Developing device

Abstract

To suppress the occurrence of image defects.SOLUTION: The absolute value of a maximum value of magnetic flux density of a second conveyance pole in a normal direction with respect to the outer circumferential surface of a second rotor is defined as MA, and the position on the outer circumferential surface of the second rotor where the magnetic flux density of the second conveyance pole becomes maximum is defined as a point A. Also, the absolute value of a maximum value of magnetic flux density of a first conveyance pole in the normal direction with respect to the outer circumferential surface of a first rotor is defined as MB, and the position on the outer circumferential surface of the first rotor where the magnetic flux density of the first conveyance pole becomes maximum is defined as a point B. Also, the absolute value of a maximum value of magnetic flux density of a transfer pole in the normal direction with respect to the outer circumferential surface of the first rotor is defined as MC, and the position on the outer circumferential surface of the first rotor where the magnetic flux density of the transfer pole becomes maximum is defined as a point C. Furthermore, a linear distance between the point A and the point B is defined as L1; a linear distance between the point A and the point C is defined as L2; and an angle formed by a line AB linking the point A and the point B and a line AC linking the point A and the point C is defined as θ. In this case, MB / L12≤(MC / L22)×cosθ is satisfied.SELECTED DRAWING: Figure 7

Description

[Technical field]

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

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

[0003] [Patent Document 1] JP 2013-254107 A Summary of the Invention [Problem to be solved by the invention]

[0004] As described in Patent Document 1, in the case of a configuration in which developer is transferred from a first developing roller to a second developing roller located vertically above, the developer is transferred by a magnetic field formed between a transfer pole of a first magnet arranged in the first developing roller and a receiving pole of a second magnet arranged in the second developing roller. The transfer pole has a polarity opposite to that of the receiving pole. In such a configuration, if the rotation direction of the second developing roller is opposite to that of the first developing roller at the position facing the first developing roller, the first magnetic pole adjacent to the upstream side of the transfer pole has a polarity opposite to that of the second magnetic pole adjacent to the downstream side of the receiving pole. Therefore, a magnetic field that attracts the developer to each roller is generated between the first magnetic pole and the second magnetic pole.

[0005] When a magnetic field that attracts the developer is generated between the first and second magnetic poles in this way, there is a risk that this magnetic field will cause the developer to move between the first and second magnetic poles. When the developer moves between the first and second magnetic poles, the moving developer may become suspended and adhere to the image carrier near the first and second developing rollers. When the developer adheres to the image carrier in this way, image defects such as vertical streak-like fog appear on the output image occur.

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a developing device capable of suppressing the occurrence of image defects. [Means for solving the problem]

[0007] One aspect of the present invention is a development device comprising: a development container that contains a developer containing a toner and a carrier; a first rotor to which the developer contained in the development container is supplied, the first rotor carrying and transporting the developer to a first development position where an electrostatic latent image formed on an image carrier is developed; a first magnet that is fixedly disposed inside the first rotor and does not rotate, the first magnet being disposed in a non-rotating manner, the first magnet being a first development pole that is disposed facing the image carrier at the first development position; a delivery pole that is disposed downstream of the first development pole in the rotation direction of the first rotor; a first magnet having a first transport pole disposed adjacent to the delivery pole upstream of the delivery pole and having a polarity different from that of the delivery pole; a second rotor disposed opposite the first rotor and receiving the developer from the first rotor by a magnetic field generated by the first magnet, the second rotor carrying and transporting the developer to a second development position where the electrostatic latent image is developed; and a second magnet disposed inside the second rotor in a non-rotating and fixed manner, the second rotor being disposed opposite the image carrier at the second development position. a second magnet having a plurality of magnetic poles including a first developing pole, a receiving pole arranged upstream of the second developing pole in the rotation direction of the second rotor and having a polarity different from that of the delivery pole, and a second transport pole arranged downstream of the receiving pole in the rotation direction of the second rotor and adjacent to the receiving pole and having a polarity different from that of the receiving pole, and the second magnet having a plurality of magnetic poles including a first developing pole, a first transport pole, and a second transport pole, the first transport pole being arranged downstream of the receiving pole in the rotation direction of the second rotor and having a polarity different from that of the receiving pole, the receiving pole is the magnetic pole of the second magnet that is disposed closest to the delivering pole, the absolute value of the maximum value of the magnetic flux density of the second conveying pole in the normal direction to the outer circumferential surface of the second rotating body is defined as point MA, the position on the outer circumferential surface of the second rotating body at which the magnetic flux density of the second conveying pole in the normal direction to the outer circumferential surface of the second rotating body is maximum is defined as point A, and the absolute value of the maximum value of the magnetic flux density of the first conveying pole in the normal direction to the outer circumferential surface of the first rotating body is defined as point MB,Let point B be the position on the outer circumferential surface of the first rotor where the magnetic flux density of the first conveying pole in the normal direction to the outer circumferential surface of the first rotor is maximum, let MC be the absolute value of the maximum value of the magnetic flux density of the delivery pole in the normal direction to the outer circumferential surface of the first rotor, let point C be the position on the outer circumferential surface of the first rotor where the magnetic flux density of the delivery pole in the normal direction to the outer circumferential surface of the first rotor is maximum, let L1 be the linear distance between point A and point B, let L2 be the linear distance between point A and point C, and let θ be the angle formed by a line AB connecting point A and point B and a line AC connecting point A and point C, then MB / L1, 2 ≦(MC / L2 2 ) × cos θ.

[0008] One aspect of the present invention is a development device comprising: a development container that contains a developer containing a toner and a carrier; a first rotor to which the developer contained in the development container is supplied, the first rotor carrying and transporting the developer to a first development position where an electrostatic latent image formed on an image carrier is developed; a first magnet that is fixedly disposed inside the first rotor and does not rotate, the first magnet being disposed in a non-rotating manner, the first magnet being a first development pole that is disposed facing the image carrier at the first development position; a delivery pole that is disposed downstream of the first development pole in the rotation direction of the first rotor; a first magnet having a first transport pole disposed adjacent to the delivery pole upstream of the delivery pole and having a polarity different from that of the delivery pole; a second rotor disposed opposite the first rotor and receiving the developer from the first rotor by a magnetic field generated by the first magnet, the second rotor carrying and transporting the developer to a second development position where the electrostatic latent image is developed; and a second magnet disposed inside the second rotor in a non-rotating and fixed manner, the second rotor being disposed opposite the image carrier at the second development position. a second magnet having a plurality of magnetic poles including a first developing pole, a receiving pole arranged upstream of the second developing pole in the rotation direction of the second rotor and having a polarity different from that of the delivery pole, and a second transport pole arranged downstream of the receiving pole in the rotation direction of the second rotor and adjacent to the receiving pole and having a polarity different from that of the receiving pole, and the second magnet having a plurality of magnetic poles including a first developing pole, a first transport pole, and a second transport pole, the first transport pole being arranged downstream of the receiving pole in the rotation direction of the second rotor and having a polarity different from that of the receiving pole, the receiving pole is the magnetic pole of the second magnet that is disposed closest to the delivering pole, the absolute value of the maximum value of the magnetic flux density of the second conveying pole in the normal direction to the outer circumferential surface of the second rotating body is defined as point MA, the position on the outer circumferential surface of the second rotating body at which the magnetic flux density of the second conveying pole in the normal direction to the outer circumferential surface of the second rotating body is maximum is defined as point A, and the absolute value of the maximum value of the magnetic flux density of the first conveying pole in the normal direction to the outer circumferential surface of the first rotating body is defined as point MB,Let point B be the position on the outer circumferential surface of the first rotor where the magnetic flux density of the first conveying pole is maximum in the normal direction to the outer circumferential surface of the first rotor, let MD be the absolute value of the maximum value of the magnetic flux density of the receiving pole in the normal direction to the outer circumferential surface of the second rotor, let point D be the position on the outer circumferential surface of the second rotor where the magnetic flux density of the receiving pole is maximum in the normal direction to the outer circumferential surface of the second rotor, let L1 be the straight-line distance between point A and point B, let L3 be the straight-line distance between point B and point D, and let θ' be the angle formed by a straight line AB connecting point A and point B and a straight line BD connecting point B and point D, then MA / L1, 2 ≦(MD / L3 2 )×cos θ′ is satisfied.

[0009] One aspect of the present invention includes a developing container that contains a developer containing a toner and a carrier; a first rotating body to which the developer contained in the developing container is supplied, the first rotating body carrying and transporting the developer to a first developing position where an electrostatic latent image formed on an image carrier is developed; a first magnet that is fixedly arranged inside the first rotating body and non-rotatable, the first magnet having a first developing pole arranged to face the image carrier at the first developing position, and a delivery pole that is arranged adjacent to the first developing pole downstream of the first developing pole in the rotation direction of the first rotating body and has a polarity opposite to that of the first developing pole; a second rotating body that is arranged to face 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 carrying and transporting the developer to a second developing position where the electrostatic latent image is developed; A developing device comprising: a second magnet having a plurality of magnetic poles including a second developing pole arranged opposite the image carrier at the second developing position, a receiving pole arranged upstream of the second developing pole in the rotational direction of the second rotating body and having a different polarity from the delivery pole, and a transport pole arranged adjacent to the receiving pole downstream of the receiving pole in the rotational direction of the second rotating body and having a different polarity from the receiving pole, wherein the rotation direction of the second rotating body at the position on the outer surface of the second rotating body where the second rotating body is closest to the first rotating body is opposite to the rotation direction of the first rotating body at the position on the outer surface of the first rotating body where the first rotating body is closest to the second rotating body, and the receiving pole is the magnetic pole arranged closest to the delivery pole among the plurality of magnetic poles of the second magnet.

