Development apparatus

Abstract

The angle in the rotation direction of a first sleeve (33) from a position at which the absolute value of the magnetic flux density of a first development pole (104) becomes maximum in a direction normal to the outer circumferential surface of the first sleeve (33) up to a position at which the absolute value of the magnetic flux density of a first development downstream pole (105) becomes maximum in a direction normal to the outer circumferential surface of the first sleeve (33) is denoted as δ[°]. The angle in the rotation direction of a second sleeve (34) from a position at which the absolute value of the magnetic flux density of a second development pole (203) becomes maximum in a direction normal to the outer circumferential surface of the second sleeve (34) up to a position at which the absolute value of the magnetic flux density of a second development downstream pole (204) becomes maximum in a direction normal to the outer circumferential surface of the second sleeve (34) is denoted as θ[°]. The radius of the first sleeve (33) is denoted as R1 [mm], and the radius of the second sleeve (34) is denoted as R2 [mm]. In this case, the relation R2 × θ > R1 × δ is satisfied.

Description

Developing device

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

[0002] As a developing device, a configuration has been proposed in which two developing rollers that develop electrostatic latent images formed on an image carrier with developer are arranged side by side in the rotation direction of the image carrier (Japanese Patent Laid-Open No. 2013-254107). In the developing device described in Japanese Patent Laid-Open No. 2013-254107, of the two developing rollers, a first developing roller that is located vertically below is supplied with developer from a supply unit, and a second developing roller that is located vertically above is passed developer from the first developing roller located below.

[0003] After the development process in which the electrostatic latent image on the image carrier is developed by the development roller, the amount of toner in the developer on the development roller is reduced compared to before the development process. As described in Patent Document 1, in a configuration using a first development roller and a second development roller, the amount of toner in the developer on the second development roller after the development process is significantly reduced compared to the developer on the first development roller before the development process.

[0004] Furthermore, if the magnet placed inside the developing roller has multiple magnetic poles, when magnetic chains of the developer are formed on the developing roller near the image carrier, if the amount of toner in the developer is low, the electric field strength between the developing roller and the image carrier may cause the carrier in the developer to fly toward the image carrier and adhere to it. If the carrier in the developer adheres to the image carrier, electrical leakage may occur during the image-forming process of development and transfer, or the carrier may remain on the recording material, resulting in image defects such as blank areas of several millimeters in the output image.

[0005] SUMMARY OF THE INVENTION An object of the present invention is to provide a configuration that can suppress the occurrence of image defects.

[0006] One aspect of the present invention is a development device including: a development container that contains a developer containing toner and a carrier; a first rotor to which the developer contained in the development container is supplied, the first rotor rotating in the same direction as the image carrier at a position on the outer circumferential surface of the first rotor that is closest to the rotating image carrier, and carrying and transporting the developer to a first development position where an electrostatic latent image formed on the image carrier is developed; a first magnet that is fixedly disposed inside the first rotor so as not to rotate, the first magnet being disposed opposite the image carrier at the first development position; a first magnet having a first downstream pole disposed downstream of the first developing pole in a rotational direction and adjacent to the first developing pole, the first downstream pole having a polarity different from that of the first developing pole, and a delivery pole disposed downstream of the first downstream pole and upstream of the first developing pole in a rotational direction of the first rotating body; and a second rotating body disposed opposite to the first rotating body and to which the developer is delivered from the first rotating body by a magnetic field generated by the first magnet, the second rotating body rotating in the same direction as the image carrier at a position on the outer circumferential surface of the second rotating body closest to the image carrier; a second rotating body that carries and transports the developer to a second developing position where the electrostatic latent image is developed; a second magnet that is fixedly disposed inside the second rotating body so as not to rotate, the second rotating body having a second developing pole that is disposed facing the image carrier at the second developing position; a second downstream pole that is disposed adjacent to the second developing pole downstream of the second developing pole in the rotation direction of the second rotating body and has a polarity opposite to that of the second developing pole; and a second magnet that is disposed adjacent to the delivery pole downstream of the second downstream pole and upstream of the second developing pole in the rotation direction of the second rotating body and has a polarity opposite to that of the delivery pole. and a second magnet having a receiving pole of a polarity opposite to the first developing pole, wherein the angle in the rotation direction of the first rotating body from a position on the outer peripheral surface of the first rotating body where the absolute value of the magnetic flux density of the first developing pole in the normal direction to the outer peripheral surface of the first rotating body is maximum to a position on the outer peripheral surface of the first rotating body where the absolute value of the magnetic flux density of the first downstream pole in the normal direction to the outer peripheral surface of the first rotating body is maximum is defined as δ [°], and from a position on the outer peripheral surface of the second rotating body where the absolute value of the magnetic flux density of the second developing pole in the normal direction to the outer peripheral surface of the second rotating body is maximum,The developing device satisfies R2×θ>R1×δ, where θ [°] is the angle in the rotation direction of the second rotating body to a position on the outer circumferential surface of the second rotating body where the absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer circumferential surface of the second rotating body is maximum, R1 [mm] is the radius of the first rotating body, and R2 [mm] is the radius of the second rotating body.

[0007] One aspect of the present invention is a development device including: a development container that contains a developer containing toner and a carrier; a first rotor to which the developer contained in the development container is supplied, the first rotor rotating in the same direction as the image carrier at a position on the outer circumferential surface of the first rotor that is closest to the rotating image carrier, and carrying and transporting the developer to a first development position where an electrostatic latent image formed on the image carrier is developed; a first magnet that is fixedly disposed inside the first rotor so as not to rotate, the first magnet being disposed opposite the image carrier at the first development position; a first magnet having a first downstream pole disposed downstream of the first developing pole in a rotational direction and adjacent to the first developing pole, the first downstream pole having a polarity opposite to that of the first developing pole, and a delivery pole disposed downstream of the first downstream pole and upstream of the first developing pole in a rotational direction of the first rotating body; and a second rotating body disposed opposite to the first rotating body and having the developer delivered from the first rotating body by a magnetic field generated by the first magnet, the second rotating body rotating in the same direction as the image carrier at a position on the outer circumferential surface of the second rotating body closest to the image carrier; a second rotating body that carries and transports the developer to a second developing position where the electrostatic latent image is developed; a second magnet that is fixedly disposed inside the second rotating body so as not to rotate, the second developing pole being disposed facing the image carrier at the second developing position; a second downstream pole that is disposed adjacent to the second developing pole downstream of the second developing pole in the rotation direction of the second rotating body and has a polarity opposite to that of the second developing pole; and a second downstream pole that is disposed adjacent to the delivery pole downstream of the second downstream pole and upstream of the second developing pole in the rotation direction of the second rotating body and has a polarity opposite to that of the delivery pole. a second magnet having a receiving pole of a polarity opposite to that of the first downstream pole, and an angle in the rotation direction of the first rotating body from a position on the outer circumferential surface of the first rotating body closest to the image carrier to a position on the outer circumferential surface of the first rotating body where the absolute value of the magnetic flux density of the first downstream pole in the normal direction to the outer circumferential surface of the first rotating body is maximum is defined as δ2 [°], and an angle in the rotation direction of the first rotating body from a position on the outer circumferential surface of the second rotating body closest to the image carrier to a position on the outer circumferential surface of the second rotating body where the absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer circumferential surface of the second rotating body is maximum is defined asWhen the angle in the rotation direction of the second rotating body is θ2 [°], the radius of the first rotating body is R1 [mm], and the radius of the second rotating body is R2 [mm], the developing device satisfies R2×θ2>R1×δ2.

[0008] One aspect of the present invention is a development device comprising: a development container that contains a developer containing toner and a carrier; a first rotor to which the developer contained in the development container is supplied, the first rotor rotating in the same direction as the rotating image carrier at a position on the outer circumferential surface of the first rotor closest to the image carrier, and carrying and transporting the developer to a first development position where an electrostatic latent image formed on the image carrier is developed; a first magnet disposed inside the first rotor in a non-rotating fixed manner, the first magnet having: a first development pole disposed opposite the image carrier at the first development position; a first downstream pole disposed downstream of the first development pole in the rotational direction of the first rotor and adjacent to the first development pole, the first downstream pole having a polarity opposite to that of the first development pole; and a delivery pole disposed downstream of the first downstream pole and upstream of the first development pole in the rotational direction of the first rotor; and a first magnet disposed opposite the first rotor, and the developer is delivered from the first rotor by a magnetic field generated by the first magnet. a second rotating body that rotates in the same direction as the image carrier at a position on its outer circumferential surface closest to the image carrier and that carries and transports the developer to a second developing position where the electrostatic latent image is developed; and a second magnet that is fixedly arranged inside the second rotating body and non-rotatable, the second magnet having: a second developing pole that is arranged facing the image carrier at the second developing position; a second downstream pole that is arranged adjacent to the second developing pole downstream of the second developing pole in the rotational direction of the second rotating body and has a polarity opposite to that of the second developing pole; and a receiving pole that is arranged adjacent to the delivery pole downstream of the second downstream pole and upstream of the second developing pole in the rotational direction of the second rotating body and has a polarity opposite to that of the delivery pole; wherein the position on the outer circumferential surface of the second rotating body where the absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer circumferential surface of the second rotating body is maximum is located vertically above a horizontal line passing through the rotation center of the second rotating body.

[0009] According to the present invention, the occurrence of image defects can be suppressed.

[0010] FIG. 1 is a cross-sectional view showing the schematic configuration of an image forming apparatus according to the first embodiment.

[0011] FIG. 2 is a cross-sectional view showing the schematic configuration of the developing device according to the first embodiment.

[0012] FIG. 3 is a diagram showing the arrangement of magnetic poles of the first developing roller according to the first embodiment.

[0013] FIG. 4 is a diagram showing the arrangement of magnetic poles of the second developing roller according to the first embodiment.

[0014] FIG. 5 is a diagram showing the arrangement of magnetic poles of the peeling roller according to the first embodiment.

