JP2009192554A - Developing device, process cartridge, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device, a process cartridge and an image forming apparatus, capable of preventing driving torque from increasing and a developer from being leaked out, even when at least two conveying members are installed in a vertical direction, out of the plurality of the members for forming a circulation route of conveying the developer in a longitudinal direction. <P>SOLUTION: The developing device or the like includes the first conveying member 13b1 for supplying the developer G to a developer carrier while conveying the developer G in the longitudinal direction, the second conveying member 13b2 arranged in an under side of the first conveying member 13b1 and for conveying the developer G in the longitudinal direction released from the developer carrier. A conveying route of the second conveying member 13b2 includes an opening 13g for pushing up the developer G reached to a downstream toward an upper conveying route. The conveying route is provided further with a detecting means 13d for detecting an amount of the developer G in the conveying route of the second conveying member 13b2. The second conveying member 13b2 makes the conveying the amount of the developer G variable based on detection results from the detecting means 13d. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, or a multifunction machine thereof, and a developing device and a process cartridge installed therein, and in particular, a developer in a longitudinal direction. The present invention relates to a developing device, a process cartridge, and an image forming apparatus in which at least two transport members among a plurality of transport members that transport and form a circulation path are installed in the vertical direction.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, a developing device that contains a two-component developer composed of a toner and a carrier (including a case where an additive or the like is added), and the developer is long. A technique is known in which at least two conveying members are installed in a vertical direction among a plurality of conveying members that are conveyed in a direction to form a circulation path (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 together with the developer in the developing device by a conveying member (agitating and conveying member) such as a conveying screw. Part of the stirred and mixed developer is supplied to a developing roller (developer carrier). After the developer carried on the developing roller is regulated to an appropriate amount by a doctor blade (developer regulating member), the toner in the two-component developer is a latent image on the photosensitive drum at a position facing the photosensitive drum. Adhere to.

  In the developing device in Patent Document 1 or the like, a first transport member (first agitation transport member) and a second transport member (second agitation transport member) are installed in the vertical direction, and development is performed by these two transport members. This forms a circulation route for the agent. The first conveying member installed above supplies the developer to the developing roller while conveying the developer in the longitudinal direction. The second conveying member installed below conveys the developer separated from the developer roller in the longitudinal direction (the direction opposite to the conveying direction by the first conveying member). The downstream side of the conveyance path (first conveyance path) by the first conveyance member and the upstream side of the conveyance path (second conveyance path) by the second conveyance member communicate with each other through the opening, and upstream of the first conveyance path. The side and the downstream side of the second transport path communicate with each other via an opening (opening). Then, the developer that has reached the downstream side of the second conveyance path (developer that has been separated from the developing roller and collected) remains at that position and is pushed up, and is an opening installed above the second conveyance path. Moved to the upstream side of the first transport path through the section.

In Patent Document 1 or the like, a magnet is provided on the upstream side of the first transport path so that the developer is smoothly transferred from the opening on the downstream side of the second transport path to the upstream side of the first transport path. A technique for installing a member is disclosed.
As described above, the developing device in which the plurality of conveying members are arranged in the vertical direction can make the developing device more compact in the horizontal direction than the developing device in which the plurality of conveying members are arranged in the horizontal direction. Therefore, a tandem type color image forming apparatus in which a plurality of developing devices are arranged in parallel in the horizontal direction is often used.

JP 2003-263012 A

In the developing device described in Patent Document 1 and the like described above, when the amount of developer staying in the vicinity of the opening on the downstream side of the second transport path increases, the load for rotating the second transport member increases. In some cases, the developer leaks from the downstream side of the second transport path.
When the load for rotationally driving the second transport member increases, the driving torque of the developing device may increase and lock. Further, when the developer leaks from the downstream side of the second transport path, the inside of the image forming apparatus becomes dirty, and the amount of developer in the developing apparatus is insufficient, and an abnormal image may be output.

  The present invention has been made to solve the above-described problems, and at least two of the plurality of transport members that transport the developer in the longitudinal direction to form a circulation path are installed in the vertical direction. Even in such a case, it is an object to provide a developing device, a process cartridge, and an image forming apparatus that do not cause an increase in driving torque or leakage of developer.