[0010] One aspect of the present invention relates to a developing device comprising: a developing container that contains a developer containing a toner and a carrier; a first rotating body to which the developer contained in the developing container is supplied, the first rotating body carrying and transporting the developer to a first developing position where an electrostatic latent image formed on an image carrier is developed; a first magnet that is fixedly arranged inside the first rotating body and non-rotatable, the first magnet having a first developing pole arranged to face the image carrier at the first developing position, a delivery pole arranged downstream of the first developing pole in a rotation direction of the first rotating body, and a transport pole that is arranged adjacent to the delivery pole upstream of the delivery pole in the rotation direction of the first rotating body and has a polarity different from that of the delivery pole; and a second rotating body that is arranged to face 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 developing position where the electrostatic latent image is developed, the first magnet having a first developing pole arranged downstream of the first developing pole in a rotation direction of the first rotating body, a delivery pole arranged downstream of the first developing pole in a rotation direction of the first rotating body, and a transport pole that is arranged adjacent to the delivery pole upstream of the delivery pole in the rotation direction of the first rotating body and has a polarity different from that of the delivery pole; a second magnet arranged inside the second rotor so as to be fixed and non-rotatable, the second magnet having a plurality of magnetic poles including a second developing pole arranged facing the image carrier at the second developing position, and a receiving pole arranged adjacent to the second developing pole upstream of the second developing pole in terms of the rotation direction of the second rotor, the receiving pole having a different polarity from the second developing pole and a different polarity from the delivery pole, wherein the rotation direction of the second rotor at a position on the outer surface of the second rotor where the second rotor is closest to the first rotor is opposite to the rotation direction of the first rotor at a position on the outer surface of the first rotor where the first rotor is closest to the second rotor, and the receiving pole is the magnetic pole arranged closest to the delivery pole among the plurality of magnetic poles of the second magnet. Effect of the Invention

[0011] According to the present invention, the occurrence of image defects can be suppressed. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic cross-sectional view of an image forming apparatus according to a first embodiment. [Diagram 2]FIG. 2 is a schematic cross-sectional view of the developing device according to the first embodiment. [Diagram 3] FIG. 4 is a diagram showing the arrangement of magnetic poles of a first developing roller according to the first embodiment. [Figure 4] FIG. 4 is a diagram showing the arrangement of magnetic poles of a second developing roller according to the first embodiment. [Diagram 5] FIG. 2 is a diagram showing the arrangement of magnetic poles of the peeling roller according to the first embodiment. [Figure 6] FIG. 4 is a diagram showing the relationship between an attractive force F1 and a repulsive force F2 in a diagram showing the relationship between the magnetic pole arrangements of the first developing roller and the second developing roller according to the first embodiment. [Figure 7] FIG. 11 is a diagram showing the relationship between an attractive force F1 and a repulsive force F2' in a diagram showing the relationship between the magnetic pole arrangements of the first developing roller and the second developing roller according to the first embodiment. [Figure 8] 6 is a table showing the results of an experiment to confirm the occurrence of abnormal images in the first embodiment. [Figure 9] FIG. 11 is a diagram showing the relationship between the attractive force F1 and the repulsive forces F2 and F2' in a diagram showing the relationship between the magnetic pole arrangements of the first developing roller and the second developing roller according to the second embodiment. [Figure 10] 10 is a table showing the results of an experiment to confirm the occurrence of abnormal images in the second embodiment. [Figure 11] FIG. 13 is a diagram showing the arrangement of magnetic poles of a first developing roller according to a third embodiment. [Figure 12] 13 is a diagram showing the relationship between the arrangement of magnetic poles of a first developing roller and a second developing roller according to a third embodiment. FIG. [Figure 13] FIG. 13 is a diagram showing the relationship between an attractive force F1 and a repulsive force F3 in a diagram showing the relationship between the magnetic pole arrangements of a first developing roller and a second developing roller according to a fourth embodiment. [Figure 14] FIG. 13 is a diagram showing the relationship between an attractive force F1 and a repulsive force F3' in a diagram showing the relationship between the magnetic pole arrangements of a first developing roller and a second developing roller according to a fourth embodiment. [Figure 15] 13 is a table showing the results of an experiment to confirm the occurrence of abnormal images in the fourth embodiment. [Figure 16] FIG. 13 is a diagram showing the relationship between an attractive force F1 and a repulsive force F3' in a diagram showing the relationship between the magnetic pole arrangements of a first developing roller and a second developing roller according to a fifth embodiment. [Figure 17] 13 is a table showing the results of an experiment to confirm the occurrence of abnormal images in the fifth embodiment. [Figure 18] FIG. 13 is a diagram showing the arrangement of magnetic poles of a second developing roller according to the sixth embodiment. [Figure 19] 13 is a diagram showing the relationship between the arrangement of magnetic poles of a first developing roller and a second developing roller according to a sixth embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] <First embodiment> The first embodiment will be described with reference to Figures 1 to 8. First, the schematic configuration of an image forming apparatus according to the present embodiment will be described with reference to Figure 1.

[0014] [Image forming equipment] The image forming apparatus 100 is a full-color image forming apparatus, and in this embodiment, for example, is an MFP (Multi-Function Peripheral) having a copy function, a printer function, and a scan function. As shown in Fig. 1, the image forming apparatus 100 has image forming units PY, PM, PC, and PK arranged in parallel, which perform image forming processes for four colors of toner images, yellow, magenta, cyan, and black, respectively.

[0015] The image forming units PY, PM, PC, and PK of the respective colors include primary chargers 21Y, 21M, 21C, and 21K, developing devices 1Y, 1M, 1C, and 1K, optical writing units (exposure devices) 22Y, 22M, 22C, and 22K, photosensitive drums 28Y, 28M, 28C, and 28K, and cleaning devices 26Y, 26M, 26C, and 26K. The image forming apparatus 100 also includes a transfer device 2 and a fixing device 3. Since the image forming units PY, PM, PC, and PK of the respective colors have the same configuration, the following description will be given using the image forming unit PY as a representative.

[0016] The photosensitive drum 28Y 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 arranged around the photosensitive drum 28Y, and charges the surface of the photosensitive drum 28Y with generated ions.

[0017] The optical writing unit 22Y incorporates a scanning optical device, and exposes the charged photosensitive drum 28Y based on image data, thereby lowering the potential of the exposed portion 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.

[0018] 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 a plurality of rollers, and is supported so as to be capable of running. The primary transfer rollers 23Y, 23M, 23C, and 23K correspond to the colors Y (yellow), M (magenta), C (cyan), and K (black) in order from the top of FIG. 1. The secondary transfer roller 25 is disposed outside the intermediate transfer belt 24, and is configured so that a recording material can pass between the secondary transfer roller 25 and the intermediate transfer belt 24. The recording material is, for example, a sheet such as paper or a plastic sheet.

[0019] 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 in which the recording material is stored. 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 onto the recording material.

[0020] The developer storage units 27Y, 27M, 27C, and 27K are provided corresponding to the developing devices 1Y, 1M, 1C, and 1K, respectively, and are loaded with replaceable bottles containing developers corresponding to the respective colors of yellow, magenta, cyan, and black, in order from the top. The developer storage units 27Y, 27M, 27C, and 27K are configured to be able to transport (supply) developers to the developing devices 1Y, 1M, 1C, and 1K corresponding to the colors of the developers stored therein.

[0021] 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.

[0022] [Developing device] Next, the developing devices 1Y, 1M, 1C, and 1K will be described in detail with reference to Figures 2 to 5. Since the developing devices 1Y, 1M, 1C, and 1K have the same configuration, the developing device 1Y will be described below as a representative. Figure 2 is a conceptual diagram explaining the developing device 1Y shown in Figure 1, and Figures 3, 4, and 5 are conceptual diagrams explaining the magnetic pole configurations of the first magnet 36, second magnet 37, and third magnet 38 arranged in the developing device 1Y.

[0023] 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 contained in a developing container 60.

[0024] The first developing roller 30 is a developer carrier that is driven to rotate, and is disposed adjacent to the photosensitive drum 28Y so that its rotation axis is substantially parallel to the rotation axis of the photosensitive drum 28Y. The first developing roller 30 has a rotating first sleeve 33 and a first magnet (fixed magnet) 36 that is fixedly disposed inside the first sleeve 33 so as not to rotate and that attracts the developer to the surface of the first sleeve 33 by magnetic force. The first developing roller 30 attracts (carries) the developer pumped up from the developer supply screw 42 by magnetic force, and develops the electrostatic latent image formed on the rotating photosensitive drum 28Y (image carrier) with the developer at the first developing position.

[0025] The first sleeve 33 as the first rotating body is a non-magnetic cylindrical member, and is driven to rotate around a rotation shaft 39. The first sleeve 33 carries and transports a developer to a first developing position where the electrostatic latent image formed on the photosensitive drum 28Y is developed. The rotation direction of the first sleeve 33 is clockwise as shown by the arrow in FIG. 2, 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 at positions facing each other. That is, this is forward development in which the photosensitive drum 28 rotates from a vertically lower position to a vertically upper position at a position facing the first sleeve 33.

[0026] The first magnet 36 serving as the first magnet is disposed inside the first sleeve 33, and has a plurality of sector-shaped magnetic poles 101 to 107 as shown in Fig. 3. Between the inner circumference of the first sleeve 33 and the outer circumference of the first magnet 36, a space is disposed to allow the first sleeve 33 to rotate.

[0027] The developer attracted onto the first sleeve 33 (on the first sleeve) is transported toward the photosensitive drum 28Y by the rotational operation of the first sleeve 33, and develops the latent image formed on the photosensitive drum 28Y. After developing the latent image formed on the photosensitive drum 28Y, the developer on the first sleeve 33 is transported to the vicinity of the second developing roller 31 by the rotational operation of the first sleeve 33. Then, in the vicinity of 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 field 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.

[0028] The second developing roller 31 is a developer carrier that is driven to rotate, 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 O2 of the second developing roller 31 is located above the rotation center O1 of the first developing roller 30 in the vertical direction, and the 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 O1 of the first developing roller 30. The second developing roller 31, like the first developing roller 30, is disposed at a position 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.

[0029] The second developing roller 31 has a rotating second sleeve 34 and a second magnet (fixed magnet) 37 that is fixedly arranged inside the second sleeve 34 in a non-rotating manner and attracts the developer to the surface of the second sleeve 34 by magnetic force. The second developing roller 31 receives the developer from the first developing roller 30 (first sleeve 33) based on the magnetic force, attracts (carries) the developer, and develops the electrostatic latent image formed on the rotating photosensitive drum 28Y with the developer at the second developing position. A peeling roller 32, which will be described later, is located on the side of the second developing roller 31.

