Developing device

Abstract

This configuration provides a way to prevent the carrier from being collected by the duct 60. [Solution] The duct 60 has a suction port 60a for sucking up the developer scattered inside the developing container 70, located upstream of the opposing part 74. The duct 60 has a first duct wall 62 and a second duct wall 61. The second developing magnet 37 has a transfer pole 207 and a transport pole 206. In a cross section perpendicular to the rotation axis of the second developing sleeve 34, if the endpoint of the first duct wall 61 is the reference point A, the position of the maximum value of the normal component of the magnetic flux density of the transport pole 206 is the surface position H, the line passing through the reference point A and the surface position H is the line line T, the line passing through the surface position H and the rotation center O of the second developing sleeve 34 is the line line L, and the angle between the line segment AH of line line T, which is sandwiched between the reference point A and the surface position H, and the part of line line L that is opposite to the rotation center O with respect to the surface position H is θ, then θ ≤ 60° is satisfied.

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 Art

[0002] An image forming apparatus includes a developing device that attaches a developer to an electrostatic latent image formed on a photosensitive drum and develops it into a toner image. As the developer, a two-component developer containing toner and carrier is widely used. In the developing device, the developer is carried on a developing roller having a developing sleeve and a magnet fixedly disposed inside the developing sleeve, and the developer is conveyed to a developing area facing the photosensitive drum as the developing sleeve rotates. Then, the electrostatic latent image on the photosensitive drum is developed into a toner image in the developing area. In such a developing device, toner is likely to scatter as the developer is conveyed by the rotating developing sleeve.

[0003] When toner scattering occurs, the scattered toner accumulates near the developing device and the photosensitive drum. Thereafter, due to vibration during image formation or maintenance, the accumulated toner may fall onto the developing sleeve or the photosensitive drum, resulting in image defects. Patent Document 1 discloses a developing device provided with a duct for sucking the scattered toner. In Patent Document 1, in order to suppress the sucked toner from adhering to and aggregating on the duct, a vibration-applying portion for applying vibration to the duct is provided.

[0004] Furthermore, when toner is sucked up by a duct, carriers may enter the duct. When carriers reach the suction path of the duct, they accumulate within the suction path, narrowing the cross-sectional area of ​​the flow path, preventing the necessary airflow from being obtained, and as a result, the scattered toner cannot be adequately sucked up. Also, if a filter for toner collection is installed in the duct path, the filter may become clogged with carriers, reducing the suction force and preventing the scattered toner from being adequately sucked up. For this reason, Patent Document 2 discloses a configuration in which a recess is formed on the lower surface of the duct path to collect carriers that have entered when scattered toner is sucked up by the duct, in order to prevent carriers that have entered from entering the filter side, and the carriers are collected by the recess. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2019-144333 [Patent Document 2] Japanese Patent Publication No. 2021-56437 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, as described in Patent Document 2, even if measures are taken to prevent carriers from being sucked into the duct, there is a risk that the sucked-in carriers may not fall into the recess on the lower surface of the duct's path but instead be carried further into the duct by the suction airflow. Also, in both configurations of Patent Documents 1 and 2, a peeling roller is provided to peel off any developer remaining on the developing roller after development. The duct's suction port is positioned near the opposing section where the developing roller and the peeling roller face each other. In this case, there is a risk that scattered carriers near the opposing section may adhere to the inner wall of the duct. Then, as the amount of scattered toner sucked in adheres to the carriers attached to the inner wall of the duct and the amount of adhesion increases, clumps of toner may fall from the inner wall of the duct onto the photosensitive drum, potentially causing toner stains on the image.

[0007] The present invention aims to provide a configuration that can prevent carriers from being collected by the duct. [Means for solving the problem]

[0008] One aspect of the present invention includes a developing container for containing a developer containing toner and a carrier, a rotating developing sleeve, a developing magnet non-rotating inside the developing sleeve and magnetically adsorbing the developer containing toner and a magnetic carrier onto the surface of the developing sleeve, and a developing roller for developing an electrostatic latent image formed on a rotating image carrier with the developer, a peeling sleeve in a facing portion opposite to the developing sleeve such that its surface moves in the same direction as the surface of the developing sleeve, a peeling magnet non-rotating inside the peeling sleeve and magnetically adsorbing the developer onto the surface of the peeling sleeve, and a peeling roller for peeling off the developer after the electrostatic latent image on the image carrier has been developed by the developing roller, and a duct in which a suction port for sucking up scattered developer inside the developing container is located upstream of the facing portion with respect to the rotation direction of the peeling sleeve, the duct extends from the suction port upstream of the peeling sleeve in the rotation direction and is arranged to face a part of the peeling roller with a gap between them. The duct comprises a first duct wall and a second duct wall positioned opposite the first duct wall and forming a space between it and the first duct wall through which the developer drawn in from the suction port flows, and the developing magnet has a transfer pole which is a magnetic pole for transferring the developer from the developing roller to the peeling roller and a transport pole adjacent to the transfer pole on the upstream side of the transfer pole with respect to the rotational direction of the developing sleeve, and in a cross section perpendicular to the rotational axis of the developing sleeve, the tip of the first duct wall on the suction port side front The developing apparatus is characterized in that, when the endpoint on the wall side of the second duct is the reference point A, the position of the maximum value of the normal component of the magnetic flux density of the transport pole on the surface of the developing sleeve is the surface position H, the line passing through the reference point A and the surface position H is the line line T, the line passing through the surface position H and the rotation center O of the developing sleeve is the line line L, and the angle between the line segment AH of the line line T, which is sandwiched between the reference point A and the surface position H, and the part of the line line L opposite to the rotation center O with respect to the surface position H, the apparatus satisfies θ ≤ 60°. [Effects of the Invention]

[0009] According to the present invention, it is possible to prevent the carrier from being collected by the duct. [Brief explanation of the drawing]

[0010] [Figure 1] A schematic cross-sectional view of the image forming apparatus according to the first embodiment. [Figure 2] A schematic cross-sectional view of the developing apparatus according to the first embodiment. [Figure 3] A diagram illustrating a coordinate plane with the rotation center of the second developing sleeve and the peeling sleeve according to the first embodiment as the origin. [Figure 4] A diagram showing the magnetic pole arrangement of the first and second developing rollers and the peeling roller according to the first embodiment. [Figure 5] (a) Cross-sectional view of the second developing roller and the area around the duct suction port to illustrate the angle θ, (b) Schematic diagram to illustrate the relationship between the angle of the magnetic tip and the angle θ. [Figure 6] A graph showing the magnetic flux density distribution of the second developing roller and the angle of the magnetic tip. [Figure 7] The diagrams show cross-sectional views of the second developing roller and the area around the suction port of the duct according to the first embodiment, with (a) showing the case where the angle θ is 60° and (b) showing the case where the angle θ is 40°. [Figure 8] A graph showing the relationship between the angle θ and the carrier collection reduction rate. [Figure 9] A cross-sectional view of the area around the suction port of the second developing roller and duct according to the second embodiment. [Figure 10] (a) Cross-sectional view of the area around the suction port of the second developing roller and duct according to another first example of the second embodiment, (b) Cross-sectional view of the area around the suction port of the second developing roller and duct according to another second example of the second embodiment. [Figure 11] The figures show cross-sectional views of the second developing roller and the area around the suction port of the duct according to the second embodiment, with (a) the case where θ = φ, (b) the case where θ > φ, and (c) the case where θ < φ. [Figure 12] A graph showing the relationship between angles θ and φ and the carrier collection reduction rate. [Figure 13]Cross-sectional view of the vicinity of the suction port of the second developing roller and the duct according to the third embodiment. [Figure 14] Schematic diagram showing the distribution of magnetic field lines when θ = 40° and ψ = 5° in the cross-sectional view of the vicinity of the suction port of the second developing roller and the duct according to the third embodiment. [Figure 15] Schematic diagram showing the distribution of magnetic field lines when θ = 40° and ψ = 10° in the cross-sectional view of the vicinity of the suction port of the second developing roller and the duct according to the third embodiment. [Figure 16] Schematic diagram showing the distribution of magnetic field lines when θ = 40°, ψ = 10°, α = 18°, and β = 7° in the cross-sectional view of the vicinity of the suction port of the second developing roller and the duct according to the third embodiment. [Figure 17] Table showing the relationship between the reduction rate of carrier collection amount and the retention phenomenon with respect to the angle ψ.

Embodiments for Carrying Out the Invention

[0011] <First Embodiment> The first embodiment will be described with reference to FIGS. 1 to 8. First, the schematic configuration of the image forming apparatus of the present embodiment will be described with reference to FIG. 1.

[0012] [Image Forming Apparatus] The image forming apparatus 100 is a full-color image forming apparatus. In the case of the present embodiment, for example, it is 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 is provided with image forming units PY, PM, PC, and PK that respectively perform image forming processes for four-color toner images of yellow, magenta, cyan, and black in parallel. The image forming apparatus 100 of the present embodiment is connected to a document reading apparatus connected to the image forming apparatus main body (apparatus main body) or a host device such as a personal computer is communicably connected to the apparatus main body. Therefore, according to the image information from the host device, a four-color full-color image of yellow (Y), magenta (M), cyan (C), and black (K) can be formed on a recording material (recording paper, plastic sheet, cloth, etc.) using the electrophotographic method.

[0013] Each color image forming unit PY, PM, PC, and PK comprises a primary charger 21Y, 21M, 21C, 21K, a developing unit 1Y, 1M, 1C, 1K, an exposure unit 22Y, 22M, 22C, 22K, a photosensitive drum 28Y, 28M, 28C, 28K, and a cleaning unit 26Y, 26M, 26C, 26K. The image forming apparatus 100 also includes a transfer unit 2 and a fixing unit 3. Since the configurations of each color image forming unit PY, PM, PC, and PK are the same, the following explanation will use the image forming unit PY as a representative example.

[0014] The photosensitive drum 28Y, which serves as the image carrier, is a photoreceptor 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 consists of corona discharge electrodes arranged around the photosensitive drum 28Y, and charges the surface of the photosensitive drum 28Y with the ions generated.

[0015] The exposure device 22Y incorporates a scanning optical device and, by exposing the photosensitive drum 28Y, which is charged based on image data, lowers the potential of the exposed area and forms a charge pattern (electrostatic latent image) corresponding to the image data. The developing device 1Y transfers the contained developer to the photosensitive drum 28Y and develops the electrostatic latent image formed on the photosensitive drum 28Y. The developer is a mixture of a carrier and toner corresponding to each color, and the electrostatic latent image is made visible by the toner.

