JPH05289520A - Developing device - Google Patents

Abstract

PURPOSE:To prevent a white stripe pattern from being generated on an image and to switch a developing state and a non-developing state with a simple constitution by forming the adjacent same pole parts on the outer periphery of a magnet roll. CONSTITUTION:In the case of developing, a solenoid is turned off, and an almost middle part between magnetic poles N2 and N3 on the magnet roll 3 is set at a position where a photosensitive body 100 and a developing roller 1 come the closest, then an almost middle part between magnetic poles S1 and S2 on the roll 3 is set at a position obtained by moving by about 20 deg.-30 deg. from an opposed part to a blade 101 in a direction shown by an arrow (a). Developer carried accompanying the rotation of the sleeve 2 is influenced by repulsive magnetic fields formed by the magnetic poles S1 and S2, so that the accumulation of the developer X1 is formed at an opposed part to the magnetic pole S1 and the developer is stirred in all the directions, whereby it is mixed not only in a carrying direction but also in an axial direction. In the case of non-developing, the solenoid is turned on, the middle part between the magnetic poles S1 and S2 is moved to the opposed part to the blade 101, the developer is regulated just before the blade 101, passes through a napping height gap DB and is not carried to a developing area.

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 by electrophotography.

[0002]

2. Description of the Related Art Conventionally, as the developing device, a developer is held on the outer periphery of a sleeve which moves around a magnet roll, and development is performed while a blade regulates the rotation of the sleeve. It is known that the agent is conveyed to the facing portion (developing region) between the photosensitive member and the sleeve.

However, the above-mentioned developer contains large-sized foreign matters such as lumps and burrs of the developer. When the foreign matter is clogged in the gap between the blade and the sleeve, there is a problem that a developer absent portion is generated in a portion where the developer is rejected by the foreign matter and a white streak pattern is generated on the image.

On the other hand, an image forming apparatus which is provided with a plurality of developing devices on the outer peripheral portion of a photoconductor and selectively drives these developing devices to form a monochromatic image or a multicolor image, wherein the photoconductor is used as the developing device. With a so-called contact type developing device in which the developer is directly contacted with the toner, the toner image formed on the upstream side in the moving direction of the photoconductor comes into contact with the developer on the downstream side developing device to reduce the image density, Defects and color mixing occur.

In view of the above, a mechanism is conventionally provided in which a shutter member is provided behind the sleeve and the supply of the developer to the sleeve is blocked by the shutter member when the developing is not performed.
No. 82 publication.

However, since the mechanism for operating the shutter member directly regulates the developer by the shutter member, there is a problem that the stress applied to the developer is large and the developer is deteriorated. ..

[0007]

SUMMARY OF THE INVENTION The present invention solves the above problems, prevents the occurrence of white streak patterns on an image, and at the same time provides a developing device capable of switching between a developing state and a non-developing state with a simple structure. An object of the present invention is to provide a magnet roll having a plurality of magnetic poles in an outer peripheral portion, a sleeve that moves while rotating around the magnet roll, and a blade that faces the outer periphery of the sleeve, and the sleeve. In the developing device in which the developer held on the outer circumference of the magnet roll is conveyed to the developing area while being regulated by the blade based on the rotation of the sleeve and brought into contact with the photoconductor, magnetic poles of the same polarity are adjacent to the outer circumference of the magnet roll. The same magnetic pole portion is formed, and at the time of development, the magnetic force drop portion of the same pole portion is set on the downstream side of the blade facing portion and on the upstream side of the development area, and when non-developing The magnetic force drop portion is obtained so as to set the blade facing portion.

[0008]

In the developing device described above, during development, the developer that has moved to the opposite portion of the blade forms a developer pool at the same pole portion.
It is disturbed in the dimensional direction and moves not only in the transport direction but also in the direction orthogonal thereto, and is uniformly leveled. Therefore,
Even if a foreign substance clogged at the tip of the blade forms a developer absent portion on the sleeve, the developer pool causes the peripheral developer to be supplied to the developer absent portion and erased. On the other hand, at the time of non-development, when the magnetic force drop portion of the same pole portion is set at the facing portion of the blade, the repulsive magnetic field formed by the same pole portion and the cooperative action of the blade convey the developer to the downstream side of the blade. Is almost completely cut off,
The contact between the developer and the photoreceptor in the developing area is stopped.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 to 3 show a cross section of a developing roller arranged in a developing section of a developing device according to the present invention. As shown in these figures, the developing roller 1 is roughly composed of a sleeve 2 and a magnet roll 3. Further, the developing roller 1 is opposed to the photoconductor 100 with a predetermined developing gap D _S, and the blade 101 for restricting the developer conveyance is opposed to the upper part with a predetermined spike height restricting gap D _B.