[0030] The second sleeve 34 as the second rotating body is a non-magnetic cylindrical member, and is rotated around the rotation shaft 40. The second sleeve 34 is disposed opposite to the first sleeve 33, and the developer is transferred from the first sleeve 33 to the second sleeve 34 by the magnetic field generated by the first magnet 36. The second sleeve 34 carries and transports the developer to a second developing position where the electrostatic latent image formed on the photosensitive drum 28Y is developed. The rotation direction of the second sleeve 34 is the clockwise direction as shown by the arrow in FIG. 2, which is the opposite direction to the rotation direction of the photosensitive drum 28Y in this embodiment. Therefore, the second sleeve 34 and the photosensitive drum 28Y rotate in the same direction at the positions facing each other. That is, the photosensitive drum 28 rotates from the lower vertical direction to the upper vertical direction at the position facing the second sleeve 34, which is forward development. The second sleeve 34 and the first sleeve 33 rotate in opposite directions at the positions facing each other. That is, the rotation direction of the second sleeve 34 at the position on the outer surface of the second sleeve 34 where the second sleeve 34 is closest to the first sleeve 33 is opposite to the rotation direction of the first sleeve 33 at the position on the outer surface of the first sleeve 33 where the first sleeve 33 is closest to the second sleeve 34.

[0031] The second magnet 37 serving as the second magnet is disposed inside the second sleeve 34, and has a plurality of sector-shaped magnetic poles 201 to 207 as shown in Fig. 4. Between the inner periphery of the second sleeve 34 and the outer periphery of the second magnet 37, a space is disposed to allow the second sleeve 34 to rotate.

[0032] The developer attracted onto the second sleeve 34 is transported toward the photosensitive drum 28Y by the rotational operation of the second sleeve 34, and develops the latent image formed on the photosensitive drum 28Y. After the latent image formed on the photosensitive drum 28Y is developed, the developer remaining on the second sleeve 34 is transported to the vicinity of the peeling roller 32 by the rotational operation of the second sleeve 34. Then, in the vicinity of 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 field generated by the second magnet 37 contained in the second developing roller 31 and the third magnet 38 contained in the peeling roller 32.

[0033] The peeling roller 32 as a peeling section is disposed on the opposite side to 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 such that its rotation center is above the rotation center R of the second developing roller 31.

[0034] 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 fixedly disposed inside the third sleeve 35 so as not to rotate 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.

[0035] The third sleeve 35 is a non-magnetic cylindrical member, and is driven to rotate around the rotation shaft 41. The rotation direction of the third sleeve 35 is counterclockwise as indicated by the arrow in Fig. 2, which is the opposite direction to the rotation direction of the second sleeve 34 in this embodiment. Therefore, the third sleeve 35 and the second sleeve 34 rotate in the same direction at positions facing each other.

[0036] The third magnet 38 is disposed inside the third sleeve 35, and has a plurality of sector-shaped magnetic poles 301-305, as shown in Fig. 5. Between the inner periphery of the third sleeve 35 and the outer periphery of the third magnet 38, a space is disposed to allow the third sleeve 35 to rotate.

[0037] The developer attracted onto the third sleeve 35 is 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.

[0038] The guide member 45 and the developer recovery screw 44 constitute a developer recovery section 47 as a recovery section that recovers the developer peeled off from the third sleeve 35 on the peeling roller 32. In the developer recovery section 47, the developer recovery screw 44 is disposed so that the center of rotation is located lower than the center of rotation of the peeling roller 32 in the vertical direction, and conveys the developer delivered (recovered) from the peeling roller 32 while stirring it.

[0039] The guide member 45 as a guide portion 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 a slope 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 slope 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.

[0040] The developer recovery screw 44, which serves as a recovery member and a transport section, transports the recovered developer to a developer circulating 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.

[0041] The developer circulating section 46 is a supply section for supplying the developer to the first developing roller 30, and includes a regulating member 50, a developer supply screw 42, and a developer stirring screw 43. In the developer circulating section 46, the developer is stirred in the developer supply screw 42 and the developer stirring screw 43 and transported in a substantially horizontal direction, and is supplied to the first developing roller 30. As described above, the developer collected by the developer collecting section 47 falls by its own weight and is introduced into the developer circulating section 46.

[0042] The developer supply screw 42, developer stirring screw 43, and developer recovery screw 44 are screw transport members that transport the developer in one direction while stirring it, and the developer supply screw 42 and developer stirring screw 43 are located vertically below the developer recovery screw 44. The developer supply screw 42, developer stirring screw 43, and developer recovery screw 44 are also arranged so that their rotation axes are approximately parallel to each other. The rotation axes of these screws are also approximately parallel to the rotation axis of the first developing roller 30.

[0043] The developer supply screw 42 is located between the first developing roller 30 and the developer stirring screw 43, and a partition wall 48 of the developing container 60 is disposed between the developer supply screw 42 and the developer stirring screw 43. The partition wall 48 of the developing container 60 extends along the rotation axis direction of the developer supply screw 42 and the developer stirring screw 43. The partition wall 48 is provided with a communication port (not shown) that communicates between a first conveying path 61, through which the developer is conveyed by the developer supply screw 42, and a second conveying path 62, through which the developer is conveyed by the developer stirring screw 43.

[0044] 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 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 above-mentioned guide member 45 is formed integrally with the partition wall 63, and the developer recovery screw 44 is disposed above the partition wall 63.

[0045] The position of the communication port through which the developer stirred by the developer recovery screw 44 falls by its own weight and is introduced into the developer circulating section 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 arranged at a position included in the range of the downstream end (terminal end) in the developer transport direction of the first transport path 61 in which the developer supply screw 42 is arranged.

[0046] The developer transport directions of the developer supply screw 42 and the developer stirring screw 43 are opposite to each other. The start side (upstream end side in the developer transport direction) and the end side (downstream end side in the developer transport direction) of the first transport path 61 in which the developer supply screw 42 is arranged communicate with the end side and the start side of the second transport path 62 in which the developer stirring screw 43 is arranged via a communication port provided in the partition wall 48. Therefore, the developer circulates in the rotation direction of the developer supply screw 42 and the developer stirring screw 43 shown by the arrows in FIG. 2 and in the approximately horizontal direction within the developing container 60, and a part of the developer is supplied toward the first developing roller 30.

[0047] 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.

[0048] 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 the toner weight ratio of the developer in developing device 1 constant.

[0049] The toner concentration detection sensor 49 (see FIG. 2) is disposed to detect the toner concentration in the developer contained in the developer circulating section 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 section 27Y. For example, when it is detected that the toner concentration has fallen below a predetermined value, developer is supplied from the developer storage section 27Y. Note that since the magnetic permeability of the developer changes depending on the toner concentration, it is possible to detect the toner concentration using the magnetic permeability.

[0050] 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 an end of the regulating member 50.

[0051] The circulation path of the developer in the developing container 60 is such that the developer is transported in a substantially horizontal direction while being stirred in the developer circulating section 46, and then is 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 then is peeled off from the peeling roller 32 by the third magnet 38 contained in the peeling roller 32, and is further collected in the developer collecting section 47, and is introduced again into the developer circulating section 46.

[0052] As described above, in this embodiment, a two-component development method is used as the development method, and the developer is a mixture of a non-magnetic toner with a negative charge polarity and a magnetic carrier. The non-magnetic toner is a resin such as polyester or styrene acrylic that contains colorants, wax components, etc., and is pulverized or polymerized to form a powder, to which fine powders such as titanium oxide and silica are added on the surface. The magnetic carrier is a core made of resin particles kneaded with ferrite particles or magnetic powder, and a resin coating is applied to the surface layer. In this embodiment, the toner concentration in the developer in the initial state (weight ratio of the toner contained in the developer) is 8%.

[0053] In general, the two-component development method using toner and carrier has the characteristic that the toner is subjected to less stress than the one-component development method using a one-component developer, because the toner and carrier are charged to a predetermined polarity by frictional contact between them. On the other hand, with long-term use, the dirt (spent) adhering to the carrier surface increases, and the ability to charge the toner gradually decreases. As a result, problems such as fogging and toner scattering occur. In order to extend the life of the two-component development device, it is possible to increase the amount of carrier contained in the development device, but this is not desirable because it leads to an increase in the size of the development device.

[0054] In order to solve the above problems associated with two-component developer, this embodiment employs an ACR (Auto Carrier Refresh) method. The ACR method is a method in which new developer is supplied little by little from the developer storage section 27Y to the developing device 1Y, and developer with deteriorated charging performance is discharged little by little from a discharge port (not shown) of the developing device 1Y, thereby suppressing an increase in deteriorated carrier. As a result, deteriorated carrier in the developing device 1Y is gradually replaced with new carrier, making it possible to maintain the charging performance of the carrier in the developing device 1Y approximately constant.

[0055] [About the magnetic poles of each magnet] Next, the magnetic pole configurations of the first magnet 36, second magnet 37 and third magnet 38 contained in the first developing roller 30, second developing roller 31 and peeling roller 32 shown in FIGS. 3, 4 and 5 will be described.

[0056] As shown in FIG. 3, the first magnet 36 contained in the first developing roller 30 has a seven-pole magnetic pole configuration having multiple magnetic poles 101, 102, 103, 104, 105, 106, and 107. Of these, the 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 rotation direction of the first sleeve 33. The magnetic pole 101 is an S pole, and is arranged at a position facing the regulating member 50 via the first sleeve 33, and adjusts the amount of developer transported on the first sleeve 33 as described above. The magnetic pole 104 as the first developing pole is an N pole, and is arranged at a position facing the photosensitive drum 28Y via the first sleeve 33 at the first developing position, 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.

[0057] The magnetic pole 106 as a delivery pole is an N pole and is a magnetic pole for delivering the 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, and hereinafter, the magnetic pole 106 may be referred to as a delivery pole 106. 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 to transport the developer attracted by the magnetic pole 107 upward as the first sleeve 33 rotates. Of these, the magnetic pole 105 is a first magnetic pole that is disposed adjacent to the delivery pole 106 on the upstream side with respect to the rotation direction of the first sleeve 33 and has a different polarity from the delivery pole 106, and hereinafter, the magnetic pole 105 may be referred to as a first transport pole 105. The first developing pole 104 is located adjacent to and upstream of the first transport pole 105 in the rotation direction of the first sleeve 33 .

[0058] The magnetic pole 107 is disposed downstream of the delivery pole 106 in the rotation 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 form a low magnetic force portion 110 having a lower magnetic force than the delivery pole 106 by a repulsive magnetic field generated in cooperation between them. This low magnetic force portion 110 causes the developer to peel off from the first sleeve 33 and promotes the delivery of the developer from the first sleeve 33 to the second sleeve 34. Note that the low magnetic force portion 110 has almost no magnetic force in this embodiment, but may have a low magnetic force, for example, a magnetic pole whose magnetic force (normal component Br of magnetic flux density) is 5 mT or less. This is also true for 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.

