Development device

Abstract

To suppress excessive discharge of a developer and suppress wear of a conveyance screw in a compatible manner.SOLUTION: A development device comprises: a discharge path, in which a developer is discharged in a first direction, a discharge port disposed oppositely to a rotary shaft for discharging a part of the developer conveyed into the discharge path in a direction crossing the first direction from the discharge path being formed in the discharge path; and a magnet. The first conveyance screw further includes a third blade part which is disposed in the discharge path, disposed at a downstream side of a second blade part with respect to the first direction and formed spirally on the outer peripheral surface of the rotary shaft and conveys the developer in the first direction. The discharge port is disposed at a downstream side of the upstream end of the third blade part with respect to the first direction, and the magnet is disposed at a downstream side of the upstream end of the discharge port with respect to the first direction. A protrusion part protruding in the radial direction of the rotary shaft is provided in the rotary shaft at a downstream side of the third blade part, at an upstream side of the magnet and in a region overlapped with the upstream end of the discharge port with respect to the first direction.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to a developing device that develops an electrostatic image formed on an image carrier with a developer containing toner and carrier. [Background technology]

[0002] In developing devices using two-component developers, a so-called trickle development method is widely used in which toner containing a small amount of carrier is replenished while excess developer is discharged from a discharge port in order to suppress deterioration of carrier particles. In developing devices using the trickle development method, the internal pressure in the developing container may increase due to driving, causing an air flow to blow out from the discharge port. In this case, the developer in the developing container is carried by the air flow and discharged in excess.

[0003] Patent document 1 describes a technology in which a developing device is provided with a magnetic field generating means such as a magnet, which attracts a portion of the discharged developer using the magnetic force of the magnetic field generating means to form a developer accumulation area, and the developer accumulation area covers the discharge outlet, thereby suppressing excessive discharge of developer due to airflow. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-39287 Summary of the Invention [Problem to be solved by the invention]

[0005] In a configuration in which excessive discharge of developer is suppressed by covering the discharge port with a developer pooling area formed by a magnetic field generating means as in Patent Document 1, the force required to discharge the developer is greater than when the discharge port is not covered. Also, since the transport screw in the developer pooling area slides against the developer whose fluidity is restricted by the magnetic force of the magnetic field generating means, there is a risk that the transport screw will wear out to a greater extent than when no developer pool is formed.

[0006] Meanwhile, in recent years, there has been a demand for a further extension of the life of a developing device, and since wear of the transport screw can be a rate-limiting factor in the life of a developing device, it is desirable to suppress wear of the transport screw.

[0007] The present invention has been made in view of the above problems, and an object of the present invention is to provide a developing device that is capable of suppressing excessive discharge of developer and suppressing wear of the conveying screw at the same time. [Means for solving the problem]

[0008] In order to achieve the above object, a developing device according to one aspect of the present invention has the following configuration: A developer carrier that carries and transports a developer containing a toner and a carrier to develop an electrostatic image formed on an image carrier, a developing container having a first chamber and a second chamber partitioned from the first chamber by a partition wall and accommodating a developer to be supplied to the developer carrier, a first transport screw disposed in the first chamber, the first transport screw having a rotating shaft, a first blade portion formed in a spiral shape on the outer circumferential surface of the rotating shaft and transporting the developer in a first direction, and a second blade portion disposed downstream of the first blade portion with respect to the first direction, formed in a spiral shape on the outer circumferential surface of the rotating shaft, transporting the developer in a second direction opposite to the first direction and for transferring the developer from the first chamber to the second chamber, a second transport screw disposed in the second chamber and transporting the developer in the second direction, and a discharge screw disposed downstream of the second blade portion with respect to the first direction and discharging the developer in the first direction. the first conveying screw is disposed in the discharge path and downstream of the second blade portion with respect to the first direction, and further has a third blade portion formed in a spiral shape on the outer peripheral surface of the rotating shaft and conveying the developer in the first direction, the discharge port being disposed downstream of the upstream end of the third blade portion with respect to the first direction, the magnet being disposed downstream of the upstream end of the discharge port with respect to the first direction, and the rotating shaft in a region downstream of the third blade portion and upstream of the magnet with respect to the first direction and overlapping with the upstream end of the discharge port is provided with a protrusion portion protruding radially of the rotating shaft. Effect of the Invention

