JP2006039250A - Developing device, process cartridge and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device designed such that developer separated from the surface of a developer carrier by an agent separating pole is prevented from being scooped onto the developer carrier by a scooping pole right after the separation and satisfactory, stable image quality is assured, and to provide a process cartridge and an image forming apparatus. <P>SOLUTION: The developer carrier 23a incorporates a magnet body used to form the agent separating pole B4 on the circumferential face of the developer carrier 23a so that developer passed through a position opposite an image carrier 21 is separated from the developer carrier 23a. The developer carrier 23a is constructed such that the rotation center of a conveying member 23b is disposed on the side where the developer carrier 23a passes through the middle position B4 having, as a boundary, a vertical line Y1 passing through the middle of the agent separating pole B4 on the circumferential face of the developer carrier 23a. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a developing device that develops a latent image formed on an image carrier, and a process cartridge and an image forming device including the developing device, and in particular, a developing device that uses a two-component developer, a process cartridge, and The present invention relates to an image forming apparatus.

Conventionally, in an image forming apparatus using an electrophotographic method such as a copying machine, a printer, a facsimile machine, or a combination machine thereof, a two-component developer composed of toner and a magnetic carrier (in some cases, an external additive or the like is added). In many cases, a developing device containing the above is used.
In such a two-component developing type developing device, a technique for supplying the developer to the developing roller while circulating the developer in the longitudinal direction of the developing device by a conveying screw is known for the purpose of downsizing the device. (For example, refer to Patent Document 1).

Specifically, the developing device includes a developing roller, two conveying screws, a doctor blade, and the like.
Then, according to toner consumption in the developing device, toner is appropriately supplied into the device from a toner supply port provided at one end of the developing device. The replenished toner is mixed with the developer in the developing device while being circulated in the longitudinal direction (the same direction as the longitudinal direction of the developing roller) by the two conveying screws. A part of the mixed developer is carried on the developing roller by a pumping pole formed on the developing roller facing one conveying screw. After the developer carried on the developing roller is regulated to an appropriate amount by the doctor blade, the toner in the developer adheres to the latent image on the photosensitive drum at a position facing the photosensitive drum (image carrier). . After that, the developer on the developing roller that has passed the position facing the photosensitive drum is detached from the developing roller at the position where the agent runs out, and returned to the developing device again.

  Since the developing device equipped with such a conveying screw positively conveys the developer in the longitudinal direction of the device, the deviation of the developer in the longitudinal direction is unlikely to occur. Thereby, the toner replenishing port can be provided at one end in the longitudinal direction instead of being provided in the entire region in the longitudinal direction. Further, the conveying screw does not require much installation space in the short direction (the direction perpendicular to the longitudinal direction). Therefore, the developing device and the image forming apparatus can be reduced in size.

  On the other hand, Patent Document 2 and the like disclose a technique for reliably detaching the developer on the developing roller at the position of the agent breakage pole. Specifically, the magnetic force acting on the developer on the developing roller is set to be smaller than the sum of gravity and centrifugal force. This prevents the developer on the developing roller from being mixed with the developer pumped up by the pumping electrode without being detached at the agent breakage pole.

JP 2000-194194 A Japanese Patent Laid-Open No. 5-249821

  The conventional technology described above may cause a problem that the developer detached from the developing roller due to the shortage of the agent is not circulated in the apparatus and is immediately pumped onto the developing roller by the pumping electrode. was there.

  This occurs when the developer detached from the developing roller due to the agent breakage pole falls above the conveying screw and is conveyed toward the pumping electrode of the developing roller by the rotation of the conveying screw. The developer immediately after being detached as described above is after being subjected to a predetermined development process, and the charged state is unstable. Therefore, the detached developer must be sufficiently circulated in the apparatus thereafter to stabilize the charged state. However, the developer immediately after detachment is pumped up to the developing roller and mixed with a developer having a good charged state, resulting in a developer having an unstable charged state. When the developer is transported to a position facing the photosensitive drum (development region), a toner image having a non-uniform image density is formed.

