Developing device

Abstract

To provide a configuration that can sufficiently crush an aggregate in a developer for replenishment.SOLUTION: A developing device has a developing chamber and a stirring chamber that form a circulation path of developer, and a conveyance path for replenishment that supplies developer for replenishment to the circulation path. The conveyance path for replenishment is arranged with a replenishment conveying screw 31 that conveys the developer in the conveyance path for replenishment toward the circulation path. The replenishment conveying screw 31 has a rotation shaft 310, and a plurality of rows of blades 311 that are formed in a spiral shape around the rotation shaft 310. At least one row of blades 311 of the plurality of rows of blades 311 have a discontinuous part 312 where the blades 311 become discontinuous in at least part in an axial direction of the rotation shaft 310.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a developing device that develops an electrostatic latent image with a developer. [Background technology]

[0002] In an image forming apparatus using an electrophotographic method or the like, an electrostatic latent image formed on an image carrier such as a photosensitive drum is developed into a toner image by a developing device. drug carrier A toner image is formed by making the carrier carry the developer and supplying the developer to the image carrier in the development section. As such a developing device, one that uses a two-component developer containing toner and carrier has been used conventionally. In the case of a developing device that uses a two-component developer, the developer is conveyed while being stirred by a screw in the circulation path of the developing container.

[0003] As a screw for transporting the developer within a circulation path in this manner, a configuration has been proposed in which a multi-thread screw has multiple blades formed in a spiral shape around a rotating shaft, and each blade has a discontinuous portion that is discontinuous in the axial direction of the rotating shaft (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-256429 A Summary of the Invention [Problem to be solved by the invention]

[0005] In a two-component developing device, the developer consumed in developing an electrostatic latent image is successively replenished with new developer, so that the amount of toner in the developing device can be maintained at a predetermined ratio to the amount of carrier while forming an image. In such a configuration, how well the replenishment developer can be agitated before being transported to the developer carrier is an important issue in reducing abnormal images.

[0006] In particular, agglomerates may occur due to the heat history that the refill developer receives during transportation, or due to the driving of the developer transport path of the image forming apparatus, and when the agglomerates are unintentionally supplied to the developing section, image defects (stained images) occur, such as stains on the image. Therefore, it is important to crush the agglomerates using the transport screw that transports the developer in order to suppress these stained images and improve image quality.

[0007] The above-mentioned Patent Document 1 discloses a screw configuration for improving the stirring property of the developer. However, there is a risk that the agglomerates in the replenishment developer cannot be sufficiently broken down by simply improving the stirring property of the developer conveying screw in the developer circulation path as in Patent Document 1.

[0008] The present invention relates to The supply conveying screw section can efficiently break down agglomerates in the supply developer. The present invention aims to provide a configuration. [Means for solving the problem]

[0009] One aspect of the present invention includes a developer carrier that carries and transports a developer including a toner and a carrier to a development position, a developing container that contains the developer, a first transport screw portion, a second transport screw portion, and a replenishment transport screw portion, and the developing container includes a first chamber for supplying developer to the developer carrier, a second chamber that is partitioned from the first chamber by a partition wall, a first communication portion that allows the developer to communicate from the first chamber to the second chamber, a second communication portion that allows the developer to communicate from the second chamber to the first chamber, and a communication portion between the first chamber and the second chamber. a supply transport path for transporting a supply developer to a circulation path in which the developer circulates between the first and second communicating portions, and a developer supply unit that supplies the supply developer to the supply transport path, the first transport screw unit being provided in the first chamber and transporting the developer in a first direction from the second communicating portion toward the first communicating portion, the second transport screw unit being provided in the second chamber and transporting the developer in a second direction from the first communicating portion toward the second communicating portion, and the supply transport screw unit being provided in the supply transport path and transporting the developer in a second direction from the developer supply unit toward the first communicating portion. The replenishment developer is transported in the third direction, the replenishment transport path is disposed upstream of the second chamber in the second direction, the second transport screw portion is disposed downstream of the first communication portion and upstream of the second communication portion in the second direction, the replenishment transport screw portion is disposed upstream of the second transport screw portion in the second direction, a rotation axis of the replenishment transport screw portion is coaxial with a rotation axis of the second transport screw portion, and the replenishment transport screw portion is disposed upstream of the second transport screw portion in the second direction. a first blade portion formed in a spiral shape on the outer circumferential surface of the rotating shaft of the screw portion for conveying the replenishment developer in the third direction, a second blade portion formed in a spiral shape on the outer circumferential surface of the rotating shaft of the replenishment conveying screw portion for conveying the replenishment developer in the third direction, and a third blade portion formed in a spiral shape on the outer circumferential surface of the rotating shaft of the replenishment conveying screw portion for conveying the replenishment developer in the third direction, wherein each of the pitch of the first blade portion, the pitch of the second blade portion, and the pitch of the third blade portion is greater than the pitch of the blades of the second conveying screw portion, The outer diameter of the first blade portion, the outer diameter of the second blade portion, and the outer diameter of the third blade portion are the same, A terminal end of the first wing portion with respect to the third direction and beforeBetween the beginning of the second wing and a region shifted in a circumferential direction of the supply conveying screw portion from the end end of the first blade portion and the start end of the second blade portion. In ,before The developing device is characterized in that the third blade portion is formed continuously. Effect of the Invention

[0010] According to the present invention, The supply conveying screw section can efficiently break down agglomerates in the supply developer. can. [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment. [Diagram 2] FIG. 2 is a cross-sectional view showing the schematic configuration of the developing device according to the first embodiment. [Diagram 3] FIG. 2 is a schematic vertical cross-sectional view of a replenishing device and a developing device. [Figure 4] FIG. 3 is a top view of the developing device with some parts omitted. [Diagram 5] FIG. 4 is a diagram showing the angle of the conveying surface of the blade. [Figure 6] 6 is a graph showing the relationship between the pitch of the blades and the amount of developer transported. [Figure 7] (a) A side view showing a conveying screw for a comparative example; (b) A side view showing a conveying screw for the first embodiment; (c) A side view and a cross-sectional view showing the range of the discontinuous portion; (d) A side view and a cross-sectional view showing the spacing between the discontinuities of each blade. [Figure 8] FIG. 1 is a schematic diagram for explaining the angle of the blades. [Figure 9] A visualization of stain images. [Figure 10] Graph (a) shows the relationship between the amount of developer supplied and the number of agglomerates, and graph (b) shows the relationship between the angle of the cut-out cross section of the discontinuous portion and the number of agglomerates. [Figure 11] FIG. 11 is a view showing a conveying screw according to a second embodiment. [Figure 12] Graph (a) showing the relationship between the cross-sectional area ratio of discontinuous parts and the number of agglomerates, and graph (b) showing the relationship between the cross-sectional area ratio of discontinuous parts and delay time. [Figure 13] 11 is a graph showing the relationship between the supply amount of developer and the number of agglomerates. [Figure 14] FIG. 11 is a cross-sectional view of the periphery of a supply transport path according to a third embodiment. [Figure 15] Graph (a) shows the relationship between the amount of developer supplied and the number of agglomerates, and graph (b) shows the relationship between the angle of the cut-out cross section of the discontinuous portion and the number of agglomerates. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] <First embodiment> The first embodiment will be described with reference to Figures 1 to 10. First, the schematic configuration of an image forming apparatus according to the present embodiment will be described with reference to Figure 1.

[0013] [Image forming equipment] The image forming apparatus 100 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 this embodiment, the image forming units PY, PM, PC, and PK are of a tandem type arranged along the rotation direction of an intermediate transfer belt 24 described later. The image forming apparatus 100 forms a toner image (image) on a recording material 27 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.

[0014] To give an overview of such an image forming process, first, the image forming stations PY, PM, PC, and PK form toner images of each color on the photosensitive drums 28Y, 28M, 28C, and 28K, respectively. The toner images of each color thus formed are transferred onto the intermediate transfer belt 24, and then transferred from the intermediate transfer belt 24 onto the recording material 27. 27 The toner image is then conveyed to the fixing device 25. 27The toner image is fixed on the toner image. This will be described in detail below. Each image forming unit PY, PM, PC, PK is composed of a drum cartridge having a photosensitive drum 28Y, 28M, 28C, 28K, which is detachable from the image forming apparatus main body, and a developing device (developing cartridge) 1Y, 1M, 1C, 1K. These may be integrated into a process cartridge, which is detachable from the image forming apparatus main body.

