Developing device

Abstract

To provide a configuration capable of suppressing the occurrence of an image defect.SOLUTION: A position of a maximum of a normal component of a magnetic flux density of a delivering pole 106 on a surface of a first sleeve is a point T. Also, of half-value positions of the maximum of the normal component of the magnetic flux density of the delivering pole 106, a position on a downstream side with respect to a rotational direction of the first sleeve is a point Hd, and a position on an upstream side with respect to the rotational direction of the first sleeve is a point Hu. Further, a rectilinear line connecting a rotation center of the first sleeve and the point T is a rectilinear line L10, a rectilinear line connecting the rotation center and the point Hd is a rectilinear line L11, and a rectilinear line connecting the rotation center and the point Hu is a rectilinear line L12. Furthermore, an angle formed by the rectilinear line L10 and the rectilinear line L12 is w1, an angle formed by the rectilinear line L10 and the rectilinear line L11 is w2, and Δw=w1-w2. In this case, the delivering pole 106 satisfies Δw≥0.SELECTED DRAWING: Figure 8

Description

[Technical field]

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

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

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

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

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

[0006] An object of the present invention is to provide a configuration capable of suppressing the occurrence of image defects. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a developing device comprising: a first developing roller having a rotating first sleeve; a first magnet that is non-rotatingly disposed inside the first sleeve and that magnetically attracts a developer containing toner and a carrier having magnetic properties to a surface of the first sleeve; and a developing roller that develops an electrostatic latent image formed on a rotating image carrier with the developer; a second developing roller that is disposed so that its center of rotation is located above the center of rotation of the first developing roller in a vertical direction and receives the developer from the first developing roller by magnetic force; the second sleeve that rotates in a direction opposite to the first sleeve; and a second magnet that is non-rotatingly disposed inside the second sleeve and that magnetically attracts the developer to the surface of the second sleeve; and a developing roller that develops an electrostatic latent image formed on the image carrier with the developer; and the second magnet has a receiving pole which is a magnetic pole for the second developing roller to receive the developer from the first developing roller, and a second magnetic pole located adjacent to the receiving pole on the downstream side in the rotation direction of the second sleeve, and the transfer pole has a point T which is a position of a maximum value of a normal component of the magnetic flux density of the transfer pole on the surface of the first sleeve, a point Hd which is a half-value position of the maximum value of the normal component of the magnetic flux density of the transfer pole on the downstream side in the rotation direction of the first sleeve, and a line connecting the rotation center R1 of the first sleeve and the point T is a line L10, a line connecting the rotation center R1 and the point Hd is a line L11, a line connecting the rotation center R1 and the point Hu is a line L12, an angle between the line L10 and the line L12 is w1, an angle between the line L10 and the line L11 is w2, and Δw=w1-w2 satisfies Δw≧0.

[0008] According to one aspect of the present invention, there is provided a first developing roller having a rotating first sleeve, a first magnet disposed inside the first sleeve in a non-rotating manner and configured to magnetically attract a developer containing toner and a magnetic carrier to a surface of the first sleeve, the first developing roller developing an electrostatic latent image formed on a rotating image carrier with the developer, and a second developing roller disposed such that a rotation center is located above the rotation center of the first developing roller in the vertical direction and the developer is transferred from the first developing roller by magnetic force, the second developing roller being configured to rotate around the first sleeve and having a rotation center located above the rotation center of the first developing roller in the vertical direction and having a rotation center located above the rotation center of the first developing roller .... a second developing roller having a second sleeve rotating in a direction opposite to that of the sleeve, and a second magnet disposed non-rotatably inside the second sleeve and configured to attract developer to a surface of the second sleeve by magnetic force, the second developing roller developing an electrostatic latent image formed on the image carrier with the developer, the first magnet having a delivery pole which is a magnetic pole for delivering developer from the first developing roller to the second developing roller, and a first magnetic pole located adjacent to the delivery pole on the upstream side with respect to the rotation direction of the first sleeve, a receiving pole which is a magnetic pole for receiving developer from the first sleeve, and a second magnetic pole located adjacent to the receiving pole on the downstream side in the rotation direction of the second sleeve, the transferring pole has a maximum value of a normal component of the magnetic flux density of the transferring pole on the surface of the first sleeve as a value Lt, a half value of the value Lt as a value Lh, a downstream position in the rotation direction of the first sleeve among the half-value positions of the maximum value of the normal component of the magnetic flux density of the transferring pole as a point Hd, and an upstream position in the rotation direction of the first sleeve among the half-value positions of the maximum value of the normal component of the magnetic flux density of the transferring pole as a point Hc. When the normal component of the magnetic flux density of the delivery pole on the surface of the first sleeve is plotted on a graph with the magnetic flux density on the vertical axis and the angle in the rotational direction of the first sleeve on the horizontal axis, a straight line parallel to the horizontal axis passing through the position of the value Lt is a straight line HLt, a straight line parallel to the horizontal axis passing through the position of the value Lh is a straight line HLh, a straight line parallel to the vertical axis passing through the point Hd is a straight line VL11, a straight line parallel to the vertical axis passing through the point Hu is a straight line VL12, and a rectangular area enclosed by the straight lines VL11, VL12, HLt, and HLh is an area S. In the graph,When the area Sa is the area obtained by integrating the normal component of the magnetic flux density of the transfer pole from the straight line VL11 to the straight line VL12 with respect to the angle in the rotational direction of the first sleeve, the developing device satisfies Sa / S≧75%.