[0059] 4, the second magnet 37 contained in the second developing roller 31 has a seven-pole magnetic pole configuration having 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 rotational direction of the second sleeve 34.

[0060] 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 receiving pole 201 is the magnetic pole that is disposed closest to the delivery pole 106 among the multiple magnetic poles of the second magnet 37. The magnetic pole 207 is a magnetic pole for delivering 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.

[0061] Further, the receiving pole 201 is an S pole different from the delivery 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 as the second developing pole is an S pole, and is disposed at a position facing the photosensitive drum 28Y via the second sleeve 34 at the second developing position, 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.

[0062] The magnetic poles 202, 204, 205, and 206 are N pole, N pole, S pole, and N pole, and are used to transport the developer attracted by the magnetic pole 201 upward as the second sleeve 34 rotates. Among them, the magnetic pole 202 is a second magnetic pole located adjacent to the downstream side of the receiving pole 201 in the rotation direction of the second sleeve 34, and hereinafter, the magnetic pole 202 may be referred to as the second transport pole 202. The second developing pole 203 is located adjacent to the downstream side of the second transport pole 202 in the rotation direction of the second sleeve 33, and has a different polarity from the second transport pole. The magnetic pole 207 is an S pole, and transfers the developer after passing through the development area with 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.

[0063] Moreover, 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 form a low magnetic force portion 210 having a lower magnetic force than the magnetic pole 207 due to a repulsive magnetic field generated between them. 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, and can suppress the pressure applied to the developer.

[0064] 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.

[0065] The magnetic pole 303 is an N pole different from the magnetic pole 207, and is used to attract the developer peeled off from the second sleeve 34 to the third sleeve 35 as described above. The magnetic poles 301, 302, and 304 are an N pole, an S pole, and an S pole, and are used to transport the developer on the third sleeve 35 as the third sleeve 35 rotates. In particular, the magnetic pole 304 is used to transport the developer attracted by the magnetic pole 303 downward as the third sleeve 35 rotates. The magnetic pole 305 is an N pole, and is a peeling pole used to peel off the developer attracted to the third sleeve 35 from the third sleeve 35 by a repulsive magnetic field generated in cooperation with the magnetic pole 301 of the same polarity.

[0066] [Magnetic pole arrangement] Next, the positional relationship between the magnetic poles of the first magnet 36 arranged inside the first developing roller 30 and the magnetic poles of the second magnet 37 arranged inside the second developing roller 31 will be described with reference to Fig. 6. Fig. 6 is a conceptual diagram illustrating the arrangement of the first developing roller 30 and the second developing roller 31 of this embodiment, and in particular shows the layout of the first transport pole 105 and the handover pole 106 of the first magnet 36 of the first developing roller 30, and the receiving pole 201 and the second transport pole 202 of the second magnet 37 of the second developing roller 31. Note that some of the magnetic poles are omitted from the illustration to avoid complication.

[0067] In this embodiment, as described above, the developer in the developing device 1Y moves from the first sleeve 33 to the second sleeve 34 of the second developing roller 31 by the magnetic fields of the delivery pole 106 in the first developing roller 30 and the receiving pole 201 in the second developing roller 31, and then moves onto the third sleeve 35 of the peeling roller 32 after being used in the developing process of the electrostatic latent image on the photosensitive drum 28Y.

[0068] Here, the first conveying pole 105 of the first developing roller 30 and the second conveying pole 202 of the second developing roller 31 have magnetic properties of S and N poles, respectively, as shown in Figs. 3 and 4. Therefore, an attractive force (F1) for transferring developer is generated between the first conveying pole 105 and the second conveying pole 202. The attractive force F1 between the first conveying pole 105 and the second conveying pole 202 causes transfer of developer between the first conveying pole 105 and the second conveying pole 202. When developer is transferred between the first conveying pole 105 and the second conveying pole 202, the developer also comes into contact with the nearby photosensitive drum 28Y, causing an abnormal image with vertical streaks to appear on the photosensitive drum 28Y.

[0069] On the other hand, since the delivery pole 106 in the first developing roller 30 and the second transport pole 202 in the second developing roller 31 have the same N pole (same pole) as shown in Figures 3 and 4, a repulsive force (F2) that presses the developer against the sleeve is generated between the delivery pole 106 in the first developing roller 30 and the second transport pole 202 in the second developing roller 31.

[0070] Next, the suppression of developer transfer between the first transport pole 105 of the first developing roller 30 and the second transport pole 202 of the second developing roller 31 will be described in detail. The dashed lines in Fig. 6 and Fig. 7, which will be described later, indicate the position of the maximum value (peak position) of the magnetic flux density in the normal direction to the second sleeve 34 in the second transport pole 202 of the second magnet 37, and the position of the maximum value (peak position) of the magnetic flux density in the normal direction to the first sleeve 33 in the first transport pole 105 and the delivery pole 106 of the first magnet 36. First, the absolute value of the maximum value of the magnetic flux density of the second transport pole 202 in the normal direction to the outer circumferential surface of the second sleeve 34 is set as MA, and the position on the outer circumferential surface of the second sleeve 34 where the magnetic flux density of the second transport pole 202 in the normal direction to the outer circumferential surface of the second sleeve 34 is maximum is set as point A. That is, the absolute value of the maximum value of the normal component of the magnetic flux density of the second transport pole 202 in the second developing roller 31 is defined as MA [mT], and the position of this maximum value on the second sleeve 34 is defined as point A. Also, the absolute value of the maximum value of the magnetic flux density of the first transport pole 105 in the normal direction to the outer circumferential surface of the first sleeve 33 is defined as MB, and the position on the outer circumferential surface of the first sleeve 33 where the magnetic flux density of the first transport pole 105 in the normal direction to the outer circumferential surface of the first sleeve 33 is maximum is defined as point B. That is, the absolute value of the maximum value of the normal component of the magnetic flux density of the first transport pole 105 in the first developing roller 30 is defined as MB [mT], and the position on the first sleeve 33 of this maximum value is defined as point B. Also, the absolute value of the maximum value of the magnetic flux density of the delivery pole 106 in the normal direction to the outer circumferential surface of the first sleeve 33 is defined as MC, and the position on the outer circumferential surface of the first sleeve 33 where the magnetic flux density of the delivery pole 105 in the normal direction to the outer circumferential surface of the first sleeve 33 is maximum is defined as point C. That is, the absolute value of the maximum value of the normal component of the magnetic flux density of the delivery pole 106 in the first developing roller 30 is defined as MC [mT], and the position of this maximum value on the first sleeve 33 is defined as point C. Furthermore, the linear distance between points A and B is defined as L1, and the linear distance between points A and C is defined as L2.

[0071] The above-mentioned attractive force F1 is a magnetic force acting on the developer in the direction of a straight line AB connecting points A and B between the second transport pole 202 on the second sleeve 34 and the first transport pole 105 on the first sleeve 33. The above-mentioned repulsive force F2 is a magnetic force acting on the developer in the direction of a straight line AC connecting points A and C between the second transport pole 202 on the second sleeve 34 and the delivery pole 106 on the first sleeve 33.

[0072] Such an attractive force F1 and a repulsive force F2 can be expressed by the following equations: where k is a coefficient set according to the permeability, radius, etc. of the magnetic carrier of the developer. F1=k×MA×MB / L1 2 ...(Formula 1) F2 = k × MA × MC / L2 2 ...(Formula 2)

[0073] In order to suppress the transfer of developer between the second transport pole 202 in the second developing roller 31 and the first transport pole 105 in the first developing roller 30, the attractive force F1 between the second transport pole 202 in the second developing roller 31 and the first transport pole 105 in the first developing roller 30 should be equal to or less than the repulsive force F2 formed by the transfer pole 106 in the first developing roller 30 and the second transport pole 202 in the second developing roller 31. That is, the following relationship should be satisfied for the above-mentioned formulas 1 and 2. F1≦F2 (Formula 3)

[0074] That is, in this embodiment, the magnetic flux densities and arrangements of the delivery pole 106, the first carrier pole 105, and the second carrier pole 202 are set so as to satisfy the formula 3. Specifically, the positions of the above-mentioned MA, MB, MC, point A, point B, and point C are set so as to satisfy the formula 3.

[0075] 7 shows the relationship between the force component F2' of the repulsive force F2 in the direction of the line AB and the attractive force F1 described above. If the angle between the lines AB and AC is θ, the point on the line AB when a perpendicular line is drawn from point C to the line AB is C', and the linear distance between points A and C' is L2', then L2' can be expressed by the following formula. L2´=L2×cosθ (Formula 4)

[0076] In order to cancel the attractive force F1 received by the second transport pole 202 in the second developing roller 31 from the first transport pole 105 in the first developing roller 30, it is desirable that the repulsive force F2' in the direction of the straight line AC' between the second transport pole 202 in the second developing roller 31 and the delivery pole 106 in the first developing roller 30 be greater than or equal to the attractive force F1. F2' is the component of the force of F2 in the direction of the straight line AB, and can be expressed by the following formula. F2′=F2×cosθ (Formula 5) In order for the repulsive force F2' to cancel out the attractive force F1, it is desirable that the following relationship be established. F1≦F2´ (Formula 6)

[0077] That is, in this embodiment, it is preferable to further satisfy formula 6, and it is preferable to set the magnetic flux density and arrangement of the delivery pole 106, the first carrier pole 105, and the second carrier pole 202 so as to satisfy formula 6. Specifically, it is preferable to set the positions of the above-mentioned MA, MB, MC, point A, point B, and point C so as to satisfy formula 6. Formula 6 can also be expressed by the following formula. MB / L1 2 ≦(MC / L2 2 ) × cosθ

[0078] [experiment] Next, an experiment to check the occurrence of streaky fog images (abnormal images) in the above-mentioned configuration will be described. In the experiment, the magnetic flux density MA of the second conveying pole 202 in the second developing roller 31, the magnetic flux density MB of the first conveying pole 105 in the first developing roller 30, and the magnetic flux density MC of the delivery pole 106 in the first developing roller 30 were varied starting from the condition of REF, and images were output using an image forming apparatus incorporating developing devices under various conditions of REF and studies 1 to 5. Then, the occurrence of streaky fog images on the output images was checked.

