JP2005091914A - Developing device and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a trickle system developing device capable of accurately detecting toner concentration and to provide an image forming apparatus using the developing device. <P>SOLUTION: The developing device is constituted so that a developer circulation path on which two component developer G is circulated and conveyed is formed by dividing a plurality of developer conveyance paths 4 in which a plurality of stirring conveyance members 3 are stored, respectively by a partition member 5 and establishing a connection port 6 near both ends of the partition member 5, a surplus developer discharge path 8 capable of discharging surplus developer is connected at an end part on the downstream side in the developer conveyance direction distant from a developer replenish port 7 among the developer conveyance paths 4 which do not face a developer carrier 2 and a concentration sensor 9 capable of detecting the toner concentration is arranged at a part near the surplus developer discharge path 8 and which does not face the connection port 6 near the surplus developer discharge path 8 among the developer conveyance paths 4 to be connected with the surplus developer discharge path 8. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an image forming apparatus such as a copying machine or a printer, and in particular, a two-component developing type developing device using a two-component developer composed of a carrier and toner and an image forming apparatus using the same. Regarding improvements.

Conventionally, various proposals have been made for developing devices used in image forming apparatuses such as copying machines and printers, depending on the type of developer to be used. Among them, a two-component developer that easily secures the toner charge amount is used. The two-component development method is widely adopted.
As a developing device of this type of two-component development system, for example, a developing housing having a developing opening opened to face a latent image carrier and a toner mainly composed of a magnetic carrier and a resin is used. A component developer (hereinafter simply referred to as a developer) is accommodated, and a developer carrier (for example, a developing roll) is disposed at a position facing the developing opening of the developing housing, and development is performed on the back side of the developing roll. In general, an auger for conveying the developer inside the housing to the developing roll while stirring and conveying is provided.

In such a developing device, the toner is consumed by the developing operation, while the carrier is not consumed and remains in the developing device. Accordingly, the carrier that is stirred together with the toner in the developing device deteriorates due to peeling of the resin coating layer on the surface and adhesion of the toner to the surface as the stirring frequency increases. As a result, the charging performance of the developer is reduced. It will gradually decline.
Therefore, a so-called trickle-type developing device is known in which a developer containing a carrier is replenished in the developing housing and a surplus developer is discharged to suppress a decrease in charging performance. ing.

By the way, at the time of image formation, if the toner concentration in the developer fluctuates, the image quality is affected.
For example, with the developer that has consumed the toner by the developing operation, only the image with the lowered image density can be obtained because the toner density is lowered. Conversely, when the toner density is increased, the charge amount of the toner is reduced. Image fogging due to the reduction occurs.
For this reason, it is necessary to accurately detect the toner concentration in the developer, and a concentration sensor is attached to the developing device to accurately detect the toner concentration in the developer.
For example, Patent Document 1 proposes an optimum position of the density sensor in the developer circulation conveyance path having two upper and lower conveyance means.
Here, in order to circulate the developer, it is shown that the developer is installed at the bottom of the portion to be lifted from the first conveying means to the second conveying means.

JP-A-11-272062 (column of embodiment of the invention, FIG. 3)

However, in the above-described technique, it cannot be said that a stable toner concentration is detected because the developer in the developing housing is in a place where a considerable amount of the developer stays.
In general, a magnetic permeability type density sensor is used as a density sensor for a two-component developer.
Therefore, in order to use this magnetic permeability type concentration sensor, first, from the viewpoint of performing stable measurement, it is necessary to arrange the developer in a place where the developer flows stably and the pressure fluctuation of the developer is small. Furthermore, from the viewpoint of accurately measuring the toner concentration, it is necessary to dispose the toner at a location far from the toner consumption site and sufficiently mixed and agitated even when there is a developer replenishment or the like and the concentration reaches a uniform level.
If a density sensor is installed at the location where the developer stays, the carrier density at this location will not change, and even if new developer is replenished, the mixing and stirring effect cannot be confirmed, and the accurate toner concentration Cannot be detected.
Therefore, it is not suitable as a position for detecting an accurate toner density.
The present invention is to solve the above-described technical problem, and among the developing methods using a two-component developer, the toner concentration can be accurately detected particularly in an embodiment using the trickle method. The present invention provides a developing device and an image forming apparatus using the same.