[0009] According to the present invention, it is possible to provide a developing device that is capable of suppressing excessive discharge of developer and suppressing wear of the conveying screw at the same time. [Brief description of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing a configuration of an image forming apparatus according to a first embodiment. [Diagram 2] 2 is a cross-sectional view showing the configuration of a developing device and a photosensitive drum according to the first embodiment. FIG. [Diagram 3] 1 is a plan view showing a developing device according to a first embodiment, with some parts omitted. [Figure 4] FIG. 2A is a schematic diagram showing a state in which the developer surface level is low, and FIG. 2B is a schematic diagram showing a state in which the developer surface level has reached a certain level or higher. [Diagram 5] 1A and 1B are schematic diagrams illustrating the mechanism of excessive discharge of developer when a trickle development method is adopted. [Figure 6] 11 is a schematic diagram showing a part of a first conveying path and a discharge path of a developing device in a conventional example. [Figure 7] FIG. [Figure 8] 5A and 5B are schematic diagrams illustrating a developer reservoir region formed by a magnetic field of a magnet member. [Figure 9] 4 is a cross-sectional view showing the positional relationship between an outlet and an extrusion shape according to the first embodiment. FIG. [Figure 10] FIG. 2A is a cross-sectional view of an extrusion profile according to the first embodiment, and FIG. 2B is a perspective view of a conveying profile and an extrusion profile of a first conveying screw according to the first embodiment. [Figure 11] FIG. 11 is a cross-sectional view of an extruded shape according to a second embodiment. [Figure 12] FIG. 11 is a cross-sectional view of an extrusion shape according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the present invention, and not all of the combinations of features described in the first embodiment are necessarily essential to the solution of the present invention. The present invention can be implemented in various applications, such as printers, various printing machines, copiers, FAX machines, and multifunction machines.

[0012] [First embodiment] (Configuration of Image Forming Apparatus) The image forming apparatus 200 is an electrophotographic full-color printer having four image forming units PY, PM, PC, and PK provided corresponding to the four colors of yellow, magenta, cyan, and black. In the first embodiment, the image forming units PY, PM, PC, and PK are arranged in tandem along the rotation direction of an intermediate transfer belt 10 described later. The image forming apparatus 200 forms a toner image (image) on a recording material in response to an image signal from a document reading device (not shown) connected to the image forming apparatus main body or a host device such as a personal computer connected to the image forming apparatus main body so as to be able to communicate with the image forming apparatus main body. Examples of the recording material include sheet materials such as paper, plastic film, and cloth.

[0013] To give an overview of such an image forming process, first, each image forming station PY, PM, PC, and PK forms a toner image of each color on the photosensitive drum 13Y, 13M, 13C, and 13K, respectively. The toner image of each color thus formed is transferred onto the intermediate transfer belt 10, and then transferred from the intermediate transfer belt 10 onto a recording material. The recording material onto which the toner image has been transferred is conveyed to a fixing device 11, where the toner image is fixed onto the recording material. A detailed explanation will be given below.

[0014] The four image forming units PY, PM, PC, and PK included in the image forming apparatus 200 have substantially the same configuration, except for the different developing colors. Therefore, hereinafter, the image forming unit PY will be described as a representative, and the configurations of the other image forming units will be shown by replacing the suffix "Y" of the reference numerals attached to the configuration of the image forming unit PY with M, C, and K, respectively, and the description will be omitted.

[0015] In the image forming section PY, a cylindrical photosensitive member, i.e., a photosensitive drum 13Y, is disposed as an image carrier. A charging roller 12Y (charging device), a developing device 1Y, a primary transfer roller 17Y, and a cleaning device 15Y are disposed around the photosensitive drum 13Y. An exposure device (laser scanner) 14Y is disposed below the photosensitive drum 13Y in the figure.

[0016] The charging roller 12Y is rotated by the photosensitive drum 13Y during image formation. The charging roller 12Y is biased toward the photosensitive drum 13Y by a pressure spring (not shown). A charging bias is applied to the charging roller 12Y from a high-voltage power supply. As a result, the photosensitive drum 13Y is almost uniformly charged by the charging roller 12Y.

[0017] In addition, an intermediate transfer belt 10 is disposed facing the photosensitive drums 13Y, 13M, 13C, and 13K. The intermediate transfer belt 10 is tensioned by a plurality of tension rollers, and is rotated by the drive roller, which is one of the plurality of tension rollers. A secondary transfer outer roller 16 is disposed as a secondary transfer member at a position facing a secondary transfer inner roller 18 of the plurality of tension rollers across the intermediate transfer belt 10, and constitutes a secondary transfer portion T2 that transfers a toner image on the intermediate transfer belt 10 to a recording material. A fixing device 11 is disposed downstream of the secondary transfer portion T2 in the recording material conveying direction. In addition, a feeding portion (not shown) is disposed at the bottom of the image forming apparatus 200. The recording material fed from the feeding portion when the image forming operation starts is conveyed to the secondary transfer portion T2 at a predetermined timing.