[0079] In the experiment, the positions of point A where the magnetic flux density on the second transport pole 202 in the second developing roller 31 is maximum, point B where the magnetic flux density of the first transport pole 105 in the first developing roller 30 is maximum, and point C where the magnetic flux density of the delivery pole 106 in the first developing roller 30 is maximum were not changed. In other words, L1 and L2 were fixed. Also, the angle θ between the straight lines AB and AC was set to 36°.

[0080] In the experiment, the occurrence of streaky fog images in output images was evaluated as follows. Ten A3 solid white images were printed and the number of vertical streaks on the output images was measured. If no vertical streaks were found among the 10 A3 solid white images, 100 A3 solid white images were printed and checked for vertical streaks.

[0081] The results of this experiment are shown in the table in Figure 8. The symbols in the abnormal image column in Figure 8 indicate the results of evaluating the occurrence of streaky fog images, and the meanings of each symbol are as follows: ×: 10 or more vertical streaks were found in one A3 image. △: Approximately one vertical line was found in one A3 image. ○: Approximately one vertical line was found among 10 A3 images. ◎: Approximately one vertical line was found among 100 A3 images. Among the above evaluations, ◯ and ⊚ indicate a level where abnormal images hardly occur in practical use.

[0082] As shown in FIG. 8, in the experiment, the magnetic flux density MB of the first conveying pole 105 in the first developing roller 30 was changed for each condition in studies 1 to 3. As is clear from FIG. 8, by lowering MB, the occurrence of vertical stripe-like fogged images became less likely. In study 2, by applying each value to formulas 1 and 2, the condition that satisfies F1≦F2 in formula 3 was obtained, and the occurrence of vertical stripe-like fogged images in the output image was evaluated as ○ level. Similarly, in study 3, by applying each value to formulas 1 and 2 and then to formula 5, the condition that satisfies F1≦F2' in formula 6 was obtained, and it was confirmed that the occurrence of vertical stripe-like fogged images in the output image became even less likely, and the evaluation was ◎ level.

[0083] In Study 4, by changing the condition of the magnetic flux density MC of the delivery pole 106 in the first developing roller 30, a condition that satisfies F1 ≤ F2 in Equation 3 was obtained, and it was confirmed that the same effect as in Study 2 could be obtained. In Study 5, by changing both the magnetic flux density MB of the first transfer pole 105 and the magnetic flux density MC of the delivery pole 106 in the first developing roller 30, a condition that satisfies F1 ≤ F2' in Equation 6 was obtained, and it was confirmed that, similar to Study 3, the occurrence situation of the vertical streak overlapping image in the output image reaches the level of ◎.

[0084] In the above experiment, the magnetic force of the magnetic flux density MB of the first transfer pole 105 in the first developing roller 30 cannot be decreased indefinitely. If the magnetic force of the magnetic flux density MB of the first transfer pole 105 in the first developing roller 30 is decreased too much, the transportability of the developer on the first developing roller 30 will decrease. Therefore, it is preferable that the magnetic flux density MB maintains a magnitude equal to or greater than the magnetic flux density MC on the delivery pole 106 in the first developing roller 30. In the present embodiment, MA ≥ MB > MC is satisfied.

[0085] Also, regarding the magnetic flux density MC on the delivery pole 106 in the first developing roller 30, if the magnetic force is increased too much, the transfer of the developer with the second developing roller 31 will be difficult to occur. If the magnetic flux density MC on the delivery pole 106 in the first developing roller 30 becomes larger than the magnetic flux density MD on the receiving pole 201 in the second developing roller 31, it will be difficult for the developer to move toward the second developing roller. MD is the absolute value of the maximum value of the magnetic flux density of the receiving pole 201 in the normal direction with respect to the outer peripheral surface of the second sleeve 34. That is, it is the absolute value of the maximum value of the normal component of the magnetic flux density of the receiving pole 201 in the second developing roller 31. Therefore, it is preferable that the magnetic flux density MC on the delivery pole 106 in the first developing roller 30 has a magnetic force equal to or lower than the magnetic force with respect to the magnetic flux density MD on the receiving pole 201 in the second developing roller. In the above experiment, the magnetic flux density MD of the receiving pole 201 in the second developing roller 31 was set to 60 [mT]. That is, in the present embodiment, it is preferable to satisfy MC ≤ MD, and it is more preferable to satisfy MC < MD.

[0086] As described above, according to this embodiment, the occurrence of image defects can be suppressed. That is, in the developing device 1Y of this embodiment, the attractive force F1 between the first conveying pole 105 in the first developing roller 30 and the second conveying pole 202 in the second developing roller 31 is set to be equal to or less than the repulsive force F2 formed by the delivery pole 106 in the first developing roller 30 and the second conveying pole 202 in the second developing roller 31, thereby suppressing the transfer of developer from the second conveying pole 202 to the first conveying pole 105 in the first developing roller 30. This makes it possible to suppress the occurrence of the above-mentioned streaky fog image.

[0087] In particular, even in an image forming apparatus having a high image formation speed (process speed), it is possible to suppress the transfer of developer from the second conveying pole 202 of the second developing roller 31 to the first conveying pole 105 of the first developing roller 30, thereby suppressing the occurrence of the above-mentioned streaky fog image. It is then possible to provide a developing device 1Y and an image forming apparatus 100 that stably circulate the developer from the first developing roller 30 through the second developing roller 31, peeling roller 32, and developer circulating section 46, thereby performing stable image output.

[0088] <Second embodiment> The second embodiment will be described with reference to Figures 9 and 10. This embodiment differs from the first embodiment in the configuration of the magnetic pole of the first transport pole 105 in the first developing roller 30A. 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 similar configurations, and the explanation and illustration will be omitted or simplified. The following description will focus on the points that are different from the first embodiment.

[0089] In this embodiment, the shape of the first transport pole 105 in the first developing roller 30A is changed from that in the first embodiment. Specifically, as shown in Fig. 9, the first transport pole 105 in the first magnet 36A of the first developing roller 30A is configured such that point B, which is the position where the normal component of the magnetic flux density in the first transport pole 105 is maximum, is closer to the first developing pole 104 in the first developing roller 30 than in the first embodiment. The dashed lines in Fig. 9 indicate the position of the maximum value (peak position) of the magnetic flux density in the normal direction of the second sleeve 34 in the second transport pole 202 of the second magnet 37, and the position of the maximum value (peak position) of the magnetic flux density in the normal direction of the first sleeve 33 in the first transport pole 105 and the delivery pole 106 of the first magnet 36A.

[0090] In this way, by moving the position of point B of the first conveying pole 105 closer to the first developing pole 104 side, the linear distance L1 from point A, which is the position on the second sleeve 34 where the maximum value of the normal component of the magnetic flux density of the second conveying pole 202 is located, to point B can be made larger than that in the first embodiment. That is, it is preferable to satisfy L1>L2. Note that, although L1>L2 is also satisfied in the above-mentioned first embodiment, in this embodiment, the difference between L1 and L2 is made larger than that in the first embodiment. When the distance L1 is increased in this way, the value of the attractive force F1 between the first conveying pole 105 in the first developing roller 30A and the second conveying pole 202 in the second developing roller 31 becomes smaller. That is, in this embodiment, the condition F1≦F2 in the above-mentioned formula 3 and further the condition F1≦F2′ in the formula 6 are satisfied by changing the distance L1.

[0091] [experiment] Next, an experiment to investigate the occurrence of streaky fogged images (abnormal images) in the above-mentioned configuration will be described. In the experiment, the above-mentioned distance L1 was varied from the condition of REF, and images were output using image forming apparatuses incorporating developing devices under various conditions of REF, and studies 6 and 7. Then, the occurrence of streaky fogged images on the output images was investigated. Other conditions and experimental evaluations were the same as those in the experiment described in the first embodiment. The results of this experiment are shown in FIG. 10.

[0092] 10, in Study 6, the position of point B was changed to a position of L1=13 mm (at this time, the angle θ between the lines AB and AC was 38°), and similarly to the first embodiment, the attractive force F1 formed by the first transport pole 105 in the first developing roller 30 and the second transport pole 202 in the second developing roller 31 and the repulsive force F2 formed by the delivery pole 106 in the first developing roller 30 and the second transport pole 202 in the second developing roller 31 were derived, and a condition that satisfies F1≦F2 in formula 3 was obtained. It was confirmed that the fog image with vertical streaks in the output image was less likely to occur, and the evaluation was rated as ○ level.

[0093] In Study 7, the position of point B was changed to L1=15 mm (the angle θ between the straight lines AB and AC was 40°) to derive the attractive force F1 formed by the first conveying pole 105 in the first developing roller 30 and the second conveying pole 202 in the second developing roller 31, and the repulsive force F2' formed by the delivery pole 106 in the first developing roller 30 and the second conveying pole 202 in the second developing roller 31, as in the first embodiment, and a condition that satisfies F1≦F2' in formula 6 was obtained. It was confirmed that the occurrence of vertical streak fog images in the output image reached the level of ⊚. In this way, in this embodiment as well, the occurrence of image defects can be suppressed, as in the first embodiment.

[0094] <Third embodiment> The third embodiment will be described with reference to Figures 11 and 12. This embodiment differs from the first embodiment in the configuration of each magnetic pole in the first developing roller 30B. Other configurations and functions are the same as those of the first embodiment described above, so the same reference numerals are used for similar configurations, and explanations and illustrations are omitted or simplified. The following description will focus on the points that are different from the first embodiment.

[0095] In this embodiment, as shown in Figures 11 and 12, the first magnet 36B in the first developing roller 30B has a five-pole magnetic pole configuration in which the first transport pole 105 and the magnetic pole (transport pole) 103 of the first developing roller 30 shown in Figure 3 are omitted. In this case, the first developing pole 104 in the first magnet 36 in Figure 3 is an N pole, but in the first magnet 36B of this embodiment, the first developing pole 104 is an S pole.

[0096] The other magnetic poles 101, 102, 106, and 107 have the same polarity as the magnetic pole of the first magnet 36 in FIG. 3. The magnetic flux density and the position where the normal component of the magnetic flux density at each magnetic pole is maximum (the position of point C at the transfer pole 106) are configured the same as the first developing roller 30 in FIG. 3. The second developing roller 31 has the same internal second magnet 37 as the second developing roller 31 shown in FIG. 4. Therefore, the magnetic flux density and the position where the normal component of the magnetic flux density at each magnetic pole is maximum (the position of point A at the second conveying pole 202) are the same as the second developing roller 31 in FIG. 4. The chain lines shown in FIG. 12 indicate the position (peak position) of the maximum magnetic flux density in the normal direction of the second sleeve 34 at the second conveying pole 202 of the second magnet 37, and the position (peak position) of the maximum magnetic flux density in the normal direction of the first sleeve 33 at the transfer pole 106 of the first magnet 36B.

