Developing device

Abstract

The invention relates to a developing device. The maximum magnetic flux density position of the second feeding pole is a point A, the absolute value of the maximum value of the magnetic flux density of the first feeding pole is MB, the maximum magnetic flux density position of the first feeding pole is a point B, the absolute value of the maximum value of the magnetic flux density of the conveying pole is MC, the maximum magnetic flux density position of the conveying pole is a point C, and the linear distance between the point A and the point B is L1. The following relationship is satisfied: MB / L12 < = (MC / L22) * cos [theta], where MB represents a linear distance between the point A and the point C, L2 represents a linear distance between the point A and the point C, and [theta] represents an angle formed by a straight line AB connecting the point A and the point B and a straight line AC connecting the point A and the point C.

Description

Technical Field

[0001] The present invention relates to a developing device for developing an electrostatic latent image formed on an image bearing member using a developer. Background Art

[0002] As a developing device, a configuration is proposed in which two developing rollers are arranged side by side with respect to the rotation direction of an image bearing member, the developing rollers being used to develop an electrostatic latent image formed on the image bearing member with a developer (U.S. Patent Application Publication No. 2013 / 0330107). In the developing device disclosed in US2013 / 0330107A1, of the two developing rollers, the developer is supplied from a supply portion to a first developing roller positioned at a lower portion in the vertical direction, and the developer is conveyed from the first developing roller positioned at the lower portion to a second developing roller positioned at an upper portion in the vertical direction.

[0003] As disclosed in US2013 / 0330107A1, in the case where the developer is conveyed from the first developing roller to the second developing roller positioned at the upper portion in the vertical direction, the developer is conveyed by a magnetic field formed between a conveying pole of a first magnet provided in the first developing roller and a receiving pole of a second magnet provided in the second developing roller. The polarity of the conveying pole is opposite to that of the receiving pole. In this configuration, when the rotation direction of the second developing roller is opposite to that of the first developing roller at a position where the second developing roller is opposite to that of the first developing roller, the polarity of the first magnetic pole adjacent to the conveying pole on the upstream side of the conveying pole is opposite to the polarity of the second magnetic pole adjacent to the receiving pole on the downstream side of the receiving pole. Therefore, between the first magnetic pole and the second magnetic pole, a magnetic field for attracting the developer to each roller is generated.

[0004] Therefore, a magnetic field for attracting the developer is generated between the first magnetic pole and the second magnetic pole, and there is a possibility that the developer movement is generated between the first magnetic pole and the second magnetic pole by the magnetic field. In addition, when the developer movement is generated between the first magnetic pole and the second magnetic pole, there is a possibility that the moved developer floats and then deposits on the image bearing member positioned near the first developing roller and the second developing roller. Therefore, when the developer is deposited on the image bearing member, an image defect such as vertical streak-like fog appears on the output image. Summary of the invention

[0005] A main object of the present invention is to provide a developing device capable of suppressing the occurrence of image defects.

[0006] According to one aspect of the present invention, there is provided a developing device, comprising: a developing container configured to accommodate a developer including a toner and a carrier; a first rotatable member to which the developer accommodated in the developing container is supplied, and the first rotatable member carries and feeds the developer to a first developing position, at which an electrostatic latent image formed on an image bearing member is developed; a first magnet, the first magnet being non-rotatably and fixedly disposed in the first rotatable member, wherein the first magnet comprises a first developing pole disposed opposite to the image bearing member at the first developing position, a conveying pole disposed downstream of the first developing pole with respect to a rotation direction of the first rotatable member, and a first magnet disposed at the first developing position with respect to a rotation direction of the first rotatable member. a first feeding pole upstream of the transport pole and adjacent to the transport pole, and the first feeding pole has a magnetic polarity different from that of the transport pole; a second rotatable member, the second rotatable member being disposed opposite to the first rotatable member and transporting a developer from the first rotatable member to the second rotatable member by a magnetic field generated by the first magnet, wherein the second rotatable member carries and feeds the developer to a second developing position for developing an electrostatic latent image, and wherein a rotation direction of the second rotatable member at a position on the outer peripheral surface of the second rotatable member at which the second rotatable member is closest to the first rotatable member is opposite to a rotation direction of the first rotatable member at a position on the outer peripheral surface of the first rotatable member at which the first rotatable member is closest to the second rotatable member;and a second magnet which is non-rotatably and fixedly disposed in the second rotatable member, wherein the second magnet includes a plurality of magnetic poles, the plurality of magnetic poles including a second developing pole disposed opposite to the image bearing member at the second developing position, a receiving pole disposed upstream of the second developing pole with respect to the rotational direction of the second rotatable member and having a magnetic polarity different from that of the conveying pole, and a second feeding pole disposed downstream of the receiving pole with respect to the rotational direction of the second rotatable member and adjacent to the receiving pole and having a magnetic polarity different from that of the receiving pole, the receiving pole being a magnetic pole disposed closest to the conveying pole among the plurality of magnetic poles, wherein in the following case: the absolute value of the maximum value of the magnetic flux density of the second feeding pole in the normal direction relative to the outer peripheral surface of the second rotatable member is MA, and the maximum value of the magnetic flux density of the second feeding pole in the normal direction relative to the second rotatable member on the outer peripheral surface of the second rotatable member is . The position where the magnetic flux density in the normal direction of the outer peripheral surface of the rotating member is the largest is point A, the absolute value of the maximum value of the magnetic flux density of the first feed pole in the normal direction relative to the outer peripheral surface of the first rotatable member is MB, the position where the magnetic flux density of the first feed pole in the normal direction relative to the outer peripheral surface of the first rotatable member is the largest on the outer peripheral surface of the first rotatable member is point B, the absolute value of the maximum value of the magnetic flux density of the conveying pole in the normal direction relative to the outer peripheral surface of the first rotatable member is MC, the position where the magnetic flux density of the conveying pole in the normal direction relative to the outer peripheral surface of the first rotatable member is the largest on the outer peripheral surface of the first rotatable member is 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, and the angle formed by the straight line AB connecting point A and point B and the straight line AC connecting point A and point C is θ, satisfying the following relationship: MB / L1; 2 ≤(MC / L2 2 )×cosθ.

[0007] According to another aspect of the present invention, there is provided a developing device, comprising: a developing container configured to accommodate a developer including a toner and a carrier; a first rotatable member to which the developer accommodated in the developing container is supplied, and the first rotatable member carries and feeds the developer to a first developing position, at which an electrostatic latent image formed on an image bearing member is developed; a first magnet, the first magnet being non-rotatably and fixedly disposed in the first rotatable member, wherein the first magnet comprises a first developing pole disposed opposite to the image bearing member at the first developing position, a conveying pole disposed downstream of the first developing pole with respect to a rotation direction of the first rotatable member, and a first magnet disposed at the first developing pole with respect to a rotation direction of the first rotatable member. a first feeding pole upstream of the transport pole and adjacent to the transport pole, and the first feeding pole has a magnetic polarity different from that of the transport pole; a second rotatable member, the second rotatable member being disposed opposite to the first rotatable member and transporting a developer from the first rotatable member to the second rotatable member by a magnetic field generated by the first magnet, wherein the second rotatable member carries and feeds the developer to a second developing position for developing an electrostatic latent image, and wherein a rotation direction of the second rotatable member at a position on the outer peripheral surface of the second rotatable member at which the second rotatable member is closest to the first rotatable member is opposite to a rotation direction of the first rotatable member at a position on the outer peripheral surface of the first rotatable member at which the first rotatable member is closest to the second rotatable member;and a second magnet which is non-rotatably and fixedly disposed in the second rotatable member, wherein the second magnet includes a plurality of magnetic poles, the plurality of magnetic poles including a second developing pole disposed opposite to the image bearing member at the second developing position, a receiving pole disposed upstream of the second developing pole with respect to the rotational direction of the second rotatable member and having a magnetic polarity different from that of the conveying pole, and a second feeding pole disposed downstream of the receiving pole with respect to the rotational direction of the second rotatable member and adjacent to the receiving pole and having a magnetic polarity different from that of the receiving pole, the receiving pole being a magnetic pole disposed closest to the conveying pole among the plurality of magnetic poles, wherein in the following case: the absolute value of the maximum value of the magnetic flux density of the second feeding pole in the normal direction relative to the outer peripheral surface of the second rotatable member is MA, and the maximum value of the magnetic flux density of the second feeding pole in the normal direction relative to the outer peripheral surface of the second rotatable member is 0. The position where the magnetic flux density in the normal direction of the outer peripheral surface of the first rotatable member is the largest is point A, the absolute value of the maximum value of the magnetic flux density of the first feed pole in the normal direction relative to the outer peripheral surface of the first rotatable member is MB, the position where the magnetic flux density of the first feed pole in the normal direction relative to the outer peripheral surface of the first rotatable member is the largest is point B on the outer peripheral surface of the first rotatable member, the absolute value of the maximum value of the magnetic flux density of the receiving pole in the normal direction relative to the outer peripheral surface of the second rotatable member is MD, the position where the magnetic flux density of the receiving pole in the normal direction relative to the outer peripheral surface of the second rotatable member is the largest is point D on the outer peripheral surface of the second rotatable member, the straight line distance between point A and point B is L1, the straight line distance between point B and point D is L3, and the angle formed by the straight line AB connecting point A and point B and the straight line BD connecting point B and point D is θ', which satisfies the following relationship: MA / L1; 2 ≤(MD / L3 2 )×cosθ'.

[0008] According to another aspect of the present invention, there is provided a developing device, comprising: a developing container configured to contain a developer including a toner and a carrier; a first rotatable member to which the developer contained in the developing container is supplied, and the first rotatable member carries and feeds the developer to a first developing position at which an electrostatic latent image formed on an image bearing member is developed; a first magnet non-rotatably and fixedly disposed in the first rotatable member, wherein the first magnet comprises a first developing pole disposed opposite to the image bearing member at the first developing position, and a conveying pole having a magnetic polarity different from that of the conveying pole and disposed downstream of the first developing pole with respect to a rotation direction of the first rotatable member and adjacent to the conveying pole; and a second rotatable member disposed opposite to the first rotatable member and conveying the developer from the first rotatable member to the second rotatable member by a magnetic field generated by the first magnet, wherein the second rotatable member carries the developer The invention relates to a second developing position for carrying and feeding an electrostatic latent image, wherein the second rotatable member at a position on the outer peripheral surface of the second rotatable member at which the second rotatable member is closest to the first rotatable member rotates in a direction opposite to the direction of rotation of the first rotatable member at a position on the outer peripheral surface of the first rotatable member at which the first rotatable member is closest to the second rotatable member; and a second magnet, which is non-rotatably and fixedly arranged in the second rotatable member, wherein the second magnet includes a plurality of magnetic poles, the plurality of magnetic poles including a second developing pole arranged opposite to the image bearing member at the second developing position, a receiving pole arranged upstream of the second developing pole with respect to the rotation direction of the second rotatable member and having a magnetic polarity different from that of the conveying pole, and a feeding pole arranged downstream of the receiving pole with respect to the rotation direction of the second rotatable member and adjacent to the receiving pole and having a magnetic polarity different from that of the receiving pole, the receiving pole being a magnetic pole arranged closest to the conveying pole among the plurality of magnetic poles.