[0018] The process of forming an image by the image forming apparatus 200 configured as described above will be described. First, when the image forming operation starts, the surface of the rotating photosensitive drum 13Y is uniformly charged by the charging roller 12Y. Next, the photosensitive drum 13Y is exposed to a laser beam corresponding to an image signal emitted from the exposure device 14Y. As a result, an electrostatic latent image (electrostatic image) corresponding to the image signal is formed on the photosensitive drum 13Y. The electrostatic latent image on the photosensitive drum 13Y is visualized by the toner contained in the development device 1Y, becoming a visible image (toner image).

[0019] The toner image formed on the photosensitive drum 13Y is primarily transferred to the intermediate transfer belt 10 at a primary transfer portion T1Y configured between the photosensitive drum 13Y and a primary transfer roller 17Y arranged with the intermediate transfer belt 10 interposed therebetween. Toner remaining on the surface of the photosensitive drum 13Y after the primary transfer (transfer residual toner) is removed by a cleaning device 15Y.

[0020] This operation is performed in turn in each of the magenta, cyan, and black image forming units, and the four color toner images are superimposed on the intermediate transfer belt 10. Thereafter, in accordance with the timing of the formation of the toner images, the recording material stored in a recording material storage cassette (not shown) in the feeding unit is conveyed to the secondary transfer unit T2, and the four color toner images on the intermediate transfer belt 10 are secondarily transferred all at once onto the recording material. Any toner that was not transferred at the secondary transfer unit T2 and remains on the intermediate transfer belt 10 is removed by an intermediate transfer belt cleaner 19.

[0021] Next, the recording material is conveyed to the fixing device 11. The fixing device 11 includes a fixing roller 20 having a heat source such as a halogen heater inside, and a pressure roller 21, which form a fixing nip portion. The recording material conveyed to the fixing device 11 is passed through the fixing nip portion, whereby the toner image is fixed to the recording material. The recording material is then discharged outside the machine. This completes the series of image forming processes. It is also possible to form a single-color or multi-color image of a desired color using only a desired image forming portion.

[0022] (Developer) Here, the two-component developer used in the first embodiment will be described. The developer is a mixture of a non-magnetic toner with a negative charge polarity and a magnetic carrier with a positive charge polarity. The non-magnetic toner is a resin such as polyester or styrene acrylic that contains colorants, wax components, etc., and is pulverized or polymerized to form a powder, to which fine powders such as titanium oxide and silica are added on the surface. The magnetic carrier is a core made of resin particles kneaded with ferrite particles or magnetic powder, and a resin coating is applied to the surface layer.

[0023] (Configuration of the developing device) Next, the detailed configuration of the developing device 1Y will be described with reference to Figures 2 and 3. The same applies to the developing devices 1M, 1C, and 1K. The developing device 1Y has a developing container 2 that contains a developer consisting of a magnetic carrier and a non-magnetic toner, and a developing sleeve 54 as a developer carrier that carries and transports the developer in the developing container. The developing sleeve 54 has its surface rotatably held, while a magnet roll 54a consisting of multiple magnetic poles (S1, S2, S3, N1, N2) is non-rotatably arranged inside.

[0024] The developing container 2 is partitioned by a partition wall 51 into a first transport path (mixing chamber) 52 as a first chamber and a second transport path (developing chamber) 53 as a second chamber, and the first transport path 52 and the second transport path 53 communicate with each other through communication ports at both ends. As a result, the first transport path 52 and the second transport path 53 form a circulation path for the developer.

[0025] The developing container 2 is provided with two screw members as transport members for transporting the developer while stirring it. That is, the first transport path 52 is provided with a first transport screw 58, and the second transport path 53 is provided with a second transport screw (second transport section) 59. The first and second transport screws 58 and 59 have rotation shafts 58a and 59a, respectively, and blades 58b and 59b spirally provided around (on) the rotation shafts 58a and 59a.

[0026] When the first conveying screw 58 rotates around the rotation shaft 58a, the spiral blade 58b (blade portion) conveys the developer in the first conveying path 52 in the direction of the arrow α (first direction) on one side of the longitudinal direction of the developing device 1Y (axial direction of the rotation shaft 58a). When the second conveying screw 59 rotates around the rotation shaft 59a, the spiral blade 59b conveys the developer in the second conveying path 53 in the direction of the arrow β (second direction opposite to the first direction) on the other side of the longitudinal direction of the developing device 1Y (axial direction of the rotation shaft 58a). This causes the developer to circulate between the first conveying path 52 and the second conveying path 53.