[0015] FIG. 6 is a diagram showing the relationship between the magnetic pole arrangements of the first and second developing rollers according to the first embodiment.

[0016] FIG. 7 is a diagram showing the relationship between the magnetic pole arrangements of the first and second developing rollers according to the first embodiment, and is a diagram showing the relationship between the transport poles of the first and second developing rollers.

[0017] FIG. 8 is a table showing the results of an experiment conducted to confirm the effects of the first embodiment.

[0018] FIG. 9 is a diagram showing the relationship between the magnetic pole arrangements of the first and second developing rollers according to the second embodiment.

[0019] FIG. 10 is a table showing the results of an experiment conducted to confirm the effects of the second embodiment.

[0020] FIG. 11 is a diagram showing the relationship between the magnetic pole arrangements of the first and second developing rollers according to the third embodiment.

[0021] 12 is a table showing the results of an experiment conducted to confirm the effects of the third embodiment.

[0022] The first embodiment will be described with reference to FIGS. 1 to 8. First, the schematic configuration of the image forming apparatus of this embodiment will be described with reference to FIG. 1. [Image forming apparatus]

[0023] The image forming apparatus 100 is a full-color image forming apparatus, and in this embodiment, is, for example, an MFP (Multi-Function Peripheral) having a copy function, a printer function, and a scan function. As shown in Figure 1, the image forming apparatus 100 has image forming units PY, PM, PC, and PK arranged in parallel, each of which performs an image forming process for forming a toner image of four colors: yellow, magenta, cyan, and black.

[0024] The image forming units PY, PM, PC, and PK for each color include primary chargers 21Y, 21M, 21C, and 21K, developing units 1Y, 1M, 1C, and 1K, optical writing units (exposure units) 22Y, 22M, 22C, and 22K, photosensitive drums 28Y, 28M, 28C, and 28K, and cleaning units 26Y, 26M, 26C, and 26K. The image forming apparatus 100 also includes a transfer unit 2 and a fixing unit 3. Since the image forming units PY, PM, PC, and PK for each color have the same configuration, the following description will be given using the image forming unit PY as a representative.

[0025] The photosensitive drum 28Y, which serves as an image carrier, is a photosensitive member having a photosensitive layer made of a resin such as polycarbonate containing an organic photoconductor (OPC), and is configured to rotate at a predetermined speed. The primary charger 21Y is made of a corona discharge electrode disposed around the photosensitive drum 28Y, and charges the surface of the photosensitive drum 28Y with generated ions.

[0026] The optical writing unit 22Y incorporates a scanning optical device and exposes the charged photosensitive drum 28Y based on image data, thereby reducing the potential of the exposed area and forming a charge pattern (electrostatic latent image) corresponding to the image data. The developing device 1Y transfers the contained developer to the photosensitive drum 28Y to develop the electrostatic latent image formed on the photosensitive drum 28Y. The developer is a mixture of carrier and toner corresponding to each color, and the electrostatic latent image is visualized by the toner.

[0027] The transfer device 2 has primary transfer rollers 23Y, 23M, 23C, and 23K, an intermediate transfer belt 24, and a secondary transfer roller 25. The intermediate transfer belt 24 is wound around the primary transfer rollers 23Y, 23M, 23C, and 23K and multiple rollers and supported so that it can run. The primary transfer rollers 23Y, 23M, 23C, and 23K, from top to bottom in FIG. 1 , correspond to the colors Y (yellow), M (magenta), C (cyan), and K (black). The secondary transfer roller 25 is disposed outside the intermediate transfer belt 24 and is configured so that a recording material can pass between it and the intermediate transfer belt 24. The recording material may be, for example, a sheet of paper, a plastic sheet, or the like.

[0028] The toner images of each color formed on the photosensitive drums 28Y, 28M, 28C, and 28K are transferred successively onto the intermediate transfer belt 24 by the primary transfer rollers 23Y, 23M, 23C, and 23K, forming a color toner image in which yellow, magenta, cyan, and black layers are superimposed. The formed toner image is transferred by the secondary transfer roller 25 onto a recording material conveyed from a cassette or the like containing the recording material. The recording material onto which the toner image has been transferred is subjected to pressure and heat in the fixing device 3. This melts the toner on the recording material, and the color image is fixed to the recording material.

[0029] Developer storage units 27Y, 27M, 27C, and 27K are provided corresponding to developing devices 1Y, 1M, 1C, and 1K, respectively, and are filled with replaceable bottles containing developers corresponding to the respective colors of yellow, magenta, cyan, and black, from top to bottom. Developer storage units 27Y, 27M, 27C, and 27K are configured to be able to transport (supply) developers to developing devices 1Y, 1M, 1C, and 1K corresponding to the colors of the developers stored therein.

[0030] For example, the toner weight ratio of the developer stored in the bottle is 80 to 95%, and the toner weight ratio of the developer in the developing devices 1Y, 1M, 1C, and 1K is 5 to 10%. Therefore, when toner is consumed by development in the developing devices 1Y, 1M, 1C, and 1K, developer containing toner corresponding to the consumed amount is replenished, and the toner weight ratio of the developer in the developing devices 1Y, 1M, 1C, and 1K is maintained constant. [Developing Device]

[0031] Next, the developing devices 1Y, 1M, 1C, and 1K will be described in detail using Figures 2 to 5. Since the developing devices 1Y, 1M, 1C, and 1K have the same configuration, the following description will focus on the developing device 1Y as a representative. Figure 2 is a conceptual diagram illustrating the developing device 1Y shown in Figure 1, and Figures 3, 4, and 5 are conceptual diagrams illustrating the magnetic pole configurations of the first magnet 36, second magnet 37, and third magnet 38 arranged in the developing device 1Y.

[0032] As shown in FIG. 2, the developing device 1Y has a first developing roller 30, a second developing roller 31, a peeling roller 32, a developer supply screw 42, a developer stirring screw 43, and a developer recovery screw 44, and these components are housed in a developing container 60.

[0033] The first developing roller 30 is a rotatably driven developer carrier and is disposed adjacent to the photosensitive drum 28Y so that its rotation axis is substantially parallel to the rotation axis of the photosensitive drum 28Y. The first developing roller 30 includes a rotating first sleeve (first rotating body) 33 and a first magnet (stationary magnet, first magnet) 36 that is disposed non-rotatably inside the first sleeve 33 and magnetically attracts developer to the surface of the first sleeve 33. The first developing roller 30 magnetically attracts (carries) developer pumped up from a developer supply screw 42 and develops an electrostatic latent image formed on the rotating photosensitive drum 28Y (image carrier) with the developer. In this embodiment, when the developing device 1Y is installed in the image forming apparatus 100, the first developing roller 30 is located at a first development position where it develops an electrostatic latent image formed on the photosensitive drum 28Y.

[0034] The first sleeve 33 is a non-magnetic cylindrical member that is driven to rotate around a rotation shaft 39 .

[0035] 2, the rotation direction of the first sleeve 33 is clockwise, which is opposite to the rotation direction of the photosensitive drum 28Y in this embodiment. Therefore, the first sleeve 33 and the photosensitive drum 28Y rotate in the same direction while facing each other. That is, forward development is performed in which the photosensitive drum 28 rotates from a vertically downward direction to a vertically upward direction while facing the first sleeve 33.

[0036] The first magnet 36 is disposed inside the first sleeve 33, and has a plurality of sector-shaped magnetic poles 101 to 107, as shown in Fig. 3. A space is disposed between the inner periphery of the first sleeve 33 and the outer periphery of the first magnet 36, allowing the first sleeve 33 to rotate.

[0037] The developer attracted to the first sleeve 33 (on the first sleeve) is carried and transported toward the photosensitive drum 28Y by the rotation of the first sleeve 33, and develops the latent image formed on the photosensitive drum 28Y at the first development position. After developing the latent image formed on the photosensitive drum 28Y, the developer on the first sleeve 33 is transported to the vicinity of the second developing roller 31 by the rotation of the first sleeve 33. Then, near the closest position between the first developing roller 30 and the second developing roller 31, the developer is peeled off from the first sleeve 33 and transferred onto the second sleeve 34 (on the second sleeve) by the magnetic fields generated by the first magnet 36 contained in the first developing roller 30 and the second magnet 37 contained in the second developing roller 31.

[0038] The second developing roller 31 is a rotationally driven developer carrier, and is disposed downstream of the first developing roller 30 in the rotation direction of the photosensitive drum 28Y and such that the rotation center P of the second developing roller 31 is located above the rotation center Q of the first developing roller 30 in the vertical direction, and developer is transferred from the first developing roller 30 by magnetic force ( FIG. 2 ). In this embodiment, the entire second developing roller 31 is located above the rotation center Q of the first developing roller 30. Like the first developing roller 30, the second developing roller 31 is disposed adjacent to the photosensitive drum 28Y such that its rotation axis is substantially parallel to the rotation axis of the photosensitive drum 28Y. Therefore, the rotation axes of the second developing roller 31 and the first developing roller 30 are substantially parallel to each other.

[0039] The second developing roller 31 includes a rotating second sleeve (second rotating body) 34 and a second magnet (stationary magnet, second magnet) 37 that is non-rotatingly disposed inside the second sleeve 34 and magnetically attracts developer to the surface of the second sleeve 34. The second developing roller 31 receives and carries (carries) developer from the first developing roller 30 (first sleeve 33) using magnetic force, and develops the electrostatic latent image formed on the rotating photosensitive drum 28Y with the developer. In this embodiment, when the developing device 1Y is installed in the image forming apparatus 100, the second developing roller 31 is located at a second developing position where it develops the electrostatic latent image formed on the photosensitive drum 28Y. A peeling roller 32, which will be described later, is located to the side of the second developing roller 31.

[0040] The second sleeve 34 is a non-magnetic cylindrical member that is driven to rotate around a rotation shaft 40 .

