JPS6161108B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic brush developing device for developing electrostatic latent images in electrophotographic copying devices, electrostatic recording devices, and the like.

A conventional developing device uses one developing roller to draw up developer and develop an electrostatic latent image. Recently, however, there has been an increasing demand for high-speed copying, and the concept of maintenance-free printing, which reduces the frequency of maintenance such as developer replacement, is increasing. In order to satisfy such demands, it is necessary to increase the amount of developer contained in the developing device. There are other methods, such as improving the developer, but they have not yet been put to practical use. By increasing the amount of developer, the number of times the developer is circulated is reduced, and fatigue of the developer, especially the carrier, is prevented as much as possible. That is, since fatigue and deterioration of the carrier is accelerated when the carrier mechanically collides with other substances or with each other, the developer that once contributed to development should be allowed to rest for a while. I did it like that. Therefore, in the developing device of a high-speed copying machine, developer is circulated at a high speed, but since the amount of developer is large, there is no significant change in toner concentration, and the degree of fatigue and deterioration of the developer can be reduced, which in turn reduces the development speed. The time required for agent replacement can also be significantly extended. However, as the amount of developer increases, the size of the developing device to accommodate the developer increases, and as in the past, a single developing roller becomes long in the horizontal direction, and there is no room for the overall layout of the copying machine. In addition, since the developer is agitated and transported from a distance by a transport means, the developer is mechanically rubbed and deteriorated during this time, which is undesirable. Particularly in a dry type developing device, if all the developer is not circulated, the developer will solidify or remain dead, resulting in various adverse effects.

Therefore, a developing device as shown in FIGS. 1 and 2 has been proposed.

In FIG. 1, a multi-stage magnetic brush developing device is used, and reference numeral 1 denotes a photosensitive drum rotating in the direction indicated by the arrow. In the developing device 2, three developing rollers 3, 4, and 5 each consisting of a nonmagnetic sleeve and a magnet are arranged close to the photosensitive drum 1 so as to be rotatable in the direction indicated by the arrow. The developing roller 3 pumps up the developer from the lower part of the developing device 2 and supplies it to the developing roller 4, and further transfers all the developer pumped up from the developing roller 4 to the developing roller 5. The electrostatic latent image on drum 1 is developed. The developer that has contributed to the development is removed from the developing roller 5 by a scraping plate 6 and dropped into a developer reservoir 7. A predetermined amount of developer passes through the gap 7a from the developer reservoir 7 to the developing roller 3.
will be supplied to. In such a developing device, since there is no doctor member before development, it is difficult to keep the amount of developer on each developing roller constant. In particular, in a system in which the developer is magnetically conveyed from one developing roller to the other, the height of the magnetic brushes of the developer on both rollers gradually increases. (The bulk density decreases.) Therefore, the gap between the developing roller and the photoreceptor drum 1 must be delicately adjusted for each roller, and the magnetic transfer creates an unstable flow of developer. It is difficult to make a uniform magnetic brush and it is difficult to perform uniform development.

On the other hand, as shown in FIG. 2, there is a developing device 10 consisting of one developing roller 8 and a pumping roller 9, but the developer is only transferred magnetically from the pumping roller 9 to the developing roller 8. However, as mentioned above, it is difficult to form a uniform magnetic brush. Although it has been proposed to provide a doctor member close to the pumping roller 9, it is not easy to uniformly align the height of the magnetic brush during development with only this.

Therefore, for example, in the developing device 10 shown in FIG. 2, a doctor member may be arranged close to the developing roller 8, but if the excess developer is removed here, the removed developer will gradually accumulate. There is no place for the developer to escape, and a large load is placed on the developing roller and pressure is applied to the developer.
This will accelerate its deterioration.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a developing device capable of eliminating the above-mentioned drawbacks, forming a uniform magnetic brush, and obtaining a uniform image.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 is a sectional view of a developing device showing an embodiment of the present invention. Reference numeral 11 denotes a photoreceptor drum that rotates at a constant speed in the direction of the arrow. As the photoreceptor, inorganic photoconductors such as zinc oxide, selenium, CDS, organic photoconductors, and combinations thereof are used. The photoreceptor is not limited to a drum-shaped one as in this embodiment, but may be a flexible one, such as a belt-shaped one. After an electrostatic latent image is formed on the photoreceptor drum 11 by being charged and exposed, it is made into a visible image by toner powder. The developing device 12 is a portion that moves below the photosensitive drum 11 and is disposed at a lower portion thereof. Developer container 1
3 is attached on the support plate 14, and the support plate 1
4 is a guide member 15 attached to the main body of the copying machine.
a, 15b and the bottom guide member 16, it can be pulled out toward the front in the figure. It is also possible to further pull out the developing device 12 and take out the developing device 12 from the copying machine.

