Developing device

Abstract

To provide a configuration that can prevent the occurrence of an image defect.SOLUTION: A developing device comprises a developer circulation part 46, a developer supply screw 42, a developer recovery part 47, a developer recovery screw 44, a first developing roller 30, a first magnet 36, a second developing roller 31, a second magnet 37, a peeling roller 32, a third magnet 38, and a shield member 10 that is arranged opposite to the second developing roller 31 and guides developer peeled off from the second developer roller 31 by a repulsive magnetic field generated by the second magnet 37 to the developer supply screw 42. A position at which the second developing roller 31 is in most proximity to the shield member 10 is present vertically above a center of rotation Q of the first developing roller 30 and is present vertically below a center of rotation R of the second developing roller 31.SELECTED DRAWING: Figure 6

Description

[Technical Field]

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

[0002] A developing device has been proposed in which two developing rollers that develop electrostatic latent images formed on an image carrier with developer are arranged side by side in the direction of rotation of the image carrier (Patent Document 1). In the developing device described in Patent Document 1, of the two developing rollers, developer is supplied from a supply unit to the first developing roller that is located vertically below, and developer is passed from the first developing roller below to the second developing roller that is located vertically above. The developer is then peeled off and collected from the second developing roller that is located above. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-254107 Summary of the Invention [Problem to be solved by the invention]

[0004] In the configuration described in Patent Document 1, the developer is peeled off from the second developing roller by a peeling roller. The developer peeled off from the second developing roller falls under its own weight or is transferred to the peeling roller. During the developer transfer process from the second developing roller to the peeling roller, an air current is generated in the gap between the second developing roller and the peeling roller. Due to the influence of this air current, some of the developer is carried by the air current and falls onto the first developing roller located directly below the second developing roller.

[0005] The developer that has fallen onto the first developing roller is used developer that has been used in the developing process on the first developing roller and the second developing roller, and the amount of toner in the developer is less than that of the normal developer present in the supply section.

[0006] If such used developer falls onto the first developing roller, the magnetic force on the first developing roller may cause the used developer to get into the developer transfer area near the closest position between the first and second developing rollers. If the used developer is transferred back to the second developing roller at the developer transfer area between the first and second developing rollers, the developer on the second developing roller will become a mixture of regular developer and used developer (developer with low toner content). As a result, unevenness occurs in the amount of toner transferred to the image carrier when developing the electrostatic latent image on the image carrier, resulting in uneven density in the final output image. This phenomenon is known as the drag phenomenon.

[0007] As described above, in a developing device having two developing rollers as described in Patent Document 1, there is a risk that image defects such as uneven density may easily occur on the output image. In particular, under conditions where the image forming apparatus is operated at high speed, the above-mentioned problem is likely to occur due to the influence of temperature rise inside the developing device.

[0008] SUMMARY OF THE INVENTION An object of the present invention is to provide a configuration that can suppress the occurrence of image defects. [Means for solving the problem]

[0009] a second chamber separated from the first chamber by a partition wall; a second chamber disposed in the second chamber and transporting the developer contained in the second chamber; a first rotor to which the developer is supplied from the first chamber, the first rotor carrying and transporting the developer to develop an electrostatic latent image formed on an image carrier; a first magnet fixedly disposed inside the first rotor; a second rotor disposed opposite the first rotor, to which the developer is transferred from the first rotor by a magnetic field generated by the first magnet, the second rotor carrying and transporting the developer to develop the electrostatic latent image; The developer development device comprises: a second magnet fixedly arranged inside the second rotating body; a third rotating body arranged opposite the second rotating body, to which the developer is transferred from the second rotating body by a magnetic field generated by the second magnet, the third rotating body carrying and transporting the developer to recover the developer to the second chamber after developing the electrostatic latent image; a third magnet fixedly arranged inside the third rotating body; and a guide portion arranged opposite the second rotating body, which guides the developer peeled off from the second rotating body by a repulsive magnetic field generated by the second magnet to the first transport screw, wherein the position at which the second rotating body is closest to the guide portion is vertically above the center of rotation of the first rotating body and vertically below the center of rotation of the second rotating body. [Effects of the Invention]

[0010] According to the present invention, the occurrence of image defects can be suppressed. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing the schematic configuration of the developing device according to the first embodiment. [Figure 3] FIG. 3 is a diagram showing the arrangement of magnetic poles of a first developing roller according to the first embodiment. [Figure 4] FIG. 4 is a diagram showing the arrangement of magnetic poles of a second developing roller according to the first embodiment. [Figure 5] FIG. 2 is a diagram showing the arrangement of magnetic poles of the peeling roller according to the first embodiment. [Figure 6] FIG. 2 is an enlarged view of the periphery of a first developing roller and a second developing roller according to the first embodiment. [Figure 7] FIG. 10 is a cross-sectional view showing the schematic configuration of a developing device according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] [First embodiment] The first embodiment will be described with reference to Figures 1 to 6. First, the schematic configuration of an image forming apparatus according to the first embodiment will be described with reference to Figure 1.

[0013] [Image forming equipment] The image forming apparatus 100 is a full-color image forming apparatus, and in the first embodiment, is, for example, an MFP (Multi-Function Peripheral) having a copy function, a printer function, and a scan function. As shown in Fig. 1, the image forming apparatus 100 has image forming units PY, PM, PC, and PK arranged in parallel, which respectively perform the image forming process of four color toner images of yellow, magenta, cyan, and black.

[0014] The image forming units PY, PM, PC, and PK for each color include primary chargers 21Y, 21M, 21C, and 21K, developing devices 1Y, 1M, 1C, and 1K, and optical writing units (exposure devices) 22Y, 22M, 22C, and 22K. The image forming units PY, PM, PC, and PK for each color also include photosensitive drums 28Y, 28M, 28C, and 28K, and cleaning devices 26Y, 26M, 26C, and 26K. The image forming apparatus 100 also includes a transfer device 2 and a fixing device 3. Since the image forming units PY, PM, PC, and PK for each color have the same configuration, the following description will be limited to the image forming unit PY.