[0041] The rotation direction of the second sleeve 34 is clockwise, as shown by the arrow in Figure 2, the same as that of the first sleeve 33, and in this embodiment, it is the opposite direction to the rotation direction of the photosensitive drum 28Y. Therefore, the second sleeve 34 and the photosensitive drum 28Y rotate in the same direction when they are positioned opposite each other. That is, when the photosensitive drum 28 is positioned opposite the second sleeve 34, the photosensitive drum 28 rotates from a lower position in the vertical direction to an upper position in the vertical direction, which is forward development. Furthermore, the second sleeve 34 and the first sleeve 33 rotate in opposite directions when they are positioned opposite each other.

[0042] The second magnet 37 is disposed inside the second sleeve 34, and has a plurality of sector-shaped magnetic poles 201 to 207, as shown in Fig. 4. A space is disposed between the inner periphery of the second sleeve 34 and the outer periphery of the second magnet 37, allowing the second sleeve 34 to rotate.

[0043] The developer attracted to the second sleeve 34 is carried and transported toward the photosensitive drum 28Y by the rotation of the second sleeve 34, and develops the latent image formed on the photosensitive drum 28Y at the second development position. After the latent image formed on the photosensitive drum 28Y is developed, the developer remaining on the second sleeve 34 is transported to the vicinity of the peeling roller 32 by the rotation of the second sleeve 34. Then, near the closest position between the second developing roller 31 and the peeling roller 32, the developer is transferred from the second sleeve 34 to the third sleeve 35 of the peeling roller 32 by the magnetic fields generated by the second magnet 37 contained in the second developing roller 31 and the third magnet 38 contained in the peeling roller 32.

[0044] The peeling roller 32 as a peeling unit is disposed on the opposite side of the photosensitive drum 28Y with respect to the rotation center of the second sleeve 34, and peels off the developer from the second developing roller 31 after the electrostatic latent image on the photosensitive drum 28Y is developed by the second developing roller 31. Specifically, the peeling roller 32 is a developer carrier that is driven to rotate, and is disposed between the second developing roller 31 and the developer recovery screw 44 so that its rotation center is above the rotation center P of the second developing roller 31.

[0045] The peeling roller 32 is disposed so that its rotation axis is substantially parallel to the rotation axis of the second developing roller 31. The peeling roller 32 has a rotating third sleeve 35 and a third magnet (fixed magnet) 38 that is disposed non-rotatingly inside the third sleeve 35 and that attracts the developer to the surface of the third sleeve 35 by magnetic force, and is configured to receive the developer from the second developing roller 31 based on the magnetic force.

[0046] The third sleeve 35 is a non-magnetic cylindrical member that is driven to rotate around a rotation shaft 41 .

[0047] 2, which is opposite to the rotation direction of the second sleeve 34. Therefore, the third sleeve 35 and the second sleeve 34 rotate in the same direction while facing each other.

[0048] The third magnet 38 is disposed inside the third sleeve 35, and has a plurality of sector-shaped magnetic poles 301 to 305, as shown in Fig. 5. A space is disposed between the inner periphery of the third sleeve 35 and the outer periphery of the third magnet 38, allowing the third sleeve 35 to rotate.

[0049] The developer attracted onto the third sleeve 35 is carried and transported downstream in the rotation direction by the rotation of the third sleeve 35, and is peeled off from the third sleeve 35 by the third magnet 38 contained in the peeling roller 32 at a position close to the developer recovery screw 44, and falls by its own weight toward the guide member 45 located vertically below. The developer that has fallen onto the guide member 45 is then guided by its own weight toward the developer recovery screw 44.

[0050] The guide member 45 and the developer recovery screw 44 constitute a developer recovery section 47 that serves as a recovery section that recovers the developer peeled off from the third sleeve 35 on the peeling roller 32. In the developer recovery section 47, the developer recovery screw 44 is disposed so that its center of rotation is positioned lower than the center of rotation of the peeling roller 32 in the vertical direction, and conveys the developer handed over (recovered) from the peeling roller 32 while stirring it.

[0051] The guide member 45 serving as a guide section is disposed vertically below the peeling roller 32 and guides the developer peeled off by the peeling roller 32 toward the developer recovery screw 44. Such a guide member 45 has an inclined surface 45a along which the developer slides down under its own weight, in order to more reliably guide the peeled off developer toward the developer recovery screw 44. The inclined surface 45a is inclined with respect to the horizontal direction so that the developer recovery screw 44 side is lower than the position below the peeling roller 32.

[0052] The developer recovery screw 44, which serves as a recovery member and a transport section, transports the recovered developer to a developer circulation section 46, which will be described next. That is, the developer recovery screw 44 is a screw transport member used to transport the recovered developer in one direction while stirring it as it slides down the inclined surface of the guide member 45.

[0053] The developer circulating unit 46 is a supply unit for supplying the developer to the first developing roller 30, and includes a regulating member 50, a developer supply screw 42, and a developer stirring screw 43. In the developer circulating unit 46, the developer is stirred in the developer supply screw 42 and the developer stirring screw 43 while being transported in a substantially horizontal direction, and is then supplied to the first developing roller 30. As described above, the developer collected by the developer collecting unit 47 falls by its own weight and is introduced into the developer circulating unit 46.

[0054] The developer supply screw 42, developer agitation screw 43, and developer recovery screw 44 are screw transport members that transport the developer in one direction while agitating it, and the developer supply screw 42 and developer agitation screw 43 are located vertically below the developer recovery screw 44. The developer supply screw 42, developer agitation screw 43, and developer recovery screw 44 are also arranged so that their rotation axes are substantially parallel to each other. The rotation axis of each screw is also substantially parallel to the rotation axis of the first developing roller 30.

[0055] The developer supply screw 42 is located between the first developing roller 30 and the developer agitating screw 43, and a partition wall 48 of the developing container 60 is disposed between the developer supply screw 42 and the developer agitating screw 43. The partition wall 48 of the developing container 60 extends along the rotational axis direction of the developer supply screw 42 and the developer agitating screw 43. The partition wall 48 is provided with a communication opening (not shown) that communicates a first transport path 61, through which the developer is transported by the developer supply screw 42, with a second transport path 62, through which the developer is transported by the developer agitating screw 43.

[0056] The developer stirred by the developer recovery screw 44 passes through a communication port (not shown) formed in a partition wall 63 of the developing container 60 located between the developer recovery screw 44 and the developer supply screw 42, and falls by its own weight toward the developer supply screw 42. The guide member 45 is formed integrally with the partition wall 63, and the developer recovery screw 44 is disposed above the partition wall 63.

[0057] The position of the communication port through which the developer stirred by the developer recovery screw 44 falls under its own weight and is introduced into the developer circulation unit 46 is preferably arranged to avoid the area where the developer is supplied toward the first developing roller 30 (the middle part with respect to the rotational axis direction of the developer supply screw 42). In this embodiment, the communication port is positioned within the range of the downstream end (terminal end) in the developer transport direction of the first transport path 61 in which the developer supply screw 42 is arranged.

[0058] The developer transport directions of the developer supply screw 42 and the developer agitation screw 43 are opposite to each other. The start side (upstream end in the developer transport direction) and end side (downstream end in the developer transport direction) of the first transport path 61 in which the developer supply screw 42 is disposed communicate with the end side and start side of the second transport path 62 in which the developer agitation screw 43 is disposed via communication ports provided in the partition wall 48. Therefore, the developer circulates in the rotation direction of the developer supply screw 42 and the developer agitation screw 43, indicated by the arrows in FIG. 2 , and in a substantially horizontal direction within the developing container 60, and a portion of the developer is supplied toward the first developing roller 30.

[0059] The developer supply port 51 (see FIG. 2) is disposed above the developer stirring screw 43 in the developing container 60, and is connected to the developer storage unit 27Y (see FIG. 1). The developer supply port 51 is configured to be able to supply the developer stored in a bottle loaded in the developer storage unit 27Y to the second conveying path 62 in which the developer stirring screw 43 is disposed.

[0060] As described above, the toner weight ratio of the developer stored in the bottle of developer storage section 27Y is greater than the toner weight ratio of the developer in developing device 1Y, so by adjusting the developer supplied to developer stirring screw 43, it is possible to maintain a constant toner weight ratio of the developer in developing device 1Y.

[0061] The toner concentration detection sensor 49 (see FIG. 2) is disposed 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 therefore used to control the supply of developer from the developer storage unit 27Y. For example, when it is detected that the toner concentration has dropped below a predetermined value, developer is replenished from the developer storage unit 27Y. Note that the magnetic permeability of the developer changes depending on the toner concentration, and therefore the toner concentration can be detected using the magnetic permeability.

[0062] The regulating member 50 is disposed adjacent to the first developing roller 30 and is used to regulate the amount of developer supplied from the developer circulating unit 46 to the first developing roller 30. The regulating member 50 can be configured to regulate the amount of developer attracted to the first developing roller 30 based on, for example, the gap between the surface of the first sleeve 33 of the first developing roller 30 and the end of the regulating member 50.

[0063] The developer circulation path in the developing container 60 is such that the developer is transported in a substantially horizontal direction while being stirred in the developer circulation section 46, and then supplied to the first developing roller 30, and is transferred from the first developing roller 30 to the second developing roller 31 above by magnetic force. Next, the developer is transferred from the second developing roller 31 to the peeling roller 32 on the side of the second developing roller 31 again by magnetic force, and is then peeled off from the peeling roller 32 by the third magnet 38 contained in the peeling roller 32, and is then collected in the developer collection section 47 and introduced into the developer circulation section 46 again.

[0064] As described above, this embodiment uses a two-component development system, and the developer is a mixture of negatively charged non-magnetic toner and magnetic carrier. The non-magnetic toner is a resin such as polyester or styrene acrylic, which contains colorants, wax components, etc. and is then pulverized or polymerized to form a powder, with fine powders such as titanium oxide and silica added to the surface. The magnetic carrier is a core made of resin particles kneaded with ferrite particles or magnetic powder, with a resin coating on the surface. In this embodiment, the toner concentration in the initial developer (the weight ratio of toner contained in the developer) is 8%.

