JPH0572902A - Developing device - Google Patents

Abstract

PURPOSE:To develop an image, such as photographic image, having gradations, dot image and solid image, such as image having a high B/W ratio and to brightly obtain a line image, such as character, and an image having a low B/W ratio. CONSTITUTION:The same pole magnetizing part N0 where two magnetic poles N1, N2 of the same pole are adjacent to each other is provided in the photosensitive body-facing part of the magnet body of the developing device which is fitted with a sleeve 2 onto the magnet body 3 fixed in a non-rotating state and develops an electrostatic latent image by bringing a developer into contact with the photosensitive body 10. A magnet body driving device for controlling the position opposite to the photosensitive body is provided. The above- mentioned device is so constituted that the developer is held continuously on the outer peripheral surface of the sleeve between the magnetic poles and that the positions can be set within the range from the position where the developer D1 held by the magnetic pole N1 existing on the upstream side in the rotating direction of the sleeve and the developer D12 held in the intermediate part of the magnetic poles come into contact with the photosensitive body and the developer D2 held in the magnetic pole N2 come into non-contact with the photosensitive body to the position where both of the developers held in the two magnetic poles N1, N2 and the intermediate part of the magnetic poles come into contact with the photosensitive body.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, as a developing device used in the above-mentioned image forming apparatus, there has been provided a developing roller composed of a magnet body and a sleeve mounted on the magnet body, and a developer held on the outer peripheral portion of the sleeve. There is proposed a method of bringing an electrostatic latent image into a visible image by bringing it into contact with a photoconductor.

In this developing device, as shown in FIGS. 11 and 12, a magnet body 23 is fixed in a non-rotating state, and a cylindrical sleeve 22 which is surrounded by the magnet body 23 in the direction of arrow a. Rotating inner pole fixed type developing devices 21a, 21b
Then, as shown in FIG. 13, the inner pole rotary type developing device 21c in which both the magnet body 23 and the sleeve 22 rotate in the direction of arrow a '.
Is roughly divided into

As shown in FIG. 11, the fixed inner pole type developing device has a plurality of magnetic poles N, S, N ...
Is provided, and one magnetic pole N is arranged so as to face the developing area Q where the sleeve 22 and the photoconductor 20 face each other, and only the developer held by the magnetic pole N is brought into contact with the photoconductor 20. With the developing device 21a, as shown in FIG.
Magnetic poles N ₁ and N ₂ of the same polarity are provided adjacent to each other on the outer peripheral portion of the magnet body near the developing area Q, and these two magnetic poles N ₁ and
It can be classified into a homopolar developing device 21b that brings the developer held in N ₂ into contact with the photoconductor 20 together.

[0005]

However, each of the developing devices 21a, 21b, 21c has the following problems. I. Monopolar developing device 21a (see FIG. 11) The first problem with the monopolar developing device 21a is the photoconductor 2
The developer 26 constrained by the magnetic pole N facing 0
Since the density is high when the toner image is separated from 0, as shown in FIG. 14, the toner adhesion amount in the peripheral edge portion (edge portion) 31 of the visible toner image 30 is larger than that in the central portion 32. That is, the so-called edge effect is emphasized too much. This edge effect is closely related to the density of the developer when it is separated from the photoconductor 20, and the higher the density of the developer in this portion, the stronger the edge effect.

Further, as shown in FIG. 15, when the toner image 30 with the edge effect emphasized is melted and fixed on the recording medium 27 such as paper, the toner at the edge portion 31 spreads around and the adjacent toner images come into contact with each other. And the image quality deteriorates. Particularly, in a halftone dot image, the halftone dot is broken and the image quality is significantly deteriorated. Further, as shown in FIG. 16, when the toner images 40a, 40b, 40c of different colors are overlapped to form an image,
The color tone differs between the edge 41 and the central portion 42, and the quality of the color image deteriorates.