  Further, the developer that has passed the position facing the photosensitive drum has a non-uniform toner concentration (the ratio of the toner in the developer). In other words, the developer corresponding to the image portion on the photosensitive drum has a toner density that decreases as the toner is consumed. On the other hand, the developer corresponding to the non-image area on the photosensitive drum has almost no toner density fluctuation because there is no toner consumption. Therefore, the developer having a non-uniform toner density due to the positional difference between the image area and the non-image area is pumped onto the developing roller immediately after the separation, resulting in a developer having a toner density different from the target. A toner image having a non-uniform image density is formed by being conveyed to the development area.

  In addition, an electrical load or a physical load is applied to the developer on the developing roller at the position facing the doctor blade (the doctor gap) and the developing area (the developing gap). Therefore, the operation of pumping up the developer immediately after detachment onto the developing roller is continuously repeated, and as a result, the life of the developer is shortened.

  Further, the toner concentration of the developer is detected by a toner concentration sensor provided in the circulation path in the developing device. Therefore, the developer whose toner density is reduced due to consumption of the toner is pumped up on the developing roller immediately after detachment, and as a result, the actual toner density fluctuation cannot be detected by the toner density sensor. The concentration becomes unstable.

  Since the magnetic force is set so that the developer on the developing roller is surely detached from the agent breakage pole, the technology disclosed in Patent Document 2 and the like described above, The phenomenon of mixing with the developer (this is called “accompaniment”) is suppressed. However, since the behavior of the developer after being detached from the developing roller is not regulated, the effect of solving the above problem cannot be expected.

  The present invention has been made to solve the above-described problems, and the developer detached from the developer carrier at the end of the agent is immediately pumped onto the developer carrier at the pumping pole. It is an object of the present invention to provide a developing device, a process cartridge, and an image forming apparatus that are stable and have good image quality.

  A developing device according to a first aspect of the present invention is a developing device for developing a latent image formed on an image carrier, the developer facing the image carrier and carrying a developer. A carrier member, and a conveying member that opposes the developer carrier and conveys the developer in the apparatus, and the developer carrier carries the developer that has passed through a position facing the image carrier. A magnet body is provided on the outer peripheral surface of the developer carrying member to form an agent cutting pole to be released from the developer carrying member, and passes through the central position of the agent breaking electrode on the outer peripheral surface of the developer carrying member. The rotation center of the conveying member is arranged on the side where the developer carrying member passes through the central position with a vertical line as a boundary.

  The developing device according to a second aspect of the present invention is the developing device according to the first aspect, wherein the central position of the agent breakage pole is on the outer peripheral surface of the developer carrier and the center of the outer peripheral surface. It is arranged below the horizontal line passing through.

  According to a third aspect of the present invention, in the developing device according to the first or second aspect, the transport member rotates in the same direction as the rotation direction of the developer carrier. .

  According to a fourth aspect of the present invention, in the developing device according to any one of the first to third aspects, the magnet body carries the developer in the device on the developer carrying member. A pumping pole is formed on the outer peripheral surface of the developer carrying member, and the rotation center of the conveying member is the developing line with a vertical line passing through the central position of the pumping electrode on the outer peripheral surface of the developer carrying member as a boundary. The agent carrier is disposed on the side toward the center position.

  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 rotation center of the conveying member is perpendicular to the central position of the agent breakage pole. It is arranged below.

  The developing device according to a sixth aspect of the present invention is the developing device according to any one of the first to fifth aspects, wherein the breaker pole is adjacent to the magnet body with two magnet portions having the same polarity. The center position of the agent breakage pole is a position corresponding to between the two magnet parts.

  A developing device according to a seventh aspect of the present invention is the developing device according to any one of the first to sixth aspects, wherein the conveying member is moved along the longitudinal direction of the developer carrying member. This is a conveying screw for conveying.

  A developing device according to an eighth aspect of the present invention is the developing device according to any one of the first to seventh aspects, wherein the developer is a two-component developer having a carrier and a toner. is there.

