JP5483088B2 - Developing device, process cartridge, and image forming apparatus - Google Patents

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 Document 1).

  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. Note that the rotation of the developing roller and the conveying member is performed by a single drive source together with the rotation of the photosensitive 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 Document 1 and the like disclose a developing device using a premix developing method, which uses an overflow method as means for discharging 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.

  On the other hand, conventionally, in a case where an image forming apparatus such as a copying machine or a printer passes a thick sheet or an OHP sheet as a recording medium, in order to obtain a sufficient fixing property, the recording medium conveyance speed (process) There is known a technique of switching to a low speed mode (special paper mode) in which an image forming process is performed by reducing a linear speed (see, for example, Patent Document 2).

  In the above-described premix developing type developing device such as Patent Document 1, the developing roller and the conveying screw are rotationally driven in synchronism with the rotational driving of the photosensitive drum. When it is varied, the rotational speed of the transport screw is also varied, and there is a problem that the amount of developer discharged from the developing port to the outside of the developing device varies. For this reason, the amount of developer circulating in the developing device also varies, resulting in an abnormal image such as a decrease in image density or uneven image density.

  The present invention has been made to solve the above-described problems, and even when the process linear velocity is varied, the amount of developer discharged from the developing device to the outside of the developing device varies. It is an object of the present invention to provide a premix developing type 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 unit that supplies the developer, and when the developer surface of the developer conveyed by one of the plurality of conveying members exceeds a predetermined height, the developer is placed outside the conveying path of the one conveying member. The discharge port formed in the partition wall of the transport path by the one transport member for discharging, the first drive unit that drives the developer carrier, and the first drive unit are provided separately from the plurality of The transport member Comprising a second driving unit, a to said first driving unit, in synchronization with the drive start and drive stop of the image bearing member performs a drive start and drive stop of the developer carrying member, said second driving unit When the rotation speed of the image carrier is set high, the drive time of the plurality of conveying members is shortened compared to the drive time of the developer carrier, and the rotation speed of the image carrier is set low. In this case, the driving time of the plurality of conveying members is made longer than the driving time of the developer carrier.

According to a second aspect of the present invention, in the developing device according to the first aspect, the driving time of the plurality of conveying members by the second driving unit is adjusted during a non-developing process. is there.

According to a third aspect of the present invention, there is provided the developing device according to the first or second aspect , wherein the plurality of conveying members are opposed to the developer carrier and have the developer in the longitudinal direction. A first conveying member that supplies developer to the developer carrying member while being conveyed, and a position that faces the first conveying member through a wall and that faces the developer carrying member. A second conveying member that is installed and conveys the developer released from the developer carrying member in the longitudinal direction; and the developer conveyed by the second conveying member on the upstream side of the conveying path by the first conveying member And 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, the one transport The first conveying member It is obtained by a wood.

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

A process cartridge according to a fifth aspect of the present invention is a process cartridge that is detachably installed on the main body of the image forming apparatus, and the developing device according to any one of the first to fourth aspects. And the image carrier.

An image forming apparatus according to a sixth aspect of the invention includes the developing device according to any one of the first to fourth 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.

  In the present invention, since the second drive unit that drives the plurality of conveying members is provided separately from the first drive unit that drives the developer carrier, even if the process linear velocity is varied, the discharge is performed. It is possible to provide a premix developing type developing device, a process cartridge, and an image forming apparatus in which there is no variation in the amount of developer discharged from the outlet to the outside of the developing device.

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. It is a perspective view which shows a developing device. (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. It is sectional drawing which shows the vicinity of the supply port of a developing device. It is sectional drawing which shows the vicinity of opening of the conveyance path | route for discharge | emission. It is a figure which shows drive control of a developing roller and a conveyance screw when a process linear velocity is varied. 4 is a graph showing a relationship between toner density and bulk density of a developer stored in a developing device. 6 is a graph showing the relationship between the number of rotations of a transport screw and the capacity of a developer stored in a developing device. It is a figure which shows another drive control of a developing roller and a conveyance screw when process linear velocity is changed.