A developing roller 17 and a pumping roller 18 are arranged vertically in the developing container 13. The developing roller 17 consists of a non-magnetic rotating sleeve 19 whose surface is knurled and magnets 20 ₁ and 20 ₂ fixed therein. The magnet 20 ₁ faces the photosensitive drum 11 and has a magnetic force of about 450G, and the magnet 20 ₂
It is tilted at an angle of about 90 _degrees , and its magnetic force is 750G. The sleeve 19 is connected to the photoreceptor drum 11 by about 2~
It is rotated at a speed of 120 to 170 rpm with a gap of 3 mm. A doctor member 21 extends toward the rotation axis of the sleeve 19 on the right side of the developing roller 17.
The gap with the tip of 1 is set to be slightly narrower than the above-mentioned gap. The doctor member 21 has an inverted L-shape and captures toner and the like that fly up into the air when the developer passes through the doctor member 21 in a space A formed by the doctor member 21, the sleeve 19, and the photoreceptor drum 11. Toner powder and the like are prevented from scattering outside the developing device 12. Developing roller 1
At the bottom of 7 there is a pumping roller 18, which consists of a non-magnetic rotating sleeve 22 and four magnets 23 ₁ - 23 ₄ fixed inside it. The pumping magnets 23 ₁ to 23 ₄ are arranged so that their magnetic poles are alternately arranged at equal angles, and the magnetic force of the magnets 23 ₁ to 23 ₃ is 550G.
The magnet ₂₃₄ is 750G. Magnet 20 ₂ and 23
₄ are inclined by about 54° to 56° from a line connecting the centers of rotation of the sleeves 19 and 22, respectively. The gap between sleeve 22 and sleeve 19 is approximately 7
mm, and the sleeve 22 is rotating at the same speed as the sleeve 19. The developer container 1 is placed opposite the sleeve 22.
A projection 13a extending in the axial direction of the sleeve 22 is formed at the bottom of the sleeve 22, and the gap between this and the sleeve 22 is about 4 mm. A scraping plate 24 is provided on the left side of the sleeve 22, and the scraping plate 24 consists of a vertical portion and a tip portion whose both ends are bent toward the sleeve 22. One end is in contact with or close to the surface of the sleeve 22 to remove the developer on the sleeve 22, and the other end is connected to the bottom of the developer container 13 with a gap of about 5 mm to remove the developer stored in the developer container 13. It regulates the flow of

On the other hand, a scraping plate 25 is also provided in the upper left portion of the developing roller 17 in contact with or in close proximity to the sleeve 19, and a scraping plate 25 is provided in contact with or in close proximity to the sleeve _19.
The developer is removed from the surface of the sleeve 19 at a location where the magnetic force does not reach, and is dropped onto the scraping plate 25 by the developer's own weight and returned to the developer container 13. Below the rear line of the scraping plate 25, a stirring blade 26 is rotated clockwise by a drive device (not shown).
The stirring blade 26 has a plurality of inclined elliptical plates attached to a shaft 26a at equal intervals. Therefore, when the stirring blades 26 are rotated by 180 degrees, the elliptical plates exhibit inclinations in opposite directions in each state. Due to this arrangement, the developer is stirred in the axial direction of the stirring blade 26.

The developer is stored between the developer container 13 and the vertical portion of the scraping plate 24, and the developer dropped from the scraping plates 24 and 25 is collected in this portion. A stirring blade 27 is provided in this portion so as to be rotated counterclockwise. The stirring blades 27 are spirally wound in opposite directions on the left and right sides with the center of the shaft 27a as a boundary, so that the developer is collected in the center of the shaft 27a.

A hole 25a is formed in the center of the scraping plate 25, and a magnetic toner concentration sensor 28 consisting of a non-magnetic hollow cylinder and a coil wound around it is provided below the hole 25a. ing. The developed developer flows down from the hole 25a into the hollow cylinder, and the mixing ratio of the toner and the magnetic carrier in the developer passing therethrough is detected by a change in the inductance of the coil. When it is detected that the toner ratio is lower than a predetermined mixing ratio, a control circuit (not shown) generates a toner replenishment command signal.