  According to a ninth aspect of the present invention, a process cartridge includes the developing device according to any one of the first to eighth aspects and the image carrier.

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

  In the present application, the “process cartridge” refers to a charging unit that charges an image carrier, a developing device that develops a latent image formed on the image carrier, and a cleaning unit that cleans the image carrier. Of these, at least one and the image carrier are defined as a unit that is integrated and detachable from the main body of the image forming apparatus.

  The present invention optimizes the position of the agent breakage pole formed on the outer peripheral surface of the developer carrying member and the position of the transport member. As a result, a developing device having a good and stable image quality, in which the developer detached from the developer carrying member due to the agent breakage pole is not caused immediately after that by the pumping electrode is pumped onto the developer carrying member, 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, 1 is a main body of a color printer as an image forming apparatus, 2 is a writing unit that emits laser light based on image information, and 20Y, 20M, 20C, and 20BK are colors (yellow, magenta, cyan, and black). The corresponding process cartridge 21 is a photosensitive drum as an image carrier housed in each of the process cartridges 20Y, 20M, 20C, and 20BK, 22 is a charging unit that charges the photosensitive drum 21, 23Y, 23M, 23C, 23BK is a developing device for developing the electrostatic latent image formed on the photosensitive drum 21, 24 is a transfer bias roller for transferring the toner image formed on the photosensitive drum 21 to the intermediate transfer belt 27, and 25 is the photosensitive member. A cleaning unit that collects untransferred toner on the drum 21 is shown.

  In addition, 27 is an intermediate transfer belt on which toner images of respective colors are transferred in an overlapping manner, 28 is a second transfer bias roller for transferring the toner image formed on the intermediate transfer belt 27 to the transfer material P, and 29 is an intermediate transfer belt. 27 is an intermediate transfer belt cleaning unit that collects untransferred toner, 30 is a transfer belt that conveys a transfer material P onto which four color toner images are transferred, and 32Y, 32M, 32C, and 32BK are developing devices 23Y. , 23M, 23C, and 23BK, a toner replenishing unit that replenishes toner of each color, 61 a paper feeding unit that accommodates a transfer material P such as transfer paper, and 66 a fixing that fixes an unfixed image on the transfer material P Indicates the part.

Here, each of the process cartridges 20Y, 20M, 20C, and 20BK is obtained by integrating the photosensitive drum 21, the charging unit 22, and the cleaning unit 25, respectively. The process cartridges 20Y, 20M, 20C, and 20BK are exchanged with respect to the apparatus main body 1 in a predetermined exchange cycle. Similarly, the developing devices 23Y, 23M, 23C, and 23BK are also replaced with a predetermined replacement cycle with respect to the apparatus main body 1 based on the lifetime of the developer.
Image formation of each color (yellow, magenta, cyan, black) is performed on the photosensitive drum 21 in each of the process cartridges 20Y, 20M, 20C, and 20BK.

Hereinafter, an operation during normal color image formation in the image forming apparatus will be described.
Each of the four photosensitive drums 21 rotates in the clockwise direction in FIG. First, the surface of the photosensitive drum 21 is uniformly charged at a position facing the charging unit 22 (a charging process). Thereafter, the surface of the charged photosensitive drum 21 reaches the irradiation position of each laser beam.

  On the other hand, in the writing unit 2, laser light corresponding to the image signal is emitted from the light source corresponding to each color. The laser light is incident on the polygon mirror 3 and reflected, and then passes through the lenses 4 and 5. The laser light after passing through the lenses 4 and 5 passes through different optical paths for each color component of yellow, magenta, cyan, and black (this is an exposure process).