[0015] The photosensitive drum 28Y, which serves as an image carrier, is a photosensitive member having a photosensitive layer made of a resin such as polycarbonate containing an organic photoconductor (OPC), and is configured to rotate at a predetermined speed. The primary charger 21Y is made of a corona discharge electrode disposed around the photosensitive drum 28Y, and charges the surface of the photosensitive drum 28Y with generated ions.

[0016] The optical writing unit 22Y incorporates a scanning optical device and exposes the charged photosensitive drum 28Y based on image data, thereby reducing the potential of the exposed area and forming a charge pattern (electrostatic latent image) corresponding to the image data. The developing device 1Y transfers the contained developer to the photosensitive drum 28Y to develop the electrostatic latent image formed on the photosensitive drum 28Y. The developer is a mixture of carrier and toner corresponding to each color, and the electrostatic latent image is visualized by the toner.

[0017] The transfer device 2 has primary transfer rollers 23Y, 23M, 23C, and 23K, an intermediate transfer belt 24, and a secondary transfer roller 25. The intermediate transfer belt 24 is wound around the primary transfer rollers 23Y, 23M, 23C, and 23K and multiple rollers and is supported so that it can run. From the top in FIG. 1, the primary transfer rollers 23Y, 23M, 23C, and 23K correspond to the colors Y (yellow), M (magenta), C (cyan), and K (black), respectively. The secondary transfer roller 25 is disposed outside the intermediate transfer belt 24 and is configured so that a recording material can pass between it and the intermediate transfer belt 24. The recording material is, for example, a sheet such as paper or a plastic sheet.

[0018] The toner images of each color formed on the photosensitive drums 28Y, 28M, 28C, and 28K are successively transferred onto the intermediate transfer belt 24 by the primary transfer rollers 23Y, 23M, 23C, and 23K. A color toner image is then formed in which layers of yellow, magenta, cyan, and black are superimposed. The formed toner image is transferred by the secondary transfer roller 25 onto a recording material conveyed from a cassette or the like containing the recording material. Pressure and heat are applied to the recording material onto which the toner image has been transferred in the fixing device 3. This melts the toner on the recording material, and the color image is fixed to the recording material.

[0019] Developer storage units 27Y, 27M, 27C, and 27K are provided corresponding to developing devices 1Y, 1M, 1C, and 1K, respectively, and are filled with replaceable bottles containing developers corresponding to the respective colors of yellow, magenta, cyan, and black, from top to bottom. Developer storage units 27Y, 27M, 27C, and 27K are configured to be able to transport (supply) developers to developing devices 1Y, 1M, 1C, and 1K corresponding to the colors of the developers stored therein.

[0020] For example, the toner weight ratio of the developer stored in the bottle is 80 to 95%, and the toner weight ratio of the developer in the developing devices 1Y, 1M, 1C, and 1K is 5 to 10%. Therefore, when toner is consumed by development in the developing devices 1Y, 1M, 1C, and 1K, developer containing toner corresponding to the consumed amount is replenished, and the toner weight ratio of the developer in the developing devices 1Y, 1M, 1C, and 1K is maintained constant.

[0021] [Developing device] Next, developing devices 1Y, 1M, 1C, and 1K will be described in detail using Figures 2 to 6. Since developing devices 1Y, 1M, 1C, and 1K have the same configuration, the following description will focus on developing device 1Y as a representative. Figure 2 is a conceptual diagram illustrating developing device 1Y shown in Figure 1, and Figures 3, 4, and 5 are conceptual diagrams illustrating the magnetic pole configurations of a first magnet 36, a second magnet 37, and a third magnet 38 arranged in developing device 1Y.

[0022] As shown in FIG. 2, the developing device 1Y has a first developing roller 30, a second developing roller 31, a peeling roller 32, a developer supply screw 42, a developer stirring screw 43, and a developer recovery screw 44, and these components are housed in a developing container 60.

[0023] The first developing roller 30, which serves as a first rotating body, is a developer carrier that is driven to rotate and is disposed adjacent to the photosensitive drum 28Y so that its rotation axis is substantially parallel to the rotation axis of the photosensitive drum 28Y. The first developing roller 30 includes a rotating first sleeve 33 and a first magnet (stationary magnet) 36, which is disposed non-rotatingly inside the first sleeve 33 and serves as a first magnet that magnetically attracts developer to the surface of the first sleeve 33. The first developing roller 30 magnetically attracts (carries) the developer pumped up by a developer supply screw 42, which serves as a first transport screw, and develops the electrostatic latent image formed on the rotating photosensitive drum 28Y (image carrier) with the developer. That is, the first developing roller 30 carries and transports the developer to develop the electrostatic latent image formed on the photosensitive drum 28Y.

[0024] The first sleeve 33 is a non-magnetic cylindrical member, and is driven to rotate around a rotation shaft 39. The rotation direction of the first sleeve 33 is clockwise as indicated by the arrow in Fig. 2, which is opposite to the rotation direction of the photosensitive drum 28Y in the first embodiment. Therefore, the first sleeve 33 and the photosensitive drum 28Y rotate in the same direction while facing each other.

[0025] The first magnet 36 is disposed inside the first sleeve 33, and as shown in Fig. 3, has a plurality of sector-shaped magnetic poles 100-106 and a sector-shaped non-magnetic pole portion 110. A space is disposed between the inner periphery of the first sleeve 33 and the outer periphery of the first magnet 36 to allow the first sleeve 33 to rotate.