It should be noted that the enhancement of the edge effect is sometimes preferable because the image clearly appears in the development of a line image such as a character. However, it is not suitable for developing a solid image having gradation such as a photographic image. The second problem is that the toner at the front edge or the rear edge of the image is scraped off by the magnetic brush to cause a blurred pattern.

Now, the process of producing the trailing edge blur pattern will be described with reference to the examples of FIGS. 17A to 17C. The phenomenon of trailing edge blurring occurs when the peripheral speed of the developing sleeve is faster than the peripheral speed of the photoconductor. In the developing area Q, the electrostatic latent image portion I ₁ (photoconductor surface potential V _i = −300
After the development of V) is completed, when the non-image area I ₀ (photoconductor surface potential V ₀ = −50 V) advances to the development area Q, the magnetic brush comes into contact with the non-image area I _0. In the carrier Ca at the tip, the toner To
A charge (negative charge) having a polarity opposite to (positive chargeability in this example) appears. In the magnetic brush, the toner To adsorbed to the carrier Ca is attracted by the developing bias (voltage V _B = −150 V in this example) applied to the sleeve 22 and moves to the sleeve side (upward in the figure). However, the negative charge remains in the trace. As a result, when the toner To at the rear end of the image adhering to the photoconductor 20 comes into contact with the carrier Ca at the tip of the magnetic brush, the mechanical scraping force of this carrier Ca and the electric attraction force cause the magnetic brush to move. The scratched marks appear on the image as a blur pattern. The front edge blurring pattern also occurs in the same manner.

The third problem is that when developing an image in which a high density image is followed by a low density image, the toner at the trailing edge of the low density image is scraped off, resulting in a so-called white spot in the lead portion. .. This phenomenon also occurs when the peripheral speed of the developing sleeve is faster than the peripheral speed of the photoconductor. The process in which the lead portion blank occurs will be described with reference to the examples of FIGS. 18A to 18C.

Low-density image electrostatic latent image I ₁ (V _i1 = -300
V) followed by the high density image electrostatic latent image I ₂ (V _i2 = −600
V) continues, electrostatic latent images I ₁ and I ₂ are successively developed in the developing area Q. At this time, the electrostatic latent image I ₂ of the high-density image is
Carrier C of the magnetic brush that developed toner and lost toner To
When “a” catches up with the toner adhering to the low-density electrostatic latent image I ₁ and comes into contact with it, the scraping force of the magnetic brush, the electric charge remaining in the mark after the toner is lost, and the electric charge adhered to the photoconductor 10. The toner To adhering to the trailing end of the electrostatic latent image I ₁ of the low-density image is scraped off due to the electric attraction force generated between the toner and the toner, and a white spot in the image is generated on the scraped trace. To do.

A fourth problem is that in the case where the regulating member 25 is faced with a minute gap held on the outer peripheral surface of the sleeve and the regulating member 25 regulates the amount of the developer conveyed to the developing area Q, If a foreign substance such as a lump of toner or paper dust is clogged between the regulating member 25 and the sleeve 22, the developer 26 is rejected by the foreign substance, and a white streak-like image defect portion is generated on the image.

The fifth problem is that, as shown in FIG. 19, the carrier Ca that has lost toner due to development has an electrostatic latent image portion (for example, -600V area) and a non-image portion (for -50V area). That is, it is attached to the photoconductor 20 by the wraparound electrolysis E generated at the boundary portion of the. B. Homopolar developing device 21b (see FIG. 12) In the homopolar developing device 21b, the monopolar developing device 21a is used.
Similarly, since the developer has a high density when it is separated from the photoconductor 20, the edge effect is emphasized too much, the leading edge portion or the trailing edge portion of the image is blurred, white spots in the lead portion occur, and carrier adhesion does not occur. There is a problem that it occurs.