The laser beam corresponding to the yellow component is reflected by the mirrors 6 to 8 and then irradiated onto the surface of the photosensitive drum 21 of the first process cartridge 20Y 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 21 by the polygon mirror 3 that rotates at high speed. Thus, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 21 charged by the charging unit 22.
Similarly, the laser beam corresponding to the magenta component is reflected by the mirrors 9 to 11 and then irradiated to the surface of the photosensitive drum 21 of the second process cartridge 20M from the left side of the paper, thereby causing an electrostatic latent image corresponding to the magenta component. An image is formed. The cyan component laser light is reflected by the mirrors 12 to 14 and then irradiated to the surface of the photosensitive drum 12 of the third process cartridge 20C from the left side of the drawing to form a cyan component electrostatic latent image. The black component laser light is reflected by the mirror 15 and then irradiated on the surface of the photosensitive drum 21 of the fourth process cartridge 20BK from the left side of the paper, thereby forming an electrostatic latent image of black component.

Thereafter, the surface of the photosensitive drum 21 on which the electrostatic latent images of the respective colors are formed further rotates to reach positions facing the developing devices 23Y, 23M, 23C, and 23BK, respectively. Then, the respective color toners are supplied from the developing devices 23Y, 23M, 23C, and 23BK onto the photosensitive drum 21, and the latent image on the photosensitive drum 21 is developed (this is a developing step).
Thereafter, the surface of the photosensitive drum 21 after the development process reaches a position facing the intermediate transfer belt 27. Here, the transfer bias roller 24 is installed at each facing position so as to contact the inner peripheral surface of the intermediate transfer belt 27. Then, the image of each color formed on the photosensitive drum 21 is sequentially transferred onto the intermediate transfer belt 27 at the position of the transfer bias roller 24 (first transfer step).

Then, the surface of the photosensitive drum 21 after the first transfer process reaches a position facing the cleaning unit 25. The untransferred toner remaining on the photosensitive drum 21 is collected by the cleaning unit 25 (this is a cleaning process).
Thereafter, the surface of the photosensitive drum 21 passes through a static elimination unit (not shown), and a series of image forming processes on the photosensitive drum 21 is completed.

On the other hand, the surface of the intermediate transfer belt 27 on which the images of the respective colors on the photosensitive drum 21 are transferred in an overlapping manner travels in the direction of the arrow in the drawing and reaches the position of the second transfer bias roller 28. Then, the full color image on the intermediate transfer belt 27 is secondarily transferred onto the transfer material P at the position of the second transfer bias roller 28 (second transfer step).
Thereafter, the surface of the intermediate transfer belt 27 reaches the position of the intermediate transfer belt cleaning unit 29. Then, the untransferred toner on the intermediate transfer belt 27 is collected by the intermediate transfer belt cleaning unit 29, and a series of transfer processes on the intermediate transfer belt 27 is completed.

Here, the transfer material P at the position of the second transfer bias roller 28 is transported from the paper feeding unit 61 via the transport guide 63, the registration roller 64, and the like.
Specifically, the transfer paper P fed by the paper feed roller 62 from the paper feed unit 61 that stores the transfer material P is guided to the registration roller 64 after passing through the conveyance guide 63. The material P to be transferred that has reached the registration roller 64 is conveyed toward the position of the second transfer bias roller 28 in synchronization with the toner image on the intermediate transfer belt 27.

Thereafter, the transfer material P onto which the full color image has been transferred is guided to the fixing unit 66 by the transfer belt 30. In the fixing unit 66, the color image is fixed on the transfer material P at the nip between the heating roller 67 and the pressure roller 68.
Then, the transfer material P after the fixing process is discharged as an output image outside the apparatus main body 1 by the paper discharge roller 69, and a series of image forming processes is completed.

Next, the image forming unit of the image forming apparatus will be described in detail with reference to FIGS. FIG. 2 is a cross-sectional view showing the image forming unit, and FIG. 3 is a cross-sectional view taken along line AA showing the developing device.
The four image forming units installed in the apparatus main body 1 have substantially the same structure except that the color of the toner T used in the image forming process is different. Therefore, the alphabet of reference numerals in the process cartridge, the developing device, and the toner replenishing unit. (Y, M, C, BK) is removed for illustration.

  As shown in FIG. 2, the process cartridge 20 mainly contains a photosensitive drum 21 as an image carrier, a charging unit 22, and a cleaning unit 25 integrally in a case 26. The cleaning unit 25 is provided with a cleaning blade 25 a and a cleaning roller 25 b that are in contact with the photosensitive drum 21.