[0097] In this embodiment, the first developing pole 104 of the first magnet 36B is located adjacent to the upstream side of the delivery pole 106 in the rotation direction of the first sleeve 33. FIG. 12 shows the magnetic characteristics of the first developing roller 30B and the second developing roller 31 of this embodiment employing such a configuration. In this embodiment, the pole that attracts with the second conveying pole 202 of the second developing roller 31 is the first developing pole 104 in the first developing roller 30B. However, the first developing pole 104 in the first developing roller 30B is farther away from the second conveying pole 202 in the second developing roller 31 than in the configuration of the first embodiment. In addition, the photosensitive drum 28Y is located at a position facing the first developing pole 104 in the first developing roller 30B across the first sleeve 33. Since the electrostatic latent image is developed by the developer between the first developing pole 104 and the photosensitive drum 28Y, the developer is unlikely to be transferred between the second conveying pole 202 of the second developing roller 31 and the first developing pole 104 in the first developing roller 30. In this embodiment, too, the occurrence of streaky fog images can be suppressed, as in the first embodiment.

[0098] <Fourth embodiment> The fourth embodiment will be described with reference to Figures 13 to 15. This embodiment differs from the first embodiment in the configurations of the first magnet 36C in the first developing roller 30C and the second magnet 37A in the second developing roller 31A. 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 similar configurations, and explanations and illustrations are omitted or simplified. The following description will focus on the points that are different from the first embodiment.

[0099] The number and polarity of each magnetic pole of the first magnet 36C and the second magnet 37A of this embodiment are the same as those of the first magnet 36 and the second magnet 37 of the first embodiment. However, in this embodiment, the following configuration is satisfied. First, as shown in FIG. 13, the absolute value of the maximum value of the magnetic flux density of the receiving pole 201 in the normal direction to the outer circumferential surface of the second sleeve 34 is MD, and the position on the outer circumferential surface of the second sleeve 34 where the magnetic flux density of the receiving pole 201 in the normal direction to the outer circumferential surface of the second sleeve 34 is maximum is point D. That is, the absolute value of the maximum value of the normal component of the magnetic flux density of the receiving pole 201 in the second developing roller 31A is MD [mT], and the position on the second sleeve 34 of the maximum value is point D. In addition, the straight-line distance between point A and point B is L1, and the straight-line distance between point B and point D is L3. Moreover, the magnetic force acting on the developer in the direction of a straight line AB connecting points A and B between the second transport pole 202 on the second sleeve 34 and the first transport pole 105 on the first sleeve 33 is denoted as F1. Furthermore, the magnetic force acting on the developer in the direction of a straight line BD connecting points B and D between the first transport pole 105 on the first sleeve 33 and the receiving pole 201 on the second sleeve 34 is denoted as F3.

[0100] At this time, the repulsive force F3 acting between the first conveying pole 105 in the first developing roller 30 and the receiving pole 201 in the second developing roller 31A is F3=k×MB×MD / L3 2 ...(Formula 7) Here, k is a coefficient similar to that in the first embodiment. Similarly to the first embodiment, the attractive force F1 can be expressed by the formula 1.

[0101] In order to suppress the transfer of developer between the second transport pole 202 in the second developing roller 31A and the first transport pole 105 in the first developing roller 30 at the first transport pole 105 in the first developing roller 30, it is sufficient that the attractive force F1 between the first transport pole 105 in the first developing roller 30 and the second transport pole 202 in the second developing roller 31A is equal to or smaller than the repulsive force F3 formed by the first transport pole 105 in the first developing roller 30 and the receiving pole 201 in the second developing roller 31A. That is, it is sufficient to satisfy the following relationship with respect to the above-mentioned formulas 1 and 7. F1 ≦ F3 (Formula 8)

[0102] That is, in this embodiment, the magnetic flux densities and arrangements of the first carrier pole 105, the second carrier pole 202, and the receiving pole 201 are set so as to satisfy the formula 8. Specifically, the positions of the above-mentioned MA, MB, MD, point A, point B, and point D are set so as to satisfy the formula 8.

[0103] 14 shows the relationship between the force component F3' of the repulsive force F3 in the direction of the line AB and the attractive force F1 described above. If the angle between the lines AB and BD is θ', the point on the line AB when a perpendicular line is drawn from point D to the line AB is D', and the linear distance between point B and point D' is L3', then L3' can be expressed by the following formula. L3´=L3×cosθ´ (Formula 9)

[0104] To cancel the attractive force F1 that the first transport pole 105 in the first developing roller receives from the second transport pole 202 in the second developing roller 31, it is desirable that the repulsive force F3' in the direction of the straight line BD' between the receiving pole 201 in the second developing roller 31 and the first transport pole 105 in the first developing roller 30 be greater than or equal to the attractive force F1. F3' is the force component of F3 in the direction of the straight line AB, and can be expressed by the following formula. F3´=F3×cosθ´ (Formula 10) In order for the repulsive force F3' to cancel out the attractive force F1, it is desirable that the following relationship be established. F1≦F3´ (Formula 11)

[0105] That is, in this embodiment, it is preferable to further satisfy formula 11, and it is preferable to set the magnetic flux density and arrangement of the first carrier pole 105, the second carrier pole 202, and the receiving pole 201 so as to satisfy formula 11. Specifically, it is preferable to set the positions of the above-mentioned MA, MB, MD, point A, point B, and point D so as to satisfy formula 11. Formula 11 can also be expressed by the following formula. MA / L1 2 ≦(MD / L3 2 )×cosθ´

[0106] [experiment] Next, an experiment to investigate the occurrence of streaky fogged images (abnormal images) in the above-mentioned configuration will be described. In the experiment, the magnetic flux density MA of the second conveying pole 202 in the second developing roller 31A, the magnetic flux density MB of the first conveying pole 105 in the first developing roller 30C, and the magnetic flux density MD of the receiving pole 201 in the second developing roller 30A were varied starting from the condition of REF, and images were output using an image forming apparatus incorporating developing devices under various conditions of REF and studies 8 to 12. Then, the occurrence of streaky fogged images on the output images was investigated.

[0107] In the experiment, the positions of point A where the magnetic flux density on the second transport pole 202 in the first developing roller 31A is maximum, point B where the magnetic flux density of the first transport pole 105 in the first developing roller 30C is maximum, and point D where the magnetic flux density of the receiving pole 201 in the second developing roller 31A is maximum were not changed. That is, L1 and L3 were fixed. Also, the angle θ' between the straight lines AB and BD was set to 40°. The other conditions and the evaluation of the experiment were the same as those of the experiment described in the first embodiment. The results of this experiment are shown in FIG. 15.

[0108] As shown in FIG. 15, in the experiment, the magnetic flux density MA of the second conveying pole 202 in the second developing roller 31A was changed in studies 8 to 10. As is clear from FIG. 15, by lowering MA, the occurrence of vertical streak-like fogged images became less likely. In study 9, by applying each value to formulas 1 and 7, the condition that satisfies F1≦F3 in formula 8 was obtained, and the occurrence of vertical streak-like fogged images in the output image was evaluated as ○ level. Similarly, in study 10, by applying each value to formulas 1 and 7 and then to formula 10, the condition that satisfies F1≦F3' in formula 11 was obtained, and it was confirmed that the occurrence of vertical streak-like fogged images in the output image became even less likely, and the evaluation was ◎ level.

[0109] In Study 11, it was confirmed that by changing the condition of the magnetic flux density MD of the receiving pole 201 in the second developing roller 31A, the condition that satisfies F1≦F3 in formula 8 could be obtained, and an effect similar to that of Study 9 could be obtained. In Study 12, by changing both the magnetic flux density MA of the second conveying pole 202 in the second developing roller 31A and the magnetic flux density MD of the receiving pole 201 in the second developing roller 31A, the condition that satisfies F1≦F3' in formula 11 could be obtained, and it was confirmed that, as in Study 10, the occurrence of vertical streak fog images in the output image reached the level of ⊚.

[0110] In the above experiment, the magnetic flux density MA of the second transport pole 202 in the second developing roller 31A cannot be reduced indefinitely. If the magnetic flux density MA of the second transport pole 202 in the second developing roller 31A is reduced too much, the transportability of the developer on the second developing roller 31A will decrease. For this reason, it is preferable to maintain the magnetic flux density MA at a value equal to or greater than the magnetic flux density MD of the receiving pole 201 in the second developing roller 31A. In this embodiment, the relationship MB≧MA>MD is satisfied.

[0111] Also, regarding the magnetic flux density MD of the receiving pole 201 in the second developing roller 31A, if the magnetic force is increased too much, the transportability of the developer on the second developing roller 31A will decrease. If the magnetic flux density MD on the receiving pole 201 in the second developing roller 31A becomes larger than the magnetic flux density MA on the second transport pole 202 in the second developing roller 31A, it will be difficult for the developer to move downstream in the rotation direction of the second sleeve 34. Therefore, it is preferable that the magnetic flux density MD on the receiving pole 201 in the second developing roller 31A has a magnetic force equal to or lower than that of the magnetic flux density MA on the second transport pole 202 in the second developing roller 31A. That is, in the present embodiment, it is preferable to satisfy MD≦MA, and more preferably to satisfy MD<MA.

[0112] As described above, according to the present embodiment, the occurrence of image defects can be suppressed. That is, in the developing device 1Y of the present embodiment, by making the attractive force F1 between the first transport pole 105 in the first developing roller 30C and the second transport pole 202 in the second developing roller 31A equal to or less than the repulsive force F3 composed of the first transport pole 105 in the first developing roller 30C and the receiving pole 201 in the second developing roller 31A, the transfer of the developer from the second transport pole 202 to the first transport pole 105 in the first developing roller 30C can be suppressed. Therefore, the occurrence of the streak-like fogging image described above can be suppressed.