[0026] The developer attracted to the first sleeve 33 is transported toward the photosensitive drum 28Y by the rotation of the first sleeve 33, and develops the latent image formed on the photosensitive drum 28Y. After developing the latent image formed on the photosensitive drum 28Y, the developer on the first sleeve 33 is transported to the vicinity of the second developing roller 31 by the rotation of the first sleeve 33. Then, near the closest position between the first developing roller 30 and the second developing roller 31, a magnetic field is generated in the first magnet 36 contained in the first developing roller 30 and the second magnet 37 contained in the second developing roller 31. This magnetic field causes the developer to be separated from the first sleeve 33 and transferred onto the second sleeve 34.

[0027] The second developing roller 31, which serves as a second rotating body, is a developer carrier that is driven to rotate. The second developing roller 31 is disposed downstream of the first developing roller 30 in the rotation direction of the photosensitive drum 28Y and above the rotation center of the first developing roller 30 in the vertical direction, and receives the developer from the first developing roller 30 by magnetic force. Similar to the first developing roller 30, the second developing roller 31 is disposed adjacent to the photosensitive drum 28Y so that its rotation axis is substantially parallel to the rotation axis of the photosensitive drum 28Y. Therefore, the rotation axes of the second developing roller 31 and the first developing roller 30 are substantially parallel to each other.

[0028] The second developing roller 31 includes a rotating second sleeve 34 and a second magnet (fixed magnet) 37 that is non-rotatingly disposed inside the second sleeve 34 and that attracts developer to the surface of the second sleeve 34 by magnetic force. The second developing roller 31 receives and attracts (carries) the developer from the first developing roller 30 (first sleeve 33) by magnetic force, and develops the electrostatic latent image formed on the rotating photosensitive drum 28Y with the developer. That is, the second developing roller 31 carries and transports the developer to develop the electrostatic latent image formed on the photosensitive drum 28Y. A peeling roller 32, which will be described later, is located to the side of the second developing roller 31.

[0029] The second sleeve 34 is a non-magnetic cylindrical member and is driven to rotate around the rotation shaft 40. The rotation direction of the second sleeve 34 is clockwise as indicated by the arrow in FIG. 2, which is opposite to the rotation direction of the photosensitive drum 28Y in the first embodiment. Therefore, the second sleeve 34 and the photosensitive drum 28Y rotate in the same direction when they face each other. Furthermore, the second sleeve 34 and the first sleeve 33 rotate in opposite directions when they face each other.

[0030] The second magnet 37 is disposed inside the second sleeve 34, and as shown in Fig. 4, has a plurality of sector-shaped magnetic poles 201-207 and a sector-shaped non-magnetic pole portion 210. A space is disposed between the inner periphery of the second sleeve 34 and the outer periphery of the second magnet 37, allowing the second sleeve 34 to rotate.

[0031] The developer attracted to the second sleeve 34 is transported toward the photosensitive drum 28Y by the rotation of the second sleeve 34, and develops the latent image formed on the photosensitive drum 28Y. After the latent image formed on the photosensitive drum 28Y is developed, the developer remaining on the second sleeve 34 is transported to the vicinity of the peeling roller 32 by the rotation of the second sleeve 34. Then, near the closest position between the second developing roller 31 and the peeling roller 32, a magnetic field is generated in the second magnet 37 contained in the second developing roller 31 and the third magnet 38 contained in the peeling roller 32. This magnetic field transfers the developer from the second sleeve 34 to the third sleeve 35 of the peeling roller 32.

[0032] The peeling roller 32, which serves as a peeling section and a third rotating body, is disposed on the opposite side of the photosensitive drum 28Y with respect to the rotation center R (see FIG. 6, which will be described later) of the second sleeve 34. The peeling roller 32 peels off the developer from the second developing roller 31 after the electrostatic latent image on the photosensitive drum 28Y has been developed by the second developing roller 31. Specifically, the peeling roller 32 is a developer carrier that is driven to rotate, and is disposed between the second developing roller 31 and the developer recovery screw 44 so that its rotation center is above the rotation center R of the second developing roller 31.

[0033] The peeling roller 32 is disposed so that its rotation axis is substantially parallel to the rotation axis of the second developing roller 31. The peeling roller 32 has a rotating third sleeve 35 and a third magnet (fixed magnet) 38 that is disposed non-rotatingly inside the third sleeve 35 and serves as a third magnet that attracts the developer to the surface of the third sleeve 35 by magnetic force. The peeling roller 32 is configured to receive the developer from the second developing roller 31 based on the magnetic force.

[0034] The third sleeve 35 is a non-magnetic cylindrical member, and is driven to rotate around the rotation shaft 41. The rotation direction of the third sleeve 35 is counterclockwise as indicated by the arrow in Fig. 2, which is opposite to the rotation direction of the second sleeve 34 in the first embodiment. Therefore, the third sleeve 35 and the second sleeve 34 rotate in the same direction while facing each other.

[0035] 5, the third magnet 38 has a plurality of sector-shaped magnetic poles 301-305 and a sector-shaped non-magnetic pole portion 310. A space that allows the third sleeve 35 to rotate is provided between the inner periphery of the third sleeve 35 and the outer periphery of the third magnet 38.

[0036] The developer attracted onto the third sleeve 35 is transported downstream in the rotation direction by the rotation of the third sleeve 35. The developer transported downstream is peeled off from the third sleeve 35 by a third magnet 38 contained in the peeling roller 32 at a position close to a developer recovery screw 44 serving as a second transport screw, and falls by its own weight toward a guide member 45 located vertically below. The developer that has fallen onto the guide member 45 is then guided by its own weight toward the developer recovery screw 44. In other words, the peeling roller 32 carries and transports the developer after developing the electrostatic latent image formed on the photosensitive drum 28Y, in order to collect the developer in a developer recovery section 47.

