Developing apparatus

Abstract

The invention relates to a developing device. A first maximum position where a magnetic flux density of the first magnetic pole is maximum is positioned downstream of the first development position and upstream of the first closest position. A second maximum position where the magnetic flux density of the third pole is maximum is positioned downstream of the second closest position and upstream of the second development position. In a case where r1 * [theta] 1 > r2 * [theta] 2 is satisfied: r1 represents a radius of the first rotatable developing member, r2 represents a radius of the second rotatable developing member, [theta] 1 represents an angle from the first maximum position to the first closest position in a rotation direction of the first rotatable developing member, and [theta] 2 represents an angle from the second maximum position to the second closest position in a rotation direction of the second rotatable developing member. And [theta] 2 represents an angle from the second closest position to the second maximum position in a rotation direction of the second rotatable developing member.

Description

Technical Field

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

[0002] As a developing device, a configuration has been proposed in which two developing rollers for developing an electrostatic latent image formed on an image bearing member with a developer are arranged side by side in the rotation direction of the image bearing member (US2013 / 0330107). In the developing device described in US2013 / 0330107, the developer is supplied from a supply unit to a first developing roller (first rotatable developing member) positioned lower in the vertical direction among the two developing rollers, and the developer is conveyed from the first developing roller positioned lower to a second developing roller (second rotatable developing member) positioned higher in the vertical direction.

[0003] As described in US2013 / 0330107, in a configuration in which the developer is conveyed from the first developing roller to the second developing roller positioned higher in the vertical direction, the developer is conveyed from the first developing roller to the second developing roller against gravity. Here, the composite magnetic force generated by the magnets built into the first developing roller and the second developing roller and the gravity act on the magnetic carrier included in the developer on the first developing roller. Therefore, in order to convey the developer from the first developing roller to the second developing roller, it is necessary to direct the force obtained by adding gravity to the composite magnetic force in a direction away from the first developing roller (toward the second developing roller).

[0004] In this regard, if the magnetic flux density of the receiving pole of the magnet in the second developing roller (which is the magnetic pole that receives the developer from the first developing roller) is increased to a certain extent, the magnetic force can be directed toward the second developing roller even when the influence of gravity is taken into account. However, when the magnetic flux density of the receiving pole of the magnet in the second developing roller is excessively increased, the developer conveyed to the second developing roller tends to stay near the receiving pole, with the result that shear force acts on the developer, which may cause deterioration of the developer, generation of agglomerates, etc. Therefore, image defects may occur.

[0005] The present invention improves the transferability of the developer from the first rotatable developing member to the second rotatable developing member while suppressing the degradation of the developer conveyed from the first rotatable developing member to the second rotatable developing member. Summary of the invention

[0006] According to one aspect of the present invention, a developing device includes: a first rotatable developing member, a developer including a colorant and a carrier is supplied to the first rotatable developing member, the first rotatable developing member is configured to carry and feed the developer to a first developing position; a first magnet, the first magnet is non-rotatably and fixedly arranged inside the first rotatable developing member, the first magnet has a first magnetic pole and a second magnetic pole, the second magnetic pole is arranged downstream of the first magnetic pole in the rotation direction of the first rotatable developing member and is adjacent to the first magnetic pole, and has a magnetic polarity identical to that of the first magnetic pole; a second rotatable developing member, the second rotatable developing member is arranged to face the first rotatable developing member, and is configured to receive the developer conveyed from the first rotatable developing member through a magnetic field generated by the first magnet, the second rotatable developing member is configured to carry the developer and feed the developer to a first developing position The image agent is carried and fed to a second developing position, the second rotatable developing member having a rotation axis positioned vertically higher than the rotation axis of the first rotatable developing member, the first rotatable developing member having a rotation direction opposite to the rotation direction of the second rotatable developing member at a first closest position, the first rotatable developing member being closest to the second rotatable developing member on the outer surface of the first rotatable developing member at the first closest position, and the second rotatable developing member being closest to the first rotatable developing member on the outer surface of the second rotatable developing member at the second closest position; and a second magnet, the second magnet being non-rotatably and fixedly disposed inside the second rotatable developing member, the second magnet having a third magnetic pole, the third magnetic pole being arranged to face the first magnetic pole and having a magnetic polarity different from that of the first magnetic pole. A first maximum position is positioned downstream of the first developing position and upstream of the first closest position in the rotation direction of the first rotatable developing member, at which the magnetic flux density of the first magnetic pole in a normal direction relative to the outer peripheral surface of the first rotatable developing member is maximum. The second maximum position is positioned downstream of the second closest position and upstream of the second developing position in the rotational direction of the second rotatable developing member, at which the magnetic flux density of the third magnetic pole in the normal direction relative to the outer peripheral surface of the second rotatable developing member is maximum. The relationship of r1×θ1>r2×θ2 is satisfied when r1 represents the radius of the first rotatable developing member, r2 represents the radius of the second rotatable developing member, θ1 represents the angle from the first maximum position to the first closest position in the rotational direction of the first rotatable developing member, and θ2 represents the angle from the second closest position to the second maximum position in the rotational direction of the second rotatable developing member.

[0007] 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

[0008] Figure 1 is a schematic cross-sectional view showing the configuration of an imaging apparatus according to the embodiment.

[0009] Figure 2 is a schematic cross-sectional view showing the configuration of a developing device according to the embodiment.

[0010] Figure 3 is a view showing a magnetic pole arrangement of a first developing roller according to the embodiment.

[0011] Figure 4 is a view showing a magnetic pole arrangement of a second developing roller according to the embodiment.

[0012] Figure 5 is a view showing a magnetic pole arrangement of a peeling roller according to an embodiment.

[0013] Figure 6 : is a view showing a magnetic pole arrangement relationship between a first developing roller and a second developing roller according to the embodiment.

[0014] Figure 7 is a detailed view showing a magnetic pole arrangement relationship between a first developing roller and a second developing roller according to a comparative example.

[0015] Figure 8 is a detailed view showing a magnetic pole arrangement relationship between a first developing roller and a second developing roller according to the embodiment.

[0016] Fig. 9 is a graph showing the magnetic characteristics of the first developing roller according to the embodiment.

[0017] Fig.10 is a graph showing the magnetic characteristics of the second developing roller according to the embodiment.

[0018] Fig.11 is a graph showing the force acting on the magnetic carrier on the first developing roller according to the embodiment.

[0019] Fig.12 is a graph showing the force acting on the magnetic carrier on the first developing roller according to Examples 1 and 2 and Comparative Examples 1 and 2.

[0020] Fig.13 is a graph showing the force acting on the magnetic carrier on the first developing roller according to Examples 1, 3, and 4.

[0021] Fig.14is a graph showing the force acting on the magnetic carrier on the first developing roller according to Examples 1 and 5 and Comparative Example 1. DETAILED DESCRIPTION

[0022] Will refer to Figures 1 to 14 First, reference will be made to the embodiment. Figure 1 A schematic configuration of the imaging apparatus of this embodiment is described.

[0023] Imaging equipment

[0024] The image forming apparatus 100 is a full-color image forming apparatus, and in the present embodiment, is, for example, a multifunction peripheral (MFP) having a copy function, a printer function, and a scanner function. Figure 1 As shown, the image forming apparatus 100 includes parallel image forming units PY, PM, PC, and PK that respectively perform image forming processes for toner images of four colors of yellow, magenta, cyan, and black.

[0025] The image forming units PY, PM, PC and PK of the respective colors include primary chargers 21Y, 21M, 21C and 21K, developing devices 1Y, 1M, 1C and 1K, optical writing units (exposure devices) 22Y, 22M, 22C and 22K, photosensitive drums 28Y, 28M, 28C and 28K, and cleaning devices 26Y, 26M, 26C and 26K. The image forming apparatus 100 includes a transfer device 2 and a fixing device 3. Since the configurations of the image forming units PY, PM, PC and PK of the respective colors are similar to each other, the image forming unit PY will be described below as a representative.

[0026] The photosensitive drum 28Y used as an image bearing member is a photosensitive member including a photosensitive layer made of a resin (e.g., a polycarbonate resin containing an organic photoconductor (OPC)), and is configured to rotate at a predetermined speed. The primary charger 21Y includes a corona discharge electrode arranged around the photosensitive drum 28Y, and charges the surface of the photosensitive drum 28Y with generated ions.

[0027] The optical writing unit 22Y includes a scanning optical device, and exposes the charged photosensitive drum 28Y based on the image data to reduce the potential of the exposed portion, thereby forming a charge pattern (electrostatic latent image) corresponding to the image data. The developing device 1Y transfers the contained developer to the photosensitive drum 28Y to develop the electrostatic latent image formed on the photosensitive drum 28Y. The developer is formed by mixing a carrier and a toner corresponding to each color, and the electrostatic latent image is visualized by the toner.