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. FIG. 3 is a perspective view showing the developing device. 4A is a schematic cross-sectional view of the upper portion of the developing device 13 (the positions of the first conveying screw 13b1 and the discharging conveying screw 13k) in the longitudinal direction, and FIG. It is the schematic sectional drawing which looked at the lower part (it is a position of the 2nd conveyance screw 13b2 and the 3rd conveyance screw 13b3) in the longitudinal direction. 5 is a cross-sectional view showing the vicinity of the third relay portion 13h of the developing device 13, FIG. 6 is a cross-sectional view showing the vicinity of the discharge port 13d of the developing device 13, and FIG. 7 is a replenishing port 13e of the developing device 13. FIG. 8 is a cross-sectional view showing the vicinity of the opening 13r of the discharge transport path.
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.
The photoconductor drum 11 as an image carrier is a negatively charged organic photoconductor, and is driven to rotate counterclockwise by a first drive unit 41 (first drive motor). The first drive unit 41 is connected to the drive gear of the developing roller 13a through a gear train (not shown), and also rotates the developing roller 13a together with the photosensitive drum 11.

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 system, and a new carrier C (developer G) is appropriately supplied from the agent cartridge 28 into the developing device 13 and deteriorated. The developer G thus discharged is discharged toward a agent storage container (not shown) through a discharge path 70 (see FIG. 4) 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 8, the developing device 13 includes a developing roller 13a as a developer carrier, conveying screws 13b1 to 13b3 (auger screws) as conveying members, a doctor blade 13c as a developer regulating member, discharge It is comprised by the discharge conveyance screw 13k etc. as a conveyance member.
The developing roller 13a has an outer diameter of 25 mm, and a sleeve formed of a non-magnetic material such as aluminum, brass, stainless steel, or conductive resin in a cylindrical shape is watched by a first drive unit 41 (first drive motor). It is configured to be rotated in the direction. 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 installed on the upstream side of the developing area, and regulates the developer G on the developing roller 13a to an appropriate amount.
In the present embodiment, a cooling unit 13n is installed in the vicinity of the doctor blade 13c. The cooling unit 13n is a hollow structure in which a plurality of fins are provided, and air is sent into the inside from a fan (not shown). As a result, the temperature rise of the doctor blade 13c made of a metal material is reduced (air-cooled), and toner sticking to the doctor blade 13c and the developing roller 13a is suppressed.

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 (rotational axis direction) (see FIG. 4A). In addition, the developer G is supplied onto the developing roller 13a (in the direction of the white arrow in FIG. 4A).

  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. 4B). Is transported horizontally in the longitudinal direction (the transport is in the right direction indicated by the broken arrow in FIG. 4B).

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. 4B).
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. Each of the three conveying screws 13b1 to 13b3 is connected to a second drive unit 42 (second drive motor) via a gear train (not shown), and each second drive unit 42 has a predetermined direction. Is driven to rotate.

In addition, the conveyance path by the 1st conveyance screw 13b1, the conveyance path by the 2nd conveyance screw 13b2, the conveyance path by the 3rd conveyance screw 13b3, the conveyance path for discharge by the discharge conveyance screw 13k (discharge conveyance member), Are isolated by a partition (wall).
Referring to FIG. 4B, 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 unit 13g. Also, referring to FIGS. 4A and 4B, the downstream side of the transport path by the first transport screw 13b1 and the upstream side of the transport path by the third transport screw 13b3 are the first relay portion 13f. It communicates through. 4A, FIG. 4B, and FIG. 5, 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. 5, the developer G staying and rising in the vicinity of the third relay portion 13h in the transport route by the third transport screw 13b3 is transported by the first transport screw 13b1 via the third relay portion 13h. 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 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.
3, 4B, and 7, the replenishment port 13e is located upstream of the upstream side of the transport path by the third transport screw 13b3 and away from the development area (the development roller 13a). Outside the range in the longitudinal direction.).

Here, referring to FIG. 2, FIG. 4A, and FIG. 6, a part of the developer G accommodated in the developing device 13 is placed outside the transport path on the partition wall of the transport path by the first transport screw 13b1. A discharge port 13d for discharging 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 developer surface (upper surface) exceeds a predetermined height, the excess developer G is discharged toward the discharge conveyance path (the discharge conveyance screw 13k is installed). is there. The developer discharged from the discharge port 13d is transported in the longitudinal direction (the left direction in FIG. 4A) by the discharge transport screw 13k and falls by its own weight from the opening 13r (also see FIG. 8). Then, after being discharged out of the apparatus (discharge path 70), it is recovered into the agent storage container (not shown) via the discharge path 70. That is, the excess developer G exceeds the height below the discharge port 13 d, is discharged from the discharge port 13 d, and stores the agent via the discharge conveyance path (discharge conveyance screw 13 k) and the discharge path 70. It is transported toward the container. 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 70 is connected to all the discharge conveyance paths of the developing devices 13 for each color (four), and the developer discharged from each developing device 13 is collected together in the agent storage container.