[0009] According to another aspect of the present invention, there is provided a developing device, comprising: a developing container configured to contain a developer including a toner and a carrier; a first rotatable member to which the developer contained in the developing container is supplied, and the first rotatable member carries and feeds the developer to a first developing position at which an electrostatic latent image formed on an image bearing member is developed; a first magnet non-rotatably and fixedly disposed in the first rotatable member, wherein the first magnet comprises a first developing pole disposed opposite to the image bearing member at the first developing position, a conveying pole disposed downstream of the first developing pole with respect to a rotation direction of the first rotatable member, and a feeding pole disposed upstream of the conveying pole with respect to a rotation direction of the first rotatable member and adjacent to the conveying pole, and the feeding pole has a magnetic polarity different from that of the conveying pole; and a second rotatable member disposed opposite to the first rotatable member and for transferring the developer from the first rotatable member to the first developing position by a magnetic field generated by the first magnet. a first rotatable member conveyed to the second rotatable member, wherein the second rotatable member carries and feeds the developer to a second developing position for developing the electrostatic latent image, and wherein the rotation direction of the second rotatable member at a position on the outer peripheral surface of the second rotatable member at which the second rotatable member is closest to the first rotatable member is opposite to the rotation direction of the first rotatable member at a position on the outer peripheral surface of the first rotatable member at which the first rotatable member is closest to the second rotatable member; a second magnet, which is non-rotatably and fixedly arranged in the second rotatable member, wherein the second magnet includes a plurality of magnetic poles, the plurality of magnetic poles including a second developing pole arranged opposite to the image bearing member at the second developing position, and a receiving pole arranged upstream of the second developing pole with respect to the rotation direction of the second rotatable member and adjacent to the second developing pole, and the receiving pole has a magnetic polarity different from that of the second developing pole and different from that of the conveying pole, and the receiving pole is a magnetic pole arranged closest to the conveying pole among the plurality of magnetic poles.

[0010] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a schematic cross-sectional view of the image forming apparatus in the first embodiment.

[0012] Figure 2 is a schematic cross-sectional view of a developing device according to the first embodiment.

[0013] Figure 3is a schematic diagram showing the magnetic pole arrangement of the first developing roller in the first embodiment.

[0014] Figure 4 is a schematic diagram showing the arrangement of magnetic poles of the second developing roller in the first embodiment.

[0015] Figure 5 is a schematic diagram showing the magnetic pole arrangement of the peeling roller in the first embodiment.

[0016] Figure 6 : is a schematic diagram showing the relationship of the magnetic pole arrangement between the first developing roller and the second developing roller in the first embodiment, in which the relationship between the attractive force F1 and the repulsive force F2 is shown.

[0017] Figure 7 : is a schematic diagram showing the relationship of the magnetic pole arrangement between the first developing roller and the second developing roller in the first embodiment, in which the relationship between the attractive force F1 and the repulsive force F2' is shown.

[0018] Figure 8 is a table showing the results of an experiment in which the occurrence state of abnormal images in the first embodiment was examined.

[0019] Fig. 9 : is a schematic diagram showing the relationship of the magnetic pole arrangement between the first developing roller and the second developing roller in the second embodiment, in which the relationship between the attractive force F1 and the repulsive forces F2 and F2' is shown.

[0020] Fig.10 is a table showing the results of an experiment in which the occurrence state of abnormal images in the second embodiment was examined.

[0021] Fig.11 is a schematic diagram showing the magnetic pole arrangement of the first developing roller in the third embodiment.

[0022] Fig.12 : is a schematic diagram showing the relationship of the magnetic pole arrangement between the first developing roller and the second developing roller in the third embodiment.

[0023] Fig.13 : is a schematic diagram showing the relationship of the magnetic pole arrangement between the first developing roller and the second developing roller in the fourth embodiment, in which the relationship between the attractive force F1 and the repulsive force F3 is shown.

[0024] Fig.14 : is a schematic diagram showing the relationship of the magnetic pole arrangement between the first developing roller and the fourth developing roller in the first embodiment, in which the relationship between the attractive force F1 and the repulsive force F3 ′ is shown.

[0025] Fig.15 is a table showing the results of an experiment in which the occurrence state of abnormal images in the fourth embodiment was examined.

[0026] Fig.16 : is a schematic diagram showing the relationship of the magnetic pole arrangement between the first developing roller and the second developing roller in the fifth embodiment, in which the relationship between the attractive force F1 and the repulsive force F3 ′ is shown.

[0027] Fig.17 is a table showing the results of an experiment in which the occurrence state of abnormal images in the fifth embodiment was examined.

[0028] Fig.18 is a schematic diagram showing the magnetic pole arrangement of the second developing roller in the sixth embodiment.

[0029] Fig.19 : is a schematic diagram showing the relationship of the magnetic pole arrangement between the first developing roller and the second developing roller in the sixth embodiment. DETAILED DESCRIPTION

[0030] [First embodiment]

[0031] Will use Figures 1 to 8 The first embodiment will be described. Figure 1 The overall structure of the imaging apparatus in this embodiment is described.

[0032] [Imaging equipment]

[0033] The image forming apparatus 100 is a full-color image forming apparatus, and in the case of the present embodiment, the image forming apparatus 100 is, for example, an MFP (Multi-Function Peripheral) having a copy function, a printer function, and a scanner function. Figure 1 As shown, the image forming apparatus 100 includes image forming portions PY, PM, PC, and PK arranged in parallel for respectively performing image forming steps of forming toner images of four colors of yellow, magenta, cyan, and black.

[0034] The image forming parts PY, PM, PC and PK for the corresponding colors include primary chargers 21Y, 21M, 21C and 21K, developing devices 1Y, 1M, 1C and 1K, light writing parts (exposure devices) 22Y, 22M, 22C and 22K, photosensitive drums 28Y, 28M, 28C and 28K, and cleaning devices 26Y, 26M, 26C and 26K, respectively. In addition, the image forming apparatus 100 includes a transfer device 2 and a fixing device 3. Incidentally, the structures of the image forming parts PY, PM, PC, PK are similar to each other, and therefore, the following description will be performed using the image forming part PY as a representative.

[0035] The photosensitive drum 28Y as an image bearing member is a photosensitive member having a photosensitive layer formed of a resin such as polycarbonate, the photosensitive layer containing an organic photoconductor (OPC), and the photosensitive drum is configured to rotate at a predetermined speed. The primary charger 21Y includes a corona discharge electrode arranged at the periphery of the photosensitive drum 28Y, and charges the surface of the photosensitive drum 28Y by the generated ions.

[0036] In the optical writing section 22Y, a scanning optical device is mounted, and by exposing the charged photosensitive drum 28Y based on the image data, the potential of the exposed portion is lowered, thereby forming a charge pattern (electrostatic latent image) corresponding to the image data. The developing device 1Y develops the electrostatic latent image formed on the photosensitive drum 28Y by transferring the developer contained therein to the photosensitive drum 28Y. The developer is prepared by mixing a carrier with a toner of a relevant color, and the electrostatic latent image is visualized (developed) with the toner.

[0037] The transfer device 2 includes primary transfer rollers 23Y, 23M, 23C, 23K, an intermediate transfer belt 24, and a secondary transfer roller 25. The intermediate transfer belt 24 is wound around the primary transfer rollers 23Y, 23M, 23C, 23K and a plurality of rollers, and is supported so as to be able to travel.

[0038] The primary transfer rollers 23Y, 23M, 23C and 23K are Figure 1 2 and 3. The secondary transfer rollers 25 are arranged in numerical order from above and correspond to the colors of Y (yellow), M (magenta), C (cyan), and K (black), respectively. The secondary transfer roller 25 is arranged 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. Incidentally, the recording material is a sheet such as paper or a plastic sheet.

[0039] The toner images of the corresponding colors formed on the photosensitive drums 28Y, 28M, 28C and 28K are successively transferred to the intermediate transfer belt 24 by the primary transfer rollers 23Y, 23M, 23C and 23K, respectively, so that a color toner image including superimposed layers of yellow, magenta, cyan and black is formed. The toner image thus formed is transferred to the recording material fed from the box in which the recording material is accommodated by the secondary transfer roller 25. The recording material on which the toner image is transferred is pressed and heated in the fixing device 3. Thereby, the toner on the recording material is melted, so that the color image is fixed on the recording material.

[0040] The developer storage portions 27Y, 27M, 27C, and 27K are provided corresponding to the developing devices 1Y, 1M, 1C, and 1K, respectively, and bottles containing developers corresponding to the colors of yellow, magenta, cyan, and black are replaceably installed in the developer storage portions in numerical order from above, respectively. The developer storage portions 27Y, 27M, 27C, and 27K are configured so that the developers can be fed (supplied) therefrom to the developing devices 1Y, 1M, 1C, and 1K corresponding to the colors of the developers stored therein, respectively.

[0041] For example, the toner weight ratio of the developer contained in each bottle is 80% to 95%, and the toner weight ratio of the developer in each of the developing devices 1Y, 1M, 1C, and 1K is 5% to 10%. Therefore, when the toner is consumed by development in each of the developing devices 1Y, 1M, 1C, and 1K, the developer containing the toner in an amount corresponding to the consumption amount of the toner is supplied so that the toner weight ratio of the developer in each of the developing devices 1Y, 1M, 1C, and 1K is maintained at a constant amount.

[0042] [Developing device]

[0043] Next, we will use Figures 2 to 5 The developing devices 1Y, 1M, 1C, and 1K are described in detail.

[0044] Incidentally, the structures of the developing devices 1Y, 1M, 1C, and 1K are the same, and therefore, the developing device 1Y will be described below as a representative. Figure 2 It is shown Figure 1 A conceptual diagram of the developing device 1Y shown in FIG. Figures 3 to 5 1Y are conceptual diagrams respectively showing the magnetic pole structures of the first magnet 36 , the second magnet 37 , and the third magnet 38 provided inside the developing device 1Y.

[0045] like Figure 2 As shown, the developing device 1Y includes a first developing roller 30 , a second developing roller 31 , a peeling roller 32 , a developer supplying screw 42 , a developer stirring screw 43 , and a developer collecting screw 44 , and these components are accommodated in a developing container 60 .

[0046] The first developing roller 30 is a developer carrying member that is driven to rotate, and is disposed at a position adjacent to the photosensitive drum 28Y so that its rotation axis is substantially parallel to the rotation axis of the photosensitive drum 28Y. The first developing roller 30 includes a rotatable first sleeve 33 and a first magnet (fixed magnet) 36 that is non-rotatably disposed in the first sleeve 33 and is used to attract the developer to the surface of the first sleeve 33 by magnetic force. Then, the first developing roller 30 attracts (carries) the developer drawn from the developer supply screw 42 based on the magnetic force, and develops the electrostatic latent image formed on the rotating photosensitive drum 28Y (image bearing member) with the developer.

[0047] The first sleeve 33 is a non-magnetic cylindrical member and is driven to rotate around the rotation axis 39. The rotation direction of the first sleeve 33 is as follows: Figure 2 The photosensitive drum 28Y rotates in the clockwise direction indicated by the arrow in the figure, and is the direction opposite to the rotation direction of the photosensitive drum 28. Therefore, the first sleeve 33 and the photosensitive drum 28Y rotate in the same direction at the position opposite to each other. That is, normal (positive) development is performed so that the photosensitive drum 28 rotates from the bottom to the top in the vertical direction in the position where the photosensitive drum 28 and the first sleeve 33 are opposite.

[0048] The first magnet 36 is arranged inside the first sleeve 33 and Figure 3 The illustrated embodiment includes a plurality of sector-shaped magnetic poles 101 to 107. Between the inner periphery of the first sleeve 33 and the outer periphery of the first magnet 36, a space is provided to allow the first sleeve 33 to rotate.

[0049] The developer attracted to the first sleeve 33 is conveyed toward the photosensitive drum 28Y by the rotation operation of the first sleeve 33, so that the electrostatic latent image formed on the photosensitive drum 28Y is developed with the developer. After the electrostatic latent image formed on the photosensitive drum 28Y is developed with the developer, the developer on the first sleeve 33 is conveyed to the vicinity of the second developing roller 31 by the rotation 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 magnetic field generated by the first magnet 36 included in the first developing roller 30 and the second magnet 37 included in the second developing roller 31 peels the developer from the first sleeve 33, and is then conveyed to the surface of the second sleeve 34.

