JP2006113407A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device which keeps or improves conveying ability for a developer and decreases irregular pumping of a developer by blades of a stirring screw, by decreasing a screw diameter beneath a developing sleeve by using a plurality of screws compared to a conventional developing device in which only one stirring screw is disposed beneath a developing sleeve and a developer is usually circulated by two screws. <P>SOLUTION: The developing device has a plurality of stirring screws 5, 6 with blades advancing in the same direction, disposed beneath a developing sleeve 1, wherein diameters of the all stirring screws are smaller than the diameter of the developing sleeve 1. When two different tangential lines are drawn from the circle formed by the surface of the developing sleeve 1 along the gravity direction, at least a part or the whole of the two stirring screws 5, 6 is included in the region between the two tangential lines, and thereby, at least each of different stirring screws 5, 6 is disposed in the developer drain side 2 and the pump-up side of the developer sleeve 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a developing device in an image forming apparatus such as a copying machine or a laser printer.

Conventionally, a developer is used in electrophotographic development type dry two-component development. It is known that a developer is a mixture of toner and a carrier that is a medium for carrying the toner. The developer is generally stirred and conveyed by a stirring screw in a developer storage tank and circulated. (For example, see Patent Documents 1 to 3).
In Patent Document 1, there is a reference to a developing device having a plurality of conveying screws, but only for improving the conveying ability, in order to separate the stirring and conveying of the dropped developer and the developer to be pumped, The position of each conveying screw and the diameter of the blade are not specified in order to reduce pumping unevenness to the sleeve.
In Patent Document 2, an improvement effect is obtained by providing a member in front of the developing doctor. However, in this method, the load on the developer increases, so that it may not be used in an apparatus that requires a long life.
In Patent Document 3, it is said that the unevenness of pumping can be reduced by attaching a protruding member to the screw itself, but it is difficult to eliminate the unevenness caused by the protruding member itself.
In the developing device, the developer stirred and conveyed by the conveying screw is attracted by the developing sleeve by the magnetic force and transported to the photosensitive member. Therefore, the agitating screw has a role of agitating the developer well and transporting the toner and the carrier in the developer accommodating tank while uniformly mixing so as not to cause unevenness depending on the location.
On the other hand, the developing sleeve has a function of dropping a developer once used for development and consuming the toner into a developer storage tank and supplying the developer (carrier) with toner.
At the same time, the developing sleeve has the role of pumping up again the developer that has been agitated by the conveying screw and replenishing the toner, and transporting it to the photoreceptor (the developer cutting portion and the pumping portion around the developing sleeve are schematically shown in FIG. Pointing out toungue).
A function generally required in such a type of developing device is that the developer is uniformly stirred by a stirring screw, and the developing sleeve uniformly pumps the developer and transports it to the photoreceptor.

FIG. 3 is a schematic view showing a configuration of a developing device having a conventional stirring screw. Only one stirring screw 4 is provided below the developing sleeve 1. When viewed from the cross-sectional direction, the blades 3a and 4a of the agitating screw 3 and the agitating screw 4 advance in opposite directions, and the developer is conveyed and circulated in the developer accommodating tank 0.
In this structure, the developer dropped at the developer cutting portion of the developing sleeve 1 and the developer pumped up from the pump-up portion are easy to mix and are pumped up before being sufficiently stirred.
In addition, since the distance d1 between the developing sleeve 1 and the blade 4a of the stirring screw 4 is small, uneven pumping of the developer is likely to occur due to the presence or absence of the blade.
Described here is a dry two-component developing device in an image forming apparatus. It has a screw that stirs and conveys the developer in the developer storage tank (hereinafter, this screw is referred to as “stirring screw”), and the developing sleeve draws the developer by its own magnetic force (hereinafter, this function is called This is called “pumping” by the developing sleeve, and the part of the developing sleeve having this function is called “pumping part”).
After the development, the developer is dropped into the storage tank to replenish the toner (hereinafter, this function is called “developer cutting” by the developing sleeve, and the portion of the developing sleeve having this function is called “developer cutting portion”. Called).
JP-A-11-143192 JP 2002-341657 A Japanese Patent Laid-Open No. 7-13420

However, as described above, the developing device is generally configured such that two conveying screws are used in total for conveying the developer, and the developer circulates in the developing unit (see FIG. 3).
Each screw blade advances in the opposite direction, and the magnetic force of the developing sleeve does not reach one conveying screw 3, and pumping and developer cutting by the developing sleeve 1 are not related. The developing sleeve 1 exists on the other conveying screw 4, and pumping and developer cutting are performed on this side.
In such a generally used transport structure, since there is only one transport screw below the developing sleeve 1, it has become clear that there is little margin for the following two problems.
First, the developer dropped by the developer cutting portion of the developing sleeve 1 is immediately pumped by the pumping portion of the developing sleeve. That is, since there is only one stirring screw 4 below the developing sleeve 1, the developer that has fallen and the developer to be pumped must be stirred and transported by the same transport screw 4, and the two cannot be separated. .
As a result, the developer that has fallen flows toward the pumping side without resistance and is pumped up by the developing sleeve before being sufficiently stirred. Since such a developer is not sufficiently replenished with toner, it causes an abnormal image.