[0016] The transfer device 2 includes primary transfer rollers 23Y, 23M, 23C, 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, 23K and multiple rollers and is supported so as to be able to move. The primary transfer rollers 23Y, 23M, 23C, 23K, which serve as primary transfer members, correspond to the colors Y (yellow), M (magenta), C (cyan), and K (black), respectively, from top to bottom in Figure 1. The secondary transfer roller 25 is positioned outside the intermediate transfer belt 24 and is configured so that the recording material can pass between it and the intermediate transfer belt 24.

[0017] The toner images of each color formed on the photosensitive drums 28Y, 28M, 28C, and 28K are transferred (primary transfer) onto the intermediate transfer belt 24 in the primary transfer section (primary transfer nip) T1 where the intermediate transfer belt 24 and the photosensitive drums 28Y, 28M, 28C, and 28K come into contact, by the action of a primary transfer bias applied to the primary transfer rollers 23Y, 23M, 23C, and 23K. For example, over time, when a four-color full-color image is created, the toners are transferred onto the intermediate transfer belt 24 in order from the photosensitive drum 28Y, forming a color toner image with superimposed layers of yellow, magenta, cyan, and black.

[0018] Meanwhile, the recording material contained in a cassette (not shown), which serves as the recording material storage section, is transported to the transfer device 2 via a pickup roller and registration roller (not shown). The recording material is transported to the secondary transfer section (nip section) T2, where the intermediate transfer belt 24 and the secondary transfer roller 25, which serves as the secondary transfer member, come into contact, in synchronization with the toner image on the intermediate transfer belt 24. The toner image formed on the intermediate transfer belt 24 is then secondarily transferred onto the recording material in the secondary transfer section T2 by the action of a secondary transfer bias applied to the secondary transfer roller 25. The recording material on which the toner image has been transferred is then subjected to pressure and heat in the fixing device 3. This melts the toner on the recording material, fixing the color image onto the recording material. After that, the recording material S is discharged outside the machine.

[0019] When image formation is performed on both sides of the recording material, the recording material that has passed through the fixing device 3 is transported to an inversion transport path (not shown), the front and back sides of the recording material are inverted, and the recording material is transported to the registration roller, where the toner image is transferred to the back side of the recording material in the secondary transfer unit T2, as described above. Then, the toner image is fixed to the back side of the recording material again in the fixing device 3.

[0020] After the primary transfer process, any toner or other deposits remaining on the photosensitive drums 28Y, 28M, 28C, and 28K are recovered by the cleaning devices 26Y, 26M, 26C, and 26K. This prepares the photosensitive drums 28Y, 28M, 28C, and 28K for the next image forming process. In addition, any toner or other deposits remaining on the intermediate transfer belt 24 after the secondary transfer process are removed by the intermediate transfer belt cleaner 29.

[0021] Furthermore, the image forming apparatus 100 of this embodiment can also form single-color or multi-color images using image forming units for a desired single color or several of the four colors, such as a black monochrome image. In addition, although Figure 1 shows the image forming units PY, PM, PC, and PK for each color arranged vertically, the arrangement direction may be horizontal or diagonal, or any other direction. Moreover, in this embodiment, the outer diameter of the photosensitive drums 28Y, 28M, 28C, and 28K is, for example, 80 [mm], and the image forming operation is performed while rotating at a peripheral speed of 513 mm / sec.

[0022] The developer storage units 27Y, 27M, 27C, and 27K are provided in accordance with the developing units 1Y, 1M, 1C, and 1K, respectively, and are loaded with replaceable bottles containing developer corresponding to the respective colors: yellow, magenta, cyan, and black, from top to bottom. The developer storage units 27Y, 27M, 27C, and 27K are configured to transport (replenish) the developer to the developing unit 1Y, 1M, 1C, and 1K corresponding to the color of the developer stored in them.

[0023] For example, the toner weight ratio of the developer stored in the bottle is 90-98%, while the toner weight ratio of the developer in developing units 1Y, 1M, 1C, and 1K is 5-11%. Therefore, when toner is consumed by developing in developing units 1Y, 1M, 1C, and 1K, developer containing an amount of toner corresponding to the consumption is replenished, and the toner weight ratio of the developer in developing units 1Y, 1M, 1C, and 1K is maintained at a constant level.

[0024] [Developing equipment] Next, developing units 1Y, 1M, 1C, and 1K will be described in detail using Figure 2. Since the configurations of developing units 1Y, 1M, 1C, and 1K are the same, developing unit 1Y will be described as a representative example below.

[0025] As shown in Figure 2, the developing apparatus 1Y includes a first developing roller 30, a second developing roller 31, a stripping roller 32, a developer supply screw 42, a developer stirring screw 43, and a developer recovery screw 44, all of which are housed in a developing container 70. The developing container 70 contains a two-component developer containing a non-magnetic toner and a magnetic carrier.

[0026] The first developing roller 30 is a rotating developer carrier, positioned adjacent to the photosensitive drum 28Y, such that its axis of rotation is approximately parallel to the axis of rotation of the photosensitive drum 28Y. The first developing roller 30 includes a rotating first developing sleeve 33 and a first developing magnet (fixed magnet) 36 that is non-rotatingly positioned inside the first developing sleeve 33 and attracts the developer to the surface of the first developing sleeve 33 by magnetic force. The first developing roller 30 then attracts (carries) the developer drawn up from the developer supply screw 42 based on magnetic force and develops the electrostatic latent image formed on the rotating photosensitive drum 28Y (on the image carrier) with the developer.

[0027] The first developing sleeve 33 is a non-magnetic cylindrical member and is rotationally driven around a rotation axis 39. The rotation direction of the first developing sleeve 33 is clockwise, as indicated by the arrow in Figure 2, and in this embodiment, it is opposite to the rotation direction of the photosensitive drum 28Y. Therefore, the first developing sleeve 33 and the photosensitive drum 28Y rotate in the same direction (forward direction) at opposing positions (opposing parts). That is, the first developing sleeve 33 rotates such that the surface facing the photosensitive drum 28Y moves from the bottom vertically upward.

[0028] The first developing magnet 36 is positioned inside the first developing sleeve 33 and, as shown in Figure 4 (described later), has a plurality of fan-shaped magnetic poles 101-107 and a fan-shaped low-magnetic-force portion 110. A space is provided between the inner circumference of the first developing sleeve 33 and the outer circumference of the first developing magnet 36 to allow rotation of the first developing sleeve 33. In Figure 4, the lines indicating the magnetic poles of each magnet indicate the position of the maximum value of the normal component of the magnetic flux density (the same applies to subsequent figures).

[0029] The developer adsorbed on the first developing sleeve 33 is transported toward the photosensitive drum 28Y by the rotational movement of the first developing 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 developing sleeve 33 is transported toward the vicinity of the second developing roller 31 by the rotational movement of the first developing sleeve 33. Then, near the closest proximity position between the first developing roller 30 and the second developing roller 31, the developer is detached from the first developing sleeve 33 by the magnetic fields generated by the first developing magnet 36 contained in the first developing roller 30 and the second developing magnet 37 contained in the second developing roller 31, and the developer is transferred to the second developing sleeve 34.

[0030] The second developing roller 31, acting as a developing roller, is a rotating developer carrier positioned downstream of the first developing roller 30 in the direction of rotation of the photosensitive drum 28Y, and above the center of rotation of the first developing roller 30 in the vertical direction. Developer is transferred from the first developing roller 30 to the second developing roller 31 by magnetic force. Similar to the first developing roller 30, the second developing roller 31 is positioned adjacent to the photosensitive drum 28Y, with its axis of rotation approximately parallel to the axis of rotation of the photosensitive drum 28Y. Therefore, the axes of rotation of the second developing roller 31 and the first developing roller 30 are approximately parallel to each other.

[0031] Such a second developing roller 31 includes a rotating second developing sleeve 34 and a second developing magnet (fixed magnet) 37 that is positioned non-rotating inside the second developing sleeve 34 and attracts the developer to the surface of the second developing sleeve 34 by magnetic force. The second developing roller 31 receives the developer from the first developing roller 30 (first developing sleeve 33) based on magnetic force, attracts (carries) the developer, and develops the electrostatic latent image formed on the rotating photosensitive drum 28Y with the developer. A peeling roller 32, which will be described later, is located to the side of the second developing roller 31.

[0032] The second developing sleeve 34 is a non-magnetic cylindrical member and is rotationally driven around the rotation axis 40. The rotation direction of the second developing sleeve 34 is clockwise, as indicated by the arrow in Figure 2, and in this embodiment, it is opposite to the rotation direction of the photosensitive drum 28Y. Therefore, the second developing sleeve 34 and the photosensitive drum 28Y rotate in the same direction (forward direction) at opposing positions (opposing parts). That is, the second developing sleeve 34 rotates such that the surface facing the photosensitive drum 28Y moves from the bottom vertically upward. Also, the second developing sleeve 34 and the first developing sleeve 33 rotate in opposite directions at opposing positions.

[0033] The second developing magnet 37 is located inside the second developing sleeve 34 and has, for example, a plurality of fan-shaped magnetic poles 201 to 207 and a fan-shaped low-magnetic-force portion 210. A space is provided between the inner circumference of the second developing sleeve 34 and the outer circumference of the second developing magnet 37 to allow rotation of the second developing sleeve 34.

[0034] The developer adsorbed on the second developing sleeve 34 is transported toward the photosensitive drum 28Y by the rotational movement of the second developing sleeve 34, and develops the latent image formed on the photosensitive drum 28Y. After developing the latent image formed on the photosensitive drum 28Y, the developer remaining in the second developing sleeve 34 is transported toward the vicinity of the peeling roller 32 by the rotational movement of the second developing sleeve 34. Then, near the closest proximity position between the second developing roller 31 and the peeling roller 32, the developer is transferred from the second developing sleeve 34 to the peeling sleeve 35 of the peeling roller 32 by the magnetic fields generated by the second developing magnet 37 contained in the second developing roller 31 and the peeling magnet 38 contained in the peeling roller 32.

[0035] The peeling roller (recovery roller) 32 is positioned on the opposite side of the photosensitive drum 28Y from the rotation center O of the second developing sleeve 34, and peels 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 rotating developer carrier, and is positioned between the second developing roller 31 and the developer recovery screw 44 such that its rotation center O' is above the rotation center O of the second developing roller 31.