[0050] The second developing roller 31 is a developer carrying member that is driven to rotate, and is disposed downstream of the first developing roller 30 with respect to the rotation direction of the photosensitive drum 28Y, and the rotation center O2 of the second developing roller 31 is positioned above the rotation center O1 of the first developing roller 30 with respect to the vertical direction. The developer is conveyed from the first developing roller 30 to the second developing roller 31 by magnetic force ( Figure 2 In the present embodiment, the entire second developing roller 31 is positioned above the rotation center O1 of the first developing roller 30 .

[0051] Similar to the first developing roller 30, the second developing roller 31 is disposed adjacent to the photosensitive drum 28Y so that its rotation axis is substantially parallel to the rotation axis of the photosensitive drum 28Y. Therefore, the second developing roller 31 and the first developing roller 30 are substantially parallel to each other in the rotation axis.

[0052] Such a second developing roller 31 includes a rotatable second sleeve 34, and a second magnet (fixed magnet) 37 which is non-rotatably provided in the second sleeve 34 and is used to attract the developer to the surface of the second sleeve 34 by magnetic force. Then, based on the magnetic force, the developer is conveyed from the first developing roller 30 (first sleeve 33) to the second developing roller 31, and the second developing roller 31 attracts (carries) the developer, and develops the electrostatic latent image formed on the rotating photosensitive drum 28Y with the developer. Incidentally, on one side of the second developing roller 31, a peeling roller 32 described later is positioned.

[0053] The second sleeve 34 is a non-magnetic cylindrical member and is driven to rotate around the rotation axis 40. Similar to the first sleeve 33, the rotation direction of the second sleeve 34 is as follows: Figure 2 , and in the present embodiment, is the direction opposite to the rotation direction of the photosensitive drum 28. Therefore, the second sleeve 34 and the photosensitive drum 28Y rotate in the same direction at positions opposite to each other. That is, normal development is performed so that the photosensitive drum 28 rotates from below to above in the vertical direction in the position where the photosensitive drum 28 and the second sleeve 34 are opposite. In addition, the first sleeve 33 and the second sleeve 34 rotate in opposite directions at positions opposite to each other.

[0054] The second magnet 37 is arranged inside the second sleeve 34 and Figure 4 The second sleeve 34 includes a plurality of sector-shaped magnetic poles 201 to 207. Between the inner periphery of the second sleeve 34 and the outer periphery of the second magnet 37, a space is provided to allow the second sleeve 34 to rotate.

[0055] The developer attracted to the second sleeve 34 is conveyed toward the photosensitive drum 28Y by the rotation operation of the second sleeve 34, so that the electrostatic latent image formed on the photosensitive drum 28Y is developed with the developer. After the electrostatic latent image formed on the photosensitive drum 28Y is developed with the developer, the developer remaining on the second sleeve 34 is conveyed to the vicinity of the peeling roller 32 by the rotation 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 conveyed 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 included in the second developing roller 31 and the third magnet 38 included in the peeling roller 32.

[0056] The peeling roller 32 as a peeling portion is provided on the side opposite to the photosensitive drum 28Y with respect to the rotation center of the second sleeve 34, and peels 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 carrying member that is rotationally driven, and is provided between the second developing roller 31 and the developer collecting screw 44 so that the rotation center thereof is positioned above the rotation center R2 of the second developing roller 31.

[0057] In addition, the peeling roller 32 is arranged so that its rotation axis is substantially parallel to the rotation axis of the second developing roller 31. This peeling roller 32 includes a rotatable third sleeve 35, and a third magnet (fixed magnet) 38 that is non-rotatably provided in the third sleeve 35 and is used to attract the developer to the surface of the third sleeve 35 by magnetic force, and is configured so that the developer is conveyed from the second developing roller 31 to the third sleeve based on the magnetic force.

[0058] The third sleeve 35 is a non-magnetic cylindrical member and is driven to rotate around the rotation axis 41. The rotation direction of the third sleeve 35 is as follows: Figure 2 The third sleeve 35 rotates in the counterclockwise direction as indicated by the arrow in the figure, and is the direction opposite to the rotation direction of the second sleeve 34. Therefore, the third sleeve 35 and the second sleeve 34 rotate in the same direction at positions opposite to each other.

[0059] The third magnet 38 is arranged inside the third sleeve 35, and Figure 5 The third sleeve 35 includes a plurality of sector-shaped magnetic poles 301 to 305. Between the inner periphery of the third sleeve 35 and the outer periphery of the third magnet 38, a space is provided to allow the third sleeve 35 to rotate.

[0060] The developer attracted to the third sleeve 35 is conveyed to the downstream side in the rotation direction by the rotation operation of the third sleeve 35, and is peeled off from the third sleeve 35 by the third magnet 38 included in the peeling roller 32 at a position close to the developer collecting screw 44, so that the developer falls by its own weight toward the guide member 45 positioned below with respect to the vertical direction. Then, the developer dropped on the guide member 45 is guided toward the developer collecting screw 44 by its own weight.

[0061] The guide member 45 and the developer collecting screw 44 constitute a developer collecting portion 47 as a collecting portion for collecting the developer peeled off from the third sleeve 35 on the peeling roller 32. In the developer collecting portion 47, the developer collecting screw 44 is arranged so that its rotation center is positioned below the rotation center of the peeling roller 32 in the vertical direction, and conveys the developer conveyed (collected) from the peeling roller 32 while stirring the developer.

[0062] The guide member 45 as a guide portion is arranged below the peeling roller 32 with respect to the vertical direction, and guides the developer peeled by the peeling roller 32 toward the developer collecting screw 44. Such a guide member 45 is provided with an inclined surface 45a along which the developer slides downward by its own weight so as to reliably guide the peeled developer toward the developer collecting screw 44. The inclined surface 45a is inclined with respect to the horizontal direction so that its position on the developer collecting screw 44 side is lower than the lower position of the peeling roller 32.

[0063] The developer collecting screw 44, which is a collecting member and a conveying (feeding) portion, conveys the collected developer to the below-described developer circulation portion 46. That is, the developer collecting screw 44 is a screw conveying (feeding) member for conveying the developer in one direction while stirring the developer collected by sliding downward along the inclined surface 45a of the guide member 45.

[0064] The developer circulation portion 46 is a supply portion for supplying the developer to the first developing roller 30, and the developer circulation portion 46 includes a regulating member 50, a developer supply screw 42, and a developer stirring screw 43. In the developer circulation portion 46, the developer is supplied to the first developing roller 30 while conveying the developer in a substantially horizontal direction while stirring the developer in the developer supply screw 42 and the developer stirring screw 43. In addition, as described above, the developer collected by the developer collecting portion 47 falls due to its own weight and is guided to the developer circulation portion 46.

[0065] The developer supply screw 42, the developer stirring screw 43, and the developer collecting screw 44 are screw conveying members for conveying the developer in one direction while stirring the developer, and the developer supply screw 42 and the developer stirring screw 43 are positioned below the developer collecting screw 44 with respect to the vertical direction. In addition, the developer supply screw 42, the developer stirring screw 43, and the developer collecting screw 44 are arranged so that their rotation axes are substantially parallel to each other. The rotation axes of these screws are also substantially parallel to the rotation axis of the first developing roller 30.

[0066] The developer supply screw 42 is positioned between the first developing roller 30 and the developer stirring screw 43, and a partition wall 48 of the developing container 60 is provided between itself 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 opening (not shown) for establishing communication between a first feeding path 61 along which the developer is fed by the developer supply screw 42 and a second feeding path 62 along which the developer is fed by the developer stirring screw 43.

[0067] The developer stirred by the developer collecting screw 44 passes through a communication opening (not shown) formed in a partition wall 63 of the developing container 60 positioned between the developer collecting screw 44 and the developer supplying screw 42, and then falls by its own weight toward the developer supplying screw 42. The above-mentioned guide member 45 is formed integrally with the partition wall 63, and the developer collecting screw 44 is arranged above the partition wall 63.

[0068] Preferably, the position of the communication opening through which the developer stirred by the developer collecting screw 44 falls due to its own weight and is guided into the developer circulation portion 46 may be arranged to avoid the area (the middle portion with respect to the rotation axis direction of the developer supply screw 42) where the developer is supplied toward the first developing roller 30. In the present embodiment, the position of the communication opening is such a position that the communication opening is included in the range of the downstream end portion (terminal portion) in the developer feeding direction with respect to the first feeding path 61 in which the developer supply screw 42 is arranged.

[0069] The developer feeding directions of the developer supply screw 42 and the developer stirring screw 43 are opposite to each other. In addition, the starting end side (upstream end side in the developer feeding direction) and the terminal end side (downstream end side in the developer feeding direction) of the first feeding path 61 in which the developer supply screw 42 is arranged and the terminal end side and the starting end side of the second feeding path 62 in which the developer stirring screw 43 is arranged are communicated with each other via the communication opening provided in the partition wall 48, respectively. Therefore, the developer is moved along the developer container 60 in the developer container 60. Figure 2 The developer supply screw 42 and the developer stirring screw 43 are rotated in the direction indicated by the arrow and circulate in a substantially horizontal direction, thereby supplying a portion of the developer toward the first developing roller 30 .

[0070] The developer supply opening 51 (see Figure 2 ) is disposed above the developer stirring screw 43 in the developing container 60 and is connected to the developer storage portion 27Y (see Figure 1 ). Further, the developer supply opening 51 is configured to be able to supply the developer contained in the bottle mounted in the developer storage portion 27Y to the second feeding path 62 in which the developer stirring screw 43 is arranged.

[0071] As described above, the toner weight ratio of the developer contained in the bottle of the developer storage portion 27Y is greater than the toner weight ratio of the developer in the developing device 1Y, and therefore, by adjusting the amount of developer supplied to the developer stirring screw 43, the toner weight ratio of the developer in the developing device 1Y can be maintained at a certain level.

[0072] A toner concentration detection sensor 49 (see Figure 2 ) is used to detect the colorant concentration of the developer contained in the developer circulation part 46. The colorant concentration detection sensor 49 is a sensor for detecting (magnetic) permeability. The colorant concentration corresponds to the consumption of the toner in the developing device 1Y, and therefore, is used to control the supply of the developer from the developer storage part 27Y. For example, when the toner concentration is detected that the toner concentration is lower than a predetermined value, the developer is supplied from the developer storage part 27Y. Incidentally, the magnetic permeability changes depending on the toner concentration, and therefore, the toner concentration can be detected by utilizing the magnetic permeability.

[0073] 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 circulation portion 46 to the first developing roller 30. The regulating member 50 may be configured to regulate the amount of developer attracted to the first developing roller 30 based on a gap between the surface of the first sleeve 33 of the first developing roller 30 and an end portion of the regulating member 50.

[0074] The circulation path of the developer in the developing container 60 is such that the developer is fed in a substantially horizontal direction while being stirred in the developer circulation portion 46, and is then supplied to the first developing roller 30, and is then conveyed from the first developing roller 30 to the second developing roller 31 positioned above the first developing roller 30 based on the magnetic force. Then, the developer is conveyed from the second developing roller 31 to the peeling roller 32 positioned beside the second developing roller 31 based on the magnetic force again, and thereafter, is peeled from the peeling roller 32 by the third magnet 38 included in the peeling roller 32. In addition, the developer is collected by the developer collecting portion 47 and is then guided into the developer circulation portion 46 again.