However, in the developing device 21b, two magnetic brushes 26a and 26b are formed in the portion facing the photoconductor 20, and the developer flies from the first magnetic brush 26a toward the second magnetic brush 26b. At this time, the developer 26
Is disturbed in the axial direction of the sleeve 22. That is, the developer is disturbed in the three-dimensional direction. Therefore, the non-developer portion formed by the toner being repelled by the foreign matter caught at the tip of the regulation section 25 is erased by the nearby developer, and even if the tip of the regulation section 25 is clogged with the foreign matter, white streaks appear on the image. The image loss part of does not appear. C. Inner pole rotation type developing device 21c (see FIG. 13) The inner pole rotation type developing device 21c has problems that the edge effect is emphasized too much and carrier adhesion is larger than that of the inner pole fixing type developing device.

The edge effect is emphasized for the same reason as in the case of the fixed inner pole type developing devices 21a and 21b. The carrier is often attached to the inner pole rotary developing device 21.
In the case of c, since the ears of the developer 26 rotate at a high speed together with the magnet body 23, the centrifugal force acting on the carrier is larger than that of the inner-pole fixed type developing devices 21a and 21b, and when separated from the photoconductor 20. This is because the magnetic attraction force for the developer changes periodically as the magnetic pole passes.

Blurring at the leading and trailing edges of an image occurs due to the following reasons.
Absent. Referring to the illustrations of FIGS. 20A to 20C, FIG.
explain. Electrostatic latent image part I₁(V_i= -300V)
After the development is completed, the non-image area I₀(V ₀= -50V) develops
As it advances to the area, the non-image part I₀Magnetic contact with
In the case of toner, toner (positive charge) is applied to the developing via of the sleeve 22.
Space V_B(= -150V) and moved to the sleeve side
However, the surface of the sleeve 22 facing the photoconductor is charged with an opposite polarity to the toner.
A load (negative charge) appears. However, the carrier Ca is a magnet
It moves to the sleeve side (upward in FIG. 13) with the rotation of 23.
The carrier Ca and the electrostatic latent image I in the image area₁To
An electric attraction acts between the toner To and the attached toner To.
Image tip, without being electrically sucked
Or, the toner To at the rear end is scraped off and the image is blurred on the image.
Does not appear.

White spots in the lead portion do not occur for the following reason. It will be described with reference to the examples of FIGS. 21A to 21C. Low-density image electrostatic latent image I ₁ (V _{i 1} = −300
V) and the high-density image electrostatic latent image I ₂ (V _i2 = −600 V)
As described above, the carrier Ca, which has lost the toner due to the development of, retracts from the photoconductor 20 as the magnet body 23 rotates,
Move to the sleeve surface side. Therefore, the carrier Ca that has lost Tote To is adhered to the photoconductor 20 by the toner To.
The toner does not come into contact with and scrape off this toner. Therefore, the lead white spot does not appear on the image.

In addition, white streak does not appear in the image even when the tip of the regulating portion is clogged with foreign matter. This is because the developer is disturbed in the three-dimensional direction by the rotation of the magnet body 23, and the developer absent portion where the developer is removed by the foreign matter is filled with the nearby developer and erased. Therefore, the present invention can solve the above-mentioned problems in the conventional developing device, and can also obtain an image in which the edge effect is emphasized according to the demand, as in the case of developing a line image, for example. An object is to provide a developing device.

[0018]

According to the present invention, in order to solve the above-mentioned problems, a sleeve is put on a magnet body fixed in a non-rotating state, and a developer held on the outer peripheral surface of the sleeve is brought into contact with a photoreceptor. In the developing device for developing the electrostatic latent image by
Two magnet poles having the same polarity are provided adjacent to each other on the photoconductor facing portion of the magnet body, and magnet body driving means for controlling the position of the two magnetic poles with respect to the photoconductor is provided.
The two magnetic poles are provided such that the developer is continuously retained on the outer peripheral surface of the sleeve between the magnetic poles, and the magnet body driving means is configured such that the two magnetic poles of the magnetized portion have the two magnetic poles. Among them, the developer held by the magnetic pole located on the upstream side in the sleeve rotation direction and the developer held by the intermediate portion of the two magnetic poles come into contact with the photoconductor and are held by the magnetic pole located on the downstream side in the sleeve rotation direction. Positions are set in a range from a position where the developer is not in contact with the photoconductor to a position where the developer held in each of the two magnetic poles and the developer held in the middle of the magnetic pole come into contact with the photoconductor. The present invention provides a developing device characterized by being configured so as to obtain.