[0036] Furthermore, the peeling roller 32 is positioned such that its axis of rotation is approximately parallel to the axis of rotation of the second developing roller 31. This peeling roller 32 includes a rotating peeling sleeve 35 and a peeling magnet (fixed magnet) 38 that is positioned non-rotating inside the peeling sleeve 35 and attracts the developer to the surface of the peeling sleeve 35 by magnetic force, and is configured to transfer the developer from the second developing roller 31 based on magnetic force.

[0037] The peeling sleeve 35 is a non-magnetic cylindrical member and is rotationally driven around the rotation axis 41. The rotation direction of the peeling sleeve 35 is counterclockwise, as indicated by the arrow in Figure 2, and in this embodiment, it is opposite to the rotation direction of the second developing sleeve 34. Therefore, the peeling sleeve 35 and the second developing sleeve 34 rotate in the same direction (forward direction) at opposing positions (opposing parts). That is, the peeling sleeve 35 rotates such that its surface moves in the same direction as the surface of the second developing sleeve 34 at the opposing part facing the second developing sleeve 34.

[0038] The peeling magnet 38 is positioned inside the peeling sleeve 35 and has, for example, a plurality of fan-shaped magnetic poles 301 to 305 and a fan-shaped low-magnetic-force portion 310. A space is provided between the inner circumference of the peeling sleeve 35 and the outer circumference of the peeling magnet 38 to allow rotation of the peeling sleeve 35.

[0039] The developer adsorbed onto the peeling sleeve 35 is transported downstream in the direction of rotation by the rotational movement of the peeling sleeve 35, and at a position close to the developer recovery screw 44, it is peeled off from the peeling sleeve 35 by the peeling magnet 38 enclosed in the peeling roller 32 and falls by its own weight toward the guide member 45 located vertically below. The developer that falls toward the guide member 45 is then guided by its own weight toward the developer recovery screw 44.

[0040] The guide member 45 and the developer recovery screw 44 constitute a developer recovery section 47, which is a recovery section for recovering the developer peeled off from the peeling sleeve 35 on the peeling roller 32. In the developer recovery section 47, the developer recovery screw 44 is located below the center of rotation of the peeling roller 32 in the vertical direction and conveys the developer received (recovered) from the peeling roller 32 while agitating it.

[0041] The guide member 45, acting as a guide, is positioned below the rotation center O' of the peeling roller 32 in the vertical direction. The guide member 45 guides the developer peeled off by the peeling roller 32 toward the developer recovery screw 44. Such a guide member 45 has a slope 45a to which the developer slides down by its own weight in order to more reliably guide the peeled developer toward the developer recovery screw 44. The slope 45a is inclined horizontally such that the side toward the developer recovery screw 44 is lower than the lower position of the peeling roller 32.

[0042] The developer recovery screw 44, which serves as both a recovery member and a transport unit, transports the recovered developer to the developer circulation unit 46, which will be described below. In other words, the developer recovery screw 44 is a screw transport member used to transport the developer that has slid down the slope of the guide member 45 in one direction while agitating it.

[0043] The developer circulation unit 46 is a supply unit for supplying developer to the first developing roller 30, and the developer circulation unit 46 includes a regulating member 50, a developer supply screw 42, and a developer stirring screw 43. In the developer circulation unit 46, the developer is supplied to the first developing roller 30 while being agitated in the developer supply screw 42 and the developer stirring screw 43 and transported in a substantially horizontal direction. Also, as described above, the developer recovered by the developer recovery unit 47 falls by its own weight and is introduced into the developer circulation unit 46. That is, the developer circulation unit 46 is located below the developer recovery unit 47 in the vertical direction.

[0044] The developer supply screw 42, developer agitation screw 43, and developer recovery screw 44 are screw conveying members that convey the developer in one direction while agitating it. The developer supply screw 42 and developer agitation screw 43 are located below the rotation center of the developer recovery screw 44 in the vertical direction. Furthermore, these developer supply screw 42, developer agitation screw 43, and developer recovery screw 44 are arranged so that their rotation axes are approximately parallel to each other. The rotation axis of each of these screws is also approximately parallel to the rotation axis of the first developing roller 30.

[0045] The developer supply screw 42 is located between the first developing roller 30 and the developer agitation screw 43, and a partition wall 48 of the developing container 70 is positioned between the developer supply screw 42 and the developer agitation screw 43. The partition wall 48 of the developing container 70 extends along the rotation axis direction of the developer supply screw 42 and the developer agitation screw 43. The partition wall 48 is provided with a communication opening (not shown) that connects a first transport path 71 through which the developer is transported by the developer supply screw 42 and a second transport path 72 through which the developer is transported by the developer agitation screw 43.

[0046] The developer, agitated by the developer recovery screw 44, passes through a communication opening (not shown) formed in the partition wall 73 of the developing container 70 located between the developer recovery screw 44 and the developer supply screw 42, and falls towards the developer supply screw 42 by its own weight. The guide member 45 described above is formed integrally with the partition wall 73, and the developer recovery screw 44 is positioned above the partition wall 73.

[0047] The location of the communication port through which the developer agitated by the developer recovery screw 44 falls by its own weight and is introduced into the developer circulation section 46 is preferably positioned to avoid the area where the developer is supplied toward the first developing roller 30 (the intermediate portion with respect to the rotation axis direction of the developer supply screw 42). In this embodiment, the location of the communication port is set to include the downstream end (terminal end) in the developer transport direction of the first transport path 71 where the developer supply screw 42 is located.

[0048] The developer transport directions of the developer supply screw 42 and the developer agitation screw 43 are opposite to each other. The starting end (upstream end in the developer transport direction) and ending end (downstream end in the developer transport direction) of the first transport path 71 where the developer supply screw 42 is located, and the ending end and starting end of the second transport path 72 where the developer agitation screw 43 is located, are in communication via a communication port provided in the partition wall 48. Therefore, the developer circulates in the rotational direction of the developer supply screw 42 and the developer agitation screw 43, as indicated by the arrows in Figure 2, and in a substantially horizontal direction within the developing container 70, with a portion of it being supplied toward the first developing roller 30.

[0049] The developer supply port 51 (see Figure 2) is located above the developer agitation screw 43 in the developing container 70 and is connected to the developer storage section 27Y (see Figure 1). The developer supply port 51 is configured to supply the developer stored in the bottle loaded in the developer storage section 27Y to the second transport path 72 where the developer agitation screw 43 is located.

[0050] As described above, the toner weight ratio of the developer stored in the bottles of the developer storage unit 27Y is greater than the toner weight ratio of the developer in the developing device 1Y. Therefore, by adjusting the amount of developer supplied to the developer stirring screw 43, it is possible to maintain a constant toner weight ratio of the developer in the developing device 1.

[0051] The toner concentration detection sensor 49 (see Figure 2) is positioned to detect the toner concentration in the developer contained in the developer circulation unit 46. 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 used to control the replenishment of developer from the developer storage unit 27Y. For example, if it is detected that the toner concentration has fallen below a predetermined value, developer is replenished from the developer storage unit 27Y. Since the magnetic permeability of the developer changes more than the toner concentration, it is possible to detect the toner concentration using the magnetic permeability.

[0052] The regulating member 50 is positioned adjacent to the first developing roller 30 and is used to regulate the amount of developer supplied from the developer circulation unit 46 to the first developing roller 30. The regulating member 50 can be configured to regulate the amount of developer adsorbed onto the first developing roller 30 based, for example, on the gap between the surface of the first developing sleeve 33 of the first developing roller 30 and the end of the regulating member 50.

[0053] The developer in the developing container 70 is transported in a substantially horizontal direction while being agitated in the developer circulation unit 46, and then supplied to the first developing roller 30. From the first developing roller 30, it is transferred to the upper second developing roller 31 based on magnetic force. Next, it is transferred from the second developing roller 31 to the peeling roller 32 on the side of the second developing roller 31, again based on magnetic force. After being peeled off the peeling roller 32 by a peeling magnet 38 embedded in the peeling roller 32, it is collected in the developer recovery unit 47 and then introduced back into the developer circulation unit 46.

[0054] Furthermore, as described above, in this embodiment, a two-component development method is used as the development method, and the developer is a mixture of a negatively charged non-magnetic toner and a magnetic carrier. The non-magnetic toner becomes negatively charged by triboelectric charging with the magnetic carrier, and the magnetic carrier becomes positively charged. The non-magnetic toner is made by encapsulating colorants, wax components, etc., in a resin such as polyester or styrene acrylic, and then crushing or polymerizing it into a powder, to which fine powders such as titanium dioxide and silica are added to the surface. The magnetic carrier is made by coating the surface of a core consisting of resin particles mixed with ferrite particles or magnetic powder with resin. In this embodiment, the toner concentration in the developer in the initial state (weight ratio of toner contained in the developer) is 8%.

[0055] Generally, two-component development systems using toner and carriers have the advantage of less stress on the toner than one-component development systems using a single-component developer, because they charge both the toner and carrier to a predetermined polarity by frictional contact. On the other hand, with prolonged use, the amount of dirt (spent) adhering to the carrier surface increases, and as a result, the ability to charge the toner gradually decreases. This results in problems such as fogging and toner scattering. Increasing the amount of carrier contained in the development unit could be considered to extend the lifespan of the two-component development unit, but this is undesirable because it would lead to a larger development unit.

[0056] To resolve the above-mentioned problems related to two-component developers, this embodiment employs an ACR (Auto Carrier Refresh) method. The ACR method is a method that suppresses the increase of degraded carriers by gradually supplying new developer from the developer storage unit 27Y into the developing device 1Y, and gradually discharging the developer with degraded charging performance from the discharge port (not shown) of the developing device 1Y. As a result, the degraded carriers in the developing device 1Y are gradually replaced with new carriers, making it possible to maintain the charging performance of the carriers in the developing device 1Y at a roughly constant level.

[0057] In the developing apparatus 1Y of this embodiment, the developer in the first transport path 71 is supplied to the first developing sleeve 33 by the developer supply screw 42. The developer supplied to the first developing sleeve 33 is carried on the first developing sleeve 33 in a predetermined amount by the magnetic field generated by the first developing magnet 36, forming a developer reservoir. As the first developing sleeve 33 rotates, the two-component developer on the first developing sleeve 33 passes through the developer reservoir and is thinly coated onto the surface of the first developing sleeve 33 by the regulating member 50, and then transported to the developing area facing the photosensitive drum 28Y. In the developing area, the developer on the first developing sleeve 33 rises up to form a magnetic pile.

[0058] In the first developing region where the first developing sleeve 33 and the photosensitive drum 28Y face each other, the developing bias applied to the first developing sleeve 33 makes the electrostatic latent image formed on the photosensitive drum 28Y visible. In this embodiment, the developing bias applied to the first developing sleeve 33 is a waveform in which both AC and DC electric fields are superimposed, but a developing bias of only a DC electric field may also be used.