A toner replenishing device 29 is provided to the left of the developing device 12. The toner replenishing device 29 includes an inner cylinder 31 having an elongated toner discharge opening 30 at the top, a pair of arms 33, 33 that rotate clockwise around a shaft 32 inside the cylinder 31, and a coil stretched between the arms. It is composed of a spring 34. Toner powder is stored in the cylinder 31, and the arm 33
usually rests on the top of the toner layer at the position of the imaginary line under its own weight. Thereby, the remaining amount of toner in the cylinder 31 is detected by a remaining toner amount detecting device (not shown) provided on the rotating shaft 32 by knowing its stop position. The arm 33 and the coil spring 34 are forcibly rotated by a drive device connected to the shaft 32, and the toner is transferred to the coil spring 34.
Capturing it inside and pumping it up, using its centrifugal force,
The toner is released from the toner discharge opening 30 into the developing device 12.
Replenish inside. When the arm 33 reaches the top, the drive is turned off and it continues to rotate due to inertia until it stops on the toner layer as described above. The coil spring 34 has a rotation locus that is substantially concentric with the cylinder 31, and rotates with a small gap between the coil spring 34 and the inner surface of the cylinder 31. When replenishing toner, a coil spring passes through the toner, so that the toner is appropriately agitated, preventing the stacking phenomenon and eliminating unused toner. Since the toner supply is discharged using centrifugal force, it has the advantage that it is dispersed appropriately within the developing device 12 and that toner lumps are loosened.

Guide plates 31a and 31b are provided above and below this cylinder 31.
are formed and guided by guide rails 35 and 36 provided in the developing device 12. When replenishing the toner supply device 29 with toner, pull it out along the guide rails 35 and 36, and
Toner is replenished into the cylinder 31 from the toner discharge opening 30 while the developing device 12 remains attached. At this time, the shaft 32 is disconnected from the drive device provided in the machine body or the developing device 12. When replenishing the cylinder 31 with toner, it is convenient to rotate the cylinder 31 counterclockwise so that the opening 30 is directly above it. This rotation may be performed after the toner replenishing device 29 is completely pulled out of the machine, or the toner replenishing device 29 may be pulled out while rotating. In the first place, the toner discharge opening 30 also serves as a toner replenishment opening, and since this opening 30 is provided above, even if the toner replenishment device 29 is pulled out of the machine, the toner will not vibrate on the floor or inside the copying machine. This is convenient because it will not fall even if it occurs.

Next, the operation of the developing device of the present invention will be explained. The magnetic developer used in the present invention is a two-component developer consisting of a non-magnetic toner and a magnetic carrier (iron powder), and the magnetic carrier used is iron powder or one coated with a resin around it. Of course, it is also possible to use a conventionally known magnetic toner in place of the non-magnetic toner. The stored developer is prevented from coming into contact with the pumping roller 18 by the scraping plate 24.
This is to prevent the developer from being subjected to unnecessary mechanical friction and deterioration of the carrier, as well as to prevent the rotational torque of the pumping roller 18 from increasing. Only the necessary amount of developer to be used is drawn out by the magnetic force of the magnet ₂₃₁ of the pumping roller 18, and the developer is controlled to an appropriate amount by the protrusion 13a and exits. The developer is magnet 23 ₁ , 23 ₂ , 23
₃ , 23 _{and 4} , the sleeve 22
and is pumped up in the direction of rotation of the sleeve 22. and the magnet 23 of the pumping roller 18
₄ and the magnet 20 of the developing roller 17. A portion of the developer on the sleeve ₂₂ is magnetically transferred to the sleeve 19, while the other developer remains on the sleeve 22 and is not scratched. It is scraped off from the sleeve 22 by the drop plate 24. The developer supplied to the developing roller 17 is
On top of that, a magnetic brush is formed again to form the sleeve 19.
Immediately before development, the blade height of the developer is again regulated to a predetermined height by the doctor member 21. Excess developer is removed at this portion, falls downward as shown in the figure, and is pumped up again to the top together with the developer on the pumping roller 18. However, since the amount of developer replenished by the protrusion 13a is constant, if the copying operation is performed for a long time, excess developer will be removed from the space formed by the pumping roller 18, the developing roller 17, and the developer container 13. B, the rotational load on both of the rollers increases, and uneven rotation of the developing roller 17 occurs, making it impossible to perform proper development. For this purpose, a means is required to gradually release the developer accumulated in the space B in small amounts. In the present invention, a gap is formed between the developing roller 17 and the drawing roller 18 through which the developer can flow, and this is achieved by the interaction between the magnets ₂₃₄ and ₂₀₂ . This principle will be explained using FIG. 4.