The magnet drive means holds two adjacent magnetic poles of the magnetized portion of the same pole at a developer held by a magnetic pole located on the upstream side in the sleeve rotation direction and an intermediate portion of the two magnetic poles. The developer is in contact with the photoconductor, and the developer held by the magnetic pole located on the downstream side in the sleeve rotation direction is not in contact with the photoconductor, or the developer held by each of the two magnetic poles and the magnetic pole. An example is one in which the developer held in the intermediate portion can be selectively arranged in two steps at positions where they both come into contact with the photoconductor. It may be something that can be set.

[0020]

According to the developing device of the present invention, in the region where the photosensitive member and the sleeve face each other, the magnetic fields of the two magnetic poles of the two magnetic poles of the same polarity repel each other, and the repulsive magnetic field is generated. Has been formed. Therefore, the developer conveyed to the portion corresponding to the upstream magnetic pole of the two magnetic poles is strongly held by the magnetic force of the magnetic pole, and there is a repulsive magnetic field on the downstream side. As a result, the developer on the sleeve corresponding to the magnetic pole forms a high-density pool in which the developer is disturbed.

The developer held in this manner is pushed by the developer sent from the upstream side in sequence and moves to the downstream side while being held on the surface of the sleeve. At this time, since a repulsive magnetic field is formed by both magnetic poles in the intermediate portion between the two magnetic poles having the same polarity, the developer passing through the intermediate portion has a low density. Further, the developer held in a portion of the two magnetic poles having the same polarity, which corresponds to the magnetic pole on the downstream side in the direction of the soot rotation, is strongly retained by the action of the magnetic pole on the downstream side. However, unlike the repulsive magnetic field, there is nothing on the downstream side of the magnetic pole that hinders the transport of the developer, so that no pool is formed unlike the portion corresponding to the upstream magnetic pole.

Then, by the magnet body driving means, the two magnetic poles of the magnetized portion having the same pole are held by the magnetic pole located on the upstream side in the sleeve rotation direction and the developer held by the intermediate portion of the two magnetic poles. Is in contact with the photoconductor and the developer held by the magnetic pole located on the downstream side in the sleeve rotation direction is not in contact with the photoconductor, the electrostatic latent image on the photoconductor is located on the upstream magnetic pole. And the developer held between both magnetic poles. That is, it is finally developed with the low-density developer.

Further, the two magnetic poles of the magnetized portion having the same polarity are arranged at positions where the developer held in each of the two magnetic poles and the developer held in the middle portion of the two magnetic poles come into contact with the photoconductor. When developed, the electrostatic latent image on the photoreceptor is developed with those developers.

[0024]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a partial cross section of a developing device according to an embodiment. This developing device belongs to the homopolar type developing device, and in the developing roller 1, the magnet body 3 contained in the sleeve 2 is provided with two magnetic poles N ₁ and N ₂ of the same polarity at the portion facing the photoconductor 10. The same pole magnetized portion N ₀ is provided adjacently to each other, magnetic fields H ₁ and H ₂ are formed at the opposing portions of the magnetic poles N ₁ and N ₂ , and a repulsive magnetic field H ₀ is formed between them. In addition to the magnetic poles N ₁ and N ₂ , magnetic poles are formed on the outer peripheral portion of the magnet body 3, and in principle, these magnetic poles are arranged so that N poles and S poles are alternately located.