  In addition, the conveyance path by the 1st conveyance screw 13b1 in this Embodiment is the vicinity of the discharge port 13d, and the ceiling part 13m adjacent to the 1st conveyance screw 13b1 is installed above the 1st conveyance screw 13b1. . Specifically, referring to FIG. 2, FIG. 4 (A), and FIG. 6, the ceiling portion 13m is opposed to narrow the gap above the first conveying screw 13b1 (screw portion) in the vicinity of the discharge port 13d. The surface is formed in an arc shape following the outer diameter shape of the screw portion of the first conveying screw 13b1. As a result, in the vicinity of the discharge port 13d, the developer surface (upper surface) of the developer is increased by the gap narrowed by the ceiling portion 13m. Accordingly, excess developer is discharged from the discharge port 13d located at a position higher than the rotation center of the first transport screw 13b1. Note that the gap amount and the longitudinal range between the ceiling portion 13m and the first conveying screw 13b1 can be determined based on the results of experiments so that the amount of developer discharged from the discharge port 13d is optimized.

  In addition, the discharge conveying screw 13k in the present embodiment has a shaft portion (outer diameter: 2 mm) extending in the longitudinal direction and a screw portion (outer diameter: spirally wound around the shaft portion). 8 mm). Further, similarly to the three transport screws 13b1 to 13b3, the discharge transport screw 13k is disposed so that the rotation shaft is substantially horizontal. And in this Embodiment, the conveyance screw 13k for discharge is also rotationally driven by the 2nd drive part 42 with the three conveyance screws 13b1-13b3.

Here, referring to FIG. 2, in the present embodiment, apart from the first drive unit 41 (first drive motor) that rotationally drives the developing roller 13 a (developer carrier), a plurality of transport screws 13 b 1 to 13 b 1. A second drive unit 42 (second drive motor) that rotationally drives 13b3 (conveyance member) is provided.
In addition, the image forming apparatus 1 in the present embodiment is configured to be able to vary the process linear speed (same speed as the conveyance speed of the recording medium P) automatically or manually. Specifically, the “medium speed mode” is normally set, and the process linear speed (the rotational speed of the photosensitive drum 11 and the traveling speed of the intermediate transfer belt 17) and the conveyance speed of the recording medium P are set to the medium speed. Is done. The “low speed mode” is selected automatically or manually when a thick paper or an OHP paper is passed as the recording medium P, and the process linear speed and the conveyance speed of the recording medium P are set to a low speed. The The “high speed mode” is selected automatically or manually when a thin paper is passed as the recording medium P or when it is desired to increase the productivity of the output image. Is set to a high speed. Such mode switching can be configured so that the user can manually select the mode manually according to the user's preference, or can be automatically selected based on the detection result of the paper thickness sensor or the like. It can also be configured.

Here, the first drive unit 41 is configured to increase or decrease the rotation number of the developing roller 13a in synchronization with increase or decrease of the rotation number (or process linear speed) of the photosensitive drum 11. In the present embodiment, the first drive unit 41 is configured to rotate the developing roller 13a together with the photosensitive drum 11, and therefore necessarily has the above-described configuration.
Specifically, as shown in FIG. 9, in the high speed mode, the rotation speeds of the photosensitive drum 11 and the developing roller 13a are set to A1 and B1, respectively, and in the medium speed mode, the rotation of the photosensitive drum 11 and the developing roller 13a. The numbers are set to A2 and B2, respectively, and in the low speed mode, the rotation speeds of the photosensitive drum 11 and the developing roller 13a are set to A3 and B3, respectively (A1>A2> A3, B1>B2> B3).
On the other hand, the second drive unit 42 is configured to keep the rotation speeds of the plurality of conveying screws 13b1 to 13b3 constant regardless of increase or decrease of the rotation speed (or process linear velocity) of the photosensitive drum 11. Has been. Since the second drive unit 42 is an independent drive source that is different from the first drive unit 41, the rotational speeds of the transport screws 13b1 to 13b3 can be independently controlled regardless of the variable process linear velocity. .
Specifically, as shown in FIG. 9, the rotation speed of the conveying screws 13b1 to 13b3 is set to a constant speed C in any of the high speed mode, the medium speed mode, and the low speed mode.