That is, the present invention includes, as shown in FIGS. 1A and 1B, a developing housing 1 that contains a two-component developer G composed of toner and a carrier and has a developing opening in a part thereof, and this developing. A developer carrier 2 disposed facing the development opening of the housing 1 and carrying the two-component developer G, and a shaft of the developer carrier 2 on the back side of the developer carrier 2 of the development housing 1 And a stirring and conveying member 3 that stirs and conveys the developer G, and a plurality of developer conveying paths 4 in which the plurality of agitating and conveying members 3 are respectively accommodated in the developing housing 1 by partition members 5. A developing device that divides and opens a communication port 6 in the vicinity of both ends of the partition member 5 to form a developer circulation path through which the developer G is circulated and conveyed. Any facing the developer circulation path A developer replenishing port 7 through which a new developer can be replenished is provided in a part of the developer conveying path 4 that does not face the developer carrying member 2, and is downstream of the developer conveying direction away from the developer replenishing port 7. The end is connected to an excess developer discharge path 8 through which excess developer can be discharged, and the developer transport path 4 communicating with the excess developer discharge path 8 is close to the excess developer discharge path 8 and A density sensor 9 capable of detecting the toner density is provided in a portion not facing the communication port 6 in the vicinity of the excess developer discharge path 8.
FIG. 1B is a cross-sectional view taken along line bb in FIG.

In such technical means, the developer carrier 2 may be any one that can carry the two-component developer G. For example, a mode in which a magnetic field generating means is provided inside a nonmagnetic sleeve is usually used. The
Moreover, the stirring conveyance member 3 should just be what can carry out stirring conveyance of the two-component developer G, for example, an auger etc. are used.
Furthermore, in the present invention, a plurality of developer transport paths 4 may be provided. However, an embodiment in which two developer transport paths 4 are disposed from the viewpoint of apparatus cost and downsizing is preferable.
Further, the partition member 5 may be used as a part of the developing housing 1.
The developer circulation path may be either the horizontal direction or the vertical direction as long as the developer G in the development housing 1 is circulated.
Furthermore, the developer replenishing port 7 has a length that allows the new developer G introduced from the developer replenishing port 7 to be sufficiently mixed and stirred with the existing developer G before reaching the site of the density sensor 9. If possible, it may be disposed at an upstream position in the developer conveyance path 4 where the density sensor 9 is installed. The developer replenishing port 7 may be configured to replenish new developer composed of toner and carrier from one place, or may be configured to replenish toner and carrier separately.

The surplus developer discharge path 8 may be, for example, a mode in which a hole is provided in the wall of the developing housing 1 and the surplus developer is allowed to flow out, and a space for storing the surplus developer that has flowed out is provided. The cover may be covered with an elastic member such as a spring so that the cover is opened if the conveying pressure of the developer G increases. Further, a path for positively discharging the developer G that has flowed out of the apparatus may be provided.
Further, it is more preferable that the density sensor 9 in the present invention is installed on the side surface side of the developer conveyance path 4 from the viewpoint of being hardly affected by the developer G conveyance failure such as stagnation. The installation location of the density sensor 9 is a position where the density sensor 9 is sufficiently covered by the developer G flowing in the developer transport path 4.
In particular, it is more preferable that the density sensor 9 is provided in the vicinity of the excess developer discharge path 8 in a range not facing the communication port 6.
Furthermore, it is preferable to provide the surplus developer discharge path 8 on the axial extension of the agitating and conveying member 3 so that the surplus developer flows smoothly and the detection by the density sensor 9 becomes more stable.
In order to positively discharge the surplus developer, it is preferable to include a transport member that transports the surplus developer to the surplus developer discharge path 8. Further, the transport member is integrated with the agitation transport member 3. It is more preferable to configure.
Note that the present invention is not limited to the above-described developing device, but also targets an image forming apparatus using these developing devices.