[0009] One aspect of the present invention is a developing roller having a rotating first sleeve, a first magnet that is non-rotatingly disposed inside the first sleeve and that magnetically attracts a developer containing toner and a carrier having magnetic properties to a surface of the first sleeve, the first developing roller developing an electrostatic latent image formed on a rotating image carrier with the developer, and a second developing roller that is disposed such that its center of rotation is located above the center of rotation of the first developing roller in the vertical direction and receives the developer from the first developing roller by magnetic force, the second developing roller being disposed in a position facing the first sleeve and rotating in a direction opposite to the first sleeve. and a second developing roller having a second sleeve rotating in a direction opposite to the rotation direction of the first sleeve and a second magnet disposed inside the second sleeve in a non-rotating manner and attracting a developer to a surface of the second sleeve by a magnetic force, the second developing roller developing an electrostatic latent image formed on the image carrier with the developer, the first magnet having a delivery pole which is a magnetic pole for delivering the developer from the first developing roller to the second developing roller, and a first magnetic pole located adjacent to the delivery pole on the upstream side with respect to the rotation direction of the first sleeve, the second magnet being a magnetic pole for the second developing roller receiving the developer from the first developing roller. a receiving pole which is a first magnetic pole and a second magnetic pole which is adjacent to the receiving pole and located downstream in the rotation direction of the second sleeve, the transferring pole is defined as a maximum value of a normal component of the magnetic flux density of the transferring pole on the surface of the first sleeve, a value C which is 10% of the value Lt, and a value D which is 90% of the value Lt, a point Cd being a downstream position in the rotation direction of the first sleeve among the positions where the normal component of the magnetic flux density of the transferring pole is the value C, and a point Cd being an upstream position in the rotation direction of the first sleeve among the positions where the normal component of the magnetic flux density of the transferring pole is the value C is defined as point Cu, a downstream position in the rotation direction of the first sleeve among the positions where the normal component of the magnetic flux density of the delivery pole becomes the value D is defined as point Dd, an upstream position in the rotation direction of the first sleeve among the positions where the normal component of the magnetic flux density of the delivery pole becomes the value D is defined as point Du, a straight line connecting the rotation center R1 of the first sleeve and the point Cd is defined as a straight line L11C, a straight line connecting the rotation center R1 and the point Cu is defined as a straight line L12C, a straight line connecting the rotation center R1 and the point Dd is defined as a straight line L11D, and a straight line connecting the rotation center R1 and the point Du is defined as a straight line L12D,The developing device is characterized in that, when the angle between the straight lines L11C and L12C is Wc, and the angle between the straight lines L11D and L12D is Wd, Wd / Wc≧45% is satisfied. Effect of the Invention