[0015] The four image forming units PY, PM, PC, and PK of the image forming apparatus 100 have substantially the same configuration, except for the different developing colors. Therefore, the image forming unit PY will be described below 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.

[0016] In the image forming section PY, a cylindrical photosensitive member, i.e., a photosensitive drum 28Y, is disposed as an image carrier. The photosensitive drum 28Y is rotated in the direction of the arrow in the figure at a predetermined process speed (circumferential speed). A charging roller 21Y (charging device), a developing device 1Y, a primary transfer roller 23Y, and a cleaning device 26Y are disposed around the photosensitive drum 28Y. An exposure device (laser scanner) 22Y is disposed above the photosensitive drum 28Y in the figure.

[0017] The charging roller 21Y rotates in response to the rotation of the photosensitive drum 28Y during image formation. The charging roller 21Y is biased toward the photosensitive drum 28Y by a pressure spring (not shown). A charging bias is applied to the charging roller 21Y from a high-voltage power source. 28Y is almost uniformly charged by the charging roller 21Y.

[0018] An intermediate transfer belt 24 is disposed facing the photosensitive drums 28Y, 28M, 28C, and 28K. The intermediate transfer belt 24 is stretched by a plurality of tension rollers including a secondary transfer inner roller 29a, and moves in a circular motion in the direction of the arrow in the figure by driving a drive roller among the plurality of tension rollers. A secondary transfer outer roller 29b is disposed at a position facing the secondary transfer inner roller 29a with the intermediate transfer belt 24 in between, as a secondary transfer member, and transfers the toner image on the intermediate transfer belt 24 to a recording material. 27 A fixing device 25 is disposed downstream of the secondary transfer portion T2 in the recording material conveying direction.

[0019] A process of forming an image by the image forming apparatus 100 configured as described above will be described. First, when the image forming operation starts, the surface of the rotating photosensitive drum 28Y is uniformly charged by the charging roller 21Y. Next, the photosensitive drum 28Y is exposed to a laser beam L corresponding to an image signal emitted from the exposure device 22Y. As a result, an electrostatic latent image corresponding to the image signal is formed on the photosensitive drum 28Y. The electrostatic latent image on the photosensitive drum 28Y is visualized by the toner contained in the developing device 1Y, becoming a visible image (toner image).

[0020] The toner image formed on the photosensitive drum 28Y is primarily transferred to the intermediate transfer belt 24 at a primary transfer section T1Y configured between the photosensitive drum 28Y and a primary transfer roller 23Y arranged with the intermediate transfer belt 24 sandwiched therebetween. Toner (transfer residual toner) remaining on the surface of the photosensitive drum 28Y after the primary transfer is removed by a cleaning device 26Y.

[0021] This operation is also performed in sequence in each of the magenta, cyan, and black image forming units, and the four color toner images are superimposed on the intermediate transfer belt 24. Thereafter, in accordance with the timing of the formation of the toner images, the recording material 27 stored in a recording material storage cassette (not shown) is conveyed to the secondary transfer unit T2, and the four color toner images on the intermediate transfer belt 24 are secondarily transferred all at once onto the recording material 27. Toner that was not transferred completely at the secondary transfer unit T2 and remains on the intermediate transfer belt 24 is removed by the intermediate transfer belt cleaner 24a.

[0022] Next, the recording material 27 is conveyed to the fixing device 25. The toner on the recording material 27 is melted and mixed by the fixing device 25 through heating and pressure, and is fixed to the recording material 27 as a full-color image. The recording material 27 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 desired colors using only desired image forming units.

[0023] [Developing device] Next, the developing device 1Y will be described with reference to Figures 2 to 4. The same applies to the developing devices 1M, 1C, and 1K. The developing device 1Y has a developing container 2 that contains a two-component developer containing non-magnetic toner and a magnetic carrier. The developing container 2 has an opening in a development area facing the photosensitive drum 28Y, and a developing sleeve 3 as a developer carrier with a magnet roll 4 non-rotatably disposed therein is rotatably installed so as to be partially exposed to the opening.

[0024] In this embodiment, the developing sleeve 3 is made of a non-magnetic material and rotates at a predetermined process speed (circumferential speed) in the direction of the arrow in Fig. 2 during the developing operation. The magnet roll 4 as a magnetic field generating means has five magnetic poles, N1, N2, N3, S1, and S2, as multiple magnetic poles along the circumferential direction, and causes the developer to be carried on the surface of the developing sleeve 3 by the magnetic field it generates.

[0025] That is, the developing sleeve 3 rotates in the direction of the arrow in the figure, and transports the developer attracted at the position of the N1 pole (attraction pole) of the magnet roll 4 toward the blade 5, which serves as a regulating member. The developer made to stand on the developing sleeve 3 by the S1 pole passes through the gap between the developing sleeve 3 and the blade 5 while the amount of the developer is regulated by the blade 5, forming a developer layer of a predetermined thickness on the developing sleeve 3. The developer layer then flows through the developing area (developing section) facing the photosensitive drum 28. , development position), and in the state where the magnetic brush is formed by the N2 pole, the developer develops the electrostatic latent image formed on the surface of the photosensitive drum 28. After being used for development, the developer is transported to the magnetic field-free zone between the N3 pole (peeling pole) and the N1 pole, where it is peeled off from the developing sleeve 3 and taken into the developer circulation path.

[0026] In this embodiment, a blade 5 is disposed below the developing sleeve 3 in order to regulate the developer on the upstream side of the rotation direction of the surface of the developing sleeve 3 with respect to the developing area, which is the opposing portion between the photosensitive drum 28Y and the developing sleeve 3.

[0027] The inside of the developing container 2 is divided into a developing chamber as a first transport path by a partition wall (partition member) 15 extending vertically. (Room 1) 11 and a mixing chamber as a second conveying path (Room 2) 4, communication sections (transfer sections, communication ports) 16 and 17 that communicate between the developing chamber 11 and the stirring chamber 12 are formed on both ends of the partition 15 in the longitudinal direction (the direction of the rotation axis of the developing sleeve 3). As a result, the developing chamber 11 and the stirring chamber 12 form a circulation path for the developer.

[0028] In addition, in the developing container 2, a first conveying screw 13 (first conveying screw portion), a second conveying screw 14 (second conveying screw portion), and a supply conveying screw 31 (supply conveying screw portion) are arranged, each of which conveys the developer while stirring it. The conveying screws shown in FIGS. 3 and 4 are schematic diagrams, and FIGS. 3 and 4 show an example in which the first conveying screw 13, the second conveying screw 14, and the supply conveying screw 31 are single-thread screws having one blade. On the other hand, in this embodiment, the following description will be given assuming that the first conveying screw 13, the second conveying screw 14, and the supply conveying screw 31 are multi-thread screws having multiple blades. Specifically, each conveying screw is a three-thread screw having a rotating shaft and three blades formed in a spiral shape around the rotating shaft. In addition, a modified example in which the supply conveying screw 31 is a multi-thread screw, while the first conveying screw 13 and the second conveying screw 14 are single-thread screws, may be used.

[0029] The first transport screw 13 is disposed in the developing chamber 11, transports the developer in the developing chamber 11 (in the first transport path) while stirring it in the direction of the arrow α in FIG. 4, which is a first direction, and supplies the developer to the developing sleeve 3. The first direction is a direction from the communication part (second communication part) 16 toward the communication part (first communication part) 17. The second transport screw 14 is disposed in the stirring chamber 12, and transports the developer in the stirring chamber 12 (in the second transport path) while stirring it in the direction of arrow β in FIG. 4, which is a second direction opposite to the first direction. The second direction is the direction from communication part 17 towards communication part 16 . In this manner, the developer is transported by the first and second transport screws 13 and 14 and is introduced into the developing container 16 and 17 via the communication portions 16 and 17. 2 Circulates within.

[0030] A supply conveying path 53 is connected to the upstream side in the conveying direction (upstream side in the second direction) of the second conveying screw 14 of the stirring chamber 12. The supply conveying path 53 is for supplying the replenishment developer to the circulation path. For this purpose, a supply port 50 is provided in the supply conveying path 53. The supply port 50 is connected to a supply conveying section (supply pipe) 83 of a developer supply device 80 shown in FIG. 3, which will be described later. The supply conveying path 53 is located upstream of the second conveying screw 14 and is installed outside the developer circulation path coaxially with the second conveying screw 14. The supply port 50 and the supply conveying section 83 are provided vertically above the upstream end of the supply conveying path 53 so as to be connected to a toner bottle 8, which is a replenishment developer container.