  The developing device 23 mainly faces the first conveying screw 23b via a developing roller 23a facing the photosensitive drum 21, a first conveying screw 23b as a conveying member facing the developing roller 23a, and a partition member 23e. The second conveying screw 23c, a doctor blade 23d facing the developing roller 23a, and a toner concentration sensor 23g for detecting the toner concentration of the developer G in the developing device 23 are configured. In the developing device 23, a two-component developer G composed of carrier C and toner T is accommodated. Referring to FIG. 3, a developing roller 23a includes a magnet body 23a1 fixed inside to form a plurality of poles on the outer peripheral surface of the roller, and a sleeve 23a2 as a developer carrier that rotates around the magnet body 23a1. , Composed of.

The above-described image forming process will be described in more detail with a focus on the developing process.
The developing roller 23a rotates in the direction of the arrow in FIG. As shown in FIG. 3, the developer G in the developing device 23 is generated by the rotation of the first conveying screw 23 b and the second conveying screw 23 c arranged so as to interpose the partition member 23 e therebetween in the arrow direction. It circulates in the longitudinal direction while being agitated and mixed with the toner T replenished from the replenishing part 32 through the replenishing port 23f (circulation in the direction of the broken arrow in FIG. 3). The first conveying screw 23b as a conveying member rotates in the same direction as the rotation direction (counterclockwise direction) of the developing roller 23a.
The toner T that is frictionally charged and adsorbed on the carrier C is carried on the developing roller 23a together with the carrier C by a pumping pole (B3 in FIG. 4) formed on the developing roller 23a.

  A plurality of poles are formed by the magnet body 23a1 on the outer peripheral surface of the sleeve 23a1 (developer carrier) of the developing roller 23a. Specifically, with reference to FIG. 4, the magnet body 23a1 includes three N-pole magnet portions and two S-pole magnet portions. These magnet portions are formed in a developing pole for pumping the developer G onto the developing roller 23a, a transport pole for transporting the developer G carried on the developing roller 23a to the doctor blade 23d, and a developing area. A magnetic force distribution is formed on the developing roller 23a. The magnetic force distribution includes a main pole and an agent-cutting pole B4 for detaching the developer G after passing through the developing region from the developing roller 23a. Due to the magnetic force distribution, the developer G moves on the developing roller 23a as the sleeve 23a2 rotates.

  The developer G carried on the developing roller 23a at the position of the pumping pole B3 is adjusted to an appropriate amount at the position of the doctor blade 23d, and then reaches a position facing the photosensitive drum 21 (developing area). In FIG. 4, a black circle (a position indicated by a symbol B <b> 3) indicates a central position (a central position of an arc having a predetermined length) in the pumping pole B <b> 3 formed on the outer peripheral surface of the developing roller 23 a. .

  Thereafter, in the development area, the toner T in the developer G adheres to the electrostatic latent image formed on the surface of the photosensitive drum 21. Specifically, the toner T is latently developed by an electric field (development electric field) formed by a potential difference (development potential) between the latent image potential of the image portion irradiated with the laser beam L and the development bias applied to the development roller 23a. Adhere to the image.

After passing through the developing region, the developer G carried on the developing roller 23a (in a state where the toner is consumed) is detached from the developing roller 23a at the position of the agent breakage pole B4. Specifically, referring to FIG. 4, the agent breaking pole B <b> 4 is formed between two adjacent N pole magnet portions. At the agent breakage pole B4, the magnetic force acting on the developer G is reduced (the force that holds the developer G on the developing roller 23a), and the developer G is detached from the developing roller 23a.
In FIG. 4, the black circle mark (the position indicated by reference numeral B4) indicates the center position (the center position of the arc having a predetermined length) in the agent breakage pole B4 formed on the outer peripheral surface of the developing roller 23a. Show. That is, the position on the outer peripheral surface corresponding to the space between the two magnet parts having the same polarity is the center position of the out-of-agent electrode B4.