[0037] The guide member 45 and the developer recovery screw 44 constitute a developer recovery section 47 as a recovery section that recovers the developer peeled off from the third sleeve 35 on the peeling roller 32. In the developer recovery section 47, the developer recovery screw 44 is positioned below the center of rotation of the peeling roller 32 in the vertical direction, and conveys the developer handed over (recovered) from the peeling roller 32 while stirring it.

[0038] The guide member 45 serving as a guide section is disposed vertically below the center of rotation of the peeling roller 32, and guides the developer peeled off by the peeling roller 32 toward the developer recovery screw 44. Such a guide member 45 has an inclined surface 45a along which the developer slides down under its own weight, in order to more reliably guide the peeled off developer toward the developer recovery screw 44. The inclined surface 45a is inclined with respect to the horizontal direction so that the developer recovery screw 44 side is lower than the position below the peeling roller 32.

[0039] The developer recovery screw 44, which serves as a recovery member and a transport unit, transports the recovered developer to a developer circulation unit 46, which will be described next. That is, the developer recovery screw 44 is a screw transport member used to transport the recovered developer in one direction while stirring it as it slides down the inclined surface of the guide member 45.

[0040] The developer circulating section 46 is a supply section for supplying the developer to the first developing roller 30, and includes a regulating member 50 and a developer supply screw 42. In the developer circulating section 46, the developer is agitated by the developer supply screw 42 and transported in a substantially horizontal direction, and is supplied to the first developing roller 30. As described above, the developer collected by the developer collecting section 47 falls under its own weight and is introduced into the developer circulating section 46. That is, the developer circulating section 46 is positioned lower than the developer collecting section 47 in the vertical direction.

[0041] The developer supply screw 42, developer stirring screw 43, and developer recovery screw 44 are screw conveying members that convey the developer in one direction while stirring it. The developer supply screw 42 and developer stirring screw 43 are positioned below the rotation center of the developer recovery screw 44 in the vertical direction. The developer supply screw 42, developer stirring screw 43, and developer recovery screw 44 are also arranged so that their rotation axes are approximately parallel to each other. The rotation axes of these screws are also approximately parallel to the rotation axis of the first developing roller 30.

[0042] The developer supply screw 42 is located between the first developing roller 30 and the developer agitating screw 43, and a partition wall 48 of the developing container 60 is disposed between the developer supply screw 42 and the developer agitating screw 43. The partition wall 48 of the developing container 60 extends along the rotational axis direction of the developer supply screw 42 and the developer agitating screw 43. The partition wall 48 is provided with a communication opening (not shown) as a communication portion that communicates a first conveying path 61, through which the developer is conveyed by the developer supply screw 42, with a second conveying path 62, through which the developer is conveyed by the developer agitating screw 43. In other words, the partition wall 48 separates the first conveying path 61 from the second conveying path 62.

[0043] A partition wall 63 of the developing container 60 is disposed between the developer recovery screw 44 and the developer supply screw 42. The developer stirred by the developer recovery screw 44 passes through a communication port (not shown) serving as a communication portion formed in the partition wall 63 of the developing container 60 and falls by its own weight toward the developer supply screw 42. The guide member 45 described above is formed integrally with the partition wall 63, and the developer recovery screw 44 is disposed above the partition wall 63.

[0044] The communication port through which the developer stirred by the developer recovery screw 44 falls under its own weight and is introduced into the developer circulation section 46 is disposed at the following position. That is, it is preferable that the communication port through which the developer is introduced into the developer circulation section 46 be disposed so as to avoid the area where the developer is supplied toward the first developing roller 30 (the middle part with respect to the rotational axis direction of the developer supply screw 42). In the first embodiment, the communication port is positioned at a position included in the range of the downstream end (terminal end) in the developer transport direction of the first transport path 61 in which the developer supply screw 42 is disposed.

[0045] The developer transport directions of the developer supply screw 42 and the developer agitating screw 43 are opposite to each other. The developer supply screw 42 is disposed in the first transport path 61, and the developer agitating screw 43 is disposed in the second transport path 62. The start side (upstream end side in the developer transport direction) and end side (downstream end side in the developer transport direction) of the first transport path 61 communicate with the end side and start side of the second transport path 62 via communication ports provided in the partition wall 48. Therefore, the developer circulates in the rotation direction of the developer supply screw 42 and the developer agitating screw 43 indicated by the arrows in FIG. 2 and in a substantially horizontal direction within the developing container 60, and a portion of the developer is supplied toward the first developing roller 30.

[0046] The developer supply port 51 (see FIG. 2) is disposed above the developer stirring screw 43 in the developing container 60, and is connected to the developer storage unit 27Y (see FIG. 1). The developer supply port 51 is configured so that the developer stored in a bottle loaded in the developer storage unit 27Y can be supplied to the second conveying path 62 in which the developer stirring screw 43 is disposed.

[0047] As described above, the toner weight ratio of the developer stored in the bottle of developer storage unit 27Y is greater than the toner weight ratio of the developer in developing device 1Y. Therefore, by adjusting the developer supplied to developer stirring screw 43, it is possible to maintain a constant toner weight ratio of the developer in developing device 1Y.

[0048] The toner concentration detection sensor 49 (see FIG. 2) is arranged to detect the toner concentration in the developer circulating through the developer circulation path in the developer container 60. The toner concentration detection sensor 49 is a sensor that detects the magnetic permeability of the developer. The toner concentration corresponds to the amount of toner consumed in the developing device 1Y, and is therefore used to control the supply of developer from the developer storage unit 27Y. For example, when it is detected that the toner concentration has dropped below a predetermined value, developer is replenished from the developer storage unit 27Y. Note that the magnetic permeability of the developer changes depending on the toner concentration, so it is possible to detect the toner concentration using the magnetic permeability.