[0065] Generally, two-component development systems using toner and carrier charge both to a predetermined polarity through frictional contact between the toner and carrier, which means that the toner is subjected to less stress than single-component development systems using single-component developers. However, over time, the amount of contaminants (spent toner) adhering to the carrier surface increases, gradually reducing the toner's ability to charge. This results in problems such as fogging and toner scattering. While increasing the amount of carrier contained in a two-component development device could be considered to extend the life of the device, this is undesirable because it would increase the size of the development device.

[0066] In order to solve the above problems associated with two-component developers, this embodiment employs an ACR (Auto Carrier Refresh) method. The ACR method is a method for suppressing an increase in degraded carrier by gradually replenishing new developer from the developer storage section 27Y into the developing device 1Y and gradually discharging developer with degraded charging performance from a discharge port (not shown) of the developing device 1Y. This allows the degraded carrier in the developing device 1Y to be gradually replaced with new carrier, making it possible to maintain the charging performance of the carrier in the developing device 1Y approximately constant. [Regarding the magnetic poles of each magnet]

[0067] Next, the magnetic pole configurations of the first magnet 36, second magnet 37, and third magnet 38 contained in the first developing roller 30, second developing roller 31, and peeling roller 32 shown in Figures 3, 4, and 5 will be described.

[0068] As shown in FIG. 3 , the first magnet 36 contained within the first developing roller 30 has a seven-pole configuration including multiple magnetic poles 101, 102, 103, 104, 105, 106, and 107. 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 sleeve 33. The magnetic pole 101 is an S pole and is positioned opposite the regulating member 50 across the first sleeve 33, and adjusts the amount of developer transported on the first sleeve 33 as described above. The magnetic pole 104, serving as the first developing pole, is an N pole and is positioned opposite the photosensitive drum 28Y across the first sleeve 33, and is a magnetic pole for developing the electrostatic latent image formed on the photosensitive drum 28Y. Hereinafter, the magnetic pole 104 may be referred to as the first developing pole 104.

[0069] The magnetic pole 106 serving as a transfer pole is an N pole and is a magnetic pole for transferring developer from the first sleeve 33 to the second sleeve 34 by a magnetic field generated in cooperation with the second magnet 37 of the second developing roller 31; hereinafter, the magnetic pole 106 may be referred to as a transfer pole 106. The transfer pole 106 is located downstream of the first developing pole 104 in the direction of rotation of the first sleeve 33 and has the same polarity as the first developing pole 104. The magnetic pole 107 is an N pole and is used to attract the developer supplied from the developer supply screw 42 onto the first sleeve 33. The magnetic poles 102, 103, and 105 are an N pole, an S pole, and an S pole, respectively, and are used as transport poles for transporting the developer attracted by the magnetic pole 107 upward as the first sleeve 33 rotates. Of these, the magnetic pole 105 is a first downstream developing pole (first downstream pole) that is located adjacent to the downstream side of the first developing pole 104 and adjacent to the upstream side of the delivery pole 106 in the rotation direction of the first sleeve 33, and hereinafter may be referred to as the first downstream developing pole 105. The first downstream developing pole 105 has a polarity different from that of the first developing pole 104.

[0070] The magnetic pole 107 is disposed downstream of the delivery pole 106 in the rotational direction of the first sleeve 33 and has the same polarity as the delivery pole 106. The delivery pole 106 and the magnetic pole 107 cooperate to generate a repulsive magnetic field, forming a low magnetic force portion 110 having a magnetic force lower than that of the delivery pole 106. This low magnetic force portion 110 causes the developer to peel off from the first sleeve 33 and promotes the transfer of the developer from the first sleeve 33 to the second sleeve 34. While the low magnetic force portion 110 has almost no magnetic force in this embodiment, it may have a low magnetic force. For example, the magnetic force (normal component Br of the magnetic flux density, magnetic flux density Br in the normal direction to the outer peripheral surface of the first sleeve 33) may be 5 mT or less. This also applies to the low magnetic force portion 210 of the second magnet 37 shown in FIG. 4 and the low magnetic force portion 310 of the third magnet 38 shown in FIG. 5.

[0071] 4, the second magnet 37 contained in the second developing roller 31 has a seven-pole configuration including multiple magnetic poles 201, 202, 203, 204, 205, 206, and 207. Of these, the magnetic pole 201 is a receiving pole for the second developing roller 31 to receive the developer from the first developing roller 30. The magnetic poles 201 to 207 are arranged in numerical order in the rotation direction of the second sleeve 34.

[0072] The magnetic pole 201 as a receiving pole is a magnetic pole for attracting the developer from the first sleeve 33 to the second sleeve 34 by a magnetic field generated in cooperation with the magnetic pole 106 of the first magnet 36 of the first developing roller 30, and hereinafter the magnetic pole 201 may be referred to as the receiving pole 201. The magnetic pole 207 is a magnetic pole for transferring the developer from the second sleeve 34 to the third sleeve 35 by a magnetic field generated in cooperation with the third magnet 38 of the peeling roller 32.

[0073] The receiving pole 201 is an S pole, different in polarity from the handover pole 106, and is used to attract the developer from the first developing roller 30 (first sleeve 33) onto the second sleeve 34, as described above. The magnetic pole 203, serving as the second developing pole, is an S pole, and is disposed in a position facing the photosensitive drum 28Y across the second sleeve 34, and is a magnetic pole for developing the electrostatic latent image formed on the photosensitive drum 28Y. Hereinafter, the magnetic pole 203 may be referred to as the second developing pole 203. The receiving pole 201 is a magnetic pole located adjacent to and upstream of the second developing pole 203 in the rotation direction of the second sleeve 34.

[0074] The magnetic poles 202, 204, 205, and 206 are N-pole, N-pole, S-pole, N-pole, and are used as transport poles to transport the developer attracted by the magnetic pole 201 upward as the second sleeve 34 rotates. Of these, the magnetic pole 202 is located adjacent to the upstream side of the second developing pole 203 and adjacent to the downstream side of the receiving pole 201 in the rotation direction of the second sleeve 34, and is a second upstream developing pole of a different polarity from the second developing pole 203; hereinafter, the magnetic pole 202 may be referred to as the second upstream developing pole 202. The magnetic pole 204 is located adjacent to the downstream side of the second developing pole 203 in the rotation direction of the second sleeve 34, and is a second downstream developing pole (second downstream pole) of a different polarity from the second developing pole 203; hereinafter, the magnetic pole 204 may be referred to as the second downstream developing pole 204. The second developing pole 203 is located adjacent to the second developing upstream pole 202 on the downstream side in the rotation direction of the second sleeve 34. The magnetic pole 207 is an S pole, and transfers the developer after passing through the development area of ​​the photosensitive drum 28Y corresponding to the magnetic pole 203 from the second sleeve 34 to the third sleeve 35 facing the second sleeve 34 by a magnetic field generated in cooperation with the magnetic pole 303 in the third magnet 38 contained in the peeling roller 32.

[0075] Furthermore, the magnetic pole 207 is disposed upstream of the receiving pole 201 in the rotation direction of the second sleeve 34, and has the same polarity as the receiving pole 201. The receiving pole 201 and the magnetic pole 207 cooperate to generate a repulsive magnetic field, thereby forming a low magnetic force portion 210 having a lower magnetic force than the magnetic pole 207. This low magnetic force portion 210 causes the developer to peel off from the second sleeve 34 and promotes the transfer of the developer from the first sleeve 33 to the second sleeve 34. Furthermore, the low magnetic force portion 210 can prevent the developer from being attracted to the closest portion between the first sleeve 33 and the second sleeve 34, thereby suppressing the pressure applied to the developer.

[0076] 5, the third magnet 38 contained in the peeling roller 32 has a plurality of magnetic poles 301, 302, 303, 304, and 305. The magnetic poles 301 to 305 are arranged in numerical order in the rotation direction of the third sleeve 35.

[0077] The magnetic pole 303 is an N pole opposite to the magnetic pole 207, and is used to attract the developer peeled off from the second sleeve 34 onto the third sleeve 35 as described above. The magnetic poles 301, 302, and 304 are N, S, and S poles, and are used to transport the developer on the third sleeve 35 as the third sleeve 35 rotates. In particular, the magnetic pole 304 is used to transport the developer attracted by the magnetic pole 303 downward as the third sleeve 35 rotates. The magnetic pole 305 is an N pole, and is a peeling pole used to peel off the developer attracted to the third sleeve 35 from the third sleeve 35 by a repulsive magnetic field generated in cooperation with the magnetic pole 301 of the same polarity. [Arrangement of the magnetic poles]

[0078] Next, the positional relationship between the magnetic poles of the first magnet 36 and the second magnet 37 disposed inside the first developing roller 30 and the second developing roller 31 and the photosensitive drum 28Y will be described using FIGS. 6 and 7. FIG. 6 is a conceptual diagram illustrating the arrangement of the first developing roller 30, the second developing roller 31, and the photosensitive drum 28Y of this embodiment, and particularly shows the layout of the second developing pole 203 and the second developing downstream pole 204 of the second magnet 37 of the second developing roller 31. As described above, the first developing roller 30 and the second developing roller 31 each have a seven-pole configuration, allowing for flexibility in the arrangement of magnetic force. However, because illustrating all the magnetic poles would be cumbersome, some of the magnetic poles are omitted from FIGS. 6, 7, and FIGS. 9 and 11, which will be described later.

[0079] As described above, the second developing pole 203 of the second developing roller 31 performs a development process on the electrostatic latent image on the photosensitive drum 28Y facing the second developing roller 31. In the development process, if the position where the normal component of the magnetic flux density of the second developing pole 203 on the second sleeve 34 is maximum (the position on the outer peripheral surface of the second sleeve 34 where the absolute value of the magnetic flux density of the second developing pole 203 in the normal direction to the outer peripheral surface of the second sleeve 34 is maximum) is defined as point A, the developer on the second sleeve 34 forms magnetic chains in the vicinity of point A, and when these magnetic chains come into contact with the electrostatic latent image on the photosensitive drum 28Y, the toner in the developer moves to the electrostatic latent image on the photosensitive drum 28Y.