  Here, the toner supply unit 32 provided in the apparatus main body includes a toner bottle 33 configured to be replaceable, a toner hopper unit 34 that holds and rotates the toner bottle 33 and supplies fresh toner T to the developing device 23. , Is composed of. The toner bottle 33 contains toner T (any one of yellow, magenta, cyan, and black). In addition, a spiral protrusion is formed on the inner peripheral surface of the toner bottle 33.

  The toner T in the toner bottle 33 is appropriately replenished into the developing device 23 from the replenishing port 23f as the toner T in the developing device 23 is consumed. The consumption of the toner T in the developing device 23 is detected by a toner concentration sensor 23g that magnetically detects the toner concentration in the device 23. The replenishing port 23f is provided at one end in the longitudinal direction of the second transport screw 23c (the left-right direction in FIG. 3) and above the second transport screw 23c.

Next, with reference to FIG. 4, the positional relationship between the agent-breaking electrode B4 and the first transport screw 23b (transport member), which is a feature of the first embodiment, will be described.
As shown in the cross-sectional view of FIG. 4, in the first embodiment, the sleeve 23 a 1 has the central position B 4 at the vertical line Y 1 passing through the central position (the black circle mark position) of the agent breakage pole B 4. The developing device 23 is configured such that the rotation center of the first transport screw 23b is disposed on the passing side (the right side in FIG. 4). That is, the vertical line Y2 passing through the center of rotation of the first conveying screw 23b is disposed on the downstream side (the pumping pole B3 side) with respect to the vertical line Y1 passing through the center position B4. In other words, when the distance Lx from the vertical line Y1 passing through the center position B4 of the agent breakage pole to the vertical line Y2 passing through the rotation center of the first conveying screw 23b is the forward direction of the downstream side of the vertical line Y1. , Lx ≧ 0.

  In addition, the rotation center of the 1st conveyance screw 23b is arrange | positioned in the perpendicular direction lower direction (lower side of FIG. 4) rather than the center position B4 of an agent cutting pole. The rotation direction of the first conveying screw 23b is the same as the rotation direction of the sleeve 23a2 of the developing roller 23a.

With such a configuration, the developer G detached from the developing roller 23a at the position of the agent breakage pole is transported downward in the apparatus 23 along the rotation direction of the first transport screw 23b. Then, the developer G transported downward circulates in the longitudinal direction while being mixed with the developer G in the apparatus as described above with reference to FIG. 3 by the transport force in the longitudinal direction of the first transport screw 23b.
That is, the developer G detached from the developing roller 23a at the position of the agent breakage pole is transported upward in the apparatus 23 immediately after the separation by the rotation of the first transport screw 23b, and at the position of the pumping pole B3. The problem of being carried on the developing roller 23a is suppressed.

In the first embodiment, the center position B4 of the agent breakage pole is formed below the horizontal line passing through the rotation center (the center of the outer peripheral surface) of the developing roller 23a. That is, the agent breakage pole B4 is formed so that the angle α shown in FIG. 4 satisfies the relationship −90 ° <α <90 °. Here, the angle α is an angle formed by a vertical line passing through the rotation center of the developing roller 23a and a straight line passing through the rotation center of the developing roller 23a and the central position B4 (the developing roller 23a The direction of rotation is the positive direction.)
With such a configuration, the developer G on the developing roller 23a reaching the agent breakage pole B4 is subjected to the gravity of the developer G, and the developer G is detached from the development roller 23a at the agent breakage pole B4. It becomes easy.

  As described above, in the first embodiment, the position of the out-of-agent pole B4 formed on the sleeve 23a2 of the developing roller 23a and the position of the first transport screw 23b are optimized. As a result, the problem that the developer G detached from the developing roller 23a at the agent-breaking pole B4 is immediately pumped onto the developing roller 23a by the pumping pole B3 is suppressed, and an output image with good and stable image quality is suppressed. Can be provided.

