JPH117195A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device capable of preventing the unevenness or the fogging by securing a space for agitating a developer and by feeding the developer being satisfactorily agitated to a developing roll. SOLUTION: In this device 1, an agitating screw 12 is provided with the exception of a feeding screw 14 and a recovering screw 16 and the agitating screw 12 is made take charge of agitating a developer being separated from feeding/recovering the developer to/from a developing roll 18, its transporting direction is made opposite to that of other screws and its transporting capacity is made larger than the other screws. Moreover, a toner feeding port 22 is provided on the downstream end of the feeding screw 14. Thus, the developer transported to the downstream of the feeding screw 14 and the recovering screw 16 and a developer newly replenished are definitely passed through the agitating screw 12 without causing stagnation before being fed to the feeding screw 14 again and are satisfactorily agitated there. Thus, the developer provided with the uneven toner density or charge state is prevented from flowing in the feeding screw 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a developing device used in an electrophotographic image forming apparatus such as a copying machine or a printer. More specifically, the present invention relates to a developing device in which the supply and recovery of a developer to a developing roll and the stirring are separated in function, so that a sufficiently stirred developer can be supplied to the developing roll.

[0002]

2. Description of the Related Art An example of a conventional developing device is disclosed in
No. 3,336,91. In this developing device, as shown in FIG. 7, two augers (screw) 82, 85 are arranged in parallel so that their conveying directions are opposite to each other. Thus, while circulating the developer as indicated by arrows c and d, the developer is supplied to a developer carrier (development roll) 87 provided adjacent to the auger 82, and the electrostatic latent image on the photoreceptor is passed therethrough. The image is developed. In this developing device, the auger 82 is responsible for supplying the developer to the developer carrier 87, and the auger 85 is responsible for collecting the developer from the developer carrier 87.

[0003]

However, the conventional developing device described above has a problem that the space for stirring the developer is insufficient. For this reason, there is a possibility that the developer having a low toner concentration collected from the developer carrier 87 into the auger 85 may be supplied from the auger 82 to the developer carrier 87 again without being sufficiently mixed. Further, when the toner is replenished, the replenished toner may be uniformly dispersed in the developer and supplied from the auger 82 to the developer carrier 87 before being sufficiently charged. For these reasons, unevenness in image density or fogging may occur due to non-uniformity of toner concentration or insufficient charging in the developer. In particular, such a phenomenon is likely to occur when continuously developing a large area image that consumes a large amount of toner. For this reason, there is a problem particularly when the apparatus is used in a color image forming apparatus which often handles a document including a large area image.

[0004] The present invention has been made to solve the above-mentioned problems of the conventional developing device. That is, the object of the present invention is to provide a developing device which secures a space for stirring the developer, supplies the sufficiently stirred developer to the developing roll, and prevents deterioration of image quality due to unevenness and fog. Is to provide.

[0005]

Means for Solving the Problems According to the first aspect of the present invention, there is provided a developing roll, a supply screw for supplying a developer to the developing roll while conveying the developer in an axial direction, and A developing device having a recovery screw for recovering the developer from the developing roll and transporting the developer in the axial direction, wherein the supply screw and the recovery screw have the same direction of transport of the developer, and have the opposite direction. It is characterized by having a stirring screw for transporting the developer.

In this developing device, the developer is supplied to the developing roll while being conveyed in the axial direction by a supply screw. Then, the developer remaining on the developing roll after the development is recovered by the recovery screw and transported in the same direction as the transport direction by the supply screw. The developer that has reached the downstream end of the collection screw is transported in the opposite direction by the stirring screw, and is circulated to the upstream end of the supply screw. In the course of conveyance by the stirring screw, the entire developer is sufficiently stirred. Therefore, only the developer having a uniform density and a good charge state is supplied to the supply screw and further supplied from the supply screw to the developing roll. For this reason, the development by the developing roll can be performed favorably without density unevenness and fog.