[0080] Similarly, in the second developing downstream pole (transport pole) 204 located adjacent to the downstream side of the second developing pole 203, if the position on the second sleeve 34 where the normal component of the magnetic flux density of the second developing downstream pole 204 is maximum (the position on the outer surface of the second sleeve 34 where the absolute value of the magnetic flux density of the second developing downstream pole 204 in the normal direction to the outer surface of the second sleeve 34 is maximum) is defined as point B, a magnetic chain is also formed by the developer on the second sleeve 34 in the vicinity of point B.

[0081] As described above, when the toner in the developer moves toward the photosensitive drum 28Y at the second developing pole 203, the developer remaining on the second sleeve 34 has a higher carrier ratio due to the decrease in the amount of toner in the developer, resulting in a decrease in the electrical resistance of the developer. Therefore, at the second developing downstream pole 204, developer with a decreased electrical resistance is transported.

[0082] The carrier in the developer near point B on the second sleeve 34 experiences charge injection due to the electric field strength between the second sleeve 34 and the photosensitive drum 28Y. The carrier loses charge or assumes the same charging characteristics as the toner, causing it to be attracted from the magnetic chain on the second sleeve to the photosensitive drum 28Y by the electric field. As a result, the charged carrier leaves the second sleeve 34 and moves to the photosensitive drum 28Y. This causes carrier adhesion on the photosensitive drum 28Y at a position facing the second downstream developing pole 204 of the second developing roller 31. Figure 6 shows a state in which carrier α has adhered downstream of the position facing the second downstream developing pole 204 in the rotational direction of the photosensitive drum 28Y. Carrier adhesion on the photosensitive drum 28Y can cause electrical leakage during the image formation process (development and transfer), or the carrier remains on the recording material, resulting in image defects such as blank areas of several millimeters in the output image.

[0083] Furthermore, points A' and B' are defined as the positions on the photosensitive drum 28Y at which the photosensitive drum 28Y is closest to points A and B on the second sleeve 34 at which the normal component of the magnetic flux density is at a maximum at the second developing pole 203 and the second developing downstream pole 204. In this case, when the distance BB' between points B and B' is small, carrier adhesion is likely to occur at the second developing downstream pole 204.

[0084] The distance BB' between point B and point B' can be expressed as the angle θ [°] between the second developing pole 203 and the second developing downstream pole 204, which are adjacent to each other on the second developing roller 31. The angle θ [°] is the angle formed when points A and B are connected by straight lines from the rotation center P of the second sleeve 34. That is, θ [°] is the angle (acute angle) formed by a line (straight line PA) connecting the position (point A) on the second sleeve 34 where the normal component of the magnetic flux density of the second developing pole 203 is at its maximum to the rotation center P of the second sleeve 34, and a line (straight line PB) connecting the position (point B) on the second sleeve 34 where the normal component of the magnetic flux density of the second developing downstream pole 204 is at its maximum to the rotation center P of the second sleeve 34. In other words, θ [°] is the angle in the rotation direction of the second sleeve 34 from the position on the outer peripheral surface of the second sleeve 34 where the absolute value of the magnetic flux density of the second developing pole 203 in the normal direction to the outer peripheral surface of the second sleeve 34 is maximum to the position on the outer peripheral surface of the second sleeve 34 where the absolute value of the magnetic flux density of the second developing downstream pole 204 in the normal direction to the outer peripheral surface of the second sleeve 34 is maximum. When the angle θ is large, the distance between point B and point B' becomes large, and carrier adhesion to the photosensitive drum 28Y by the second developing downstream pole 204 becomes less likely to occur.

[0085] The above-described carrier adhesion to the photosensitive drum 28Y caused by the second downstream pole 204 in the second developing roller 31 occurs not only in the second developing roller 31 but also in the first developing roller 30 in the same manner. As shown in Figure 6, the angle formed by the first developing pole 104 and the first developing downstream pole (transport pole) 105, which are adjacent to each other on the first developing roller 30, can be specified as the angle δ [°] formed when a straight line is drawn from the rotation center Q of the first sleeve 33 to point C on the first sleeve 33 where the normal component of the magnetic flux density of the first developing pole 104 is maximum (the position on the outer peripheral surface of the first sleeve 33 where the absolute value of the magnetic flux density of the first developing pole 104 in the normal direction to the outer peripheral surface of the first sleeve 33 is maximum), and point D on the first sleeve 33 where the normal component of the magnetic flux density of the first developing downstream pole 105 is maximum (the position on the outer peripheral surface of the first sleeve 33 where the absolute value of the magnetic flux density of the first developing downstream pole 105 in the normal direction to the outer peripheral surface of the first sleeve 33 is maximum). That is, δ [°] is the angle (acute angle) formed by a line (straight line QC) connecting the position (point C) on the first sleeve 33 where the normal component of the magnetic flux density of the first developing pole 104 is maximum to the rotation center Q of the first sleeve 33, and a line (straight line QD) connecting the position (point D) on the first sleeve 33 where the normal component of the magnetic flux density of the first developing downstream pole 105 is maximum to the rotation center Q of the first sleeve 33. In other words, δ [°] is the angle in the rotation direction of the first sleeve 33 from the position on the outer peripheral surface of the first sleeve 33 where the absolute value of the magnetic flux density of the first developing pole 104 in the normal direction to the outer peripheral surface of the first sleeve 33 is maximum to the position on the outer peripheral surface of the first sleeve 33 where the absolute value of the magnetic flux density of the first developing downstream pole 105 in the normal direction to the outer peripheral surface of the first sleeve 33 is maximum.

[0086] As with the angle θ of the second developing roller 31, the larger the angle δ of the first developing roller 30, the greater the distance between the photosensitive drum 28Y and point D on the first sleeve 33 of the first developing downstream pole 105. Therefore, as with the second developing roller 31, the larger the angle δ, the less carrier is deposited on the photosensitive drum 28Y by the first developing downstream pole 105.

[0087] 7 , the first downstream developing pole 105 of the first developing roller 30 and the second upstream developing pole (transport pole) 202 of the second developing roller 31 have magnetic characteristics of an S pole and an N pole, respectively. That is, the first downstream developing pole 105 is adjacent to the delivery pole 106 and therefore has a polarity opposite to that of the delivery pole 106, and the second upstream developing pole 202 is adjacent to the receiving pole 201 and therefore has a polarity opposite to that of the receiving pole 201. Because the delivery pole 106 and the receiving pole 201 have polarities opposite to that of the receiving pole 201, the first downstream developing pole 105 and the second upstream developing pole 202 adjacent to the respective magnetic poles also have polarities opposite to that of the receiving pole 201. Therefore, an attractive force F that transfers the developer is generated between the first downstream developing pole 105 in the first developing roller 30 and the second upstream developing pole 202 in the second developing roller 31. Then, due to the attractive force F between the first downstream developing pole 105 and the second upstream developing pole 202, developer transfer occurs between the first downstream developing pole 105 and the second upstream developing pole 202. If developer transfer occurs between the first downstream developing pole 105 and the second upstream developing pole 202, the developer will also come into contact with the nearby photosensitive drum 28Y, causing streaky fogging (abnormal image) on the photosensitive drum 28Y. For this reason, the angle δ of the first developing roller 30 cannot be set greater than a predetermined setting range.

[0088] On the other hand, the angle θ of the second developing roller 31 has a higher degree of freedom in the angle setting range than the angle δ of the first developing roller 30. Also, as described above, the developer on the second developing roller 31 has a lower amount of toner in the developer than the developer on the first developing roller 30. For this reason, the second downstream developing pole 204 of the second developing roller 31 is the main cause of carrier adhesion that occurs on the photosensitive drum 28Y.

[0089] Therefore, in this embodiment, when the outer diameter of the first developing roller 30 and the outer diameter of the second developing roller 31 are the same, the angle δ of the first developing roller 30 and the angle θ of the second developing roller 31 are set to satisfy the following relationship: θ>δ (Formula 1a) By satisfying this relationship, it is possible to suppress carrier adhesion from the developing device 1Y to the photosensitive drum 28Y.

[0090] In this embodiment, the outer diameter of the first developing roller 30 and the outer diameter of the second developing roller 31 are exemplified, but the present invention can be similarly applied to a case where the outer diameter of the first developing roller 30 and the outer diameter of the second developing roller 31 are different. That is, when the sleeve radius of the first sleeve 33 is R1 [mm] and the sleeve radius of the second sleeve 34 is R2 [mm], it is sufficient to satisfy the following relationship: R2×θ>R1×δ (Formula 1b).

[0091] By satisfying this relationship, it is possible to suppress carrier adhesion from the developing device 1Y to the photosensitive drum 28Y. This is clear from the fact that when the outer diameter of the first developing roller 30 and the outer diameter of the second developing roller 31 are the same, R1 = R2, and therefore the above-mentioned (Equation 1b) can be converted to (Equation 1a). For the sake of simplicity, the following explanation will be given using an example in which the outer diameter of the first developing roller 30 and the outer diameter of the second developing roller 31 are the same, unless otherwise specified. [Experiment 1]

[0092] Next, an experiment using an actual machine to verify the setting of the angle θ of the second developing roller 31 will be described. The experimental results are shown in FIG. 8. In the experiment, developing devices 1Y were prepared in which the conditions for the angle θ of the second developing roller 31 were changed in Studies 1 to 7, and each developing device 1Y was installed in an image forming apparatus 100 to check the image output. In the developing device 1Y used in this experiment, the outer diameter of the first developing roller 30 and the outer diameter of the second developing roller 31 were the same, so R1 = R2. In this experiment, the occurrence of carrier adhesion on the output image was investigated.

[0093] In this experiment, from the viewpoint of developability, the position of point A where the normal component of the magnetic flux density on the second developing pole 203 in the second developing roller 31 is at its maximum was not changed. Furthermore, the positions of point D where the normal component of the magnetic flux density of the first developing downstream pole 105 in the first developing roller 30 is at its maximum, and point C where the normal component of the magnetic flux density of the first developing pole 104 is at its maximum, i.e., angle δ, were also not changed from the setting of 30° in this experiment because they would cause the abnormal images described above.