[0010] According to the present invention, the occurrence of image defects can be suppressed. [Brief description of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to a first embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view of the developing device according to the first embodiment. [Diagram 3] FIG. 4 is a diagram showing the arrangement of magnetic poles of a first developing roller according to the first embodiment. [Figure 4] FIG. 4 is a diagram showing the arrangement of magnetic poles of a second developing roller according to the first embodiment. [Diagram 5] FIG. 2 is a diagram showing the arrangement of magnetic poles of the peeling roller according to the first embodiment. [Figure 6] FIG. 4 is a diagram showing the relationship between the arrangement of magnetic poles of a first developing roller and a second developing roller according to the first embodiment. [Figure 7] 5 is a graph showing magnetic characteristics of the first developing roller according to the first embodiment. [Figure 8] 6 is a graph showing magnetic characteristics around a transfer pole of the first developing roller according to the first embodiment. [Figure 9] 5A and 5B are schematic diagrams illustrating the state of magnetic flux lines and magnetic flux density between a first developing roller and a second developing roller according to the first embodiment. [Figure 10] 13 is a graph showing magnetic characteristics of a first developing roller according to a comparative example. [Figure 11] 11 is a graph showing magnetic characteristics around a transfer pole of a first developing roller according to a comparative example. [Figure 12] 5A and 5B are schematic diagrams illustrating the state of magnetic flux lines and magnetic flux density between a first developing roller and a second developing roller according to a comparative example. [Figure 13] 10 is a graph showing magnetic characteristics of a first developing roller according to a second embodiment. [Figure 14] 10 is a graph showing magnetic characteristics around a transfer pole of a first developing roller according to a second embodiment. [Figure 15] 15 is a graph showing an enlarged view of the magnetic characteristics of the receiving pole of FIG. 14 . [Figure 16] A graph showing the magnetic characteristics around three types of receiving poles with different area ratios Sa / S. [Figure 17] 13 is a graph showing magnetic characteristics around a transfer pole of a first developing roller according to a third embodiment. [Figure 18] 18 is a graph showing an enlarged view of the magnetic characteristics of the receiving pole of FIG. 17. [Figure 19] 13 is a graph showing an enlarged view of the magnetic characteristics of a delivery pole of a first developing roller according to a fourth embodiment. [Figure 20] 13 is a graph showing an enlarged view of magnetic characteristics of a delivery pole of a first developing roller according to a fifth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] <First embodiment> The first embodiment will be described with reference to Figures 1 to 12. First, the schematic configuration of an image forming apparatus according to the present embodiment will be described with reference to Figure 1.

[0013] [Image forming equipment] The image forming apparatus 100 is a full-color image forming apparatus, and in this embodiment, for example, is an MFP (Multi-Function Peripheral) having a copy function, a printer function, and a scan function. As shown in Fig. 1, the image forming apparatus 100 has image forming units PY, PM, PC, and PK arranged in parallel, which perform image forming processes for four colors of toner images, yellow, magenta, cyan, and black, respectively.

[0014] The image forming units PY, PM, PC, and PK of the respective colors include primary chargers 21Y, 21M, 21C, and 21K, developing devices 1Y, 1M, 1C, and 1K, optical writing units (exposure devices) 22Y, 22M, 22C, and 22K, photosensitive drums 28Y, 28M, 28C, and 28K, and cleaning devices 26Y, 26M, 26C, and 26K. The image forming apparatus 100 also includes a transfer device 2 and a fixing device 3. Since the image forming units PY, PM, PC, and PK of the respective colors have the same configuration, the following description will be given using the image forming unit PY as a representative.

[0015] The photosensitive drum 28Y as an image carrier is a photosensitive member having a photosensitive layer made of a resin such as polycarbonate containing an organic photoconductor (OPC), and is configured to rotate at a predetermined speed. The primary charger 21Y is made of a corona discharge electrode arranged around the photosensitive drum 28Y, and charges the surface of the photosensitive drum 28Y with generated ions.

[0016] The optical writing unit 22Y incorporates a scanning optical device, and exposes the charged photosensitive drum 28Y based on image data, thereby lowering the potential of the exposed portion and forming a charge pattern (electrostatic latent image) corresponding to the image data. The developing device 1Y transfers the contained developer to the photosensitive drum 28Y to develop the electrostatic latent image formed on the photosensitive drum 28Y. The developer is a mixture of carrier and toner corresponding to each color, and the electrostatic latent image is visualized by the toner.

[0017] The transfer device 2 has primary transfer rollers 23Y, 23M, 23C, and 23K, an intermediate transfer belt 24, and a secondary transfer roller 25. The intermediate transfer belt 24 is wound around the primary transfer rollers 23Y, 23M, 23C, and 23K and a plurality of rollers, and is supported so as to be capable of running. The primary transfer rollers 23Y, 23M, 23C, and 23K correspond to the colors Y (yellow), M (magenta), C (cyan), and K (black) in order from the top of FIG. 1. The secondary transfer roller 25 is disposed outside the intermediate transfer belt 24, and is configured so that a recording material can pass between the secondary transfer roller 25 and the intermediate transfer belt 24. The recording material is, for example, a sheet such as paper or a plastic sheet.