[0031] Further, a supply conveying screw 31 is disposed in the supply conveying path 53. The supply conveying screw 31 conveys the developer in the supply conveying path 53 (inside the supply conveying path) toward the circulation path. That is, the supply conveying screw 31 conveys the supply developer in a third direction from the supply port 50 toward the communication portion 17. The supply conveying screw 31 is formed integrally with the second conveying screw 14, in other words, it is a part of the second conveying screw 14. That is, the supply conveying screw 31 is a section from the upstream end of the second conveying screw 14 to the connection with the developer circulation path. Therefore, the supply developer is supplied from the developer supply device 80 to the supply conveying path 53 via the supply conveying section 83 and the supply port 50, and is further supplied into the stirring chamber 12 by the supply conveying screw 31 arranged in the supply conveying path 53.

[0032] 4, the developing container 2 is provided with an inductance sensor 43 as a toner concentration sensor that detects the toner concentration in the developing container 2. In this embodiment, the inductance sensor 43 is provided on the downstream side of the stirring chamber 12 in the developer transport direction.

[0033] As shown in Fig. 3, a toner bottle 8 containing a replenishment developer containing toner but not carrier, or a replenishment developer containing toner and carrier, is disposed above the developing device 1Y so as to be detachable from the image forming device main body. For example, the toner bottle 8 contains a developer with a toner concentration (the ratio of the weight of toner particles to the total weight of carrier particles and toner particles, T / D ratio) of 90%. On the other hand, the toner concentration of the developer in the developing device 1Y is 10% or less, for example, about 7% to 10% (7% or more and 10% or less). For this reason, the toner bottle 8 contains a developer with a toner concentration higher than the toner concentration of the developer circulating in the developing device 1Y.

[0034] The developer replenishing device 80 described above comprises this toner bottle 8, a replenishing mechanism 81, and a replenishing and conveying section 83. The toner bottle 8 is configured with a spiral groove carved into the inner wall of a cylindrical container, and the toner bottle 8 itself rotates to generate a conveying force for the developer in the longitudinal direction (the direction of the rotation axis). The replenishing mechanism 81 is connected to the downstream end of the toner bottle 8 in the developer conveying direction. The replenishing mechanism 81 replenishing toner from the toner bottle 8. Transport to be sent Developer The pump portion 81a discharges the developer from the discharge port 82. The pump portion 81a is formed in a bellows shape, and when driven to rotate, the volume of the pump portion 81a changes to generate air pressure, and the developer transported from the toner bottle 8 is discharged from the discharge port 82.

[0035] An upper end of the supply conveying section 83 is connected to the discharge port 82, and a lower end of the supply conveying section 83 is connected to the developer supply port 50 of the developing device 1Y. That is, the supply conveying section 83 communicates between the discharge port 82 and the supply port 50. Therefore, the developer discharged from the discharge port 82 by the pump section 81a is replenished into the developing container 2 of the developing device 1Y through the supply conveying section 83.

[0036] In the above-described developing device 1Y, the replenishment transport path 53 in which the replenishment port 50 is formed is provided on the upstream side of the stirring chamber 12 in the developer transport direction and outside the developer circulation path formed by the developing chamber 11 and the stirring chamber 12. Specifically, the replenishment transport path 53 is provided on the upstream side of the stirring chamber 12 in the developer transport direction from one of the communication parts 17. Therefore, in the vicinity of the replenishment port 50, there is almost no developer in the developer circulation path, and only the replenishment developer passes through.

[0037] Such replenishment by developer replenishment device 80 is performed by automatic toner replenishment control (hereinafter referred to as "ATR (Automatic Toner Replenisher) control"). This ATR control controls the operation of developer replenishment device 80 according to the image ratio during image formation, the inductance sensor 43, and the result of detection of the density of a patch image by density sensor 101 (FIG. 1) that detects the density of the toner image, to replenish developer to developing device 1Y.

[0038] 1, the density sensor 101 is disposed downstream of the most downstream image forming unit PK and upstream of the secondary transfer unit T2 in relation to the rotation direction of the intermediate transfer belt 24, facing the surface of the intermediate transfer belt 24. In control using the density sensor 101, for example, at the start of an image forming job or after each predetermined number of images are formed, a control toner image (patch image) is transferred onto the intermediate transfer belt 24, and the density sensor 101 detects the density of the patch image. Then, based on the detection result, developer replenishment control by the developer replenishment device 80 is performed.

[0039] The configuration for supplying developer to the developing device 1Y is not limited to this configuration, and a conventionally known configuration may be used. For example, a hopper having a developer storage section for temporarily storing developer supplied from the toner bottle may be provided between the toner bottle and the developing device, and the developer may be supplied from this hopper to the developing device. In this configuration, the hopper has a screw for supplying developer to the developing device, and the supply to the developing device is performed by controlling the drive of this screw, similar to the above-mentioned developer supply device 80.

[0040] [Developer circulation] Next, the circulation of the developer in the developing container 2 will be described in more detail with reference to Fig. 4. The first transport screw 13 and the second transport screw 14 are disposed approximately parallel to each other along the rotation axis direction of the developing sleeve 3. The first transport screw 13 and the second transport screw 14 transport the developer in opposite directions to each other along the rotation axis direction of the developing sleeve 3. In this way, the developer is circulated in the developing container 2 via the communication parts 16 and 17 by the first transport screw 13 and the second transport screw 14.

[0041] That is, by the conveying forces of the first conveying screw 13 and the second conveying screw 14, the developer on the developing sleeve 3, in which the toner concentration has decreased as a result of toner consumption in the developing process, is collected in the developing chamber 11, conveyed to the stirring chamber 12 via the communicating portion 17, and moves within the stirring chamber 12. In addition, the developer in the developing chamber 11 that has not been coated on the developing sleeve 3 also moves within the developing chamber 11, and moves into the stirring chamber 12 via the communicating portion 17.

[0042] Here, upstream of the communication portion 17 of the stirring chamber 12 in the developer transport direction of the second transport screw 14, a supply transport path 53 to which the developer is replenished from the developer replenishing device 80 is provided. Therefore, in the stirring chamber 12, the developer transported from the developing chamber 11 via the communication portion 17 and the replenishment developer supplied from the supply transport path 53 are transported while being stirred by the second transport screw 14. Then, the developer transported by the second transport screw 14 moves to the developing chamber 11 via the communication portion 16.

[0043] Generally, in a two-component development method using a toner and a carrier, the toner and the carrier are charged to a predetermined polarity by frictional contact between them. Therefore, the toner is subjected to less stress than in a one-component development method using a single-component developer.

[0044] In addition, since the surface area of ​​the carrier in the developer is larger than that of the toner, the carrier is less likely to become soiled by the toner adhering to the carrier surface. However, with long-term use, the amount of dirt (spent) adhering to the carrier surface increases, which gradually reduces the carrier's ability to charge the toner. As a result, problems such as fogging and toner scattering occur. In order to extend the life of a two-component development device, it is possible to increase the amount of carrier contained in the development device, but this is undesirable because it would result in an increase in the size of the development device.

[0045] For this reason, the developing device 1Y of this embodiment employs an ACR (Auto Carrier Refresh) system. In the ACR system, as described above, new developer is gradually replenished into the developing container 2, and developer with deteriorated charging performance is gradually discharged from the developing device, thereby suppressing an increase in deteriorated carrier. Such a developing device 1Y is configured to utilize the bulk fluctuation of the developer to discharge surplus deteriorated developer and keep the bulk level of the developer in the developing container 2 approximately constant. According to the developing device 1Y of this ACR system, deteriorated carrier in the developing container 2 is gradually replaced with new carrier, and it becomes possible to keep the charging performance of the carrier in the developing container 2 approximately constant. The developing device 1Y of the ACR system uses a replenishing developer with a high toner ratio. Usually, the weight ratio of carrier to toner is about 5 to 10%. In other words, the replenishing developer is a developer with a toner concentration of 90% or more, for example, about 90 to 95% (90% or more and 95% or less).

[0046] [Developer] Here, the two-component developer used in this 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. In this embodiment, the concentration of toner in the developer in the initial state is 10%.