According to a second aspect of the present invention, in the developing device according to the first aspect, the conveying capacity of the stirring screw is larger than the conveying capacity of the supply screw and the conveying capacity of the recovery screw. Identified as a feature.

In this developing device, the developer reaching the downstream ends of the supply screw and the recovery screw is transported in the opposite direction by the stirring screw having a large transport capacity, so that the developer circulates without stagnation and is supplied. There is no shortage of the developer with the screw, and the development with the developing roll is performed well. In addition, the large conveying capacity of the stirring screw means that the stirring of the developer in the stirring screw is performed better. Note that the transfer capacity of each screw is determined by the effective diameter, pitch, and number of threads of the screw blades, so that at least one of these may be adjusted as described above.

According to a third aspect of the present invention, in the developing device according to the first or second aspect, the supply screw is disposed above the recovery screw, and the stirring screw is further disposed above the supply screw. It is specified as a feature of being arranged.

In this developing device, since the recovery screw, the supply screw and the stirring screw are arranged vertically, the width in the horizontal direction is small and compact. Therefore, it is suitable for a color image forming apparatus having a large number of developing devices.

According to a fourth aspect of the present invention, there is provided the developing device according to any one of the first to third aspects, wherein a region facing the developing roll in a stirring direction of the stirring screw is arranged. This is characterized in that a developer supply port is provided at an upstream position.

In this developing device, when a new developer is supplied to the developer supply port, the supplied developer is conveyed in the reverse direction by the stirring screw and then supplied to the supply screw. In the course of conveyance by the stirring screw, the new developer and the entire developer are sufficiently stirred, mixed, and charged. Therefore, only the developer having a uniform density and a good charge state is supplied to the supply screw and further supplied from the supply screw to the developing roll. For this reason,
The development by the developing roll is performed favorably without density unevenness and fog.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. As shown in FIG. 1, the developing device 1 according to the present embodiment includes a developer accommodating tank 10 in which a stirring screw 12, a supply screw 14, and a recovery screw 16 are provided in parallel with each other. In each of these, a large number of screw blades are obliquely provided on a rotatable shaft.
These three screws are arranged in the vertical direction as shown in the side sectional view of FIG. 2, and the stirring screw 12 is provided in the upper part, the supply screw 14 is provided in the middle part, and the collecting screw 16 is provided in the lower part. positioned. A part of the supply screw 14 and a part of the recovery screw 16 are provided with reverse winding parts 14a and 16a, respectively, in which the inclination direction of the screw blades is reversed with respect to other parts, and the reverse winding part 14a of the supply screw 14 is recovered. It is longer than the reverse winding portion 16a of the screw 16. The stirring screw 12 is not provided with a reverse winding portion.

Further, in a region other than the reverse winding portion 14a of the supply screw 14 at a height position between the supply screw 14 and the collection screw 16, a developing roll 18 is provided.
A part thereof is provided so as to protrude from the developer storage tank 10. Further, a partition wall 20 is provided between the stirring screw 12 and the supply screw 14. However, the partition wall 20 is provided only in a region corresponding to the developing roll 18, and upper and lower spaces communicate with each other on both left and right sides in FIG. Further, a developer storage tank 1
At 0, a toner supply port 22 is provided immediately above the reverse winding portion 14a of the supply screw 14. When viewed from the area where the developing roll 18 is located,
This is on the upstream side in the transport direction of the stirring screw 12.

The developing device 1 is provided with a stirring screw 1 from a motor (not shown) provided on the image forming apparatus main body side.
2, the supply screw 14 and the recovery screw 16 are rotationally driven. The rotation direction of the supply screw 14 and the direction of rotation of the recovery screw 16 are opposite to each other. By this rotation, portions other than the reverse winding portions 14a and 16a of the supply screw 14 and the recovery screw 16 are turned leftward in FIG. 1 and the reverse winding portions 14a and 16a are turned rightward in FIG.
In the stirring screw 12, the flow of the developer is generated rightward in FIG. By this flow, the developer circulates inside the developing device 1. In the following description, the “transport direction” of the supply screw 14 or the recovery screw 16 refers to the reverse winding portion 14a, 1
It refers to the transport direction in a portion other than 6a.