[0075] In addition, as described above, in this embodiment, a two-component developing type is used as a developing type, and a developer obtained by mixing a non-magnetic colorant having a negative charge with a carrier having magnetism is used as a developer. The non-magnetic colorant is a toner obtained by including a colorant, a wax component, etc. in a resin (such as polyester fiber or styrene acrylic resin), forming a powdery mixture by pulverizing or polymerizing, and then adding fine powders of titanium dioxide, silicon dioxide, etc. to the surface of the powder. The magnetic carrier is a carrier obtained by coating a resin material on the surface layer of a core (containing resin particles obtained by kneading ferrite particles or magnetic powder). In this embodiment, the toner concentration (weight ratio of toner to developer) in the developer in the initial state is 8%.

[0076] Generally, a two-component developer using a toner and a carrier has a feature that, because the toner and the carrier are charged to a predetermined polarity by bringing the toner and the carrier into frictional charging contact, the stress applied to the toner is less than the stress applied to the toner in a single-component developer using a single-component developer. On the other hand, due to long-term use, the amount of pollutants (waste) deposited on the surface of the carrier increases, and thus the toner charging performance gradually decreases. As a result, problems of fogging and toner scattering occur. Although it is considered to increase the amount of the carrier contained in the developing device in order to extend the life of the two-component developer, this leads to an increase in the size of the developing device, and is therefore undesirable.

[0077] In order to solve the above-mentioned problem about the two-component developer, in the present embodiment, the ACR (Automatic Carrier Refresh) type is adopted. The ACR type is a type that suppresses the increase in the amount of deteriorated developer by not only gradually supplying fresh developer from the developer storage portion 27Y to the developing device 1Y little by little, but also gradually discharging the developer with deteriorated charging performance little by little through the discharge opening (not shown) of the developing device 1Y. Thus, the deteriorated carrier in the developing device 1Y is gradually replaced by fresh carrier little by little, so that the charging performance of the carrier in the developing device 1Y can be maintained at a substantially constant level.

[0078] [Magnetic poles of a magnet]

[0079] Next, we will describe Figure 3 , 4 5 and 6 respectively include the magnetic pole configurations of the first magnet 36, the second magnet 37 and the third magnet 38 in the first developing roller 30, the second developing roller 31 and the peeling roller 32.

[0080] like Figure 3 As shown, the first magnet 36 included in the first developing roller 30 has a 7-pole magnetic pole configuration including a plurality of magnetic poles 101, 102, 103, 104, 105, 106, and 107. Among these magnetic poles, the magnetic pole 106 is a conveying pole for conveying the developer from the first developing roller 30 to the second developing roller 31. The magnetic poles 101 to 107 are arranged in numerical order along the rotation direction of the first sleeve 33. The magnetic pole 101 is an S pole, and is arranged at a position opposite to the regulating member 50 through the first sleeve 33, and regulates the amount of the developer conveyed 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 opposite to the photosensitive drum 28Y through the first sleeve 33, and is a magnetic pole for developing the electrostatic latent image formed on the photosensitive drum 28Y with the developer. Hereinafter, in some cases, the magnetic pole 104 is referred to as the first developing pole 104.

[0081] The magnetic pole 106 as a transport pole is an N pole and is a magnetic pole for transporting the developer from the first sleeve 33 to the second sleeve 34 by generating a magnetic field in cooperation with the second magnet 37 of the second developing roller 31 , and hereinafter, the magnetic pole 106 is referred to as the transport pole 106 in some cases.

[0082] The magnetic pole 107 is an N pole, and is used to attract the developer supplied from the developer supply screw 42 to 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 a feed pole for feeding the developer attracted by the magnetic pole 107 upward with the rotation of the first sleeve 33. Among these magnetic poles, the magnetic pole 105 is the first magnetic pole upstream of and adjacent to the conveying pole 106 with respect to the rotation direction of the first sleeve 33, and the magnetic pole 105 is hereinafter referred to as the first feed pole 105 in some cases. The first development pole 104 is positioned upstream of and adjacent to the first feed pole 105 with respect to the rotation direction of the first sleeve 33.

[0083] In addition, the magnetic pole 107 is arranged on the downstream side of the conveying pole 106 relative to the rotation direction of the first sleeve 33, and has the same polarity as the conveying pole 106. The conveying pole 106 and the magnetic pole 107 cooperate with each other to form a low magnetic force portion 110 with a smaller magnetic force than the conveying pole 106 through a repulsive magnetic field therebetween. Through the low magnetic force portion 110, the developer is peeled off from the first sleeve 33, and the conveyance of the developer from the first sleeve 33 to the second sleeve 34 is promoted. Incidentally, the low magnetic force portion 110 may have essentially no magnetic force in the present embodiment, but may have a low magnetic force, and may, for example, be a magnetic pole having a magnetic force (normal component Br of the magnetic flux density) of 5 mT or less. The same applies to Figure 4 The low magnetic force portion 210 of the second magnet 37 is shown Figure 5 The low magnetic force portion 310 of the third magnet 38 is shown.

[0084] like Figure 4 As shown, the second magnet 37 included in the second developing roller 31 has a seven-pole-based configuration including a plurality of magnetic poles 201, 202, 203, 204, 205, 206, and 207. Among these magnetic poles, the magnetic pole 201 is a receiving pole for receiving the developer from the first developing roller 30 through the second developing roller 31. The magnetic poles 201 to 207 are arranged in numerical order along the rotation direction of the second sleeve 34.

[0085] The magnetic pole 201 as the receiving pole is a magnetic pole for attracting the developer from the first sleeve 33 to the second sleeve 34 by the magnetic field generated in cooperation with the magnetic pole 106 of the first magnet 36 of the first developing roller 30, and hereinafter, in some cases, the magnetic pole 201 is referred to as the receiving pole 201. The magnetic pole 207 is a magnetic pole for conveying the developer from the second sleeve 34 to the third sleeve 35 by the magnetic field generated in cooperation with the third magnet 38 of the stripping roller 32.

[0086] In addition, the magnetic pole 201 is an S pole having a different polarity from the conveying pole 106, and is used to attract the developer from the first developing roller 30 (first sleeve 33) to the second sleeve 34 as described above. The magnetic pole 203 as the second developing pole is an S pole, and is a magnetic pole arranged in a position opposite to the photosensitive drum 28Y through the second sleeve 34 and used to develop the electrostatic latent image formed on the photosensitive drum 28Y. Hereinafter, the magnetic pole 203 is referred to as the second developing pole 203 in some cases.

[0087] The magnetic poles 202, 204, 205, and 206 are N poles, N poles, S poles, and N poles, and are used to feed the developer attracted by the magnetic pole 201 upward with the rotation of the second sleeve 34. Among these magnetic poles, the magnetic pole 202 is a second magnetic pole positioned downstream of and adjacent to the receiving pole 201 with respect to the rotation direction of the second sleeve 34, and the magnetic pole 202 is hereinafter referred to as the second feeding pole 202 in some cases. The second developing pole 203 is positioned downstream of and adjacent to the second feeding pole 202 with respect to the rotation direction of the second sleeve 34.

[0088] The magnetic pole 207 is an S pole, and through the magnetic field generated in cooperation with the magnetic pole 303 in the third magnet 38 included in the peeling roller 32, the developer is transported from the second sleeve 34 to the third sleeve 35 opposite to the second sleeve 34 after passing through the developing area of ​​the photosensitive drum 28Y corresponding to the magnetic pole 203.

[0089] In addition, the magnetic pole 207 is arranged on the upstream side of the receiving pole 201 with respect to 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 by the repulsive magnetic field generated by cooperation with each other. Through this low magnetic force portion 210, the developer is peeled off from the second sleeve 34, and the conveyance of the developer from the first sleeve 33 to the second sleeve 34 is promoted. In addition, through the low magnetic force portion 210, the developer can be prevented from being attracted to the closest portion between the first sleeve 33 and the second sleeve 34, and the pressure applied to the developer can be suppressed.

[0090] like Figure 5As shown, the third magnet 38 included in the peeling roller 32 is provided with 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.

[0091] The magnetic pole 303 is an N pole having a different polarity from the magnetic pole 207, and is used to attract the developer stripped from the second sleeve 34 as described above to the third sleeve 35. The magnetic poles 301, 302, and 304 are an N pole, an S pole, and an S pole, and are used to feed the developer on the third sleeve 35 as the third sleeve 35 rotates. Specifically, the magnetic pole 304 is used to feed downward the developer attracted by the magnetic pole 303 as the third sleeve 35 rotates. The magnetic pole 305 is an N pole, and is a stripping pole for stripping the developer attracted to the third sleeve 35 from the third sleeve 35 by generating a repulsive magnetic field in cooperation with the magnetic pole 301 having the same polarity as the magnetic pole 305.

[0092] [Magnetic pole arrangement relationship]

[0093] Next, we will use Figure 6 Describing the magnetic pole arrangement relationship between the first magnet 36 and the second magnet 37 respectively arranged in the first developing roller 30 and the second developing roller 31, Figure 6 1 is a conceptual diagram for illustrating the arrangement of the first developing roller 30 and the second developing roller 31 in the present embodiment, and particularly illustrates the layout of the first feeding pole 105 and the transporting pole 106 of the first magnet 36 of the first developing roller 30 and the receiving pole 201 and the second feeding pole 202 of the second magnet 37 of the second developing roller 31. Incidentally, a part of the magnetic poles is omitted in the illustration due to complexity.

[0094] In this embodiment, as described above, the developer in the developing device 1Y moves from the surface of the first sleeve 33 of the first developing roller 30 to the surface of the second sleeve 34 of the second developing roller 31 through the magnetic fields of the conveying pole 106 in the first developing roller 30 and the receiving pole 201 in the second developing roller 31, and then moves to the surface of the third sleeve 35 of the peeling roller 32 after the development step of the electrostatic latent image on the photosensitive drum 28Y.

[0095] Here, the first feeding pole 105 in the first developing roller 30 and the second feeding pole 202 in the second developing roller 31 have Figure 3 and 4Magnetic properties of the S pole and the N pole shown in . Therefore, an attractive force (F1) for conveying the developer is also generated between the first feed pole 105 and the second feed pole 202. Then, the developer is conveyed between the first feed pole 105 and the second feed pole 202 by the attractive force F1 between the first feed pole 105 and the second feed pole 202. When the developer is conveyed between the first feed pole 105 and the second feed pole 202, the developer also contacts the photosensitive drum 28Y, so that an abnormal image in the form of vertical stripes is generated on the photosensitive drum 28Y.

[0096] On the other hand, Figure 3 and 4 As shown, the conveying pole 106 in the first developing roller 30 and the second feeding pole 202 in the second developing roller 31 are N poles (same poles), and therefore, a repulsive force (F2) is generated between the conveying pole 106 in the first developing roller 30 and the second feeding pole 202 in the second developing roller 31 for pressing the developer toward one side of the sleeve.

[0097] Next, suppression of developer conveyance between the first feed pole 105 in the first developing roller 30 and the second feed pole 202 in the second developing roller 31 will be described in detail. Figure 6 and Figure 7 The dashed line shown in shows the position of the maximum value (peak position) of the magnetic flux density in the second feed pole 202 of the second magnet 37 in the normal direction of the second sleeve 34, and shows the position of the maximum value (peak position) of the magnetic flux density in the first feed pole 105 and the conveying pole 106 of the first magnet 36 in the normal direction of the first sleeve 33. First, the absolute value of the maximum value of the normal component of the magnetic flux density of the second feed pole 202 in the second developing roller 31 is MA [mT], and the position of this maximum value on the second sleeve 34 is point A. Furthermore, the absolute value of the maximum value of the normal component of the magnetic flux density of the first feed pole 105 in the first developing roller 30 is MB [mT], and the position of this maximum value on the first sleeve 33 is point B. Furthermore, the absolute value of the maximum value of the normal component of the magnetic flux density of the conveying pole 106 in the first developing roller 30 is MC [mT], and the position of this maximum value on the first sleeve 33 is point C. Furthermore, the straight-line distance between point A and point B is L1, and the straight-line distance between point A and point C is L2.