[0027] The developing device 1Y has a toner concentration sensor (magnetic permeability sensor) 61 as a concentration detection means capable of detecting a toner concentration (a ratio of a toner particle weight to a total weight of carrier particles and toner particles, T / D ratio) in the developing container 2. The toner concentration sensor 61 is provided at a predetermined position in the first direction of the first conveying path 52, and detects the toner concentration in the first conveying path 52.

[0028] In the first embodiment, an inductance sensor is used as the toner concentration sensor 61, and a sensor surface (detection surface) of the inductance sensor is exposed inside the first conveying path 52. The inductance sensor detects magnetic permeability within a predetermined detection range from the sensor surface. When the toner concentration of the developer changes, the magnetic permeability changes according to the mixture ratio of the magnetic carrier and the non-magnetic toner, so the toner concentration can be detected by detecting the change in magnetic permeability with the inductance sensor.

[0029] The developer in the second transport path 53 is pumped up into the magnetic force range of the S2 pole by a second transport screw 59 installed below the developing sleeve 54 inside the second transport path 53, and is carried on the surface of the developing sleeve 54. The carried developer is carried as the surface of the developing sleeve 54 rotates. A regulating blade 55 is disposed near the magnetic pole N1 of the developing sleeve 54, with a predetermined gap therebetween, as a member for forming a thin layer of developer. The gap between the developing sleeve 54 and the regulating blade 55 is generally set to about 200 to 500 μm, and the wider the gap, the greater the amount of developer carried on the developing sleeve 54.

[0030] The transported developer forms a magnetic brush at the N1 pole, and a desired amount of developer is formed into a thin layer on the surface of the developing sleeve 54 by a regulating blade 55 installed at a predetermined interval from the developing sleeve 54. Thereafter, the developer transported to the opposing portion of the photosensitive drum 13Y forms a magnetic brush again at the S1 pole, and a development nip is formed between the photosensitive drum 13Y and the developer.

[0031] As described above, the surface of the photosensitive drum 13Y is charged to a constant potential by the charging roller 12Y, while the image portion is exposed by the exposure device 14Y to form an exposure potential. Meanwhile, a development bias is applied to the developing sleeve 54 through a high-voltage circuit (not shown). The development bias is, for example, a bias in which a rectangular AC waveform is superimposed on a DC waveform of a constant voltage. The toner charged in the developing device 1Y is driven by the potential difference between the development bias and the drum surface in the development nip, and adheres to the exposed portion, completing the development process.

[0032] The carrier and undeveloped toner are further transported downstream in the rotation direction of the developing sleeve 54, where they lose their magnetic binding force in the zero gauss zone (the area where the radial magnetic flux density is zero) formed between the S2 pole and the S3 pole, and are again collected in the second transport path 53.

[0033] When the developing operation is performed, only the toner in the developer is consumed, so the weight ratio of the developer to the toner (T / D ratio) decreases. Therefore, the T / D ratio is controlled to a predetermined value by performing a toner supply operation. In the first embodiment, the predetermined T / D ratio is set to 8%.

[0034] Toner is replenished through a toner replenishing port 40 provided in the developing container 2 (see FIG. 3). In the first embodiment, the toner replenishing port is provided at the upstream end of the first conveying screw 58 in the first direction, vertically above and outside the conveying path of the first conveying passage 52. However, the position of the replenishing port is not limited to this location and may be set in various locations depending on the main body configuration of the image forming apparatus. The replenished toner circulates through the first conveying passage 52 and the second conveying passage 53 while being stirred and conveyed together with the developer by the first conveying screw 58 and the second conveying screw 59.

[0035] (Trickle development method) The developing device 1Y in the first embodiment employs a trickle development method (hereinafter referred to as trickle) for suppressing deterioration of the carrier in the developer. Trickle is a development method in which, when the volume of the developer in the developing container 2 reaches a certain level or more, excess developer is discharged from an outlet 100 (see FIG. 6, etc.) provided in the developing container 2, and carrier is replenished using a small amount of carrier contained in the replenishment toner.

[0036] 4(a) and (b) are diagrams for explaining an example of the configuration and mechanism of a typical trickle. Hereinafter, when the terms "upstream" and "downstream" are used, they refer to the upstream (right side of the drawing) and downstream (left side of the drawing) of the conveying direction (first direction) of the blades 58b of the first conveying screw 58.