The spacing of the magnetic poles N ₁ and N ₂ is the magnetic force distribution of the magnetic poles N _1, N _2, as shown in FIG. 2, the valley is formed at an intermediate portion of the magnetic pole N _1, N _2, and, The magnetic force Md of the depressed portion (valley portion) Pd is the peak portion (peak portion) P
It is set to be 70 to 90% of the magnetic force Mu of u. In this developing device, a two-component developer composed of toner and carrier is supplied to the developing roller 1. The developer supplied to the developing roller 1 is held on the outer peripheral surface of the sleeve by the magnetic force of the magnet body 3. The developer is sleeve 2
Is conveyed in the direction of the arrow a with the rotation of and is regulated by the regulation plate 4. The developer D that has passed through the tip of the regulation plate 4 passes through a region in which the photoconductor 10 and the sleeve 2 in which the magnetic poles N ₁ and N ₂ face each other are close to each other.

[0026] Here, the magnetic field H ₁ of the magnetic poles N _1, N _2, H ₂
Are formed toward the magnetic poles S ₁ and S ₂ , respectively, and the magnetic pole N
The magnetic field H _{0 at} the intermediate portion between ₁ and N ₂ exists as a repulsive magnetic field. Accordingly, as shown in FIG. 3, the developer conveyed to the opposing portion of the magnetic pole N ₁ is strongly held by the magnetic brush state by the magnetic force of the magnetic pole N _1, the magnetic field H ₁
Along the direction inclining in the direction opposite to the traveling direction (direction of arrow a).

Therefore, the developer D bound to the magnetic pole N _1
1 forms a puddle and is disturbed in the three-dimensional direction in this puddle. The developer D ₁ held by the magnetic pole N ₁ is pushed by the developer conveyed from the upstream side, and sequentially moves to the magnetic pole N ₂ from the _one which cannot be held by the magnetic pole N ₁ . Here, the depression Pd in the middle of the magnetic poles N ₁ and N ₂
Since the magnetic force Md is set to 70 to 90% of the magnetic force Mu of the peak portion Pu, the developer D ₁₂ is held in a magnetic brush state even on the sleeve located in the intermediate portion.
However, since the magnetic field repels in the intermediate portion, the density of the developer is extremely low, and the surface of the developing sleeve can be observed through the developer. That is, this low density area can be visually confirmed.

Next, the developer which has passed through the intermediate portion has a magnetic pole N.
It is strongly held again on the outer circumference of the sleeve by the magnetic force of ₂ .
However, the downstream side of the magnetic pole N ₂ there is also that which the same polarity magnetic poles of the absence, the developer held on the magnetic pole N ₂ D
₂ is smoothly transported to the downstream side without forming a puddle. Therefore, the developer D held by the magnetic force of the magnetic pole N _2
2 has a higher density than the developer D ₁₂ in the middle portion and a lower density than the developer D ₁ held by the magnetic pole N ₁ . That is, the density is medium.

The magnet body 3 is driven to rotate. The drive device will be described with reference to FIG. The magnet body drive device 7 includes a member 71 connected to an end of the magnet body 3 which is rotatably supported by an appropriate support means, and a spring 7 which constantly applies a rotational moment to the member 71 in a predetermined direction.
2 and a solenoid 74 connected to the member 71 via a link mechanism 73. According to this drive,
When the solenoid 74 is not energized, the two magnetic poles N ₁ and N ₂ of the magnetized portion N ₀ of the magnet body 3 are the magnetic poles N ₁ located upstream of the spring 72 acting on the magnet body 3. The developer D ₁ held on the magnetic pole N ₂ and the developer D ₁₂ held on the intermediate portion of the two magnetic poles contact the photoconductor 10, and the developer D ₂ held on the magnetic pole N ₂ located on the downstream side is the photoconductor. It is arranged at a position where it does not contact 10 (the state shown in FIG. 3A). Further, when the solenoid 74 is energized, the magnet body 3 moves to the spring 7
The two magnetic poles N ₁ and N ₂ are rotated against ₂ and the magnetic pole N
_The photoconductor 10 contacts the developer D ₁ held at ₁ , the developer D ₁₂ held at the middle of the two magnetic poles, and the developer D ₂ held at the downstream magnetic pole N _2. They are arranged (state shown in FIG. 3B).