  As a result, even when the process linear speed is varied (when the high speed mode, the medium speed mode, or the low speed mode is selected), the process is discharged from the discharge port 13d to the outside of the developing device 13. It is possible to reliably reduce a problem that the amount of developer (or the amount of developer accommodated in the developing device 13) varies.

FIG. 10 is a graph showing the relationship between the toner density and the bulk density of the developer G accommodated in the developing device 13.
In the present embodiment, the above-described magnetic sensor is used to control the developer G contained in the developing device 13 so that the toner concentration is 5 to 9 wt%. At this time, the bulk density of the developer G accommodated in the developing device 13 is 1.75 to 1.55 g / ml. As described above, the developer G in the developing device 13 has some variation in the bulk density depending on the toner concentration.

FIG. 11 is a graph showing the relationship between the number of rotations of the transport screws 13b1 to 13b3 and the capacity of the developer G accommodated in the developing device 13 when the developing device 13 in this embodiment is operated for a predetermined time. is there.
From FIG. 11, when the number of rotations of the conveying screws 13b1 to 13b3 increases, the amount of developer staying in the vicinity of the discharge port 13d increases (the level of the developer G increases) and is discharged from the discharge port 13d. It can be seen that the amount of developer G contained in the developing device 13 (developer amount) decreases because the amount of developer to be increased increases. On the other hand, when the number of rotations of the transport screws 13b1 to 13b3 is decreased, the amount of the developer staying in the vicinity of the discharge port 13d is reduced (the level of the developer G is lowered) and discharged from the discharge port 13d. It can be seen that the amount of developer G contained in the developing device 13 (developer amount) increases because the amount of developer to be developed decreases.

Therefore, as in the case of a conventional developing device, if the rotational speed of the transport screws 13b1 to 13b3 increases or decreases as the process linear speed increases or decreases, the amount of developer discharged from the discharge port 13d (or accommodated in the developing device 13). Variation in the amount of developer produced). When the developer amount stored in the developing device 13 is too small, problems such as image density reduction and image density unevenness occur. When the developer amount stored in the developing device 13 is excessive, developer leakage or developer occurs. Problems such as conveyance failure will occur.
On the other hand, in the present embodiment, since the rotation speed of the transport screws 13b1 to 13b3 is set to the constant speed C in any of the high speed mode, the medium speed mode, and the low speed mode, the discharge port 13d. Therefore, it is possible to reliably reduce a problem that the amount of developer discharged from the developing device 13 to the outside (or the amount of developer accommodated inside the developing device 13) varies.

  In the present embodiment, the rotation speed of the developing roller 13a is increased or decreased in accordance with the process line speed in any of the high speed mode, the medium speed mode, and the low speed mode. Therefore, the linear speed ratio of the developing roller 13a to the photosensitive drum 11 can be kept constant. Therefore, the developing ability in the developing region is maintained constant regardless of the process linear speed, and the same developing ability can be exhibited in any of the high speed mode, the medium speed mode, and the low speed mode.

In the present embodiment, the rotation speed of the conveying screws 13b1 to 13b3 is controlled by the second driving section 42 provided separately from the first driving section 41 that rotationally drives the developing roller 13a regardless of the variable process linear speed. Is configured to be constant.
On the other hand, the driving time of the conveying screws 13b1 to 13b3 is varied by the second driving unit 42 provided separately from the first driving unit 41 that rotationally drives the developing roller 13a according to the variable process linear velocity. It can also be configured.

Specifically, as shown in FIG. 12, the first drive unit 41 is configured to start and stop driving of the developing roller 13a in synchronization with the start and stop of driving of the photosensitive drum 11. Since the first drive unit 41 rotates the developing roller 13a together with the photosensitive drum 11, the first drive unit 41 necessarily has the above-described configuration.
Specifically, in any mode, the photosensitive drum 11 and the developing roller 13a are rotationally driven by the first driving unit 41 at the same timing and for the same driving time.