[0028] The transfer device 2 includes primary transfer rollers 23Y, 23M, 23C, and 23K, an intermediate transfer belt 24, and a secondary transfer roller 25. The intermediate transfer belt 24 is wound around the primary transfer rollers 23Y, 23M, 23C, and 23K and a plurality of rollers, and is supported so as to be able to travel. Figure 1 The secondary transfer roller 25 is arranged outside the intermediate transfer belt 24 and is configured to allow the recording material to pass between the secondary transfer roller 25 and the intermediate transfer belt 24. Note that the recording material is, for example, a sheet (e.g., paper or a plastic sheet).

[0029] The toner images of the respective colors formed on the photosensitive drums 28Y, 28M, 28C, and 28K are sequentially transferred to the intermediate transfer belt 24 by the primary transfer rollers 23Y, 23M, 23C, and 23K, thereby forming toner images of the respective colors of yellow, magenta, cyan, and black layered in a superimposed manner. The formed toner images are transferred to the recording material conveyed from a box or the like storing the recording material by the secondary transfer roller 25. In the fixing device 3, pressure and heat are applied to the recording material to which the toner images are transferred. As a result, the toner on the recording material is melted, and the color image is fixed to the recording material.

[0030] 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 respective colors of yellow, magenta, cyan, and black are replaceably loaded in order from the top. The developer storage portions 27Y, 27M, 27C, and 27K are configured to be able to feed (replenish) developers to the developing devices 1Y, 1M, 1C, and 1K corresponding to the colors of the contained developers.

[0031] For example, the weight ratio of the toner of the developer contained in the bottle is 80% to 95%, and the weight ratio of the toner of the developer in each of the developing devices 1Y, 1M, 1C, and 1K is 5% to 10%. Therefore, once the toner is consumed to perform development in the developing devices 1Y, 1M, 1C, and 1K, the developer containing the toner is replenished by the consumed amount, and the weight ratio of the toner of the developer in each of the developing devices 1Y, 1M, 1C, and 1K is maintained constant.

[0032] Development equipment

[0033] Next, we will refer to Figures 2 to 5 The developing devices 1Y, 1M, 1C, and 1K are described in detail. Since the configurations of the developing devices 1Y, 1M, 1C, and 1K are the same as one another, the developing device 1Y will be described below as a representative. Figure 2 It shows Figure 1 The conceptual diagram of the developing device 1Y shown in FIG. Figure 3 , Figure 4 and Figure 5 1Y is a conceptual diagram showing the magnetic pole configuration of the first magnet 36 , the second magnet 37 , and the third magnet 38 arranged in the developing device 1Y.

[0034] 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 .

[0035] The first developing roller 30 is a developer carrying member that is rotationally driven, and is arranged 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 rotating first sleeve (first rotatable developing member) 33 and a first magnet (fixed magnet) 36 that is non-rotatably provided inside the first sleeve 33 and attracts the developer to the surface of the first sleeve 33 by magnetic force. Then, the first developing roller 30 attracts (carries) the developer from the developer supply screw 42 based on the magnetic force, and develops the electrostatic latent image formed on the rotating photosensitive drum 28Y (on the image bearing member) with the developer.

[0036] The first sleeve 33 is a non-magnetic cylindrical member having an outer diameter of 25 mm (radius r1 = 12.5 mm), and is rotationally driven around the rotation axis 39. The rotation direction of the first sleeve 33 is as follows: Figure 2 , and in the present embodiment, is the clockwise direction indicated by the arrow in , and is the direction opposite to the rotation direction of the photosensitive drum 28Y. Therefore, the first sleeve 33 and the photosensitive drum 28Y rotate in the same direction at a position facing each other. That is, forward development is performed in which the photosensitive drum 28 rotates upward in the vertical direction at a position where the photosensitive drum 28 faces the first sleeve 33.

[0037] The first magnet 36 is arranged inside the first sleeve 33 and has a plurality of magnetic poles 101 to 107. Figure 3 shown. Figure 3 Each solid line for magnetic poles 101 to 107 shown in FIG. 1 indicates the position of the maximum value (peak position or magnetic pole position) of the normal component distribution of the magnetic flux density of the first magnet 36. A space allowing the first sleeve 33 to rotate is arranged between the inner periphery of the first sleeve 33 and the outer periphery of the first magnet 36.

[0038] The developer attracted to the first sleeve 33 is fed toward the photosensitive drum 28Y by the rotation operation of the first sleeve 33, thereby developing the latent image formed on the photosensitive drum 28Y at the first development position. After the latent image formed on the photosensitive drum 28Y is developed, the developer on the first sleeve 33 is fed 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 of the first developing roller 30 and the second developing roller 31, the developer is peeled off from the first sleeve 33 by the magnetic field generated by the first magnet 36 in the first developing roller 30 and the second magnet 37 in the second developing roller 31, and is conveyed to the second sleeve 34.

[0039] As described below, the second developing roller 31 of the developing device 1Y of the present embodiment is positioned vertically higher than the first developing roller 30. Therefore, it is also necessary to perform the conveyance of the developer from the first sleeve 33 to the second sleeve 34 upward in the vertical direction against the gravity. Note that the first sleeve 33 and the second sleeve 34 are arranged with a gap of 3 mm between the closest portions.

[0040] The second developing roller 31 is a developer carrying member that is rotationally driven, is arranged downstream of the first developing roller 30 in the rotation direction of the photosensitive drum 28Y so that the rotation center O2 of the second developing roller 31 is positioned higher than the rotation center O1 of the first developing roller 30 in the vertical direction, and receives the developer conveyed from the first developing roller 30 by magnetic force ( Figure 2 ). In the present embodiment, the entire second developing roller 31 is positioned higher than the rotation center O1 of the first developing roller 30. Similar to the first developing roller 30, the second developing roller 31 is arranged 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. Therefore, the rotation axes of the second developing roller 31 and the first developing roller 30 are substantially parallel to each other.

[0041] This second developing roller 31 includes a second sleeve (second rotatable developing member) 34 that rotates and a second magnet (fixed magnet) 37 that is non-rotatably provided inside the second sleeve 34 and attracts the developer to the surface of the second sleeve 34 by magnetic force. Then, the second developing roller 31 receives the developer conveyed from the first developing roller 30 (first sleeve 33) based on the magnetic force, attracts (carries) the developer, and develops the electrostatic latent image formed on the rotating photosensitive drum 28Y with the developer. The peeling roller 32 described below is positioned on one side of the second developing roller 31.

[0042] The second sleeve 34 is a non-magnetic cylindrical member having an outer diameter of 25 mm (radius r2 = 12.5 mm), and is rotationally driven around the rotation axis 40. The rotation direction of the second sleeve 34 is as follows: Figure 2, which is the clockwise direction indicated by the arrow in (which is the same as the rotation direction of the first sleeve 33), and in the present embodiment, is the direction opposite to the rotation direction of the photosensitive drum 28Y. Therefore, the second sleeve 34 and the photosensitive drum 28Y rotate in the same direction at a position facing each other. That is, forward development is performed in which the photosensitive drum 28 rotates upward in the vertical direction at a position where the photosensitive drum 28 faces the second sleeve 34. The second sleeve 34 and the first sleeve 33 rotate in opposite directions at a position facing each other.

[0043] The second magnet 37 is arranged inside the second sleeve 34 and has a plurality of magnetic poles 201 to 207. Figure 4 shown. Figure 4 Each solid line for magnetic poles 201 to 207 shown in FIG.

[0044] The developer attracted to the second sleeve 34 is fed toward the photosensitive drum 28Y by the rotation operation of the second sleeve 34, thereby developing the latent image formed on the photosensitive drum 28Y at the second development position. After the latent image formed on the photosensitive drum 28Y is developed, the developer remaining on the second sleeve 34 is fed 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 of the second developing roller 31 and the peeling roller 32, the developer is transported 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 in the second developing roller 31 and the third magnet 38 in the peeling roller 32.

[0045] The peeling roller 32 serving as a peeling portion is arranged 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 arranged between the second developing roller 31 and the developer collecting screw 44 so that its rotation center is positioned higher than the rotation center O2 of the second developing roller 31.

[0046] The peeling roller (third rotatable member) 32 is arranged so that its rotation axis is substantially parallel to the rotation axis of the second developing roller 31. The peeling roller 32 includes a rotating third sleeve 35 and a third magnet (fixed magnet) 38 which is non-rotatably provided inside the third sleeve 35 and attracts the developer to the surface of the third sleeve 35 by magnetic force, and is configured to receive the developer conveyed from the second developing roller 31 based on the magnetic force.

[0047] The third sleeve 35 is a non-magnetic cylindrical member having an outer diameter of 18 mm (radius of 9 mm), and is rotationally driven around the rotation axis 41. The rotation direction of the third sleeve 35 is as follows: Figure 2 , and in this embodiment, is the counterclockwise direction indicated by the arrow in , 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 a position facing each other.

[0048] The third magnet 38 is arranged inside the third sleeve 35 and has a plurality of magnetic poles 301 to 305. Figure 5 shown. Figure 5 Each solid line for magnetic poles 301 to 305 shown in FIG.

