JPH0934264A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely and uniformly mix replenished toner and developer lying in a developing device in a short time by extending a magnet on the rear side of the lower wall of a lower casing part for a stirring screw and also providing a magnetic material on the shaft of the stirring screw. SOLUTION: The magnet 22 is extended in the axial direction of the stirring screw 16 constituted of a screw shaft 12 and a screw blade 14 so as to come into contact with the rear side of the lower wall 4 of the lower casing part which is within the extent of a toner replenishing part on the upstream side in a carrying direction. An iron core 23 is buried within an extent corresponding to the extensive installation area of the magnet 22 in the screw shaft 12 of the stirring screw 16. A large number of chains 25 of developer including magnetic carrier is formed by a magnetic force between the iron core 23 and the magnet 22. The developer 30 carried by the stirring screw 16 and the replenished toner 31 are carried while pushing the curtain of the chains 25 a side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device of an image forming apparatus using a two-component developer composed of toner and magnetic carrier.

[0002]

2. Description of the Related Art As a developer for an image forming apparatus utilizing an electrostatic recording process such as an electrostatic copying machine, an electrostatic printer or a facsimile, a two-component developer composed of a toner and a magnetic carrier is widely used. .

In a developing device using a two-component developer, the toner in the developer is consumed as the number of developed sheets is increased, the toner density is gradually lowered, and the image density is lowered accordingly, and the developed image is developed. Quality is reduced. Therefore, the toner concentration of the developer in the developing device is constantly detected by known means such as optical and magnetic means, and when the toner concentration drops to a predetermined value, replenishment toner is placed in the developing device. The toner is appropriately supplied and agitated and mixed with the developer in the developing device to maintain a predetermined toner concentration.

A device for stirring and mixing the replenishment toner and the developer to obtain a uniform toner concentration is, for example, in the developer accommodating portion of the developing device as disclosed in Japanese Utility Model Laid-Open No. 1-67651. In parallel with the developing roller, a pair of parallel passages, which are partitioned by partition walls having openings at both ends and communicate with each other at both ends, are provided with stirring screws arranged so as to oppose each other in the conveying direction. It has a developer circulating path formed by the developer conveying path formed and provided, one developer conveying path is provided opposite to the developing roller, supplies the developer to the developing roller, and develops the developed toner. There is known a structure in which the developer is received from the developing roller, and a toner replenishing portion is provided at the upstream end of the other developer conveying path in the conveying direction to replenish the developer with the toner.

In the developing device having such a structure, the toner is replenished from above by the toner replenishing portion to the developer circulated and conveyed by the conveying screw, and the replenished toner and the developer are agitated by the agitating screw. It is conveyed while being mixed, and is supplied to the developing roller as described above in the conveying path on the developing roller side.

However, in the apparatus of this construction, it takes a certain amount of time from when the toner is supplied to when the toner is uniformly mixed in the circulating developer. It is not always easy to properly maintain the toner density in a region, and deterioration of image quality is inevitable.

As a means for solving this inconvenience, in the developing device disclosed in Japanese Utility Model Laid-Open No. 1-67651, the conveying speed of the developer is from the toner replenishment position to the position where the developer is supplied to the developing roller. The pitch or diameter of the screw blades of the transport screw is partially changed so as to be delayed near the toner replenishment position and the final position where the developer is supplied to the developing roller.

By doing so, the toner supplied to the developer at the toner replenishment position is in a state of being slightly retained, and is rapidly and sufficiently mixed with the existing developer, and thereafter at a higher speed. When the toner is conveyed and reaches the portion facing the developing roller, the conveying speed becomes slower, and the developer is supplied to the developing roller in this portion in a state where the toner concentration in the developer is uniform. It is said that unevenness can be avoided.

However, since the toner has a smaller specific gravity than that of a developer mainly composed of a carrier, even if the toner and the developer replenished from above the conveyed developer are agitated by an agitating screw, FIG. As shown schematically in FIG. 3, the toner 31 floats on the developer 30, and the carrier tends to settle, which is difficult to mix, and the toner is conveyed while floating on the surface of the developer being stirred and circulated. It is difficult to obtain a uniform mixed state, and charging becomes slow. Also, the rotating screw 1
Even if the replenished toner 31 is mixed into the developer 30 by the method 6, the toner lumps 32 are not easily subdivided into fine particles and are in a uniform mixed state only by being stirred and conveyed by the screw 16. Hateful. In particular, when the image forming speed is increased, the consumption of toner progresses rapidly, and the stirring and supply of the replenishment toner cannot keep up. For this reason, when the rotation speed of the stirring screw is increased, the above phenomenon occurs remarkably,
Inadequate toner mixing.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-mentioned problems of the conventionally proposed and proposed apparatus, and the developer is agitated by a stirring screw through a toner replenishing section and a developer supplying section to a developing roller. In a developing device using a two-component developer of an image forming apparatus having a developer circulation path for agitating, conveying, and circulating the toner, the toner replenished by the toner replenishing unit and the developer in the developing device can be reliably and quickly provided. It is an object of the present invention to provide a developing device capable of uniformly mixing with each other.