[0059] The two-component developer is subjected to the development process in the first development area, then transferred to the second development sleeve 34 at a position close to the second development sleeve 34, and transported to the second development area opposite the second development sleeve 34 and the photosensitive drum 28Y. In the second development area, the same development bias as in the first development area is applied, and the toner image is uniformly adjusted by developing and supplementing the toner that is insufficient relative to the potential of the electrostatic latent image on the photosensitive drum 28Y, and recovering the toner that has been developed in excess. Here, the development bias applied to the first development sleeve 33 and the development bias applied to the second development sleeve 34 may have different waveforms.

[0060] The developer that has passed through the second developing region is then peeled off in the peeling magnetic field region formed by the second developing magnet 37 enclosed in the second developing sleeve 34. The developer peeled off from the second developing sleeve 34 is attracted to the surface of the peeling sleeve 35 by the magnetic field formed by the peeling magnet 38 enclosed in the peeling sleeve 35 of the peeling roller 32, and is conveyed along the rotational direction of the peeling sleeve 35. Then, due to the peeling magnetic field formed by the peeling magnet 38, it detaches from the surface of the peeling sleeve 35 and is collected in the developer recovery unit 47.

[0061] [duct] The developing apparatus 1Y is equipped with a duct (suction duct) 60 above the second developing region and the peeling magnetic field region of the second developing sleeve 34 described above, for collecting toner that has been released from the magnetic tip in the second developing region and the transport magnetic pole downstream in the developer transport direction and scattered into the air. The duct 60 is configured to suction and clean scattered toner generated by the second developing roller 31 and the peeling roller 32, and as shown in Figure 2, it has a first duct wall 61 and a second duct wall 62. The developing apparatus 1Y is also equipped with an air suction device 69 connected to the duct 60.

[0062] The first duct wall 61 covers a portion of the internal space of the developing container 70, where the first developing roller 30, the second developing roller 31, and the peeling roller 32 are installed and the developer is stored, preventing the developer from scattering from the internal space to the outside. In this embodiment, the first duct wall 61 covers the area above the peeling roller 32 and the developer recovery section 47. Specifically, the first duct wall 61 has a first wall portion 61a located above the vertical apex of the peeling roller 32, and a second wall portion 62b extending from the first wall portion 61a toward the upstream side in the rotational direction of the peeling sleeve 35, and positioned closer to the peeling roller 32 than the first wall portion 61a. That is, in this embodiment, the first duct wall 61 extends from a position above the peeling roller 32 toward the upstream side in the rotational direction of the peeling sleeve 35, and is formed to bend diagonally downward along the way.

[0063] As described above, the first duct wall 61 covers the upper part of a portion of the internal space of the developing container 70, but a second duct wall 62 is provided on the outside of the first duct wall 61. In this embodiment, the second duct wall 62 constitutes a part of the outer wall of the developing container 70, but it may be separate from the outer wall of the developing container 70. The second duct wall 62 extends above the second developing roller 31, with its tip facing the photosensitive drum 28Y with a gap between them, and covers the area above the second developing roller 31. Specifically, the second duct wall 62 extends further toward the second developing roller 31 (developing roller side) than the tip of the first duct wall 61 on the suction port 60a side. In this embodiment, the second duct wall 62 extends from vertically above the first duct wall 61 to a position facing the second developing roller 31.

[0064] Furthermore, above the second developing roller 31, a suction port 60a of the duct 60, which consists of the first duct wall 61 and the second duct wall 62, is provided. Specifically, the suction port 60a is an opening at one end of the duct 60, formed between the tip of the first duct wall 61 and a part of the second duct wall 62. With respect to the rotational direction of the peeling roller 32, the suction port 60a is located upstream of the opposing portion 74 where the second developing roller 31 and the peeling roller 32 face each other.

[0065] The other end of duct 60 is connected to a main duct (not shown). The main duct is where the ducts for each color developing device converge and is connected to an air suction device 69. The air suction device 69 is, for example, a fan, and by driving the air suction device 69, developer scattered inside the developing container during developing is sucked up through the duct 60 and into the suction port 60a. The air sucked up by duct 60 is exhausted to the outside through a filter (not shown). This reduces the amount of developer scattered from inside the developing container 70 to the outside. In addition, the suction port 60a of duct 60 sucks up toner scattered in the area between the second developing area and the delamination magnetic field area, as well as toner floating within the range of the airflow, reducing the adhesion of toner to the area around the developing device and the developing device itself. When the image forming operation is performed, the air suction device 69 is operated to suck up the scattered developer. This suction operation is performed continuously during image forming.

[0066] On the other hand, in the developing apparatus 1Y with the above configuration, if carrier particles are sucked in along with the toner by the duct 60, there is a risk of reduced suction efficiency of scattered toner due to filter clogging, and reduced suction efficiency due to carriers adhering to the inner wall of the duct 60. In order to suppress carrier scattering and achieve high-quality, stable image formation over a long period of time, it is necessary to suppress the supply of carriers from the second developing sleeve 34 to the duct 60 and to suppress the suction of carrier particles into the duct 60 by airflow.

[0067] To achieve this, it is necessary to reduce the transfer of carrier particles from the second developing sleeve 34 to the duct 60. For this purpose, in this embodiment, the configuration of the transport pole 206 (see Figure 4) of the second developing magnet 37 is optimized, as will be described later.

[0068] In this embodiment, the developing apparatus 1Y has a regulating member 50 positioned below a plurality of developing rollers (first developing roller 30 and second developing roller 31) that transport the developer, and is configured to transport the developer upward through the plurality of developing rollers, particularly against gravity. In addition, a duct 60 is positioned downstream in the direction of transport of the developer by the plurality of developing rollers to suck up scattered toner. In such a configuration, the faster the image formation speed (process speed), the more likely it is that carrier particles will scatter.

[0069] In this embodiment, the first developing sleeve 33 has a diameter of φ25 [mm] and rotates at a peripheral speed of 513 [mm / sec], the same as the photosensitive drum 28Y. The second developing sleeve 34 has the same diameter of φ25 [mm] as the first developing sleeve 33 and rotates at a peripheral speed of 616 [mm / sec], which is faster than the peripheral speed of the first developing sleeve 33. Furthermore, the peeling sleeve 35 has a smaller diameter of φ18 [mm] than the first developing sleeve 33 and the second developing sleeve 34 and rotates at a peripheral speed of 744 [mm / sec], which is faster than the peripheral speed of the second developing sleeve 34.

[0070] [Placement of duct suction ports] Figure 3 shows a schematic diagram on the right side that is an enlarged view of the area around the second developing roller 31 and the suction port 60a of the duct 60, and on the left side that shows each quadrant of the coordinate plane. The diagram on the right side of Figure 3 is a cross-section of the developing apparatus 1Y such that the second developing region is located on the left and the peeling magnetic field region is located on the right, as shown in Figure 2. Specifically, it shows the case where the second developing roller 31 is located to the left of the peeling roller 32 in a cross-section perpendicular to the rotation axis of the second developing sleeve 34 when the developing apparatus 1Y is mounted on the image forming apparatus 100.

[0071] In this embodiment, in the first coordinate plane, which is composed of a horizontal x-axis and a vertical y-axis with the rotation center O of the second developing sleeve 34 as the origin, the rotation center O' of the peeling sleeve 35 is located in the first quadrant. Furthermore, in the second coordinate plane, which is composed of a horizontal x-axis and a vertical y-axis with the rotation center O' of the peeling sleeve 35 as the origin, the suction port 60a of the duct 60 is located in the second quadrant.

[0072] Specifically, the duct 60 is positioned above the developing apparatus 1Y, and as described above, the other end of the duct 60 is connected to the main duct extending from the image forming apparatus body. The suction port 60a at one end of the duct 60 is located inside the developing container 70. Inside the developing apparatus 1Y, the duct 60 extends approximately horizontally and is formed to bend above the peeling roller 32 towards the second developing area. The tip of the first duct wall (inner guide) 61 on the suction port 60a side is located near the area between the peeling roller 32 and the second developing roller 31. Here, the endpoint of the tip of the first duct wall 61 on the suction port 60a side of the duct 60 on the second duct wall (outer guide) 62 side is defined as the reference point (first reference point) A. In this case, reference point A lies in the first quadrant of the first coordinate plane with the rotation center O of the second developing sleeve 34 as the origin, and in the second quadrant of the second coordinate plane with the rotation center O' of the peeling sleeve 35 as the origin.

[0073] [About the magnetic poles of each magnet] Next, Figure 4 shows the magnetic pole arrangement of the first developing magnet 36, second developing magnet 37, and peeling magnet 38, which are enclosed in the first developing roller 30, second developing roller 31, and peeling roller 32. The first developing magnet 36, enclosed in the first developing roller 30, has multiple magnetic poles 101 to 107. In Figure 4, S and N within each magnet indicate whether the magnetic pole is an S pole or an N pole, and the radial lines within each magnet indicate the position of the maximum value of the normal component of the magnetic flux density at that magnetic pole. In this embodiment, the first developing magnet 36 has a total of 7 magnetic poles. Of these, magnetic pole 106 is a transfer pole for transferring developer from the first developing roller 30 to the second developing roller 31. The magnetic poles 101 to 107 are arranged in numerical order in the rotational direction of the first developing sleeve 33.

[0074] Magnetic pole 106 is a magnetic pole that transfers developer from the first developing sleeve 33 to the second developing sleeve 34 by a magnetic field generated in conjunction with the second developing magnet 37 of the second developing roller 31, and may hereafter be referred to as the transfer pole 106. Magnetic pole 107 is an N pole and is used to attract the developer supplied from the developer supply screw 42 onto the first developing sleeve 33. Magnetic poles 101, 102, 103, 104 and 105 are S poles, N poles, S poles, N poles and S poles, and are used to transport the developer attracted by magnetic pole 107 upward as the first developing sleeve 33 rotates. Magnetic pole 106 is an N pole and, as described above, transfers developer from the first developing sleeve 33 to the second developing sleeve 34 facing the first developing sleeve 33 by a magnetic field generated in conjunction with magnetic pole 201 in the second developing magnet 37 enclosed in the second developing roller 31.

