JPH05313497A - Developing device - Google Patents

Abstract

PURPOSE:To easily remove and recover a foreign matter from developer carried on a sleeve and to facilitate the design of a magnet roll by setting the magnetic force of four magnetic poles, which are obtained by alternately arranging an N pole and an S pole continuously in a peripheral direction, out of the magnetic poles on the outer peripheral part of the magnet roll to specified relation. CONSTITUTION:The magnetic force M1-M4 of four magnetic poles N1, S1, N2, and S2 which are obtained by alternately arranging the N pole and the S pole on the outer peripheral part of the magnet roll 9 is set to the relation expressed by an inequality. M1-M4 mean the magnetic force of the 1st-4th magnetic poles N1, S1, N2, and S2 along the moving direction of the sleeve 10, respectively. By thus doing, the developer forms accumulation at an opposed part to the 2nd magnetic pole S1 out of the four magnetic poles in the moving direction of the sleeve, and the developer is stirred and mixed. When the developer moves from the 2nd magnetic pole S1 to the opposed part to the 3rd magnetic pole N2, it flies and the up and down sides of the magnetic brush constituted of the developer are reversed. Therefore, the developer moving from the 2nd magnetic pole to the opposed part to the 3rd magnetic pole N2 becomes stable in a sparse state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an image forming apparatus such as a copying machine or a printer.

[0002]

2. Description of the Related Art Conventionally, a sleeve is provided on a fixed magnet roll, and a magnetic brush developer held on the outer peripheral surface of the sleeve is conveyed to the lower outer peripheral surface of the fixed magnet roll as a developing device. Magnetic poles of different polarities are alternately arranged along the circumferential direction, and a container is provided in the housing portion facing the outer peripheral surface of the lower part of the sleeve to prevent foreign matter such as paper dust falling from the developer conveyed as the sleeve rotates. There is known a device provided with a foreign matter removing mechanism that is captured by the container.

Further, a foreign matter removing mechanism is provided on the outer peripheral portion of the lower portion of the fixed magnet roll, where a same pole portion having adjacent magnetic poles of the same polarity is provided, and foreign matter is dropped from the developer passing through a region facing the same pole portion. , JP-A-60-2139980.

[0004]

However, in the former foreign matter collecting mechanism, the magnetic fields of the magnetic poles formed on the lower outer peripheral surface of the fixed magnet roll facing the container are adjacent to each other as shown in FIG. 6 (b). The magnetic fields are connected between the matching magnetic poles. Therefore, as shown in FIG. 6A, the magnetic brush on the outer peripheral surface of the sleeve stably moves to the adjacent magnetic pole while falling along the magnetic field. That is, the magnetic brush of the S pole facing portion is turned upside down when moving to the N pole facing portion. Therefore, since the developer moving between the magnetic poles is transported in a high density state with little disturbance, the foreign matter sandwiched between the magnetic brushes does not easily fall, and the foreign matter collection efficiency is poor.

On the other hand, in the latter foreign matter collecting mechanism, the magnetic field formed in the portion facing the same pole portion is as shown in FIG.
As shown in, magnetic fields originating from adjacent magnetic poles of the same polarity extend in opposite directions and repel each other. Therefore,
As shown in (a), the magnetic brush flies to the adjacent magnetic pole without standing upside down while standing up, and at that time, the magnetic brush changes from the “<” shape to the “reverse” shape. And changes. Therefore, there is a problem that the toner in the magnetic brush cannot follow the movement of the carrier and is scattered away from the carrier. In addition, there is a problem in that the presence of the same pole portion restricts the arrangement of other magnetic poles and the setting of magnetic force.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and in a developing device having a fixed magnet roll and a sleeve rotating around the fixed magnet roll, the magnet roll has an outer peripheral portion. The magnetic forces of four magnetic poles each having a plurality of magnetic poles, in which the N poles and the S poles are alternately arranged continuously in the circumferential direction, are set to satisfy the following equation. M ₂ / M ₁ + M ₃ / M ₄ <1.3 M ₁ : Magnetic force of the first magnetic pole in the above magnetic pole group along the moving direction of the sleeve M ₂ : 〃 2 〃 M ₃ : 〃 3 〃 M ₄ : 〃 4 〃

[0007]

In the developing device described above, the 4
Of the two magnetic poles, the developer forms a pool at the second magnetic pole facing portion along the sleeve movement direction, where the developer is agitated and mixed. Further, when the magnetic brush flies when moving from the second magnetic pole to the third magnetic pole facing portion, the magnetic brush composed of the developer is turned upside down. Therefore, the developer moving from the second to the third magnetic pole facing portions is stable in the sparse state.

[0008]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a developing unit of the developing device. An opening 2 is formed in the housing 1 in a portion facing the photoconductor along the axial direction of the photoconductor 100, and a space 3 is formed adjacent to the opening 2. ing. A developer supply unit 4 is formed at the rear portion (right side in the figure) of the space 3. The space 3 accommodates the developing roll 5, and the upper housing 1
The blade 6 provided on u is opposed to the upper outer peripheral surface of the developing roller 5. On the other hand, the lower housing 1d has a drop opening 7
Is formed, and the container 8 is detachably attached to the bottom of the container.