Secondly, uneven pumping is likely to occur due to the blades of the stirring screw. In order to ensure the stirring / conveying ability of the developer, it is necessary to use a conveying screw having blades having a certain diameter or more. However, uneven pumping occurs due to the blades of the screw having a large diameter.
That is, since there is a space where the developer exists between the blades, the pumping performance is good. However, the developer cannot exist in a portion where the blades exist, and therefore the pumping is insufficient. Due to this pumping unevenness, an abnormal image such as pitch unevenness occurs.
In order to reduce the pumping unevenness, the diameter of the blade of the stirring screw may be reduced. However, this causes a trade-off because the stirring / conveying capability is reduced this time.
For example, in Patent Document 2 described above, an improvement effect can be obtained by providing a member in front of the developing doctor. However, in this method, the load on the developer increases, so that it may not be used in an apparatus that requires a long life.
Further, for example, in Patent Document 3 described above, it is possible to reduce unevenness in pumping by attaching a protruding member to the screw itself, but it is difficult to eliminate unevenness due to the protruding member itself.
In view of the above situation, the object of the present invention is to use a plurality of screws that are normally circulated with two screws as compared with a conventional developing device in which only one stirring screw is installed below the developing sleeve. Thus, by reducing the diameter of the agitating screw under the developing sleeve, a developing device is provided that simultaneously reduces the developer pumping unevenness due to the agitating screw blades while maintaining or improving the developer conveying capability.

In order to solve the above problems, the invention described in claim 1 is directed to a developing device including a plurality of stirring screws having blades having the same spiral direction below the developing sleeve. The diameter of the screw is smaller than the diameter of the developing sleeve, and at least two of the plurality of stirring screws are in a region between two tangents depending from both horizontal surfaces of the developing sleeve. And at least two of the agitation screws are installed on the developer cutting side and the pumping side of the developing sleeve, respectively.
According to a second aspect of the present invention, in the first aspect, the central position of the central axis of the stirring screw closest to the pumping side of the developing sleeve among the plurality of stirring screws is developed more than the tangent on the pumping side of the developing sleeve. It is located on the sleeve side.
According to a third aspect of the present invention, in the first or second aspect, the central position of the central axis of the stirring screw closest to the developer cutting side of the developing sleeve among the plurality of stirring screws is the developer cutting of the developing sleeve. It is characterized in that it is located on the developing sleeve side with respect to the tangent on the side.
The invention of claim 4 is different from claim 1, 2 or 3 in the position of the center height of the shaft, the rotational speed, the pitch width of the blade, the diameter of the blade, or the inclination of the blade. It is characterized by having.
According to a fifth aspect of the present invention, in the first, second, third, or fourth aspect, the bottom surface of the developer accommodating tank that accommodates the developing sleeve is inclined at a portion located below the developing sleeve. Features.
A sixth aspect of the invention is characterized by comprising the developing device according to any one of the first to fifth aspects.

According to the present invention, since the diameter of the blade of the stirring screw is small compared to the conventional developing device in which only one stirring screw is installed below the developing sleeve, the distance between the blade and the developing sleeve can be increased. It is possible to reduce unevenness in pumping the agent by the blades.
In addition, since the diameter of each agitating screw is made smaller than the diameter of the developing sleeve, one different agitating screw is installed on each of the developer cutting side and the pumping side of the developing sleeve, and the developer on the developer cutting side is provided. And a stirring screw suitable for each developer on the pumping side.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view showing the structure of a developing device according to the present invention. In the present embodiment, a case where two developing screws in which a plurality of stirring screws are arranged below the developing sleeve will be described.
As shown in FIG. 1, a developing sleeve 1, a stirring screw 5, and a 6 stirring screw 3 are arranged substantially in parallel in the developer storage tank 0. By making the diameters of the spiral blades 5a, 6a constituting the stirring screws 5, 6 installed below the developing sleeve 1 facing the photosensitive member (not shown) relatively smaller than the diameter of the developing sleeve 1, The distance d2 between the blades 5a and 6a and the developing sleeve 1 can be widened, and uneven pumping of the developer by the blades 5a and 6a of the screw can be reduced.
In this case, the spiral blades 5a and 6a of the two stirring screws 5 and 6 are traveling in the same direction (the spiral winding directions are the same). And the conveyance capability can be maintained or improved by arranging a plurality of stirring screws. In the figure, reference numeral 2 denotes a developer carry-in port (supply port) provided in the storage tank, 3 denotes a supply-side stirring screw, and 3a denotes a spiral blade portion thereof.
Further, by installing one each of the different stirring screws 5 and 6 on the developer cutting portion side and the pumping portion side of the developing sleeve 1, the stirring screws for stirring and transporting them are separated, and the developer cutting portion side A mechanism that can install a stirring screw suitable for the developer and the developer on the pumping part side is born.

