JP2012093400A - Developing device, process cartridge, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device employing a premixed developing system that prevents temporary rapid reduction of bulk of developer that flows in the developing device due to environmental change, a process cartridge, and an image forming apparatus.SOLUTION: A developing device includes: a storage part (provided with a conveyance screw 13j for returning developer) that temporarily stores a portion of developer discharged from an exhaust port 13d that is formed on a partition wall of a first conveyance path formed of a first conveyance member 13b1; and a returning path 13 m (returning port 13 m1) that returns a portion of the developer stored in the storage part, when the surface of the developer conveyed through the first conveyance path is not reached a predetermined level, toward the inside of the first conveyance path.

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile machine, or a multi-function machine thereof, and a developing device and a process cartridge installed therein. The present invention relates to a premix developing type developing device, a process cartridge, and an image forming apparatus that appropriately supply a carrier and a developer.

  Conventionally, in an image forming apparatus such as a copying machine or a printer, a new carrier is appropriately replenished to a developing device containing a two-component developer composed of toner and carrier (including the case where an additive is added). There is a known technique (referred to as a premix development method) (see, for example, Patent Documents 1 and 2).

  In a developing device using a two-component developer, toner is appropriately replenished into the developing device from a toner replenishing port provided in a part of the developing device according to toner consumption in the developing device. The replenished toner is agitated and mixed by a conveying screw (conveying member) together with the developer in the developing device. Part of the stirred and mixed developer is supplied to a developing roller (developer carrier). The developer carried on the developing roller is regulated to an appropriate amount by a doctor blade (developer regulating member), and then the toner in the two-component developer is located at a position facing the photoreceptor drum (image carrier). It adheres to the latent image on the drum.

  As described above, since the carrier in the two-component developer accommodated in the developing device in the normal developing process remains in the developing device without being consumed, the carrier deteriorates with time. Specifically, the carrier is agitated and mixed for a long time in the developing device, so that the coating layer of the carrier is worn or peeled off and the charging ability of the carrier is reduced, or the toner on the surface of the carrier. The “spent phenomenon” in which the chargeability of the carrier decreases due to adhesion of components and additives occurs.

The premix development method is for preventing the deterioration of the image quality of the output image due to the deterioration of the carrier over time. That is, a new carrier (or a new two-component developer) is appropriately supplied into the developing device, and a part of the two-component developer accommodated in the developing device is appropriately discharged to the outside of the developing device. The number of deteriorated carriers in the apparatus is reduced to maintain the amount of carriers accommodated in the developing apparatus and the charging ability.
An image forming apparatus using such a premix developing system has an image quality of an output image over time as compared to a developing apparatus or an apparatus that needs to replace the carrier with a new one every time the carrier deteriorates over time. Will be stabilized.

  Patent Documents 1, 2 and the like disclose a developing device using a premix developing method and using an overflow method as a means for discharging the developer from the developing device to the outside. Specifically, the developing device is provided with a discharge port (discharge means), and when the developer surface transported to that position exceeds a predetermined height, the developer (development that has become excessive due to the replenishment of the carrier) Is discharged from the outlet.

  The above-described premix development type development apparatus such as Patent Document 1 supplies a new carrier into the apparatus when the developer charge amount, toner concentration, and fluidity change drastically due to environmental fluctuations or the like. However, there is a case in which the bulk (agent amount) of the developer flowing in the apparatus is temporarily lowered suddenly without being in time. When such problems occur, abnormal images such as reduced image density or uneven image density may occur, or toner scattering may occur due to changes in internal pressure in the device. .

  The present invention has been made to solve the above-described problems, and premix development in which the volume of the developer flowing in the developing device is not temporarily reduced suddenly due to environmental fluctuations or the like. Another object is to provide a developing device, a process cartridge, and an image forming apparatus.

  According to a first aspect of the present invention, there is provided a developing device for storing a developer having a carrier and a toner and developing a latent image formed on an image carrier, the image carrier. A developer carrying body facing the body and carrying the developer, a plurality of conveying members that convey the developer contained in the apparatus in the longitudinal direction to form a circulation path, and a new carrier in the apparatus A supply path for supplying the developer, and when the developer surface of the developer conveyed by one of the plurality of conveying members exceeds a first predetermined height, the developer is conveyed by the one conveying member. A discharge port formed in a partition wall of a conveyance path by the one conveyance member, a storage unit for temporarily storing a part or all of the developer discharged from the discharge port, Conveying by one conveying member When the developer surface of the developer transported in step S2 does not reach the second predetermined height, a part of the developer stored in the storage portion is returned again toward the inside of the transport path by the one transport member. Therefore, there is provided a return port formed in the partition wall of the transport path by the one transport member.

  The developing device according to a second aspect of the present invention is the developing device according to the first aspect, wherein the storage portion is configured such that the developer surface stored in the storage portion exceeds a predetermined height. A second discharge port for discharging the developer to the outside of the apparatus is provided.

  According to a third aspect of the present invention, there is provided the developing device according to the first or second aspect, wherein the first predetermined height is the second predetermined height in the transport path by the one transport member. It is set higher than the height.