[0018] The toner images of each color formed on the photosensitive drums 28Y, 28M, 28C, and 28K are transferred successively onto the intermediate transfer belt 24 by the primary transfer rollers 23Y, 23M, 23C, and 23K, forming a color toner image in which yellow, magenta, cyan, and black layers are superimposed. The formed toner image is transferred by the secondary transfer roller 25 onto a recording material conveyed from a cassette or the like in which the recording material is stored. The recording material onto which the toner image has been transferred is subjected to pressure and heat in the fixing device 3. This melts the toner on the recording material, and the color image is fixed onto the recording material.

[0019] The developer storage units 27Y, 27M, 27C, and 27K are provided corresponding to the developing devices 1Y, 1M, 1C, and 1K, respectively, and are loaded with replaceable bottles containing developers corresponding to the respective colors of yellow, magenta, cyan, and black, in order from the top. The developer storage units 27Y, 27M, 27C, and 27K are configured to be able to transport (supply) developers to the developing devices 1Y, 1M, 1C, and 1K corresponding to the colors of the developers stored therein.

[0020] For example, the toner weight ratio of the developer stored in the bottle is 80 to 95%, and the toner weight ratio of the developer in the developing devices 1Y, 1M, 1C, and 1K is 5 to 10%. Therefore, when toner is consumed by development in the developing devices 1Y, 1M, 1C, and 1K, developer containing toner corresponding to the consumed amount is replenished, and the toner weight ratio of the developer in the developing devices 1Y, 1M, 1C, and 1K is maintained constant.

[0021] [Developing device] Next, the developing devices 1Y, 1M, 1C, and 1K will be described in detail with reference to Figures 2 to 5. Since the developing devices 1Y, 1M, 1C, and 1K have the same configuration, the developing device 1Y will be described below as a representative. Figure 2 is a conceptual diagram explaining the developing device 1Y shown in Figure 1, and Figures 3, 4, and 5 are conceptual diagrams explaining the magnetic pole configurations of the first magnet 36, second magnet 37, and third magnet 38 arranged in the developing device 1Y.

[0022] As shown in FIG. 2, the developing device 1Y has a first developing roller 30, a second developing roller 31, a peeling roller 32, a developer supply screw 42, a developer stirring screw 43 and a developer recovery screw 44, and these components are contained in a developing container 60.

[0023] The first developing roller 30 is a developer carrier that is driven to rotate, and is disposed adjacent to the photosensitive drum 28Y so that its rotation axis is substantially parallel to the rotation axis of the photosensitive drum 28Y. The first developing roller 30 has a rotating first sleeve 33 and a first magnet (fixed magnet) 36 that is disposed inside the first sleeve 33 in a non-rotating manner and attracts the developer to the surface of the first sleeve 33 by magnetic force. The first developing roller 30 attracts (carries) the developer pumped up from the developer supply screw 42 by magnetic force, and develops the electrostatic latent image formed on the rotating photosensitive drum 28Y (image carrier) with the developer.

[0024] The first sleeve 33 is a non-magnetic cylindrical member, and is driven to rotate around a rotation shaft 39. The rotation direction of the first sleeve 33 is clockwise as shown by the arrow in FIG. 2, which is the opposite direction to the rotation direction of the photosensitive drum 28Y in this embodiment. Therefore, the first sleeve 33 and the photosensitive drum 28Y rotate in the same direction at positions facing each other. That is, this is forward development in which the photosensitive drum 28 rotates from a vertically downward direction to a vertically upward direction at a position facing the first sleeve 33.

[0025] The first magnet 36 is disposed inside the first sleeve 33, and has a plurality of sector-shaped magnetic poles 101-107 as shown in Fig. 3. Between the inner periphery of the first sleeve 33 and the outer periphery of the first magnet 36, a space is disposed to allow the first sleeve 33 to rotate.

[0026] The developer attracted onto the first sleeve 33 (on the first sleeve) is transported toward the photosensitive drum 28Y by the rotational operation of the first sleeve 33, and develops the latent image formed on the photosensitive drum 28Y. After developing the latent image formed on the photosensitive drum 28Y, the developer on the first sleeve 33 is transported to the vicinity of the second developing roller 31 by the rotational operation of the first sleeve 33. Then, in the vicinity of the closest position between the first developing roller 30 and the second developing roller 31, the developer is peeled off from the first sleeve 33 and transferred onto the second sleeve 34 (on the second sleeve) by the magnetic field generated by the first magnet 36 contained in the first developing roller 30 and the second magnet 37 contained in the second developing roller 31.

