Developing apparatus having recycling paths for recycling of toner and image forming apparatus including the same

A developing apparatus that develops an electrostatic latent image on an image supporting body using developer including toner and carrier includes a circulation path where the developer circulates, a discharge path connected to the circulation path through which some of the developer passes, and a first recycle path connected to the discharge path and allowing some of the developer flowing into the discharge path to return to the circulation path. The discharge path includes a discharge opening for discharging the developer flowing into the discharge path, and a first return opening for connecting to the first recycle path. The first return opening is located on an upper side in a vertical direction with respect to the discharge opening and located on an upstream side in a pass-through direction of the developer flowing into the discharge path.

The entire disclosure of Japanese Patent Application No. 2014-098800 filed on May 12, 2014 including description, claims, drawings, and abstract are incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a developing apparatus and an image forming apparatus and more particularly to a developing apparatus that develops an electrostatic latent image on an image supporting body, using developer including toner and carrier, and an image forming apparatus including the developing apparatus.

2. Description of the Related Art

Conventionally, for a developing apparatus mounted on an image forming apparatus of an electrophotographic system, there is known a developing apparatus that develops an electrostatic latent image formed on a photoconductor, using two-component developer including carrier and toner. In recent years, there has been proposed a developing apparatus of a system called a trickle system in which developer including toner in which a small amount of carrier is mixed is replenished in a developing bath according to the amount of toner consumed, and a certain amount of developer accumulated in the developing bath is discharged.

Meanwhile, to discharge a certain amount of developer, in the developing apparatus of the trickle system, like a developing apparatus described in JP 2010-217501 A, a discharge path where a certain amount of developer is discharged is provided and a discharge opening for discharging the certain amount of developer is provided in the discharge path. However, when the developing apparatus is tilted more than expected and accordingly excess developer flows into the discharge path, even essentially necessary developer is discharged through the discharge opening. As a result, there are problems such as the occurrence of uneven density in a developed image.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a developing apparatus capable of suppressing the occurrence of uneven density in a developed image by maintaining an appropriate amount of developer in a developing bath, and an image forming apparatus including the developing apparatus.

To achieve the abovementioned object, according to an aspect, a developing apparatus that develops an electrostatic latent image on an image supporting body, using developer including toner and carrier, the developing apparatus reflecting one aspect of the present invention comprises: a circulation path where the developer circulates; a discharge path which is connected to the circulation path and through which some of the developer passes; and a first recycle path connected to the discharge path and allowing some of the developer flowing into the discharge path to return to the circulation path, wherein the discharge path is provided with: a discharge opening for discharging the developer flowing into the discharge path; and a first return opening for connecting to the first recycle path, and the first return opening is located on an upper side in a vertical direction with respect to the discharge opening and located on an upstream side in a pass-through direction of the developer flowing into the discharge path.

According to another aspect of the present invention, an image forming apparatus preferably includes the developing apparatus.

In the developing apparatus according to the aspect of the present invention, the first return opening that allows developer to return to the circulation path is located on the upper side in the vertical direction with respect to the discharge opening through which the developer is discharged. At normal times, developer passes through an area more on the lower side in the vertical direction than the first return opening and thus does not return to the circulation path through the first return opening. Meanwhile, the discharge opening is present more on the lower side than the first return opening, i.e., at a position where the developer passes through. Thus, a certain amount of developer is discharged through the discharge opening, and accordingly, an appropriate amount of developer is maintained in the circulation path. In addition, the first return opening is located on the upstream side in the pass-through direction of the developer with respect to the discharge opening. By this, when excess developer flows into the discharge path, some of the developer returns to the circulation path through the first return opening before the developer is discharged through the discharge opening. Therefore, essentially necessary developer is suppressed from being discharged from the developing bath. By the above, the developing apparatus according to the aspect can suppress the occurrence of uneven density in a developed image by maintaining an appropriate amount of developer in the developing bath.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples.

(Schematic Configuration of an Image Forming Apparatus, SeeFIG. 1)

A developing apparatus which is a first embodiment and an embodiment of an image forming apparatus including the developing apparatus will be described below with reference to the accompanying drawings. In the drawings, the same members and portions are denoted by common reference sings and overlapping description is omitted.

An image forming apparatus1shown inFIG. 1is an electrophotographic printer of a tandem system, and includes imaging units10(10y,10m,10c, and10k) for forming a toner image of each of Y (yellow), M (magenta), C (cyan), and K (black) colors; and an intermediate transfer unit20.