[0049] The regulating member 50 is disposed adjacent to the first developing roller 30 and is used to regulate the amount of developer supplied from the developer circulating unit 46 to the first developing roller 30. The regulating member 50 can be configured to regulate the amount of developer attracted to the first developing roller 30 based on, for example, the gap between the surface of the first sleeve 33 of the first developing roller 30 and the end of the regulating member 50.

[0050] The developer circulation path in the developing container 60 is such that the developer is transported in a substantially horizontal direction while being stirred in the developer circulation section 46, and then supplied to the first developing roller 30, and is transferred from the first developing roller 30 to the second developing roller 31 above it by magnetic force. Next, the developer is transferred from the second developing roller 31 to the peeling roller 32 on the side of the second developing roller 31 by magnetic force again. Thereafter, the developer is peeled off from the peeling roller 32 by a third magnet 38 contained in the peeling roller 32, and then recovered in the developer recovery section 47 and introduced into the developer circulation section 46 again.

[0051] As described above, the first embodiment uses a two-component development system, and the developer is a mixture of negatively charged non-magnetic toner and magnetic carrier. The non-magnetic toner is a resin such as polyester or styrene acrylic that contains colorants, wax components, etc., and is then 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, with a resin coating on the surface. In the first embodiment, the toner concentration in the developer in the initial state (weight ratio of toner contained in the developer) is 8%.

[0052] Generally, two-component development systems using toner and carrier charge both to a predetermined polarity through frictional contact, resulting in less stress on the toner than single-component development systems using single-component developers. Because the surface area of ​​the carrier in the developer is larger than that of the toner, the carrier is less likely to be contaminated by toner adhering to the carrier surface. However, with long-term use, the amount of contaminants (spent toner) adhering to the carrier surface increases, gradually reducing the toner's ability to charge. This results in problems such as fogging and toner scattering. While increasing the amount of carrier contained in the development device is one way to extend the life of a two-component development device, this is undesirable because it increases the size of the development device.

[0053] To solve the above problems associated with two-component developers, the first embodiment employs an ACR (Auto Carrier Refresh) method. The ACR method is a method for suppressing an increase in degraded carrier by gradually replenishing new developer from the developer storage unit 27Y into the developing device 1Y and gradually discharging developer with degraded charging performance from a discharge port (not shown) of the developing device 1Y. This allows the degraded carrier in the developing device 1Y to be gradually replaced with new carrier, making it possible to maintain the charging performance of the carrier in the developing device 1Y at a substantially constant level.

[0054] [About the magnetic poles of each magnet] Next, the magnetic pole configurations of the first magnet 36, second magnet 37, and third magnet 38 contained in the first developing roller 30, second developing roller 31, and peeling roller 32 shown in Figures 3, 4, and 5 will be described.

[0055] 3, the first magnet 36 contained in the first developing roller 30 has a plurality of magnetic poles 101, 102, 103, 104, 105, 106, and 108. The magnetic poles 101 to 106 and 108 are arranged in numerical order in the rotation direction of the first sleeve 33.

[0056] The magnetic pole 106 is a magnetic pole for transferring developer from the first sleeve 33 to the second sleeve 34 by a magnetic field generated in cooperation with the second magnet 37 of the second developing roller 31. In this embodiment, a non-magnetic pole portion 110 serving as a low magnetic force portion having a magnetic force lower than that of the magnetic pole 106 is disposed adjacent to the downstream side of the magnetic pole 106 in the rotational direction of the first sleeve 33. The magnetic pole 108 is disposed adjacent to the downstream side of the non-magnetic pole portion 110 in the rotational direction of the first sleeve 33. In this embodiment, the non-magnetic pole portion 110 has no magnetic force, but may be a magnetic pole having a low magnetic force, for example, a magnetic pole having a magnetic force of 5 mT or less. The same applies to the non-magnetic pole portions 210 and 310.

[0057] Furthermore, magnetic pole 101 is an S pole and is used to attract the developer supplied from developer supply screw 42 onto first sleeve 33. Magnetic poles 102, 103, 104, and 105 are an N pole, an S pole, an N pole, and an S pole and are used to transport the developer attracted by magnetic pole 101 upward as first sleeve 33 rotates. Magnetic pole 106 is an N pole and transfers the developer from first sleeve 33 to second sleeve 34 facing first sleeve 33 by a magnetic field generated in cooperation with magnetic pole 201 in second magnet 37 contained within second developing roller 31 as described above.

[0058] 4, the second magnet 37 contained in the second developing roller 31 has a plurality of magnetic poles 201, 202, 203, 204, 205, 206, and 207. The magnetic poles 201 to 207 are arranged in numerical order in the rotation direction of the second sleeve .

[0059] The magnetic pole 201 is a magnetic pole for attracting the developer from the first sleeve 33 to the second sleeve 34 by a magnetic field generated in cooperation with the magnetic pole 106 of the first magnet 36 of the first developing roller 30. The magnetic pole 207 is a magnetic pole for transferring the developer from the second sleeve 34 to the third sleeve 35 by a magnetic field generated in cooperation with the third magnet 38 of the peeling roller 32.

[0060] Furthermore, magnetic pole 201 is an S pole and is used to attract developer from first developing roller 30 (first sleeve 33) onto second sleeve 34 as described above. Magnetic poles 202, 203, 204, 205, and 206 are an N pole, an S pole, an N pole, an S pole, and an N pole and are used to transport the developer attracted by magnetic pole 201 upward as second sleeve 34 rotates. Magnetic pole 207 is an S pole. After passing through the development region of photosensitive drum 28Y corresponding to magnetic pole 203, the developer is transferred from second sleeve 34 to third sleeve 35 facing second sleeve 34 by a magnetic field generated in cooperation with magnetic pole 303 in third magnet 38 contained within peeling roller 32.