[0047] Next, the pitch of blade 402 and the transportability of developer when a single-thread transport screw 400 shown in Fig. 5 is used as a screw member for transporting developer in a developing container will be described. The transport screw 400 is provided with a single-thread blade 402 formed in a spiral shape around a rotating shaft 401. In the illustrated example, the screw outer diameter is 14 mm.

[0048] The amount of developer transported per rotation of the transport screw 400 varies depending on the pitch 403 of the blade 402. Assuming that all of the developer is transported by following the spiral blade 402, the distance traveled by the developer during one rotation of the transport screw 400 is equal to the pitch 403 of the blade 402. However, in reality, some developer slides on the blade 402, so not all of the developer is transported by following the blade 402. When the pitch 403 is widened, the angle α of the transport surface of the blade 402 becomes smaller, and the amount of developer sliding on the blade 402 increases. In contrast to the behavior of the developer described above, the toner has lower fluidity than the two-component developer, so it is less likely to slide on the blade and is more likely to be transported while holding the toner between the blades, resulting in higher transport efficiency.

[0049] Fig. 6 shows the results of investigating the amount of developer transported per rotation when the pitch 403 of the blade 402 is changed. The relationship between the pitch 403 of the transport screw 400 and the amount of developer transported per rotation is shown as an upwardly convex graph as shown in Fig. 6. In Fig. 6, the amount of developer transported per rotation is the largest when the pitch 403 is 30 mm. Note that if the outer diameter of the screw is changed, the shape of the graph shown in Fig. 6 will be different, so the pitch to which this embodiment can be applied is not limited to this.

[0050] [About agglomerates in developer] Here, in recent years, the development device has been made smaller and more space-saving, and the amount of two-component developer filled inside the development device tends to be small. Therefore, in order to reduce abnormal images, it is important to agitate the replenishment developer well before it is transported to the development sleeve. In particular, clumps may be generated due to the heat history that the replenishment developer receives during transportation or the driving of the developer transport path of the image forming device, and when the clumps are unintentionally supplied to the development section, image defects such as stains on the image (stained images) occur. Therefore, it is important to crush the clumps by the transport screw that transports the developer installed inside the development device in order to suppress these stained images and improve image quality.

[0051] However, since the aggregates mixed in the developer have a different specific gravity from the developer, they are often transported while floating on the surface of the developer and become evident as stain images in the development section. For this reason, as described in Patent Document 1, even if the second transport screw 14 arranged in the stirring chamber 12 is a multi-thread screw and has discontinuous parts in the blades, it cannot be said that it has a sufficient function of crushing the aggregates. Furthermore, since emphasis is placed on stirring, the developer transport ability decreases, and there is a risk that toner supply will be delayed relative to the consumed toner.

[0052] In addition, when using a developing device that is small and has a small amount of developer to achieve space saving compared to the conventional configuration as described above, the ratio of toner replenished to the amount of developer is high and the circulation path of the developer is short. Furthermore, the diameter of the conveying screw is small. This is disadvantageous in terms of crushing agglomerates that cause stained images. On the other hand, if a stirring member such as a paddle is provided on the conveying screw to crush the agglomerates, the developer conveying ability will be reduced.

[0053] Furthermore, in this embodiment, in order to save space in the image forming apparatus body, the developer is directly replenished from the toner bottle 8 into the developing device 1Y without using a hopper which is a storage part for the replenishment developer. In such a configuration, there is a possibility that the amount of developer replenished is greater than the amount replenished in the conventional configuration due to a large fluctuation in measurement, and the developer is easily affected by agglomerates in the replenishment developer. For this reason, as the image forming apparatus body and the developing device become smaller, a developing device that can crush agglomerates more effectively is required. Therefore, in this embodiment, in order to improve the crushing efficiency of agglomerates while suppressing the decrease in the conveying ability even when a small and space-saving developing device is used, and to reduce the occurrence of stained images, the replenishment conveying screw 31 is configured as follows.

[0054] [Supply conveyor screw] Next, the configuration of the supply conveying screw 31 of this embodiment will be described. As shown in Fig. 7(b), the supply conveying screw 31 has a rotating shaft 310 and a plurality of blades 311 formed in a spiral shape around the rotating shaft 310. At least one of the plurality of blades 311 has a discontinuous portion (notch portion) 312 where the blade 311 is discontinuous in at least a part of the axial direction of the rotating shaft 310.

[0055] As described above, the supply conveying path 53 is connected to the upstream side of the second conveying screw 14 of the mixing chamber 12 in the second direction, which is the developer conveying direction. The supply conveying screw 31 disposed in the supply conveying path 53 is disposed upstream of the second conveying screw 14 in the second direction, and the second conveying screw 14 The supply conveying screw 31 and the second conveying screw 14 have a common rotation shaft 310. That is, the supply conveying screw 31 and the second conveying screw 14 have the same rotation shaft 310 and are integrally formed.

[0056] In addition, the second conveying screw 14 Each screw 31 also has a rotating shaft 310 and a plurality of blades 14a formed in a spiral shape around the rotating shaft 310. At least one blade 14a among the plurality of blades 14a has a discontinuous portion (notch portion) 14b where the blade 14a is discontinuous at least in a part of the axial direction of the rotating shaft 310. In this embodiment, the supply conveying screw 31 and the second conveying screw 14 are three-strand screws having three blades 311, 14a, and two or more of the blades 311, 14a have discontinuous portions 312, 14b. Specifically, the three blades 311, 14a have discontinuous portions 312, 14b at multiple locations.

[0057] In this manner, in this embodiment, a multi-thread screw having a plurality of spiral blades 311 on a rotating shaft (screw shaft) 310 is used as the supply conveying screw 31. As described above, the multi-thread screw has a plurality of spiral blades on the screw shaft, and therefore the number of blades passing through a certain cross section when the screw makes one rotation increases by the number of threads. This improves the conveying performance of the screw. However, if the number of blades is increased too much, the volume of the screw per unit volume increases, and the conveying force decreases because the developer cannot be contained. Therefore, by making the supply conveying screw 31 a multi-thread screw, the efficiency of conveying the supply developer newly supplied to the developing container 2 per rotation of the supply conveying screw 31 is also improved, and the developer can be efficiently supplied into the developing container 2.

[0058] Fig. 7(a) shows, as a comparative example, a supply conveying screw 410 having no discontinuous parts in its blades and a second conveying screw 14 having discontinuous parts. In this comparative example, the supply conveying screw 410 and the second conveying screw 14 are also triple-thread screws. The second conveying screw 14 has discontinuous parts 14b in its blades 14a. Meanwhile, Fig. 7(b) shows the supply conveying screw 31 and the second conveying screw 14 of this embodiment as described above, Fig. 7(c) shows the range of the discontinuous parts 312, and Fig. 7(d) shows the intervals between the discontinuous parts 312.

[0059] Figure 8 shows the outer circumference of the three-toed screw described above, developed in a plan view for one revolution of the screw. In Figure 8, the vertical direction indicates the outer circumference of the screw in the direction perpendicular to the rotation axis of the conveying screw, and the horizontal direction indicates the screw pitch (pitch of the blades) in the direction of the rotation axis of the conveying screw. Also, each diagonal straight line indicates the distance of the outermost circumference of the screw when the three-toed screw makes one revolution. (The distance traveled by the outermost part) The angle α of the blade is the angle between the diagonal line and the horizontal axis when the length of the circumference of a circle whose diameter is the outer diameter of the blade (the outer circumference of the screw) is taken on the vertical axis and one pitch of the blade is taken on the horizontal axis. The outer diameter of the blade is the outer diameter of the conveying screw, and corresponds to the outer diameter of a circle whose radius is the distance from the center of the rotation shaft to the outer circumference of the blade in a cross section perpendicular to the rotation shaft.

[0060] The distance of the outermost circumference of the three-lobe screw when it rotates once corresponds to the amount of developer transported per revolution of the screw. The larger this distance, the more developer is transported, and in other words, the more developer is transported and mixed with the replenishment developer. Here, the distance of the outermost circumference of the screw is determined by the outer diameter of the screw, the blade angle α, or the screw pitch, and it is necessary to select the outer diameter and angle α of the screw that provide good transportability of the transport screw as described above.

[0061] The outermost peripheral distance of the screw in the multi-start screw is FeatherThis corresponds to the sum of the outermost peripheral distances of the screws, and as the number of threads increases, the outermost peripheral distance increases in proportion to the number of threads. This can be said to mean that the mixing performance of the screw improves in proportion to the number of threads. However, as mentioned above, if the number of threads is too large, it can actually reduce the conveying force.