  A developing device according to a fourth aspect of the present invention is the developing device according to any one of the first to third aspects, wherein the return port is transported more than the discharge port in the transport path by the one transport member. It is arranged upstream in the direction.

  A developing device according to a fifth aspect of the present invention is the developing device according to any one of the first to fourth aspects, wherein the plurality of conveying members are opposed to the developer carrier and have a developer. A first conveying member that supplies developer to the developer carrying member while being conveyed in the longitudinal direction, and a position that faces the first conveying member via a wall and faces the developer carrying member. A second transport member that transports the developer that is disposed at the position and separated from the developer carrier in the longitudinal direction; and a transport path that transports the developer transported by the second transport member by the first transport member A third transport member that transports the developer that has reached the downstream side of the transport path by the first transport member to the upstream side of the transport path by the first transport member, One conveying member is 1 is obtained by the conveying member.

  The developing device according to a sixth aspect of the present invention is the developing device according to the fifth aspect, wherein the return port is located between the central portion in the longitudinal direction and the downstream side in the transport direction in the transport path by the first transport member. Are arranged.

  According to a seventh aspect of the present invention, there is provided the developing device according to any one of the first to sixth aspects, wherein the supply means newly supplies toner together with the carrier into the apparatus. is there.

  The process cartridge according to an eighth aspect of the present invention is a process cartridge that is detachably installed on the main body of the image forming apparatus, and is according to any one of the first to seventh aspects. The developing device and the image carrier are integrated.

  An image forming apparatus according to a ninth aspect of the present invention includes the developing device according to any one of the first to seventh aspects and the image carrier.

  In the present application, the “process cartridge” refers to a charging unit that charges the image carrier, a developing unit (developing device) that develops a latent image formed on the image carrier, and a cleaning on the image carrier. At least one of the cleaning units and the image carrier are defined as a unit that is integrated and detachably installed on the image forming apparatus main body.

  The present invention provides a storage unit for temporarily storing the developer discharged from the discharge port of the transport path, and a return port for returning a part of the developer stored in the storage unit toward the inside of the transport path again. Therefore, the premix developing type developing device, the process cartridge, and the image formation, in which the bulk of the developer flowing in the developing device due to environmental fluctuations or the like is not temporarily reduced rapidly. An apparatus can be provided.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. It is a block diagram which shows an image creation part. (A) The schematic sectional view which looked at the upper part of the developing device in the longitudinal direction, (B) The schematic sectional view which looked at the lower part of the developing device in the longitudinal direction. It is sectional drawing which shows the vicinity of the 3rd relay part of a developing device. It is sectional drawing which shows the vicinity of the discharge port of a developing device. FIG. 4 is a cross-sectional view showing the vicinity of an opening where a developer is transferred to a storage unit of the developing device. It is sectional drawing which shows the vicinity of the return port of a developing device. It is sectional drawing which shows the vicinity of the 2nd discharge port of a developing device in a longitudinal direction. It is sectional drawing which shows the vicinity of the supply port of a developing device.

Embodiment.
Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, reference numeral 1 denotes an apparatus main body of a tandem color copier as an image forming apparatus, 2 a writing unit that emits laser light based on input image information, and 3 an original conveying unit that conveys an original D to an original reading unit 4. 4 is a document reading unit that reads image information of the document D, 7 is a paper feeding unit that accommodates a recording medium P such as transfer paper, 9 is a registration roller that adjusts the conveyance timing of the recording medium P, and 11Y, 11M, and 11C. , 11BK are photosensitive drums on which toner images of respective colors (yellow, magenta, cyan, and black) are formed, 12 is a charging unit that charges the photosensitive drums 11Y, 11M, 11C, and 11BK, and 13 is each photosensitive drum. A developing device for developing electrostatic latent images formed on 11Y, 11M, 11C, and 11BK, and a toner image formed on each of the photosensitive drums 11Y, 11M, 11C, and 11BK Transfer bias roller for transferring superimposed on the recording medium P (1 transfer bias roller), 15 denotes the photosensitive drums 11Y, 11M, 11C, cleaning unit for collecting the untransferred toner on 11BK, a.

Reference numeral 16 denotes an intermediate transfer belt cleaning unit that cleans the intermediate transfer belt 17, 17 an intermediate transfer belt on which toner images of a plurality of colors are transferred and superimposed, and 18 a color toner image on the intermediate transfer belt 17 on the recording medium P. A secondary transfer bias roller 20 for transferring the toner image onto the recording medium P indicates a fixing device for fixing an unfixed image on the recording medium P.
Although not shown in the drawing, a carrier (magnetic carrier) and toner (toner particles) of each color (yellow, cyan, magenta, black) are developed above the photosensitive drums 11Y, 11C, 11M, and 11BK. Each color agent cartridge is installed as a supply means for supplying to 13.

Hereinafter, an operation during normal color image formation in the image forming apparatus will be described. Note that FIG. 2 can also be referred to for the image forming process performed on the photosensitive drums 11Y, 11M, 11C, and 11BK.
First, the document D is transported from the document table in the direction of the arrow in the drawing by the transport rollers of the document transport unit 3 and placed on the contact glass 5 of the document reading unit 4. Then, the document reading unit 4 optically reads the image information of the document D placed on the contact glass 5.