In FIG. 4, a developer having a thickness ho is pumped onto the sleeve 22, and a developer having a thickness _h1 is magnetically transferred to the sleeve 19 of the developing roller 17 against gravity. The developer having a thickness h ₂ remains on the sleeve 22 while being moved. In the initial stage, the relationship ho=h ₁ + h ₂ is established, but since the developer on the sleeve 19 is regulated to a thickness h ₃ by the doctor member 21 immediately before development (h ₁ −
The developer having a thickness of h ₃ ) falls onto the sleeve 22 of the pumping roller 18, and the thickness of the developer on the sleeve 22 becomes ho+(h ₁ −h ₃ ). If h ₂ is constant, then in space B, V=∫ ^t _p
Developer of (h ₁ −h ₃ )・Sdt will accumulate.
Here, S is the unit area of the developer formed on the sleeve in the axial direction. Strictly speaking, the thickness h of the developer is affected by the decrease in bulk density due to the transport of the developer, passage through the magnetic poles, transfer between sleeves, etc., but for the purpose of explaining the basic concept, this is The explanation was omitted.

If the range of the magnetic field that can magnetically attract the developer of the magnet ₂₃₄ in the sleeve 22 is C, and that of the magnet ₂₀₂ is D, then since the above two magnetic poles are different from each other, the magnetic carrier on the sleeve 22 is Magnet 23 ₄
A south pole appears on the opposite side and a north pole appears on the opposite side, so that the magnetic carrier is magnetically attracted to the south pole of the magnet ₂₀₂ . However, instead of all magnetic carriers being attracted by magnet ₂₀₂ , magnet 2
Since there are also 3 _{and 4} magnetic attraction forces, they will be separated when the balance between the two magnetic attraction forces is broken. Further, since the developer has a residual force on the sleeve 22 due to the action of gravity, the amount of developer that the magnet ₂₀₂ attracts from above the sleeve 22 by its magnetic force is constant. Therefore, sleeve 2
Even if the thickness of the developer ho on the sleeve 19 varies somewhat, the thickness of the developer transferred to the sleeve 19 is approximately close to _h1 . Therefore, if ho changes, the amount of change is h ₂
As a result of this variation, excess developer is returned to the developer container 13 by the rotation of the sleeve 22.

Now, assuming that the axis of the developing roller 17 is O and the axis of the pumping roller 18 is O', the angle between the line connecting O and O' and the magnet ₂₀₂ is 53°30', and the angle between the magnet ₂₃₄ and the above line is 53°30'. It was found that when the angles were set at 55 degrees, approximately 1/3 to 1/4 of the developer on the sleeve 22 remained on the sleeve 22 without being transferred to the developing roller. Further, when the magnet ₂₃₄ is further rotated clockwise to increase the above angle, the thickness h ₁ of the developer transferred to the sleeve 19 increases, and when the magnet 234 is moved in the opposite direction, the thickness h ₂ increases. Such a relationship varies depending on the distance between the magnets ₂₀₂ and ₂₃₄ , their mounting angles, and the magnitude of their respective magnetizing forces, and is not uniquely determined. It can be changed arbitrarily according to each request. Therefore, since the thickness _h2 of the developer remaining on the sleeve 22 and moving changes variously, the gap between the sleeve 19 and the sleeve 22 is
It must be large enough so that it does not block the movement of developer between them.

The developer thus transferred to the sleeve 19 is adjusted by the doctor member 21 between the magnets 20 ₁ and 20 ₂ so that a magnetic brush having an appropriate thickness and uniformity is formed, and is brought into contact with the photoreceptor drum 11 . Ru. The developer that has passed through the developing section is removed from the sleeve 19 by the scraping plate 25, a part of which passes through the toner concentration sensor 28 section and returns to the developer container 13, and most of the other part is below the scraping plate 25. By the action of a stirring blade 26 which is rotatably provided, the liquid is distributed to the left and right in the direction of its rotation axis 26a. By doing so, even if the toner consumption amount varies in the axial direction of the developing roller 17 and there is uneven density, it is convenient because it can be made uniform. A stirring blade 27 is provided in the developer reservoir in the developer container 13.
is partially or entirely embedded in the developer and rotates. This moves the developer to its rotating shaft 27a.
This is to make the density distribution constant by moving the toner in the same direction, and to promote frictional electrification between the toner and the carrier. The developer is thus circulated within the developing device 12. In particular, as mentioned above, the developing device 12 has two circulation paths for developer.