It is also conceivable to employ a drive device for the magnet body as shown in FIG. The device 70 of FIG. 5 is configured such that the shaft 75 of the magnet body 3 can be rotated forward and backward by a motor 77 via a gear transmission device 76.
The photo-coupler 79 detects the light-transmitting portion of the light-shielding disk 78 provided on the magnet shaft 75, and controls the motor operation in accordance with this detection signal to expose the magnetic poles N ₁ and N ₂ of the magnet 3 to light. The position relative to the body can be controlled as in the device 7.

When the solenoid 74 in the drive unit 7 is in the non-energized state, while the developer is being conveyed as described above, the photosensitive member 10 has the magnetic pole N as shown in FIG. _The developer D ₁ held at ₁ and the developer D ₁₂ held at the intermediate portion are brought into contact with each other, and the bias V _B and the photoconductor 10
The toner adheres to the electrostatic latent image based on the potential difference between the electrostatic latent image formed on the outer peripheral surface of the toner and the electrostatic latent image for development, and the development is completed by the developer D ₁₂ in the intermediate portion. In other words,
The development of the electrostatic latent image on the photoconductor 10 is terminated by contact with the low density developer. Then, it does not come into contact with the medium-density developer D ₂ held by the downstream magnetic pole N ₂ . At this time, since the N ₂ portion is not in contact with the position where the development of the developer D ₁₂ is completed, the position higher than N ₁ is better in image quality.

According to this development, the amount of toner adhering to the edge portion of the electrostatic latent image does not become much larger than the amount of toner adhering to the central region surrounded by this. Therefore, as shown in FIG. 6, a flat toner image 6 having a uniform toner adhesion amount and a weak edge effect is obtained, and as shown in FIG. 7, even if toner images 6a, 6b, 6c of different colors are superposed, The overall color tone can be the same.

Further, since the developer does not fly from the magnetic pole N ₁ to the magnetic pole N ₂ , toner fog does not occur in front of the image portion. That is, when the flying developer D collides with the photoconductor 10, as shown in FIGS. 10A to 10C, the toner To attached to the electrostatic latent image portion I ₂ is repelled. The ejected toner To adheres to the non-image portion I ₀ and causes toner fogging.
In this developing device, the developer is always held on the outer circumference of the sleeve 2 and does not fly, so that toner fogging does not occur due to the flight of the developer.

If the developer flies, a large amount of toner scatters from the developer ears due to the collision force with the sleeve when it is collected again in the sleeve, which causes toner fogging and in-machine contamination. However, since the developer does not fly in this developing device, such toner fogging and in-machine contamination do not occur. Further, when the developer flies, a part of the flying developer flies around, but since the developer does not fly in the present developing device, such a problem due to the flying of the developer does not occur.

Magnetic pole N₁The part corresponding to is shown in FIG.
So that the magnetic field H₁Is the magnetic pole S on the upstream side ₁Formed towards
The magnetic field H₁Formed along
And the developer on the tip side of the magnetic brush is the magnetic pole S₁Transport towards
Receives a force in the opposite direction. In addition, the diagram (A) of FIG.
(C) as shown in FIG.₀Magnetic contact with
In the brush, the toner bound to the carrier is
Ias V_BElectrically sucked by (eg -150V)
Is moved to the sleeve side and the carrier Ca faces the photoconductor
Charges of the opposite polarity to the toner appear in the area, but as described above,
Since the magnetic brush receives a force in the direction opposite to the transport direction,
The carrier at the tip of the brush moves to the sleeve side. Obey
The carrier's electrical scraping force against toner is weak.
There is no blurring pattern at the front and rear edges of the image.
Yes. For the same reason, it is shown in FIGS. 9 (A) to 9 (C).
As described above, the low-density image electrostatic latent image I₁High density image behind
Image electrostatic latent image I₂Even if the
Is scraped off by the magnetic brush, causing white spots on the lead.
There is no such thing.