[0011]

In order to solve the above problems, the present invention is directed to a developing device having the above-mentioned structure, wherein the toner in the path of the developer circulating path from the toner replenishing section to the developer supplying section is used. A magnet is extended over the lower surface of the casing lower wall of the lower portion of the stirring screw over a certain range of the replenishment section, and a magnetic body is provided on the shaft of the stirring screw of at least approximately the extension range. Alternatively, the shaft is made of a magnetic material.

Further, the pitch of the screw blades of the stirring screw between the toner replenishing portion and the developer supplying portion of the developer circulating path is alternately changed to a large or small value.

[0013]

Due to the main characteristics described above, a large number of developer chains containing magnetic carriers are generated between the magnetic body and the magnet of the shaft of the stirring screw due to the magnetic force to form a chain curtain. Therefore, the developer and the replenishment toner conveyed by the stirring screw are conveyed by scraping the curtain of the chain, so that friction and collision occur between the chain and the developer and the replenishment toner, so that the mixing and the stirring are efficiently performed. As a result, the toner mass is subdivided into fine particles. In addition, innumerable fine waviness occurs on the developer surface on the magnetic part of the screw shaft, and the toner supplied on it is finely dispersed, and in combination with the above action, the developer and the efficiency are improved. It mixes well and improves the charging efficiency of the toner.

Further, by changing the pitch of the screw blades so as to be alternately large and small, the conveyance of the developer is slowed down, and the newly supplied toner and the developer are mixed more quickly and quickly. It can be carried out.

[0015]

Embodiments of the present invention will now be described with reference to the drawings.
This will be described in detail.

1 and 2 are a sectional view and a plan view of a developing device using a two-component developer according to an embodiment of the present invention, respectively. The developing device 1 has a developing roller 3 which is in contact with the photosensitive drum 2 at a predetermined gap and rotates, and a developer accommodating portion 5 which is formed by being surrounded by a lower wall 4 of the device casing. Note that the upper wall is omitted in the figure in order to avoid stagnation.
In the developer accommodating portion 5, the developing roller 3 is provided on the upper surface of the lower wall 4.
A partition wall 6 is provided upright over the entire width in parallel with the axis of the. As shown in FIG. 2, openings 7 and 8 are formed at both ends of the partition wall 6 to connect the spaces on both sides. Openings 7, 8
Is appropriately determined according to the amount of the developer stored therein. In the embodiment, the opening 8 is larger than the opening 7.

Partitioned by a partition wall 6 to store the developer 5
Inside the pair of adjacent parallel passages 9 and 10 formed inside, the screw shaft 1 is parallel to the axis of the developing roller 3, respectively.
1st stirring screw 15 and 2nd stirring screw 16 which consist of 1 and 12 and screw blades 13 and 14 are provided, respectively.

The first and second stirring screws 15 and 16 are
During development, a gear train (not shown) is driven to rotate so that the conveying directions are opposite to each other, and as a result, the first conveying passage 17 formed by the passage 9 and the first stirring screw 15, the passage 8 and the first conveying passage 17 are formed. A second circulation path 18 formed by the two-stirring screw 16 and the openings 7 and 8 form a developer circulation path indicated by an arrow in FIG.

A toner replenishing section 20 is provided at the upstream end of the second conveying path 18 in the conveying direction, and a toner cartridge 21 for replenishment (FIG. 1) 21 is supplied in accordance with the result of the toner concentration detection of the developer by the sensor 19. A predetermined amount of toner 31 is dropped and replenished on the circulating developer.

The replenished toner is agitated with the developer by the second agitating screw 16 and is conveyed in the direction of the arrow, and then enters the first conveying path 18 serving as a developer supplying portion through the opening 8 to reach the first conveying path 18. While being agitated and conveyed along the developing roller 3 by the agitating screw 15, the developer that has been developed is received and conveyed in the direction of the arrow, and is conveyed from the opening 7 to the second conveying path 10 for circulation. To do.