According to the present invention, the density sensor for detecting the toner density in the developer is provided with the excess developer discharge path at the downstream end portion of the developer conveyance path not facing the developer carrying member, and is close to the excess developer discharge path. Because it is located in the area that does not face the communication port in the vicinity, the developer pressure and developer density will not be abnormally high, and it will be possible to prevent the influence of developer retention, and more accuracy. A high toner density can be detected, and a stable image developing device can be provided.
Also, by using this developing device, it is possible to provide a high-quality image forming apparatus with stable development characteristics.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
Embodiment 1
2 and 3 show Embodiment 1 of an image forming apparatus including a developing device to which the present invention is applied. FIG. 2 is a side sectional view and FIG. 3 is an AA sectional view of FIG. is there.
In these drawings, the image forming apparatus according to the present embodiment includes a developing device 20 at a position facing a photosensitive drum 10 as a latent image carrier.
The developing device 20 in the present embodiment has a developing housing 21 in which a portion facing the photosensitive drum 10 is opened and a two-component developer is accommodated, and development is performed at a location facing the opening 22 of the developing housing 21. A developing roll 23 serving as a developer carrying member is disposed, and a pair of augers 24 and 25 serving as agitating and conveying members for agitating and conveying the developer are disposed in the developing housing 21 on the back side of the developing roll 23. ing.

Here, the developing roll 23 has a rotatable developing sleeve 23 a in which a magnet body 23 b in which a plurality of magnetic poles are arranged is fixedly included. The developing sleeve 23 a is a member of the photosensitive drum 10. It is driven to rotate while maintaining a predetermined distance from the peripheral surface.
Further, for example, a bias power source (not shown) for applying a developing bias composed of a DC bias on which an alternating current is superimposed is connected to the developing sleeve 23a.
Further, a trimmer 26 as a layer thickness regulating member is disposed at a position separated from the developing roll 23 upstream of the developing site of the developing roll 23 so as to regulate the amount of developer on the developing roll 23. ing.

Further, in the developing housing 21 in the present embodiment, a pair of developer conveying paths 28 and 29 in which the respective augers 24 and 25 are accommodated by the partition wall 27 are formed. Further, by providing communication ports 30 (specifically, 30a and 30b) in the vicinity of both ends of the partition wall 27, a developer circulation path 31 (see FIG. 5) through which the developer is circulated and conveyed through the pair of developer conveyance paths 28 and 29. 3 is indicated by a virtual line with an arrow).
Further, in the vicinity of one end of the developer transport path 28 which is a part of the developer circulation path 31, an opening is provided vertically above the developer housing 21, and this opening is newly provided in the developer housing 21. A developer replenishing port 32 for replenishing an appropriate developer or the like (in some cases, toner or carrier alone).
In particular, in the present embodiment, a discharge unit 33 is disposed at the downstream end of the developer transport path 29, and the excess developer in the developing housing 21 is discharged. In addition, an external discharge port 34 for discharging the developer in the discharge unit 33 to the outside is provided at a lower portion of the discharge housing 33a of the discharge unit 33.

The auger 24 disposed in the developer conveying path 28 in the present embodiment has a rotating shaft 24a and a blade 24b that is helically attached to the outer periphery of the rotating shaft 24a. It is designed to be transported.
In the vicinity of the developer supply port 32, a spiral blade 24 c opposite to the blade 24 b is formed on the rotating shaft 24 a of the auger 24, and new developer is supplied from the developer supply port 32. In this case, the flow of the developer is restricted in one direction so that the developer is directed toward the developer conveyance path 29 via the communication port 30a.

On the other hand, the auger 25 disposed in the developer transport path 29 also has a rotating shaft 25a and blades 25b attached to the outer periphery of the rotating shaft 25a so as to transport the developer upward in FIG. It has become.
Further, in the vicinity of the communication port 30b of the auger 25, a spiral blade 25c having a pitch smaller than that of the blade 25b and opposite to the blade 25b is formed so as to suppress the flow of the developer.
Further, in the present embodiment, the rotation shaft 25a of the auger 25 extends to the discharge unit 33. In the discharge unit 33, the rotation shaft 25a of the auger 25 has a narrow diameter and pitch in the same direction as the blades 25b. A spiral blade 25 d is formed, and a part of the blade 25 d extends to the developer transport path 29 through the discharge port 35 through which the developer is discharged from the developing housing 21 to the discharge unit 33. Therefore, the rotation of the auger 25 is smoothly performed without the developer reaching the shaft support portion of the rotation shaft 25a of the auger 25.

  Further, in the present embodiment, the magnetic permeability for detecting the toner concentration of the developer in the vicinity of the communication port 30b of the developer conveyance path 29 and on the upstream side in the developer conveyance direction at a portion not facing the communication port 30b. A mold sensor 36 is provided. And this sensor 36 is installed not in the bottom part of the developer conveyance path 29 but in the side surface side (part covered by the developer to the extent that this sensor 36 does not interfere with sensing).