  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 plurality of conveying members that are opposed to the body and that carry a developer, and a plurality of conveying members that convey the developer contained in the apparatus in the longitudinal direction to form a circulation path. The member faces the developer carrying member and supplies the developer to the developer carrying member while conveying the developer in the longitudinal direction. The member is below the first carrying member and is located below the developing member. A second transport member that is disposed at a position facing the developer carrier and transports the developer detached from the developer carrier in the longitudinal direction, and a transport path by the second transport member is: The current state that reached the downstream side in the transport direction An opening for pushing up the agent toward the upper conveyance path, and further comprising detection means for detecting the amount of developer in the conveyance path by the second conveyance member, wherein the second conveyance member comprises the detection means The developer transport amount is varied based on the detection result.

  According to a second aspect of the present invention, there is provided the developing device according to the first aspect, wherein the developer transport amount is increased or decreased by increasing or decreasing the rotation speed of the second transport member based on the detection result of the detection means. Is variable.

  According to a third aspect of the present invention, in the developing device according to the first or second aspect, the variable control of the developer transport amount by the second transport member is performed in two stages. It is.

  According to a fourth aspect of the present invention, in the developing device according to the first or second aspect, the variable control of the developer transport amount by the second transport member is performed in three or more stages. Is.

  The 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 detecting means is in the vicinity of the opening portion of the transport path by the second transport member. The amount of developer in is detected.

  According to a sixth aspect of the present invention, there is provided the developing device according to the fifth aspect, wherein the detecting means detects whether the developer exceeds a predetermined height in the vicinity of the opening. is there.

  According to a seventh aspect of the present invention, in the developing device according to the fifth aspect, the detection means detects a state in which the developer contacts the upper wall surface of the transport path in the vicinity of the opening. Is.

  Further, in the developing device according to an eighth aspect of the present invention, in the invention according to any one of the first to seventh aspects, the variable control of the developer transport amount by the second transport member is performed by the image carrier. This is performed at the time of non-image without developing the latent image on the body.

  According to a ninth aspect of the present invention, in the development device according to the eighth aspect, the variable control of the developer conveyance amount by the second conveyance member corresponds to a gap between sheets during continuous sheet feeding. It is done with timing.

  In the developing device according to the tenth aspect, in the invention according to the eighth or ninth aspect, the variable control of the developer conveyance amount by the second conveyance member is performed in the image quality adjustment mode. Is.

  The developing device according to an eleventh aspect of the present invention is the developing device according to any one of the first to tenth aspects, wherein the first conveying path is located above the conveying path by the second conveying member. This is a conveyance path by a member.

  A process cartridge according to a twelfth 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 eleventh aspects. The developing device and the image carrier are integrated.

  According to a thirteenth aspect of the present invention, an image forming apparatus includes the developing device according to any one of the first to eleventh 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, even when at least two of the plurality of transport members that transport the developer in the longitudinal direction to form a circulation path are installed in the vertical direction, the second transport disposed below is provided. Since the amount of developer in the path is detected and the developer transport amount in the second transport path is varied based on the detection result, no increase in driving torque or leakage of developer occurs. A developing device, a process cartridge, and an image forming apparatus can be provided.

  Hereinafter, the best mode 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.

Embodiment 1 FIG.
The first embodiment of the present invention will be described in detail with reference to FIGS.
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 is a photosensitive drum as an image carrier on which toner images of each color (yellow, magenta, cyan, black) are formed, 12 is a charging unit that charges the photosensitive drums 11Y, 11M, 11C, and 11BK, 13 Is a developing device for developing an electrostatic latent image formed on each of the photosensitive drums 11Y, 11M, 11C, and 11BK, and 14 is formed on each of the photosensitive drums 11Y, 11M, 11C, and 11BK. A transfer bias roller (primary transfer bias roller) for transferring the toner image superimposed on the recording medium P, and a cleaning unit 15 for collecting untransferred toner on the photosensitive drums 11Y, 11M, 11C, and 11BK. Show.

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, each color toner (toner particles) that supplies toner (toner particles) of each color (yellow, cyan, magenta, black) to the developing device 13 is disposed above each of the photosensitive drums 11Y, 11C, 11M, and 11BK. Each container is installed.

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 rotational 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 after being charged by the charging unit 12.