[0062] As shown in Fig. 6, the relationship between the blade pitch of the transport screw and the amount of developer transported per rotation can be expressed as an upwardly convex graph. In this case, when transporting developer in the developing device, the amount of developer transported per rotation is the largest when the blade pitch is 30 mm, and when transporting refill developer with a higher toner concentration than this developer, the amount of developer transported per rotation is the largest when the blade pitch is 50 mm. This is because the fluidity of the developer is different between the reinforcing developer that contains a lot of toner (for example, a toner concentration of 90% or more) and the developer circulating in the developing device (for example, a toner concentration of 10% or less).

[0063] On the other hand, when a developer is transported by a multi-thread screw, the transport force is high, but the space between the blades and between the threads is small, and the developer behavior is small, so it is difficult to obtain stirring performance in a microscopic area. Therefore, when agglomerates are contained in the refill developer, it is difficult to sufficiently crush the agglomerates if the refill transport screw 410 is a multi-thread screw without discontinuities, as shown in Figure 7(a).

[0064] Therefore, in this embodiment, as described above, the supply and conveyance screw 31 is a multi-thread screw, and the blades 311 are provided with discontinuous portions. (gap) By providing the discontinuous portion 312, the agglomerates in the replenishment developer can be easily crushed. In the present embodiment, as shown in FIG. 7B, each of the three blades 311 of the replenishment conveying screw 31 has one discontinuous portion 312. Moreover, the single blade 311 has a first blade portion 3111 and a second blade portion 3112 with a discontinuous portion 312 therebetween. The other two of the three blades 311 each have a third blade portion 3113 and a fourth blade portion 3114. And, between the terminal end of the first blade portion 3111 in the third direction and the starting end of the second blade portion 3112 in the third direction, the third blade portion 3113 is formed continuously with being shifted in the circumferential direction of the supply conveying screw 31 from the terminal end of the first blade portion 3111 and the starting end of the second blade portion 3112. In this embodiment, the fourth blade portion 3114 is also formed between the end of the first blade portion 3111 in the third direction and the starting end of the second blade portion 3112 in the third direction, contiguous to the end of the first blade portion 3111 and the starting end of the second blade portion 3112, shifted circumferentially of the supply conveying screw 31.

[0065] In the present embodiment, the pitch (screw pitch) of the blades 311 of the supply conveying screw 31 is larger than the pitch of the blades 14a of the second conveying screw 14. This is because, as described above, the fluidity of the supply developer conveyed by the supply conveying screw 31 is different from that of the developer circulating in the developing device conveyed by the second conveying screw 14. Specifically, since the fluidity of the supply developer having a high toner concentration is low, narrowing the pitch of the blades 311 reduces the behavior of the developer sliding forward in the conveying direction through the gaps of the blades 311, and widening the pitch of the blades 311 reduces the behavior of the developer sliding backward in the conveying direction on the blades 311. Therefore, as shown in FIG. 6, the supply developer has a strong tendency to be conveyed while being held between the blades 311, and the peak of the conveyed amount appears on the side where the pitch of the blades 311 is wider than that of the normal developer.

[0066] As shown in Fig. 7(c), the cross section of the discontinuous portion 312 faces perpendicularly to the developer transport direction, and the range of the discontinuous portion 312 is set to a range of 45 degrees per revolution in the circumferential direction of the screw. The range of the discontinuous portion 312 is preferably in the range of 30 degrees to 90 degrees (30 degrees or more and 90 degrees or less). If it is less than 30 degrees, the space is narrow and the developer being transported by the screw flows in front of the cross section of the discontinuous portion 312, reducing the probability of the developer colliding with the cross section. On the other hand, if it is more than 90 degrees, the transport performance, which is an advantage of the multi-thread screw, begins to decrease significantly.

[0067] In addition, the cross section of the blade 311 at the discontinuous portion 312, i.e., the cutout surface 313, is flat and is formed so as to collide with the developer being transported. In addition, the cutout surface 313 is a cross section cut in a direction perpendicular to the rotation shaft 310 or in a range of ±20° (-20° or more and +20° or less) from the perpendicular direction. In other words, the cutout surface 313 is provided in a direction perpendicular to the circumferential surface of the rotation shaft of the supply transport screw 31. It is desirable that the cutout surface 313 is about ±20° in the direction perpendicular to the circumferential surface of the rotation shaft. If the direction in which the cross section faces is the + side, if the cutout surface is inclined by more than 20 degrees to the plus side, the supply developer is transported as if it is wrapped around it by rotation, which reduces the ability to crush the agglomerates. In addition, if the cutout surface is inclined to the minus side more than -20 degrees, the supply developer is transported as if it is sliding on the cutout surface 313, which reduces the ability to crush the agglomerates.

[0068] Also, the cutout surface 313 is a cross section cut in a direction parallel to the developer transport direction by the supply transport screw 31 or in a range of ±30° (-30° or more +30° or less) with respect to the parallel direction. That is, the cutout surface 313 is a cross section cut parallel to the transport direction, and when inclined in a direction parallel to the developer transport direction, it is desirable to have an inclination of up to about ±30°. When the cutout surface 313 is inclined with its surface facing the downstream side (positive side) of the developer transport direction, if it is inclined more positively than +30° in the parallel direction, the relative speed when the transported developer and the cutout surface 313 collide with each other is reduced. This reduces the ability to crush the aggregates. On the other hand, when the cutout surface 313 is inclined with its surface facing the upstream side (negative side) of the developer transport direction, if it is inclined more negatively than -30° in the parallel direction, it collides in a direction that hinders the transport of the developer, so the crushing ability is slightly improved but the transport speed is reduced.

[0069] As described above, the discontinuous portions 312 are provided at one location on each of the three blades 311 of the supply and conveyance screw 31. In this case, as shown in FIG. 7(d), it is preferable that the discontinuous portions 312 are arranged at equal intervals in the rotation axis direction and that the centers of the discontinuous portions 312 are spaced at intervals of 120 degrees when viewed from a cross section perpendicular to the rotation axis of the supply and conveyance screw 31. If the discontinuous portions 312 are arranged side by side or close to each other in the axial or circumferential direction, there will be a portion where the driving force of the blades 311 of the supply and conveyance screw 31 is not transmitted to the developer, and the conveying force and the stirring force will decrease. For this reason, it is preferable that the portion of the blade 311 of another blade 311 adjacent to the discontinuous portion 312 of one blade 311 is a continuous portion of the blade, not a discontinuous portion 312.

[0070] On the other hand, it is desirable that the container shape of the supply conveying path 53 between the supply port 50 and the circulation path of the developer is sealed. By making the periphery of the supply conveying screw 31 sealed (for example, tunnel-shaped), the supply developer that is stirred up by the blades 311 of the supply conveying screw 31 hits the ceiling and returns to within the rotation radius of the supply conveying screw 31. This increases the frequency with which the toner collides with the notched surface 313 of the discontinuous portion 312 described above, and minimizes the loss of the conveying force by the blades 311. Furthermore, by the same mechanism, the probability of collision with the notched surface 313 increases, improving the crushing ability and conveying performance of the agglomerates.

[0071] [Verification of effectiveness] Next, the results of verifying the relationship between the transport performance of the supply transport screw 31 and the agglomerate crushing performance in the developer will be described. In this verification, in order to verify the agglomerate crushing performance of the supply transport screw 31, the supply developer was placed in a high-temperature, high-humidity tank and left for a long period of time to accelerate the formation of agglomerates in the supply developer. Specifically, the supply developer for agglomerate verification that had been left in a thermostatic tank at a temperature of 50°C and a humidity of 50% for 72 hours was used.

[0072] Regarding the agglomerate crushing performance, a developing device equipped with a prototype supply conveying screw 31 was prepared. Then, evaluation was performed by counting the number of agglomerates appearing on the developing sleeve 3 when a predetermined amount of supply developer for agglomerate verification, which was prepared by the above-mentioned acceleration method, was poured into the supply port 50 of the supply developer.

[0073] In addition, in order to verify the influence of the agglomerate crushing performance on the developer transport performance as a detriment to the agglomerate crushing performance, the transport speed was evaluated using an inductance sensor 43 (FIG. 4) installed in the developer circulation path downstream of the supply transport screw 31.