  Specifically, the document reading unit 4 scans the image of the document D on the contact glass 5 while irradiating light emitted from an illumination lamp. Then, the light reflected by the document D is imaged on the color sensor via the mirror group and the lens. The color image information of the document D is read for each RGB (red, green, blue) color separation light by the color sensor, and then converted into an electrical image signal. Further, color conversion processing, color correction processing, spatial frequency correction processing, and the like are performed by the image processing unit based on the RGB color separation image signals to obtain yellow, magenta, cyan, and black color image information.

  Then, the image information of each color of yellow, magenta, cyan, and black is transmitted to the writing unit 2. The writing unit 2 emits laser light L (see FIG. 2) based on the image information of each color toward the corresponding photosensitive drums 11Y, 11M, 11C, and 11BK.

On the other hand, the four photosensitive drums 11Y, 11M, 11C, and 11BK are rotated clockwise in FIG. First, the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK are uniformly charged at a portion facing the charging unit 12 (this is a charging process). Thus, a charged potential is formed on the photosensitive drums 11Y, 11M, 11C, and 11BK. Thereafter, the charged surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK reach the irradiation positions of the respective laser beams.
In the writing unit 2, laser light corresponding to the image signal is emitted from the four light sources corresponding to each color. Each laser beam passes through a separate optical path for each of the yellow, magenta, cyan, and black color components (this is an exposure process).

  Laser light corresponding to the yellow component is irradiated on the surface of the first photosensitive drum 11Y from the left side of the drawing. At this time, the yellow component laser light is scanned in the rotation axis direction (main scanning direction) of the photosensitive drum 11Y by a polygon mirror that rotates at high speed. Thus, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 11Y charged by the charging unit 12.

  Similarly, the laser beam corresponding to the magenta component is irradiated onto the surface of the second photosensitive drum 11M from the left side of the paper, and an electrostatic latent image corresponding to the magenta component is formed. The cyan component laser light is applied to the surface of the third photosensitive drum 11C from the left side of the paper, and an electrostatic latent image of the cyan component is formed. The black component laser beam is applied to the surface of the fourth photosensitive drum 11BK from the left side of the paper, and an electrostatic latent image of the black component is formed.

Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK on which the electrostatic latent images of the respective colors are formed reach positions facing the developing device 13, respectively. Then, the respective color toners are supplied from the developing devices 13 onto the photosensitive drums 11Y, 11M, 11C, and 11BK, and the latent images on the photosensitive drums 11Y, 11M, 11C, and 11BK are developed (development process). .)
Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK after the development process reach the facing portions of the intermediate transfer belt 17, respectively. Here, a transfer bias roller 14 is installed at each facing portion so as to contact the inner peripheral surface of the intermediate transfer belt 17. Then, the toner images of the respective colors formed on the photosensitive drums 11Y, 11M, 11C, and 11BK are sequentially superimposed and transferred onto the intermediate transfer belt 17 at the position of the transfer bias roller 14 (in the primary transfer process). is there.).

Then, the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK after the transfer process reach positions facing the cleaning unit 15, respectively. Then, the untransferred toner remaining on the photosensitive drums 11Y, 11M, 11C, and 11BK is collected by the cleaning unit 15 (this is a cleaning process).
Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK pass through a neutralization unit (not shown), and a series of image forming processes on the photoconductive drums 11Y, 11M, 11C, and 11BK is completed.

On the other hand, the intermediate transfer belt 17 on which the toners of the respective colors on the photosensitive drums 11Y, 11M, 11C, and 11BK are transferred (carrying) are run in the clockwise direction in the drawing and are connected to the secondary transfer bias roller 18. Reach the opposite position. Then, a color toner image carried on the intermediate transfer belt 17 is transferred onto the recording medium P at a position facing the secondary transfer bias roller 18 (secondary transfer step).
Thereafter, the surface of the intermediate transfer belt 17 reaches the position of the intermediate transfer belt cleaning unit 16. Then, the untransferred toner adhered on the intermediate transfer belt 17 is collected by the intermediate transfer belt cleaning unit 16, and a series of transfer processes in the intermediate transfer belt 17 is completed.

Here, the recording medium P transported between the intermediate transfer belt 17 and the secondary transfer bias roller 18 (secondary transfer nip) is transported from the paper supply unit 7 via the registration roller 9 and the like. It is a thing.
Specifically, the recording medium P fed by the paper feeding roller 8 from the paper feeding unit 7 that stores the recording medium P is guided to the registration roller 9 after passing through the conveyance guide. The recording medium P that has reached the registration roller 9 is conveyed toward the secondary transfer nip at the same timing.

Then, the recording medium P on which the full-color image is transferred is guided to the fixing device 20 by the transport belt. In the fixing device 20, the color image (toner) is fixed on the recording medium P at the nip between the fixing belt and the pressure roller.
Then, the recording medium P after the fixing step is discharged as an output image outside the apparatus main body 1 by a paper discharge roller, and a series of image forming processes is completed.