  Similarly, the laser beam corresponding to the magenta component is irradiated to 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 photosensitive 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 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 toner container 28. 3A is a schematic cross-sectional view (horizontal cross-sectional view) of the upper portion of the developing device 13 (the position of the first transport screw 13b1) in the longitudinal direction, and FIG. 3B is a developing device. It is the schematic sectional drawing which looked at the lower part of 13 (it is a position of the 2nd conveyance screw 13b2) in the longitudinal direction. FIG. 4 is a schematic cross-sectional view (vertical cross-sectional view) of the circulation path of the developing device 13 as viewed in the longitudinal direction. FIG. 5 is a view showing a state where the developer stays on the downstream side of the second transport path shown in FIG.
Since each image forming unit has substantially the same structure and each toner container has almost the same structure, the image forming unit and the toner container 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 photosensitive drum 11 as an image carrier is a negatively charged organic photosensitive member, and is rotated counterclockwise by a rotation driving mechanism (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.

Referring to FIG. 2, toner container 28 contains toner T to be supplied into developing device 13 therein. 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 toner container 28 into the developing device 13.
The supply of the toner T is not limited to the toner density information, but may be 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. Good. Further, the implementation of the supply of the toner T may be determined by combining these different pieces of information.

  The supply pipe 29 is for reliably guiding the toner T supplied from the toner container 28 into the developing device 13. That is, the toner T discharged from the toner container 28 is supplied into the developing device 13 from the supply port 13e (toner supply port) via the supply pipe 29.

Hereinafter, the developing device 13 in the image forming apparatus will be described in detail.
2 to 5, the developing device 13 includes a developing roller 13a as a developer carrying member, conveying screws 13b1 and 13b2 (auger screws) as conveying members, a doctor blade 13c (developer regulating member), and detection. It comprises a height sensor 13d as a means.
The developing roller 13a is configured such that a sleeve formed of a non-magnetic material such as aluminum, brass, stainless steel, conductive resin or the like in a cylindrical shape is rotated clockwise by a rotation driving mechanism (not shown). Referring to FIG. 3, 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. In the first embodiment, the developing roller 13a is rotationally driven at 250 to 300 rotations / minute (rpm).
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.

The two conveying screws 13b1 and 13b2 (conveying members) 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 is in the left direction indicated by the dashed arrow in FIG. 3B).
Then, the second transport screw 13b2 has a second developer G circulated from the downstream side of the transport path by the first transport screw 13b1 via the first relay portion 13f to the upstream side of the transport path by the first transport member 13b1. It conveys via the relay part 13g (it is the conveyance of the left direction shown by the broken-line arrow of FIG. 4 (B)).
The two conveying screws 13b1 and 13b2 are arranged so that the rotation shaft is substantially horizontal, like the developing roller 13a and the photosensitive drum 11. Further, the two conveying screws 13b1 and 13b2 are formed by spirally winding a screw portion around a shaft portion.

In addition, the conveyance path by the 1st conveyance screw 13b1 and the conveyance path by the 2nd conveyance screw 13b2 are isolated by the wall part.
Referring to FIGS. 3 and 4, the downstream side of the conveyance path by the second conveyance screw 13b2 and the upstream side of the conveyance path by the first conveyance screw 13b1 communicate with each other via the second relay part 13g as an opening. is doing. That is, in the second transport path by the second transport screw 13b2, the developer that has reached the downstream side in the transport direction is pushed up toward the upper transport path (the first transport path by the first transport screw 13b1). A second relay portion 13g is provided as an opening. Then, the developer G that has risen and stays in the vicinity of the second relay portion 13g (opening portion) in the transport route (second transport route) by the second transport screw 13b2 passes through the first relay screw 13g. It is transported (supplied) to the upstream side of the transport path by 13b1.
3 and 4, the downstream side of the transport path by the first transport screw 13b1 and the upstream side of the transport path by the second transport screw 13b2 are connected via the first relay portion 13f (opening). Communicate. Then, the developer G that has not been supplied onto the developing roller 13a in the first conveying path by the first conveying screw 13b1 falls by its own weight at the first relay portion 13f and reaches the upstream side of the second conveying path. become.

  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 two conveying screws 13b1 and 13b2. 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 FIGS. 3 and 4. Thus, the developer G supply path (the first transport path by the first transport screw 13a1) to the developing roller 13a and the developer G recovery path (second transport screw) separated from the developing roller 13a. 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 second conveyance screw 13b2. Then, based on the toner density information detected by the magnetic sensor, new toner T is supplied from the toner container 28 into the developing device 13 through the supply port 13e.
3 and 4, the replenishing port 13e is located above the upstream side of the transport path by the second transport screw 13b2 and away from the developing area (in the longitudinal direction of the developing roller 13a). It is outside). In the first embodiment, the replenishment port 13e is disposed in the conveyance path by the second conveyance screw 13a2, but the position of the replenishment port 13e is not limited to this.