[0094] In this experiment, the occurrence of carrier adhesion on the output image was evaluated as follows: 10 A3 solid images were output, and the number of "white spots" due to carrier adhesion on the output image was counted. Here, white spots refer to abnormal images in which image voids of about several mm appear on the output image. If there were no white spots among the 10 A3 solid images, 20 A3 solid images were printed and the white spots were checked.

[0095] The results of this experiment are shown in the table of Figure 8. The results of carrier adhesion were calculated based on the occurrence of white spots per 10 A3 images and evaluated using the following three levels. The details of each evaluation are as follows: ×: Six or more white spots were observed per 10 A3 images. ○: Approximately 2 to 5 white spots were observed per 10 A3 images. ⊚: Approximately one or less white spots were observed per 10 A3 images. Of the above evaluations, ○ and ⊚ indicate that the white spots are at a level that does not pose a problem in practical use.

[0096] In this experiment, as described above, in Studies 1 to 7, the angle θ, which indicates the position of point B where the normal component of the magnetic flux density of the second downstream pole 204 in the second developing roller is maximized, was changed. As is clear from FIG. 8 , increasing the angle θ reduced the occurrence of blank areas due to carrier adhesion. In Study 3, since θ > δ was satisfied, it was confirmed that the occurrence of blank areas in the output image was evaluated as ○ level. Similarly, in Studies 4 to 6, it was confirmed that further increasing the angle θ further reduced the occurrence of blank areas in the output image, resulting in an evaluation result of ⊚ level. Therefore, it is preferable that the angle θ satisfy θ > 30°.

[0097] In Study 7, the upper limit of the angle θ was examined. Increasing the angle θ increases the distance between point B and point B' between the second downstream developing pole 204 and the photosensitive drum 28Y in the second developing roller 31 (see FIG. 6 ), reducing the likelihood of carrier adhesion to the photosensitive drum 28Y. However, if the angle θ is set to 90° or greater, the distance between the maximum normal component of the magnetic flux density of the second downstream developing pole 204 and the maximum normal component of the magnetic flux density of the second downstream developing pole 203 on the second sleeve 34 becomes too great, reducing the transport efficiency of the developer between the second downstream developing pole 204 and the second downstream developing pole 203. This causes the developer to fall from the second sleeve 34. It was confirmed that setting the angle θ to 90° or greater increases the likelihood of white areas occurring in the carrier that falls from the second sleeve 34 to the photosensitive drum 28Y. Therefore, it is preferable to satisfy θ<90°.

[0098] According to this embodiment, the occurrence of image defects can be suppressed. That is, by satisfying θ>δ, the distance BB' between points B and B' shown in FIG. 6 can be increased, making it difficult for the second downstream developing pole 204 to cause carrier adhesion to the photosensitive drum 28Y. On the other hand, by increasing the angle δ, carrier adhesion to the photosensitive drum 28Y caused by the first downstream developing pole 105 can be suppressed. However, as described above, this increases the likelihood of developer transfer between the first downstream developing pole 105 and the second upstream developing pole 202, which may result in streaky abnormal images.

[0099] As described above, the developer on the second developing roller 31 has a lower amount of toner in the developer compared to the developer on the first developing roller 30, and therefore, carrier adhesion occurring on the photosensitive drum 28Y is mainly caused by the second downstream developing pole 204 of the second developing roller 31. Therefore, if carrier adhesion to the photosensitive drum 28Y can be suppressed by the second downstream developing pole 204, the occurrence of abnormal images due to carrier adhesion can be suppressed. Furthermore, by satisfying θ>δ, δ can be reduced, and the occurrence of the above-mentioned streaky abnormal images can be suppressed. From the above, by satisfying θ>δ, the occurrence of image defects can be suppressed. <Second Embodiment>

[0100] The second embodiment will be described with reference to FIGS. 9 and 10 . In the first embodiment described above, the angles θ and δ were defined as the angles from the position where the normal component of the magnetic flux density of the development pole of each development roller is at its maximum to the position where the normal component of the magnetic flux density of the second development downstream pole 204 or the first development downstream pole 105 is at its maximum. In contrast, in the present embodiment, θ2 and δ2 are defined as the angles from the position where each development roller is closest to the photosensitive drum to the position where the normal component of the magnetic flux density of the second development downstream pole 204 or the first development downstream pole 105 is at its maximum. Since the other configurations and functions are the same as those of the first embodiment described above, the same reference numerals are used for the same configurations, and their description and illustration will be omitted or simplified. The following description will focus on the differences from the first embodiment.

[0101] 9 , a line is drawn so that the distance from the rotation center P of the second sleeve 34 of the second developing roller 31 to the surface of the photosensitive drum 28Y is the shortest, and if the point on this line on the second sleeve 34 is point E and the point on the photosensitive drum 28Y is point E', then EE' indicates the closest distance between the second sleeve 34 and the photosensitive drum 28Y. Furthermore, as in the first embodiment, the angle formed between the line PE' connecting the rotation center P of the second sleeve 34 and point E' on the photosensitive drum 28Y and the line PB connecting the rotation center P of the second sleeve 34 and the position (point B) where the normal component of the magnetic flux density of the second developing downstream pole 204 is maximum is defined as θ2 [°]. That is, θ2 [°] is the angle (acute angle) formed by a line (straight line PE) connecting the position (point E) on the second sleeve 34 where the second sleeve 34 and the photosensitive drum 28Y are closest to each other and the center of rotation P of the second sleeve 34, and a line (straight line PB) connecting the position (point B) on the second sleeve 34 where the normal component of the magnetic flux density of the second developing downstream pole 204 is maximum and the center of rotation P of the second sleeve 34. In other words, θ2 [°] is the angle in the rotation direction of the second sleeve 34 from the position on the outer circumferential surface of the second sleeve 34 closest to the photosensitive drum 28Y to the position on the outer circumferential surface of the second sleeve 34 where the absolute value of the magnetic flux density of the second developing downstream pole 204 in the normal direction to the outer circumferential surface of the second sleeve 34 is maximum.

[0102] Similarly, if a line is drawn so that the distance from the rotation center Q of the first sleeve 33 of the first developing roller 30 to the surface of the photosensitive drum 28Y is the shortest, and the point on this line on the first sleeve 33 is designated as point G and the point on the photosensitive drum 28Y is designated as point G', then GG' indicates the closest distance between the first sleeve 33 and the photosensitive drum 28Y. Furthermore, as in the first embodiment, the angle formed between the line PG' connecting the rotation center Q of the first sleeve 33 and point G' on the photosensitive drum 28Y and the line QD connecting the rotation center Q of the first sleeve 33 and the position (point D) where the normal component of the magnetic flux density of the first developing downstream pole 105 is maximum is designated as δ2 [°]. That is, the angle (acute angle) formed by the line (straight line QG) connecting the position (point G) on the first sleeve 33 where the first sleeve 33 and the photosensitive drum 28Y are closest to each other and the center of rotation Q of the first sleeve 33 and the line (QD) connecting the position (point D) on the first sleeve 33 where the normal component of the magnetic flux density of the first developing downstream pole 105 is maximum and the center of rotation Q of the first sleeve 33 is maximum is defined as δ2 [°]. In other words, the angle in the rotation direction of the first sleeve 33 from the position on the outer circumferential surface of the first sleeve 33 closest to the photosensitive drum 28Y to the position on the outer circumferential surface of the first sleeve 33 where the absolute value of the magnetic flux density of the first developing downstream pole 105 in the normal direction to the outer circumferential surface of the first sleeve 33 is maximum is defined as δ2 [°]. Furthermore, the sleeve radius of the first sleeve 33 is defined as R1 [mm], and the sleeve radius of the second sleeve 34 is defined as R2 [mm].

[0103] In this case, in this embodiment, as in the first embodiment, the following relationship is satisfied: R2×θ2>R1×δ2 (Equation 2). Note that if the outer diameter of the first developing roller 30 and the outer diameter of the second developing roller 31 are the same, R1=R2, and therefore (Equation 2) is converted to the relationship θ2>δ2. By satisfying this relationship, it is possible to suppress carrier adhesion from the developing device 1Y to the photosensitive drum 28Y. This point was confirmed by the following experiment. [Experiment 2]

[0104] In this experiment, similar to Experiment 1 described above, in Studies 8 to 14, the angle θ2 of the first developing roller 30 and the angle θ2 of the second developing roller 31 were changed to check the occurrence of carrier adhesion on the image of the output image. The experimental results are shown in FIG. 10. The experimental conditions and evaluation of carrier adhesion were the same as in Experiment 1. In this experiment, the angle δ2 was also set to 30° and remained unchanged. In the developing device 1Y used in this experiment, the outer diameter of the first developing roller 30 and the outer diameter of the second developing roller 31 were the same, so R1 = R2.

[0105] As is clear from Figure 10, increasing the angle θ2 made it less likely for white spots to occur due to carrier adhesion. In Study 10, it was confirmed that the condition θ2 > δ2 was satisfied, and the evaluation of the occurrence of white spots in the output image was rated as ○ level. Similarly, in Studies 11 to 13, it was confirmed that by further increasing the angle θ, the occurrence of white spots in the output image was even less likely, and the evaluation result was rated as ⊚ level. Therefore, it is preferable that the angle θ2 satisfy θ > 30°.