[0027] The second developing roller 31 is a developer carrier that is driven to rotate, and is disposed downstream of the first developing roller 30 in the rotation direction of the photosensitive drum 28Y and such that the rotation center RR2 of the second developing roller 31 is located above the rotation center R1 of the first developing roller 30 in the vertical direction, and the developer is transferred from the first developing roller 30 by magnetic force (FIG. 2). In this embodiment, the entire second developing roller 31 is located above the rotation center R1 of the first developing roller 30. The second developing roller 31, like the first developing roller 30, is disposed at a position adjacent to the photosensitive drum 28Y such that its rotation axis is substantially parallel to the rotation axis of the photosensitive drum 28Y. Therefore, the rotation axes of the second developing roller 31 and the first developing roller 30 are substantially parallel to each other.

[0028] The second developing roller 31 has a rotating second sleeve 34 and a second magnet (fixed magnet) 37 that is non-rotatingly disposed inside the second sleeve 34 and attracts the developer to the surface of the second sleeve 34 by magnetic force. The second developing roller 31 receives the developer from the first developing roller 30 (first sleeve 33) based on the magnetic force, attracts (carries) the developer, and develops the electrostatic latent image formed on the rotating photosensitive drum 28Y with the developer. A peeling roller 32, which will be described later, is located on the side of the second developing roller 31.

[0029] The second sleeve 34 is a non-magnetic cylindrical member, and is driven to rotate around the rotation shaft 40. The rotation direction of the second sleeve 34 is the same clockwise direction as the first sleeve 33 as shown by the arrow in FIG. 2, and in this embodiment, it is the opposite direction to the rotation direction of the photosensitive drum 28Y. Therefore, the second sleeve 34 and the photosensitive drum 28Y rotate in the same direction at the position where they face each other. That is, this is forward development in which the photosensitive drum 28 rotates from the lower vertical direction to the upper vertical direction at the position where the photosensitive drum 28 faces the second sleeve 34. Also, the second sleeve 34 and the first sleeve 33 rotate in the opposite directions at the position where they face each other.

[0030] The second magnet 37 is disposed inside the second sleeve 34, and has a plurality of sector-shaped magnetic poles 201-207 as shown in Fig. 4. Between the inner periphery of the second sleeve 34 and the outer periphery of the second magnet 37, a space is disposed to allow the second sleeve 34 to rotate.

[0031] The developer attracted onto the second sleeve 34 is transported toward the photosensitive drum 28Y by the rotational operation of the second sleeve 34, and develops the latent image formed on the photosensitive drum 28Y. After the latent image formed on the photosensitive drum 28Y is developed, the developer remaining on the second sleeve 34 is transported to the vicinity of the peeling roller 32 by the rotational operation of the second sleeve 34. Then, in the vicinity of the closest position between the second developing roller 31 and the peeling roller 32, the developer is transferred from the second sleeve 34 to the third sleeve 35 of the peeling roller 32 by the magnetic field generated by the second magnet 37 contained in the second developing roller 31 and the third magnet 38 contained in the peeling roller 32.

[0032] The peeling roller 32 as a peeling section is disposed on the opposite side to the photosensitive drum 28Y with respect to the rotation center of the second sleeve 34, and peels off the developer from the second developing roller 31 after the electrostatic latent image on the photosensitive drum 28Y is developed by the second developing roller 31. Specifically, the peeling roller 32 is a developer carrier that is driven to rotate, and is disposed between the second developing roller 31 and the developer recovery screw 44 such that its rotation center is above the rotation center R of the second developing roller 31.

[0033] The peeling roller 32 is disposed so that its rotation axis is substantially parallel to the rotation axis of the second developing roller 31. The peeling roller 32 has a rotating third sleeve 35 and a third magnet (fixed magnet) 38 that is non-rotatingly disposed inside the third sleeve 35 and that attracts the developer to the surface of the third sleeve 35 by magnetic force, and is configured to receive the developer from the second developing roller 31 based on the magnetic force.

[0034] The third sleeve 35 is a non-magnetic cylindrical member, and is driven to rotate around the rotation shaft 41. The rotation direction of the third sleeve 35 is counterclockwise as indicated by the arrow in Fig. 2, which is the opposite direction to the rotation direction of the second sleeve 34 in this embodiment. Therefore, the third sleeve 35 and the second sleeve 34 rotate in the same direction at positions facing each other.

[0035] The third magnet 38 is disposed inside the third sleeve 35, and has a plurality of sector-shaped magnetic poles 301-305, as shown in Fig. 5. Between the inner periphery of the third sleeve 35 and the outer periphery of the third magnet 38, a space is disposed to allow the third sleeve 35 to rotate.