Next, the image forming unit in the image forming apparatus will be described in detail with reference to FIGS.
FIG. 2 is a configuration diagram illustrating the image forming unit and the agent cartridge 28. 3A is a schematic cross-sectional view of the upper portion of the developing device 13 (the positions of the first conveying screw 13b1, the discharging conveying screw 13k, and the returning conveying screw 13j) in the longitudinal direction, and FIG. B) is a schematic cross-sectional view of the lower part of the developing device 13 (the positions of the second transport screw 13b2 and the third transport screw 13b3) as viewed in the longitudinal direction. 4 is a cross-sectional view showing the vicinity of the third relay portion 13h of the developing device 13, FIG. 5 is a cross-sectional view showing the vicinity of the discharge port 13d of the developing device 13, and FIG. FIG. 7 is a cross-sectional view showing the vicinity of the opening 13s where the developer is transferred, FIG. 7 is a cross-sectional view showing the vicinity of the return port 13m1 of the developing device 13, and FIG. 8 is a second discharge port 13t of the developing device 13. FIG. 9 is a cross-sectional view (side cross-sectional view) showing the vicinity of the (second discharge port) in the longitudinal direction, and FIG. 9 is a cross-sectional view showing the vicinity of the supply port 13e of the developing device 13.
Since each image forming unit has almost the same structure, and each agent cartridge has almost the same structure, the image forming unit and the agent cartridge are denoted by alphabets (Y, C, M, BK) is shown in the figure.

As shown in FIG. 2, the image forming unit includes a photosensitive drum 11 as an image carrier, a charging unit 12, a developing device 13 (developing unit), a cleaning unit 15, and the like.
A photosensitive drum 11 as an image carrier is a negatively charged organic photosensitive member, and is rotated counterclockwise by a drive motor (not shown).

The charging unit 12 is a charging roller having elasticity in which a foamed urethane layer having a medium resistance in which a urethane resin, carbon black as conductive particles, a sulfurizing agent, a foaming agent, and the like are formed in a roller shape on a core metal. The material of the middle resistance layer of the charging unit 12 is urethane, ethylene-propylene-diene polyethylene (EPDM), butadiene acrylonitrile rubber (NBR), silicone rubber, isoprene rubber, etc. It is also possible to use a rubber material in which a conductive material such as the above is dispersed or a foamed material of these materials.
The cleaning unit 15 is provided with a cleaning brush (or a cleaning blade) that is in sliding contact with the photosensitive drum 11, and mechanically removes and collects untransferred toner on the photosensitive drum 11.

  The developing device 13 is arranged such that a developing roller 13a as a developer carrying member is close to the photosensitive drum 11, and a developing region where the photosensitive drum 11 and the magnetic brush are in contact with each other is formed. Is done. A developer G (two-component developer) composed of toner T and carrier C is accommodated in the developing device 13. The developing device 13 develops the electrostatic latent image formed on the photosensitive drum 11 (forms a toner image). The configuration and operation of the developing device 13 will be described in detail later.

Here, the developing device 13 in the present embodiment is of a premix developing type, and a new carrier C (developer G) is appropriately supplied from the agent cartridge 28 into the developing device 13. Although not shown, the deteriorated developer G is discharged toward the agent storage container via a discharge path installed outside the developing device 13.
Referring to FIG. 2, the agent cartridge 28 accommodates developer G (toner T and carrier C) to be supplied into the developing device 13 therein. The agent cartridge 28 functions as a toner cartridge that supplies new toner T to the developing device 13, and also functions as a supply unit that supplies new carrier C to the developing device 13. Specifically, based on information on toner density (which is the ratio of toner in the developer G) detected by a magnetic sensor (not shown) installed in the developing device 13, the shutter driving unit performs shutter. The mechanism 80 is opened and closed to appropriately supply the developer G from the agent cartridge 28 serving as a supply unit into the developing device 13. Here, in the present embodiment, the mixing ratio of the carrier C in the toner T in the developer G of the agent cartridge 28 is set to about 10 wt%.
The supply of the developer G is not limited to the toner density information, but is performed based on the image density information detected from the reflectance of the toner image formed on the photosensitive belt or the intermediate transfer belt. Also good. Further, the implementation of the supply of the developer G may be determined by combining these different pieces of information.

  The supply pipe 29 as a supply means is for reliably guiding the developer G (toner T and carrier C) supplied from the agent cartridge 28 into the developing device 13. That is, the developer G discharged from the agent cartridge 28 is supplied into the developing device 13 through the supply pipe 29 from the supply port 13e (developer supply port).

Hereinafter, the developing device 13 in the image forming apparatus will be described in detail.
2 to 9, the developing device 13 includes a developing roller 13a as a developer carrying member, conveying screws 13b1 to 13b3 (auger screws) as conveying members, a doctor blade 13c as a developer regulating member, discharge. It comprises a discharge conveying screw 13k as a conveying member, a returning conveying screw 13j as a returning conveying member, and the like.