[0037] The first conveying screw 58 includes a rotating shaft 58a, a blade 58b that conveys the developer in the first direction in the first conveying path 52, and a reverse conveying portion 58c that pushes the developer back in the upstream direction at the downstream end of the first conveying screw 58. A discharge path 56 for discharging excess developer is connected downstream of the first conveying path 52, and a discharge port 100 is opened downward in the direction of gravity downstream of the discharge path 56. The discharge port 100 is disposed opposite the rotating shaft 58a of the first conveying screw 58, and discharges a part of the developer conveyed to the discharge path 56 from the discharge path 56 in a direction intersecting the first direction. The discharge path 56 is provided outside the circulation path of the developing container 2 and is connected to the first conveying path 52. The bottom surface of the discharge path 56 is located vertically above the bottom surface of the first conveying path 52.

[0038] A conveying shape 58d is provided in the discharge path 56. The conveying shape 58d is a conveying screw having a spiral blade formed on a rotating shaft 58a, which is the same rotating shaft as the first conveying screw 58, and serves to convey the developer downstream toward the discharge port 100. The inner diameter of the discharge path 56 is smaller than the inner diameter of the first conveying path 52, and the outer diameter of the conveying shape 58d is smaller than the blade 58b.

[0039] In Figures 4(a) and (b), the matte part is an imitation of the area where the developer exists. As shown in Figure 4(a), when the volume of the developer in the first conveying path 52 is small and the developer level is low, the developer conveyed by the blade 58b is pushed back by the reverse conveying part 58c. On the other hand, as shown in Figure 4(b), when the volume of the developer in the first conveying path 52 increases and the developer level rises to a certain level or higher, the developer that cannot be pushed back by the reverse conveying part 58c overcomes the reverse conveying part 58c. Then, when the developer that has overcome the step accumulates to exceed the step 60 between the first conveying path 52 and the discharge path 56, it becomes possible to convey it by the conveying shape 58d, and it is conveyed to the discharge port 100 and discharged as excess developer.

[0040] In this way, in the trickle development method, the amount of developer in the developing container 2 increases with the supply of toner containing a small amount of carrier. When the volume reaches a certain level, some of the developer containing degraded carrier spills further into the reverse transport section 58c and is discharged from the discharge port 100, thereby suppressing the deterioration of the carrier.

[0041] (Excessive discharge of developer) As described above, the trickle development method is an effective technique for suppressing the deterioration of the carrier in the developer. However, the trickle development method may result in the discharge of more developer than expected.

[0042] For example, when the driving speed of the developing device 1Y increases in accordance with the recent increase in the speed of image forming apparatuses, the amount of air taken into the developing container 2 increases with the rotation of the developing sleeve 54, and the internal pressure of the developing container 2 increases. As a result of the internal pressure inside the developing container 2 increasing while the outside of the developing container 2 is at atmospheric pressure, a difference in pressure between the inside and outside occurs, and an air current that blows out of the developing container 2 from the discharge port 100 is generated as shown in FIG. 5. Since this air current contains the developer that has been stirred up by the screw, the developer reaches the discharge path 56 and is transported downstream by the transport shape 58d. In this way, even when the developer is at a volume that should not be discharged, a small amount of developer flows out from the discharge port 100.

[0043] If this "excessive discharge" state continues in which trickle discharge occurs even though the volume of developer is small, the amount of developer in the developing container 2 will gradually decrease, and there is a risk that the developer will not be able to be supplied satisfactorily to the developing sleeve 54.

[0044] (Measures to prevent excessive developer discharge) 6, a method has been devised in which a ring-shaped magnet member 101, which is a magnetic field generating means, is disposed downstream in the transport direction of the transport shape 58d from the end of the discharge port 100. This prevents the developer in the developing container 2 from being excessively discharged.

[0045] 7, the magnet member 101 is formed in a ring shape, and is fixed around the entire circumference to the inner wall of the discharge path 56 downstream of the conveying shape 58d. Specifically, the magnet member 101 is disposed at a predetermined interval from the upstream end 103 of the discharge port 100 in the first direction.

[0046] Such a ring-shaped magnet member 101 has a shape as shown in Fig. 7, and in the first embodiment, has an outer diameter of 14 mm, an inner diameter of 8 mm, and a thickness of 1.5 mm. The rotating shaft 58a passes through the center of the magnet member 101. As a result, the inner peripheral surface 101a of the magnet member 101 faces the outer peripheral surface of the rotating shaft 58a over the entire circumference with a small gap therebetween.

[0047] The magnet member 101 is magnetized with an S pole on one side and an N pole on the other side, and has a surface magnetic flux density of 50 mT to 60 mT (measured with GX-100 manufactured by Nippon Denji Sokki Co., Ltd.). In the first embodiment, the N pole surface is arranged on the discharge port 100 side, but there is no problem whether the pole faces the discharge port 100 side. If the magnetic flux density of the magnet member 101 is too large, the friction between the attached developer and the rotating shaft 58a of the transport shape 58d becomes strong, and the toner may be stuck, and if the magnetic flux density is too small, the effect of the first embodiment cannot be obtained. For this reason, in the first embodiment, the magnetic flux density is set to the above-mentioned range, but the magnetic flux density can be appropriately set depending on the configuration of the device.