The developer held on the magnetic pole N ₁ is 3
Since it is disturbed in the dimensional direction, even if a foreign matter is clogged between the regulation plate 4 and the sleeve 2, the developer is supplied to the nonexistent portion of the developer which is rejected by the foreign matter, and an image defect portion such as a white streak. An image without Further, since the density of the developer when it is separated from the photoconductor 10 is low, the carrier that has lost the toner rarely adheres to the photoconductor 10 due to the wraparound electric field at the peripheral edge portion of the electrostatic latent image, and thus the toner to the photoconductor 10 is removed. Carrier adhesion is reduced.

Table 1 shows the results of observing the background fog and the like in each case by changing the magnetic force and the positional relationship of the magnetic poles N ₁ and N ₂ in the same polarity portion of the developer.

[0038]

[Table 1]

The observation items and observation results in the above table are as follows. Observation items a: Background fogging Observation results ○: Good (no problem) b: Edge effect △: No problem in practical use C: White spots on lead part ×: Problems d: White streaks As shown in Table 1 above, (a) When Md / Mu = 1.0, problems occurred in the items of B, C, and D. (B) M
In the case of d / Mu = 0.69 to 0.9, all the items were in a practically unimpeded state. (C) Md / Mu = 0.4
In the case of 9, there was a problem in terms of fog.

Therefore, Md / Mu is approximately 0.7 to 0.9.
Within the range of, the developer is retained even in the middle of the same polar part,
It can be understood that the development is finally performed by the developer held in the middle, and a high-quality image without background fog, edge effect, white spots on the lead portion, and white streaks can be obtained. As can be understood from the above description, development by low density developer D ₁₂ of which is held between the magnetic poles N developer held on the ₁ D ₁ and the magnetic pole N _1, N ₂ is the tone like a photograph image It can be said that it is suitable for developing a solid image such as an image having a dot, a halftone image, or an image having a high B / W ratio.

In the magnet body driving device 7, the solenoid 74 is energized, and as shown in FIG. 3B, the magnetic poles N ₁ and N ₂ are held between these magnetic poles and the developer D ₁ held between the magnetic poles. When developing with D ₁₂ and D ₂ , the medium-density developer D ₂ also contributes to the development, so that the same edge effect as in the conventional magnet type fixed homopolar type developing device can be obtained, and lines of characters and the like can be obtained. It can be used for clearly obtaining an image or an image having a low B / W ratio.

The developing bias voltage V _B is set to a low value suitable for solid image development, and a high value is set to develop a line image so that the edge effect can be improved. May be obtained. In addition, the solid image is B from the line image.
Since the / W ratio is high and a large amount of toner is consumed, in order to increase the developer supply amount for a solid image, the peripheral speed ratio between the developing sleeve and the photoconductor is increased so that the developing sleeve can be rotated quickly. If the development gap (the gap between the development sleeve and the photoconductor) is narrowed, the concentration of electric lines of force at the edge part is eliminated, so the edge effect is small and it is suitable for solid images. When the gap is made small and the developing bias V _B is made large to enhance the edge effect, the potential difference from the surface potential of the photoconductor becomes small and the image density (ID) is lowered. Therefore, in order to prevent this, the bias V _B is set. When it is increased, the photoreceptor surface potential is also increased. As with the case described above, in order to increase the developer supply amount for the solid image, the height of the brush height regulating member and the developing sleeve are increased. For the solid image, the gap (peak height regulation gap) may be made larger than that for the line image, and if necessary, alternating current may be weight-applied and the frequency and voltage thereof may be changed during development. Such switching can be interlocked with the attitude control of the magnet body by the magnet body drive device.

Further, the development suitable for the solid image or the development suitable for the line image may be arbitrarily or automatically selected according to a user's instruction of the image forming apparatus or according to the B / W ratio.

[0044]

As described above, according to the present invention, a solid image such as an image having gradation such as a photographic image, a halftone image, an image having a high B / W ratio, a line of characters, etc. It is possible to provide a developing device capable of performing any of the developments capable of clearly obtaining an image or an image having a low B / W ratio.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of a developing device according to the present invention.