The developing roller 13a has an outer diameter of 25 mm, and a sleeve formed of a nonmagnetic material such as aluminum, brass, stainless steel, or conductive resin in a cylindrical shape is rotated clockwise by a drive motor (not shown). It is configured. Referring to FIG. 4, a magnet 13 a 1 that forms a magnetic field is fixed in the sleeve 13 a 2 of the developing roller 13 a so as to cause the developer G to rise on the peripheral surface of the sleeve. The carrier C in the developer G rises in a chain shape on the sleeve 13a2 so as to follow the normal line of magnetic force emitted from the magnet 13a1. The charged toner T is attached to the carrier C that is spiked in a chain shape to form a magnetic brush. The magnetic brush is transferred in the same direction (clockwise) as the sleeve 13a2 by the rotation of the sleeve 13a2.
Referring to FIG. 2, the doctor blade 13c is a substantially plate-like member installed on the upstream side of the developing region, and regulates the developer G on the developing roller 13a to an appropriate amount.

The three conveying screws 13b1 to 13b3 stir and mix the developer G accommodated in the developing device 13 while circulating in the longitudinal direction (the direction perpendicular to the paper surface of FIG. 2).
The first transport screw 13b1 as the first transport member is disposed at a position facing the developing roller 13a, and transports the developer G horizontally in the longitudinal direction (rotation axis direction) (see FIG. 3A). In addition, the developer G is supplied onto the developing roller 13a (in the direction of the white arrow in FIG. 3A).

  The second conveyance screw 13b2 as the second conveyance member is disposed below the first conveyance screw 13b1 and at a position facing the developing roller 13a. Then, the developer G separated from the developing roller 13a (the developer G forcibly separated from the developing roller 13a by the agent separation pole after the developing step, and separated in the direction of the white arrow in FIG. 3B). Is horizontally transported in the longitudinal direction (the transport in the right direction indicated by the broken arrow in FIG. 3B).

The 3rd conveyance screw 13b3 as a 3rd conveyance member is a position adjacent to the 2nd conveyance screw 13b2, and is arrange | positioned diagonally below the 1st conveyance member 13b1. The third transport screw 13b3 transports the developer G transported by the second transport screw 13b2 to the upstream side of the transport path by the first transport member 13b1, and from the downstream side of the transport path by the first transport screw 13b1. The developer G circulated through the first relay portion 13f is transported to the upstream side of the transport path by the first transport member 13b1 (the transport in the left direction indicated by the broken-line arrow in FIG. 3B).
The three conveying screws 13b1 to 13b3 are arranged so that the rotation shaft is substantially horizontal, like the developing roller 13a and the photosensitive drum 11. In addition, the three conveying screws 13b1 to 13b3 are obtained by spirally winding a screw part around a shaft part, and the outer diameter of the screw part is set to 22 mm. And although illustration is abbreviate | omitted, as for the three conveyance screws 13b1-13b3, each drive gear is connected with the drive motor via the gear train, and it is rotationally driven by the drive motor in the predetermined direction, respectively.

In addition, the conveyance path (1st conveyance path) by 1st conveyance screw 13b1, the conveyance path (2nd conveyance path) by 2nd conveyance screw 13b2, the conveyance path (3rd conveyance path) by 3rd conveyance screw 13b3, The discharge conveyance path by the discharge conveyance screw 13k and the storage section in which the return conveyance screw 13j is installed are separated from each other by a partition wall (wall portion).
With reference to FIG. 3 (B), the downstream side of the conveyance path by the second conveyance screw 13b2 and the upstream side of the conveyance path by the third conveyance screw 13b3 communicate with each other via the second relay portion 13g. Also, referring to FIGS. 3A and 3B, the downstream side of the conveyance path by the first conveyance screw 13b1 and the upstream side of the conveyance path by the third conveyance screw 13b3 are the first relay portion 13f. It communicates through. 3A, FIG. 3B, and FIG. 4, the downstream side of the transport path by the third transport screw 13b3 and the upstream side of the transport path by the first transport screw 13b1 are the third. It communicates via the relay part 13h. Referring to FIG. 4, the developer G staying and rising in the vicinity of the third relay portion 13 h in the transport route by the third transport screw 13 b 3 is transported by the first transport screw 13 b 1 via the third relay portion 13 h. It is conveyed (supplied) to the upstream side.

  With such a configuration, a circulation path for circulating the developer G in the longitudinal direction in the developing device 13 is formed by the three transport screws 13b1 to 13b3. That is, when the developing device 13 is operated, the developer G accommodated in the device flows in the direction of the broken line arrow in FIG. In this way, the developer G supply path to the developing roller 13a (the transport path by the first transport screw 13a1) and the developer G recovery path to be separated from the developing roller 13a (by the second transport screw 13a2). , The density deviation of the toner image formed on the photosensitive drum 11 can be reduced.

Although illustration is omitted, a magnetic sensor for detecting the toner concentration of the developer circulating in the apparatus is installed in the conveyance path by the third conveyance screw 13b3. Then, based on the toner density information detected by the magnetic sensor, a developer G having a predetermined toner density is supplied from the agent cartridge 28 serving as a supply unit into the developing device 13 through the supply port 13e.
3B and 9, the replenishment port 13e is located on the upstream side of the conveyance path by the third conveyance screw 13b3 and away from the development area (the longitudinal direction of the development roller 13a). It is outside the range.).