In FIG. 1, two tangents 1 and 2 that hang from both ends of the surface of the developing sleeve 1 in the horizontal direction will be described assuming that the developer cutting side tangent is 1 and the tangent on the pumping side is 2.
That is, when the tangent line on the pumping portion side of the developing sleeve 1 is tangent line 2, the central position of the central shaft 6 b of the stirring screw 6 closest to the pumping of the developing sleeve 1 is the tangent line 2. Is on the developing sleeve 1 side.
Thus, the developing sleeve 1 can pump up the developer that has been transported outside the central shaft 6 b of the stirring screw 6. Since the developer conveyed outside the agitation screw 6 on the pumping-up portion side has been conveyed over a longer distance, the agitation is best performed. As a result, the developer that has been most stirred can be efficiently pumped by the developing sleeve.
In FIG. 1, when the tangent on the developer cutting part side is tangent 1, the central position of the central shaft 5b of the stirring screw 5 closest to the developer cutting of the developing sleeve 1 out of the plurality of stirring screws 5 and 6. Is on the developing sleeve 1 side with respect to the tangent line 1 of the developing sleeve 1.
As a result, the developer falling from the developing sleeve 1 is conveyed while turning around the outer side of the central shaft 5b of the stirring screw 5, so that it is conveyed over a longer distance until it is pumped up to the developing sleeve 1 again. Therefore, stirring and conveyance are performed more efficiently.
That is, according to the present invention, in the developing device provided with a plurality of stirring screws 5 and 6 having blades having the same spiral direction below the developing sleeve 1, the diameters of all the stirring screws are the same as those of the developing sleeve. A part or the whole of at least two of the plurality of stirring screws is included in a region between two tangents 1 and 2 that are smaller than the diameter and hang from both horizontal surfaces of the developing sleeve. It is characteristic that at least two of the agitating screws are installed on the developer cutting side and the pumping side of the developing sleeve.

In FIG. 1, the plurality of stirring screws 5 and 6 are made different in the center height or rotation speed of each shaft 5b and 6b, the pitch width of the blades 5a and 6a, the blade diameter, or the blade inclination. .
The developer separated from the developing sleeve 1 at the developer cutting portion of the developing sleeve 1 is a developer having a low toner concentration, and is more efficient than the developer having a high toner concentration supplied from the toner supply side (stirring screw 3). Need to mix.
On the other hand, the developer on the pumping portion side needs to be agitated so that the toner concentration and charge are uniform. That is, both developers are developers in different situations, and a stirring method suitable for each developer is required. According to the present invention, it is possible to install a stirring screw suitable for stirring and conveying ability for each developer.
FIG. 2 is a schematic view showing a modification of FIG. 1 of the configuration of the developing device according to the present invention. As shown in FIG. 2, in this modification, the bottom surface of the developer storage tank 0 below the developing sleeve 1 is inclined. In the figure, reference numeral 2 denotes a developer carry-in port (supply port), 3 denotes a supply-side stirring screw, and 3a denotes a blade portion thereof.
As a result, a mechanism for moving the developer can also be provided in the direction perpendicular to the axis of the developing sleeve 1, and the developer can be conveyed more smoothly from developer cutting to pumping.
In the developer storage tank 0, there is a moving mechanism by a stirring screw in the axial direction of the developing sleeve 1. However, there is no mechanical movement mechanism in the direction perpendicular to the axis of the developing sleeve 1.
Therefore, by providing the bottom surface of the developer storage tank 0 with an inclination, it is possible to provide a mechanism for moving the developer also in the direction perpendicular to the axis of the developing sleeve 1. Thereby, it is possible to smoothly perform the interval between the agent cutting and the pumping.

1 is a schematic diagram showing the configuration of a developing device according to the present invention. Schematic which shows the modification of FIG. Schematic which shows the structure of the image development apparatus which has the conventional stirring screw.

Explanation of symbols

0 developer storage tank, 1 developing sleeve, 3 stirring screw (developer supply side), 5 stirring screw, 5a stirring blade, 6 stirring screw, 6a stirring screw blade

Claims (6)

  In the developing device having a plurality of stirring screws having blades having the same spiral direction below the developing sleeve, the diameter of all the stirring screws is smaller than the diameter of the developing sleeve, and the developing sleeve A part or all of at least two of the plurality of stirring screws is included in a region between two tangents depending from both surfaces of the horizontal direction of the at least two stirring screws. The developing device is characterized in that at least one developer is installed on each of the developer cutting side and the pumping side of the developing sleeve.   Among the plurality of stirring screws, the center position of the central axis of the stirring screw closest to the pumping side of the developing sleeve is located closer to the developing sleeve than the tangent line on the pumping side of the developing sleeve. The developing device according to claim 1.   Among the plurality of stirring screws, the center position of the central axis of the stirring screw closest to the developer cutting side of the developing sleeve is positioned on the developing sleeve side with respect to the tangent on the developer cutting side of the developing sleeve. The developing device according to claim 1, wherein:   The center height position of the shaft or the rotational speed, the pitch width of the blades, the diameter of the blades, or the inclination of the blades of the plurality of stirring screws are different from each other. The developing device according to 1.   5. The developing device according to claim 1, wherein an inclination is given to a bottom surface of a developer accommodating tank that accommodates the developing sleeve and located below the developing sleeve. An image forming apparatus comprising the developing device according to claim 1.

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