[0036] The developer attracted onto the third sleeve 35 is transported downstream in the rotation direction by the rotation of the third sleeve 35, and is peeled off from the third sleeve 35 by the third magnet 38 contained in the peeling roller 32 at a position close to the developer recovery screw 44, and falls by its own weight toward the guide member 45 located vertically below. The developer that has fallen onto the guide member 45 is then guided by its own weight toward the developer recovery screw 44.

[0037] The guide member 45 and the developer recovery screw 44 constitute a developer recovery section 47 as a recovery section that recovers the developer peeled off from the third sleeve 35 on the peeling roller 32. In the developer recovery section 47, the developer recovery screw 44 is disposed so that the center of rotation is located lower than the center of rotation of the peeling roller 32 in the vertical direction, and conveys the developer delivered (recovered) from the peeling roller 32 while stirring it.

[0038] The guide member 45 as a guide portion is disposed vertically below the peeling roller 32, and guides the developer peeled off by the peeling roller 32 toward the developer recovery screw 44. Such a guide member 45 has a slope 45a along which the developer slides down under its own weight in order to more reliably guide the peeled off developer toward the developer recovery screw 44. The slope 45a is inclined with respect to the horizontal direction so that the developer recovery screw 44 side is lower than the position below the peeling roller 32.

[0039] The developer recovery screw 44, which serves as a recovery member and a transport section, transports the recovered developer to a developer circulating section 46, which will be described next. That is, the developer recovery screw 44 is a screw transport member used to transport the recovered developer in one direction while stirring it as it slides down the inclined surface of the guide member 45.

[0040] The developer circulating section 46 is a supply section for supplying the developer to the first developing roller 30, and includes a regulating member 50, a developer supply screw 42, and a developer stirring screw 43. In the developer circulating section 46, the developer is stirred in the developer supply screw 42 and the developer stirring screw 43 and transported in a substantially horizontal direction, and is supplied to the first developing roller 30. As described above, the developer collected by the developer collecting section 47 falls by its own weight and is introduced into the developer circulating section 46.

[0041] The developer supply screw 42, developer stirring screw 43, and developer recovery screw 44 are screw transport members that transport the developer in one direction while stirring it, and the developer supply screw 42 and developer stirring screw 43 are located vertically below the developer recovery screw 44. The developer supply screw 42, developer stirring screw 43, and developer recovery screw 44 are also arranged so that their rotation axes are approximately parallel to each other. The rotation axes of these screws are also approximately parallel to the rotation axis of the first developing roller 30.

[0042] The developer supply screw 42 is located between the first developing roller 30 and the developer stirring screw 43, and a partition wall 48 of the developing container 60 is disposed between the developer supply screw 42 and the developer stirring screw 43. The partition wall 48 of the developing container 60 extends along the rotation axis direction of the developer supply screw 42 and the developer stirring screw 43. The partition wall 48 is provided with a communication port (not shown) that communicates between a first conveying path 61, through which the developer is conveyed by the developer supply screw 42, and a second conveying path 62, through which the developer is conveyed by the developer stirring screw 43.

[0043] The developer stirred by the developer recovery screw 44 passes through a communication port (not shown) formed in a partition wall 63 of the developing container 60 between the developer recovery screw 44 and the developer supply screw 42, and falls by its own weight toward the developer supply screw 42. The above-mentioned guide member 45 is formed integrally with the partition wall 63, and the developer recovery screw 44 is disposed above the partition wall 63.

[0044] The position of the communication port through which the developer stirred by the developer recovery screw 44 falls by its own weight and is introduced into the developer circulating section 46 is preferably arranged to avoid the area where the developer is supplied toward the first developing roller 30 (the middle part with respect to the rotational axis direction of the developer supply screw 42). In this embodiment, the communication port is arranged at a position included in the range of the downstream end (terminal end) in the developer transport direction of the first transport path 61 in which the developer supply screw 42 is arranged.

[0045] The developer transport directions of the developer supply screw 42 and the developer stirring screw 43 are opposite to each other. The start side (upstream end side in the developer transport direction) and the end side (downstream end side in the developer transport direction) of the first transport path 61 in which the developer supply screw 42 is arranged communicate with the end side and the start side of the second transport path 62 in which the developer stirring screw 43 is arranged via a communication port provided in the partition wall 48. Therefore, the developer circulates in the rotation direction of the developer supply screw 42 and the developer stirring screw 43 shown by the arrows in FIG. 2 and in the approximately horizontal direction within the developing container 60, and a part of the developer is supplied toward the first developing roller 30.