Here, with reference to FIG. 2, FIG. 3 (A) and FIG. 5, a part of the developer G accommodated in the developing device 13 is first transported to the partition wall of the transport path by the first transport screw 13b1. A discharge port 13d for discharging to the outside of the route (conveyance route by the first conveyance screw 13b1) is provided.
In detail, the discharge port 13d (discharge means) is supplied with the developer G into the developing device 13 by the supply means 28, 29, 80, and the developer amount in the device increases to be conveyed to that position. When the agent surface (upper surface) exceeds a predetermined height H1 (first predetermined height, which can be referred to FIG. 5), the excess developer G is discharged through a discharge conveyance path (discharge A conveying screw 13k is installed.) The developer discharged from the discharge port 13d is conveyed in the longitudinal direction (the left direction in FIG. 3A) by the discharge conveying screw 13k. Then, after a part of the conveyed developer falls by its own weight from the opening 13r and is discharged to the outside of the apparatus (discharge path), the agent storage container (not illustrated) is passed through the discharge path (not shown). To be recovered. In other words, the excess developer G exceeds the lower portion of the discharge port 13d and is discharged from the discharge port 13d to be discharged through the discharge conveyance path (discharge conveyance screw 13k) and the agent storage container via the discharge path. It is conveyed toward. As described above, the carrier deteriorated by being contaminated with the base resin or the external additive of the toner T is automatically discharged to the outside of the developing device, so that deterioration of the image quality can be suppressed over time. The discharge path is connected to all of the discharge conveyance paths of the developing devices 13 for each color (four), and the developer discharged from each developing device 13 is collected and collected in the agent storage container.

Here, in the present embodiment, the return conveying screw 13j is located at a position adjacent to the first conveying path (the conveying path by the first conveying screw 13b1) via the discharging conveying path on which the discharging conveying screw 13k is installed. A storage part in which is installed is disposed. The storage unit functions as a buffer unit that temporarily stores a part of the developer discharged from the discharge port 13d of the first transport path (a developer that flows in the transport path for discharge).
Furthermore, when the developer surface of the developer transported in the first transport path by the first transport screw 13b1 does not reach the predetermined height H2 (the second predetermined height, which can refer to FIG. 7). A return port 13m1 is formed in the partition wall of the first transport path in order to return a part of the developer stored in the storage part toward the inside of the first transport path again.

Specifically, referring to FIG. 3A and FIG. 6, an upstream side of the opening 13 r for discharging to the outside of the developing device 13 (upstream in the transport direction) is provided in the discharge transport path by the discharge transport screw 13 k. 13) is provided with an opening 13 s for delivering the developer from the discharge conveyance path to the storage portion. The opening 13s is set at a predetermined height in the discharge conveyance path so that a part of the developer conveyed toward the discharge opening 13r to the outside in the discharge conveyance path flows into the storage portion. Yes. Then, the developer supplied from the discharge transport path to the storage section through the opening 13s is transported in the longitudinal direction by the return transport screw 13j in the storage section (in the broken line arrow in FIG. 3A). This is the right-hand conveyance shown.)
On the other hand, with reference to FIG. 3A and FIG. 7, in the storage part by the return conveyance screw 13j, the first conveyance path by the first conveyance screw 13b1 is located at the downstream side in the conveyance direction from the central part in the longitudinal direction. A return path 13m communicating with is formed. The return path 13m is formed so as to incline downward from the inlet 13m2 formed in the storage part toward the return port 13m1 formed in the first transport path.

With such a configuration, when the developer surface in the first transport path by the first transport screw 13b1 does not reach the predetermined height H2 (the second predetermined height, which can be referred to FIG. 7). A part of the developer stored in the storage unit is re-supplied toward the inside of the first transport path via the return path 13m (return port 13m1).
In contrast, when the developer surface of the developer in the first transport path reaches the predetermined height H2, the return path 13m (return port 13m1) is buried with the developer and stagnates in the return path 13m. The developer does not flow from the reservoir to the first transport path due to the developer pressure (the developer remains in the reservoir).
The second predetermined height H2 described above is set lower than the first predetermined height H1 described above with reference to FIG. 5 (so that H1> H2). This is set through experiments and simulations so that the bulk (agent amount) of the developer flowing in the transport path does not decrease and abnormal images such as image density reduction and image density unevenness and toner scattering do not occur.

  With such a configuration, when the developer charge amount, the toner concentration, and the fluidity of the developer in the developing device 13 suddenly and greatly change due to environmental fluctuations or the like, a new cartridge from the agent cartridge 28 into the developing device 13 can be obtained. Even in the case where the supply of the developer is not in time, the return conveying screw 13j is installed without the volume (agent surface) of the developer flowing in the developing device 13 being suddenly lowered temporarily. The developer is instantaneously supplied from the storage section (buffer section) into the developing device 13 (first transport path) through the return path 13m (return port 13m1). Accordingly, it is possible to reliably reduce the occurrence of abnormal images such as image density reduction and image density unevenness due to a temporary and rapid decrease in the volume (agent surface) of the developer flowing in the developing device 13, and the occurrence of toner scattering. can do.