According to the present embodiment, further, according to the present invention, the lower wall 4 of the casing of the lower part of the second stirring screw 16 in a certain range of the toner replenishing part 20 on the upstream side in the conveying direction.
The magnet 22 contacts the lower surface of the stirring screw 16
Extending in the axial direction of the second stirring screw 1
The iron core 23, which is a magnetic body, is embedded in the resin screw shaft 12 of No. 6 over a range substantially corresponding to the extending range of the magnet 22. The screw blades 13, 1
4 is made of resin. In addition, the shaft 1 of the first stirring screw 15
Both the shafts 12 of the first and second stirring screws 16 may be magnetic bodies.

Since this developing device is constructed as described above, the iron core 23 in the screw shaft 12 of the stirring screw and the magnet 22 attached to the lower surface of the lower wall 4 are schematically shown in FIG. A large number of developer chains 25 containing a magnetic carrier are formed between the magnetic field and the magnetic field, and a chain curtain is formed by these groups.

The developer 30 and the replenishment toner 31 carried by the stirring screw 16 are carried while scraping the curtain of the chain 25. As a result, friction and collision occur between the toner 31 and the developer 30 and the chain 25, the lumps of the toner 31 are subdivided, efficient stirring and mixing are performed, and the magnetic force of the magnet 22 conveys the toner. As shown in FIG. 3, an infinite number of minute ripples 26 are generated on the upper surface of the developer to be mixed, and the toner 31 dropped and supplied from above is finely dispersed and mixed with the developer, thereby efficiently mixing. As a result, a uniform toner distribution is obtained and the toner is conveyed to a portion facing the developing roller 3 and is supplied to the developing roller, so that good image quality is obtained.

In this embodiment, as shown in FIG. 2, the pitch of the screw blades 14 of the second stirring screw 16 is changed so as to be alternately large and small. As a result, the newly replenished toner and the circulating developer can be mixed more quickly and quickly.

The above-mentioned magnet 22 and screw shaft 12
According to the experimental results, it is preferable that the magnetic force of each of the upper part and the side part (portions shown by A and B in FIG. 3) of the above is within the following range. Magnetic force of magnet: 1000-2000 gauss Magnetic force of screw shaft upper part (point A): 100-180 gauss Magnetic force of screw shaft side part (point B): 400-1000 gauss

[0026]

As described above, according to the present invention,
The magnetic field generated between the magnet and the magnetic part of the screw shaft forms a curtain of chains by the magnetic carrier in the developer, and the developer and toner carried by the stirring screw are the curtain of chains by the magnetic carrier. While being scraped and conveyed, friction and collision occur with the chain, and they are mixed uniformly in a short time.
In particular, the pitch of the screw blades is alternately changed to be large or small to cause a gradual flow of the developer and further improve the stirring efficiency between the toner and the carrier to improve the charging efficiency of the toner.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a developing roller of a developing device according to an exemplary embodiment of the present invention, taken along a direction perpendicular to an axis of a developing roller.

FIG. 2 is a plan view of the developing device of the above embodiment.

FIG. 3 is a schematic diagram illustrating the operation of the present invention.

FIG. 4 is a schematic diagram illustrating a problem of a conventional developing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Developing device 3 Developing roller 4 Lower wall 6 Partition 7, 8 Opening 15 1st stirring screw 16 2nd stirring screw 17 1st conveyance path (developer supply part) 18 2nd conveyance path 20 Toner supply part 22 Magnet 23 Iron core (Magnetic material part) 25 Magnetic carrier chain 26 Rippling 30 Developer 31 Toner

Claims (2)

[Claims] 1. A toner replenishment section for replenishing the developer with a two-component developer comprising toner and a magnetic carrier to maintain the toner density of the developer, and a developer for supplying the developer to a developing roller. In a developing device of an image forming apparatus having a developer circulation path for agitating and transporting a developer by a stirring screw via a supply section and circulating the developer, a path from the toner supply section to the developer supply section of the developer circulation path. The magnet is extended over the lower surface of the casing lower wall of the lower portion of the stirring screw over a certain range of the toner replenishing section, and at least approximately the shaft of the stirring screw in the extended range is extended. Provide a magnetic body,
Alternatively, the developing device is characterized in that the shaft is made of a magnetic material. 2. The pitch of the screw blades of the stirring screw between the toner replenishment section and the developer supply section of the developer circulation path is alternately changed to a large or small value. The developing device described.