Next, the operation of the image forming apparatus according to the present embodiment will be described focusing on the developing device 20.
When the two-component developer stirred and conveyed by the pair of augers 24 and 25 is conveyed to the developing roll 23 side, a developer layer made of the two-component developer is formed on the developing sleeve 23a by the magnetic force of the magnet body 23b. .
When this developer layer passes through the trimmer 26 as the developing sleeve 23a rotates,
The developer layer on the developing sleeve 23 a is regulated to a predetermined thickness, and is conveyed to the opening 22 facing the photosensitive drum 10 with a predetermined conveyance amount.
At this time, a predetermined developing bias is applied to the developing sleeve 23a from a bias power source (not shown), so that the developer layer on the developing sleeve 23a is in the developing region closest to the photosensitive drum 10 in the photosensitive drum. The electrostatic latent image on 10 is developed to make a visible image.
Thereafter, the developer that has passed through the opening 22 and completed development is carried and conveyed on the developing sleeve 23a, peeled off from the developing roll 23 by the repulsive magnetic field formed by the magnetic poles of the magnet body 23b, and again in the developing housing 21. Then, it is agitated and transported by the pair of augers 24 and 25 and waits for the next development.

During the execution of this series of development processes, the developer in the development housing 21 is also replenished. This will be specifically described as follows.
When a new developer is supplied from the developer supply port 32, the developer is guided to the developer transport path 29 side through the communication port 30 a by the blade 24 c at the end of the auger 24. Therefore, when the developer reaches the blade 25c while being mixed and stirred with the existing developer in the developer transport path 29 by the blade 25b of the auger 25, the rotation of the blade 25c prevents the developer from proceeding. .
Here, as shown in FIG. 4A, for example, when the developer in the developer transport path 29 (see FIG. 3) is an appropriate amount, the transport force by the blades 25b and the deterrent force by the blades 25c are the developer. In addition, the developer is guided to the developer conveyance path 28 (see FIG. 3) through the communication port 30b.
On the other hand, as shown in FIG. 4B, when the developer in the developer transport path 29 is large (excess amount), the deterring force at the blades 25c (specifically, the developer toward the developer transport path 28 side). The force for moving the toner is insufficient, and most of the developer is guided to the developer conveyance path 28 side, but a part of the developer gets over the blade 25c. The developer that has passed over the blades 25c is guided to the discharge unit 33 through the discharge port 35 by the blades 25d. Then, the toner is discharged from the external discharge port 34 in the discharge unit 33 to the outside of the developing device.
FIG. 4C shows a cross-sectional view taken along the line BB in FIG.
In this embodiment, since such a configuration is adopted, an appropriate amount of developer in the developing housing 21 can be secured.

Further, in such a developer agitation and conveyance process, the sensor 36 is moved in the developer conveyance direction, particularly in the vicinity of the communication port 30b of the developer conveyance path 29, which is a feature of the present invention, and at a portion not facing the communication port 30b. The reason for the arrangement on the upstream side is as follows.
First, on the developer conveyance path 28 side, by supplying the developer to the developing roll 23, the toner concentration by the developing roll 23 cannot be detected due to toner consumption.
Further, when a new developer (having a different toner concentration from the existing developer in the developer housing 21) is added from the developer supply port 32, the developer is sufficiently mixed and stirred while reaching the sensor 36. Therefore, the position of the sensor 36 needs to be separated from the developer supply port 32.
Further, the place where the developer is likely to stay in the developer transport path 29 is in the vicinity of both ends of the developer circulation path 31, and in particular, the developer is transferred from the developer transport path 29 to the developer transport path 28. It is necessary to pay attention to staying in the vicinity of the communication port 30b (near the blade 25c of the auger 25).
Furthermore, at the bottom of the developer transport path 29, the developer housing 21 and the blade 25b of the rotating auger 25 have an appropriate gap, so that the developer tends to stay here.

For the reasons described above, the sensor 36 is disposed on the side of the developer conveyance path 29 at a position not facing the communication port 30b on the downstream side of the developer conveyance path 29 and at a position upstream of the communication port 30b. Thus, it becomes possible to detect the toner density of the developer more accurately.
That is, by arranging the sensor 36 as described above, even if the amount of developer increases, excess developer in the vicinity of the sensor 36 is discharged out of the developing device 20, and the developer does not stay at this position. For this reason, the developer pressure and developer density do not become abnormally high, and there is no need to consider the influence of retention. Therefore, it is possible to accurately detect the toner density.