[0075] Furthermore, in this embodiment, a low-magnetic-force portion 110 is formed by a repulsive magnetic field generated in cooperation between a magnetic pole 107, which is positioned downstream of the magnetic pole 106 with respect to the rotational direction of the first developing sleeve 33 and is the same pole as the magnetic pole 106, and the magnetic pole 107, which is positioned downstream of the magnetic pole 106 and is the same pole as the magnetic pole 106. This low-magnetic-force portion 110 facilitates the transfer of developer from the first developing sleeve 33 to the second developing sleeve 34. In this embodiment, the low-magnetic-force portion 110 has almost no magnetic force, but it may have a low magnetic force, for example, its magnetic force (the absolute value of the normal component Br of the magnetic flux density) may be 10 mT or less, or even 5 mT or less. The same applies to the low-magnetic-force portion 210 of the second developing magnet 37 and the low-magnetic-force portion 310 of the peeling magnet 38.

[0076] The second developing magnet 37, enclosed within the second developing roller 31, has multiple magnetic poles 201 to 207 (a total of 7 poles). Of these, magnetic pole 201 is the receiving pole for the second developing roller 31 to receive developer from the first developing roller 30. The magnetic poles 201 to 207 are arranged in numerical order in the rotational direction of the second developing sleeve 34.

[0077] Magnetic pole 201 is a magnetic pole that attracts developer from the first developing sleeve 33 to the second developing sleeve 34 by the magnetic field generated in conjunction with the magnetic pole 107 of the first developing magnet 36 of the first developing roller 30, and may hereafter be referred to as the receiving pole 201. Magnetic pole 207 is a magnetic pole that transfers developer from the second developing sleeve 34 to the peeling sleeve 35 by the magnetic field generated in conjunction with the peeling magnet 38 of the peeling roller 32, and may hereafter be referred to as the transfer pole (peeling pole) 207.

[0078] Furthermore, magnetic pole 201 is a south pole, opposite to magnetic pole 106, and is used to attract developer from the first developing sleeve 33 onto the second developing sleeve 34, as described above. Magnetic poles 202, 203, 204, 205, and 206 are north poles, south poles, north poles, south poles, and north poles, and are used to transport the developer attracted by magnetic pole 201 upward as the second developing sleeve 34 rotates. Note that, as will be described in more detail later, magnetic pole 206 is sometimes called the transport pole 206. Magnetic pole 207, as a transfer pole, is a south pole, and the developer that has passed through the developing area with the photosensitive drum 28Y facing magnetic pole 203 is transferred from the second developing sleeve 34 to the peeling sleeve 35 facing the second developing sleeve 34 by a magnetic field generated in conjunction with magnetic pole 303 in the peeling magnet 38 enclosed in the peeling roller 32.

[0079] Furthermore, in this embodiment, a low-magnetic-force portion 210 is formed by a repulsive magnetic field generated in cooperation between a magnetic pole 207, which is positioned upstream of the magnetic pole 201 with respect to the rotational direction of the second developing sleeve 34 and is the same pole as the magnetic pole 201, and the magnetic force of the magnetic pole 207. This low-magnetic-force portion 210 facilitates the transfer of developer from the first developing sleeve 33 to the second developing sleeve 34. In addition, the low-magnetic-force portion 210 prevents the developer from being attracted to the closest point between the first developing sleeve 33 and the second developing sleeve 34, thereby suppressing the pressure on the developer.

[0080] The peeling magnet 38 enclosed in the peeling roller 32 has multiple magnetic poles 301 to 305 (a total of 5 poles). The magnetic poles 301 to 305 are arranged in numerical order in the rotational direction of the peeling sleeve 35. The magnetic pole 303, which acts as a receiving pole, is used to attract the developer from the second developing sleeve 34 to the peeling sleeve 35 by the magnetic field generated in conjunction with the magnetic pole 207 of the second developing magnet 37 of the second developing roller 31, and may hereafter be referred to as the receiving pole 303. The magnetic pole 303 is an N pole, opposite to the magnetic pole 207, and is used to attract the developer peeled from the second developing sleeve 34 to the peeling sleeve 35 as described above. The magnetic poles 301, 302, and 304 are N pole, S pole, and S pole, and are used to transport the developer on the peeling sleeve 35 as the peeling sleeve 35 rotates. The magnetic pole 301 is a north pole and is a peeling pole used to peel off the developer adsorbed on the peeling sleeve 35 from the peeling sleeve 35 by the repulsive magnetic field generated in conjunction with the same pole, magnetic pole 305. Hereafter, it may be referred to as the peeling pole 301. A low-magnetic-force portion 310, in which the magnetic force is lower than that of magnetic pole 301, is formed between magnetic pole 301 and magnetic pole 305.

[0081] Thus, the first developing magnet 36 and the second developing magnet 37 are each composed of seven magnetic poles. The second developing sleeve 34 receives the developer at the receiving pole 201 facing the first developing sleeve 33, transports the developer from vertically downward to upward, and develops the toner into an electrostatic latent image on the photosensitive drum 28Y by the magnetic pole (developing pole) 203 in the second developing region. The developer that has gone through the developing process is transported through multiple transport poles and is peeled off from the second developing roller 31 in the peeling magnetic field region formed by the transfer pole 207 and transferred to the peeling roller 32. After that, the developer is collected inside the developing container 70.

[0082] [Regarding carrier particle detachment] Next, we will explain the relationship between the position of the transport pole 206 of the second developing magnet 37, which is located upstream of the suction port 60a of the duct 60 in the direction of air suction by the duct 60, and the duct 60. As shown in Figure 5(a), the duct 60 is installed so that the suction port (opening) 60a faces the region between the second developing region and the delamination magnetic field region. The transport pole 206 of the second developing roller 31 is located facing the suction port 60a of the duct 60.

[0083] The transport pole 206 is a magnetic pole located in the section from point I to the transfer pole 207 with respect to the rotational direction of the second developing sleeve 34, where point I is the point on the surface of the second developing sleeve 34 that is closest to the inner wall surface of the second duct wall 62 of the duct 60. It is desirable that there is only one magnetic pole in this section. If the length of the second duct wall 62 is short enough that the inner wall surface of the second duct wall 62 does not face the surface of the second developing sleeve 34, point I may be the closest point between a virtual surface extended from the tip of the second duct wall 62 and the surface of the second developing sleeve 34.

[0084] At the transport pole 206, the magnetic field lines extend perpendicular to the surface of the second developing magnet 37. As the developer is transported by the rotation of the second developing sleeve 34 and passes through the transport pole 206, carrier particles in the developer form magnetic spikes along the magnetic field formed by the transport pole 206. Between the transport pole 206 and the upstream magnetic pole 205, magnetic spikes are formed circumferentially along the surface of the second developing magnet 37.

[0085] Here, surface position H is defined as the position of the maximum value of the normal component of the magnetic flux density of the transport pole 206 on the surface of the second developing sleeve 34. As the magnetic fin approaches surface position H, it gradually rises, and at surface position H, it becomes perpendicular to the surface of the second developing sleeve 34. Subsequently, as it is transported toward the delamination magnetic field region, the magnetic fin tilts in the direction of travel as it is transported. It is desirable that surface position H is downstream in the rotational direction of the second developing sleeve 34 from the vertical apex of the second developing sleeve 34, that is, in the first quadrant of the first coordinate plane (see Figure 3) with the rotation center O of the second developing sleeve 34 as the origin.

[0086] Next, the scattering of carrier particles at the transport electrode 206 will be described. In the configuration of this embodiment, the carrier particles at the tip of the magnetic tip of the transport electrode 206 are subjected to the rotational force and centrifugal force of the second developing sleeve 34, making it easy for the carrier particles at the tip of the magnetic tip to detach from the magnetic tip. Also, since the carrier particles at the tip of the magnetic tip are furthest from the second developing magnet 37, the magnetic restraining force is relatively weak, making them easy to detach from the magnetic tip. The detached carrier particles are then thrown upward, generally in a tangential direction, with the peripheral speed of the second developing sleeve 34 and the moving speed of the magnetic tip as the initial velocity. The ease with which carrier particles detach from the magnetic tip varies depending on the particle size and magnetic properties of the carrier particles, the contact state with adjacent particles on the magnetic tip, the length of the magnetic tip, and the distance from the surface of the second developing magnet 37. For this reason, even if carrier particles detach from the magnetic tip, it is necessary to suppress the attraction of the carrier particles into the duct 60.

[0087] To prevent carrier particles from scattering into the duct 60, the positional relationship between the transport electrode 206 and the duct 60 is considered to have a significant impact. The relationship between the reference point A of the duct 60 and the surface position H of the transport electrode 206 will be explained below. First, if we let the line passing through surface position H and the rotation center O of the second developing sleeve 34 be line L, and the line passing through reference point A and surface position H be line T, then the relationship between line L and line T represents the relationship between the position where the magnetic tip of the transport electrode 206 is highest and the direction from this position toward the duct 60.

[0088] Let θ be the angle on the reference point A side formed by the straight line L and the straight line T, that is, the angle (acute angle) formed between the line segment AH of the straight line T, which is sandwiched between the reference point A and the surface position H, and the part of the straight line L opposite to the rotation center O with respect to the surface position H. When θ = 90°, the suction port 60a of the duct 60 will be located in the direction of transport of the magnetic tip of the transport pole 206. As shown in Figure 5(b), at the surface position H of the transport pole 206 of the second developing roller 31, the normal component of the magnetic flux density Br is largest, and the magnetic tip stands up vertically to its highest point. At this time, the tangential velocity and centrifugal force of the second developing sleeve 34 of the magnetic tip are at their maximum. On the other hand, as the magnetic tip stands up, the tip of the magnetic tip moves away from the second developing magnet 37, so the magnetic restraining force weakens. At this time, carrier particles detach from the tip of the magnetic tip due to the centrifugal force mrω 2 This is the moment when the magnetic force Fr between carrier particles is exceeded.

[0089] That is, mrω 2 When the Fr value is satisfied, the detached carrier particles are thrown upward from the tangential direction of the second developing sleeve 34 in a direction approximately perpendicular to the magnetic tip. This means that at the transport pole 206, carrier particles are most likely to detach between the time the magnetic tip rises up and when it reaches its peak, and they are also most likely to move towards the duct 60. In this case, if carrier particles detach from the tip of the magnetic tip at the transport pole 206, they will fly straight towards the duct 60, be carried by the airflow of the duct 60 to the main duct, and be collected by the filter inside the image forming apparatus.

[0090] On the other hand, if the magnetic tip reaches an angle beyond the surface position H relative to the transport pole 206, and begins to lie down downstream in the rotational direction of the second developing sleeve 34, even if carrier particles detach from the tip of the magnetic tip, they will be projected toward the surface of the second developing sleeve 34 and will be recovered by the second developing magnet 37.