Hereinafter, a characteristic configuration and operation of the developing device 13 according to the first embodiment will be described.
Referring to FIG. 4, a height sensor as a detection unit that detects the amount of developer in the second transport path is provided in the second transport path (the transport path by the second transport screw 13 b 2) of the developing device 13. 13d (position sensor) is installed. Specifically, the height sensor 13d is a piezoelectric sensor that detects the amount of developer in the vicinity of the second relay portion 13g (opening portion) in the second transport path, and is in the vicinity of the second relay portion 13g (opening portion). It is detected whether or not the developer G exceeds a predetermined height.
On the other hand, the second conveying screw 13b2 is rotationally driven by a driving unit 75 provided separately from a driving unit that rotationally drives the developing roller 13a and the first conveying screw 13b1. This drive part 75 is a speed change drive part, Comprising: It is comprised so that the rotation speed of the 2nd conveyance screw 13b2 can be varied.
Then, based on the detection result of the height sensor 13d (detection means), the transport amount of the developer in the second transport path is varied by the second transport screw 13b2. Specifically, the detection result of the height sensor 13d (detection means) is sent to the control unit 70, and the speed change drive unit 75 is controlled by the control unit 70, so that the rotation speed of the second transport screw 13b2 is optimized. The More specifically, as shown in FIG. 5, when the developer stays in excess of a predetermined amount in the vicinity of the second relay portion 13g (opening portion) in the second transport path, the state is indicated by a height sensor. Detected at 13d, the rotational speed of the second conveying screw 13b2 is increased compared with the normal time (the state shown in FIG. 4). As a result, the state as shown in FIG. 5 is immediately resolved, and an increase in load when the second conveying screw 13b2 is rotationally driven and leakage of the developer G from the downstream side of the second conveying path are suppressed. Can do.

  Note that the retention of the developer in the vicinity of the second relay portion 13g as shown in FIG. 5 is caused when the toner concentration of the developer G in the developing device 13 is increased and the volume of the developer is increased, or when the humidity is high. This tends to occur when the fluidity of the developer decreases. When the bulk of the developer is increased, the ratio of the developer in the second transport path is increased, so that the developer is liable to stay. Further, when the humidity is high, the flowability of the developer is deteriorated, and the developer conveyed to the downstream side of the second conveyance path is less likely to rise.

Here, the above-described variable control of the developer conveyance amount by the second conveyance screw 13b2 is performed during non-image (when the latent image on the photosensitive drum 11 is not developed). As a result, the linear velocity of the developing roller 13a in the developing region is slightly increased or decreased due to vibration generated when the rotational speed of the second conveying screw 13b2 is increased or decreased, and image density unevenness is generated in the toner image formed on the photosensitive drum 11. It is possible to suppress problems that occur.
Specifically, the variable control of the rotation speed of the second conveying screw 13b2 corresponds to (1) the interval between continuous sheets (between the recording medium P and the recording medium P to be passed next). (2) timing when an image quality adjustment mode such as toner density adjustment and image alignment is performed during warm-up, and (3) timing before and after the toner image is formed on the photosensitive drum 11. It is carried out. After detecting the stay of the developer shown in FIG. 5 by the height sensor 13d, variable control of the rotation speed of the second conveying screw 13b2 is performed at the timing shifted first among the three timings described above. As a result, the state as shown in FIG. 5 is immediately eliminated, and an increase in the load on the second conveyance screw 13b2 and leakage of the developer G from the downstream side of the second conveyance path can be suppressed. In addition, the variable control of the rotation speed of the 2nd conveyance screw 13b2 requires time of 40-200 msec.

6 and 7 are flowcharts showing the variable control of the developer conveyance amount by the second conveyance screw 13b2.
Referring to FIG. 6, first, rotation driving of second conveyance screw 13b2 is started at a low rotation speed (the normal rotation speed is 900 rotations / minute) (step S1). Then, the height sensor 13d (detecting means) detects the height (position) of the developer in the vicinity of the second relay portion 13g in the second transport path (step S2). Specifically, detection by the height sensor 13d is performed every 100 msec after the rotation of the second transport screw 13b2 is started. Then, based on the detection result, it is determined whether or not the developer stays exceeding a predetermined amount in the vicinity of the second relay portion 13g (step S3).