[0049] The developer attracted to the third sleeve 35 is fed downstream in the rotation direction by the rotation operation of the third sleeve 35, is peeled off from the third sleeve 35 by the third magnet 38 in the peeling roller 32 at a position close to the developer collecting screw 44, and falls by its own weight toward the guide member 45 positioned lower in the vertical direction. Then, the developer dropped onto the guide member 45 is guided toward the developer collecting screw 44 by its own weight.

[0050] The guide member 45 and the developer collecting screw 44 constitute a developer collecting portion 47, which serves as a collecting portion (collecting chamber) for collecting the developer peeled off from the third sleeve 35 of the peeling roller 32. In the developer collecting portion 47, the developer collecting screw 44 is arranged so that the rotation center is positioned lower than the rotation center of the peeling roller 32 in the vertical direction, and feeds the developer conveyed (collected) from the peeling roller 32 while stirring the developer.

[0051] The guide member 45 serving as a guide portion is arranged below the peeling roller 32 in the vertical direction, and guides the developer peeled by the peeling roller 32 toward the developer collecting screw 44. This guide member 45 has an inclined surface 45a on which the developer slides downward by its own weight so as to more 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 the portion positioned below the peeling roller 32 is positioned higher than the portion adjacent to the developer collecting screw 44.

[0052] The developer collecting screw 44 serving as a collecting member and a feeding portion feeds the collected developer to a developer circulation portion 46 described below. That is, the developer collecting screw 44 is a screw feeding member for feeding the developer in one direction while stirring the developer sliding down along the inclined surface of the guide member 45 and being collected.

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

[0054] The developer supply screw 42, the developer stirring screw 43, and the developer collecting screw 44 are screw feeding members that feed the developer in one direction while stirring the developer, and the developer supply screw 42 and the developer stirring screw 43 are positioned vertically lower than the developer collecting screw 44. 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 axis of each screw is substantially parallel to the rotation axis of the first developing roller 30.

[0055] The developer supply screw 42 is positioned between the first developing roller 30 and the developer stirring screw 43, and the partition wall 48 of the developing container 60 is arranged between the developer supply screw 42 and the developer stirring screw 43. The partition wall 48 of the developing container 60 extends in the direction of the rotation axis of the developer supply screw 42 and the developer stirring screw 43. The partition wall 48 has a communication port (not shown) for communication between a first feeding path 61 through which the developer is fed by the developer supply screw 42 and a second feeding path 62 through which the developer is fed by the developer stirring screw 43.

[0056] The developer stirred by the developer collecting screw 44 passes through a communication port (not shown) formed in a partition wall 63 of the developing container 60 between the developer collecting screw 44 and the developer supplying screw 42, and 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.

[0057] The position of the communication port through which the developer stirred by the developer collecting screw 44 falls by its own weight and is introduced into the developer circulation portion 46 is preferably arranged to avoid the area (the middle portion of the developer supply screw 42 in the rotation axis direction) where the developer is supplied toward the first developing roller 30. In the present embodiment, it is assumed that the position of the communication port is a position within the range of the downstream end portion (terminal end portion) in the developer feeding direction of the first feeding path 61 in which the developer supply screw 42 is arranged.

[0058] The developer feeding directions of the developer supply screw 42 and the developer stirring screw 43 are opposite to each other. 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 are connected to the terminal end side and the starting end side of the second feeding path 62 in which the developer stirring screw 43 is arranged via the communication port provided in the partition wall 48. Therefore, the developer is fed along Figure 2 The developer supply screw 42 and the developer stirring screw 43 rotate in the direction indicated by the arrow in FIG. 4 and circulate in a substantially horizontal direction inside the developing container 60 , and a portion of the developer is supplied toward the first developing roller 30 .

[0059] The developer supply port 51 (see 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 The developer replenishing port 51 is configured to be able to replenish the developer contained in the bottle loaded in the developer storage portion 27Y to the second feeding path 62 in which the developer stirring screw 43 is arranged.

[0060] As described above, since the weight ratio of the colorant of the developer contained in the bottle of the developer storage portion 27Y is higher than the weight ratio of the colorant of the developer in the developing device 1Y, the weight ratio of the colorant of the developer in the developing device 1 can be maintained constant by adjusting the amount of developer to be replenished to the developer stirring screw 43.

[0061] A toner concentration detection sensor 49 (see Figure 2 ) to detect the toner concentration in the developer contained in the developer circulation portion 46. The toner concentration detection sensor 49 is a sensor that detects the magnetic permeability of the developer. Since the toner concentration corresponds to the toner consumption in the developing device 1Y, the toner concentration is used to control the developer replenishment from the developer storage portion 27Y. For example, when it is detected that the toner concentration is lower than a predetermined value, the developer is replenished from the developer storage portion 27Y. Since the magnetic permeability of the developer changes according to the toner concentration, the toner concentration can be detected using the magnetic permeability.

[0062] The regulating member 50 is arranged 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. For example, 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.

[0063] In the developer circulation path in the developing container 60, the developer is fed in a substantially horizontal direction while being stirred in the developer circulation portion 46, and then is supplied to the first developing roller 30, and is conveyed from the first developing roller 30 to the second developing roller 31 positioned higher than the first developing roller 30 based on the magnetic force. Then, the developer is conveyed again from the second developing roller 31 to the peeling roller 32 positioned at one side of the second developing roller 31 based on the magnetic force, and then is peeled from the peeling roller 32 by the third magnet 38 in the peeling roller 32, is further collected by the developer collecting portion 47, and is introduced into the developer circulation portion 46 again.

[0064] As described above, in this embodiment, a two-component developing method is used as a developing method, and a mixture of a non-magnetic toner having a negatively charged polarity and a magnetic carrier is used as a developer. The non-magnetic toner is obtained by including a colorant, a wax component, etc. in a resin (for example, a polyester resin or a styrene acrylic resin), crushing or polymerizing the resin into a powder, and adding fine powders of titanium oxide, silicon dioxide, etc. to the surface. The magnetic carrier is obtained by applying a resin coating to the surface layer of a core formed by ferrite particles or resin particles kneaded with magnetic powder. In this embodiment, the toner concentration in the developer in the initial state (the weight ratio of the toner contained in the developer) is 8%.

[0065] Note that in an applied magnetic field of 1000 oersted (79577 A / m), the magnetic carrier preferably has 40Am 2 / kg and above and 80Am 2 / kg or less of the magnetization amount per unit weight. When the magnetization amount of the magnetic carrier is reduced, there is an effect of suppressing the removal of the magnetic brush, but it becomes difficult for the magnetic carrier to adhere to the non-magnetic sleeve through the magnet inside the developing roller, and image defects such as the magnetic carrier adhering to the photosensitive drum may occur. Note that removal is a phenomenon in which the developed colorant is scraped off by the magnetic carrier that has completed development. When the magnetization amount of the magnetic carrier is greater than the above range, as described above, image defects may occur due to the removal of the magnetic brush. In this embodiment, a magnetization amount of 63Am per unit weight is used. 2 / kg of magnetic carrier.

[0066] The magnetization amount of the magnetic carrier is measured using an oscillating magnetic field type automatic magnetic property recording device BHV-30 manufactured by RIKEN Denshi Co., Ltd. For the magnetic property value of the magnetic carrier, an external magnetic field of 1000 oersted is generated, and the magnetization intensity at this time is obtained. The magnetic carrier is packed in a cylindrical plastic container in a sufficiently dense manner. In this state, the magnetization torque is measured, the actual weight when the sample is put in is measured, and the magnetization intensity (Am 2 / kg).

[0067] The true specific gravity of the magnetic carrier was determined by a dry automatic density type AccuPyc 1330 manufactured by Shimadzu Corporation. In this example, a true specific gravity (density) of 4.6 (g / cm 3 ) A magnetic carrier having a weight average diameter of 35 μm (radius b=17.5 μm) was used.

[0068] Generally, in a two-component developing method using a toner and a carrier, the toner and the carrier are charged to a predetermined polarity by frictional contact with each other, and therefore have a characteristic that the stress received by the toner is smaller than the stress in a single-component developing method using a single-component developer. On the other hand, long-term use increases the dirt (waste) attached to the surface of the carrier, and thus the ability of the toner to be charged gradually decreases. Therefore, problems such as atomization and toner scattering occur. In order to extend the life of a two-component developing device, it is conceivable to increase the amount of the carrier contained in the developing device. However, in this case, the size of the developing device may increase, which is not desirable.

[0069] In order to solve the above-mentioned problems related to the two-component developer, an automatic carrier renewal (ACR) method is adopted in this embodiment. The ACR method is a method of suppressing the increase of deteriorated carriers by gradually replenishing new developer from the developer storage portion 27Y into the developing device 1Y and gradually discharging the developer with deteriorated charging performance from the discharge port (not shown) of the developing device 1Y. Therefore, the deteriorated carrier in the developing device 1Y is gradually replaced by a new carrier, and the charging performance of the carrier in the developing device 1Y can be kept substantially constant.

[0070] The magnetic poles of each magnet

[0071] Next, we will describe Figure 3 , Figure 4 and Figure 5 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 are shown in .

