the inner circumferential surface of the developing sleeve and the other magnetic pole facing the rotation center side of the developing sleeve. Of the magnets inside the developing sleeves adjacent to each other, the magnetic poles facing the inner peripheral surface of the developing sleeve of each of the magnets serving as main poles provided at a position facing the latent image carrier are mutually identical. The inner circumference of the developing sleeve of the magnet between the main pole magnets among the magnets provided inside the developing sleeve on the downstream side in the moving direction of the latent image carrier among the developing sleeves adjacent to each other and having a polarity. The magnetic pole of the main pole magnet has a polarity opposite to the magnetic pole polarity of the main pole magnet, and is provided in the developing sleeve adjacent to the latent image carrier and adjacent to each other, and is positioned adjacent to each other. A developing device, wherein each magnetic pole facing the inner peripheral surface of the developing sleeve of each magnet has a polarity opposite to that of the magnetic pole of the main pole magnet and has the same polarity as each other. suggest.

〔Example〕

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

In FIGS. 1 and 2, reference numeral 1 denotes a drum-shaped photoconductor as an example of a configuration of a latent image carrier, and the photoconductor 1 is driven to rotate counterclockwise as indicated by an arrow. Further, two developing sleeves 2 and 3 made of a non-magnetic material are provided on the photosensitive member 1 so as to be adjacent to each other so as to be adjacent to each other. Inside the developing sleeve 2, the four magnets _{P 1, P 2, P 3} , P 4 are fixed arranged along the circumferential direction.
The magnet P ₁ provided on the side facing the photoconductor 1 among them
Is the main pole mentioned earlier. Each magnet P ₁ , P ₂ ,
The polarities of the magnetic poles P ₃ and P ₄ are as shown in FIGS. 1 and 2 with S and N attached.

The four magnets P ₁ ′, P ₂ ′, and P ₃ are also provided inside the developing sleeve 3 located on the downstream side in the movement direction of the surface of the photoconductor 1 with respect to the developing sleeve 2 along the circumferential direction. ′, P ₄ ′
Are fixedly arranged. The magnet P ₁ ′ provided at a position facing the photoconductor ₁ is a main pole. The polarities of the magnetic poles of the magnets P ₁ ′, P ₂ ′, P ₃ ′, P ₄ ′ are as shown in FIGS. 1 and 2 by adding S and N.

The two developing sleeves 2 and 3 arranged so as to be adjacent to each other around the photoreceptor 1 are driven to rotate in the same direction, that is, clockwise in the example of FIG.

As described above, the developing device of the present example has a plurality of magnets P ₁ , P ₂ , P ₃ , P ₄ ; P ₁ ′, P ₂ ′, P ₃ ′, P
_A plurality of developing sleeves 2 and 3 having a fixed arrangement are arranged around the photoconductor 1 as an example of a latent image carrier so that the developing sleeves 2 and 3 having the fixed arrangement are adjacent to each other. The magnets are rotated in the same direction, and each of the magnets is arranged such that one magnetic pole faces the inner peripheral surface of the developing sleeve and the other magnetic pole faces the rotation center side of the developing sleeve.

The polarity of the magnetic poles of each magnet will be described below. All the magnetic poles described here mean the magnetic poles (outer magnetic poles) facing the inner peripheral surface of each of the developing sleeves 2 and 3. I have.

Of the magnets inside the developing sleeves adjacent to each other, the inner peripheral surfaces of the developing sleeves of the magnets P ₁ and P ₁ ′ serving as main poles provided at positions facing the latent image carrier made of the photoreceptor 1 faced. Each magnetic pole has the same polarity (N pole as shown in this example).

Also, of the developing sleeves 2 and 3 adjacent to each other,
Inner peripheral surface of the magnet P ₄ ′ between the two main pole magnets P ₁ , P ₁ ′ among the magnets provided inside the developing sleeve 3 on the downstream side in the moving direction of the latent image carrier Is opposite to the above-mentioned magnetic pole polarity of the main pole magnets P ₁ and P ₁ ′ (S pole in this example).