[0048] The developer transported by the transport shape 58d is discharged by dropping from the discharge port 100, but a part of the discharged developer is attracted by the magnetic force of the magnet member 101 and adheres to the surface of the magnet member 101. When the amount of developer adhering to the surface of the magnet member 101 gradually increases, a developer pool area 102 is formed by the adhering developer, as shown in FIG.

[0049] This agent accumulation area 102 is formed to extend from the magnet member 101 toward the upstream end 103 of the discharge outlet 100 (to the right in Figure 8), so that the discharge outlet 100 is covered by the agent accumulation area 102 formed as shown in Figure 8.

[0050] When the discharge port 100 is covered by the agent pooling area 102, the flow path through which the developer flows from the discharge port 100 to the outside of the developing container 2 as shown in Fig. 5 is blocked by the agent pooling area 102, so that the flow rate of the airflow flowing out to the outside can be reduced. Therefore, it is possible to prevent the developer from being discharged to the outside from the discharge port 100 by this airflow.

[0051] On the other hand, although the discharge port 100 is covered by the developer pooling area 102, the developer transported by the transport shape 58d is pushed toward the developer pooling area 102 by the transport force of the transport shape 58d. When the amount of developer exceeds the amount that can be supported by the magnetic force of the magnet member 101, the developer is naturally discharged downward from the discharge port 100 by gravity, so that the developer does not get clogged near the discharge port 100. In this way, it is possible to achieve both the suppression of excessive developer discharge due to airflow and the normal discharge of developer by the transport shape 58d.

[0052] The transport screw transports the developer by rotating the screw, and the developer that comes into contact with the blades of the transport screw receives a force in the direction of the rotation axis of the transport screw. In this way, the transport screw comes into contact with the developer by rotating, and provides the force to transport the developer. Generally, the transport screw that transports the developer is often made of a resin material, and if it continues to rotate to transport the developer and provide force to the developer, wear will occur in the part that comes into contact with the developer.

[0053] As described above in FIG. 8, in the configuration in which the discharge port 100 is covered by the developer pooling region 102 formed by the magnet member 101, when excess developer is discharged, the developer is pushed into the developer pooling region by the transport force of the transport shape 58d and discharged. In this manner, in the configuration in which the discharge port 100 is covered by the developer pooling region 102 formed by the magnet member 101, excessive discharge of developer is suppressed, but the force required to discharge the developer is greater than when the discharge port 100 is not covered. In addition, since the transport shape 58d in the developer pooling region 102 slides against the developer whose fluidity is restricted by the magnetic force of the magnet member 101, there is a risk that the degree of wear of the transport shape 58d will be greater than when no developer pool is formed.

[0054] This amount of wear is not a problem if the developing device can function without problems even after the expected period of use. However, in recent years, there has been a demand for a longer life for developing devices, and since wear of the conveying screw can be the rate-limiting factor for the life of the developing device, it is desirable to suppress wear of the conveying shape 58d.

[0055] In the first embodiment, the following configuration is adopted to suppress excessive discharge of developer and to suppress wear of the conveying screw. The details are described below.

[0056] In the first embodiment, as shown in Fig. 9, the extrusion shape 58e is provided downstream of the conveying shape 58d of the first conveying screw 58 in the conveying direction of the conveying shape 58d, and the extrusion shape 58e is provided vertically above the discharge port 100. Also, as shown in Fig. 10, the extrusion shape 58e is a protruding portion that protrudes in the radial direction of the rotating shaft 58a relative to the rotating shaft 58a, and the protruding portion is composed of a convex portion 58f and an extrusion surface 58g.

[0057] The transport shape 58d has a function of transporting the developer in a direction parallel to the rotation shaft 58a (the direction of the rotation axis of the first transport screw 58) by the rotation of the first transport screw 58. On the other hand, the push-out shape 58e has a function of transporting the developer in the radial direction of the rotation shaft 58a by the push-out surface 58g that moves by the rotation of the first transport screw 58.

[0058] If the push-out shape 58e is not present, the discharge port 100 is perpendicular to the direction in which the developer is transported by the transport shape 58d, so that the developer needs to be transported by the transport shape 58d until the amount of developer exceeds the amount that can be supported by the magnetic force of the magnet member 101.

[0059] In contrast, when the extrusion shape 58e is provided, the extrusion shape is located vertically above the discharge port 100 and moves the developer in the radial direction, so that the developer forming the developer pool area 102 can be transported in the direction of the discharge port 100.