As a result, when it is determined that a large stagnation of the developer has not occurred, the flow after step S2 is repeated. On the other hand, when it is determined that a large stagnation of the developer occurs, 1 is added to the counter N (a counter for stagnation of the agent) of the control unit 70 (step S4).
Thereafter, it is determined whether the counter N of the control unit 70 is equal to or greater than a predetermined value Na (step S5). If the counter N is not greater than or equal to the predetermined value Na, the flow after step S2 is repeated. On the other hand, when the counter N is greater than or equal to the predetermined value Na, the rotation speed of the second conveying screw 13b2 is increased at the next timing (any one of the three timings for the non-image described above). This is performed (step S6). In the first embodiment, the predetermined value Na of the counter N described above is set to “3”.
Thereafter, the counter N of the control unit 70 is reset to 0 (step S7), and the process proceeds to step S9 in FIG.

  Referring to FIG. 7, when the rotation of second conveying screw 13b2 is started at a high rotational speed (1200 revolutions / minute) (step S9), the second conveying is performed by height sensor 13d (detecting means). The height (position) of the developer in the vicinity of the second relay portion 13g in the path is detected (step S10). Specifically, detection by the height sensor 13d is performed every 100 msec after the rotation of the second transport screw 13b2 is started. Then, based on the detection result, it is determined whether a large stagnation of developer has occurred in the vicinity of the second relay portion 13g (step S11).

As a result, when it is determined that the developer stays, the flow after step S10 is repeated. On the other hand, when it is determined that no developer retention has occurred, 1 is added to the counter M (a counter for agent retention) of the control unit 70 (step S12).
Thereafter, it is determined whether the counter M of the control unit 70 is equal to or greater than a predetermined value Ma (step S13). If the counter M is not greater than or equal to the predetermined value Ma, the flow after step S10 is repeated. On the other hand, when the counter M is equal to or greater than the predetermined value Ma, the rotational speed of the second conveying screw 13b2 is decelerated at the next timing (any one of the three timings at the time of non-image described above). (Step S14). In the first embodiment, the predetermined value Ma of the counter M described above is set to “2”.
Thereafter, the counter M of the control unit 70 is reset to 0 (step S15), and the process proceeds to step S1 in FIG.

FIG. 8 is a graph showing the relationship between the number of rotations of the second transport screw 13b2 and the developer pumping amount in the second relay portion 13g (opening). Here, the developer pumping amount shown on the vertical axis of the graph is the amount of developer G pushed up from the downstream side of the second transport path to the upstream side of the first transport path via the second relay portion 13g in a predetermined time. It is.
As shown in FIG. 8, as the rotation speed of the second transport screw 13b2 is set larger, the developer pumping amount in the second relay portion 13g (opening) increases, and the developer near the second relay portion 13g. Is less likely to occur. However, if the rotational speed of the second transport screw 13b2 is set too large, (1) the bearing of the second transport screw 13b2 generates heat and toner solidification is likely to occur. (2) the amount of developer in the second transport path (3) The bearing of the second conveying screw 13b2 is worn, (4) Stress on the developer is increased, and the lifetime of the developer is increased. Inconveniences such as shortening (5) the balance of the developer in the first transport path and the second transport path may be lost. In particular, in the case of (1), the second conveying screw 13b2 is locked by the solidified toner, or the solidified toner is sandwiched between the developing roller 13a and the doctor blade 13c, and there is a toner supply defect in that portion. This may cause a white streak image. In the case of (2), the toner is insufficiently frictionally charged, resulting in toner scattering and a background smear image.
In the first embodiment, the rotation speed of the second conveying screw 13b2 during high-speed rotation is set to 1200 rotations / minute so that the above-described problems do not occur. In addition, when the rotation speed of the 2nd conveyance screw 13b2 was increased from 900 rotation / min to 1200 rotation / min, the temperature rise of the bearing of the 2nd conveyance screw 13b2 was settled in about 3 degree | times.