FIG. 2 is a magnetic force distribution diagram of a homopolarized portion.

3A and 3B are diagrams showing a state of a developer in a portion where a sleeve and a photoconductor face each other. FIG. 3A shows a state suitable for developing a solid image and FIG. 3B shows a state suitable for developing a line image. Shows.

FIG. 4 is a perspective view of a magnet drive device.

FIG. 5 is a perspective view of another example of the magnet drive device.

FIG. 6 is a cross-sectional view showing an example of a state where toner is attached to a photoconductor.

FIG. 7 is a cross-sectional view showing an example of a toner adhesion state on a photoconductor in a color image.

FIG. 8 is an explanatory diagram of a reason why image blurring does not occur.

FIG. 9 is an explanatory diagram of the reason why white spots in the lead portion do not occur.

FIG. 10 is a diagram illustrating the reason why toner fogging does not occur.

FIG. 11 is a partial cross-sectional view of a single-pole type inner pole fixed type developing device.

FIG. 12 is a partial cross-sectional view of a homopolar inner-pole fixed developing device.

FIG. 13 is a partial cross-sectional view of an inner pole rotation type developing device.

FIG. 14 is a cross-sectional view showing a toner adhesion state on a photoconductor in a conventional monopolar developing device.

FIG. 15 is a cross-sectional view showing an attached state of toner fixed on a recording medium by using a conventional monopolar developing device.

FIG. 16 is a cross-sectional view of superimposed toner images.

FIG. 17 is a diagram showing a process in which a blurring pattern is generated in a conventional monopolar developing device.

FIG. 18 is a diagram showing a process in which white spots in a lead portion occur in a conventional monopolar developing device.

FIG. 19 is an explanatory diagram showing a state in which a carrier adheres to a photoconductor in a conventional monopolar developing device.

FIG. 20 is an explanatory diagram of a reason why a blurring pattern does not occur in a conventional inner pole rotation type developing device.

FIG. 21 is an explanatory diagram of a reason why white spots in a lead portion do not occur in a conventional inner pole rotation type developing device.

[Explanation of symbols]

1 developing roller 2 sleeve 3 magnet body 4 regulation plate 10 photoconductor N ₀ homopolar magnetized parts N ₁ , N ₂ magnetic poles D ₁ , D ₂ , D ₁₂ developer 7, 70 magnet body drive device

Front page continuation (72) Inventor Masahiko Matsuura 2-3-13 Azuchi-cho, Chuo-ku, Osaka Inside Osaka Kokusai Building Minolta Camera Co., Ltd. (72) Susumu Mikawa 2-3-13 Azuchi-cho, Chuo-ku, Osaka Osaka International Building Minolta Camera Co., Ltd.

Claims (1)

[Claims] 1. A developing device for developing an electrostatic latent image by covering a sleeve on a magnet body fixed in a non-rotating state, and bringing a developer held on the outer peripheral surface of the sleeve into contact with a photoreceptor to develop an electrostatic latent image. A homopolar magnetized portion in which two magnetic poles of the same polarity are adjacent to each other is provided on the photosensitive member facing portion of the body, and magnet body driving means for controlling the position of the two magnetic poles with respect to the photosensitive member is provided, and the two magnetic poles are provided. Is provided so that the developer is continuously retained on the outer peripheral surface of the sleeve between the magnetic poles, and the magnet body driving means is configured such that the two magnetic poles of the same-polarized portion rotate the sleeve among the two magnetic poles. The developer held by the magnetic pole located on the upstream side in the direction of contact and the developer held by the middle portion of the two magnetic poles come into contact with the photoconductor, and the developer held by the magnetic pole located on the downstream side in the sleeve rotation direction is exposed. From the position where it does not contact the body, A developing device characterized in that the developer held in each of them and the developer held in the magnetic pole middle portion can be set in a range up to a position where they come into contact with the photoconductor.