On the other hand, the second drive unit 42 has a plurality of conveying screws 13b1 to 13b3 that are compared with the driving time of the developing roller 13a when the rotational speed (or process linear speed) of the photosensitive drum 11 is set high. When the driving time is shortened and the rotational speed (or process linear velocity) of the photosensitive drum 11 is set low, the driving time of the plurality of conveying screws 13b1 to 13b3 is increased as compared with the driving time of the developing roller 13a. It is configured as follows.
Specifically, in the medium speed mode, the plurality of conveying screws 13b1 to 13b3 are rotationally driven by the second driving unit 42 for the same driving time as the developing roller 13a (and the photosensitive drum 11).
In the high speed mode, the plurality of transport screws 13b1 to 13b3 are rotationally driven by the second drive unit 42 shorter by Δt1 time than the driving time of the developing roller 13a (and the photosensitive drum 11). As a result, even if the number of rotations of the plurality of conveying screws 13b1 to 13b3 increases in the high-speed mode, it is discharged from the discharge port 13d to the outside of the developing device 13 as much as the driving time is shortened by Δt1 time. The amount of developer can be reduced.
Further, in the low speed mode, the plurality of transport screws 13b1 to 13b3 are rotationally driven by the second drive unit 42 longer by Δt2 hours than the drive time of the developing roller 13a (and the photosensitive drum 11). As a result, even if the number of rotations of the plurality of conveying screws 13b1 to 13b3 becomes low in the low speed mode, it is discharged from the discharge port 13d to the outside of the developing device 13 as much as the driving time is increased by Δt2. The amount of developer can be increased.

  As a result, even when the process linear speed is varied (when the high speed mode, the medium speed mode, or the low speed mode is selected), the process is discharged from the discharge port 13d to the outside of the developing device 13. It is possible to reliably reduce a problem that the amount of developer (or the amount of developer accommodated in the developing device 13) varies.

The adjustment of the driving time of the plurality of transport screws 13b1 to 13b3 by the second drive unit 42 described above is preferably performed during the non-development process in consideration of the influence on the development process. Specifically, as shown in FIG. 12, in both the high speed mode and the low speed mode, the driving start of the transport screws 13b1 to 13b3 is synchronized with the driving start of the developing roller 13a, and the entire driving is adjusted by adjusting the driving stop timing. By increasing / decreasing the driving time, it is possible to prevent a problem that toner charging failure due to insufficient stirring of the developer G due to insufficient driving time of the conveying screws 13b1 to 13b3 before the developing process.
In the embodiment shown in FIG. 12, the control (the control described in FIG. 9) for making the rotation speed of the transport screws 13b1 to 13b3 constant regardless of the increase or decrease in the process linear velocity can be used together. .

  As described above, in the present embodiment, in addition to the first driving unit 41 that drives the developing roller 13a (developer carrier), the second driving that drives the plurality of conveying screws 13b1 to 13b3 (conveying members). Since the portion 42 is provided, even when the process linear velocity is varied, it is possible to reliably reduce the problem that the amount of developer discharged from the discharge port 13d to the outside of the developing device 13 varies. .

In the present embodiment, the discharge port 13d is disposed in the conveyance path by the first conveyance screw 13a1, and the replenishment port 13e is disposed in the conveyance path by the third conveyance screw 13a3. The position of the supply port 13e is 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.

  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. Also in this case, a second drive unit that drives a plurality of transport screws (conveyance members) is provided separately from the first drive unit that drives the developing roller 13a, and these drive units are provided according to variations in the process linear velocity. By controlling optimally, the same effect as this embodiment can be obtained.

  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,
13k discharge transport screw (discharge transport member),
13m ceiling part, 13n cooling part,
13r opening,
28 agent cartridge (supply means), 29 supply pipe (supply means),
41 1st drive part,
42 second drive unit,
70 discharge route, P recording medium,
G developer (two-component developer), T toner, C carrier.

JP 2007-272201 A JP 2002-166593 A

Claims (6)

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 surface of the developer conveyed by one conveyance member exceeds a predetermined height among the plurality of conveyance members. A discharge port formed in the partition wall of the transport path by one transport member;
A first drive unit for driving the developer carrying member;
A second driving unit that is provided separately from the first driving unit and drives the plurality of conveying members;
Equipped with a,
The first drive unit starts / stops driving of the developer carrier in synchronization with the start / stop of driving of the image carrier,
The second driving unit shortens the driving time of the plurality of transport members when compared with the driving time of the developer carrier when the rotational speed of the image carrier is set high. A developing device characterized in that when the number of rotations is set low, the driving time of the plurality of conveying members is made longer than the driving time of the developer carrier. The developing device according to claim 1, wherein the adjustment of the driving time of the plurality of conveying members by the second driving unit is performed during a non-developing process. 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 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,
5. A process cartridge in which 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