[0113] <The Fifth Embodiment> The fifth embodiment will be described with reference to FIGS. 16 and 17. In this embodiment, the configuration of the magnetic poles of the second transport pole 202 in the second developing roller 31B is different from that of the fourth embodiment. Since the other configurations and operations are the same as those of the above-described fourth embodiment, the same reference numerals are given to the same configurations, and the description and illustration are omitted or simplified. Hereinafter, the differences from the fourth embodiment will be mainly described.

[0114] In this embodiment, the shape of the second transport pole 202 in the second developing roller 31B is changed from that in the fourth embodiment. Specifically, as shown in Fig. 16, the second transport pole 202 of the second magnet 37B of the second developing roller 31B is configured such that point A, which is the position where the normal component of the magnetic flux density in the second transport pole 202 is maximum, is closer to the second developing pole 203 in the second developing roller 31B than in the fourth embodiment. The dashed lines in Fig. 16 indicate the positions (peak positions) of the maximum magnetic flux density in the normal direction of the second sleeve 34 in the receiving pole 201 and second transport pole 202 of the second magnet 37B, and the positions (peak positions) of the maximum magnetic flux density in the normal direction of the first sleeve 33 in the first transport pole 105 of the first magnet 36C.

[0115] By moving the position of point A of the second conveying pole 202 closer to the second developing pole 203 in this way, the linear distance L1 from point B, which is the position on the first sleeve 33 where the maximum value of the normal component of the magnetic flux density of the first conveying pole 105 is located, to point A can be made larger than that in the fourth embodiment. That is, it is preferable to satisfy L1>L3. Note that, although L1>L3 is also satisfied in the above-mentioned fourth embodiment, in this embodiment, the difference between L1 and L3 is made larger than that in the fourth embodiment. When the distance L1 is increased in this way, the value of the attractive force F1 between the first conveying pole 105 in the first developing roller 30C and the second conveying pole 202 in the second developing roller 31B becomes smaller. That is, in this embodiment, the condition F1≦F3 in the above-mentioned formula 8 and further the condition F1≦F3′ in the formula 11 are satisfied by changing the distance L1.

[0116] [experiment] Next, an experiment to investigate the occurrence of streaky fogged images (abnormal images) in the above-mentioned configuration will be described. In the experiment, the above-mentioned distance L1 was varied from the condition of REF, and images were output using an image forming apparatus incorporating developing devices under various conditions of REF and studies 13 and 14. Then, the occurrence of streaky fogged images on the output images was investigated. Other conditions and the evaluation of the experiment were the same as those of the experiment described in the first embodiment. The results of this experiment are shown in FIG. 17.

[0117] 17, in Study 13, the position of point A was changed to a position of L1=11 mm (at this time, the angle θ' between the lines AB and BD was 44°), and similarly to the fourth embodiment, the attractive force F1 formed by the first transport pole 105 in the first developing roller 30C and the second transport pole 202 in the second developing roller 31B, and the repulsive force F3 formed by the first transport pole 105 in the first developing roller 3C0 and the receiving pole 201 in the second developing roller 31B were derived, and a condition that satisfies F1≦F3 in formula 8 was obtained. It was confirmed that the fog image with vertical streaks in the output image was less likely to occur, and the evaluation was rated as ○ level.

[0118] In Study 14, the position of point A was changed to L1=13 mm (the angle θ' between the straight lines AB and BD was 49°) to derive the attractive force F1 formed by the first conveying pole 105 in the first developing roller 30C and the second conveying pole 202 in the second developing roller 31B, and the repulsive force F3' formed by the first conveying pole 105 in the first developing roller 30C and the receiving pole 201 in the second developing roller 31B, as in the fourth embodiment, and a condition that satisfies F1≦F3' in formula 11 was obtained. It was confirmed that the occurrence of vertical streak fog images in the output image reached the level of ⊚. In this way, in this embodiment as well, as in the fourth embodiment, the occurrence of image defects can be suppressed.

[0119] Sixth embodiment The sixth embodiment will be described with reference to Figures 18 and 19. This embodiment differs from the fourth embodiment in the configuration of each magnetic pole in the second developing roller 31C. Since the other configurations and functions are the same as those of the fourth embodiment described above, the same reference numerals are used for the similar configurations, and the description and illustrations are omitted or simplified. The following description will focus on the points that are different from the fourth embodiment.

[0120] In this embodiment, as shown in Figures 18 and 19, the second magnet 37C in the second developing roller 31C has a five-pole magnetic pole configuration in which the second transport pole 202 and the magnetic pole (transport pole) 204 of the second developing roller 31 shown in Figure 4 are omitted. In this case, the second developing pole 203 in the second magnet 37 in Figure 4 is an S pole, but in the second magnet 37C of this embodiment, the second developing pole 203 is an N pole.

[0121] The other magnetic poles 201, 205, 206, and 207 have the same polarity as the magnetic pole of the second magnet 37 in FIG. 4. The magnetic flux density and the position where the normal component of the magnetic flux density at each magnetic pole is maximum (the position of point D at the receiving pole 201) are configured the same as the second developing roller 31 in FIG. 4. The first developing roller 30C has the same internal first magnet 36C as the first developing roller 30C shown in FIG. 13. Therefore, the magnetic flux density and the position where the normal component of the magnetic flux density at each magnetic pole is maximum (the position of point B at the first conveying pole 105) are the same as the first developing roller 30C in FIG. 13. In addition, the dotted lines shown in Figure 19 indicate the position of the maximum value (peak position) of the magnetic flux density in the normal direction of the second sleeve 34 at the receiving pole 201 of the second magnet 37C, and the position of the maximum value (peak position) of the magnetic flux density in the normal direction of the first sleeve 33 at the first conveying pole 105 of the first magnet 36C.

[0122] In this embodiment, the second developing pole 203 of the second magnet 37C is located adjacent to the downstream side of the receiving pole 201 in the rotation direction of the second sleeve 34. FIG. 19 shows the magnetic characteristics of the first developing roller 30C and the second developing roller 31C of this embodiment employing such a configuration. In this embodiment, the pole that attracts with the first conveying pole 105 in the first developing roller 30C is the second developing pole 203 in the second developing roller 31C. However, the second developing pole 203 in the second developing roller 31C is farther away from the first conveying pole 105 in the first developing roller 30 than in the fourth embodiment. In addition, the photosensitive drum 28Y is located at a position facing the second developing pole 203 in the second developing roller 31C across the second sleeve 34. Since the electrostatic latent image is developed by the developer between the second developing pole 203 and the photosensitive drum 28Y, the transfer of the developer between the first conveying pole 105 in the first developing roller 30C and the second developing pole 203 in the second developing roller 31C is unlikely to occur. In this embodiment, too, the occurrence of streaky fog images can be suppressed, as in the fourth embodiment.

[0123] <Other embodiments> The above-mentioned first, second and third embodiments have the effect of suppressing vertical streak images that occur during developer transfer between the first transport pole 105 in the first developing roller 30, 30A and 30B and the second transport pole 202 in the second developing roller 31, due to the relationship between the repulsive force F2 formed by the delivery pole 106 in the first developing roller 30, 30A and 30B and the second transport pole 202 in the second developing roller 31, and the attractive force F1 formed by the first transport pole 105 in the first developing roller 30, 30A and 30B and the second transport pole 202 in the second developing roller 31. On the other hand, the above-mentioned fourth, fifth and sixth embodiments have the effect of suppressing vertical stripe images that occur during developer transfer between the first transport pole 105 in the first developing roller 30C and the second transport pole 202 in the second developing roller 31A, 31B and 31C due to the relationship between the repulsive force F3 formed by the receiving pole 201 in the second developing roller 31A, 31B and 31C and the first transport pole 105 in the first developing roller 30C, and the attractive force F1 formed by the first transport pole 105 in the first developing roller 30C and the second transport pole 202 in the second developing roller 31A, 31B and 31C. By combining such first, second and third embodiments with any of the fourth, fifth and sixth embodiments, the effect of suppressing vertical stripe fog images can be further enhanced. That is, by configuring the first and second developing rollers to satisfy the condition of the formula 8 or 11 in addition to the condition of the formula 3 or 6, the occurrence of image defects can be further suppressed.

[0124] The present invention is not limited to the configurations of the above-mentioned embodiments. For example, the image forming apparatus 100 is not limited to an MFP, and may be a copier, a printer, or a facsimile machine. In addition, the configurations of the developer supply screw 42, the developer stirring screw 43, and the developer recovery screw 44 are not particularly limited as long as they can transport the developer, and for example, a spiral blade or a paddle-shaped blade can be applied.

[0125] In the above embodiment, the first sleeve 33 and the photosensitive drum 28Y rotate in the same direction at positions facing each other, and the second sleeve 34 and the photosensitive drum 28Y rotate in the same direction at positions facing each other, but the present invention is not limited to this. The rotation center O2 of the second developing roller 31 may be disposed vertically above the rotation center O1 of the first developing roller 30, and the first sleeve 33 and the photosensitive drum 28Y may rotate in opposite directions at positions facing each other, and the second sleeve 34 and the photosensitive drum 28Y may rotate in opposite directions at positions facing each other. That is, the photosensitive drum 28 may rotate from the upper side in the vertical direction to the lower side in the vertical direction at a position facing the first developing roller 30, and the photosensitive drum 28 may rotate from the upper side in the vertical direction to the lower side in the vertical direction at a position facing the second developing roller 31. The present invention may be applied to such a configuration. Furthermore, in the case where three or more developing rollers are provided, the present invention can be applied to any two of the developing rollers. [Explanation of symbols]

[0126] 1Y, 1M, 1C, 1K... Developing device 33...First sleeve 34...Second sleeve 36, 36A, 36B, 36C...1st magnet 37, 37A, 37B, 37C...Second magnet 60...Developing container 104...First developing pole 105 1st conveying pole (1st magnetic pole) 106... Delivery pole 201 Receiving pole 202 Second carrying pole (second magnetic pole) 203...Second developing pole