Each imaging unit10has an electrostatic charger12, a developing apparatus40A, and the like, which are disposed around a photoconductor drum11. The developing apparatus40A develops an electrostatic latent image which is drawn on the photoconductor drum11by light irradiated from a laser scanning optical unit14, and thereby forms a toner image of a corresponding color. The intermediate transfer unit20includes an intermediate transfer belt21which is endlessly and rotatingly driven in a direction of arrow W. The intermediate transfer unit20performs primary transfer of the toner images formed on each photoconductor drum11, onto the intermediate transfer belt21by electric fields provided from primary transfer rollers22facing their corresponding photoconductor drums11, to combine the toner images. Note that such an image forming process by an electrophotographic method is a known process and thus a detailed description thereof is omitted.

An automatic paper feeding unit30that feeds materials on which transfer is performed (hereinafter, referred to as paper) one by one is disposed at the bottom of a main body of the apparatus1. The paper passes through a pair of timing rollers31from a paper feed roller (not shown) and is then transported to a nip portion between the intermediate transfer belt21and a secondary transfer roller25. Then, secondary transfer of the toner image (combined color image) is performed on the paper by an electric field provided from the secondary transfer roller25. Thereafter, the paper is transported to a fusing unit35to heat and fuse the toner, and is discharged onto a tray portion2disposed at the top of the main body of the apparatus1.

(Configuration of the Developing Apparatus, SeeFIGS. 2 to 4)

Each developing apparatus40A which is the first embodiment uses two-component developer including carrier and toner. As shown inFIG. 2, the developing apparatus40A has a developing roller44, a supply screw46, and a stirring screw48which are provided in a casing42in parallel with each other. Note that in the following a direction in which the developing roller44, the supply screw46, and the stirring screw48extend is defined as an x-axis direction. Note also that a direction orthogonal to the x-axis direction and to a vertical direction is defined as a y-axis direction.

The developing roller44forms a sleeve configuration including a magnet having a plurality of magnetic poles (not shown). The developing roller44is rotatingly driven with a slight space provided between the photoconductor drum11and the developing roller44. A developing bath50is provided at the bottom of the developing roller44. As shown inFIG. 3, the developing bath50is a container extending in the x-axis direction. In addition, the developing bath50is divided into two baths, a supply bath52and a stirring bath54, by a separating wall56extending in the x-axis direction.

The supply bath52plays the role of supplying developer to the developing roller44and collecting developer remaining after the development. In addition, the supply screw46is provided in the supply bath52. By rotation of the supply screw46, the developer is transported to the positive direction side of the x-axis direction of the supply bath52. Note that blades46anear the center in the x-axis direction of the supply screw46are blades that are twisted in an opposite direction to that of blades46bprovided at other portions of the supply screw46. Therefore, unless a pressure exerted by the developer in the supply bath52exceeds a predetermined value, there is no chance that the developer crosses the blades46aand is transported to the positive direction side of the x-axis direction. Note that in the present embodiment in order to transport the developer from the negative direction side to positive direction side of the x-axis direction of the supply bath52, the supply screw46rotates clockwise when viewed from the negative direction side of the x-axis direction.

The stirring bath54is adjacent, in parallel, to the supply bath52with the separating wall56therebetween, and stirs and mixes the developer. In addition, the stirring bath54is provided with the stirring screw48. By rotation of the stirring screw48, the developer is stirred and transported to the negative direction side of the x-axis direction of the stirring bath54. Note that, as shown inFIG. 4, the stirring bath54is provided with a replenishing opening64. New developer is replenished through the replenishing opening64.

Here, as shown inFIG. 3, an opening58is provided at a position that is near the center in the x-axis direction of the separating wall56separating the supply bath52and the stirring bath54and that is more on the negative direction side of the x-axis direction than the blades46a. Furthermore, an opening60is provided at an end of the separating wall56on the negative direction side of the x-axis direction. By this, developer transported to the positive direction side of the x-axis direction in the supply bath52passes through the opening58and enters the stirring bath54. The developer entering the stirring bath54is transported, by the stirring screw48, to the negative direction side of the x-axis direction and returns to the supply bath52through the opening60. As such, the developer circulates through a section of the supply bath52from the opening60to the opening58and a section of the stirring bath54from the opening58to the opening60. That is, the section of the supply bath52from the opening60to the opening58and the section of the stirring bath54from the opening58to the opening60form a circulation path A of the developer.

When the pressure exerted by the developer in the supply bath52exceeds the predetermined value, some of the developer transported within the supply bath52does not enter the stirring bath54through the opening58, but crosses the blades46aof the supply screw46and goes toward an end of the supply bath52on the positive direction side of the x-axis direction. Then, some of the developer going toward the end of the supply bath52on the positive direction side of the x-axis direction is discharged outside the developing apparatus40A through a discharge opening66which is provided to discharge extra developer to refresh developer. That is, a portion of the supply bath52more on the positive direction side of the x-axis direction than the blades46aforms a discharge path B through which the extra developer passes.