[0098] In addition, the above-mentioned attractive force F1 is a magnetic force acting on the developer in the direction of the straight line AB between the second feed pole 202 on the second sleeve 34 and the first feed pole 105 on the first sleeve 33 about the connection point A and point B. In addition, the above-mentioned repulsive force F2 is a magnetic force acting on the developer in the direction of the straight line AC between the second feed pole 202 on the second sleeve 34 and the conveying pole 106 on the first sleeve 33 about the connection point A and point C.

[0099] Such attractive force F1 and repulsive force F2 can be respectively expressed by the following Formula 1 and Formula 2. Incidentally, k is a coefficient set by the (magnetic) permeability, radius, etc. of the magnetic carrier of the developer.

[0100] F1 = k×MA×MB / L1 2 (Formula 1)

[0101] F2 = k×MA×MC / L2 2 (Formula 2)

[0102] In the second feed pole 202 of the second developing roller 31, in order to suppress the transport of the developer between the second feed pole 202 in the second developing roller 31 and the first feed pole 105 in the first developing roller 30, it can be required that the attraction F1 from the second feed pole 202 in the second developing roller 31 toward the first feed pole 105 in the first developing roller 30 is not greater than the repulsion F2 based on the transport pole 106 in the first developing roller 30 and the second feed pole 202 in the second developing roller 31.

[0103] That is, for the above equations 1 and 2, it is only required to satisfy the following relationship:

[0104] F1≤F2 (Formula 3)

[0105] That is, in this embodiment, the magnetic flux density and arrangement of the transport pole 106, the first feed pole 105 and the second feed pole 202 are set to satisfy Formula 3. Specifically, the positions of the above-mentioned MA, MB and MC and points A, B and C are set to satisfy Formula 3.

[0106] In addition, Figure 7 In FIG. 4 , the relationship between the component force F2′ of the repulsive force F2 in the direction of the straight line AB and the above-mentioned attractive force F1 is shown. When the angle formed by the straight line AB and AC is θ, when a perpendicular line is drawn from point C to the straight line AB, the point on the straight line AB is C′, and the straight line distance between point A and point C′ is L2′, L2′ can be expressed by the following formula 4:

[0107] L2' = L2 × cosθ (Equation 4)

[0108] In the second feed pole 202 in the second developing roller 31, in order to offset the attraction force F1 received from the first feed pole 105 in the first developing roller 30, it is desirable that the repulsive force F2' in the straight line AC' direction between the second feed pole 202 in the second developing roller 31 and the conveying pole 106 in the first developing roller 30 is the attraction force F1 or greater. F2' is the component force of F2 in the straight line AB direction, and can be expressed by the following formula 5:

[0109] F2' = F2 × cosθ (Equation 5)

[0110] Furthermore, in order to counteract the attractive force F1 by the repulsive force F2', it is desirable to maintain the following relationship:

[0111] F1≤F2' (Formula 6)

[0112] That is, in the present embodiment, it is preferable that Formula 6 is further satisfied, and it is preferable that the magnetic flux density and arrangement of the transport pole 106, the first feed pole 105, and the second feed pole 202 are set to satisfy Formula 6. Specifically, the positions of the above-mentioned MA, MB, and MC and the points A, B, and C are set to satisfy Formula 6.

[0113] [experiment]

[0114] Next, an experiment for checking the occurrence state of the streak-like fog image (abnormal image) in the above-mentioned configuration will be described. In the example, the magnetic flux density MA of the second feed pole 202 in the second developing roller 31, the magnetic flux density MB of the first feed pole 105 in the first developing roller 30, and the magnetic flux density MC of the conveying pole 106 in the first developing roller 30 are changed from the condition REF, and an image is output by an image forming apparatus in which the various conditions REF and the conveying poles of STUDY1 to STUDY5 are combined. Then, the occurrence state of the streak-like fog image on the output image is checked.

[0115] Incidentally, in the experiment, the position of each of the point A where the magnetic flux density on the second feed pole 202 in the second developing roller 31 becomes maximum, the point B where the magnetic flux density on the first feed pole 105 in the first developing roller 30 becomes maximum, and the point C where the magnetic flux density on the conveying pole 106 in the first developing roller 30 becomes maximum is not changed. That is, L1 and L2 are fixed. In addition, the angle θ formed by the straight lines AB and AC is set to 36°.

[0116] In the example, the occurrence state of the streak-like fog image on the output image was evaluated in the following manner.

[0117] A pure white image was formed on 10 A3-size sheets, and the number of vertical streaks on the output image was measured.

[0118] In the case where there were no vertical streaks on the pure white images on 10 A3-size sheets, pure white images were formed on 100 A3-size sheets, and then vertical streaks were checked.

[0119] The results of this experiment are shown in Figure 8 in the table.

[0120] Figure 8 The symbols in each row of the abnormal image in , the evaluation results of the occurrence state of the streak-like fog image (abnormal image) and their contents are as follows.

[0121] ×: On a single A3 size sheet, 10 or more vertical streaks were recognized.

[0122] △: On a single A3-size sheet, about one vertical streak was recognized.

[0123] ○: About one vertical streak was recognized on 10 A3-size sheets.

[0124] ◎: About one vertical streak was recognized on 100 A3-size sheets.

[0125] In the development evaluation, "○" and "◎" show levels such that abnormal images do not substantially occur significantly.

[0126] like Figure 8 As shown, in the experiment, for each condition, the magnetic flux density MB of the first feeding pole 105 in the first developing roller 30 was changed in STUDY 1 to STUDY 3. Figure 8 It can be clearly seen that by reducing MB, vertical streak-like fog images are less likely to appear. In STUDY 2, when the corresponding values ​​are applied to Formula 1 and Formula 2, the conditions of F1≤F2 that each satisfies Formula 3 are obtained, so that the evaluation of the occurrence state of vertical streak-like fog images of the output image becomes the "○" level. Similarly, in STUDY 3, when the corresponding values ​​are applied to Formula 1 and Formula 2 and then to Formula 5, the condition of F1≤F2' that satisfies Formula 6 is obtained, making it possible to confirm that vertical streak-like fog images are no longer likely to appear, and the evaluation becomes the "◎" level.

[0127] In STUDY 4, by changing the condition of the magnetic flux density MC of the conveying pole 106 in the first developing roller 30, the condition of F1≤F2 satisfying the formula 3 was obtained, so that it was confirmed that an effect similar to that of STUDY 2 could be obtained. In STUDY 5, by changing the two conditions of the magnetic flux density MB of the first feeding pole 105 in the first developing roller 30 and the magnetic flux density MC of the conveying pole 106 in the first developing roller 30, the condition of F1≤F2' satisfying the formula 6 was obtained, so that similar to STUDY 3, it was confirmed that the occurrence state of the vertical streak-like gray fog image of the output image became the "◎" level.

[0128] In the above-mentioned experiment, the magnetic flux density MB of the first feeding pole 105 in the first developing roller 30 cannot always be reduced to any value. When the magnetic force of the magnetic flux density MB of the first feeding pole 105 in the first developing roller 30 is excessively reduced, the developer feeding performance of the first developing roller 30 is reduced. Therefore, the magnetic flux density MB can preferably be maintained at a magnitude not less than the magnetic flux density MC on the conveying pole 106 in the first developing roller 30. In the present embodiment, MA≥MB>MC is satisfied.

[0129] In addition, also with respect to the magnetic flux density MC on the conveying pole 106 in the first developing roller 30, when the magnetic force is excessively increased, the conveyance of the developer with the second developing roller 31 is not easily established. When the magnetic flux density MC on the conveying pole 106 in the first developing roller 30 becomes greater than the magnetic flux density MD on the receiving pole 201 in the second developing roller 31, the developer is not easily moved toward the second developing roller 31. MD 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. For this reason, it is preferred that the magnetic flux density MC on the conveying pole 106 in the first developing roller 30 is equal to or less than the magnetic flux density MD on the receiving pole 201 in the second developing roller 31 in terms of magnetic force. In the above embodiment, the magnetic flux density MD of the receiving pole 201 in the second developing roller 31 is set to 60 [mT]. That is, in the present embodiment, MC≤MD can be preferably satisfied, and MC<MD can be more preferably satisfied.

[0130] 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, the attraction force F1 between the first feeding pole 105 in the first developing roller 30 and the second feeding pole 202 in the second developing roller 31 is made not greater than the repulsion force F2 based on the conveying pole 106 in the first developing roller 30 and the second feeding pole 202 in the second developing roller 31, so that the conveyance of the developer from the second feeding pole 202 toward the first feeding pole 105 in the first developing roller 30 can be suppressed. Therefore, the generation of the above-mentioned streak-like fog image can be suppressed.

[0131] Specifically, even in an image forming apparatus having a high image forming speed (processing speed), it is possible to suppress the conveyance of the developer from the second feed pole 202 in the second developing roller 31 toward the first feed pole 105 in the first developing roller 30, thereby suppressing the occurrence of the above-mentioned streak-like fog image. In addition, the developer is stably circulated starting from the first developing roller 30 and then through the second developing roller 31, the peeling roller 32, and the developer circulating portion 46, so that the developing device 1Y and the image forming apparatus 100 in which stable image output is performed can be provided.

[0132] <Second Embodiment>

[0133] The following will use Figures 9 to 10 A second embodiment is described. This embodiment is different from the first embodiment in the configuration of the first feed pole 105 in the first developing roller 30A. Other configurations and actions are similar to those in the first embodiment, and therefore, with regard to similar configurations, descriptions and explanations are omitted or briefly described and explained by adding the same reference numerals or symbols, and hereinafter, the differences from the first embodiment will be mainly described.

[0134] In this embodiment, the shape of the first feeding pole 105 in the first developing roller 30A is changed compared with the configuration of the first embodiment. Specifically, Fig. 9 As shown, the first feed pole 105 in the first magnet 36A of the first developing roller 30A has a configuration in which point B, which is the position where the normal component of the magnetic flux density in the first feed pole 105 becomes maximum, is closer to the first transport pole 104 in the first developing roller 30A than in the first embodiment. Fig. 9 The dotted line shown in the figure indicates the position (peak position) of the maximum value of the magnetic flux density in the second feed pole 202 of the second magnet 37 in the normal direction of the second sleeve 34, and indicates the position (peak position) of the maximum value of the magnetic flux density in the first feed pole 105 and the transport pole 106 of the first magnet 36A in the normal direction of the first sleeve 33.

[0135] Therefore, by making the position of point B of the first feed pole 105 closer to the first conveying pole 104 side, the straight line L1 from point A, which is the position of the maximum value of the normal component of the magnetic flux density of the second feed pole 202 on the second sleeve 34, to point B can be made longer than in the first embodiment. That is, it is preferable to satisfy L1>L2. By the way, L1>L2 is also satisfied in the above-mentioned first embodiment, but in this embodiment, the difference between L1 and L2 is made larger than the difference in the first embodiment. Therefore, when the distance L1 increases, the value of the attraction F1 between the first feed pole 105 in the first developing roller 30A and the second feed pole 202 in the second developing roller 31 becomes smaller. That is, in this embodiment, by changing the distance L1, the condition of F1≤F2 in the above-mentioned formula 3 and the condition of F1≤F2' in the above-mentioned formula 6 are satisfied.