[0091] Therefore, in this embodiment, the flight direction of the carrier particles and the position of the suction port 60a of the duct 60 are optimized to reduce filter clogging in the image forming apparatus body. Specifically, a configuration is proposed that reduces the amount of carrier particles riding on the airflow of the duct 60 using the surface position H, reference point A, straight line L, and straight line T described above.

[0092] [Regarding the angle θ] Figure 6 shows the relationship between the normal component Br of the magnetic flux density near the transport pole 206 on the surface of the second developing sleeve 34, the tangential component Bθ of the magnetic flux density, and the angle of the magnetic field lines as the magnetic thorn angle. The horizontal axis of Figure 6 shows the angle when the point where the line connecting the rotation center O of the second developing sleeve 34 and the rotation center of the photosensitive drum 28Y intersects with the surface of the second developing sleeve 34 is defined as 0°, and the clockwise direction in Figure 4 (the rotation direction of the second developing roller 31) is considered positive. The magnetic thorn angle is the angle of the magnetic thorn with respect to the tangential direction of the surface of the second developing sleeve 34.

[0093] When the magnetic tip angle is 90°, it is perpendicular to the surface of the second developing sleeve 34. At this time, the normal component Br of the magnetic flux density shows a peak, while the change in the tangential component Bθ of the magnetic flux density is large, and the carrier particles at the tip of the magnetic tip are further accelerated circumferentially toward Bθ=0. Here, let δ be the angle of the magnetic tip from the perpendicular to the tangent to the surface of the second developing sleeve 34. Furthermore, angle δ is considered positive when the tip of the magnetic tip tilts in the opposite direction to the rotation direction of the second developing sleeve 34. That is, angle δ is the angle within the range in which the magnetic tip stands upright. Figure 5(b) shows the angle δ of the magnetic tip with respect to the perpendicular to the tangent to the surface of the second developing sleeve 34 (i.e., the straight line L) at surface position H. From the relationship between angle δ and the angle θ mentioned above, when δ+θ is 90°, the direction of carrier flight from the tip of the magnetic tip is in the direction of the duct 60.

[0094] In Figure 6, the magnetic tip angle at which the change in Bθ is large is generally in the range of 60° to 90°. That is, as shown in Figure 5(b), in this range, carrier particles at the tip of the magnetic tip of the transport electrode 206 are more likely to detach from the magnetic tip. When the magnetic tip angle is approximately 60°, δ ≈ 30°, so by setting θ ≤ 60°, δ + θ becomes generally less than 90°, and the flight direction of the carriers can be directed downward relative to the direction toward the duct 60. From this, by setting the angle θ ≤ 60°, it is possible to suppress the flight of carrier particles that have detached from the magnetic tip of the transport electrode 206 and thrown upward from the reference point A of the suction port 60a of the duct 60 in the vertical direction upward, thereby reducing clogging of the filter by carrier particles.

[0095] Similarly, in Figure 6, the change in Bθ is large, and the acceleration of the carrier particles at the tip of the magnetic tip is maximum when δ ≈ 50°. In this case, by setting the angle θ to θ ≤ 40°, the scattering of carrier particles in the direction of the suction port 60a of the duct 60 can be further suppressed.

[0096] [Example 1] Figures 7(a) and 7(b) show the magnetic pole configurations for Example 1 when the angle θ is 60° and 40°. Figure 7(a) shows the same diagram as Figure 5(a) for the case of θ=60°, and Figure 7(b) shows the same diagram as Figure 5(a) for the case of θ=40°. In addition to the cases where the angle θ is 60° and 40°, we will describe experiments to investigate the carrier collection level for the configurations when θ is 75°, 45°, and 35°. In these experiments, the carrier collection level for each configuration was investigated using a developing apparatus with each configuration. However, as described above, the duct 60 was not connected to the main duct, and carrier particles transported by airflow to the outside of the developing apparatus were collected by a magnet. In other words, the experiment did not investigate the amount of clogging in the filter, but rather the amount of carrier particles attracted to the duct 60 was collected by a magnet installed separately from the developing apparatus, and the amount of collected particles was investigated. A large amount of carrier particles collected by the magnet means that the filter is more likely to clog.

[0097] Figure 8 shows the results of the experiment described above. In Figure 8, the reduction rate relative to the amount of carrier particles collected at θ = 75° is shown, with the amount collected at this time being used as a baseline. At θ = 75°, a relatively large amount of carrier particles were drawn into and collected in duct 60, but by making θ smaller, the amount collected could be reduced. At θ = 60°, the amount was reduced by approximately 60%, and at θ = 40°, it was possible to reduce it by more than 80%.

[0098] The reason why setting θ≦40° significantly reduced the amount of carriers collected is, as mentioned above, because the tangential direction of the second developing sleeve 34 at surface position H relative to the reference point A of the duct 60 is directed downward, causing the carriers thrown up from the magnetic tip of the transport pole 206 to fly in the direction of the peeling roller 32.

[0099] On the other hand, when the angle is θ ≤ 30°, the transport pole 206 becomes close to the transfer pole 207 on the downstream side of the rotation direction of the second developing sleeve 34 and the receiving pole 303 on the peeling roller 32 side, making it easier to generate a repulsive magnetic field between the poles, which hinders the transfer of developer from the second developing roller 31 to the peeling roller 32. Specifically, when θ ≤ 30°, the accuracy of developer transfer decreases, and some developer is carried around the second developing sleeve 34. For this reason, it is preferable to satisfy θ > 30°.

[0100] Thus, in this embodiment, since θ ≤ 60° is satisfied, even if carrier particles detach from the magnetic tip of the transport pole 206, the carrier particles fly toward the peeling roller 32 side rather than the suction port 60a of the duct 60. Therefore, it is possible to suppress the recovery of carriers by the duct 60. Furthermore, by satisfying θ ≤ 40°, it is possible to further suppress the recovery of carriers by the duct 60.

[0101] In this embodiment, the suction of carrier particles was verified by fixing the shape of the first duct wall 61 and the position of reference point A, and changing the position of the transport pole 206. However, if the position of reference point A is in one of the quadrants described above, the verification can be considered equivalent to the above verification.

[0102] <Second Embodiment> A second embodiment will be described with reference to Figures 9 to 12. In this embodiment, a second reference point B is newly established with respect to the duct 60 to further suppress the recovery of carriers by the duct 60. In this embodiment, a configuration in which the shape of the first duct wall 61 of the duct 60 differs from that of the first embodiment will also be described. Since the other configurations and operations are the same as in the first embodiment described above, the same components are denoted by the same reference numerals, and their descriptions and illustrations are omitted or simplified. The following description will focus on the differences from the first embodiment.

[0103] As shown in Figure 9, in a cross-section perpendicular to the rotation axis of the second developing sleeve 34, reference point A is defined as the first reference point A, and the second reference point B is defined as a point on the inner wall surface 61c, which is the wall surface of the first duct wall 61 on the side of the second duct wall 62, and is located on the side to which the duct 60 extends, further than the first reference point A. In this case, the second reference point B is the point where the first surface 61b1 of the inner wall surface 61c, which is on the side of the first reference point A further than the second reference point B, is inclined with respect to the second surface 61a1 of the inner wall surface 61c, which is on the opposite side of the first reference point A further than the second reference point B. That is, the second reference point B is the point on the inner wall surface 61c of the portion where the first duct wall 61 bends, specifically, the portion where the first wall portion 61a and the second wall portion 61b are continuous. Therefore, the first surface 61b1 is the wall surface of the second wall portion 61b on the second duct wall 62 side, and the second surface 61a1 is the wall surface of the first wall portion 61a on the second duct wall 62 side.

[0104] In this embodiment, the second reference point B is a part of the first duct wall 61, located above the peeling roller 32, and is the starting point for the first duct wall 61 to change direction toward the second developing area. If there are multiple points where the direction changes, the point furthest upward in the vertical direction is designated as the second reference point B. Furthermore, the second reference point B is located in the first quadrant of the first coordinate plane, with the rotation center O of the second developing sleeve 34 as the origin, as shown in Figure 3, and is located in either the first or second quadrant of the second coordinate plane, with the rotation center O' of the peeling sleeve 35 as the origin.

[0105] In Figure 9 and the first embodiment, the second duct wall 62 and the first duct wall 61 are arranged in a straight line from the second reference point B to the first reference point A. As described in the first embodiment, when carrier particles fly from the magnetic tip of the transport electrode 206 and pass the position of the first reference point A on the first duct wall 61 of the duct 60, they are more easily transported to the back of the duct 60 by the airflow. Also, if carrier particles fall onto the inclined section between the first reference point A and the second reference point B (i.e., the first surface 61b1), vibrations acting on the developing device 1Y may cause the fallen carrier particles to move along the first duct wall 61 and be collected onto the second developing roller 31.

[0106] On the other hand, if the carrier particles sucked into the duct 60 exceed the second reference point B, they will accumulate in the duct 60 or on the filter without returning to the second developing roller 31 (inside the developing device 1). Therefore, the angle and shape of the first duct wall 61 between the first reference point A and the second reference point B are also factors that affect the amount of carrier particles sucked in.

[0107] The shape of the first duct wall 61 (the shape of the second wall portion 61b) between the first reference point A and the second reference point B does not have to be on a straight line. For example, it may be hook-shaped as shown in Figure 10(a), or it may be arc-shaped as shown in Figure 10(b). In the duct 60A shown in Figure 10(a), a projection 63 is formed at the end of the second wall portion 61Ab of the first duct wall 61A on the suction port 60a side, and the end of the projection 63 is set as the first reference point A. In this case, the corner of the projection 63 closest to the second duct wall 62 is set as the first reference point A. Also, in the duct 60B shown in Figure 10(b), the second wall portion 61Bb of the first duct wall 61B is curved into an arc shape so as to be convex toward the second duct wall 62. In this case, the position where the curvature changes is set as the second reference point B. If there are multiple points where the curvature changes, the point furthest upward in the vertical direction shall be designated as the second reference point B.

[0108] Here, let F be the line passing through the second reference point B and the surface position H. Let φ be the angle (acute angle) between the line segment BH of line F, which is bounded by the second reference point B and the surface position H, and the part of line L that is opposite the rotation center O with respect to the surface position H. In this case, as shown in Figure 11(a), in the first duct wall 61C where line F and line T overlap, φ = θ. Also, as shown in Figure 11(b), in the duct 60D, when φ < θ, the slope of the portion of the first duct wall 61D between the first reference point A and the second reference point B (second wall portion 61b) becomes steeper. That is, the angle of the second wall portion 61b with respect to the horizontal is larger than when θ = φ. Furthermore, as shown in Figure 11(c), when φ > θ, the inclination of the portion of the first duct wall 61E between the first reference point A and the second reference point B (second wall portion 61b) becomes gentler. That is, the angle of the second wall portion 61b with respect to the horizontal becomes smaller than when θ = φ.