[0061] 5, the third magnet 38 contained in the peeling roller 32 has a plurality of magnetic poles 301, 302, 303, 304, and 305. The magnetic poles 301 to 305 are arranged in numerical order in the rotation direction of the third sleeve 35.

[0062] The magnetic pole 303 is an N pole and is used to attract the developer peeled off from the second sleeve 34 onto the third sleeve 35 as described above. The magnetic poles 301, 302, and 304 are an N pole, an S pole, and an S pole and are used to transport the developer on the third sleeve 35 as the third sleeve 35 rotates. In particular, the magnetic pole 304 is used to transport the developer attracted by the magnetic pole 303 downward as the third sleeve 35 rotates. The magnetic pole 305 is an N pole and is a peeling pole used to peel off the developer attracted to the third sleeve 35 from the third sleeve 35 by a repulsive magnetic field generated in cooperation with the magnetic pole 301 of the same polarity.

[0063] 2, near the closest position between the second developing roller 31 and the peeling roller 32, a magnetic field is generated in the second magnet 37 contained in the second developing roller 31 and the third magnet 38 contained in the peeling roller 32. This magnetic field transfers the developer from the second sleeve 34 to the third sleeve 35 of the peeling roller 32.

[0064] In the process of transferring the developer from the second developing roller 31 to the peeling roller 32, an air current is generated in the gap between the second developing roller 31 and the peeling roller 32. Due to the influence of this air current, some of the developer may be carried by the air current and fall onto the first developing roller 30 located directly below the second developing roller 31.

[0065] The developer that has fallen onto the first developing roller 30 is used developer that has been used in the developing process on the first developing roller 30 and the second developing roller 31, and the amount of toner in the developer is less than that of the normal developer present in the developer circulation section 46.

[0066] If such used developer falls onto the first developing roller 30, there is a risk that the used developer will get into the developer transfer section located near the closest position between the first developing roller 30 and the second developing roller 31 due to the influence of the magnetic force on the first developing roller 30.

[0067] If used developer is transferred back onto the second developing roller 31 at the developer transfer section between the first developing roller 30 and the second developing roller 31, the developer on the second developing roller 31 will be a mixture of regular developer and used developer (developer with little toner). As a result, unevenness occurs in the amount of toner transferred to the photosensitive drum 28Y when developing the electrostatic latent image on the photosensitive drum 28Y, resulting in uneven density in the final output image. This phenomenon is known as the drag phenomenon.

[0068] When the dragging phenomenon occurs, there is a risk that image defects such as uneven density will easily occur on the output image, particularly in the developing device 1Y having two developing rollers (first developing roller 30 and second developing roller 31). In particular, under usage conditions such as high-speed operation of the image forming apparatus 100, the above-mentioned problem is likely to occur due to the influence of temperature rise inside the developing device 1Y.

[0069] Therefore, in the invention according to the first embodiment, as shown in Figure 2, a shielding member 10 is provided in the developing device 1Y so as to be close to the second developing roller 31. This prevents some of the developer on the second developing roller 31 from being carried by the air current and falling onto the first developing roller 30 located directly below the second developing roller 31 during the developer transfer process from the second developing roller 31 to the peeling roller 32. According to the invention according to the first embodiment, the occurrence of image defects is suppressed. The details will be explained below.

[0070] [Shielding material] The configuration of the shielding member 10 according to the first embodiment will be described with reference to Fig. 6. Fig. 6 is an enlarged view of the first developing roller 30 and the second developing roller 31 and their surroundings.

[0071] 2, the developer in the developing device 1Y moves from the first sleeve 33 of the first developing roller 30 onto the second sleeve 34 of the second developing roller 31, and then onto the third sleeve 35 of the peeling roller 32. However, when the developer in the developing device 1Y moves from the second sleeve 34 onto the third sleeve 35, not all of the developer on the second sleeve 34 moves onto the third sleeve 35, and some of the developer on the second sleeve 34 remains on the second sleeve 34.

[0072] The developer (used developer) remaining on the second sleeve 34 is transported from the vicinity of the magnetic pole 207 of the second magnet 37 contained in the second developing roller 31 to the downstream side in the rotation direction of the second sleeve 34. Then, the used developer transported to the downstream side in the rotation direction of the second sleeve 34 separates from the second sleeve 34 due to gravity and falls downward in the direction of gravity downstream in the rotation direction of the second sleeve 34 of a horizontal line L2 passing through the rotation center R of the second sleeve 34.

[0073] As shown in FIG. 6, a point P is defined as a point where a horizontal line L2 passing through the rotation center R of the second sleeve 34 intersects with the surface of the second sleeve 34 (the intersection point closer to the third sleeve 35).

[0074] If the shielding member 10 were not provided in the developing device 1Y, the used developer that has fallen from point P on the second sleeve 34 would move toward the first sleeve 33 that is located vertically below it. As the used developer that has fallen from point P on the second sleeve 34 approaches the vicinity of the first sleeve 33, it is attracted toward the closest portion of the first sleeve 33 and the second sleeve 34 by the magnetic field of the magnetic pole 106 of the first magnet 36. As a result, the used developer that has fallen from point P on the second sleeve 34 is attracted to the vicinity of the magnetic pole 106 on the first sleeve 33, generally along the falling path of the developer indicated by the thin dotted line in FIG. 6.

[0075] If the used developer attracted near the magnetic pole 106 accumulates near the closest part of the first sleeve 33 and the second sleeve 34, it will affect the flow of developer being transferred at the developer transfer section between the first developing roller 30 and the second developing roller 31. As a result, unevenness in the distribution density of the developer on the second developing roller 31 may occur, or the used developer transferred from the first developing roller 30 to the second developing roller 31 may be distributed unevenly, which may affect the developing operation of the second developing roller 31 and result in uneven density.