The sleeve 2 is made of a cylindrical body of aluminum or the like, and the shaft members 4 and 6 are fitted in the openings at both ends. The shaft member 4 on one side (the left side in FIG. 3) has a bearing through hole at the center. 5 is formed, and the other (right side in FIG. 3) shaft member 6 has a bearing 7 and a shaft portion 8 inside and outside, respectively.
Is formed, and the gear 9 is fixed to the shaft portion 8.

The magnet roll 3 is provided with a magnet 12 around the support shaft 11 and is housed in the sleeve 2.
One end of the support shaft 11 is supported by the bearing 7, and the other end of the support shaft 11 projects from the sleeve 2 via the bearing through hole 5.
The lever 13 is fixed to this protrusion. Further, as shown in FIG. 4, the lever 13 is biased by the spring 14 in the direction of the arrow a, and abuts the stopper 15 to regulate the position. Further, a plunger 17 of a solenoid 16 is rotatably connected to the lever 13, and based on the drive of the solenoid 16, the lever 13 is in contact with the stopper 15 and moves in the direction of arrow a ′ from about 20 ° to 30 °. ° It can be switched to the rotated state.

The magnet 12 of the magnet roll 3 includes
As shown in FIG. 1, a plurality of magnetic poles N ₁ , S ₁ , S ₂ , N ₂ , N ₃ , S ₃ , and N ₄ extending in the axial direction are sequentially formed on the outer peripheral portion in the direction of arrow a, and Among the magnetic poles, the magnetic poles S ₁ and S ₂ having the same polarity and the magnetic poles N ₂ and N ₃ are arranged close to each other. Further, the magnetic poles N ₁ , ..., N ₄ have substantially the middle portions of the magnetic poles N ₂ , N _{3 when} the lever 13 is in contact with the stopper 15 (hereinafter, this state is referred to as “developing state”). It is set at the closest position between the photoconductor 100 and the developing roller 1, and the substantially middle part of the magnetic poles S ₁ and S ₂ is set at a position moved by about 20 ° to 30 ° in the direction of arrow a from the facing part of the blade 101.

Meanwhile, a state where the lever 13 is rotated in the arrow a 'direction based on the driving of the solenoid 16 (hereinafter, this state is referred to as "non-development state.") In, as shown in FIG. 2, the magnetic pole S ₁ , S ₂ and the magnetic pole S ₁ ,
The magnetic force drop portion in the magnetic force distribution formed by S ₂ is set at the facing portion of the blade 101, and the magnetic poles N ₂ and N ₃ are about 20 ° to 30 ° from the facing portion of the photoconductor 100.
The position is set at the position moved in the direction of the arrow a '. The amount of depression of the magnetic force depression portion is preferably about 30% of the peak magnetic force.

The developing device having the above construction is
The solenoid 16 is turned off, and the magnet roll 3 is set to the developing state shown in FIG. In this state, the rotation of the sleeve 2 is transmitted from the drive source (not shown) to the gear 9 via the drive gear 10, and the sleeve 2 rotates in the direction of arrow a. Further, the developer is supplied to the sleeve 2 from the developer supply unit 20 behind the sleeve 2 to a portion facing the magnetic pole N ₁ .

The developer supplied to the sleeve 2 is conveyed in the direction of the arrow a along with the rotation of the sleeve 2 and is conveyed by the blade 10.
The developer regulated to 1 and passed through the spike height regulation gap D _B is conveyed to the facing portion of the magnetic poles S ₁ and S ₂ . Here, the developer is influenced by the repulsive magnetic field formed by the magnetic poles S ₁ and S ₂ , and forms a developer pool X ₁ at the facing portion of the magnetic pole S ₁ . Further, the developer in the developer reservoir X ₁ is pushed out by the developer conveyed from the rear and sequentially moves while flying to the facing portion of the magnetic pole S ₂ . However, depending on the magnetized state of the magnetic poles S ₁ and S ₂ , the developer does not fly and is conveyed while being held on the surface of the sleeve 2.

In the developer pool X ₁ , the developer is disturbed in all directions. That is, the developer is mixed not only in the transport direction (direction of arrow a) but also in the axial direction. Therefore, even if a foreign substance such as a lump or a burr of the developer is clogged in the spike height regulating gap D _B and the developer is absent in the portion where the developer is rejected by the foreign substance, the non-developed portion is the above-mentioned developing portion. The surrounding developer is supplied and erased in the agent reservoir X ₁ .