[0046] The developer supply port 51 (see FIG. 2) is disposed above the developer stirring screw 43 in the developing container 60, and is connected to the developer storage unit 27Y (see FIG. 1). The developer supply port 51 is configured to be able to supply the developer stored in a bottle loaded in the developer storage unit 27Y to the second conveying path 62 in which the developer stirring screw 43 is disposed.

[0047] As described above, the toner weight ratio of the developer stored in the bottle of developer storage section 27Y is greater than the toner weight ratio of the developer in developing device 1Y, so by adjusting the developer supplied to developer stirring screw 43, it is possible to maintain the toner weight ratio of the developer in developing device 1 constant.

[0048] The toner concentration detection sensor 49 (see FIG. 2) is disposed to detect the toner concentration in the developer contained in the developer circulating section 46. The toner concentration detection sensor 49 is a sensor that detects the magnetic permeability of the developer. The toner concentration corresponds to the amount of toner consumed in the developing device 1Y, and is therefore used to control the supply of developer from the developer storage section 27Y. For example, when it is detected that the toner concentration has fallen below a predetermined value, developer is supplied from the developer storage section 27Y. Note that since the magnetic permeability of the developer changes depending on the toner concentration, it is possible to detect the toner concentration using the magnetic permeability.

[0049] The regulating member 50 is disposed adjacent to the first developing roller 30, and is used to regulate the amount of developer supplied from the developer circulating unit 46 to the first developing roller 30. The regulating member 50 can be configured to regulate the amount of developer attracted to the first developing roller 30 based on, for example, the gap between the surface of the first sleeve 33 of the first developing roller 30 and an end of the regulating member 50.

[0050] The circulation path of the developer in the developing container 60 is such that the developer is transported in a substantially horizontal direction while being stirred in the developer circulating section 46, and then is supplied to the first developing roller 30, and is transferred from the first developing roller 30 to the second developing roller 31 above by magnetic force. Next, the developer is transferred from the second developing roller 31 to the peeling roller 32 on the side of the second developing roller 31 again by magnetic force, and then is peeled off from the peeling roller 32 by the third magnet 38 contained in the peeling roller 32, and is further collected in the developer collecting section 47, and is introduced again into the developer circulating section 46.

[0051] As described above, in this embodiment, a two-component development method is used as the development method, and the developer is a mixture of a non-magnetic toner with a negative charge polarity and a magnetic carrier. The non-magnetic toner is a resin such as polyester or styrene acrylic that contains colorants, wax components, etc., and is pulverized or polymerized to form a powder, to which fine powders such as titanium oxide and silica are added on the surface. The magnetic carrier is a core made of resin particles kneaded with ferrite particles or magnetic powder, and a resin coating is applied to the surface layer. In this embodiment, the toner concentration in the developer in the initial state (weight ratio of the toner contained in the developer) is 8%.

[0052] In general, the two-component development method using toner and carrier has the characteristic that the toner is subjected to less stress than the one-component development method using a one-component developer, because the toner and carrier are charged to a predetermined polarity by frictional contact between them. On the other hand, with long-term use, the dirt (spent) adhering to the carrier surface increases, and the ability to charge the toner gradually decreases. As a result, problems such as fogging and toner scattering occur. In order to extend the life of the two-component development device, it is possible to increase the amount of carrier contained in the development device, but this is not desirable because it leads to an increase in the size of the development device.

[0053] In order to solve the above problems associated with two-component developer, this embodiment employs an ACR (Auto Carrier Refresh) method. The ACR method is a method in which new developer is supplied little by little from the developer storage section 27Y to the developing device 1Y, and developer with deteriorated charging performance is discharged little by little from a discharge port (not shown) of the developing device 1Y, thereby suppressing an increase in deteriorated carrier. As a result, deteriorated carrier in the developing device 1Y is gradually replaced with new carrier, making it possible to maintain the charging performance of the carrier in the developing device 1Y approximately constant.

[0054] [About the magnetic poles of each magnet] Next, the magnetic pole configurations of the first magnet 36, second magnet 37 and third magnet 38 contained in the first developing roller 30, second developing roller 31 and peeling roller 32 shown in FIGS. 3, 4 and 5 will be described.