[0074] The developing device used in this verification has the same configuration as that shown in FIG. 2, and includes a developing sleeve 3 that supplies toner to the photosensitive drum, a first conveying screw 13, a second conveying screw 14, a supply conveying screw 31, an inductance sensor 43, and the like.

[0075] Here, the inductance sensor 43 will be described. The inductance sensor 43 is a concentration sensor that detects information related to the magnetic permeability of the developer. As shown in FIG. 4, the inductance sensor 43 is disposed in a region downstream of the second conveying screw 14 in the conveying direction so that the detection surface protrudes from the inner wall of the developing container 2 and faces the second conveying screw 14. The inventors have found that the closest distance between the outer periphery of the second conveying screw 14 and the sensor surface of the inductance sensor 43 is preferably about 0.2 to 2.5 mm in terms of the sensitivity of the sensor. If the sensor is placed too close to the outer periphery of the second conveying screw 14, there is a risk that the detection surface will come into contact with the screw and shavings will be generated. On the other hand, if the sensor is placed farther away than 2.5 mm, the developer in the space that the sensor can detect will not be replaced, making it impossible to measure the change in toner concentration due to developer circulation. In consideration of these study results, the closest distance is set to 0.5 mm in this embodiment.

[0076] Since the inductance sensor 43 detects the magnetic permeability within a predetermined detection range from the detection surface, the detected magnetic permeability also changes with the movement of the second conveying screw 14. Specifically, the developer passes through the detection surface of the inductance sensor 43 along with the rotation cycle of the second conveying screw 14. For this reason, the signal waveform of the magnetic permeability detected by the inductance sensor 43 has maximum and minimum values ​​according to the movement of the second conveying screw 14. do.

[0077] Here, the magnetic permeability of the developer is detected every 10 ms by the inductance sensor 43. Then, the detection every 10 ms is performed for one revolution of the screw (the time required for one revolution based on the rotation speed of the screw) corresponding to the period between the maximum values ​​of the waveform, and the average value of these is calculated to obtain the detection value of the inductance sensor 43.

[0078] As described above, the developer (two-component developer) is composed of a magnetic carrier and a non-magnetic toner. When the toner concentration of this developer (the ratio of the weight of toner particles to the total weight of carrier particles and toner particles) changes, the magnetic permeability due to the mixture ratio of the magnetic carrier and non-magnetic toner also changes. The toner concentration is measured by detecting the change in magnetic permeability with the inductance sensor 43. This makes it possible to obtain various information such as the excess or shortage of toner in the developing device and the circulation cycle of the replenishment developer, and to control so that a uniform toner image can be formed on the photosensitive drum.

[0079] Next, the evaluation conditions for crushing the aggregates in this verification will be described. In this verification, 200 g of developer with a toner concentration of 10% was placed in the developing device, and the device was set in a jig for driving the developing device. In addition, a line camera was installed facing the opening of the developing sleeve 3 of the developing device. The line camera was focused on the opening of the developing sleeve 3 facing the photosensitive drum, and the angle of view was adjusted so that the entire longitudinal area of ​​the developer coated area of ​​the developing sleeve 3 was included. The shooting conditions were set to shoot 10 images for 1.0 second, equivalent to one A4 image, at 500 fps.

[0080] In addition, a predetermined amount of replenishment developer containing the above-mentioned agglomerates was put into the supply port 50 of the stationary developing device as a replenishment developer, and the above-mentioned line camera was started to capture images at the same time as the development drive started, and images were recorded. From about the fifth sheet, when the replenishment developer was transported by the second transport screw 14 and began to reach the developing sleeve 3, the agglomerates appeared in the images. At this time, if the replenishment developer and the developer filled in the developing device are developers of different colors, evaluation becomes easier. In this verification, yellow toner was used as the replenishment developer, and cyan toner was used as the developer filled in the developing device.

[0081] The captured images were separated into RGB using the image processing software ImageJ, and contrast enhancement processing was performed on the G element images to visualize the images of the aggregates. An example of the image is shown in Figure 9. The number of aggregates that appeared in the 10 images captured in this way was counted to verify the effect of this embodiment.

[0082] In order to verify the effect of this embodiment, a configuration in which the blade 311 of the supply and conveying screw 31 has a discontinuous portion 312 (FIG. 7(b), Example 1) and a configuration in which the blade 311 of the supply and conveying screw 410 has no discontinuous portion (FIG. 7(a), Comparative Example) were prepared. Then, using each supply and conveying screw, the number of agglomerates generated on the developing sleeve 3 was counted as described above. The amount of supply developer at this time was Developer Assuming image formation jobs with low to high consumption, four levels of toner consumption were set: 0.125 g, 0.250 g, 0.400 g, and 0.800 g.

[0083] The results of the above verification are shown in Fig. 10(a). Obvious As described above, there was no difference between Example 1 and the Comparative Example when the amount of replenishment developer was small, 0.125 g and 0.250 g, and in both configurations, the generation of agglomerates on the developing sleeve 3 was small and favorable. However, when the replenishment amount was 0.400 g or more, the agglomerates were not completely crushed in the Comparative Example, and a large amount of agglomerates was generated on the developing sleeve 3.

[0084] On the other hand, in Example 1, the generation of agglomerates on the developing sleeve 3 could be significantly suppressed, particularly in the replenishment amount range of 0.400 g. Also, even in the replenishment amount range of 0.800 g, the generation of agglomerates could be sufficiently suppressed compared to the comparative example.

[0085] 10(b) shows the tendency of the amount of agglomerates generated when the angle of the cutout surface 313 is changed. Here, the cutout surface 313 is set at 0° on a cross section perpendicular to the rotation axis 310 of the supply and conveying screw 31, and the number of agglomerates is compared when the cutout surface 313 is set within a range of ±30° from the perpendicular direction. The amount of supply developer was 0.400g and 0.800g.

[0086] It was found that the agglomerates can be crushed most effectively when the cutout surface 313 is in the vertical direction (0°), and the crushing ability begins to decrease significantly when the angle exceeds ±20° from the vertical direction. For this reason, it is desirable to set the angle of the cutout surface 313 within the range of ±20° from the vertical direction of the rotation axis 310 as described above.

[0087] As is clear from the above verification results, by using the configuration of this embodiment, it is possible to sufficiently break up the agglomerates in the refill developer, and to suppress the occurrence of stained images. In particular, even when applied to a small developing device, it is possible to suppress the occurrence of stained images, and it is possible to provide a good, high-quality image forming device.

[0088] <Second embodiment> The second embodiment will be described with reference to Figures 11 to 13. In this embodiment, the cross-sectional area of ​​the cutout surface of the discontinuous portion is different from that of the first embodiment described above. The other configurations and functions are the same as those of the first embodiment described above. For this reason, the same reference numerals are used for the same configurations, and the description and illustration are omitted or simplified, and the following description will focus on the points that are different from the first embodiment.

[0089] 11 shows the supply conveying screw 31A and the second conveying screw 14 of this embodiment. In this embodiment, the cross section of the blade 311A ​​at the discontinuous portion 312A, that is, the shape of the notched surface 313A, is changed to increase the cross-sectional area. A The cross-sectional area of ​​the supply conveying screw 31A is made larger than the average cross-sectional area of ​​the continuous portion where the blades 311A ​​of the supply conveying screw 31A are continuous.

[0090] Specifically, the spiral blade 311A ​​of the supply and transport screw 31A is shaped to periodically have knot-like portions that are thicker than the normal thickness, and discontinuous portions 312A are formed in the thickened portions of the blade 311A. By providing discontinuous portions 312A in the thick portions of the blade 311A ​​in this way, the cross-sectional shape of the cutout surface 313A is a trapezoid with a wider width than the cutout surface 313 of the first embodiment. As a result, A The cross-sectional area of ​​the bearing is increased in the direction of the axis of rotation.

[0091] Increasing the cross-sectional area of ​​the cutout surface 313A in this way increases the probability of contact with the agglomerates, improving the ability to crush the agglomerates. On the other hand, increasing the cross-sectional area affects the developer transport performance of the supply / transport screw 31A. If the cross-sectional area of ​​only the knotty discontinuous portion 312A is increased, the blade shape around it will widen like a skirt, creating a surface perpendicular to the transport direction, improving the agglomerate crushing ability but impeding transport.