[0106] In Study 14, the upper limit of angle θ2 was examined. Increasing angle θ2 increases the distance between point B and point B' between the second downstream developing pole 204 and the photosensitive drum 28Y in the second developing roller 31 (see FIG. 9 ), reducing the likelihood of carrier adhesion to the photosensitive drum 28Y. However, if angle θ2 is set to 90° or greater, the distance between the maximum normal component of the magnetic flux density of the second downstream developing pole 204 and the maximum normal component of the magnetic flux density of the second downstream developing pole 203 on the second sleeve 34 becomes too great, reducing the transport efficiency of the developer between the second downstream developing pole 204 and the second downstream developing pole 203. This causes the developer to fall from the second sleeve 34. It was confirmed that setting angle θ2 greater than 90° increases the likelihood of white areas occurring in the carrier that falls from the second sleeve 34 to the photosensitive drum 28Y. Therefore, it is preferable to satisfy θ2 < 90°.

[0107] In the above-mentioned Experiment 2, the conditions were examined by changing the angle θ2. However, changing θ2 changes the distance BB' between the position on the second sleeve 34 where the normal component of the magnetic flux density of the second developing downstream pole 204 is at its maximum and the photosensitive drum 28Y. The change in distance BB' when the angle θ2 is changed is also affected by the radius of the second sleeve 34. If the radius of the second sleeve 34 is R2 [mm], the distance BB' between point B on the second sleeve 34 and the photosensitive drum 28 when the angle θ2 used in this study is changed can be expressed as the following approximate formula, where the change in distance is the amount of change X, based on the closest distance EE' between the second sleeve 34 and the photosensitive drum 28: Amount of change X = BB' - EE' ≒ R2 × (1 - cos θ2) (Equation 3)

[0108] In the above-described experiment, the second sleeve 34 used had a radius R2 of 12.5 mm. As is clear from Fig. 10, in the configuration of this embodiment, it was confirmed that carrier adhesion is reduced when the distance BB' between point B on the second sleeve 34 and the photosensitive drum 28Y is approximately 2.2 mm or more, preferably 2.9 mm or more, away from the closest distance EE' between the second sleeve 34 and the photosensitive drum 28. That is, in this embodiment, it is preferable to satisfy the following expression: R2 x (1 - cos θ2) ≥ 2.2 mm (Equation 4), and it is more preferable to satisfy the following expression: R2 x (1 - cos θ2) ≥ 2.9 mm (Equation 5).

[0109] In this embodiment, when the closest distance EE' between the second sleeve 34 and the photosensitive drum 28Y is 0.3 mm, the distance to the closest distance EE' is defined as a distance ratio Y as follows for the above-mentioned change amount X, and comparisons were made under various conditions in the above-mentioned experiment: Distance ratio Y = BB' / EE' ≈ R2 × (1 - cos θ2) / EE' + 1.0 (Equation 6)

[0110] As is clear from the results of the distance ratio Y in Figure 10, it was confirmed that carrier adhesion is reduced when the distance BB' between point B on the second sleeve 34 and the photosensitive drum 28Y is approximately 8.5 times or more, and preferably 10 times or more, the closest distance EE' between the second sleeve 34 and the photosensitive drum 28Y.

[0111] That is, if the distance (EE') between the photosensitive drum 28Y and the position (point E) on the second sleeve 34 where the second sleeve 34 and the photosensitive drum 28Y are closest to each other is D3 [mm], and the distance (BB') between the photosensitive drum 28Y and the position (point B) on the second sleeve 34 where the normal component of the magnetic flux density of the second developing downstream pole 204 is maximum is D2 [mm], then it is preferable to satisfy D2≧D3×8.5 ... (Equation 7), and it is more preferable to satisfy D2≧D3×10 ... (Equation 8).

[0112] Similarly, the distance AA' between point A on the second sleeve relative to the second developing pole 203 in the second developing roller and point A' on the photosensitive drum 28Y facing point A was also confirmed as a distance ratio Y' as follows: Distance ratio Y'=BB' / AA' (Equation 9)

[0113] In this embodiment, AA' was the closest distance (EE') between the second sleeve 34 and the photosensitive drum 28Y, that is, the position (point A) where the magnetic flux density of the second development pole 203 was maximum and the position (point E) where the second sleeve 34 was closest to the photosensitive drum 28Y were roughly the same, so the same results were obtained for the above-mentioned distance ratio Y' as for the distance ratio Y.

[0114] That is, as shown in FIG. 6 described in the first embodiment, when the distance (AA') between the position (point A) on the second sleeve 34 where the normal component of the magnetic flux density of the second developing pole 203 is maximum and the photosensitive drum 28Y is D1 [mm], and the distance (BB') between the position (point B) on the second sleeve 34 where the normal component of the magnetic flux density of the second developing downstream pole 204 is maximum and the photosensitive drum 28Y is D2 [mm], it is preferable to satisfy D2≧D1×8.5 ... (Equation 10), and it is more preferable to satisfy D2≧D1×10 ... (Equation 11).

[0115] Similarly, the distance AA' between point A on the second sleeve for the second developing pole 203 in the second developing roller and point A' on the photosensitive drum 28Y facing point A was also confirmed as a change amount X' as follows: Change amount X'=BB'-AA'≈R2×(1-cos θ) (Equation 12)

[0116] In this embodiment, AA' was the closest distance (EE') between the second sleeve 34 and the photosensitive drum 28Y, that is, the position (point A) where the magnetic flux density of the second development pole 203 was maximum and the position (point E) where the second sleeve 34 was closest to the photosensitive drum 28Y were roughly the same, so the same results were obtained with the above-mentioned change amount X' as with the change amount X.

[0117] That is, as shown in FIG. 6 described in the first embodiment, it is preferable to satisfy the following relationship: R2×(1−cos θ)≧2.2 mm (Formula 13), and it is more preferable to satisfy the following relationship: R2×(1−cos θ)≧2.9 mm (Formula 14).

[0118] In the above description, AA' is the closest distance (EE') between the second sleeve 34 and the photosensitive drum 28Y, and therefore the change amount X' and the distance ratio Y' are treated the same as the change amount X and the distance ratio Y. However, even if AA' and EE' are not the same, the change amount X' and the distance ratio Y' can be treated the same as the change amount X and the distance ratio Y. That is, AA' is the distance between the position (point A) on the second sleeve 34 where the normal component of the magnetic flux density of the second development pole 203 is maximum and the photosensitive drum 28Y. However, point A is usually located at or near the position closest to the photosensitive drum 28Y from the viewpoint of developability. Therefore, even if point A and point E are slightly offset, the difference is small, and there is no problem in treating the change amount X' and the distance ratio Y' the same as the change amount X and the distance ratio Y. <Third Embodiment>

[0119] The third embodiment will be described with reference to FIGS. 11 and 12 . In the first embodiment described above, the angle θ was defined as the angle from the position where the normal component of the magnetic flux density of the second developing pole 203 is at its maximum to the position where the normal component of the magnetic flux density of the second developing downstream pole 204 is at its maximum. In contrast, in this embodiment, the angle from the horizontal line L passing through the rotation center of the second sleeve 34 to the position where the normal component of the magnetic flux density of the second developing downstream pole 204 is at its maximum is defined as θ3 [°]. The other configurations and functions are similar to those of the first embodiment described above. Therefore, similar configurations are denoted by the same reference numerals, and their description and illustration will be omitted or simplified. The following description will focus on the differences from the first embodiment.

[0120] In this embodiment, when the developing device 1Y is installed in the image forming apparatus 100 (i.e., when the first developing roller 30 is located at the first developing position where the electrostatic latent image formed on the photosensitive drum 28Y is developed, and the second developing roller 31 is located at the second developing position where the electrostatic latent image formed on the photosensitive drum 28Y is developed), the position (point H) on the second sleeve 34 where the normal component of the magnetic flux density of the second developing downstream pole 204 is maximum is located vertically above a horizontal line L passing through the rotation center P of the second sleeve 34. In other words, when the developing device 1Y is installed in the image forming apparatus 100 and a horizontal line L passing through the rotation center P of the second sleeve 34 is drawn with respect to the second developing roller 31, the position on the second sleeve 34 where the normal component of the magnetic flux density of the second developing downstream pole 204 is maximum is defined as point H, and the angle (acute angle) formed by the horizontal line L and a straight line PH formed by the rotation center P and point H is defined as θ3 [°]. Point H is located vertically above the horizontal line L. Therefore, when a magnetic brush is formed on the second sleeve 34 at point H, the magnetic brush is less likely to fall from the second sleeve 34 toward the photosensitive drum 28Y due to the force of gravity, and as a result, carrier adhesion to the photosensitive drum 28Y is suppressed. This point was confirmed by the following experiment. [Experiment 3]

[0121] An experiment to investigate the occurrence of blank areas due to carrier adhesion in the above-mentioned configuration will be described. In this experiment, in Studies 15 to 18, the angle θ3 relative to the horizontal line L1 was varied, and images were output using image forming apparatuses incorporating developing devices under various conditions. The occurrence of blank areas in the output images was then investigated. The other conditions and experimental evaluation were the same as in Experiment 1 described in the first embodiment. The results of this experiment are shown in Figure 12.

[0122] 12, under the conditions of Studies 15 to 17, it was confirmed that the white voids in the output image were less likely to occur, and the evaluation was rated as ⊚ level. In Study 18, the angle θ3 was too large, and as in the previous embodiments, carrier adhesion occurred due to poor transport of the developer on the second sleeve 34.

[0123] Therefore, in this embodiment, if the angle (acute angle) formed by the line (PH) connecting the position (point H) on the second sleeve 34 where the normal component of the magnetic flux density of the second developing downstream pole 204 is maximum and the rotation center P of the second sleeve 34, and a horizontal line L passing through the rotation center P of the second sleeve 34 that is closer to the photosensitive drum 28Y (image carrier side) than the rotation center P of the second sleeve 34, is θ3, it is preferable to satisfy θ3≧5° ... (Equation 15), and it is more preferable to satisfy θ3<48° ... (Equation 16).

[0124] In this way, in this embodiment as well, it is possible to suppress the occurrence of white spots due to carrier adhesion, similarly to the first embodiment.

[0125] The present invention is not limited to the configurations of the above-described embodiments. For example, the image forming apparatus 100 is not limited to an MFP, but may be a copier, printer, or facsimile machine. Furthermore, the configurations of the developer supply screw 42, developer stirring screw 43, and developer recovery screw 44 are not particularly limited as long as they can transport the developer. For example, spiral blades or paddle-shaped blades can be used.