When the toner concentration sensor 28 detects that the toner concentration has decreased, a predetermined amount of toner is replenished from the toner replenishing device 29. Since the amount of toner replenished by one rotation of the arm 33 is as small as a few grams, the toner is replenished by making several rotations. The toner is released by centrifugal force, but a sufficient distance must be provided to prevent the toner from being thrown directly into the toner concentration sensor 28, or a wire mesh or obstruction must be provided between the toner release opening 30 and the toner concentration sensor 28. This can be prevented by arranging a plate.

Above and to the left of the developing device 12, a shield plate 37 is fixed to the main body of the copying apparatus at a predetermined distance therebetween. The tip 37a of the shield plate 37 forms an opening 39 facing the photoreceptor drum 11 with a lid 38 provided at the top of the developing device 12. A space E formed by the shield plate 37 and the developing device 12 serves as a duct for an air suction device (not shown). The toner powder scattered from the developing device 12 is particularly large at the inlet portion of the developing device 12 of the photosensitive drum 11 because the toner is scattered in the connection direction at the portion of the developing roller 17 facing the photosensitive drum 11 . Therefore, an opening 39 of the duct is provided in this part, and the toner scattered and floating there is sucked by an air suction device to prevent the toner powder from adhering to the exposure optical system and other devices. There is.

Note that in the above-described embodiment, in order to change the amount of developer pumped from the sleeve 22 to the sleeve 19 or the amount of developer collected into the developer container 13 by the sleeve 22, a controller is provided outside the developing device 12. Sleeve 2 with a tab (not shown)
The magnets 23 ₁ to 23 ₄ in 2 can be rotated as a whole, or only the magnet 23 ₄ can be displaced. Of course, a device for detecting the amount of surplus developer accumulated in the space B of the developing device 12 is provided, and by automatically rotating or displacing the magnet ₂₃₄ immediately before an abnormality occurs, the amount of developer collected by the sleeve 22 is reduced. The amount may be increased.

The detection device may be one consisting of an acoustic oscillator and a receiver, or a known photoelectric or magnetic developer presence/absence detection device can be used.

Although an electrophotographic copying apparatus has been described in this embodiment, it goes without saying that any apparatus that forms an electrostatic latent image on a recording medium and develops it, such as an electrostatic recording apparatus, can be used.

As described above, according to the present invention, in development in which the developer is magnetically transferred from one magnetic roller to the other, it is possible to adjust the magnetic brush to be uniform just before development, resulting in excellent quality. It is possible to obtain a duplicate image. Furthermore, since a large capacity of developer can be stored, the time for replacement due to developer exhaustion can be significantly extended. Furthermore, it has two developer circulation passages, and the excess developer accumulated in the space is gradually and automatically carried out according to the amount, so the rotational torque of the magnetic roller is kept constant and development without unevenness is achieved. It became possible to do so. Further, it has the advantage that it can be used for high-speed development with a relatively simple device.

[Brief explanation of the drawing]

1 and 2 are schematic sectional views of a conventional developing device, FIG. 3 is a sectional view of a magnetic brush developing device showing an embodiment of the present invention, and FIG. 4 is for explaining the principle of the present invention. This is a diagram. 1, 11... Photosensitive drum, 12... Developing device, 13... Developer container, 17... Developing roller, 18... Pumping roller, 19, 22...
Sleeve, 20 ₁ , 20 ₂ , 23 ₁ to 23 ₄ ...
Magnet, 21... Doctor member, 24, 25... Scraping plate.

Claims (1)

[Scope of Claims] 1. A non-magnetic rotating sleeve containing a plurality of magnetic field generating means, which is arranged with a plurality of magnetic rollers each rotating in the same direction, and sequentially pumps up magnetic developer to generate an electrostatic latent material. In a developing device that develops an image, a doctor member that regulates the height of the magnetic brush before development is used as a doctor member that controls the height of the magnetic brush.
A second magnetic roller is disposed close to the first magnetic roller and supplies a magnetic developer to the first magnetic roller. The amount of magnetic developer supplied to the roller is regulated to a constant level, and at least one of the mutually opposing magnetic field generating means in both magnetic rollers is made movable to adjust the respective magnetic force, and the doctor member A magnetic brush developing device characterized in that the surplus magnetic developer removed from the magnetic roller is carried out from between the first and second magnetic rollers. 2. Claim 1, characterized in that the second magnetic roller is disposed almost directly below the first magnetic roller, and the magnetic field generating means within this roller is rotatable. magnetic brush developing device.