Further, the inventors investigated the distance (D) between the optimum sensor 36 and the discharge port 35 by using the distance (L) of the developer conveyance path 29 and the pitch (p) of the blades 25b of the auger 25 as parameters. .
As a result, the distance (D) between the sensor 36 and the discharge port 35 is 1/10 or less of the distance (L) of the developer conveying path 29, and the pitch (p) of the blade 25b of the auger 25 is 2. By configuring it to be 5 times or less, the mixing and stirring of the developer is sufficient, the developer is not retained, the developer pressure and the developer density are not increased abnormally, and the accurate toner concentration Has been recognized as a position that can be detected.

Embodiment 2
5 and 6 show a second embodiment of the developing device to which the present invention is applied. FIG. 5 is a side sectional view, and FIG. 6 is a sectional view taken along the line CC in FIG.
The basic configuration of the developing device 20 according to the present embodiment is substantially the same as that of the first embodiment, except that the two developer transport paths 28 and 29 are arranged in the vertical direction. Different.
Components similar to those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and detailed description thereof is omitted here.

In these drawings, the developer conveyance paths 28 and 29 in the present embodiment are arranged in two stages in the vertical direction, but the shapes of the augers 24 and 25 arranged in the respective conveyance paths are the same as those in the first embodiment. Since the developer transport state is substantially the same as that of the first embodiment, the description thereof is omitted here.
In this embodiment, the blade 25c of the auger 25 is devised so that the developer discharge to the discharge unit 33 does not become excessive.
Therefore, also in the present embodiment, since the position of the sensor 36 is set in the vicinity of the upstream side of the communication port 30b, the developer pressure and the developer density are not increased abnormally, and the toner density can be accurately detected. Is possible.

(A) is explanatory drawing which shows the outline | summary of the image development apparatus concerning this invention, (b) is bb sectional drawing of (a). 1 is a cross-sectional view illustrating an image forming apparatus according to a first embodiment to which the present invention is applied. It is AA sectional drawing of FIG. (A) and (b) are explanatory drawings which show the outline | summary of the discharge principle of the excess developer of Embodiment 1, (c) is BB sectional drawing of (b). It is sectional drawing which shows the developing device which concerns on Embodiment 2 to which this invention was applied. It is CC sectional drawing of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Development housing, 2 ... Developer carrier, 3 ... Agitation conveyance member, 4 ... Developer conveyance path, 5 ... Partition member, 6 ... Communication port, 7 ... Developer supply port, 8 ... Excess developer discharge path, 9 ... density sensor, G ... two-component developer

Claims (6)

A developing housing containing a two-component developer comprising a toner and a carrier and having a developing opening in a part thereof;
A developer carrying member disposed facing the developing opening of the developing housing and carrying a two-component developer;
A stirring and conveying member that extends in the axial direction of the developer carrying member on the back side of the developer carrying member of the developing housing and stirs and conveys the developer;
In the developing housing, a plurality of developer conveying paths each accommodating a plurality of agitating and conveying members are partitioned by a partition member, and the developer circulates by opening communication ports in the vicinity of both ends of the partition member. A developing device configured to form a developer circulation path to be conveyed;
While a part of the developing housing facing the developer circulation path is provided with a developer replenishing port capable of replenishing a new developer,
In the developer transport path that does not face the developer carrying member, a surplus developer discharge path capable of discharging surplus developer is connected to the downstream end portion in the developer transport direction away from the developer replenishing port, and is connected.
A density sensor capable of detecting the toner density is disposed in a portion of the developer transport path communicating with the excess developer discharge path that is close to the excess developer discharge path and does not face the communication port near the excess developer discharge path. A developing device characterized by being provided. The developing device according to claim 1,
The developing device, wherein the surplus developer discharge path is on an axial extension of the agitating and conveying member. The developing device according to claim 1,
The developing device, wherein the density sensor is disposed in the vicinity of the excess developer discharge path in a range not facing the communication port. The developing device according to claim 1,
A developing device, wherein a transport member for transporting surplus developer is disposed in the surplus developer discharge path. The developing device according to claim 4.
A developing device, wherein the agitating and conveying member and the conveying member of the excess developer discharge path are integrally formed.   An image forming apparatus comprising the developing device according to claim 1.

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