[0136] [experiment]

[0137] Next, an experiment for checking the occurrence state of streak-like fog images (abnormal images) in the above-mentioned configuration will be described. In the example, the above-mentioned distance 1 is changed starting from the condition REF, and an image is output by an imaging device in which the transport poles of various conditions REF, STUDY 6, and STUDY 7 are combined. Then, the occurrence state of streak-like fog images on the output image is checked.

[0138] The other conditions and evaluations of the experiment were the same as those described in the first embodiment. The results of this experiment are shown in Fig.10 middle.

[0139] like Fig.10As shown, in STUDY 6, the position of point B is changed to a position of L1=13 mm (at this time, the angle θ formed by the straight line AB and the straight line AC is 38°), and then, similar to the first embodiment, when the attractive force F1 based on the first feed pole 105 in the first developing roller 30 and the second feed pole 202 in the second developing roller 31 and the repulsive force F2 based on the conveying pole 106 in the first developing roller 30 and the second feed pole 202 in the second developing roller 31 are derived, the condition of F1≤F2 satisfying Formula 3 is obtained. In addition, it can be confirmed that the vertical streak-like fog image of the output image is not easy to appear, and therefore the evaluation becomes the "○" level.

[0140] In STUDY 7, the position of point B is changed to a position of L1=15 mm (at this time, the angle θ formed by the straight line AB and the straight line AC is 40°), and then, similar to the first embodiment, when the attractive force F1 based on the first feed pole 105 in the first developing roller 30 and the second feed pole 202 in the second developing roller 31 and the repulsive force F2 based on the conveying pole 106 in the first developing roller 30 and the second feed pole 202 in the second developing roller 31 are derived, the condition of F1≤F2 satisfying Formula 6 is obtained. In addition, it can be confirmed that the occurrence state of the vertical streak-like fog image of the output image becomes the "◎" level. Therefore, also in this embodiment, similar to the first embodiment, the occurrence of image defects can be suppressed.

[0141] <Third Embodiment>

[0142] The following will use Fig.11 and 12 A third embodiment is described. This embodiment differs from the first embodiment in the configuration of the respective magnetic poles in the first developing roller 30B. Other configurations and functions are similar to those in the first embodiment, and therefore, with respect to similar configurations, descriptions and explanations are omitted or briefly described and explained by adding the same reference numerals or symbols, and hereinafter, the differences from the first embodiment will be mainly described.

[0143] In this embodiment, if Fig.11 and 12 As shown, the first magnet 36B in the first developing roller 30B has a 5-pole magnetic pole structure, wherein the magnetic poles included in the first developing roller 30B are omitted. Figure 3 The first feeding pole 105 and the magnetic pole (feeding pole) 103 in the first developing roller 30 shown. In this configuration, Figure 3 The first transport pole 104 in the first magnet 36 of the embodiment is an N pole, but in the first magnet 36B of the present embodiment, the first transport pole 104 is an S pole.

[0144] In addition, the polarities of the other magnetic poles 101, 102, 106 and 107 are the same as Figure 3In addition, the magnetic flux density and the position where the normal component of the magnetic flux density becomes maximum in each magnetic pole (the position of point C for the transport pole 106) are the same as Figure 3 The same as the first developing roller 30 in FIG. In addition, the second developing roller 31 is Figure 4 The second developing roller 31 having the second magnet 37 inside is the same as shown in FIG. For this reason, the magnetic flux density and the position where the normal component of the magnetic flux density becomes maximum in each magnetic pole (the position of point A for the second feed pole 202) are the same as Figure 4 The same as the second developing roller 31 in.

[0145] By the way, Fig.12 The dotted line shown in the figure indicates the position (peak position) of the maximum value of the magnetic flux density in the second feed pole 202 of the second magnet 37 in the normal direction of the second sleeve 34, and indicates the position (peak position) of the maximum value of the magnetic flux density in the conveying pole 106 of the first magnet 36B in the normal direction of the first sleeve 33.

[0146] In this case of the present embodiment, the first conveying pole 104 of the first magnet 36B is positioned upstream of and adjacent to the conveying pole 106 with respect to the rotation direction of the first sleeve 33. In the present embodiment adopting such a configuration, the magnetic properties of the first developing roller 30B and the second developing roller 31 are as follows: Fig.12 As shown. In the present embodiment, the magnetic pole attracted between itself and the second feed pole 202 in the second developing roller 31 is the first conveying pole 104 in the first developing roller 30B. However, when compared with the configuration of the first embodiment, the first conveying pole 104 in the first developing roller 30B is distant from the second feed pole 202 in the second developing roller 31. In addition, the photosensitive drum 28Y is provided at a position opposite to the first conveying pole 104 in the first developing roller 30B through the first sleeve 33. Between the first conveying pole 104 and the photosensitive drum 28Y, development of the electrostatic latent image by the developer is performed, and therefore, developer transport between the second feed pole 202 in the second developing roller 31 and the first conveying pole 104 in the first developing roller 30B is not likely to occur. In addition, in this case of the present embodiment, similarly to the first embodiment, the occurrence of a streak-like gray fog image can be suppressed.

[0147] <Fourth Embodiment>

[0148] The following will use Figures 13 to 15A fourth embodiment is described. This embodiment is different from the first embodiment in the configuration of the first magnet 36C in the first developing roller 30C and the second magnet 37A in the second developing roller 31A. Other configurations and actions are similar to those in the first embodiment, and therefore, with regard to similar configurations, descriptions and explanations are omitted or briefly described and explained by adding the same reference numerals or symbols, and hereinafter, the differences from the first embodiment will be mainly described.

[0149] The number and polarity of the magnetic poles of the first magnet 36C and the second magnet 37A in the present embodiment are the same as those of the first magnet 36 and the second magnet 37 in the first embodiment. However, in the present embodiment, the following configuration is satisfied.

[0150] First, if Fig.13 As shown, 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 of the maximum value on the second sleeve 34 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. In addition, the magnetic force acting on the developer in the direction of the straight line AB connecting points A and B between the second feed pole 202 on the second sleeve 34 and the first feed pole 105 on the first sleeve 33 is F1. In addition, the magnetic force acting on the developer in the direction of the straight line BD connecting points B and point D between the first feed pole 105 on the first sleeve 33 and the receiving pole 201 on the second sleeve 34 is F3.

[0151] At this time, the repulsive force F3 acting between the first feeding pole 105 in the first developing roller 30 and the receiving pole 201 in the second developing roller 31A can be expressed as:

[0152] F3 = k×MB×MD / L3 2 (Formula 7)

[0153] Incidentally, k is a coefficient similar to that in the first embodiment. Furthermore, the attraction force F1 can also be expressed by Formula 1 similarly to the first embodiment.

[0154] In the first feeding pole 105 in the first developing roller 30, in order to suppress the transport of the developer between the second feeding pole 202 in the second developing roller 31A and the first feeding pole 105 in the first developing roller 30, it may be required that the attraction force F1 from the first feeding pole 105 in the first developing roller 30 toward the second feeding pole 202 in the second developing roller 31A is not greater than the repulsion force F3 based on the first feeding pole 105 in the first developing roller 30 and the receiving pole 201 in the second developing roller 31A. That is, for the above-mentioned equations 1 and 7, it may be required that the following relationship is satisfied:

[0155] F1≤F3 (Formula 8)

[0156] That is, in this embodiment, the magnetic flux density and arrangement of the first feed pole 105, the second feed pole 202 and the receiving pole 201 are set to satisfy Formula 8. Specifically, the positions of MA, MB, MD and the positions of points A, B and D are set to satisfy Formula 8.

[0157] In addition, Fig.14 In FIG. 1 , the relationship between the component force F3′ of the repulsive force F3 in the direction of the straight line AB and the above-mentioned attractive force F1 is shown. When the angle formed by the straight lines AB and BD is θ, when a perpendicular line is drawn from point D to the straight line AB, the point on the straight line AB is D′, and the straight-line distance between point B and point D′ is L3′, L3′ can be expressed by the following equation 9:

[0158] L3' = L3 × cosθ' (Equation 9)

[0159] In the first feeding pole 105 in the first developing roller 30, in order to offset the attraction force F1 received from the second feeding pole 202 in the second developing roller 31, it is desirable that the repulsive force F3' in the straight line BD' direction between the receiving pole 201 in the second developing roller 31 and the first feeding pole 105 in the first developing roller 30 is the attraction force F1 or greater. F3' is the component force of F3 in the straight line AB direction, and can be expressed by the following formula 10:

[0160] F3' = F3 × cosθ' (Equation 10)

[0161] Furthermore, in order to counteract the attractive force F1 by the repulsive force F3', it is desirable to maintain the following relationship:

[0162] F1≤F3' (Formula 11)

[0163] That is, in the present embodiment, it is preferred that Formula 11 is further satisfied, and it is preferred that the magnetic flux density and arrangement of the first feed pole 105, the second feed pole 202, and the receiving pole 201 are set to satisfy Formula 6. Specifically, the positions of the above-mentioned MA, MB, and MD and the positions of point A, point B, and point D are set to satisfy Formula 11.

[0164] [experiment]

[0165] Next, an experiment for checking the occurrence state of the streak-like fog image (abnormal image) in the above-mentioned configuration will be described. In the example, the magnetic flux density MA of the second feeding pole 202 in the second developing roller 31A, the magnetic flux density MB of the first feeding pole 105 in the first developing roller 30C, and the magnetic flux density MD of the receiving pole 201 in the second developing roller 31A are changed from the condition REF, and an image is output by an image forming apparatus in which the various conditions REF and the conveying poles of STUDY 8 to STUDY 12 are combined. Then, the occurrence state of the streak-like fog image on the output image is checked.

[0166] Incidentally, in the experiment, the position of each of the point A where the magnetic flux density on the second feed pole 202 in the second developing roller 31A becomes maximum, the point B where the magnetic flux density on the first feed pole 105 in the first developing roller 30C becomes maximum, and the point C where the magnetic flux density on the receiving pole 201 in the second developing roller 31A becomes maximum is not changed. That is, L1 and L3 are fixed. In addition, the angle θ' formed by the straight lines AB and BD is set to 40°. The other conditions and evaluations of the experiment are the same as those in the first embodiment. The results of the experiment are shown in Fig.15 middle.

[0167] like Fig.15 As shown, in the experiment, the magnetic flux density MA of the second feeding pole 202 in the second developing roller 31A was changed from STUDY 8 to STUDY 10. Fig.15 It can be clearly seen that by reducing MA, vertical streak-like fog images are less likely to appear. In STUDY 9, when the corresponding values ​​are applied to Formula 1 and Formula 7, the conditions of F1≤F3 that each satisfies Formula 8 are obtained, so that the evaluation of the occurrence state of vertical streak-like fog images of the output image becomes the "○" level. Similarly, in STUDY 10, when the corresponding values ​​are applied to Formula 1 and Formula 7 and then to Formula 10, the condition of F1≤F3' that satisfies Formula 11 is obtained, making it possible to confirm that vertical streak-like fog images are no longer likely to appear, and the evaluation becomes the "◎" level.

[0168] In STUDY 11, by changing the condition of the magnetic flux density MD of the receiving pole 201 in the second developing roller 31A, the condition of F1≤F3 satisfying Formula 8 was obtained, so that it was confirmed that an effect similar to that of STUDY 9 could be obtained. In STUDY 12, by changing the conditions of both the magnetic flux density MA of the second feeding 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 of F1≤F3' satisfying Formula 11 was obtained, so that similar to STUDY 10, it was confirmed that the occurrence state of the vertical stripe-like gray fog image of the output image became the "◎" level.