[0072] like Figure 3As shown, the first magnet 36 in the first developing roller 30 has a plurality of magnetic poles 101, 102, 103, 104, 105, 106 and 107. The magnetic pole 107 is a transport pole for transporting 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 in the rotation direction of the first sleeve 33. As described above, Figure 3 Each solid line of the magnetic poles 101 to 107 shown in FIG. 1 represents the position (magnetic pole position) of the peak value (maximum value) of the magnitude of the normal component Br of the magnetic flux density of the first magnet 36 relative to the surface of the first sleeve 33. The same applies to Figure 4 The magnetic poles 201 to 207 of the second magnet 37 shown in FIG. Figure 5 Magnetic poles 301 to 305 of the third magnet 38 are shown in FIG.

[0073] The magnetic pole 107 used as a conveying pole (first magnetic pole) is a magnetic pole for conveying the developer from the first sleeve 33 to the second sleeve 34 by a magnetic field generated in cooperation with the second magnet 37 of the second developing roller 31, and hereinafter, may be referred to as the conveying pole 107. The magnetic pole 101 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, 104, 105, and 106 are respectively an S pole, an N pole, an S pole, an N pole, and an S pole, and are used to feed upward the developer attracted by the magnetic pole 101 as the first sleeve 33 rotates. The magnetic pole 107 is an N pole, and conveys the developer from the first sleeve 33 to the second sleeve 34 facing the first sleeve 33 by a magnetic field generated in cooperation with the magnetic pole 201 in the second magnet 37 in the second developing roller 31 as described above.

[0074] In the present embodiment, a repulsive magnetic field cooperatively generated between the conveying pole 107 and a magnetic pole 101 serving as a second magnetic pole (which is arranged downstream of the conveying pole 107 in the rotation direction of the first sleeve 33 and has the same magnetic polarity as the conveying pole 107) forms a low magnetic force portion 110 having a magnetic force lower than that of the conveying pole 107. The low magnetic force portion 110 promotes the conveyance of the developer from the first sleeve 33 to the second sleeve 34. Note that in the present embodiment, the low magnetic force portion 110 has almost no magnetic force, but may have a relatively low magnetic force, and may be, for example, 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 shown in FIG. Figure 5 The low magnetic force portion 310 of the third magnet 38 is shown in FIG.

[0075] like Figure 4As shown, the second magnet 37 in the second developing roller 31 has a plurality of magnetic poles 201, 202, 203, 204, 205, 206 and 207. The magnetic pole 201 is a receiving pole for the second developing roller 31 to receive the developer from the first developing roller 30. The magnetic poles 201 to 207 are arranged in numerical order in the rotation direction of the second sleeve 34.

[0076] The magnetic pole 201 used as the receiving pole (third magnetic 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 107 of the first magnet 36 of the first developing roller 30, and hereinafter, may be referred to as the receiving pole 201. The magnetic pole (fifth 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.

[0077] Furthermore, the receiving pole 201 is an S pole having a magnetic polarity different from that of the conveying pole 107, 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 poles 202, 203, 204, 205, and 206 are respectively an N pole, an S pole, an N pole, an S pole, and an N pole, and are used to feed upward the developer attracted by the magnetic pole 201 as the second sleeve 34 rotates. The magnetic pole 207 is an S pole, and the developer having passed through the developing area corresponding to the magnetic pole 203 between the second magnet 37 and the photosensitive drum 28Y is conveyed from the second sleeve 34 to the third sleeve 35 facing the second sleeve 34 by the magnetic field generated in cooperation with the magnetic pole 303 of the third magnet 38 in the peeling roller 32.

[0078] In the present embodiment, a repulsive magnetic field generated by cooperation between the receiving pole 207 and a magnetic pole 207 serving as a fifth magnetic pole (which is arranged upstream of the receiving pole 201 in the rotation direction of the second sleeve 34 and has the same magnetic polarity as the receiving pole 201) forms a low magnetic force portion 210 having a magnetic force lower than that of the magnetic pole 207. The low magnetic force portion 210 promotes the conveyance of the developer from the first sleeve 33 to the second sleeve 34. In addition, the low magnetic force portion 210 can prevent the developer from being attracted to the closest portion of the first sleeve 33 and the second sleeve 34, so that the pressure applied to the developer can be suppressed.

[0079] like Figure 5 As shown, the third magnet 38 in the peeling roller 32 has a plurality of magnetic poles 301, 302, 303, 304, and 305. The magnetic poles 301 to 305 are arranged in numerical order in the rotation direction of the third sleeve 35.

[0080] The magnetic pole 303 is an N pole having a magnetic polarity different from that of the magnetic pole 207, and is used to attract the developer stripped from the second sleeve 34 to the third sleeve 35 as described above. The magnetic poles 301, 302, and 304 are an N pole, an S pole, and an S pole, respectively, and are used to feed the developer on the third sleeve 35 as the third sleeve 35 rotates. In particular, 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 magnetic polarity.

[0081] Magnetic pole arrangement relationship

[0082] Next, we will refer to Figures 6 to 8 The arrangement relationship between the magnetic poles of the first magnet 36 arranged inside the first developing roller 30 and the magnetic poles of the second magnet 37 arranged inside the second developing roller 31 is described. Figure 6 1 is a conceptual diagram showing the arrangement of the first developing roller 30 and the second developing roller 31 of the present embodiment, and particularly shows the layout of the conveying pole 107 of the first magnet 36 of the first developing roller 30 and the receiving pole 201 of the second magnet 37 of the second developing roller 31. Note that some magnetic poles are omitted in the drawings to avoid complexity.

[0083] Figure 7 and Figure 8 A schematic configuration of an area where the first and second developing rollers 30 and 31 face each other (ie, an adjacent area where the conveying pole 107 of the first magnet 36 or 36A of the first developing roller 30 and the receiving pole 201 of the second magnet 37 of the second developing roller 31 face each other) is shown. Figure 7 The configuration of a comparative example is shown, and the first developing roller 30 includes a first magnet 36A. Figure 8 An exemplary configuration is shown, and the first developing roller 30 includes a first magnet 36 .

[0084] exist Figure 7 and Figure 8 , the center O2 of the second developing roller 31 is located vertically higher than the center O1 of the first developing roller 30. This means that, as described above, the developer is conveyed from the first sleeve 33 to the second sleeve 34 upward against the gravity.

[0085] The intersection points A1 and A2 between the line (dashed line in the figure) connecting the center O1 of the first developing roller 30 and the center O2 of the second developing roller 31 and the first sleeve 33 and the second sleeve 34 are the closest positions of the sleeves 33 and 34. That is, the intersection point A1 is the closest position (first closest position) of the first sleeve 33 relative to the second sleeve 34. The intersection point A2 is the closest position (second closest position) of the second sleeve 34 relative to the first sleeve 33.

[0086] In addition, the magnetic pole position (the position of the maximum value of the magnitude of the normal component Br of the magnetic flux density (peak position, first magnetic pole position or first maximum position)) of the conveying pole 107 of the first magnet 36 or 36A of the first developing roller 30 on the first sleeve 33 is B1, and the magnetic pole position (the position of the maximum value of the magnitude of the normal component Br of the magnetic flux density (peak position, second magnetic pole position or second maximum position)) of the receiving pole 201 of the second magnet 37 of the second developing roller 31 on the second sleeve 34 is B2. In this case, the first magnetic pole position B1 of the conveying pole 107 on the first sleeve 33 is positioned upstream of the first closest position A1 of the first sleeve 33 relative to the second sleeve 34 in the rotation direction of the first sleeve 33. The second magnetic pole position B2 of the receiving pole 201 on the second sleeve 34 is positioned downstream of the second closest position A2 of the second sleeve 34 relative to the first sleeve 33 in the rotation direction of the second sleeve 34.

[0087] When the first magnetic pole position B1 of the conveying pole 107 and the second magnetic pole position B2 of the receiving pole 201 are arranged in this manner, the developer fed on the first sleeve 33 of the first developing roller 30 is conveyed to the second sleeve 34 of the second developing roller 31 before reaching the closest positions A1 and A2 of the two sleeves 33 and 34. Since the closest positions A1 and A2 are narrower in space than other positions of the two sleeves 33 and 34, when the developer passes through the closest positions A1 and A2, a greater pressure is applied to the developer, and therefore, the developer may be deteriorated due to shear force, etc. Therefore, in the present embodiment, the first magnetic pole position B1 and the second magnetic pole position B2 are arranged as described above.

[0088] Here, the angle formed by the magnetic pole position B1 of the conveying pole 107 of the first magnet 36 of the first developing roller 30 relative to the first closest position A1 of the first sleeve 33 relative to the second sleeve 34 is θ1. That is, the angle formed by the line L1 connecting the first magnetic pole position B1 and the rotation center O1 of the first sleeve 33 and the line L2 connecting the first closest position A1 and the rotation center O1 of the first sleeve 33 is θ1. The angle formed by the magnetic pole position B2 of the receiving pole 201 of the second magnet 37 of the second developing roller 31 relative to the second closest position A2 of the second sleeve 34 relative to the first sleeve 33 is θ2. That is, the angle formed by the line L3 connecting the second magnetic pole position B2 and the rotation center O2 of the second sleeve 34 and the line L4 connecting the second closest position A2 and the rotation center O2 of the second sleeve 34 is θ2. Figure 7 In the comparative example shown, θ1<θ2, and in Figure 8 In the embodiment shown, θ1>θ2.