The developing roll 5 is provided with a cylindrical magnet roll 9 having a diameter of 23.9 mm, and a cylindrical sleeve 10 having a diameter of 24.5 mm and a wall thickness of 0.5 mm, which is rotationally driven in the direction of arrow a around the magnet roller 9. The magnet roll 9 is
As shown in FIG. 1, formed in turn a plurality of magnetic poles N ₁ extending in the axial _{direction, S 1, N 2, S} 2, S 3, N 3, S 4, N 4 is in the direction of arrow a on the outer peripheral portion Has been done. Further, the magnetic poles N ₄ and N ₁ having the same polarity are arranged close to the facing portion of the photoconductor 100,
Magnetic poles S ₂ and S ₃ having the same polarity are arranged adjacent to the facing portion of the developer supply unit 4, and a substantially middle portion between the magnetic pole S ₁ and the magnetic pole N ₂ faces the drop opening 7.

As shown in FIG. 2, the magnetic forces of the magnetic poles measured on the outer peripheral surface of the sleeve opposed to the magnetic poles N ₁ , ..., N ₄ are, as shown in FIG. 2, M _N1 = 1220G (G: Gauss), M _S1 = 780.
G, M _N2 = 450G, M _S2 = 820G, M _S3 = 700
G, M _N3 = 750G, M _S4 = 800G, M _N4 = 1200
G. As shown in FIG. 3, the magnetic force was measured by using a Gauss meter (GM-102) 11 manufactured by Denshi Kogaku Kogyo Co., Ltd., with the probe 12 in contact with the outer peripheral surface of the sleeve 10.

In the developing device having the above structure, the two-component developer including toner and carrier is supplied to the outer peripheral surface of the sleeve 10 from the supplying device 13 of the developer supplying section 4. The developer supplied to the sleeve 10 is held on the outer periphery of the sleeve 10 by the magnetic force of the magnetic pole S ₃ , is conveyed in the direction of the arrow a as the sleeve 10 rotates, is regulated by the blade 6, and then the developer of the magnetic poles N ₄ and N ₁ . The opposing portion (hereinafter referred to as “developing region”) contacts the outer peripheral surface of the photoconductor 100, and the photoconductor 1
00 develops the electrostatic latent image formed on the outer peripheral surface thereof. The developer that has passed through the developing area moves in the facing portions of the magnetic poles S ₁ , N ₂ , and S ₂ , is released from the magnetic force of the magnet roll 9 between the magnetic poles S ₂ and S _3, and is supplied to the developer supplying portion 4 Will be collected. In addition, foreign matters such as paper powder and toner lumps contained in the developer are separated from the developer when moving from the magnetic pole S ₁ to the magnetic pole N _2, and are collected in the container 8 through the dropping port 7.

A phenomenon in which the foreign matter is separated from the developer will be described. As described above, the magnet roll 9 facing the lower housing 1d is provided with a group of magnetic poles N ₁ , S ₁ , N ₂ , and S _{2 in} which N poles and S poles are alternately arranged along the arrow a direction. cage, force M _S1 (= 780G) of the magnetic pole S ₁ is than the magnetic force M _N1 of the upstream pole N ₁ (= 1220G) is set to low magnetic, magnetic force M _N2 pole N ₂ (= 450G) also downstream pole The magnetic force is set to be lower than the magnetic force M _S2 (= 820 G) of S _{2, and} the magnetic force distribution coefficient α (M _S1 / M _N1 + M _N2 / M _S2 )
Has been adjusted to 1.19. As a result, on the outer peripheral surface of the sleeve 10 extending from the magnetic pole S ₁ to the magnetic pole N ₂ , FIG.
As shown in (b), most of the magnetic field starting from the magnetic pole S ₁ converges on the upstream magnetic pole N ₁ , and similarly, the magnetic pole starting from the downstream magnetic pole S ₂ converges on the magnetic pole N ₂ . Only a small part of the magnetic field originating from the magnetic pole S _{1 is} focused on the magnetic pole N ₂ .

Therefore, as shown in FIG. 4A, the developer forms a puddle at the portion facing the magnetic pole S ₁ . Further, the magnetic brush 14 composed of the developer flies when moving from the facing portion of the magnetic pole S _{1 to} the facing magnetic pole N ₂ , and the magnetic brush 14 is turned upside down at that time. Further, as shown in FIG. 7, the magnetic brush does not move while changing from the "dogleg" shape to the "inverted" letter shape. Therefore, an unreasonable force is not applied to the toner on the brush 14, and the toner is stably moved without being separated from the toner and the carrier. Further, since the magnetic brushes 14 are in a sparse state when the developer is flying,
The foreign matter sandwiched between the magnetic brushes 14 easily separates and falls. Therefore, the toner is not scattered and the foreign matter can be efficiently collected in the container 8.