[0076] To solve the above problem, in the invention according to the first embodiment, as shown in Figures 2 and 6, a shielding member 10 is provided in the developing device 1Y so as to be close to the second developing roller 31. The shielding member 10 blocks the falling path of the developer, preventing the used developer from falling onto the first developing roller 30, thereby preventing the used developer from affecting the developed image.

[0077] In order to block the developer fall path with the shielding member 10, it is necessary to provide the shielding member 10 in an area where the developer fall path is located. In the first embodiment, as shown in Fig. 6, the developer fall path passes on the second developing roller 31 side (the dotted area in Fig. 6) with respect to a tangent to the second sleeve 34 (a vertical line L3 drawn from point P on the second sleeve 34) that passes through point P on the second sleeve 34. Therefore, in the first embodiment, at least a part of the shielding member 10 is provided on the second developing roller 31 side of the vertical line L3.

[0078] Furthermore, in the first embodiment, the shielding member 10 is provided continuously up to the point on the opposite side of the second developing roller 31 with respect to the vertical line L3 where it joins with the developer in the developer circulating portion 46. This allows the used developer captured on the shielding member 10 to be transported from the dotted area in FIG. 6 and join with the developer in the developer circulating portion 46 at a point other than the closest portion between the first sleeve 33 and the second sleeve 34. This prevents the used developer from falling onto the first sleeve 33, thereby preventing the used developer from entering the developer transfer portion near the closest position between the first developing roller 30 and the second developing roller 31.

[0079] 2 and 6, in the first embodiment, the shielding member 10 is disposed with an incline so as to descend toward the developer circulation portion 46, and the lower end of the shielding member 10 reaches above the developer supply screw 42. With this configuration, the developer that has fallen from the second sleeve 34 is captured by the shielding member 10 near the tip of the shielding member 10 on the second developing roller 31 side, and slides on the shielding member 10 toward the developer supply screw 42 according to the inclination of the shielding member 10. As a result, the used developer captured by the shielding member 10 reaches the lower end of the shielding member 10, falls within the range of the rotation locus of the developer supply screw 42, and is stirred and mixed with the developer transported by the developer supply screw 42.

[0080] On the other hand, if the inclination of the shielding member 10 cannot be made too large, it may be difficult to make the used developer captured by the shielding member 10 slide along the inclination of the shielding member 10. In such a case, a modification may be made in which a vibrating member (not shown) is provided in the developing device 1 and vibration is applied to the developing device 1Y by the vibrating member when no image is being formed, thereby assisting the used developer to slide on the shielding member 10. Furthermore, the means for assisting the used developer to slide on the shielding member 10 is not limited to the application of vibration, and electrostatic force, magnetic force, etc. may also be used as appropriate.

[0081] 2 and 6, in the first embodiment, the shielding member 10 is a flat surface having an inclination such that the destination of the used developer is downward in the direction of gravity, but this is not limited to this. On the premise that a means for assisting the sliding of the used developer on the shielding member 10 is provided, the shielding member 10 may be a flat surface having an inclination such that the destination of the used developer is upward in the direction of gravity.

[0082] For example, when applying vibration to the developing device 1Y, it may be effective to provide irregularities on the surface of the shielding member 10 (for example, sawtooth irregularities consisting of inclined surfaces and vertical lines, with the normal to the inclined surfaces having a component in the transport direction). Alternatively, it may be effective to bend the tip of the shielding member 10 upstream in the rotation direction of the second developing roller 31.

[0083] As described above, in the invention according to the first embodiment, the shielding member 10 is provided in the developing device 1Y so as to be close to the second developing roller 31, as shown in FIGS.

[0084] That is, the developing device 1Y includes a developer circulation unit 46, a developer supply screw 42, a developer recovery unit 47, a developer recovery screw 44, a first developing roller 30, a first magnet 36, a second developing roller 31, a second magnet 37, a peeling roller 32, and a third magnet 38. The developing device 1Y also includes a shielding member 10 that is disposed opposite the second developing roller 31 and that guides the developer peeled off from the second developing roller 31 to the developer supply screw 42 by a repulsive magnetic field generated by the second magnet 37. In the developing device 1Y, the position at which the second developing roller 31 is closest to the shielding member 10 is vertically above the rotation center Q of the first developing roller 30 and vertically below the rotation center R of the second developing roller 31.

[0085] This makes it possible to prevent some of the developer on the second developing roller 31 from being carried by the air current and falling onto the first developing roller 30 located directly below the second developing roller 31 during the developer transfer process from the second developing roller 31 to the peeling roller 32. According to the invention related to the first embodiment, it is possible to prevent the occurrence of image defects.

[0086] [Second embodiment] In the first embodiment described above, an example was described in which a shielding member 10 is provided in the developing device 1Y so as to be close to the second developing roller 31 in order to prevent used developer from falling onto the first developing roller 30.

[0087] On the other hand, in the second embodiment, the configuration around the shielding member is different from that of the first embodiment. Since the other configurations and functions are the same as those of the first embodiment described above, the same reference numerals are used for the same configurations, and explanations and illustrations thereof are omitted or simplified. The following description will focus on the points that are different from the first embodiment.

[0088] The configuration of the shielding member according to the second embodiment will be described in detail with reference to Fig. 7. Fig. 7 is a cross-sectional view showing the schematic configuration of a developing device 1Y' according to the second embodiment.

[0089] In the second embodiment, the shielding member 11 provided in the developing device 1Y' so as to be adjacent to the second developing roller 31 also serves as a guide member that guides the used developer received by the peeling roller 32 from the second developing roller 31 to the developer recovery screw 44. That is, the shielding member 11 according to the second embodiment serves as both the shielding member 10 and the guide member 45 according to the first embodiment.