[0089] Assuming that the radius of the first sleeve 33 is r1 and the radius of the second sleeve is r2, if θ1 and θ2 are in radians, the circumferential distance between the first magnetic pole position B1 and the first closest position A1 of the conveying pole 107 on the first sleeve 33 is r1×θ1, and the circumferential distance between the second magnetic pole position B2 and the second closest position A2 of the receiving pole 201 on the second sleeve 34 is r2×θ2. As described above, the radii r1 and r2 of the first sleeve 33 and the second sleeve 34 of the developing device 1Y of this embodiment are both 12.5 mm.

[0090] Therefore, in Figure 7 In the comparative example shown in , since θ1<θ2, (r1×θ1)<(r2×θ2). That is, the distance between the first closest position A1 and the first magnetic pole position B1 is shorter than the distance between the second closest position A2 and the second magnetic pole position B2. On the other hand, in Figure 8 In the present embodiment shown, since θ1>θ2, (r1×θ1)>(r2×θ2). That is, the distance between the first closest position A1 and the first magnetic pole position B1 is longer than the distance between the second closest position A2 and the second magnetic pole position B2. In the present embodiment, the case where the radius r1 and the radius r2 of the first sleeve 33 and the second sleeve 34 are the same has been described. However, even when the radii are different from each other, it is sufficient if (r1×θ1)>(r2×θ2).

[0091] As described above, ideal conveyance of the developer is performed such that the developer on the first sleeve 33 is fed on the first sleeve 33 until reaching the first magnetic pole position B1 of the conveying pole 107 while receiving a force in a direction toward the center (O1) of the first sleeve 33, and after passing through the first magnetic pole position B1 of the conveying pole 107, the developer is smoothly conveyed to the second sleeve 34 by receiving a force in a direction away from the center (O1) of the first sleeve 33 (i.e., in a direction toward the second sleeve 34) until reaching the first closest position A1 relative to the second sleeve 34. When the developer is smoothly conveyed as described above, retention of the developer between the two sleeves 33 and 34 is less likely to occur, and image defects due to developer deterioration associated with the retention can be suppressed.

[0092] In such Figure 7 In the case of the magnetic pole arrangement in the comparative example shown, in order to achieve smooth developer conveyance as described above, there are the following problems. Figure 7 In the comparative example, the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first magnetic pole position B1 of the conveying pole 107 is shorter than the distance r2×θ2 from the second closest position A2 of the second sleeve 34 to the second magnetic pole position B2 of the receiving pole 201. Therefore, the developer is fed on the first sleeve 33 while receiving a force in the direction (O1) toward the center of the first sleeve 33, and reaches the magnetic pole position B1 of the conveying pole 107 after passing the position of the second magnetic pole position B2 of the receiving pole 201 facing the second sleeve 34.

[0093] Therefore, after the developer on the first sleeve 33 is fed to the first magnetic pole position B1 of the conveying pole 107, in order to overcome the gravity and receive the force in the direction toward the second sleeve 34, it is necessary to increase the magnitude (peak value) of the magnetic flux density Br (normal component) of the receiving pole 201 of the second magnet 37 of the second developing roller 31. When the magnitude of the magnetic flux density Br of the receiving pole 201 increases, the developer is easily constrained at the position of the receiving pole 201, and the possibility of developer degradation increases due to shearing accompanying the rotation of the second sleeve 34.

[0094] On the other hand, Figure 8 In the present embodiment shown, the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first magnetic pole position B1 of the conveying pole 107 is longer than the distance r2×θ2 from the second closest position A2 of the second sleeve 34 to the second magnetic pole position B2 of the receiving pole 201. Therefore, the developer is fed to the magnetic pole position B1 of the conveying pole 107 on the first sleeve 33 in a state where it receives a force in a direction toward the center (O1) of the first sleeve 33, and then reaches a position facing the second magnetic pole position B2 of the receiving pole 201 of the second sleeve 34.

[0095] Therefore, after the developer on the first sleeve 33 is fed to the first magnetic pole position B1 of the conveying pole 107, the magnetic flux density of the conveying pole 107 from the first magnet 36 gradually decreases toward the downstream, and the force in the direction toward the center (O1) of the first sleeve 33 for the developer gradually weakens. On the other hand, since the magnetic flux density of the receiving pole 201 from the second magnet 37 gradually increases toward the downstream as the distance to the position facing the receiving pole 201 decreases, the force in the direction toward the second sleeve 34 (i.e., the force in the direction away from the center (O1) of the first sleeve 33) gradually increases.

[0096] Then, after the developer on the first sleeve 33 is fed to the first magnetic pole position B1 of the conveying pole 107, the developer overcomes gravity and receives a force in the direction toward the second sleeve 34, and smooth conveyance of the developer is easily achieved. Figure 8 In the present embodiment shown in FIG. , there is no need for Figure 7 The magnitude (peak value) of (the normal component of) the magnetic flux density Br of the receiving pole 201 of the second magnet 37 of the second developing roller 31 is forcibly increased as in the comparative example shown in , and the possibility of developer degradation can also be reduced.

[0097] Fig. 9 2 is a view schematically showing the distribution of the normal component Br of the magnetic flux density of the first magnet 36 on the first sleeve 33 according to the present embodiment. Fig.10 : is a view schematically showing the distribution of the normal component Br of the magnetic flux density of the second magnet 37 of the present embodiment on the second sleeve 34. Note that the magnetic flux density Br accurately refers to the component of the magnetic flux density B in the normal direction relative to the sleeve. In the following, according to convention, the "normal component Br of the magnetic flux density" may be referred to as "magnetic flux density". It is assumed that the simple term "magnetic flux density" refers to the "normal component Br of the magnetic flux density". The magnetic flux density Br (normal component Br of the magnetic flux density) of each magnet is measured using a magnetic field meter ("MS-9902" manufactured by FWBELL), where the distance between the probe (which is a component of the magnetic field meter) and the surface of the sleeves 33 and 34 is about 100μm.

[0098] exist Fig. 9 In FIG. 1 , the position corresponding to the first closest position A1 of the first sleeve 33 and the first magnetic pole position B1 of the transport pole 107 is indicated by a dotted line. Fig.10The positions corresponding to the second closest position A2 of the second sleeve 34 and the second magnetic pole position B2 of the receiving pole 201 are shown. The angle θ1 formed by the first closest position A1 of the first sleeve 33 and the first magnetic pole position B1 of the transport pole 107 is larger than the angle θ2 formed by the second closest position A2 of the second sleeve 34 and the second magnetic pole position B2 of the receiving pole 201.

[0099] Fig.11 The magnetic attraction force Fr is schematically shown, by which the magnetic carrier of the developer on the first sleeve 33 is attracted in the direction toward the center (O1) of the first sleeve 33. In the following, the "magnetic attraction force Fr in the direction toward the center (O1) of the first sleeve" may be simply referred to as the "magnetic attraction force". It is assumed that the simple term "magnetic attraction force" refers to the "magnetic attraction force Fr in the direction toward the center (O1) of the first sleeve 33". The magnetic attraction force Fr of the first sleeve 33 can be derived from the normal component Br of the magnetic flux density and is expressed by the following formula 1.

[0100] Mathematical formula 1

[0101]

[0102] In Formula 1, μ represents the magnetic permeability of the magnetic carrier, μ0 represents the vacuum magnetic permeability, and b represents the radius of the magnetic carrier. The tangential component Bθ of the magnetic flux density is obtained from Formula 2 below using the value of the normal component Br of the magnetic flux density.

[0103] Mathematical formula 2

[0104]

[0105] For the magnetic attraction force Fr received by the magnetic carrier on the first sleeve 33, in addition to the influence of the first magnet 36, the influence of the second magnet 37 needs to be considered. To this end, it is necessary to obtain the normal component Br of the magnetic flux density and the tangential component Bθ of the magnetic flux density in the calculation of the magnetic attraction force Fr of the above formula 1 by considering the influence of both the first magnet 36 and the second magnet 37. In addition, it is necessary to consider the influence of gravity on the magnetic carrier. Therefore, Fig.11 The figure shows an overview of the force (=magnetic attraction Fr+gravity) by which the magnetic carrier of the developer on the first sleeve 33 is attracted in the direction toward the center (O1) of the first sleeve 33, and the force is obtained by considering the influence of both the first magnet 36 and the second magnet 37 plus the influence of gravity. The gravity on the magnetic carrier is represented by the product Mg of the weight M of the magnetic carrier and the gravitational acceleration g, and the weight M of the magnetic carrier is calculated by the volume (4πb 3In this graph, the portion related to the transport of the developer is shown in an enlarged manner, and the position corresponding to the first closest position A1 of the first developing roller 30 and the first magnetic pole position B1 of the transport pole 107 is also indicated by a dotted line.