Further, focusing on the diameters of the stirring screw 12, the supply screw 14, and the recovery screw 16,
Mutually equal to the diameter D ₂ of diameter D ₁ and the recovery screw 16 of the feed screw 14, is larger than the diameter D ₃ of the stirring screw 12 thereof. Therefore, the stirring screw 12 has a greater developer transfer capacity than the two lower screws 14 and 16.

In the image forming apparatus, the developing device 1 is arranged such that the developing roll 18 is positioned in parallel and close to the photosensitive drum 90, and operates as follows.

That is, when the stirring screw 12, the supply screw 14, and the recovery screw 16 are rotated by the driving of the motor provided on the image forming apparatus main body side, each screw is conveyed into the developer storage tank 10. The force causes a flow of the developer. The flow is the partition 2
The portion above 0 is directed rightward in FIG. 1 by the stirring screw 12. This flow causes the stirring screw 12
The developer which has reached the right end in FIG. 1, that is, the downstream end, drops by gravity and moves to the lower supply screw 14 because there is no partition wall 20 there. Then, in the portion below the partition wall 20, the flow of the developer is controlled by the supply screw 14 and the collection screw 16 to the reverse winding portion 14.
1, except for a and 16a. Due to this flow, the developer of the supply screw 14 and the recovery screw 16 which has reached the left end in FIG. 1, that is, the downstream end, overflows upward by the reverse transport of the reverse winding portions 14a and 16a, and from the recovery screw 16 to the supply screw 14 It moves from the supply screw 14 to the stirring screw 12. As described above, the developer inside the developer storage tank 10 is filled with the partition wall 20.
1 is circulated clockwise in FIG.

Here, the developer conveyed leftward in FIG. 1 by the supply screw 14 and the developer conveyed leftward in FIG. 1 by the recovery screw 16 are supplied to the upstream end of the stirring screw 12. Will merge and flow in. However, as mentioned above, stirring screw 1
2 has a larger transfer capacity than the supply screw 14 and the recovery screw 16,
The developer does not stay in this portion due to the insufficient transport capacity. Therefore, the circulation of the developer in the developer storage tank 10 is performed smoothly.

In the circulation of the developer, the stirring screw 12 is in charge of stirring the developer. That is, the toner concentration and charge state of the developer are made uniform.
The supply screw 14 is in charge of supplying the developer to the developing roll 18, and the collecting screw 16 is in charge of collecting the excess developer from the developing roll 18.
Therefore, the developer moved to the stirring screw 12 downstream of the supply screw 14 and the recovery screw 16 is transferred to the stirring screw 12 having a large conveying capacity as shown in FIG.
While being conveyed in the middle right direction, it is agitated without being supplied to the developing roll 18. For this reason, the developer
When moving from the downstream end of the stirring screw 12 to the supply screw 14, the stirring is sufficiently performed, and the toner concentration and the charged state are uniform. Therefore, the development roller 18 performs development without density unevenness due to non-uniform toner density and fog due to insufficient charging.

The developer recovered from the developing roller 18 to the recovery screw 16 has a reduced toner concentration by the amount of toner consumed by the development. Therefore, if the development is continued as it is, the toner concentration of the entire developer gradually decreases. Therefore, it is necessary to supply toner from the toner supply port 22 and replenish the toner appropriately.

The supplied toner is supplied to a supply screw 14.
Is first conveyed rightward in FIG. The developer moving from the collection screw 16 to the supply screw 14 and the supply screw 1
The portion other than the reverse winding portion 14 a of FIG. 4 joins the developer conveyed leftward in FIG. 1 and moves to the stirring screw 12. Immediately after being charged, the toner is not sufficiently mixed with the entire developer, and is insufficiently charged. However, before reaching the supply screw 14 and being supplied to the developing roll 18, it is conveyed rightward in FIG. 1 over substantially the entire length of the stirring screw 12, and is sufficiently stirred during that time. For this reason, when moving from the downstream end of the stirring screw 12 to the supply screw 14, the charged toner is sufficiently mixed with the entire developer to have a uniform toner concentration, and the charged state is good. It has become. Therefore, even when the toner is supplied from the toner supply port 22, the developing roll 18 performs development without density unevenness due to non-uniform toner density and fog due to insufficient charging.