[0090] 7, the upstream end of the shielding member 11 in the transport direction is disposed close to the second developing roller 31, and the downstream end of the shielding member 11 in the transport direction is connected to a developer recovery section 47 in which a developer recovery screw 44 is disposed. Therefore, the used developer peeled off from the second developing roller 31 is captured by the shielding member 11, and then slides down along the inclination of the shielding member 11 to join the developer recovery screw 44.

[0091] As described above, in the second embodiment, the shielding member 11 also serves as a guide member that guides the used developer that the peeling roller 32 receives from the second developing roller 31 to the developer recovery screw 44. For this reason, most of the used developer that the peeling roller 32 receives from the second developing roller 31 is peeled off at the peeling portion of the peeling roller 32, and mainly falls directly onto the developer recovery screw 44.

[0092] A part of the used developer peeled off from the peeling roller 32 falls onto the shielding member 11, and this, together with the used developer peeled off from the second developing roller 31 and captured by the shielding member 11, slides down along the inclination of the shielding member 11 and joins the developer recovery screw 44.

[0093] That is, all the used developer transported to the peeling roller 32 eventually meets up at the developer recovery screw 44, where it is agitated and transported, and falls through the communication port downstream of the developer supply screw 42 outside the image area to meet again. This makes it possible to keep the state of the developer inside the developer supply screw 42 constant within the image area, thereby suppressing uneven density.

[0094] As described above, in the invention according to the second embodiment, as shown in FIG. 7, the shielding member 11 is provided in the developing device 1Y' so as to be close to the second developing roller 31. This makes it possible to prevent a portion of the developer on the second developing roller 31 from being carried by the air current and falling onto the first developing roller 30 located directly below the second developing roller 31 during the developer transfer process from the second developing roller 31 to the peeling roller 32. According to the invention according to the second embodiment, it is possible to prevent the occurrence of image defects.

[0095] In the first embodiment described above, the inclination of the shielding member can be made greater than in the second embodiment, so that the first embodiment is more advantageous than the second embodiment in terms of efficiency in transporting the used developer that has fallen onto the shielding member on the shielding member. In the second embodiment, as in the first embodiment described above, the transport efficiency may be improved by providing a means for assisting the used developer to slide on the shielding member 10 (for example, by applying vibration to the developing device 1Y' by a vibration member when no image is being formed).

[0096] On the other hand, the shielding member 11 according to the second embodiment serves the functions of both the shielding member 10 according to the first embodiment and the guide member 45, and therefore the second embodiment is more advantageous than the first embodiment in terms of reducing the number of parts that make up the developing device.

[0097] (Other embodiments) The present invention is not limited to the configurations of the above-described embodiments. For example, the image forming apparatus 100 is not limited to an MFP, but may be a copier, printer, or facsimile machine. Furthermore, the configurations of the developer supply screw 42, developer stirring screw 43, and developer recovery screw 44 are not particularly limited as long as they can transport the developer. For example, spiral blades or paddle-shaped blades can be applied. [Explanation of symbols]

[0098] 1Y, 1M, 1C, 1K developing device 10 Shielding member 30 First developing roller 31 Second developing roller 32 Peeling roller 36 First Magnet 37 Second Magnet 38 Third Magnet 42 Developer supply screw 44 Developer recovery screw 46 Developer circulation section 47 Developer recovery section

Claims

1. a first chamber containing a developer containing toner and a carrier; a first conveying screw disposed in the first chamber and configured to convey the developer contained in the first chamber; a second chamber separated from the first chamber by a partition wall; a second conveying screw disposed in the second chamber and configured to convey the developer contained in the second chamber; a first rotating body to which the developer is supplied from the first chamber, the first rotating body carrying and transporting the developer to develop an electrostatic latent image formed on an image carrier; a first magnet fixedly disposed inside the first rotor; a second rotating body disposed opposite the first rotating body, to which the developer is transferred from the first rotating body by a magnetic field generated by the first magnet, the second rotating body carrying and transporting the developer to develop the electrostatic latent image; a second magnet fixedly disposed inside the second rotor; a third rotating body disposed opposite the second rotating body, to which the developer is transferred from the second rotating body by a magnetic field generated by the second magnet, the third rotating body carrying and transporting the developer to recover the developer into the second chamber after the electrostatic latent image has been developed; a third magnet fixedly disposed inside the third rotor; a guide portion disposed opposite the second rotating body and configured to guide the developer separated from the second rotating body by a repulsive magnetic field generated by the second magnet to the first conveying screw; Equipped with The position where the second rotating body is closest to the guide portion is located vertically above the rotation center of the first rotating body and vertically below the rotation center of the second rotating body. A developing device characterized by:

2. a second guide portion disposed opposite the second rotating body and the third rotating body, and configured to guide the developer separated from the third rotating body by a repulsive magnetic field generated by the third magnet to the second conveying screw; 2. The developing device according to claim 1, further comprising:

3. a rotation center of the second conveying screw is located vertically above a rotation center of the first conveying screw, a rotation center of the second rotating body is located vertically above a rotation center of the first rotating body, The rotation center of the third rotating body is located vertically above the rotation center of the second rotating body.

2. The developing device according to claim 1.

4. a communication portion that allows the developer to communicate from the second chamber to the first chamber; 2. The developing device according to claim 1, further comprising:

5. a third chamber separated from the first chamber by another partition wall; a third conveying screw disposed in the third chamber and configured to convey the developer contained in the third chamber; a first communication portion that allows the developer to communicate from the third chamber to the first chamber; a second communication portion that allows the developer to communicate from the first chamber to the third chamber; 2. The developing device according to claim 1, further comprising:

Images