[0106] from Fig.11 It can be seen that the force (magnetic attraction Fr+gravity) received by the magnetic carrier on the first sleeve 33 in the direction toward the center (O1) of the first sleeve 33 is an attraction force until the magnetic carrier reaches the first magnetic pole position B1 of the conveying pole 107, and then changes to a repulsive force against gravity until the magnetic carrier reaches the first closest position A1 while being fed. That is, among the forces acting on the carrier contained in the developer on the first sleeve 33 and obtained by adding gravity to the magnetic attraction force of both the first magnet 36 and the second magnet 37, the component in the direction toward the rotation center O1 of the first sleeve 33 is an attraction force at the first magnetic pole position B1, and changes from an attraction force to a repulsive force while the developer is fed from the first magnetic pole position B1 to the first closest position A1 in the rotation direction of the first sleeve 33. The repulsive force refers to a force in a direction away from the center (O1) of the first sleeve 33. Therefore, it is considered that the magnetic carrier on the first sleeve 33 is fed on the first sleeve 33 until reaching the first magnetic pole position B1 of the conveying pole 107, and then the developer is smoothly conveyed from the first sleeve 33 to the second sleeve 34 upward in the vertical direction until reaching the first closest position A1.

[0107] Fig.12 The force (magnetic attraction Fr+gravity) received by the magnetic carrier on the first sleeve 33 in the direction toward the center (O1) of the first sleeve 33 is shown when the angle θ1 between the first magnetic pole position B1 and the first closest position A1 of the conveying pole 107 changes and the angle θ2 between the second magnetic pole position B2 and the second closest position A2 of the receiving pole 201 is fixed under the condition that the magnitude of the magnetic flux density Br of the conveying pole 107 of the first developing roller 30 is 40mT and the magnitude of the magnetic flux density Br of the receiving pole 201 of the second developing roller 31 is 50mT. The conditions are shown in Table 1.

[0108] Table 1

[0109]

[0110] In Table 1, it should be understood that θ1 and θ2 must be converted to radians before being multiplied by r1 and r2, respectively.

[0111] In Examples 1 and 2, the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first magnetic pole position B1 of the conveying pole 107 is longer than the distance r2×θ2 from the second closest position A2 of the second sleeve 34 to the second magnetic pole position B2 of the receiving pole 201. Fig.12 From the distribution of the magnetic attraction force Fr+gravity of Examples 1 and 2 in FIG. 1 , it can be seen that a repulsive force is generated upstream of the first closest position A1. Therefore, it is considered that the developer fed to the first magnetic pole position B1 of the conveying pole 107 on the first sleeve 33 overcomes gravity and is smoothly conveyed to the second sleeve 34 until it reaches the first closest position A1. In the actual research of the inventors, under the conditions of these configurations, the degradation of the developer due to idling is suppressed. Idling is an operation in which the first developing roller 30, the second developing roller 31, the stripping roller 32, the developer supply screw 42, the developer stirring screw 43 and the developer collecting screw 44 of the developing device are rotated in a state in which the developer is contained in the developing container 60, but is not accompanied by a developing operation of developing the electrostatic latent image on the photosensitive drum using the developer.

[0112] Meanwhile, in Comparative Example 2, the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first magnetic pole position B1 of the conveying pole 107 is shorter than the distance r2×θ2 from the second closest position A2 of the second sleeve 34 to the second magnetic pole position B2 of the receiving pole 201. Fig.12 It can be seen from the distribution of the magnetic attraction force Fr+gravity of Comparative Example 2 in that no repulsive force against gravity is generated. Therefore, it is considered that the developer fed to the first magnetic pole position B1 of the conveying pole 107 on the first sleeve 33 is delayed in conveyance to the second sleeve 34, and retention may occur. In the actual study of the inventors, in the case of the configuration of Comparative Example 2, developer degradation due to idling occurs.

[0113] In Comparative Example 1, the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first magnetic pole position B1 of the conveying pole 107 is the same as the distance r2×θ2 from the second closest position A2 of the second sleeve 34 to the second magnetic pole position B2 of the receiving pole 201. Fig.12From the distribution of the magnetic attraction force Fr+gravity of Comparative Example 1, it can be seen that a repulsive force is generated to resist the gravity, but the magnitude of the repulsive force is small. The moment when the repulsive force is generated is the moment immediately before the upstream of the first closest position A1 or the moment when the first closest position A1 is reached. Therefore, the developer fed to the first magnetic pole position B1 of the conveying pole 107 on the first sleeve 33 is slightly lacking in smoothness in conveyance to the second sleeve 34, and therefore, it is considered that retention begins to occur near the first closest position A1. In the actual research of the inventor, in the case of the construction of Comparative Example 1, the deterioration of the developer due to idling is more suppressed than that of Comparative Example 2, but the deterioration of the developer due to idling occurs more than that of Examples 1 and 2.

[0114] As described above, the degradation of the developer can be suppressed by making the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first magnetic pole position B1 of the conveying pole 107 longer than the distance r2×θ2 from the second closest position A2 of the second sleeve 34 to the second magnetic pole position B2 of the receiving pole 201 (i.e., by satisfying r1×θ1>r2×θ2). In addition, if the degradation of the developer can be suppressed, the occurrence of image defects can be suppressed.

[0115] The magnetic pole position of the magnet fluctuates slightly during manufacturing. In view of this, it is preferred to increase the distance by a distance corresponding to 3°, that is, it is preferred that the above relationship between the magnetic pole position and the closest position satisfies r1×(θ1-3°)≥r2×θ2. In addition, it is more preferred to increase the distance by a distance corresponding to 5°, that is, r1×(θ1-5°)≥r2×θ2 is satisfied. In addition, it is more preferred to increase the distance by a distance corresponding to 7°, that is, r1×(θ1-7°)≥r2×θ2 is satisfied. With the above construction, even when the magnetic pole position of the magnet fluctuates during manufacturing, the deterioration of the developer can be suppressed. In the inequality, it should be understood that all angles should be in radians before multiplying by r1 or r2, or all angles should be in degrees. If the same unit is used consistently, each side of the inequality is multiplied by a coefficient.

[0116] As described above, in the present embodiment, the effect of suppressing the deterioration of the developer can be obtained by making the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first magnetic pole position B1 of the conveying pole 107 longer than the distance r2×θ2 from the second closest position A2 of the second sleeve 34 to the second magnetic pole position B2 of the receiving pole 201. However, the effect of further suppressing the deterioration of the developer can be obtained by adopting the following configuration.

[0117] exist Fig. 9In the magnetic flux density Br distribution (normal component Br distribution of magnetic flux density) of the first magnet 36 of the first developing roller 30 on the first sleeve 33, the angle x on the downstream side of the first magnetic pole position B1 in the rotation direction of the first sleeve 33 is shown within the half-peak width of the normal component of the magnetic flux density of the conveying pole 107. For reference, Fig. 9 Also shown is the position of the second magnetic pole position B2 of the receiving pole 201 facing the second sleeve 34. At this time, it is preferred that the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first magnetic pole position B1 of the conveying pole 107 is longer than the distance r2×θ2 from the second closest position A2 of the second sleeve 34 to the second magnetic pole position B2 of the receiving pole 201 by a distance corresponding to the angle x on the downstream side in the rotation direction of the first sleeve 33 within the half-peak width of the magnetic flux density Br distribution of the conveying pole 107, that is, r1×(θ1-x)≥r2×θ2.

[0118] In the above-described configuration, after the magnetic flux density Br of the conveying pole 107 is reduced by more than half, the developer fed on the first sleeve 33 reaches the position of the second magnetic pole position B2 facing the receiving pole 201 of the second sleeve 34. Therefore, when the magnetic flux density Br of the conveying pole 107 is sufficiently weakened, the developer that has passed through the first magnetic pole position B1 of the conveying pole 107 on the first sleeve 33 can receive the magnetic attraction force from the magnetic flux density Br of the receiving pole 201. Therefore, the developer fed to the first magnetic pole position B1 of the conveying pole 107 on the first sleeve 33 overcomes the gravity and is smoothly conveyed to the second sleeve 34 until it reaches the first closest position A1.

[0119] The angle x of Examples 1 and 2 described above, which is located on the downstream side of the first sleeve 33 in the rotation direction of the first magnet 36 within the half-peak width of the magnetic flux density Br distribution, is 7°. In Example 2, the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first magnetic pole position B1 of the conveying pole 107 is longer than the distance r2×θ2 from the second closest position A2 of the second sleeve 34 to the second magnetic pole position B2 of the receiving pole 201 by a certain distance, which corresponds to an angle of 7° on the downstream side within the half-peak width of the conveying pole (r1×(θ1-7°)=r2×θ2). Although the distance is further increased in Example 1, from Fig.12It can be seen that there is no significant difference in repulsive force between Example 1 and Example 2. It is believed that this is because, in Example 2, the distance has been increased by a distance corresponding to an angle of 7° on the downstream side within the half-value width of the conveying pole, and therefore, a sufficient effect is obtained at this stage. In the inequality, it should be understood that all angles should be in radians before multiplying by r1 or r2, or all angles should be in degrees. If the same units are used consistently, each side of the inequality is multiplied by a coefficient.