The magnetic force distribution coefficient α was changed by variously setting the magnetic forces of the magnetic poles N ₁ , S ₁ , N ₂ , and S ₂ , and the toner scattering state was observed. The moving speed of the sleeve 10 is 4
It was set to 0 cm / sec. The results of the experiment are shown in the table below. No M _N1 M _S1 M _N2 M _S2 α Toner scattering 1 1300 700 700 500 800 1.15 Low 2 1200 650 500 500 800 1.16 〃 3 1220 750 500 500 800 1.23 〃 4 1180 820 580 880 1.36 Many 5 1320 1020 480 790 1.38 〃

As is clear from the above table, it can be understood that the toner scattering is small when the magnetic force distribution coefficient α is 1.3 or less, and the toner scattering is large when the magnetic force distribution coefficient α is 1.3 or more.

Next, N is attached to the outer periphery of the upper portion of the magnet roll 9.
A group of magnetic poles S ₃ , N ₃ , with alternating poles and S poles,
A case where the magnetic force distribution coefficient α of S ₄ and N ₄ is set to 1.3 or less will be described with reference to FIG. In this case, blade 6
Developer passing through the tip of the form a developer reservoir 15 in the opposing portion of the magnetic pole N _3, flies to the opposing portion of sequential magnetic pole S ₄ from the developer reservoir 15, the magnetic brush when the top and bottom is reversed .. That is, the developer moves in the state shown in FIG.

Therefore, the toner is not separated from the developer and scattered. Further, the developer is mixed in the developer pool 15 by being disturbed in all directions. for that reason,
Even if a foreign substance such as a lump of toner is clogged at the tip of the blade 6 to form a non-developed portion on the sleeve 10, the non-developed portion of the developer in the developer reservoir 15 may cause a peripheral portion of the non-existent portion. The developer is supplied and erased.

In the above embodiment, the N pole and the S pole are shown in FIG.
Although they are arranged in the order shown in, the polarities of the N pole and the S pole may be different.

[0019]

As is apparent from the above description, in the developing device according to the present invention, the magnet roll has a plurality of magnetic poles on the outer peripheral portion, and among these magnetic poles, the N pole and the S pole are continuously arranged in the circumferential direction. The magnetic force distribution coefficient of the magnetic pole group consisting of four magnetic poles alternately arranged is set to less than 1.3.

Therefore, of the four magnetic poles set in the above relationship, the developer forms a pool at the second magnetic pole facing portion along the sleeve movement direction, where the developer is disturbed and mixed. .. Therefore, by disposing the magnetic pole group set in the above relationship on the downstream side of the blade, even if the developer absent portion is formed by the foreign matter caught at the blade tip, the developer formed by the magnetic pole is formed. In the pool, the developer is supplied to the developer-absent portion and erased, and an image without white streaks is obtained.

Also, when the magnetic brush composed of the developer flies when moving from the second magnetic pole to the third magnetic pole facing portion, and the magnetic brush composed of the developer is reversed up and down, it is impossible for the magnetic brush. The force is not applied and the toner is prevented from scattering. In addition, since the developer moving from the second to the third magnetic pole facing portion is stable in a sparse state, foreign matters such as paper dust can be easily removed from the developer conveyed on the sleeve and collected. can do.

Further, since the magnetic poles set in the above relationship are the N poles and the S poles arranged alternately and not the same poles adjacent to each other, the arrangement of the other magnetic poles is simplified and the magnet rolls Design becomes easy.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of a developing device.

FIG. 2 is a magnetic force distribution diagram of a magnet roll.

FIG. 3 is an explanatory diagram of magnetic force measurement.

FIG. 4 is a diagram showing a moving state of a developer and a magnetic field distribution state.

FIG. 5 is a partial cross-sectional view of another embodiment of the developing device.

FIG. 6 is a diagram showing a moving state of a developer and a magnetic field distribution state in a conventional example.

FIG. 7 is a diagram showing a moving state of a developer and a magnetic field distribution state in a conventional example.

[Explanation of symbols]

5 ... Developing roll, 9 ... Magnet roll, 10 ... Sleeve.

Claims (1)

[Claims] 1. A developing device comprising a fixed magnet roll and a sleeve which rotates around the fixed magnet roll, wherein the magnet roll has a plurality of magnetic poles on an outer peripheral portion, and among these magnetic poles, an N pole is continuously formed in a circumferential direction. And a magnetic pole of a magnetic pole group composed of four magnetic poles having S poles alternately arranged, the developing device having the following relationship. M ₂ / M ₁ + M ₃ / M ₄ <1.3 M ₁ : Magnetic force of the first magnetic pole in the above magnetic pole group along the moving direction of the sleeve M ₂ : 〃 2 〃 M ₃ : 〃 3 〃 M ₄ : 〃 4 〃