FIG. 9 is a graph showing conditions under which the developer does not leak from the downstream side of the second transport path.
In FIG. 9, the horizontal axis indicates the rotational speed of the developing roller 13a, and the vertical axis indicates the rotational speed of the second transport screw 13b2. A range indicated by a broken line in FIG. 9 (a range in the arrow direction with respect to the graph) is a range in which the developer does not leak from the downstream side of the second transport path. That is, when the rotation speed of the developing roller 13a is increased, the developer is transferred from the first conveyance path to the second conveyance path, so that the rotation speed of the second conveyance screw 13b2 needs to be set large. In the first embodiment, since the rotation speed of the developing roller 13a is set to 200 to 300 rotations / minute, the rotation speed of the second conveying screw 13b2 at the low speed rotation is set to 900 rotations / minute. . The rotation speed of the first conveying screw 13b1 is set to 900 rotations / minute (fixed value).

In the first embodiment, a speed change drive unit 75 (speed change drive motor) that drives only the second transport screw 13b2 is installed to variably control the rotation speed (developer transport amount) of the second transport screw 13b2. Are performed in two stages (low speed and high speed). On the other hand, when performing variable control of the rotation speed (developer transport amount) of the second transport screw 13b2 using the speed change clutch, the configuration of the entire drive system of the developing device 13 is relatively simplified. Can do.
In addition, variable control of the rotation speed (developer transport amount) of the second transport screw 13b2 can be performed in three or more stages. In this case, the balance of the developer in the circulation path can be controlled more optimally.

  In the first embodiment, the developer transport amount in the second transport path is varied by increasing / decreasing the rotation speed of the second transport screw 13b2, but the screw diameter and screw pitch of the second transport screw 13b2 are variable. It is also possible to change the developer conveyance amount in the second conveyance path by the variable control.

  As described above, in the first embodiment, even when the two conveying screws 13b1 and 13b2 (conveying members) that convey the developer in the longitudinal direction to form a circulation path are installed in the vertical direction, Since the developer amount in the second transport path disposed below is detected and the developer transport amount in the second transport path is varied based on the detection result, the driving torque of the developing device 13 Rise and developer leakage can be suppressed.

Embodiment 2. FIG.
A second embodiment of the present invention will be described in detail with reference to FIG.
FIG. 10 is a cross-sectional view showing the developing device in the second embodiment, and corresponds to FIG. 4 in the first embodiment. The developing device according to the second embodiment is different from that of the first embodiment in the configuration of the detection unit that detects the amount of developer in the second transport path.

  Referring to FIG. 10, the developing device 13 according to the second embodiment also has a developing roller 13a (developer carrier), two conveying screws 13b1 and 13b2 (conveying members), a doctor, as in the first embodiment. The blade 13c and the like are configured. The two conveying screws 13b1 and 13b2 are arranged in the vertical direction to form a developer circulation path.

Here, in the second embodiment, the pressure sensor 13h as the detecting means is in a state where the developer contacts the upper wall surface of the second transport path in the vicinity of the second relay part 13g (opening) of the second transport path. Is detected. Specifically, when the pressure detected by the pressure sensor 13h exceeds a predetermined value, it is determined that the developer stays in excess of a predetermined amount in the vicinity of the second relay portion 13g.
Then, based on the detection result of the pressure sensor 13h (detection means), the rotational speed of the second transport screw 13b2 is optimized as in the first embodiment. As a result, the state as shown in FIG. 5 is immediately eliminated, and an increase in the load on the second conveyance screw 13b2 and leakage of the developer G from the downstream side of the second conveyance path can be suppressed.

  In the second embodiment, the retention of the developer is detected based on the pressure detected by the pressure sensor 13h. However, the developer contacts the upper wall surface of the second transport path in the vicinity of the second relay portion 13g. It is also possible to detect the stagnation of the developer by detecting the size of the area to be developed. Furthermore, by using a resistance detection sensor instead of the pressure sensor, a change in the resistance of the developer G is detected and a change in the amount of the carrier C having resistance is detected, so that the developer moves on the second transport path. It is also possible to detect a state in contact with the wall surface.

  As described above, in the second embodiment, similarly to the first embodiment, the two conveying screws 13b1 and 13b2 (conveying members) that convey the developer in the longitudinal direction to form a circulation path are moved in the vertical direction. Even in the case where it is installed, the amount of developer in the second transport path disposed below is detected, and the transport amount of developer in the second transport path is varied based on the detection result. Therefore, an increase in driving torque of the developing device 13 and leakage of the developer can be suppressed.