[0060] Therefore, the excess developer can be discharged before the amount of developer exceeds the amount that can be carried by the magnetic force of the magnet member 101, and the amount of developer that needs to be pushed in is reduced, thereby suppressing wear on the transport shape 58d.

[0061] Here, the shape of the extrusion shape 58e will be described in more detail.

[0062] 10(a), the pushing surface 58g is formed to connect one end close to the rotation shaft 58a and the other end close to the tip of the convex portion 58f. The pushing surface 58g is inclined with respect to a plane perpendicular to the rotation direction of the first conveying screw 58 so that one end of the pushing surface 58g close to the rotation shaft 58a is located upstream in the rotation direction relative to the other end close to the tip of the convex portion 58f. When the pushing surface 58g is inclined in this manner, when the first conveying screw 58 rotates, the pushing surface 58g can effectively convey the developer in the vicinity of the one end close to the rotation shaft 58a toward the other end close to the tip of the convex portion 58f.

[0063] Also, as shown in FIG. 10(b), one of the convex portions 58f of the extrusion shape 58e is continuously connected to the blade of the transport shape 58d, and the outer diameter of the transport shape 58d and the outer diameter of the extrusion shape 58e are the same. That is, the protrusion (extrusion shape 58e) formed on the rotating shaft 58a of the first transport screw 58 is provided continuously with no gap from the downstream end of the transport shape 58d in the transport direction of the transport shape 58d. Also, the outer diameter of the protrusion (extrusion shape 58e) formed on the rotating shaft 58a of the first transport screw 58 is the same as the outer diameter of the transport shape 58d. As a result, the developer transported to the extrusion shape 58e by the transport shape 58d can be transported continuously in the radial direction, so that the developer can be efficiently transported in the direction of the discharge port 100.

[0064] As described above, in the first embodiment, the magnet member 101 is disposed downstream of the upstream end of the discharge port 100 in the conveying direction of the conveying shape 58d. In addition, the extrusion shape 58e protruding in the radial direction of the rotating shaft 58a is provided in a region downstream of the upstream end of the discharge port 100 and upstream of the magnet member 101 in the conveying direction of the conveying shape 58d, overlapping with the upstream end of the discharge port 100. By providing the extrusion shape 58e, the extrusion shape is located vertically above the discharge port 100 and moves the developer in the radial direction, so that the developer forming the developer accumulation region 102 can be conveyed toward the discharge port 100. Therefore, the excess developer can be discharged before the amount of developer that can be carried by the magnetic force of the magnet member 101 is exceeded, and the amount of developer that must be pushed in is reduced, so that wear of the conveying shape 58d can be suppressed. As a result, it is possible to achieve both suppression of excessive discharge of developer and suppression of wear of the conveying screw.

[0065] [Second embodiment] In the above-described first embodiment, an example in which the extruded surface 58g of the extruded shape 58e is a flat surface has been described. Meanwhile, in the second embodiment, an example in which the extruded surface 58g of the extruded shape 58e is a curved surface rather than a flat surface will be described.

[0066] The basic configuration and operation of the image forming apparatus of the second embodiment are the same as those of the image forming apparatus of the first embodiment. Therefore, in the image forming apparatus of the second embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of the first embodiment are given the same reference numerals as those of the first embodiment, and detailed explanations are omitted.

[0067] As shown in FIG. 11, in the second embodiment, the shape of an extrusion surface 58g of an extrusion shape 58e is curved, which is different from that in the first embodiment.

[0068] 11, the rotation of the extrusion shape 58e allows the extrusion surface 58g to transport the developer in the vicinity of the rotation shaft 58a in the radial direction toward the tip of the protrusion 58f. Therefore, even in the transport shape 58d shown in the second embodiment, the excess developer can be discharged before the amount of developer exceeds the amount that can be carried by the magnetic force of the magnet member 101, and the amount of developer that must be pushed in is reduced, thereby suppressing wear of the transport shape 58d.

[0069] [Third embodiment] The first embodiment described above is an example in which the extrusion surface 58g is inclined such that one end of the extrusion surface 58g closer to the rotation shaft 58a is located upstream in the rotation direction than the other end closer to the tip of the convex portion 58f with respect to a plane perpendicular to the rotation direction of the first conveying screw 58. Also, the first and second embodiments are examples in which the extrusion shape 58e has four convex portions 58f.

[0070] On the other hand, in the third embodiment, an example in which the pushing surface 58g is not inclined and the number of the protruding portions 58f is three will be described below.