The developer that has moved to the opposite portion of the magnetic pole S ₂ further moves in the direction of arrow a as the sleeve 2 rotates, and the magnetic pole N
_The electrostatic latent image formed on the photoconductor 100 is developed by coming into contact with the photoconductor 100 at the facing portion (development region) of ₂ and N ₃ .
The developer conveyed through the facing portion of the magnetic poles N ₂ and N ₃ forms a developer pool X ₂ at the facing portion of the magnetic pole N ₁ , and the magnetic pole N _1
It moves while flying to the opposite part of ₃ . However, the magnetic poles N ₂ , N
Depending on the magnetization state of _3, the developer in the developer pool X ₂ moves while being held by the sleeve 2 without flying. Further, the developer pool X ₂ further supplies the developer to the non-developer portion, and the developer is smoothed.

The developer which has passed through the developing area is treated by the magnetic pole S ₃ ,
After passing through the facing portion of N ₄ and passing through the facing portion of the magnetic pole N ₄ , it falls from the sleeve 2 and is collected by the developer supplying portion 20.

At the time of non-developing, the solenoid 16 is set to the ON state, the magnet roll 3 is set to the non-developing state,
The magnetic force drop portions of the magnetic poles S ₁ and S ₂ move to the facing portion of the blade 101, and the magnetic poles N ₂ and N ₃ retract from the facing portion of the photoconductor 100. Further, the supply of the developer from the developer supply unit 20 to the sleeve 20 is also stopped. However, sleeve 2
Keeps rotating.

As a result, among the developers held on the sleeve 2, the developer held upstream of the magnetic poles S ₁ and S _{2 in} the developer carrying direction is formed by the magnetic poles S ₁ and S ₂ . It is regulated just before the blade 101 due to the cooperative action of the repulsive magnetic field and the blade 101, and is not conveyed to the developing area through the spike height regulating gap D _B. Further, even if there is a developer that passes through the spike height regulating gap D _B , the amount thereof is extremely small.

On the other hand, the developer remaining on the downstream side of the magnetic poles S ₁ and S _{2 in the} developer conveying direction (direction of arrow a) is the sleeve 2
Is conveyed in the direction of the arrow a along with the rotation of, and is dropped and collected in the developer supply unit 20 at the place where it passes through the facing portion of the magnetic pole N ₄ . As a result, the developer is set to be almost nonexistent on the outer peripheral surface of the sleeve 2 on the downstream side of the magnetic poles S ₁ and S ₂ , so that the electrostatic latent image on the photoconductor 100 moving to the opposed portion of the sleeve 2 is set. Is not developed by the developer in the developing device.

In the above embodiment, the photoconductor 1 is used at the time of development.
Although the adjacent magnetic poles N ₂ and N ₃ of the same pole are used as the magnetic poles opposed to 00, that is, the developing magnetic poles, the developing magnetic poles may be a single magnetic pole. Further, the switching mechanism of the magnet roll 3 is not limited to the above embodiment.

[0023]

As is apparent from the above description, according to the developing device of the present invention, even if the developer-absent portion is formed on the sleeve due to the foreign matter clogged at the blade tip,
The developer absent portion is a developer pool formed in the same pole portion, and the surrounding developer is supplied and erased. Therefore,
A high-quality image without white streaks can be obtained.

Further, with a simple structure for rotating the magnet roll, the developer can be moved from the homopolar portion to the downstream side in the developer conveying direction based on the cooperative action of the repulsive magnetic field of the homopolar portion and the blade. It is possible to easily form a state in which the outer peripheral surface of the sleeve is regulated and the developer does not exist on the downstream side of the blade. In addition, the restriction of the developer by the repulsive magnetic field of the homopolar portion exerts significantly less stress on the developer than the restriction by the shutter member or the like, and the deterioration of the developer is prevented.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of a developing roller in a developing state.

FIG. 2 is a vertical sectional view of a developing roller in a non-developing state.

FIG. 3 is a cross-sectional view of a developing roller.

FIG. 4 is a perspective view of a magnet roll switching mechanism.

[Explanation of symbols]

1 ... developing roll, 2 ... sleeve, 3 ... magnet roll, 100 ... photoconductor, 101 ... blade, X _1, X ₂ ... reservoir developer.

Claims (1)

[Claims] 1. A magnet roll having a plurality of magnetic poles on its outer periphery, a sleeve that moves while rotating around the magnet roll, and a blade that faces the outer periphery of the sleeve, and is held on the outer periphery of the sleeve. In the developing device in which the developing agent is brought into contact with the photosensitive member by being conveyed to the developing area while being regulated by the blade based on the rotation of the sleeve, the same pole portion where the magnetic poles of the same polarity are adjacent to the outer circumference of the magnet roll is provided. At the time of development, the magnetic force drop portion of the homopolar portion is set on the downstream side of the blade facing portion and on the upstream side of the developing area, and the magnetic force drop portion is set on the blade facing portion when not developing. A developing device characterized in that