[0023] Ensuring good stirring of the developer is as follows.
Not only is the stirring screw 12 provided separately from the supply screw 14 and the collection screw 16, but also the conveyance direction of the supply screw 14 and the collection screw 16 is the same, and the conveyance direction of the stirring screw 12 is reversed. It is realized by. That is, the three possible circulation paths of the three screws including the stirring screw are schematically illustrated in FIGS. 3, 4, and 5. The circulation path in the developing device 1 is
This is shown in FIG.

In the circulation path shown in FIG. 4, the stirring screw and the recovery screw have the same conveying direction, and the supply screw has the opposite direction. In the circulation path in FIG. 5, the stirring screw and the supply screw are set in the same conveyance direction, and the recovery screw is set in the opposite direction. According to these circulation paths, although the space itself for agitation is provided, the developer can circulate by bypassing the agitating screw, so that the collection screw does not pass through the agitating screw to the supply screw. The developer is supplied. For this reason, the effect of providing the stirring screw does not appear so much. In addition, in the circulation path shown in FIG. 4, the movement of the developer from the collecting screw is hindered by the developer falling from the stirring screw, so that smooth circulation cannot be performed. Further, in the circulation path of FIG. 5, the developer moving from the collecting screw flows into the supply screw exclusively, and hardly flows into the stirring screw.

On the other hand, in the circulation path of the developing device 1 shown in FIG. 3, the developer cannot circulate by bypassing the stirring screw. For this reason, the supply screw 14
Therefore, the developer that does not pass through the stirring screw 12 is not supplied, and the effect of the provision of the stirring screw 12 greatly appears. In addition, since the conveying capacity of the stirring screw 12 is inevitably increased in this circulation path, the stirring in the stirring screw 12 is performed more favorably.

As described above in detail, according to the developing device 1 according to the present embodiment, the supply screw 1 for supplying and collecting the developer to the developing roll 18 is provided.
4, a stirring screw 12 is provided separately from the collecting screw 16 to take charge of stirring of the developer, and the conveying direction of the stirring screw 12 is changed to the supply screw 14 and the collecting screw 1.
6, the developer conveyed to the downstream by the supply screw 14 or the recovery screw 16 always passes through the stirring screw 12 before being supplied again to the upstream of the supply screw 14, and is sufficiently there. Stir. For this reason, an excellent developing device is realized in which a developer having a non-uniform toner concentration or charged state due to insufficient stirring does not flow into the supply screw 14 to cause unevenness in image density and fogging.

Further, the diameter D ₃ of the stirring screw 12, the diameter D ₂ of diameter D ₁ and the recovery screw 16 of the feed screw 14
Since the transfer capacity is larger, the transfer capacity of the stirring screw 12 is larger than the transfer capacity of the supply screw 14 and the recovery screw 16, and therefore, the developer can be smoothly circulated downstream of the supply screw 14 and the recovery screw 16 without stagnation. Is realized. In addition, since the conveying capacity of the stirring screw 12 is large, the stirring of the developer in the stirring screw 12 is more favorably performed, and the unevenness of the toner concentration and the charged state is more reliably eliminated.

Further, since the supply screw 14, the recovery screw 16 and the stirring screw 12 are arranged vertically, a compact developing device having a small size in the width direction (horizontal direction in FIG. 2) is realized. I have. In particular, it is suitable for a color image forming apparatus having a plurality of developing devices.