[0126] According to the present invention, a developing device capable of suppressing the occurrence of image defects is provided.

[0127] The present invention is not limited to the above-described embodiments, and various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the following claims are appended to apprise the public of the scope of the present invention.

[0128] This application claims priority based on Japanese Patent Application No. 2024-107389 filed on July 3, 2024, and Japanese Patent Application No. 2025-067175 filed on April 16, 2025, the entire contents of which are incorporated herein by reference.

Claims

1. A developing container that contains a developer containing toner and a carrier; a first rotating body to which the developer contained in the developing container is supplied, the first rotating body rotating in the same direction as the rotating image carrier at a position on the outer circumferential surface of the first rotating body that is closest to the image carrier, and carrying and transporting the developer to a first developing position where an electrostatic latent image formed on the image carrier is developed; a first magnet that is fixedly disposed inside the first rotating body and non-rotatable, the first magnet having: a first developing pole disposed facing the image carrier at the first developing position; a first downstream pole disposed adjacent to the first developing pole downstream of the first developing pole in the rotational direction of the first rotating body and having a polarity opposite to that of the first developing pole; and a delivery pole disposed downstream of the first downstream pole and upstream of the first developing pole in the rotational direction of the first rotating body. a second rotating body disposed opposite the first rotating body and to which the developer is transferred from the first rotating body by a magnetic field generated by the first magnet, the second rotating body rotating in the same direction as the image carrier at a position on the outer circumferential surface of the second rotating body closest to the image carrier and carrying and transporting the developer to a second developing position where the electrostatic latent image is developed; and a second magnet disposed inside the second rotating body and fixed so as not to rotate, the second magnet having a second developing pole disposed opposite to the image carrier at the second developing position, a second downstream pole disposed adjacent to the second developing pole downstream of the second developing pole in the rotational direction of the second rotating body and having a polarity opposite to that of the second developing pole, and a receiving pole disposed adjacent to the delivering pole downstream of the second downstream pole and upstream of the second developing pole in the rotational direction of the second rotating body and having a polarity opposite to that of the delivering pole, an angle in the rotation direction of the first rotor from a position on the outer peripheral surface of the first rotor at which the absolute value of the magnetic flux density of the first development pole in the normal direction to the outer peripheral surface of the first rotor is maximum to a position on the outer peripheral surface of the first rotor at which the absolute value of the magnetic flux density of the first downstream pole in the normal direction to the outer peripheral surface of the first rotor is maximum is defined as δ [°];A developing device that satisfies R2×θ>R1×δ, where θ [°] is the angle in the rotational direction of the second rotating body from a position on the outer peripheral surface of the second rotating body where the absolute value of the magnetic flux density of the second developing pole in the normal direction to the outer peripheral surface of the second rotating body is maximum to a position on the outer peripheral surface of the second rotating body where the absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer peripheral surface of the second rotating body is maximum, R1 [mm] is the radius of the first rotating body, and R2 [mm] is the radius of the second rotating body.

2. The developing device according to claim 1, further satisfying the following condition: R2×(1−cos θ)≧2.

2.

3. The developing device according to claim 1, further satisfying the following condition: R2×(1−cos θ)≧2.

9.

4. A developing device as described in claim 1, further satisfying D2 ≧ D1 × 8.5, where D1 [mm] is the distance between the image carrier and a position on the outer circumferential surface of the second rotating body where the absolute value of the magnetic flux density of the second developing pole in the normal direction to the outer circumferential surface of the second rotating body is maximum, and D2 [mm] is the distance between the image carrier and a position on the outer circumferential surface of the second rotating body where the absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer circumferential surface of the second rotating body is maximum.

5. A developing device as described in claim 1, further satisfying D2 ≧ D1 × 10, where D1 [mm] is the distance between the image carrier and a position on the outer circumferential surface of the second rotating body where the absolute value of the magnetic flux density of the second developing pole in the normal direction to the outer circumferential surface of the second rotating body is maximized, and D2 [mm] is the distance between the image carrier and a position on the outer circumferential surface of the second rotating body where the absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer circumferential surface of the second rotating body is maximized.

6. The developing device according to claim 1, further satisfying θ<90°.

7. The developing device according to claim 1, further satisfying θ>30°.

8. A developing container containing a developer containing toner and a carrier; a first rotating body to which the developer contained in the developing container is supplied, the first rotating body rotating in the same direction as the rotating image carrier at a position on the outer circumferential surface of the first rotating body closest to the image carrier, and carrying and transporting the developer to a first developing position where an electrostatic latent image formed on the image carrier is developed; a first magnet arranged non-rotatably and fixedly inside the first rotating body, the first magnet having: a first developing pole arranged to face the image carrier at the first developing position; a first downstream pole arranged adjacent to the first developing pole downstream of the first developing pole in the rotational direction of the first rotating body and having a polarity opposite to that of the first developing pole; and a delivery pole arranged downstream of the first downstream pole and upstream of the first developing pole in the rotational direction of the first rotating body. a second rotating body disposed opposite the first rotating body and to which the developer is transferred from the first rotating body by a magnetic field generated by the first magnet, the second rotating body rotating in the same direction as the image carrier at a position on the outer circumferential surface of the second rotating body closest to the image carrier and carrying and transporting the developer to a second developing position where the electrostatic latent image is developed; and a second magnet disposed inside the second rotating body and fixed so as not to rotate, the second magnet having a second developing pole disposed opposite to the image carrier at the second developing position, a second downstream pole disposed adjacent to the second developing pole downstream of the second developing pole in the rotational direction of the second rotating body and having a polarity opposite to that of the second developing pole, and a receiving pole disposed adjacent to the delivering pole downstream of the second downstream pole and upstream of the second developing pole in the rotational direction of the second rotating body and having a polarity opposite to that of the delivering pole, an angle in the rotation direction of the first rotating body from a position on the outer peripheral surface of the first rotating body that is closest to the image carrier to a position on the outer peripheral surface of the first rotating body at which the absolute value of the magnetic flux density of the first downstream pole in the normal direction to the outer peripheral surface of the first rotating body is maximum is defined as δ2 [°];A developing device that satisfies R2×θ2>R1×δ2, where θ2 [°] is the angle in the rotational direction of the second rotating body from the position on the outer peripheral surface of the second rotating body that is closest to the image carrier to the position on the outer peripheral surface of the second rotating body where the absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer peripheral surface of the second rotating body is maximum, R1 [mm] is the radius of the first rotating body, and R2 [mm] is the radius of the second rotating body.

9. The developing device according to claim 8, further satisfying R2×(1−cos θ2)≧2.

2.

10. The developing device according to claim 8, further satisfying the following condition: R2×(1−cos θ2)≧2.

9.

11. A developing device as described in claim 8, further satisfying D2 ≧ D3 × 8.5, where D2 [mm] is the distance between the image carrier and a position on the outer circumferential surface of the second rotating body at which the absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer circumferential surface of the second rotating body is maximum, and D3 [mm] is the distance between the image carrier and a position on the outer circumferential surface of the second rotating body that is closest to the image carrier.

12. A developing device as described in claim 8, further satisfying D2 ≧ D3 × 10, where D2 [mm] is the distance between the image carrier and a position on the outer circumferential surface of the second rotating body at which the absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer circumferential surface of the second rotating body is maximum, and D3 [mm] is the distance between the image carrier and a position on the outer circumferential surface of the second rotating body that is closest to the image carrier.

13. The developing device according to claim 8, further satisfying θ2<90°.

14. The developing device according to claim 8, further satisfying θ2>30°.

15. A developing container containing a developer containing toner and a carrier; a first rotating body to which the developer contained in the developing container is supplied, the first rotating body rotating in the same direction as the rotating image carrier at a position on the outer circumferential surface of the first rotating body closest to the image carrier, and carrying and transporting the developer to a first developing position where an electrostatic latent image formed on the image carrier is developed; a first magnet arranged non-rotatably and fixedly inside the first rotating body, the first magnet having: a first developing pole arranged facing the image carrier at the first developing position; a first downstream pole arranged adjacent to the first developing pole downstream of the first developing pole in the rotational direction of the first rotating body and having a polarity opposite to that of the first developing pole; and a delivery pole arranged downstream of the first downstream pole and upstream of the first developing pole in the rotational direction of the first rotating body. a second rotating body disposed opposite the first rotating body and to which the developer is transferred from the first rotating body by a magnetic field generated by the first magnet, the second rotating body rotating in the same direction as the image carrier at a position on the outer circumferential surface of the second rotating body closest to the image carrier and carrying and transporting the developer to a second developing position where the electrostatic latent image is developed; and a second magnet disposed inside the second rotating body and fixed so as not to rotate, the second magnet having a second developing pole disposed opposite to the image carrier at the second developing position, a second downstream pole disposed adjacent to the second developing pole downstream of the second developing pole in the rotational direction of the second rotating body and having a polarity opposite to that of the second developing pole, and a receiving pole disposed adjacent to the delivering pole downstream of the second downstream pole and upstream of the second developing pole in the rotational direction of the second rotating body and having a polarity opposite to that of the delivering pole, A developing device in which the position on the outer surface of the second rotating body where the absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer surface of the second rotating body is maximum is vertically above a horizontal line passing through the center of rotation of the second rotating body.

16. A developing device as described in claim 15, further satisfying θ3≧5°, where θ3 is the angle in the rotational direction of the second rotating body from a horizontal line passing through the center of rotation of the second rotating body to a position on the outer peripheral surface of the second rotating body at which the absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer peripheral surface of the second rotating body is maximum.

17. A developing device as described in claim 15, further satisfying θ3 < 48°, where θ3 is the angle in the rotational direction of the second rotating body from a horizontal line passing through the center of rotation of the second rotating body to a position on the outer peripheral surface of the second rotating body at which the absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer peripheral surface of the second rotating body is maximum.

Images