Particularly, in the first transport path, the developer is supplied onto the developing roller 13a while transporting the developer in the longitudinal direction from the left to the right in FIG. 3A by the first transport screw 13b1. The absolute height of the developer surface on the downstream side in the transport direction (right side in FIG. 3A) compared to the upstream side in the transport direction (left side in FIG. 3A). The thickness (bulk) is lowered. For this reason, if the overall amount (bulk) of the developer flowing in the developing device 13 is reduced, an image density drop, an image density unevenness, or the like on the output image corresponding to the downstream side in the transport direction in the first transport path. Abnormal images are likely to occur. That is, if the phenomenon that the developer surface of the developer rapidly decreases on the downstream side in the transport direction in the first transport path can be suppressed, the occurrence of abnormal images such as image density decrease and image density unevenness can be substantially suppressed.
For this reason, in the present embodiment, as shown in FIG. 3A, the return port 13m1 is located between the center in the longitudinal direction and the downstream side in the transport direction in the first transport path by the first transport screw 13b1. It is arranged. As a result, when the developer surface of the developer does not reach the predetermined height H2 on the downstream side in the transport direction in the first transport path, the developer stored in the storage section is returned via the return path 13m (return port 13m1). It is immediately supplied toward the downstream side in the transport direction of one transport path.

  As shown in FIG. 3A, the return port 13m1 is disposed on the upstream side in the transport direction (to the left of FIG. 3A) of the discharge port 13d in the first transport path. Specifically, in the first transport path, the discharge port 13d is disposed in the vicinity of the most downstream position in the transport direction, and the return port 13m1 is upstream from that and from the center in the longitudinal direction to the downstream in the transport direction. It is arranged. As a result, excessive developer G can be discharged without increasing the amount of developer in the developing device 13 while suppressing the phenomenon that the developer surface rapidly decreases on the downstream side in the transport direction in the first transport path. It is possible to reliably discharge from the outlet 13d toward the discharge conveyance path.

Further, in the present embodiment, when the developer surface stored in the storage portion by the return conveying screw 13j exceeds a predetermined height H3 (see FIG. 8), A second discharge port 13t (second discharge port) for discharging the developer to the outside of the developing device 13 is provided.
Specifically, referring to FIG. 3A and FIG. 8, the storage unit is configured to discharge the developer to the outside of the developing device 13 at a position downstream in the transport direction of the return transport screw 13j. A second discharge port 13t is provided. The second discharge port 13t is set to a predetermined height in the wall portion of the storage portion so that the developer amount in the storage portion does not exceed a predetermined amount. When the developer level in the storage unit exceeds a predetermined height H3, a part of the developer stored in the storage unit falls by its own weight from the second discharge port 13t and is discharged outside the apparatus (discharge path). Then, it is collected in the agent storage container via a discharge path (not shown) (the movement in the direction indicated by the broken line arrow in FIG. 8). That is, of the developer stored in the reservoir, excess developer exceeds the lower height of the second discharge port 13t and is discharged from the second discharge port 13t, and the discharge conveyance path opening 13r. Together with the developer discharged from the container, it is collected in the agent storage container.
In this way, by setting the upper limit of the amount of developer stored in the storage unit, it is possible to suppress a problem that a large amount of developer is supplied from the storage unit toward the first transport path via the return path 13m. Can do.

  In the present embodiment, the discharge transport screw 13k and the return transport screw 13j each have a shaft portion (outer diameter: 2 mm) extending in the longitudinal direction and a spiral shape on the shaft portion. And a wound screw part (outer diameter: 8 mm). Further, the discharge conveying screw 13k and the return conveying screw 13j are both arranged so that the rotation shaft is substantially horizontal, like the three conveying screws 13b1 to 13b3. In this embodiment, the discharge transport screw 13k and the return transport screw 13j are rotationally driven by a drive motor together with the three transport screws 13b1 to 13b3.

  As described above, in the present embodiment, the storage unit that temporarily stores the developer discharged from the discharge port 13d of the first transport path by the first transport screw 13b1, and the developer stored in the storage unit Since a return port 13m1 (return path 13m) for returning a part toward the inside of the first transport path is provided, the volume of the developer flowing in the developing device 13 due to environmental fluctuations is temporarily It is possible to reduce the problem of suddenly decreasing.

In the present embodiment, the discharge port 13d and the return port 13m1 are arranged in the conveyance path by the first conveyance screw 13a1, and the replenishment port 13e is arranged in the conveyance path by the third conveyance screw 13a3. The positions of the discharge port 13d, the return port 13m1, and the supply port 13e are not limited to this.
Moreover, in this Embodiment, although the 3rd conveyance screw 13b3 was arrange | positioned horizontally, the 3rd conveyance screw 13b3 can also be arrange | positioned diagonally with respect to a horizontal direction. Further, the vertical and horizontal positions of the three conveying screws 13b1 to 13b3 are not limited to those in the present embodiment.

  Further, in the present embodiment, a part of the developer discharged from the discharge port 13d of the first transfer path (the developer flowing in the discharge transfer path by the discharge transfer screw 13k) is partly returned. It was comprised so that it could store temporarily in the storage part by the screw 13j. On the other hand, all the developer discharged from the discharge port 13d of the first transport path can also be configured to be temporarily stored in the storage portion by the return transport screw 13j. That is, in the developing device according to the present embodiment, the second discharge port 13t of the storage portion by the return conveyance screw 13j without discharging to the outside from the opening 13r in the discharge conveyance path (without providing the opening 13r). It is also possible to make the discharge to the outside only from the outside so that the discharge conveyance path by the discharge conveyance screw 13k can also function as a storage section. And even if it is such a case, the effect similar to this Embodiment can be acquired.