Embodiment 2. FIG.
The second embodiment of the present invention will be described in detail with reference to FIG.
FIG. 5 is a configuration diagram illustrating the developing device 23 according to the second embodiment, and corresponds to FIG. 4 of the first embodiment. The second embodiment is mainly different from the first embodiment in the rotation direction of the photosensitive drum 21 and the developing roller 23a, the position of the doctor blade 23d, and the like.

  As shown in FIG. 5, in the image forming apparatus according to the second embodiment, the photosensitive drum 21 rotates counterclockwise. Around the photosensitive drum 21, a developing device 23, a charging unit (not shown), a transfer unit, a cleaning unit, and the like are disposed. Then, an image forming process similar to that in the first embodiment is performed on the photosensitive drum 21.

As in the first embodiment, the developing device 23 includes a developing roller 23a, a first conveying screw 23b (conveying member), a second conveying screw 23c, a doctor blade 23d, and the like. A two-component developer is accommodated in the developing device 23.
Here, in the second embodiment, the developing roller 23a and the first conveying screw 23b rotate in the clockwise direction. The doctor blade 23d is disposed below the developing roller 23a. Also in the second embodiment, as in the first embodiment, the developer G is moved by the poles on the developing roller 23a (the pumping pole, the transport pole, the main pole, and the agent cutting pole). It will be.

  Also in the second embodiment, as in the first embodiment, the positional relationship between the agent breakage pole B4 and the first conveying screw 23b (conveying member) is optimized. That is, the center of rotation of the first conveying screw 23b is arranged on the side (the left side in FIG. 5) where the sleeve 23a1 passes the central position B4, with the vertical line Y1 passing through the central position B4 of the agent cutting pole as a boundary. It is installed.

Further, the rotation center of the first transport screw 23b is disposed vertically below the center position B4 of the agent breakage pole. The rotation direction of the first conveying screw 23b is the same as the rotation direction of the sleeve 23a2 of the developing roller 23a.
Further, similarly to the first embodiment, the agent breaker pole B4 is formed so as to satisfy the relationship that the angle α shown in FIG. 5 satisfies −90 ° <α <90 °.

  With such a configuration, the developer G detached from the developing roller 23a at the position of the agent breakage pole is transported upward in the apparatus 23 immediately after the separation by the rotation of the first transport screw 23b, and the pumping pole The problem of being carried on the developing roller 23a at the position B3 is suppressed.

Here, in the second embodiment, in addition to the above-described configuration, the positional relationship between the pumping pole B3 and the first conveying screw 23b is optimized.
Specifically, as shown in the cross-sectional view of FIG. 5, the sleeve 23a1 faces the center position B3 (on the right side of FIG. 5) on the vertical line Y3 passing through the center position B3 of the pumping pole. The developing device 23 is configured such that the rotation center of the one transport screw 23b is disposed. That is, the vertical line Y2 passing through the center of rotation of the first conveying screw 23b is disposed upstream of the vertical line Y3 passing through the center position B3 of the pumping pole (on the side of the agent breakage pole B4). In other words, when the distance Mx from the vertical line Y3 passing through the center position B3 of the pumping pole to the vertical line Y2 passing through the center of rotation of the first transport screw 23b is the positive direction on the upstream side of the vertical line Y3, It arrange | positioned so that it might become Mx> = 0.

  As a result, the developer G in the developing device 23 is transported upward in the device 23 along the rotation direction of the first transport screw 23b. Then, the developer G conveyed upward is held on the developing roller 23a by the magnetic force of the pumping pole B3. That is, the developer G in the developing device 23 is efficiently supplied onto the developing roller 23a at the position of the pumping pole B3.

  As described above, in the second embodiment, the position of the out-of-agent electrode B4 and the pumping electrode B3 formed on the sleeve 23a2 of the developing roller 23a and the position of the first conveying screw 23b are optimized. Yes. As a result, the problem that the developer G detached from the developing roller 23a at the agent breakout pole B4 is immediately pumped onto the developing roller 23a by the pumping pole B3 is suppressed, and is carried on the developing roller 23a. In this way, the pumping failure due to insufficient developer G is suppressed, and an output image with good and stable image quality can be provided.