[0092] Specifically, when the cross-sectional area becomes about 2.5 times or more that of the first embodiment, the developer transport capacity decreases by 15% or more, and it is not possible to achieve both the agglomerate crushing capacity and the developer transport capacity. Note that, while discontinuous portion 312 in the first embodiment is formed without changing the thickness of blade 311, discontinuous portion 312A in the second embodiment is formed in a portion where the thickness of blade 311A ​​is increased as described above.

[0093] Next, the supply conveying screw 31 (Example 1) of the first embodiment and the supply conveying screw 31A (Example 2) of the second embodiment were prepared, and an experiment to examine the number of agglomerates for each will be described. In the experiment, the ratio of the cross-sectional area of ​​the cutout surface 313A of Example 2 to the cross-sectional area of ​​the cutout surface 313 of Example 1 (cross-sectional area ratio = cross-sectional area of ​​cutout surface 313A / cross-sectional area of ​​cutout surface 313) was changed, and the number of agglomerates was examined in the same manner as in the above-mentioned verification. The cross-sectional area ratio was changed by changing the cross-sectional area of ​​the cutout surface 313A. In addition, at this time, the peak change value Δ [%] of the inductance sensor 43 was used to examine the time (delay time) until the supply developer reached the inductance sensor 43.

[0094] The results are shown in Figs. 12(a) and 12(b). Fig. 12(a) shows the relationship between the cross-sectional area ratio and the number of agglomerates, and Fig. 12(b) shows the relationship between the cross-sectional area ratio and the delay time. As is clear from Figs. 12(a) and 12(b), the experiment showed a tendency that the conveying ability and the agglomerate crushing ability can be compatible if the cross-sectional area ratio of the cutout surface 313A of Example 2 to the cross-sectional area of ​​the cutout surface 313 of Example 1 is up to 2.0 times. For example, the cross-sectional area of ​​the thinnest part of the blade 311A ​​of the supply conveying screw 31A of the second embodiment is the same as the cross-sectional area of ​​the cutout surface 313 of Example 1. In this case, if the cross-sectional area of ​​the cutout surface 313A is 2.0 times or less the cross-sectional area of ​​the thinnest part of the blade 311A, the agglomerate crushing ability can be improved while suppressing the decrease in the developer conveying ability.

[0095] Next, we will explain the results of verifying the agglomerate crushing ability in a configuration in which the cross-sectional area of ​​cutout surface 313A in Example 2 is 1.8 times that of cutout surface 313 in Example 1, i.e., the cross-sectional area ratio is 1.8, in the same manner as in the verification of the first embodiment.

[0096] In Example 2, the supply conveying screw 31A is a three-thread screw with one discontinuous portion 312A per thread. As in Example 1, the three discontinuous portions 312A are evenly arranged in both the axial and circumferential directions so that they are not adjacent to each other. The detailed dimensions of the supply conveying screw 31A are a screw pitch of 50 mm, a diameter of the blades 311A ​​of φ14 mm, and a diameter of the rotating shaft 310 of φ6 mm.

[0097] In the second embodiment, the cutout surface 313 A In order to increase the cross-sectional area of ​​the notch surface 313A, the thickness of the blade 311A ​​of the supply conveying screw 31A is changed so that it is thicker at the discontinuous portion 312A, as shown in Fig. 11. However, the method of increasing the cross-section of the notch surface 313A may be other than changing the thickness of the blade. For example, a rib-shaped member may be provided on the notch surface of the blade to increase the area of ​​the notch surface.

[0098] In this configuration, similarly to the verification of the first embodiment, a stain image that appears on the developing sleeve 3 when a replenishment developer for verifying agglomerates containing agglomerates is placed in the developing container 2 was confirmed. The results are shown in FIG. 13. The graph in FIG. 13 shows the number of agglomerates on the developing sleeve 3 relative to the replenishment amount in the stain image. FIG. 13 also shows the results of the comparative example and Example 1 shown in FIG. 10(a). As is clear from FIG. 13, it was found that the number of agglomerates can be reduced more in Example 2 than in Example 1.

[0099] As is clear from the above verification results, by using the configuration of this embodiment, it is possible to sufficiently crush the agglomerates in the refill developer, and to suppress the occurrence of stained images, more than in the configuration of the first embodiment. In particular, even when applied to a small developing device, it is possible to suppress the occurrence of stained images, and it is possible to provide a good, high-quality image forming device.

[0100] <Third embodiment> The third embodiment will be described with reference to Figs. 14 to 15(b). In this embodiment, the supply conveying path 53 is shaped to cover the periphery of the supply conveying screw 31A, and a discontinuous portion 312A is disposed at the junction 57 where the developer conveyed from the supply conveying path 53 joins with the developer in the stirring chamber 12. The other configurations and functions are the same as those of the second embodiment described above. For this reason, the same reference numerals are used for the same configurations, and explanations and illustrations are omitted or simplified, and the following description will focus on the points that are different from the second embodiment. The same applies even if the supply conveying screw disposed in the supply conveying path 53 is the supply conveying screw 31 of the first embodiment.

[0101] 14 shows the supply conveying path 53 and the supply conveying screw 31A and the second conveying screw 14 arranged in the stirring chamber 12 of this embodiment. In this embodiment as well, the supply conveying path 53 is configured to cover the periphery of the supply conveying screw 31A in the section from the supply port 50 where the developer is replenished to the circulation path. Also in this embodiment, a discontinuous portion 312A is arranged at a junction 57 where the developer conveyed from the supply conveying path 53 joins with the developer in the stirring chamber 12. A part of the supply conveying screw 31A enters the stirring chamber 12.

[0102] Specifically, in the present embodiment, as in the first and second embodiments, a supply conveying screw 31A having discontinuous portions 312A on each blade 311A ​​of the three-row screw is used. The supply conveying screw 31A is disposed coaxially with the second conveying screw 14, and the supply conveying path 53 has a supply developer at the most upstream portion. Accommodated The toner bottle 8 is connected to a supply port 50 (FIG. 3) which is connected to the supply conveying section 83.

[0103] Furthermore, in order to more efficiently break up clumps in the replenishment developer with the above-mentioned configuration, the container shape between the junction 57 of the replenishment conveying screw 31A and the second conveying screw 14 and the replenishment port 50 is made into a tunnel shape along the outer periphery of the replenishment conveying screw 31A. When replenishment developer mainly composed of toner with a low specific gravity is conveyed by the replenishment conveying screw 31A, the developer is likely to splash up or scatter. For this reason, by making the replenishment conveying path 53 into a tunnel shape in this way, the developer is kept within the diameter of the blade 311A ​​by the ceiling part 56, making it easier for the developer to be affected by the replenishment conveying screw 31A.

[0104] Next, the arrangement of the discontinuous portions 312A of the supply conveying screw 31A of this embodiment will be described. In this embodiment, a three-thread screw is used as the supply conveying screw 31A, so that the discontinuous portions 312A are provided at one location on each thread, for a total of three locations. In order to efficiently crush and stir the agglomerates in the supply developer, Regarding the third direction It is important that the discontinuous portion 312A is not located at the position of the supply port 50, but is located at the junction 57 with the developer circulation path.

[0105] Therefore, in this embodiment, the first location from the upstream side of the discontinuous portion 312A in the transport direction is disposed in the replenishment transport path 53 downstream of the supply port 50. When the discontinuous portion 312A is disposed at the position of the supply port 50, the space above in the vertical direction is wide, so that the developer that collides with the cutout surface 313A of the discontinuous portion 312A or the blade 311A ​​temporarily becomes suspended in the air, and is difficult to be taken into the transport path, resulting in reduced transport efficiency.

[0106] In contrast, by arranging the discontinuous portion 312A at the portion of the supply conveying path 53 where the ceiling portion 56 is located, the aggregates that collide with the cutout surface 313A collide with the ceiling portion 56 again, bounce back, and return to within the rotation radius of the supply conveying screw 31A. Then, the probability of colliding with the cutout surface 313A again is increased, and the conveying loss due to the bounce is suppressed, so that the conveying efficiency can be maintained. The ceiling portion 56 of the supply conveying path 53 may be arranged so as to extend over the entire area between the supply port 50 and the junction portion 57 of the supply conveying screw 31A, or may be arranged only above the discontinuous portion 312A. The second discontinuous portion 312A is arranged in the center of the supply conveying path 53, so that the same effect as the first discontinuous portion can be obtained.