[0109] In this case, either φ or θ satisfies the angle described in the first embodiment. That is, θ ≤ 60° or φ ≤ 60°. Preferably, θ ≤ 40° or φ ≤ 40°. More preferably, both φ and θ satisfy the above angles. That is, θ ≤ 60° and φ ≤ 60°. Preferably, θ ≤ 40° and φ ≤ 40°. It is also preferable that φ > 30°.

[0110] [Example 2] As Example 2, we will describe an experiment that investigated the carrier collection level for configurations where the angles θ and Φ are 75°, 60°, 45°, 60°, and 35°, respectively, similar to Example 1. Figure 12 shows the results of this experiment. In Figure 12, similar to Example 1, a comparison of collection amounts is shown based on θ=75° and φ=75°. That is, Figure 12 shows the reduction rate relative to the collection amount when the carrier particles are collected at θ=75° and φ=75°, with the collection amount at that time being the baseline. The horizontal axis in Figure 12 represents the angle θ. Different marks are plotted on the graph in Figure 12 for the angle φ. The relationship between the numerical value of φ and the marks is as shown in Figure 12.

[0111] Figure 12 shows that if either φ or θ is below a predetermined angle, approximately 60° or less, the effect of reducing the amount of carrier particles drawn in can be obtained, similar to the experiment in Figure 8 of Example 1. The trend was that the smaller both φ and θ angles were, the higher the carrier collection level compared to the evaluation in the experiment in Figure 8. On the other hand, reducing the angle θ with respect to the first reference point A near the tip of the duct 60 resulted in a slightly greater effect of reducing the amount of carrier particles drawn in than reducing the angle φ with respect to the second reference point B. Furthermore, carrier particles that reached the first duct wall 61 were also transported to the back of the duct 60 by airflow depending on the size of φ.

[0112] Therefore, it is desirable that both θ and φ be 60° or less, and to obtain a greater effect in reducing the amount of carrier particles aspirated, a configuration where θ < φ is desirable.

[0113] This embodiment allows for a configuration that reduces the suction of carrier particles even when the shape is more complex than that of the first embodiment, such as with ducts 60A to 60E, and provides a higher quality developing apparatus 1Y.

[0114] <Third Embodiment> A third embodiment will be described with reference to Figures 13 to 17. In this embodiment, the position of the transport pole (first transport pole) 206 of the second developing magnet 37 and the transport pole (second transport pole) 302 of the peeling magnet 38 is appropriately positioned relative to the duct 60F, thereby suppressing the scattering of carrier particles due to the magnetic field formed by these transport poles 206 and 302. Since the other configurations and operations are the same as in the first embodiment described above, the same reference numerals are used for the same configurations, and their descriptions and illustrations are omitted or simplified. The following description will focus on the differences from the first embodiment.

[0115] In this embodiment, we will explain using the configuration described in the first embodiment above, in which the relationship between the transport pole 206 of the second developing magnet 37 and the reference point A is θ = 40°. In this embodiment, the configuration is θ < φ. As shown in Figure 13, the transport pole 302 is one of the magnetic poles located upstream in the rotational direction of the peeling sleeve 35 from the closest point between the second developing roller 31 and the peeling roller 32. Also, the transport pole 206 and the transport pole 302 are opposite poles to each other.

[0116] As described in the first embodiment, by setting the angle θ to 60° or less, the carrier particles projected from the magnetic tip of the transport electrode 206 will face downwards in the duct 60, that is, towards the peeling roller 32. Therefore, when carrier particles are projected from the tip of the magnetic tip at the transport electrode 206, in addition to the momentum due to the initial velocity, these carrier particles are subjected to forces due to gravity, the magnetic field formed between the transport electrode 206 and the transport electrode 302, and the airflow in the duct 60F. The flying carrier particles are mainly affected by the airflow from the duct 60F, but their flight direction is corrected by the magnetic field towards the transport electrode 302 from the transport electrode 206.

[0117] In this case, the height of reference point A on the first duct wall 61 should be such that it does not obstruct the trajectory of the carrier particles as they fly towards the peeling roller 32. Specifically, reference point A is positioned so as not to face the transport poles 206 and 302, and the first duct wall 61 of the duct 60F is positioned so as not to cross the magnetic field lines formed by the transport poles 206 and 302. If the first duct wall 61 of the duct 60F is positioned so as to cross the magnetic field lines from the transport pole 206 to the transport pole 302, carrier particles flying from the transport pole 206 will be more likely to land on the first duct wall 61. This configuration helps to attract the carrier particles with the airflow of the duct 60F.

[0118] Here, in a cross-section perpendicular to the rotation axis of the second developing sleeve 34, the position of the maximum value of the normal component of the magnetic flux density of the transport pole 302 on the surface of the peeling sleeve 35 is defined as surface position J. Also, the line passing through surface position J and the rotation center O' of the peeling sleeve 35 is defined as line E, and the line passing through reference point A and the rotation center O' is defined as line G. Furthermore, assuming the rotation direction of the peeling sleeve 35 is positive, the angle from the line segment AO' between reference point A and the rotation center O' in line G to the line segment JO' between surface position J and the rotation center O' in line E is defined as ψ. In this case, in order to prevent the first duct wall 61 from crossing the magnetic field lines from the transport pole 206 to the transport pole 302, it is preferable to satisfy ψ > 0.

[0119] Figure 14 shows the magnetic field line distribution between the transport pole 206 of the second developing magnet 37 and the transport pole 302 of the peeling magnet 38 when θ = 40° and ψ = 5°, representing the configuration of this embodiment. The transport pole 302 is located approximately opposite the reference point A. At this time, as mentioned above, it can be seen that the first duct wall 61 is overlapping a portion of the magnetic field lines from the transport pole 206 to the transport pole 302.

[0120] On the other hand, Figure 15 shows the magnetic field line distribution between the carrier pole 206 and the carrier pole 302 when θ = 40° and ψ = 10°, as in the configuration of this embodiment. In this case, the magnetic field lines extending from the carrier pole 206 to the carrier pole 302 are distributed without interfering with the first duct wall, and the risk of flying carrier particles being assisted by magnetic force to move in the direction of the duct 60F is reduced.

[0121] In contrast, if the position of reference point A is lower than the line E, or if the position of the transport pole 302 is upstream of the line G in the rotational direction of the peeling sleeve 35, then ψ < 0°, and the magnetic field lines from the transport pole 206 to the transport pole 302 are blocked by the first duct wall 61. As a result, carrier particles are more easily attracted into the duct 60F.

[0122] Next, the positional relationship between the transfer pole 207 and the receiving pole 303, which are adjacent to the downstream side in the rotational direction of the respective sleeves with respect to the transport pole 206 and transport pole 302, is such that they do not face each other in the nip section between the second developing roller 31 and the peeling roller 32. In this case, the transfer pole 207 and the receiving pole 303 are opposite poles, and it is desirable that the receiving pole 303 is located further downstream in the rotational direction of the peeling sleeve 35 than the transfer pole 207 in the nip section. If the transfer pole 207 and the receiving pole 303 are positioned facing each other, the magnetic restraining force between the poles will increase, which may accelerate the deterioration of the developer during the transfer of the developer.

[0123] Here, the term "opposing" is defined as follows. As shown in Figure 13, first, let surface position U be the position of the maximum value of the normal component of the magnetic flux density of the transfer pole 207 on the surface of the second developing sleeve 34, and surface position V be the position of the maximum value of the normal component of the magnetic flux density of the receiving pole 303 on the surface of the peeling sleeve 35. Also, let α be the angle between the straight line OO' passing through the rotation center O of the second developing sleeve 34 and the rotation center O' of the peeling sleeve 35, and the line segment DO connecting surface position U and the rotation center O of the second developing sleeve 34. Furthermore, let β be the angle between the straight line OO' and the line segment RO' connecting surface position V and the rotation center O' of the peeling sleeve 35. Also, let R be the radius of the second developing sleeve 34, and r be the radius of the peeling roller 32. In this case, the term "opposing" means satisfying the relationship Rsinα≈rsinβ. In the configuration of Figure 13 used in the explanation, α=19° and β=27°. Therefore, in order to satisfy the "opposing" condition described above, the angle of β must be reduced (the surface position V must be shifted to the downstream side in the rotational direction of the peeling sleeve 35).

[0124] Furthermore, the surface position U is preferably located upstream of the point where the straight line OO' intersects with respect to the rotational direction of the second developing sleeve 34, and satisfies 5°≦α≦30°. More preferably, the surface position U is located in the range of 10°≦α≦20°. Furthermore, the surface position V is preferably located upstream of the point where the straight line OO' intersects with respect to the rotational direction of the peeling sleeve 35, and satisfies 5°≦β≦30°. More preferably, the surface position V is located in the range of 10°≦β≦20°.

[0125] Figure 16 shows the distribution of magnetic field lines between the transport pole 206 and the transport pole 302 when θ=40°, ψ=10°, α=18°, and β=7°. Here, the arrangement of the magnetic poles of the peeling magnet 38 is changed from the configuration shown in Figure 13, and with respect to the rotation direction of the peeling sleeve 35, the magnetic poles from the receiving pole 303 downstream of the transport pole 302 are moved downstream. Specifically, in the configurations of the first and second embodiments, the angle between the poles of the transport pole 302 and the receiving pole 303 was 52°, but in the configuration shown in Figure 16, the angle between the poles is 60°.

[0126] As a result, in the configuration shown in Figure 16, the phases of the transfer electrode 207 and the receiving electrode 303 are shifted, causing the magnetic field lines to extend in the circumferential direction. Therefore, it becomes possible to efficiently transfer the developer while suppressing its degradation. Based on the above, it is preferable that the relationship between the transfer electrode 207 and the receiving electrode 303 satisfies α < β, where the magnetic field lines are oriented in the direction of the developer flow.

[0127] [Example 3] As Example 3, we will describe an experiment investigating the carrier collection level when the angle ψ is varied. Figure 17 shows the results of this experiment. In Figure 17, as in Example 1, the reduction rate relative to the amount of carrier particles collected when ψ = 5° is used as the reference. In the experiment, the first duct wall 61 was evaluated based on whether the magnetic field lines from the transport pole 206 to the transport pole 302 crossed it, and the level of carrier particle collection. The position of the transport pole 302 of the peeling magnet 38 was set with ψ in the range of -5° to 40°, with the position opposite the reference point A as the reference.