[0169] In the above-mentioned experiment, the magnetic flux density MA of the second feeding pole 202 in the second developing roller 31A cannot always be reduced to any value. When the magnetic force of the magnetic flux density MA of the second feeding pole 202 in the second developing roller 31A is excessively reduced, the developer feeding characteristic of the second developing roller 31A is reduced. For this reason, the magnetic flux density MA can be preferably maintained at a value not less than the magnetic flux density MD on the receiving pole 201 in the second developing roller 31A. In the present embodiment, MB≥MA>MD is satisfied.

[0170] In addition, also with respect to the magnetic flux density MD on the receiving pole 201 in the second developing roller 31A, when the magnetic force is excessively increased, the feeding characteristics of the developer on the second developing roller 31A are reduced. When the magnetic flux density MD on the receiving pole 201 in the second developing roller 31A becomes greater than the magnetic flux density MA on the second feeding pole 202 in the second developing roller 31A, the developer is not easily moved toward the downstream side of the rotation direction of the second sleeve 34. For this reason, it is preferred that the magnetic flux density MD on the receiving pole 201 in the second developing roller 31A is equal to or less than the magnetic flux density MD on the second feeding pole 202 in the second developing roller 31A in terms of magnetic force. That is, in the present embodiment, MD≤MA may be preferably satisfied, and MD<MA may be further preferably satisfied.

[0171] 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, the attraction force F1 between the first feeding pole 105 in the first developing roller 30C and the second feeding pole 202 in the second developing roller 31A is made not greater than the repulsion force F3 based on the first feeding pole 105 in the first developing roller 30C and the receiving pole 201 in the second developing roller 31A, so that the developer can be suppressed from being transported from the second feeding pole 202 toward the first feeding pole 105 in the first developing roller 30C. Therefore, the generation of the above-mentioned streak-like fog image can be suppressed.

[0172] <Fifth Embodiment>

[0173] The following will use Figures 16 to 17 A fifth embodiment is described. This embodiment is different from the fourth embodiment in the configuration of the second feed pole 202 in the second developing roller 31B. Other configurations and actions are similar to those in the fourth embodiment, and therefore, with regard to similar configurations, descriptions and explanations are omitted or briefly described and explained by adding the same reference numerals or symbols, and hereinafter, the differences from the fourth embodiment will be mainly described.

[0174] In this embodiment, the shape of the second feeding pole 202 in the second developing roller 31B is changed compared with the configuration of the fourth embodiment. Specifically, Fig.16As shown, the second feed pole 202 in the second magnet 37B of the second developing roller 31B has a configuration in which point A, which is the position where the normal component of the magnetic flux density in the second feed pole 202 becomes maximum, is closer to the second transport pole 203 in the second developing roller 31B than in the fourth embodiment. Fig.16 The dotted line shown in the figure indicates the position (peak position) of the maximum value of the magnetic flux density in the receiving pole 201 and the second feed pole 202 of the second magnet 37B in the normal direction of the second sleeve 34, and indicates the position (peak position) of the maximum value of the magnetic flux density in the first feed pole 105 of the first magnet 36C in the normal direction of the first sleeve 33.

[0175] Therefore, by making the position of point A of the second feed pole 202 closer to the second conveying pole 203 side, the straight line L1 from point B, which is the position on the first sleeve 33 where the normal component of the magnetic flux density of the first feed pole 105 is the maximum value, to point A can be made longer than in the fourth embodiment. That is, it is preferable to satisfy L1>L3. Incidentally, L1>L3 is also satisfied in the above-mentioned fourth embodiment, but in the present embodiment, the difference between L1 and L3 is made larger than that in the fourth embodiment. Therefore, when the distance L1 increases, the value of the attraction force F1 between the first feed pole 105 in the first developing roller 30C and the second feed pole 202 in the second developing roller 31B becomes smaller. That is, in the present embodiment, by changing the distance L1, the condition of F1≤F3 in the above-mentioned formula 8 is satisfied, and the condition of F1≤F3' in the above-mentioned formula 11 is satisfied.

[0176] [experiment]

[0177] Next, an experiment for checking the occurrence state of streak-like fog image (abnormal image) in the above-mentioned configuration will be described. In the example, the above-mentioned distance 1 is changed starting from the condition REF, and an image is output by an imaging device in which the transport poles of various conditions REF, STUDY 13 and STUDY 14 are combined. Then, the occurrence state of streak-like fog image on the output image is checked.

[0178] The other conditions and evaluations of the experiment were the same as those described in the first embodiment. The results of the experiment are shown in Fig.17 middle.

[0179] like Fig.17As shown, in STUDY 13, the position of point A is changed to a position of L1=11 mm (at this time, the angle θ' formed by the straight line AB and the straight line BD is 44°), and then, similarly to the fourth embodiment, when the attractive force F1 based on the first feed pole 105 in the first developing roller 30C and the second feed pole 202 in the second developing roller 31B and the repulsive force F3 based on the first feed pole 105 in the first developing roller 30C and the receiving pole 201 in the second developing roller 31B are derived, the condition of F1≤F3 satisfying Formula 8 is obtained. In addition, it can be confirmed that the vertical streak-like fog image of the output image is not easy to appear, and therefore the evaluation becomes the "○" level.

[0180] In STUDY 14, the position of point A is changed to a position of L1=13 mm (at this time, the angle θ' formed by the straight line AB and the straight line BD is 49°), and then, similarly to the fourth embodiment, when the attraction force F1 based on the first feed pole 105 in the first developing roller 30C and the second feed pole 202 in the second developing roller 31B and the repulsion force F3' based on the first feed pole 105 in the first developing roller 30C and the receiving pole 201 in the second developing roller 31B are derived, the condition of F1≤F3' satisfying Formula 11 is obtained. In addition, it can be confirmed that the occurrence state of the vertical streak-like fog image of the output image becomes the "◎" level. Therefore, also in this embodiment, similarly to the fourth embodiment, the occurrence of image defects can be suppressed.

[0181] <Sixth Embodiment>

[0182] The following will use Fig.18 and 19 A sixth embodiment is described. This embodiment differs from the fourth embodiment in the configuration of the respective magnetic poles in the second developing roller 31C. Other configurations and functions are similar to those in the fourth embodiment, and therefore, with respect to similar configurations, descriptions and explanations are omitted or briefly described and explained by adding the same reference numerals or symbols, and hereinafter, the differences from the fourth embodiment will be mainly described.

[0183] In this embodiment, if Fig.18 and 19 As shown, the second magnet 37C in the second developing roller 31C has a 5-pole magnetic pole structure, wherein the magnetic poles included in the magnetic poles are omitted. Figure 4 The second feeding pole 202 and the magnetic pole (feeding pole) 204 in the second developing roller 31 are shown. In this configuration, Figure 4 The second transport pole 203 in the second magnet 37 of the embodiment is an S pole, but in the second magnet 37C of the present embodiment, the second transport pole 203 is an N pole.

[0184] In addition, the polarities of the other magnetic poles 201, 205, 206 and 207 are similar to Figure 4 The same as the second magnet 37 in the receiving pole. In addition, the magnetic flux density and the position where the normal component of the magnetic flux density becomes maximum in each magnetic pole (the position of point D for the receiving pole 201) are the same as Figure 4 The first developing roller 30C is the same as the second developing roller 31 in FIG. Fig.13 The first developing roller 30C having the first magnet 36 inside is the same as shown in FIG. For this reason, the magnetic flux density and the position where the normal component of the magnetic flux density becomes maximum in each magnetic pole (the position of point B for the first feed pole 105) are the same as Fig.13 The same as the first developing roller 30C in.

[0185] By the way, Fig.19 The dotted line shown in the figure indicates the position (peak position) of the maximum magnetic flux density in the receiving pole 201 of the second magnet 37C in the normal direction of the second sleeve 34, and indicates the position (peak position) of the maximum magnetic flux density in the first feeding pole 105 of the first magnet 36C in the normal direction of the first sleeve 33.

[0186] In this case of the present embodiment, the second conveying pole 203 of the second magnet 37C is positioned downstream of and adjacent to the receiving pole 201 with respect to the rotation direction of the second sleeve 34. In the present embodiment adopting such a configuration, the magnetic properties of the first developing roller 30C and the second developing roller 31C are as follows: Fig.19 As shown. In the present embodiment, the magnetic pole attracted between itself and the first feed pole 105 in the first developing roller 30C is the second conveying pole 203 in the second developing roller 31C. However, when compared with the configuration of the fourth embodiment, the second conveying pole 203 in the second developing roller 31C is away from the first feed pole 105 in the second developing roller 31C in terms of distance. In addition, the photosensitive drum 28Y is provided at a position opposite to the second conveying pole 203 in the second developing roller 31C through the second sleeve 34. Between the second conveying pole 203 and the photosensitive drum 28Y, development of the electrostatic latent image by the developer is performed, and therefore, the conveyance of the developer between the first feed pole 105 in the first developing roller 30C and the second conveying pole 203 in the second developing roller 31C is not likely to occur. In addition, in this case of the present embodiment, similarly to the fourth embodiment, the occurrence of a streak-like fog image can be suppressed.

[0187] <Other embodiments>

[0188] The above-mentioned first, second and third embodiments have the effect of suppressing vertical streak-like gray fog images generated by the delivery of the developer between the first feed pole 105 in the first developing roller 30, 30A and 30B and the second feed pole 202 in the second developing roller 31 based on the following relationship, which is based on the relationship between the repulsive force F2 of the conveying pole 106 in the first developing roller 30, 30A and 30B and the second feed pole 202 in the second developing roller 31 and the attractive force F1 between the first feed pole 105 in the first developing roller 30, 30A and 30B and the second feed pole 202 in the second developing roller 31. On the other hand, the fourth, fifth and sixth embodiments described above have the effect of suppressing the vertical streak-like fog image generated by the transportation of the developer between the first feeding pole 105 in the first developing roller 30C and the second feeding pole 202 in the second developing rollers 31A, 31B and 31C based on the relationship based on the repulsive force F3 of the receiving pole 201 in the second developing rollers 31A, 31B and 31C and the first feeding pole 105 in the first developing roller 30C and the attractive force F1 between the first feeding pole 105 in the first developing roller 30C and the second feeding pole 202 in the second developing rollers 31A, 31B and 31C. By combining with each of the fourth, fifth and sixth embodiments, such first, second and third embodiments can further enhance the effect of suppressing the vertical streak-like fog image. That is, the first developing roller and the second developing roller are configured to satisfy the condition of the above-mentioned formula 8 or formula 11 in addition to the condition of the above-mentioned formula 3 or formula 6.

[0189] The present invention is not limited to the configuration of the above-described embodiment. For example, the imaging device 100 is not limited to an MFP, but may also be a copier, a printer, or a fax machine. In addition, there is no particular limitation on the configuration of the developer supply screw 42, the developer stirring screw 43, and the developer collecting screw 44, as long as the configuration can convey the developer, and, for example, a spiral blade, a paddle blade may be applied.

[0190] Furthermore, in the above embodiment, a configuration is described in which the first sleeve 33 and the photosensitive drum 28Y rotate in the same direction at positions opposite to each other and the second sleeve 34 and the photosensitive drum 28Y rotate in the same direction at positions opposite to each other, but the present invention is not limited thereto.

[0191] A structure may be adopted in which the rotation center O2 of the second developing roller 31 is arranged above the rotation center O1 of the first developing roller 30, in which the first sleeve 33 and the photosensitive drum 28Y rotate in opposite directions at positions relative to each other, and in which the second sleeve 34 and the photosensitive drum 28Y rotate in opposite directions at positions relative to each other. That is, in this structure, reverse development is performed so that the photosensitive drum 28 rotates from top to bottom in the vertical direction at the position where the photosensitive drum 28 is relative to the first developing roller 30, and reverse development is performed so that the photosensitive drum 28 rotates from top to bottom in the vertical direction at the position where the photosensitive drum 28 is relative to the second developing roller 31. The present invention is also applicable to this structure. In addition, in the case where three or more developing rollers are provided, the present invention may also be applied to any two developing rollers.