[0107] On the other hand, the third discontinuous portion 312A was disposed at the junction 57. In other words, the supply conveying screw 31A is provided extending from the supply conveying path 53 to the communication portion 17 (see FIG. 4). At the confluence 57, the two types of powders, the replenishment developer mainly made of toner particles and the developer mainly made of carrier particles, which have different specific gravities, are mixed and transported. Here, the replenishment developer and the developer are difficult to mix because their specific gravities are significantly different. In reality, it is expected that the replenishment developer and the developer are mixed and transported. However, when the replenishment transport screw 410 without discontinuous parts as shown in FIG. 7(a) is used, the behavior of the replenishment developer with a light specific gravity often collides with the developer in the circulation path and is temporarily retained without mixing, and then gradually mixed and transported. Then, the effect of dispersing the replenishment developer by the replenishment transport screw 410 is lost.

[0108] To avoid this, in this embodiment, discontinuous portion 312A is disposed at junction 57 so that the replenishment developer and the developer in the circulation path are mixed without stagnation. That is, by disposing discontinuous portion 312A at junction 57, the developer in the circulation path collides with notched surface 313A, and the developer density at junction 57 is substantially reduced, and the space is created so that the developer is mixed with the replenishment developer. This makes it possible to supply the replenishment developer to the developer circulation path without impeding the transport force while crushing the agglomerates.

[0109] Next, an experiment is described in which the agglomerate crushing ability is verified in the same manner as in the verification of the first embodiment using the above-mentioned configuration (Example 3), and an experiment is performed to investigate the delay time described in the second embodiment. That is, in the experiment, an evaluation of agglomerate crushing when agglomerate verification replenishment developer containing agglomerates is placed in the developing container 2 and a peak change value Δ [%] of the inductance sensor 43 is confirmed. In addition, the cross-sectional area ratio of the replenishment conveying screw 31A in Example 3 is set to 2.5.

[0110] The results of this experiment are shown in Figures 15(a) and (b). The graph in Figure 15(a) shows the number of agglomerates on the developing sleeve 3 relative to the amount of replenishment in the stain image. Figure 15(a) also shows the results of the comparative example and Examples 1 and 2 shown in Figure 13. The graph in Figure 15(b) shows the results of changing the cross-sectional area ratio and investigating the time (delay time) it takes for the replenishment developer to reach the position of the inductance sensor 43.

[0111] As is clear from Fig. 15(a), in the case of Example 3, the number of stain images that appear on the developing sleeve 3 tends to decrease as the amount of replenishment developer increases, compared to the configurations of the comparative example and Examples 1 and 2. Also, as is clear from Fig. 15(b), it was found that even in Example 3, which has a cross-sectional area ratio of 2.5 that can reduce agglomerates, an increase in delay time can be suppressed. This shows that by using the configuration of Example 3, a configuration with little loss in transport speed can be obtained even when the agitation property is improved.

[0112] As is clear from the above experimental results, the configuration of this embodiment can provide a developing device that can efficiently crush agglomerates and does not cause delays in the transport of replenishment developer.

[0113] <Other embodiments> The discontinuous portion described in each of the above embodiments may be any portion that does not connect the blades, and may be, for example, a blade having a smaller outer diameter than adjacent blades in the direction along the spiral. In other words, a part of the outer periphery of a blade that is continuous in the axial direction may be cut out in the axial direction, and this cut-out part may be used as a gap.

[0114] In the above-mentioned embodiments, the image forming apparatus is a printer, but the present invention is also applicable to copiers, facsimiles, multifunction machines, etc. Also, in the above-mentioned embodiments, the developing device is configured to supply developer from a developing chamber to a developing sleeve and collect developer from the developing sleeve in the developing chamber. However, the present invention is also applicable to a configuration in which developer is supplied from a developing chamber (first transport path) and collected in a stirring chamber (second transport path) arranged on either side of the developing chamber by a partition wall. Furthermore, the present invention is also applicable to a configuration in which the first transport path and the second transport path are arranged in a horizontal line in addition to a developing device in which the first transport path and the second transport path are arranged in a vertical direction or in a positional relationship inclined with respect to the horizontal direction. [Explanation of symbols]

[0115] 1Y, 1M, 1C, 1K ···Developing device / 2···Developing container / 3···Developing sleeve (developer carrier) / 11···Developing chamber (first transport path) / 12···Mixing chamber (second transport path) / 13···First transport screw (first transport screw section) / 14···Second transport screw (second transport screw section) / 14a···Blade / 14b···Discontinuous section / 31, 31A···Supply transport screw (supply transport screw section) / 50···Supply port / 53···Supply transport path / 310···Rotating shaft / 311, 311A···Blade / 312A···Discontinuous section / 313A···Notched surface

Claims

1. a developer carrier that carries and transports a developer containing a toner and a carrier to a development position; a developer container for accommodating the developer; A first conveying screw portion; A second conveying screw portion; A supply conveying screw portion; Equipped with The developing container is a first chamber for supplying a developer to the developer carrier; a second chamber separated from the first chamber by a partition wall; a first communication portion that allows developer to communicate from the first chamber to the second chamber; a second communication portion that allows developer to communicate from the second chamber to the first chamber; a supply transport path for transporting a supply developer to a circulation path in which the developer circulates between the first chamber and the second chamber; a developer supply section that supplies a supply developer to the supply transport path; having the first conveying screw portion is provided in the first chamber and conveys the developer in a first direction from the second communicating portion toward the first communicating portion, the second conveying screw portion is provided in the second chamber and conveys the developer in a second direction from the first communicating portion toward the second communicating portion, the supply conveying screw portion is provided in the supply conveying path and conveys the supply developer in a third direction from the developer supply portion toward the first communication portion, the supply transport path is disposed upstream of the second chamber in the second direction, the second conveying screw portion is disposed downstream of the first communicating portion and upstream of the second communicating portion in the second direction, the supply conveying screw portion is disposed upstream of the second conveying screw portion in the second direction, a rotation axis of the supply conveying screw portion is coaxial with a rotation axis of the second conveying screw portion, The supply conveying screw portion is a first blade portion formed in a spiral shape on an outer circumferential surface of a rotation shaft of the supply conveying screw portion, the first blade portion conveying the supply developer in the third direction; a second blade portion formed in a spiral shape on an outer circumferential surface of a rotation shaft of the supply conveying screw portion, the second blade portion conveying the supply developer in the third direction; a third blade portion formed in a spiral shape on an outer circumferential surface of a rotation shaft of the supply conveying screw portion, the third blade portion conveying the supply developer in the third direction; having each of the pitch of the first blade portion, the pitch of the second blade portion, and the pitch of the third blade portion is greater than the pitch of the blade of the second conveying screw portion; The outer diameter of the first blade portion, the outer diameter of the second blade portion, and the outer diameter of the third blade portion are the same, a developing device characterized in that the third blade portion is formed continuously in a region between the end end of the first blade portion and the start end of the second blade portion in the third direction and shifted circumferentially from the end end of the first blade portion and the start end of the second blade portion in the replenishment conveying screw portion.

2. 2. The developing device according to claim 1, wherein a gap is provided between the terminal end of the first blade portion and the starting end of the second blade portion in the direction of the rotation axis of the replenishment conveying screw portion.

3. The developing device according to claim 1 or 2, wherein, in the second direction, the end of the first blade portion and the start of the second blade portion are each located upstream of the first communication portion.

4. 4. The developing device according to claim 1, wherein the replenishment conveying screw portion is provided so as to extend from the replenishment conveying path to the first communication portion.

5. the supply conveying screw portion has a gap formed by the terminal end of the first blade portion and the starting end of the second blade portion, 2. The developing device according to claim 1, wherein the gap has a range of 30 degrees or more and 90 degrees or less in the circumferential direction of the replenishment conveying screw portion.

6. 6. The developing device according to claim 5, wherein the gap is disposed at a junction where the replenishment transport path and the circulating path join together.

7. 7. The developing device according to claim 5, wherein the gap is disposed at a position offset from the developer supply portion in the third direction.

8. 8. The developing device according to claim 1, wherein the second conveying screw portion has a portion in which the blade is discontinuous at least in a portion in a direction of a rotation axis of the second conveying screw portion.

9. 9. The developing device according to claim 1, wherein the supply conveying screw portion further includes a fourth blade portion formed in a spiral shape on an outer peripheral surface of a rotating shaft of the supply conveying screw portion for conveying the supply developer in the third direction.

Images