[0128] As mentioned above, when the angle ψ≧5°, magnetic field lines no longer act on the first duct wall 61, and the amount of carrier particles collected decreases. However, when ψ≧10°, the collection level remains stably high, which is more desirable. On the other hand, when ψ=40°, the transport pole 302 becomes close to the transfer pole 207 of the second developing magnet 3738. Since the transport pole 302 and the transfer pole 207 are the same pole, the repulsive field increases, reducing the transfer of developer from the second developing roller 31 to the peeling roller 32, and causing stagnation between the second developing roller 31 and the peeling roller 32. When stagnation occurs, toner fusion to the roller surface and developer degradation are more likely to occur. In Figure 17, "×" indicates that stagnation occurred between the second developing roller 31 and the peeling roller 32, "△" indicates that some stagnation occurred but was not a problem, and "〇" indicates that almost no stagnation occurred.

[0129] Therefore, ψ≧5° is preferred, and ψ≧10° is more preferred. Also, from Figure 17, ψ≦30° is preferred, and ψ≦20° is more preferred. That is, the position of the transport pole 302 is preferably set in the range of 5°≦ψ≦30° with respect to the reference point A, and more preferably in the range of 10°≦ψ≦20°.

[0130] When setting ψ, the position of the reference point A may be changed so that ψ satisfies the above range, or the peeling magnet 38 may be rotated in the rotational direction of the peeling sleeve 35 from the first and second working diameter positions so that ψ satisfies the above range. Alternatively, the position of the transport pole 302 and the magnetic pole adjacent to it may be changed so that ψ satisfies the above range.

[0131] Based on the above, even with the configuration of this embodiment, the suction of carrier particles by the duct 60F can be effectively suppressed, and a high-quality developing apparatus can be provided.

[0132] [Other embodiments] Although the above embodiments describe a developing apparatus with two developing rollers, the present invention can also be applied to a configuration with only one developing roller. That is, the present invention can be applied to a configuration in which there is one developing roller for developing an electrostatic latent image on an image carrier such as a photosensitive drum, and a peeling roller for peeling the developed material from this developing roller.

[0133] The present invention is not limited to the configurations of the embodiments described above. 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, the developer agitation screw 43, and the developer recovery screw 44 are not particularly limited as long as they can transport the developer, and for example, spiral blades or paddle-shaped blades can be applied. [Explanation of Symbols]

[0134] 1Y, 1M, 1C, 1K... Developing equipment 28Y, 28M, 28C, 28K... Photosensitive drum (image carrier) 30...First developing roller 31...Second developing roller (developing roller) 32... Stripping roller 33...First developing sleeve 34. Second developing sleeve (developing sleeve) 35...Removal sleeve 36...First developing magnet 37. Second developing magnet (developing magnet) 38... Peel-off magnet 60, 60A~60F... Duct 60a...Suction port 61...First duct wall 61a...First wall section 61b...Second wall part 61c...Interior wall surface 62...Second duct wall 70... Developing container 74... Opposite section 100...Image forming apparatus 206...Conveyor pole (First conveyor pole) 207...Delivery Pole 302...Conveyor pole (second conveyor pole) 303... Receiving address

Claims

1. A developing container containing a developer including toner and carrier, A developing roller having a rotating developing sleeve, a developing magnet positioned non-rotating inside the developing sleeve and using magnetic force to attract a developer containing toner and a magnetic carrier to the surface of the developing sleeve, and developing an electrostatic latent image formed on a rotating image carrier with the developer, The opposing portion facing the developing sleeve includes a release sleeve whose surface rotates so as to move in the same direction as the surface of the developing sleeve, and a release magnet which is non-rotatingly positioned inside the release sleeve and attracts developer to the surface of the release sleeve by magnetic force, and a release roller which releases the developer from the developing roller after the electrostatic latent image on the image carrier has been developed by the developing roller, A duct having a suction port for sucking up the developer scattered in the developing container, located upstream of the opposing portion with respect to the rotational direction of the peeling sleeve, comprising: a first duct wall extending upstream from the suction port in the rotational direction of the peeling sleeve and positioned opposite a part of the peeling roller with a gap between them; and a second duct wall positioned opposite the first duct wall and forming a space between it and the first duct wall through which the developer sucked from the suction port flows, The developing magnet has a transfer pole which is a magnetic pole for transferring developer from the developing roller to the peeling roller, and a transport pole which is upstream of the transfer pole and adjacent to the transfer pole with respect to the rotational direction of the developing sleeve. In a cross-section perpendicular to the rotation axis of the developing sleeve, The tip of the first duct wall on the suction port side and the endpoint on the second duct wall side are reference point A, The position of the maximum value of the normal component of the magnetic flux density of the transport pole on the surface of the developing sleeve is defined as surface position H, Let the straight line passing through the reference point A and the surface position H be the straight line T. The line passing through the surface position H and the rotation center O of the developing sleeve is called the line L. The angle between the line segment A-H, which is bounded by the reference point A and the surface position H in the aforementioned line T, and the portion of the aforementioned line L opposite to the rotation center O with respect to the surface position H is θ. In that case, θ ≤ 60° satisfies A developing apparatus characterized by the following features.

2. In a cross-section perpendicular to the rotation axis of the developing sleeve, assuming that the developing roller is located to the left of the peeling roller, The reference point A and the rotation center O' of the peeling sleeve are located in the first quadrant of a coordinate plane composed of the horizontal x-axis and the vertical y-axis, with the rotation center O of the developing sleeve as the origin. The developing apparatus according to feature 1.

3. The aforementioned reference point A is located in the second quadrant of a coordinate plane composed of the horizontal x-axis and the vertical y-axis, with the rotation center O' of the peeling sleeve as the origin. The developing apparatus according to feature 2.

4. θ ≤ 40° satisfies The developing apparatus according to feature 1.

5. θ > 30° satisfies The developing apparatus according to feature 1.

6. In a cross-section perpendicular to the rotation axis of the developing sleeve, When the aforementioned reference point A is designated as the first reference point A, and the second reference point B is a point on the inner wall surface of the first duct wall that is on the side of the second duct wall, located on the side of the first reference point A that extends further than the first reference point A, the second reference point B is a point on the inner wall surface where the first surface on the side of the second reference point B that is closer to the first reference point A is inclined with respect to the second surface on the inner wall surface that is opposite to the first reference point A than the second reference point B. The line passing through the second reference point B and the surface position H is called line F. The angle between the line segment B-H of the line F, which is bounded by the second reference point B and the surface position H, and the portion of the line L opposite to the rotation center O with respect to the surface position H is φ. In that case, φ≦60° satisfies The developing apparatus according to feature 1.

7. In a cross-section perpendicular to the rotation axis of the developing sleeve, assuming that the developing roller is located to the left of the peeling roller, The second reference point B is located in the first quadrant of the first coordinate plane, which is composed of the horizontal x-axis and the vertical y-axis with the rotation center O of the developing sleeve as the origin, and is located in the first or second quadrant of the second coordinate plane, which is composed of the horizontal x-axis and the vertical y-axis with the rotation center O' of the peeling sleeve as the origin. The developing apparatus according to feature 6.

8. φ≦40° satisfies The developing apparatus according to feature 6.

9. θ < φ satisfies The developing apparatus according to feature 6.

10. The transport pole of the developing magnet is designated as the first transport pole. The peeling magnet has a receiving pole which is a magnetic pole for the peeling roller to receive developer from the developing roller, and which is an opposite pole to the receiving pole, and a second transport pole which is an adjacent magnetic pole to the receiving pole on the upstream side of the receiving pole with respect to the rotational direction of the peeling sleeve. In a cross-section perpendicular to the rotation axis of the developing sleeve, The position of the maximum value of the normal component of the magnetic flux density of the second transport pole on the surface of the peeling sleeve is defined as surface position J. The line passing through the surface position J and the rotation center O' of the peeling sleeve is called line E. The line passing through the reference point A and the rotation center O' is called line G. When the rotation direction of the peeling sleeve is considered positive, the angle from the line segment A-O' bounded by the reference point A and the rotation center O' in the straight line G to the line segment J-O' bounded by the surface position J and the rotation center O' in the straight line E is ψ. In that case, ψ>0 satisfies The developing apparatus according to feature 1.

11. ψ≧5° satisfies The developing apparatus according to feature 10.

12. ψ≧10° satisfies The developing apparatus according to feature 10.

13. ψ≦30° satisfies The developing apparatus according to feature 10.

14. ψ≦20° satisfies The developing apparatus according to feature 10.

15. The surface position J is located below the reference point A in the vertical direction. The developing apparatus according to feature 10.

16. The position of the maximum value of the normal component of the magnetic flux density of the transfer pole on the surface of the developing sleeve is defined as surface position U. The position of the maximum value of the normal component of the magnetic flux density of the receiving pole on the surface of the peeling sleeve is defined as surface position V. Let α be the angle between the straight line O-O' passing through the rotation center O of the developing sleeve and the rotation center O' of the peeling sleeve, and the line segment D-O connecting the surface position U and the rotation center O of the developing sleeve. The angle between the straight line O-O' and the line segment R-O' connecting the surface position V and the rotation center O' of the peeling sleeve is β. In that case, α＜β satisfies The developing apparatus according to feature 10.

17. The surface position U is located upstream of the point where the straight line O-O' intersects with respect to the rotational direction of the developing sleeve, ５°≦α≦３０° satisfies The developing apparatus according to feature 16.

18. The surface position V is located upstream of the point where the straight line O-O' intersects with respect to the rotational direction of the peeling sleeve, ５°≦β≦３０° satisfies The developing apparatus according to feature 16.

19. A first developing roller having a rotating first developing sleeve and a first developing magnet which is non-rotatingly positioned inside the first developing sleeve and attracts developer to the surface of the first developing sleeve by magnetic force, and which develops an electrostatic latent image formed on the rotating image carrier with developer, The system further comprises a supply unit for supplying developer to the first developing roller, The developing sleeve is a second developing sleeve, the developing magnet is a second developing magnet, and the developing roller is a second developing roller. The second developing roller is positioned downstream of the first developing roller with respect to the rotation direction of the image carrier, and above the center of rotation of the first developing roller with respect to the vertical direction, and the developer is transferred from the first developing roller by magnetic force. The developing apparatus according to feature 1.

Images