Claims

1. a developer container that contains a developer including a toner and a carrier; a first rotating body to which the developer contained in the developing container is supplied, the first rotating body carrying and transporting the developer to a first developing position where an electrostatic latent image formed on an image carrier is developed; a first magnet disposed inside the first rotor in a non-rotatable and fixed manner, the first magnet having a first developing pole disposed facing the image carrier at the first developing position, a delivery pole disposed downstream of the first developing pole in a rotational direction of the first rotor, and a first transport pole disposed upstream of the delivery pole in the rotational direction of the first rotor adjacent to the delivery pole and having a polarity different from that of the delivery pole; a second rotating body that is disposed opposite to 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 carrying and transporting the developer to a second developing position where the electrostatic latent image is developed; a second magnet disposed inside the second rotating body so as to be fixed and non-rotatable, the second magnet having a plurality of magnetic poles including a second developing pole disposed facing the image carrier at the second developing position, a receiving pole disposed upstream of the second developing pole in the rotational direction of the second rotating body and having a polarity different from that of the delivery pole, and a second transport pole disposed downstream of the receiving pole in the rotational direction of the second rotating body so as to be adjacent to the receiving pole and having a polarity different from that of the receiving pole; Equipped with a rotation direction of the second rotating body at a position on the outer surface of the second rotating body where the second rotating body is closest to the first rotating body is opposite to a rotation direction of the first rotating body at a position on the outer surface of the first rotating body where the first rotating body is closest to the second rotating body, The receiving pole is a magnetic pole that is disposed closest to the transferring pole among the plurality of magnetic poles of the second magnet, The absolute value of the maximum magnetic flux density of the second conveying pole in a normal direction to the outer circumferential surface of the second rotating body is defined as MA, a position on the outer circumferential surface of the second rotor at which the magnetic flux density of the second conveying pole in a normal direction to the outer circumferential surface of the second rotor is maximized is defined as point A; an absolute value of a maximum value of the magnetic flux density of the first conveying pole in a normal direction to an outer circumferential surface of the first rotating body is defined as MB; a position on the outer circumferential surface of the first rotor at which the magnetic flux density of the first conveying pole in a normal direction to the outer circumferential surface of the first rotor is maximized is defined as point B; an absolute value of a maximum value of the magnetic flux density of the delivery pole in a normal direction to an outer circumferential surface of the first rotor is defined as MC; A position on the outer circumferential surface of the first rotor at which the magnetic flux density of the delivery pole in a normal direction to the outer circumferential surface of the first rotor is maximized is defined as point C, The straight-line distance between point A and point B is L1, The straight-line distance between point A and point C is L2, If the angle between the line AB connecting the point A and the point B and the line AC connecting the point A and the point C is θ, <h2 style=";text-align:left;direction:ltr">111<h2 style=";text-align:left;direction:ltr"> ２ <h2 style=";text-align:left;direction:ltr"> ≦(MC / L2<h2 style=";text-align:left;direction:ltr"> ２ <h2 style=";text-align:left;direction:ltr"> )×cosθ A developing device characterized by satisfying the above.

2. MA≧MB>MC 2. The developing device according to claim 1, further comprising:

3. When the absolute value of the maximum value of the magnetic flux density of the receiving pole in the normal direction to the outer circumferential surface of the second rotor is defined as MD, MC≦MD 2. The developing device according to claim 1, further comprising:

4. When the absolute value of the maximum value of the magnetic flux density of the receiving pole in the normal direction to the outer circumferential surface of the second rotor is defined as MD, MC < MD 2. The developing device according to claim 1, further comprising:

5. L1>L2 2. The developing device according to claim 1, further comprising:

6. an absolute value of a maximum value of the magnetic flux density of the receiving pole in a normal direction to an outer circumferential surface of the second rotor is defined as MD; A position on the outer circumferential surface of the second rotor at which the magnetic flux density of the receiving pole in a normal direction to the outer circumferential surface of the second rotor is maximized is defined as point D, The straight-line distance between point B and point D is L3, If the angle between the line AB connecting the point A and the point B and the line BD connecting the point B and the point D is θ', <h2 style=";text-align:left;direction:ltr">MA / L1<h2 style=";text-align:left;direction:ltr"> ２ <h2 style=";text-align:left;direction:ltr"> ≦(MD / L3<h2 style=";text-align:left;direction:ltr"> ２ <h2 style=";text-align:left;direction:ltr"> )×cosθ´ 2. The developing device according to claim 1, further comprising:

7. MB≧MA>MD 7. The developing device according to claim 6, further comprising:

8. M.D.≦M.A.

7. The developing device according to claim 6, further comprising:

9. MD < MA 7. The developing device according to claim 6, further comprising:

10. L1>L3 7. The developing device according to claim 6, further comprising:

11. a developer container that contains a developer including a toner and a carrier; a first rotating body to which the developer contained in the developing container is supplied, the first rotating body carrying and transporting the developer to a first developing position where an electrostatic latent image formed on an image carrier is developed; a first magnet disposed inside the first rotor in a non-rotatable and fixed manner, the first magnet having a first developing pole disposed facing the image carrier at the first developing position, a delivery pole disposed downstream of the first developing pole in a rotational direction of the first rotor, and a first transport pole disposed upstream of the delivery pole in the rotational direction of the first rotor adjacent to the delivery pole and having a polarity different from that of the delivery pole; a second rotating body that is disposed opposite to 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 carrying and transporting the developer to a second developing position where the electrostatic latent image is developed; a second magnet disposed inside the second rotating body so as to be fixed and non-rotatable, the second magnet having a plurality of magnetic poles including a second developing pole disposed facing the image carrier at the second developing position, a receiving pole disposed upstream of the second developing pole in the rotational direction of the second rotating body and having a polarity different from that of the delivery pole, and a second transport pole disposed downstream of the receiving pole in the rotational direction of the second rotating body so as to be adjacent to the receiving pole and having a polarity different from that of the receiving pole; Equipped with a rotation direction of the second rotating body at a position on the outer surface of the second rotating body where the second rotating body is closest to the first rotating body is opposite to a rotation direction of the first rotating body at a position on the outer surface of the first rotating body where the first rotating body is closest to the second rotating body, The receiving pole is a magnetic pole that is disposed closest to the transferring pole among the plurality of magnetic poles of the second magnet, The absolute value of the maximum magnetic flux density of the second conveying pole in a normal direction to the outer circumferential surface of the second rotating body is defined as MA, a position on the outer circumferential surface of the second rotor at which the magnetic flux density of the second conveying pole in a normal direction to the outer circumferential surface of the second rotor is maximized is defined as point A; an absolute value of a maximum value of the magnetic flux density of the first conveying pole in a normal direction to an outer circumferential surface of the first rotating body is defined as MB; a position on the outer circumferential surface of the first rotor at which the magnetic flux density of the first conveying pole in a normal direction to the outer circumferential surface of the first rotor is maximized is defined as point B; an absolute value of a maximum value of the magnetic flux density of the receiving pole in a normal direction to an outer circumferential surface of the second rotor is defined as MD; A position on the outer circumferential surface of the second rotor at which the magnetic flux density of the receiving pole in a normal direction to the outer circumferential surface of the second rotor is maximized is defined as point D, The straight-line distance between point A and point B is L1, The straight-line distance between point B and point D is L3, If the angle between the line AB connecting the point A and the point B and the line BD connecting the point B and the point D is θ', <h2 style=";text-align:left;direction:ltr">MA / L1<h2 style=";text-align:left;direction:ltr"> ２ <h2 style=";text-align:left;direction:ltr"> ≦(MD / L3<h2 style=";text-align:left;direction:ltr"> ２ <h2 style=";text-align:left;direction:ltr"> )×cosθ´ A developing device characterized by satisfying the above.

12. MB≧MA>MD 12. The developing device according to claim 11, further comprising:

13. M.D.≦M.A.

12. The developing device according to claim 11, further comprising:

14. MD < MA 12. The developing device according to claim 11, further comprising:

15. L1>L3 12. The developing device according to claim 11, further comprising:

16. a developer container that contains a developer including a toner and a carrier; a first rotating body to which the developer contained in the developing container is supplied, the first rotating body carrying and transporting the developer to a first developing position where an electrostatic latent image formed on an image carrier is developed; a first magnet that is fixedly disposed inside the first rotating body and non-rotatably, the first magnet having a first developing pole that is disposed facing the image carrier at the first developing position, and a transfer pole that is disposed adjacent to the first developing pole downstream of the first developing pole in the rotational direction of the first rotating body and has a polarity different from that of the first developing pole; a second rotating body that is disposed opposite to 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 carrying and transporting the developer to a second developing position where the electrostatic latent image is developed; a second magnet disposed inside the second rotating body so as to be fixed and non-rotatable, the second magnet having a plurality of magnetic poles including a second developing pole disposed facing the image carrier at the second developing position, a receiving pole disposed upstream of the second developing pole in the rotational direction of the second rotating body and having a polarity different from that of the delivery pole, and a transport pole disposed downstream of the receiving pole in the rotational direction of the second rotating body so as to be adjacent to the receiving pole and having a polarity different from that of the receiving pole; Equipped with a rotation direction of the second rotating body at a position on the outer surface of the second rotating body where the second rotating body is closest to the first rotating body is opposite to a rotation direction of the first rotating body at a position on the outer surface of the first rotating body where the first rotating body is closest to the second rotating body, The receiving pole is the magnetic pole that is disposed closest to the passing pole among the plurality of magnetic poles of the second magnet. A developing device characterized by the above.

17. a developer container that contains a developer including a toner and a carrier; a first rotating body to which the developer contained in the developing container is supplied, the first rotating body carrying and transporting the developer to a first developing position where an electrostatic latent image formed on an image carrier is developed; a first magnet disposed inside the first rotor in a non-rotatable and fixed manner, the first magnet having a first developing pole disposed facing the image carrier at the first developing position, a delivery pole disposed downstream of the first developing pole in a rotational direction of the first rotor, and a transport pole disposed upstream of the delivery pole in the rotational direction of the first rotor adjacent to the delivery pole and having a polarity different from that of the delivery pole; a second rotating body that is disposed opposite to 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 carrying and transporting the developer to a second developing position where the electrostatic latent image is developed; a second magnet disposed inside the second rotating body so as to be fixed and non-rotatable, the second magnet having a plurality of magnetic poles including a second developing pole disposed facing the image carrier at the second developing position, and a receiving pole disposed adjacent to the second developing pole upstream of the second developing pole in the rotational direction of the second rotating body, the receiving pole having a polarity different from that of the second developing pole and a polarity different from that of the delivery pole; Equipped with a rotation direction of the second rotating body at a position on the outer surface of the second rotating body where the second rotating body is closest to the first rotating body is opposite to a rotation direction of the first rotating body at a position on the outer surface of the first rotating body where the first rotating body is closest to the second rotating body, The receiving pole is the magnetic pole that is disposed closest to the passing pole among the plurality of magnetic poles of the second magnet. A developing device characterized by the above.

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