[0192] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. A developing device, comprising: a developing container configured to contain a developer including a toner and a carrier; a first rotatable member to which a developer contained in the developing container is supplied and which carries and feeds the developer to a first developing position where an electrostatic latent image formed on an image bearing member is developed; a first magnet non-rotatably and fixedly disposed in the first rotatable member, wherein the first magnet includes a first developing pole disposed opposite to the image bearing member at the first developing position, a conveying pole disposed downstream of the first developing pole with respect to the rotational direction of the first rotatable member, and a first feeding pole disposed upstream of the conveying pole with respect to the rotational direction of the first rotatable member and adjacent to the conveying pole, and the first feeding pole has a magnetic polarity different from that of the conveying pole; a second rotatable member disposed opposite to the first rotatable member and conveying a developer from the first rotatable member to the second rotatable member by a magnetic field generated by the first magnet, wherein the second rotatable member carries and feeds the developer to a second developing position where an electrostatic latent image is developed, and wherein a rotation direction of the second rotatable member at a position on the outer peripheral surface of the second rotatable member where the second rotatable member is closest to the first rotatable member is opposite to a rotation direction of the first rotatable member at a position on the outer peripheral surface of the first rotatable member where the first rotatable member is closest to the second rotatable member; as well as a second magnet which is non-rotatably and fixedly disposed in the second rotatable member, wherein the second magnet includes a plurality of magnetic poles including a second developing pole disposed opposite to the image bearing member at the second developing position, a receiving pole disposed upstream of the second developing pole with respect to the rotational direction of the second rotatable member and having a magnetic polarity different from that of the transport pole, and a second feeding pole disposed downstream of the receiving pole with respect to the rotational direction of the second rotatable member and adjacent to the receiving pole and having a magnetic polarity different from that of the receiving pole, the receiving pole being a magnetic pole disposed closest to the transport pole among the plurality of magnetic poles, In the following cases: an absolute value of a maximum value of the magnetic flux density of the second feed pole in a normal direction relative to the outer peripheral surface of the second rotatable member is MA, On the outer peripheral surface of the second rotatable member, the position where the magnetic flux density of the second feed pole in the normal direction relative to the outer peripheral surface of the second rotatable member is the largest is point A, an absolute value of a maximum value of the magnetic flux density of the first feed pole in a normal direction relative to the outer peripheral surface of the first rotatable member is MB, On the outer peripheral surface of the first rotatable member, the position where the magnetic flux density of the first feed pole in the normal direction relative to the outer peripheral surface of the first rotatable member is the largest is point B, the absolute value of the maximum value of the magnetic flux density of the transport pole in the normal direction relative to the outer peripheral surface of the first rotatable member is MC, The position where the magnetic flux density of the transport pole is maximum in the normal direction relative to the outer peripheral surface of the first rotatable member is point C on the outer peripheral surface of the first rotatable member. The straight-line distance between point A and point B is L1. The straight-line distance between point A and point C is L2, and The angle between the straight line AB connecting points A and B and the straight line AC connecting points A and C is θ. The following relations are satisfied: <h2 style=";text-align:left;direction:ltr">MB / L1<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。 2. The developing device according to claim 1, wherein: The following relationship is also satisfied: MA≥MB>MC.

3. The developing device according to claim 1, wherein: In the case where the absolute value of the maximum value of the magnetic flux density of the receiving pole in the normal direction with respect to the outer peripheral surface of the second rotatable member is MD, the following relationship is also satisfied: MC≤MD.

4. The developing device according to claim 1, wherein: In the case where the absolute value of the maximum value of the magnetic flux density of the receiving pole in the normal direction with respect to the outer peripheral surface of the second rotatable member is MD, the following relationship is also satisfied: MC<MD.

5. The developing device according to claim 1, wherein: The following relationship is also satisfied: L1>L2.

6. The developing device according to claim 1, wherein: In the following cases: The absolute value of the maximum value of the magnetic flux density of the receiving pole in the normal direction relative to the outer peripheral surface of the second rotatable member is MD, On the outer peripheral surface of the second rotatable member, the position where the magnetic flux density of the receiving pole in the normal direction relative to the outer peripheral surface of the second rotatable member is the largest is point D, The straight-line distance between point B and point D is L3, and The angle formed by the straight line AB connecting points A and B and the straight line BD connecting points B and D is θ'. The following relations are satisfied: <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'。 7. The developing device according to claim 6, wherein: The following relationship is also satisfied: MB≥MA>MD.

8. The developing device according to claim 6, wherein: The following relationship is also satisfied; MD≤MA.

9. The developing device according to claim 6, wherein: The following relationship is also satisfied: MD<MA.

10. The developing device according to claim 6, wherein: The following relationship is also satisfied: L1>L3.

11. A developing device, comprising: a developing container configured to contain a developer including a toner and a carrier; The first rotatable member is configured to supply the developer contained in the developing container to the developing container. a first rotatable member, and the first rotatable member carries and feeds the developer to a first developing position where the electrostatic latent image formed on the image bearing member is developed; a first magnet non-rotatably and fixedly disposed in the first rotatable member, wherein the first magnet includes a first developing pole disposed opposite to the image bearing member at the first developing position, a conveying pole disposed downstream of the first developing pole with respect to the rotational direction of the first rotatable member, and a first feeding pole disposed upstream of the conveying pole with respect to the rotational direction of the first rotatable member and adjacent to the conveying pole, and the first feeding pole has a magnetic polarity different from that of the conveying pole; a second rotatable member disposed opposite to the first rotatable member and conveying a developer from the first rotatable member to the second rotatable member by a magnetic field generated by the first magnet, wherein the second rotatable member carries and feeds the developer to a second developing position where an electrostatic latent image is developed, and wherein a rotation direction of the second rotatable member at a position on the outer peripheral surface of the second rotatable member where the second rotatable member is closest to the first rotatable member is opposite to a rotation direction of the first rotatable member at a position on the outer peripheral surface of the first rotatable member where the first rotatable member is closest to the second rotatable member; as well as a second magnet which is non-rotatably and fixedly disposed in the second rotatable member, wherein the second magnet includes a plurality of magnetic poles including a second developing pole disposed opposite to the image bearing member at the second developing position, a receiving pole disposed upstream of the second developing pole with respect to the rotational direction of the second rotatable member and having a magnetic polarity different from that of the transport pole, and a second feeding pole disposed downstream of the receiving pole with respect to the rotational direction of the second rotatable member and adjacent to the receiving pole and having a magnetic polarity different from that of the receiving pole, the receiving pole being a magnetic pole disposed closest to the transport pole among the plurality of magnetic poles, In the following cases: an absolute value of a maximum value of the magnetic flux density of the second feed pole in a normal direction relative to the outer peripheral surface of the second rotatable member is MA, On the outer peripheral surface of the second rotatable member, the position where the magnetic flux density of the second feed pole in the normal direction relative to the outer peripheral surface of the second rotatable member is maximum is point A, an absolute value of a maximum value of the magnetic flux density of the first feed pole in a normal direction relative to the outer peripheral surface of the first rotatable member is MB, On the outer peripheral surface of the first rotatable member, the position where the magnetic flux density of the first feed pole in the normal direction relative to the outer peripheral surface of the first rotatable member is the largest is point B, The absolute value of the maximum value of the magnetic flux density of the receiving pole in the normal direction relative to the outer peripheral surface of the second rotatable member is MD, On the outer peripheral surface of the second rotatable member, the position where the magnetic flux density of the receiving pole in the normal direction relative to the outer peripheral surface of the second rotatable member is the largest is 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, and The angle formed by the straight line AB connecting points A and B and the straight line BD connecting points B and D is θ'. The following relations are satisfied: <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'。 12. The developing device according to claim 11, wherein: The following relationship is also satisfied: MB≥MA>MD.

13. The developing device according to claim 11, wherein: The following relationship is also satisfied; MD≤MA.

14. The developing device according to claim 11, wherein: The following relationship is also satisfied: MD<MA.

15. The developing device according to claim 11, wherein: The following relationship is also satisfied: L1>L3.

16. A developing device, comprising: a developing container configured to contain a developer including a toner and a carrier; a first rotatable member to which a developer contained in the developing container is supplied and which carries and feeds the developer to a first developing position where an electrostatic latent image formed on an image bearing member is developed; a first magnet non-rotatably and fixedly disposed within the first rotatable member, wherein the first magnet includes a first developing pole disposed opposite to the image bearing member at the first developing position, and a conveying pole disposed downstream of the first developing pole with respect to the rotational direction of the first rotatable member and adjacent to the conveying pole and having a magnetic polarity different from that of the conveying pole; a second rotatable member disposed opposite to the first rotatable member and conveying a developer from the first rotatable member to the second rotatable member by a magnetic field generated by the first magnet, wherein the second rotatable member carries and feeds the developer to a second developing position where an electrostatic latent image is developed, and wherein a rotation direction of the second rotatable member at a position on the outer peripheral surface of the second rotatable member where the second rotatable member is closest to the first rotatable member is opposite to a rotation direction of the first rotatable member at a position on the outer peripheral surface of the first rotatable member where the first rotatable member is closest to the second rotatable member; as well as A second magnet, which is non-rotatably and fixedly arranged in the second rotatable member, wherein the second magnet includes a plurality of magnetic poles, the plurality of magnetic poles including a second developing pole arranged opposite to the image bearing member at the second developing position, a receiving pole arranged upstream of the second developing pole with respect to the rotation direction of the second rotatable member and having a magnetic polarity different from that of the conveying pole, and a feeding pole arranged downstream of the receiving pole with respect to the rotation direction of the second rotatable member and adjacent to the receiving pole and having a magnetic polarity different from that of the receiving pole, the receiving pole being the magnetic pole arranged closest to the conveying pole among the plurality of magnetic poles.

17. A developing device, comprising: a developing container configured to contain a developer including a toner and a carrier; a first rotatable member to which a developer contained in the developing container is supplied and which carries and feeds the developer to a first developing position where an electrostatic latent image formed on an image bearing member is developed; a first magnet non-rotatably and fixedly disposed in the first rotatable member, wherein the first magnet includes a first developing pole disposed opposite to the image bearing member at the first developing position, a conveying pole disposed downstream of the first developing pole with respect to the rotational direction of the first rotatable member, and a feeding pole disposed upstream of the conveying pole with respect to the rotational direction of the first rotatable member and adjacent to the conveying pole, and the feeding pole has a magnetic polarity different from that of the conveying pole; a second rotatable member disposed opposite to the first rotatable member and conveying a developer from the first rotatable member to the second rotatable member by a magnetic field generated by the first magnet, wherein the second rotatable member carries and feeds the developer to a second developing position where an electrostatic latent image is developed, and wherein a rotation direction of the second rotatable member at a position on the outer peripheral surface of the second rotatable member where the second rotatable member is closest to the first rotatable member is opposite to a rotation direction of the first rotatable member at a position on the outer peripheral surface of the first rotatable member where the first rotatable member is closest to the second rotatable member, A second magnet, which is non-rotatably and fixedly arranged in the second rotatable member, wherein the second magnet includes a plurality of magnetic poles, the plurality of magnetic poles including a second developing pole arranged opposite to the image bearing member at the second developing position, and a receiving pole arranged upstream of the second developing pole relative to the rotation direction of the second rotatable member and adjacent to the second developing pole, and the receiving pole has a magnetic polarity different from the magnetic polarity of the second developing pole and different from the magnetic polarity of the conveying pole, and the receiving pole is the magnetic pole arranged closest to the conveying pole among the plurality of magnetic poles.

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