Further, since the toner supply port 22 is provided at a position just above the reverse winding portion 14a downstream of the supply screw 14, newly supplied toner always flows into the stirring screw 12 before flowing into the supply screw 14. Is stirred with the whole developer. For this reason, the developer is sufficiently mixed with the entire developer until it flows into the supply screw 14 to have a uniform concentration, and is in a well-charged state. Therefore, even when the toner is replenished as in the case of continuously developing a large area image that consumes a large amount of toner, the developer with uneven toner concentration and charged state due to insufficient stirring. The developing device does not cause the unevenness of the image to flow into the supply screw 14 and cause image density unevenness and fogging. In this respect, there is provided a developing apparatus which does not cause any problem even when used in a color image forming apparatus which often handles an original including a large area image.

The present embodiment is merely an example, and does not limit the present invention. Therefore, naturally, the present invention can be variously modified and modified without departing from the gist thereof. For example, in this embodiment, the stirring screw 12 is slightly shorter than the supply screw 14 and the recovery screw 16 and the toner supply port 22 is provided immediately above the reverse winding portion 14a of the supply screw 14, but as shown in FIG. The length of the stirring screw 12 may be the same as the length of the supply screw 14 or the like, and the toner supply port 22 may be provided immediately above the upstream end of the stirring screw 12.
In the present embodiment, the transfer capacity of the stirring screw 12 is made larger than the transfer capacity of the other screws by adjusting the diameter of each screw. However, the present invention is not limited to this, and the shaft diameter, the effective center angle of the screw blade, Adjustment of the pitch, the number of strips, etc. may be used. Further, the developer is not limited to the two-component type, but may be a one-component type.

[0031]

As is apparent from the above description, according to the present invention, a space for stirring the developer is secured, so that only the sufficiently stirred developer is supplied to the developing roll, and There has been provided a developing device in which image quality is unlikely to be degraded due to fogging or fogging. Further, there is provided a developing device in which the smooth circulation of the developer is not hindered by the shortage of the conveying capacity of the stirring screw, and the developer is sufficiently stirred in the stirring screw. Further, there is provided a developing device in which three screws are arranged in a vertical direction and are compactly arranged. Further, there is provided a developing device in which even when the developer is replenished, the replenished developer is sufficiently mixed with the entire developer before reaching the supply screw.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a developing device according to an embodiment.

FIG. 2 is a side sectional view of the developing device in FIG. 1;

FIG. 3 is a schematic diagram illustrating a circulation path of a developer in the developing device of FIG. 1;

FIG. 4 is a schematic diagram showing another circulation path for comparison.

FIG. 5 is a schematic diagram showing another circulation path for comparison.

FIG. 6 is a view showing a modification of the developing device according to the embodiment.

FIG. 7 is a diagram illustrating a configuration of a conventional developing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Developing device 12 Stirring screw 14 Supply screw 16 Recovery screw 18 Developing roll 22 Toner supply port

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Kentaro Katori 2-13-13 Azuchicho, Chuo-ku, Osaka City Inside Osaka International Building Minolta Co., Ltd. (72) Shinichi Yoshimoto 2-chome Azuchicho, Chuo-ku, Osaka City No. 13 Osaka International Building Minolta Co., Ltd.

Claims (4)

[Claims] 1. A developing device comprising: a developing roll; a supply screw that supplies the developer to the developing roll while transporting the developer in the axial direction; and a collecting screw that recovers the developer from the developing roll and transports the developer in the axial direction. , The developer is transported in the same direction between the supply screw and the recovery screw, and a stirring screw is provided for transporting the developer in the opposite direction. 2. The developing device according to claim 1, wherein
A developing device, wherein the conveying capacity of the stirring screw is larger than the conveying capacity of the supply screw and the conveying capacity of the recovery screw. 3. The developing device according to claim 1, wherein the supply screw is disposed above the recovery screw, and the stirring screw is further disposed above the recovery screw. apparatus. 4. One of claims 1 to 3
In the developing device described in (1), a developer supply port is provided at a position upstream of a region facing the developing roll in a stirring direction of the stirring screw.