[0120] As described above, by making the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first magnetic pole position B1 of the conveying pole 107 longer than the distance r2×θ2 from the second closest position A2 of the second sleeve 34 to the second magnetic pole position B2 of the receiving pole 201 by a certain distance (the distance corresponds to the angle x on the downstream side of the rotation direction of the first sleeve 33 within the half-peak width of the magnetic flux density Br distribution of the conveying pole 107) (r1×(θ1-x)≥r2×θ2), the developer can be smoothly conveyed from the first sleeve 33 to the second sleeve 34 while more effectively suppressing the deterioration of the developer.

[0121] Figure 8 The third magnetic pole position (third maximum position) B3 of the magnetic pole 202 (fourth magnetic pole) located downstream of the receiving pole 201 in the rotation direction of the second sleeve 34 on the second sleeve 34 is shown. The magnetic pole 202 corresponds to the fourth magnetic pole of the second magnet 37, which has a magnetic polarity different from that of the receiving pole 201, and is located downstream of the receiving pole 201 in the rotation direction of the second sleeve 34 to be adjacent to the receiving pole 201. The position (peak position) of the maximum value of the normal component of the magnetic flux density of the magnetic pole 202 is defined as the third magnetic pole position B3. The angle formed by the magnetic pole 202 and the second closest position A2 is θ3. That is, the angle formed by the line L5 connecting the third magnetic pole position B3 and the rotation center O2 of the second sleeve 34 and the line L4 connecting the second closest position A2 and the rotation center O2 of the second sleeve 34 is θ3. Figure 8 Angle θ3 is also shown.

[0122] It is not preferred that the portion from the first closest position A1 of the first sleeve 33 to the first magnetic pole position B1 of the conveying pole 107 faces the magnetic pole 202 located downstream of the receiving pole 201 in the rotation direction of the second sleeve 34. This is because since the conveying pole 107 and the magnetic pole 202 have the same magnetic polarity, a repulsive magnetic field is generated due to the magnetic poles with the same magnetic polarity facing each other, as a result of which problems are prone to occur when conveying the developer. Therefore, it is preferred that the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first magnetic pole position B1 of the conveying pole 107 is shorter than the distance r2×θ3 from the second closest position A2 of the second sleeve 34 to the third magnetic pole position B3 of the magnetic pole 202, that is, r1×θ1<r2×θ3. In the present embodiment, θ3=47°, which is sufficiently larger than θ1 of the present embodiment. In the present embodiment, r1=r2=12.5mm. Therefore, as Figure 8 As shown in , r1×θ1<r2×θ3.

[0123] When the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first magnetic pole position B1 of the conveying pole 107 is longer than the distance r2×θ2 from the second closest position A2 of the second sleeve 34 to the second magnetic pole position B2 of the receiving pole 201 as in Examples 1 and 2, a sufficient repulsive force is generated upstream of the first closest position A1 in the distribution of the magnetic attraction force Fr+gravity, as Fig.12 As shown. Therefore, in this configuration, even when the magnitude of (the normal component of) the magnetic flux density Br of the receiving pole 201 is reduced, sufficient repulsive force can be obtained. When the magnitude of (the normal component of) the magnetic flux density Br of the receiving pole 201 can be reduced, the developer is less likely to be constrained at the position of the receiving pole 201, and the deterioration of the developer due to shearing accompanying the rotation of the second sleeve 34 can be further suppressed.

[0124] Fig.13 The force (magnetic attraction Fr+gravity) received by the magnetic carrier on the first sleeve 33 in the direction toward the center (O1) of the first sleeve 33 when the magnitude of the magnetic flux density Br of the receiving pole 201 of the second developing roller 31 changes, when the angle θ1 between the first magnetic pole position B1 and the first closest position A1 of the conveying pole 107 and the angle θ2 between the second magnetic pole position B2 and the second closest position A2 of the receiving pole 201 are fixed and the magnitude of the magnetic flux density Br of the conveying pole 107 of the first developing roller 30 is 40mT is shown. The conditions are shown in Table 2. Fig.13 The results of Example 1 in Table 1 are also shown for comparison.

[0125] Table 2

[0126]

[0127] In Table 2, it should be understood that θ1 and θ2 must be converted to radians before multiplying by r1 and r2, respectively.

[0128] from Fig.13 From the distribution of the magnetic attraction force Fr+gravity in FIG, it can be seen that even when the magnitude of the magnetic flux density Br of the receiving pole 201 is equal to or less than the magnitude of the magnetic flux density Br of the conveying pole 107 as in Examples 3 and 4, a repulsive force is generated upstream of the first closest position A1. Therefore, it is considered that the developer fed to the first magnetic pole position B1 of the conveying pole 107 on the first sleeve 33 is smoothly conveyed to the second sleeve 34 against the gravity until it reaches the first closest position A1. In the actual study of the inventors, in the case of these configurations, the deterioration of the developer due to idling is suppressed, and the deterioration of the developer is suppressed more than when the magnitude of the magnetic flux density Br of the receiving pole 201 of Example 1 is 50 mT.

[0129] This is considered to be because, since the magnitude of (the normal component of) the magnetic flux density Br of the receiving pole 201 can be reduced, the developer is less likely to be confined at the position of the receiving pole 201, and further the degradation of the developer due to shearing accompanying the rotation of the second sleeve 34 is suppressed. Therefore, as long as a repulsive force is generated upstream of the first closest position A1 in the distribution of the magnetic attraction force Fr+gravity, the magnitude of (the normal component of) the magnetic flux density Br of the receiving pole 201 can be reduced to make the developer less likely to be confined at the position of the receiving pole 201, and further the degradation of the developer due to shearing accompanying the rotation of the second sleeve 34 is suppressed.

[0130] The magnitude of (the normal component of) the magnetic flux density Br of the receiving pole 201 in Example 4 is smaller than that in Example 3. However, the deterioration of the developer due to idling is almost the same between Example 3 and Example 4. Although the magnitude of (the normal component of) the magnetic flux density Br of the receiving pole 201 in Example 4 is smaller, Fig.13 The repulsive force generated upstream of the first closest position A1 is also smaller. Therefore, the point that the force used to constrain the developer at the position of the receiving pole 201 is smaller is conducive to suppressing the degradation of the developer due to idling, while the point that the force used to move the developer to the second sleeve 34 is smaller is not conducive to suppressing the degradation of the developer due to idling. Therefore, it is considered that the degradation of the developer is basically the same between Example 3 and Example 4. As described above, it is not preferred to reduce the magnitude of the magnetic flux density Br (normal component) of the receiving pole 201 to the extent that no repulsive force is generated upstream of the first closest position A1 in the distribution of the magnetic attraction force Fr+gravity.

[0131] The magnitude of (the normal component of) the magnetic flux density Br of the receiving pole 201 is preferably 0.5 times or more the magnitude of (the normal component of) the magnetic flux density Br of the transport pole 107. As in Example 4, the magnitude of (the normal component of) the magnetic flux density Br of the receiving pole 201 is more preferably 0.75 times or more the magnitude of (the normal component of) the magnetic flux density Br of the transport pole 107, and further more preferably 1.0 times or more.

[0132] On the other hand, as described above, when the magnitude of (the normal component of) the magnetic flux density Br of the receiving pole 201 excessively increases, the developer may be confined at the position of the receiving pole 201, and therefore, there is a possibility that the developer may be deteriorated due to shearing accompanying the rotation of the second sleeve 34. Therefore, the magnitude of (the normal component of) the magnetic flux density Br of the receiving pole 201 is preferably 1.5 times or less, and more preferably 1.25 times or less, the magnitude of (the normal component of) the magnetic flux density Br of the transport pole 107.

[0133] Similar to Examples 1 and 2 and Comparative Examples 1 and 2, Fig.14 It shows the magnetic attraction force Fr (+ gravity) received by the magnetic carrier on the first sleeve 33 in the direction toward the center (O1) of the first sleeve 33 when the angle θ2 between the second magnetic pole position B2 and the second closest position A2 of the receiving pole 201 is changed and the angle θ1 between the first magnetic pole position B1 and the first closest position A1 of the conveying pole 107 is the same as that in Comparative Example 1 under the condition that the magnitude of the magnetic flux density Br of the conveying pole 107 of the first developing roller 30 is 40mT and the magnitude of the magnetic flux density Br of the receiving pole 201 of the second developing roller 31 is 50mT. The conditions are shown in Table 3. Fig.14 The results of Example 1 and Comparative Example 1 are also shown.

[0134] Table 3

[0135]

[0136] In Table 3, it should be understood that θ1 and θ2 must be converted to radians before being multiplied by r1 and r2, respectively.