Meanwhile, the discharge path B is provided with a return opening68(first return opening). The return opening68is a hole for returning, when the developing apparatus40A is tilted more than expected and accordingly excess developer flows into the discharge path B, some of the flowed developer to the circulation path A. The return opening68is provided, as shown inFIG. 4, on the upper side in the vertical direction with respect to the discharge opening66and is provided, as shown inFIG. 3, on the negative direction side of the x-axis direction with respect to the discharge opening66(the upstream side in the pass-through direction of the developer). In addition, the return opening68is disposed so as to be adjacent, in the x-axis direction, to the discharge opening66.

The developer having passed through the return opening68enters the stirring bath54and is transported, by the stirring screw48, to the negative direction side of the x-axis direction. As a result, the developer having passed through the return opening68gets back to the circulation path A from a portion of the stirring bath54near where the opening58is provided. That is, a section from the return opening68to the portion of the stirring bath54near where the opening58is provided forms a recycle path C (first recycle path) that allows the developer excessively flowing into the discharge path B to return to the circulation path A.

In addition, a return opening70(second return opening) is provided at an end of the discharge path B on the positive direction side of the x-axis direction, i.e., the end of the supply bath52on the positive direction side of the x-axis direction (the downstream side of the pass-through direction of the developer). The return opening70is to prevent developer having reached the end of the supply bath52on the positive direction side of the x-axis direction without discharged through the discharge opening66, from being accumulated in the supply bath52. Therefore, the return opening70is provided on the lower side in the vertical direction with respect to the discharge opening66.

By this, the developer having passed through the return opening70enters the stirring bath54and is transported, by the stirring screw48, to the negative direction side of the x-axis direction. As a result, the developer having passed through the return opening70gets back to the circulation path A from the portion of the stirring bath54near where the opening58is provided. That is, a section from the return opening70to the portion of the stirring bath54near where the opening58is provided forms a recycle path D (second recycle path) that allows the developer excessively flowing into the discharge path B to return to the circulation path A.

Effects

In the developing apparatuses40A and the image forming apparatus1including the developing apparatuses40A, the return opening68that allows developer to return to the circulation path A is located on the upper side in the vertical direction with respect to the discharge opening66through which developer is discharged. At normal times, as shown inFIG. 5, developer passes through an area more on the lower side in the vertical direction than the return opening68and thus does not return to the circulation path A through the return opening68. Meanwhile, the discharge opening66is present more on the lower side in the vertical direction than the return opening68, i.e., at a position where the developer passes through. Thus, a certain amount of developer is discharged through the discharge opening66, and accordingly, an appropriate amount of developer is maintained in the circulation path A. In addition, the return opening68is located on the upstream side in the pass-through direction of the developer with respect to the discharge opening66. Therefore, as shown inFIG. 6, when excess developer flows into the discharge path B, some of the developer returns to the circulation path A through the return opening68before the developer is discharged through the discharge opening66. By this, essentially necessary developer is suppressed from being discharged from the developing bath50. By the above, the developing apparatuses40A and the image forming apparatus1including the developing apparatuses40A can suppress the occurrence of uneven density in a developed image by maintaining an appropriate amount of developer in each developing bath50.

Meanwhile, when, as shown inFIG. 7, the return opening68is provided on the upstream side with respect to the discharge opening66, i.e., provided on the negative direction side of the x-axis direction so as to be away from the discharge opening66, if the image forming apparatus1is tilted upon its installation and accordingly a large amount of developer is present in the discharge path B, most of the developer is located more on the downstream side than the return opening68. When in this state the image forming apparatus1starts up and the supply screw46starts to rotate, most of the developer present in the discharge path B is discharged through the discharge opening66without returning to the stirring bath54through the return opening68. As a result, it becomes difficult to maintain an appropriate amount of developer in the developing bath50. However, the return opening68of the developing apparatus40A according to the first embodiment is disposed so as to be adjacent to the discharge opening66. Hence, even if a large amount of developer flows into the positive direction side of the x-axis direction through the return opening68, the developer returns to the circulation path A by the return opening70. That is, an appropriate amount of developer can be maintained in the developing bath50.

Second Embodiment

See FIGS.8and9

A developing apparatus40B according to a second embodiment differs from a developing apparatus40A according to the first embodiment in the disposition of a discharge opening66, the disposition of a return opening68, and the absence of a return opening70. Specifically, as shown inFIG. 8, the developing apparatus40B does not have a return opening70. In addition, the discharge opening66of the developing apparatus40B is provided at an end of a supply bath52on the positive direction side of an x-axis direction and at a substantially lower end in a vertical direction.