  In each of the above embodiments, the developing device 23 is configured separately from the process cartridge 20. On the other hand, the developing device 23 can be integrated with the process cartridge 20. Further, the developing device 23 is integrated with at least one of the photosensitive drum 21, the charging unit 22, the transfer unit 24, the cleaning unit 25, and the toner replenishing unit 32 to constitute a unit. It can also be detachably installed in the apparatus main body 1.

  Further, in each of the above embodiments, the first transport screw 23b provided with a screw portion formed in a spiral shape in the longitudinal direction is used as the transport member. However, the conveying member is not limited to this form, and the present invention can be applied to other forms of conveying members. For example, a conveyance member having a coil portion formed in a spiral shape in the longitudinal direction can be used, or a conveyance member having a paddle portion formed radially in the radial direction can be used. Even when such a transport member is used, the same effects as those of the above-described embodiments can be obtained by optimizing the positional relationship between the rotation center of the transport member and the out-of-agent electrode B4. .

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

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a side cross-sectional view showing an image forming unit in the image forming apparatus of FIG. 1. FIG. 3 is a cross-sectional view showing an AA cross section of the developing device in the image forming unit of FIG. FIG. 3 is a diagram illustrating a relationship between a material breakage pole and a conveying screw in the developing device of FIG. 2. 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), 2 writing unit,
20, 20Y, 20M, 20C, 20BK Process cartridge,
21 photosensitive drum (image carrier), 22 charging unit,
23, 23Y, 23M, 23C, 23BK developing device,
23a developing roller, 23a1 magnet body,
23a2 sleeve (developer carrier),
23b 1st conveyance screw (conveyance member),
23c second conveying screw, 23d doctor blade,
23e partition member, 23g toner density sensor, 25 cleaning unit,
32, 32Y, 32M, 32C, 32BK toner supply unit,
33 toner bottle, 34 toner hopper,
B3 pumping electrode, B4 agent cutting electrode.

Claims (10)

A developing device for developing a latent image formed on an image carrier,
A developer carrying body facing the image carrying body and carrying a developer;
A conveying member that faces the developer carrying member and conveys the developer in the apparatus,
The developer carrier has an internal magnet body that forms on the outer peripheral surface of the developer carrier an agent breakage pole that separates the developer that has passed through a position facing the image carrier from the developer carrier. And
The rotation center of the conveying member is disposed on the side where the developer carrier passes through the central position on the outer peripheral surface of the developer carrier on the side of the vertical line passing through the central position of the agent breakage pole. A developing device configured as described above. 2. The developing device according to claim 1, wherein a central position of the agent breakage pole is disposed on an outer peripheral surface of the developer carrying member and below a horizontal line passing through a center of the outer peripheral surface. The developing device according to claim 1, wherein the conveying member rotates in the same direction as a rotation direction of the developer carrying member. The magnet body is formed on the outer peripheral surface of the developer carrying body with a pumping electrode for carrying the developer in the apparatus on the developer carrying body.
The rotation center of the conveying member is disposed on the side toward the central position with a vertical line passing through the central position of the pumping pole on the outer peripheral surface of the developer supporting body as a boundary. The developing device according to claim 1, wherein: 5. The developing device according to claim 1, wherein a rotation center of the transport member is disposed vertically below a center position of the agent breakage pole. The agent-breaking pole is formed by adjoining the magnet body with two magnet parts having the same polarity,
The developing device according to claim 1, wherein a central position of the agent breakage pole is a position corresponding to a position between the two magnet portions. The developing device according to claim 1, wherein the conveying member is a conveying screw that conveys the developer along a longitudinal direction of the developer carrying member. The developing device according to claim 1, wherein the developer is a two-component developer having a carrier and a toner. 9. A process cartridge comprising the developing device according to claim 1 and the image carrier integrally. An image forming apparatus comprising the developing device according to claim 1 and the image carrier.

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