[0071] The basic configuration and operation of the image forming apparatus of the third embodiment are the same as those of the image forming apparatus of the first embodiment. Therefore, in the image forming apparatus of the third embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of the first embodiment are given the same reference numerals as those of the first embodiment, and detailed explanations are omitted.

[0072] 12, in the third embodiment, unlike the first embodiment, the shape of the pushing surface 58g is not inclined but is a plane perpendicular to the rotation direction. Also, the number of protrusions 58f is three in the third embodiment, whereas it is four in the first and second embodiments.

[0073] 12, the rotation of the extrusion shape 58e allows the extrusion surface 58g to transport the developer in the vicinity of the rotation shaft 58a in the radial direction toward the tip of the protrusion 58f. Therefore, even in the transport shape 58d shown in the third embodiment, the excess developer can be discharged before the amount of developer exceeds the amount that can be carried by the magnetic force of the magnet member 101, and the amount of developer that must be pushed in is reduced, thereby suppressing wear of the transport shape 58d.

[0074] (Other embodiments) The present invention is not limited to the above-described embodiments, and various modifications (including organic combinations of the respective embodiments) are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0075] In the above embodiment, as shown in FIG. 1, the image forming apparatus 200 performs primary transfer of the toner images carried on the photosensitive drums 13Y, 13M, 13C, and 13K onto the intermediate transfer belt 10. Thereafter, the image forming apparatus 200 brings the recording material into contact with the intermediate transfer belt 10 and performs secondary transfer of the toner images carried on the intermediate transfer belt 10 onto the recording material. In the above embodiment, the image forming apparatus 200 configured as described above has been described as an example, but is not limited to this. The present invention can also be applied to an image forming apparatus configured to directly transfer the toner images carried on the photosensitive drums 13Y, 13M, 13C, and 13K onto the recording material by bringing the recording material into direct contact with the photosensitive drums 13Y, 13M, 13C, and 13K. [Explanation of symbols]

[0076] 1 Developing device 2 Developing container 52 First conveyor route 53 Second conveyor route 54 Developing sleeve 56 Exhaust channel 58 First conveying screw 58a Rotation axis 58b Feather 58c Reverse conveying section 58d Transport shape 58e Extrusion Shape 59 Second conveying screw 100 outlet 101 Magnet parts

Claims

1. a developer carrier that carries and transports a developer containing toner and a carrier in order to develop an electrostatic image formed on the image carrier; a developing container having a first chamber and a second chamber partitioned from the first chamber by a partition wall, the developing container containing a developer to be supplied to the developer carrier; a first conveying screw disposed in the first chamber, the first conveying screw having a rotating shaft, a first blade portion formed in a spiral shape on an outer circumferential surface of the rotating shaft and configured to convey the developer in a first direction, and a second blade portion disposed downstream of the first blade portion in the first direction, the second blade portion formed in a spiral shape on the outer circumferential surface of the rotating shaft and configured to convey the developer in a second direction opposite to the first direction and to transfer the developer from the first chamber to the second chamber; a second conveying screw disposed in the second chamber and configured to convey the developer in the second direction; a discharge path that is disposed downstream of the second blade portion with respect to the first direction and through which the developer is discharged in the first direction, the discharge path being disposed opposite the rotation shaft and having a discharge opening formed therein for discharging a portion of the developer transported to the discharge path from the discharge path in a direction intersecting the first direction; A magnet and Equipped with the first conveying screw is disposed in the discharge passage, and is disposed downstream of the second blade portion in the first direction, and further includes a third blade portion that is spirally formed on an outer circumferential surface of the rotating shaft and conveys the developer in the first direction, the discharge port is disposed downstream of an upstream end of the third blade portion with respect to the first direction, The magnet is disposed downstream of an upstream end of the discharge port in the first direction, A protrusion protruding in a radial direction of the rotating shaft is provided on the rotating shaft in a region that is downstream of the third blade portion and upstream of the magnet in the first direction and overlaps with an upstream end of the discharge port. A developing device characterized by the above.

2. The protrusion is provided continuously with the downstream end of the third blade portion without any gap therebetween in the first direction.

2. The developing device according to claim 1,

3. The outer diameter of the protrusion is the same as the outer diameter of the third blade portion.

3. The developing device according to claim 1, wherein the developing device is a developing unit.

4. The bottom surface of the discharge passage is located vertically above the bottom surface of the first chamber.

3. The developing device according to claim 1, wherein the developing device is a developing unit.

5. The outer diameter of the third blade portion is smaller than the outer diameter of the first blade portion.

3. The developing device according to claim 1, wherein the developing device is a developing unit.

6. In the second chamber, the developer is supplied to the developer carrier.

3. The developing device according to claim 1, wherein the developing device is a developing unit.

Images