Further, the magnets P ₂ and P ₃ ′ are provided in the developing sleeves 2 and 3 adjacent to each other on the side opposite to the latent image carrier formed of the photoconductor 1 and are positioned adjacent to each other.
Each of the magnetic poles facing the inner peripheral surface of the developing sleeve has the opposite polarity to the above-mentioned magnetic pole polarities of the main pole magnets P ₁ and P ₁ ′, and has the same polarity (S pole in this example). ing.

The magnetic poles of the other magnets P ₃ and P ₄ among the magnets inside the developing sleeve 2 are magnets having mutually different polarities alternately between adjacent magnets. Further, among the magnets inside the developing sleeve 3 on the downstream side, the magnetic pole of the other magnet P ₂ ′ has the opposite polarity to the magnetic pole of the main magnet P ₁ ′.

By arranging the magnets in this way and determining the polarity thereof, a magnetic field as shown in FIG. 2 is formed.

Among such fields, the magnetic field back to the magnet P ₁ through the magnet P _1, P ₄ ', a P ₂ respectively forms a loop,
The developer is transferred between the developing sleeves 2 and 3 along the magnetic field that crosses the two developing sleeves 2 and 3 of the loop-shaped magnetic field. Transported in the same direction. In this embodiment, since the magnetic field lying horizontally in the diagonal direction from the magnet P ₁₃ ′ to the magnet P ₁₂ as in the conventional example is not generated, the developer carrying amount of the lower developing sleeve 3 is reduced to the upper developing sleeve 2. Is prevented from increasing as compared with that of. Further, since the magnetic pole polarity of the magnet P ₃ ′ is the same as the magnetic pole polarity of the magnet P _2, no magnetic field is formed between the two magnets, and the above-described loop-shaped magnetic field is independent. Will be formed.

As the developer, a powdery material at least a part of which is made of a magnetic material, for example, a two-component developer having a magnetic carrier and a toner, or a one-component developer made of a magnetic toner is used.

The present invention can be widely applied to an image forming apparatus using a belt-shaped photoconductor as a latent image carrier, an image forming apparatus using a latent image carrier other than the photoconductor, and the like.
The present invention is also applicable to a developing device provided with three or more developing sleeves.

〔The invention's effect〕

According to the present invention, the amount of developer carried on the plurality of developing sleeves is not unbalanced between the developing sleeves as in the related art, and the rotation of the latent image carrier hardly fluctuates in load. Can be suppressed from occurring.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a flow of a developer in a developing device according to an embodiment of the present invention, FIG. 2 is an explanatory view of a magnetic field formed between two developing sleeves in the embodiment, and FIG. FIG. 4 is an explanatory diagram regarding a magnetic field between developing sleeves and a flow of a developer in the case of (1). 2, 3 ...... developing sleeve, P ₁ ~P ₄ ...... magnet P ₁ '~P _4' ...... magnet

Claims (1)

(57) [Claims] A developing sleeve having a plurality of magnets fixedly arranged along the inner circumferential direction is provided around a latent image carrier so as to be adjacent to each other, and the developing sleeves adjacent to each other are provided. In the same direction, each magnet is arranged with one magnetic pole facing the inner circumferential surface of the developing sleeve, and the other magnetic pole is arranged with the rotation center side of the developing sleeve facing, and are adjacent to each other. Of the magnets inside each developing sleeve, the magnetic poles facing the inner peripheral surface of the developing sleeve of the respective magnets, which are main poles provided at positions facing the latent image carrier, have the same polarity and are mutually the same. Of the developing sleeves adjacent to the magnetic poles facing the inner circumferential surface of the developing sleeve of the magnet between the main pole magnets, of the magnets provided inside the developing sleeve on the downstream side in the moving direction of the latent image carrier. To The polarity of the magnetic pole of the pole magnet is opposite to that of the magnetic pole, and the developing sleeve inner peripheral surface of each magnet is provided in the developing sleeve adjacent to the latent image carrier and adjacent to each other, and is positioned adjacent to each other. A developing device, wherein the magnetic poles facing each other are set to have the opposite polarity to the magnetic pole polarity of the main pole magnet and to have the same polarity as each other.