  In this embodiment, the developer G (toner T and carrier C) is supplied from the agent cartridge 28 serving as the supply unit toward the developing device 13. However, only the carrier C is supplied from the supply unit toward the developing device 13. It can also be supplied. In that case, a toner cartridge containing only toner is installed separately from the agent cartridge (carrier cartridge), and the toner contained in the toner cartridge is developed based on the detection result of the magnetic sensor installed in the developing device 13. It will be replenished appropriately toward 13. Even in such a case, the same effect as in the present embodiment can be obtained.

  Further, in the present embodiment, the present invention is applied to an image forming apparatus in which the developing device 13 is configured as a unit that is detachably attached to the main body of the image forming apparatus. However, the application of the present invention is not limited to this, and the present invention can naturally be applied to an image forming apparatus in which the image forming unit is a process cartridge.

  Further, in the present embodiment, the present invention is applied to the developing device 13 in which three conveying screws as conveying members are installed, but the developing device in which two or four or more conveying screws are installed. The present invention can also be applied. Even in this case, the same effect as that of the present embodiment can be obtained by providing the storage section and the return path 13m as in the present embodiment.

  It should be noted that the present invention is not limited to the present embodiment, and it is obvious that the present embodiment can be modified as appropriate within the scope of the technical idea of the present invention, other than suggested in the present embodiment. is there. In addition, the number, position, shape, and the like of the constituent members are not limited to the present embodiment, and the number, position, shape, and the like suitable for implementing the present invention can be achieved.

1 image forming apparatus body (apparatus body),
11, 11Y, 11C, 11M, 11BK Photosensitive drum (image carrier),
13 Developing device (developing part),
13a Development roller (developer carrier),
13b1 first conveying screw (first conveying member),
13b2 second conveying screw (second conveying member),
13b3 third conveying screw (third conveying member),
13c Doctor blade (developer regulating member),
13d outlet,
13e Supply port,
13f 1st relay part, 13g 2nd relay part, 13h 3rd relay part,
13j return transport screw (return transport member),
13k discharge transport screw (discharge transport member),
13m return path,
13m1 return port, 13m2 inlet port,
13r, 13s opening,
13t second outlet (second outlet),
28 agent cartridge (supply means), 29 supply pipe (supply means),
G developer (two-component developer), T toner, C carrier.

JP 2007-272201 A JP 2008-287155 A

Claims (9)

A developing device that contains a developer having a carrier and toner and that develops a latent image formed on an image carrier,
A developer carrying body facing the image carrying body and carrying a developer;
A plurality of transport members that transport the developer contained in the apparatus in the longitudinal direction to form a circulation path;
Supply means for supplying a new carrier into the apparatus;
In order to discharge the developer to the outside of the conveyance path by the one conveyance member when the developer surface of the developer conveyed by one conveyance member of the plurality of conveyance members exceeds the first predetermined height. A discharge port formed in the partition wall of the transport path by the one transport member;
A reservoir for temporarily storing a part or all of the developer discharged from the discharge port;
When the developer surface conveyed by the conveyance path by the one conveyance member does not reach the second predetermined height, a part of the developer stored in the storage unit is conveyed by the one conveyance member. A return port formed in the partition wall of the transport path by the one transport member to return again toward the inside of the path;
A developing device comprising:   The storage section includes a second discharge port for discharging the developer to the outside of the apparatus when the developer level stored in the developer exceeds a predetermined height. The developing device according to claim 1.   3. The developing device according to claim 1, wherein the first predetermined height is set to be higher than the second predetermined height in the transport path by the one transport member. 4.   The developing device according to claim 1, wherein the return port is disposed upstream of the discharge port in the transport direction in the transport path by the one transport member. The plurality of conveying members are:
A first conveying member facing the developer carrying member and supplying the developer to the developer carrying member while conveying the developer in the longitudinal direction;
The developer that is disposed at a position facing the first transport member through the wall and facing the developer carrier and transports the developer detached from the developer carrier in the longitudinal direction. A second conveying member that
The developer transported by the second transport member is transported to the upstream side of the transport path by the first transport member, and the developer that has reached the downstream side of the transport path by the first transport member is transferred to the first transport member. A third transport member for transporting upstream of the transport path by
Comprising
The developing device according to claim 1, wherein the one transport member is the first transport member.   The developing device according to claim 5, wherein the return port is disposed between a central portion in the longitudinal direction and a downstream side in the transport direction in a transport path by the first transport member.   The developing device according to claim 1, wherein the supply unit newly supplies toner together with the carrier into the apparatus. A process cartridge that is detachably installed on the main body of the image forming apparatus,
8. A process cartridge, wherein the developing device according to claim 1 and the image carrier are integrated.   An image forming apparatus comprising the developing device according to claim 1 and the image carrier.

Images