Furthermore, as shown inFIG. 9, the return opening68is provided on the negative direction side of a y-axis direction of a discharge path B, with a perpendicular line L1passing through a central axis of a supply screw46being a boundary. In addition, the supply screw46rotates clockwise when viewed from the negative direction side of the x-axis direction. By this rotation, at normal times, developer is likely to be biased on the positive direction side (one side) of the y-axis direction. That is, the return opening68is provided in a separating wall56(a side wall of a discharge path) which is provided on the opposite side of the positive direction side of the y-axis direction where developer is likely to be biased at normal times.

The developing apparatus40B configured in the above-described manner does not have a return opening70and thus is smaller in size in the x-axis direction than the developing apparatus4OA according to the first embodiment. In addition, the discharge opening66is provided at the end of the supply bath52on the positive direction side of the x-axis direction and at the lower end in the vertical direction. Thus, developer can be suppressed from being accumulated at the end of the supply bath52on the positive direction side of the x-axis direction.

In addition, the return opening68of the developing apparatus40B is provided on the opposite side of the positive direction side of the y-axis direction where developer easily passes through at normal times. By this, at normal times, developer is prevented from returning to a circulation path A through the return opening68, and an appropriate amount of developer is discharged through the discharge opening66. Note that other configurations of the second embodiment are the same as those of the first embodiment. Therefore, in the second embodiment, description of those other than the disposition of the discharge opening66, the disposition of the return opening68, and the absence of a return opening70is as made in the first embodiment.

Third Embodiment

See FIG.10

A developing apparatus40C according to a third embodiment differs from a developing apparatus40B according to the second embodiment in that a return opening72is added. Specifically, as shown inFIG. 10, in the developing apparatus40C, a discharge path B has the return opening72present more on the negative direction side of an x-axis direction than a return opening68. That is, the return openings68and72are located more on the negative direction side of the x-axis direction than a discharge opening66.

The developing apparatus40C configured in the above-described manner has the plurality of return openings68and72provided more on the negative direction side of the x-axis direction than the discharge opening66. Therefore, when the developing apparatus40C is tilted more than expected and accordingly excess developer flows into the discharge path B, the developing apparatus40C which is the third embodiment can return more developer to a circulation path A than the developing apparatus40B which is the second embodiment. Note that other configurations of the third embodiment are the same as those of the second embodiment. Therefore, in the third embodiment, description of those other than the addition of the return opening72is as made in the second embodiment.

Fourth Embodiment

See FIG.11

A developing apparatus40D according to a fourth embodiment differs from a developing apparatus40B according to the second embodiment in the size of a return opening68and the rotation of a supply screw46at startup of the developing apparatus40D. Specifically, as shown inFIG. 11, the developing apparatus40D has the return opening68provided in substantially the entire area of a discharge path B, i.e., substantially the entire area ranging from a portion of a supply bath52where blades46aof the supply screw46are located (a connecting portion between a circulation path and a discharge path) to a discharge opening66. In addition, at startup of an image forming apparatus including the developing apparatus40D, the developing apparatus40D turns the supply screw46a quarter rotation in an opposite direction to a normal direction.

The size of the return opening68of the developing apparatus40D configured in the above-described manner is larger than that of a return opening68of the developing apparatus40B according to the second embodiment. Therefore, when the developing apparatus40D is tilted more than expected and accordingly excess developer flows into the discharge path B, the developing apparatus40D which is the fourth embodiment can return more developer to a circulation path A than the developing apparatus40B which is the second embodiment. In addition to this, at startup of the image forming apparatus including the developing apparatus40D, the developing apparatus40D turns the supply screw46a quarter rotation in the opposite direction to the normal direction. By this, the developing apparatus40D can more securely return developer to the circulation path A through the return opening68. In addition, at startup of the developing apparatus40D, by repeating reverse rotation and forward rotation, the developing apparatus40D can further securely return developer to the circulation path A. Note that other configurations of the fourth embodiment are the same as those of the second embodiment. Therefore, in the fourth embodiment, description of those other than the size of the return opening68is as made in the second embodiment.

Other Embodiments

Developing apparatuses and image forming apparatuses according to the present invention are not limited to those of the above-described embodiments, and various changes may be made within the spirit and scope of the invention. For example, the shapes and numbers of the return openings are any shape and number. Furthermore, the embodiments may be combined together.

As described above, the present invention is useful for developing apparatuses and image forming apparatuses. Particularly, the present invention is excellent in that the invention can suppress the occurrence of uneven density in a developed image by maintaining an appropriate amount of developer in a developing bath.