[0137] from Fig.14 From the distribution of the magnetic attraction force Fr (+ gravity) in , it can be seen that a repulsive force is generated upstream of the first closest position A1 in Example 5. In actual studies by the inventors, in the case of these configurations, developer degradation due to idling is suppressed.

[0138] Compared with Comparative Example 1, Example 1 has achieved r1×θ1>r2×θ2 by changing the angle θ1 between the first magnetic pole position B1 and the first closest position A1 of the transport pole 107, and Example 5 has achieved r1×θ1>r2×θ2 by changing the angle θ2 between the second magnetic pole position B2 and the second closest position A2 of the receiving pole 201, and thus similar effects are obtained. This shows that the relative positional relationship between the first magnetic pole position B1 of the transport pole 107 and the second magnetic pole position B2 of the receiving pole 201 is important, and there is no limitation on the means for achieving the relative positional relationship.

[0139] Other embodiments

[0140] The present invention is not limited to the configurations of the above-described embodiments. For example, the imaging device 100 is not limited to an MFP, but may be a copier, a printer, or a fax machine. In addition, the configurations of the developer supply screw 42, the developer stirring screw 43, and the developer collecting screw 44 are not particularly limited as long as the developer can be fed, and, for example, a spiral blade or a paddle blade may be applied.

[0141] In the above embodiment, the configuration in which the first sleeve 33 and the photosensitive drum 28Y rotate in the same direction at positions facing each other and the second sleeve 34 and the photosensitive drum 28Y rotate in the same direction at positions facing each other has been described, but the present technology is not limited thereto. The rotation center O2 of the second developing roller 31 may be positioned vertically higher than the rotation center O1 of the first developing roller 30, the first sleeve 33 and the photosensitive drum 28Y may rotate in opposite directions at positions facing each other, and the second sleeve 34 and the photosensitive drum 28Y may rotate in opposite directions at positions facing each other. That is, reverse development is performed in which the photosensitive drum 28 rotates downward in the vertical direction at a position where the photosensitive drum 28 faces the first developing roller 30, and the photosensitive drum 28 rotates downward in the vertical direction at a position where the photosensitive drum 28 faces the second developing roller 31. The present technology may also be applied to such a configuration. In the case where three or more developing rollers are provided, the present technology may also be applied to any two developing rollers.

[0142] 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 modifications and equivalent structures and functions.

Claims

1. A developing device, comprising: a first rotatable developing member to which a developer including a toner and a carrier is supplied, the first rotatable developing member being configured to carry and feed the developer to a first developing position; a first magnet that is non-rotatably and fixedly disposed inside the first rotatable developing member, the first magnet having a first magnetic pole and a second magnetic pole, the second magnetic pole being disposed downstream of and adjacent to the first magnetic pole in the rotation direction of the first rotatable developing member and having the same magnetic polarity as that of the first magnetic pole; a second rotatable developing member, the second rotatable developing member being arranged to face the first rotatable developing member and being configured to receive the developer conveyed from the first rotatable developing member by a magnetic field generated by the first magnet, the second rotatable developing member being configured to carry and feed the developer to a second developing position, the second rotatable developing member having a rotation axis positioned vertically higher than the rotation axis of the first rotatable developing member, the first rotatable developing member having a rotation direction opposite to the rotation direction of the second rotatable developing member at a first closest position, the first rotatable developing member being closest to the second rotatable developing member on an outer surface of the first rotatable developing member at the first closest position, and the second rotatable developing member being closest to the first rotatable developing member on an outer surface of the second rotatable developing member at the second closest position; as well as a second magnet that is non-rotatably and fixedly disposed inside the second rotatable developing member, the second magnet having a third magnetic pole that is arranged to face the first magnetic pole and has a magnetic polarity different from that of the first magnetic pole, in a first maximum position located downstream of the first developing position and upstream of the first closest position in the rotational direction of the first rotatable developing member, at which the magnetic flux density of the first magnetic pole in a normal direction relative to an outer peripheral surface of the first rotatable developing member is maximum, a second maximum position at which the magnetic flux density of the third magnetic pole in a normal direction relative to an outer peripheral surface of the second rotatable developing member is maximum, and is positioned downstream of the second closest position and upstream of the second developing position in the rotation direction of the second rotatable developing member, In the following case, the relationship r1×θ1>r2×θ2 is satisfied, where r1 represents the radius of the first rotatable developing member, r2 represents the radius of the second rotatable developing member, θ1 represents an angle from the first maximum position to the first closest position in the rotation direction of the first rotatable developing member, and θ2 represents an angle from the second closest position to the second maximum position in the rotation direction of the second rotatable developing member.

2. The developing device according to claim 1, wherein the second magnet further has a fourth magnetic pole which is disposed downstream of and adjacent to the third magnetic pole in the rotational direction of the second rotatable developing member and has a magnetic polarity different from that of the third magnetic pole, a third maximum position at which the magnetic flux density of the fourth magnetic pole in a normal direction relative to an outer peripheral surface of the second rotatable developing member is maximum and is positioned downstream of the second maximum position and upstream of the second developing position in the rotation direction of the second rotatable developing member, Where θ3 represents an angle from the second closest position to the third maximum position in the rotational direction of the second rotatable developing member, a relationship of r1×θ1<r2×θ3 is satisfied.

3. The developing device according to claim 1 or 2, wherein When x represents the angle on the downstream side of the first maximum position in the rotation direction of the first rotatable developing member within the half-peak width of the magnetic flux density of the first magnetic pole in the normal direction relative to the outer peripheral surface of the first rotatable developing member, the relationship r1×(θ1-x)≥r2×θ2 is satisfied.

4. The developing device according to claim 1 or 2, wherein The relationship r1×(θ1-3°)≥r2×θ2 is satisfied.

5. The developing device according to claim 1 or 2, wherein The relationship r1×(θ1-5°)≥r2×θ2 is satisfied.

6. The developing device according to claim 1 or 2, wherein The relationship r1×(θ1-7°)≥r2×θ2 is satisfied.

7. The developing device according to claim 1 or 2, wherein The absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction relative to the outer peripheral surface of the second rotatable developing member is more than 0.5 times the absolute value of the maximum value of the magnetic flux density of the first magnetic pole in the normal direction relative to the outer peripheral surface of the first rotatable developing member.

8. The developing device according to claim 1 or 2, wherein The absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction relative to the outer peripheral surface of the second rotatable developing member is more than 0.75 times the absolute value of the maximum value of the magnetic flux density of the first magnetic pole in the normal direction relative to the outer peripheral surface of the first rotatable developing member.

9. The developing device according to claim 1 or 2, wherein The absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction relative to the outer peripheral surface of the second rotatable developing member is more than 1.0 times the absolute value of the maximum value of the magnetic flux density of the first magnetic pole in the normal direction relative to the outer peripheral surface of the first rotatable developing member.

10. The developing device according to claim 1 or 2, wherein The absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction relative to the outer peripheral surface of the second rotatable developing member is less than 1.5 times the absolute value of the maximum value of the magnetic flux density of the first magnetic pole in the normal direction relative to the outer peripheral surface of the first rotatable developing member.

11. The developing device according to claim 1 or 2, wherein The absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction relative to the outer peripheral surface of the second rotatable developing member is less than 1.25 times the absolute value of the maximum value of the magnetic flux density of the first magnetic pole in the normal direction relative to the outer peripheral surface of the first rotatable developing member.

12. The developing device according to claim 1 or 2, wherein The radius of the second rotatable developing member is the same as the radius of the first rotatable developing member.

13. The developing device according to claim 1 or 2, wherein The radius of the second rotatable developing member is different from the radius of the first rotatable developing member.

14. The developing device according to claim 1 or 2, wherein The second magnet also has a fifth magnetic pole which is disposed upstream of and adjacent to the third magnetic pole in the rotation direction of the second rotatable developing member and has the same magnetic polarity as that of the third magnetic pole.

15. The developing device according to claim 1 or 2, wherein The first magnet has a plurality of magnetic poles including the first magnetic pole and the second magnetic pole, and The number of the plurality of magnetic poles is seven.

16. The developing device according to claim 1 or 2, wherein The second magnet has a plurality of poles including the third pole, and The number of the plurality of magnetic poles is seven.

17. The developing device according to claim 1 or 2, further comprising a developing container configured to accommodate the developer, wherein The developer contained in the developing container is supplied to the first rotatable developing member, The first developing position is a position where an electrostatic latent image formed on an image bearing member is developed, and The second developing position is a position where the electrostatic latent image is developed.

18. The developing device according to claim 17, further comprising: a third rotatable member disposed to face the second rotatable developing member, the third rotatable member being configured to receive the developer conveyed from the second rotatable developing member through a magnetic field generated by the second magnet; as well as a third magnet, the third magnet being non-rotatably and fixedly disposed inside the third rotatable member, wherein the developing container comprises a supply chamber configured to supply the developer to the first rotatable developing member, and a collecting chamber separated from the supply chamber by a partition wall and configured to collect the developer after developing the electrostatic latent image, and The third rotatable member is configured to carry and feed the developer to collect the developer into the collection chamber after developing the electrostatic latent image.

Images