  In each of the above embodiments, the detection unit is installed in the vicinity of the second relay unit 13g to detect the amount of developer in the second transport path, but the detection unit is installed at a position away from the second relay unit 13g. Then, when the amount of developer in the second transport path can be detected (for example, when the developer near the second relay portion 13g can be expected at the upstream position), the detecting means is provided at that position. It can also be installed.

  In each of the above embodiments, the toner T is supplied from the toner container 28 toward the developing device 13. However, the developer G (toner T and carrier C) is directed toward the developing device 13 from the toner container (developer container). Can also be supplied. In that case, a means for appropriately discharging excess developer from the developing device 13 is provided. Even in such a case, it is possible to obtain the same effects as those of the above embodiments.

  In each of the above embodiments, 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 a part or all of the image forming unit is formed as a process cartridge.

  Further, in each of the above embodiments, the present invention is applied to the developing device 13 in which two conveying screws as conveying members are installed. However, three or more conveying screws are installed, and at least two conveying screws are included. The present invention can also be applied to a developing device in which is installed in the vertical direction. Also in that case, each of the above-described embodiments is obtained by detecting the amount of the developer in the second conveyance path disposed below and varying the conveyance amount of the developer in the second conveyance path based on the detection result. The same effect can be obtained.

  It should be noted that the present invention is not limited to the above-described embodiments, and within the scope of the technical idea of the present invention, the embodiments can be modified as appropriate in addition to those suggested in the embodiments. Is clear. In addition, the number, position, shape, and the like of the constituent members are not limited to the above embodiments, and can be set to a number, position, shape, and the like that are suitable for carrying out the present invention.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 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 the schematic sectional drawing which looked at the circulation path of the developing device in the longitudinal direction. FIG. 6 is a diagram illustrating a state where developer stays on the downstream side of a second transport path. 10 is a flowchart illustrating variable control of a developer conveyance amount by a second conveyance member. It is a flowchart following FIG. 6 is a graph showing the relationship between the number of rotations of a second conveying member and the amount of developer pumped at an opening. It is a graph which shows the conditions where a developer does not leak from the downstream of the 2nd conveyance path. It is sectional drawing which shows the developing device in Embodiment 2 of this invention.

Explanation of symbols

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),
13c doctor blade,
13d height sensor (detection means),
13e Supply port,
13f 1st relay part,
13g 2nd relay part (opening part),
13h Pressure sensor (detection means),
28 toner container, P recording medium,
G developer (two-component developer), T toner, C carrier.

Claims (13)

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;
With
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;
A second conveying member disposed below the first conveying member and facing the developer carrying member and conveying the developer detached from the developer carrying member in the longitudinal direction;
Comprising
The transport path by the second transport member includes an opening for pushing the developer that has reached the downstream side in the transport direction toward the upper transport path,
Further comprising a detecting means for detecting the amount of the developer in the transport path by the second transport member,
The developing device according to claim 1, wherein the second transport member varies a transport amount of the developer based on a detection result of the detection unit.   The developing device according to claim 1, wherein the developer conveyance amount is varied by increasing or decreasing the rotation speed of the second conveyance member based on a detection result of the detection unit.   The developing device according to claim 1, wherein the variable control of the developer conveyance amount by the second conveyance member is performed in two stages.   The developing device according to claim 1, wherein the variable control of the developer transport amount by the second transport member is performed in three or more stages.   5. The developing device according to claim 1, wherein the detection unit detects the amount of the developer in the vicinity of the opening of the conveyance path by the second conveyance member.   The developing device according to claim 5, wherein the detection unit detects whether the developer exceeds a predetermined height in the vicinity of the opening.   The developing device according to claim 5, wherein the detection unit detects a state in which the developer contacts the upper wall surface of the transport path in the vicinity of the opening.   8. The variable control of the developer transport amount by the second transport member is performed during a non-image time when the latent image on the image carrier is not developed. The developing device described.   The developing device according to claim 8, wherein the variable control of the developer conveyance amount by the second conveyance member is performed at a timing corresponding to the interval between continuous sheets.   The developing device according to claim 8, wherein the variable control of the developer transport amount by the second transport member is performed in an image quality adjustment mode.   The developing device according to claim 1, wherein the transport path above the transport path by the second transport member is a transport path by the first transport member. A process cartridge that is detachably installed on the main body of the image forming apparatus,
12. 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