[0055] As shown in FIG. 3, the first magnet 36 contained in the first developing roller 30 has a seven-pole magnetic pole configuration having multiple magnetic poles 101, 102, 103, 104, 105, 106, and 107. Of these, the magnetic pole 106 is a transfer pole for transferring developer from the first developing roller 30 to the second developing roller 31. The magnetic poles 101 to 107 are arranged in numerical order in the rotation direction of the first sleeve 33. The magnetic pole 101 is an S pole, and is arranged at a position facing the regulating member 50 via the first sleeve 33, and adjusts the amount of developer transported on the first sleeve 33 as described above. The magnetic pole 104 as the first developing pole is an N pole, and is arranged at a position facing the photosensitive drum 28Y via the first sleeve 33, and is a magnetic pole for developing the electrostatic latent image formed on the photosensitive drum 28Y. Hereinafter, the magnetic pole 104 may be referred to as the first developing pole 104.

[0056] The magnetic pole 106 as a delivery pole is an N pole and is a magnetic pole for delivering the developer from the first sleeve 33 to the second sleeve 34 by a magnetic field generated in cooperation with the second magnet 37 of the second developing roller 31, and hereinafter, the magnetic pole 106 may be referred to as a delivery pole 106. The magnetic pole 107 is an N pole and is used to attract the developer supplied from the developer supply screw 42 onto the first sleeve 33. The magnetic poles 102, 103, and 105 are an N pole, an S pole, and an S pole, respectively, and are used as transport poles to transport the developer attracted by the magnetic pole 107 upward as the first sleeve 33 rotates. Of these, the magnetic pole 105 is a first magnetic pole located adjacent to the upstream side of the delivery pole 106 in the rotation direction of the first sleeve 33, and hereinafter, the magnetic pole 105 may be referred to as a first transport pole 105. The first developing pole 104 is located adjacent to and upstream of the first transport pole 105 in the rotation direction of the first sleeve 33 .

[0057] The magnetic pole 107 is disposed downstream of the delivery pole 106 in the rotation direction of the first sleeve 33, and has the same polarity as the delivery pole 106. The delivery pole 106 and the magnetic pole 107 form a low magnetic force portion 110 having a lower magnetic force than the delivery pole 106 by a repulsive magnetic field generated in cooperation between them. This low magnetic force portion 110 causes the developer to peel off from the first sleeve 33 and promotes the delivery of the developer from the first sleeve 33 to the second sleeve 34. Note that the low magnetic force portion 110 has almost no magnetic force in this embodiment, but may have a low magnetic force, for example, a magnetic pole whose magnetic force (normal component Br of magnetic flux density) is 5 mT or less. This is also true for the low magnetic force portion 210 of the second magnet 37 shown in FIG. 4 and the low magnetic force portion 310 of the third magnet 38 shown in FIG. 5.

[0058] 4, the second magnet 37 contained in the second developing roller 31 has a seven-pole magnetic pole configuration having multiple magnetic poles 201, 202, 203, 204, 205, 206, and 207. Of these, the magnetic pole 201 is a receiving pole for the second developing roller 31 to receive the developer from the first developing roller 30. The magnetic poles 201 to 207 are arranged in numerical order in the rotational direction of the second sleeve 34.

[0059] The magnetic pole 201 as a receiving pole is a magnetic pole for attracting the developer from the first sleeve 33 to the second sleeve 34 by a magnetic field generated in cooperation with the magnetic pole 106 of the first magnet 36 of the first developing roller 30, and hereinafter, the magnetic pole 201 may be referred to as the receiving pole 201. The magnetic pole 207 is a magnetic pole for transferring the developer from the second sleeve 34 to the third sleeve 35 by a magnetic field generated in cooperation with the third magnet 38 of the peeling roller 32.

[0060] Moreover, the receiving pole 201 is an S pole different from the delivery pole 106, and is used to attract the developer from the first developing roller 30 (first sleeve 33) onto the second sleeve 34 as described above. The magnetic pole 203 as the second developing pole is an S pole, and is disposed at a position facing the photosensitive drum 28Y via the second sleeve 34, and is a magnetic pole for developing the electrostatic latent image formed on the photosensitive drum 28Y. Hereinafter, the magnetic pole 203 may be referred to as the second developing pole 203.

[0061] The magnetic poles 202, 204, 205, and 206 are N pole, N pole, S pole, and N pole, and are used to transport the developer attracted by the magnetic pole 201 upward as the second sleeve 34 rotates. Among them, the magnetic pole 202 is a second magnetic pole located adjacent to the downstream side of the receiving pole 201 in the rotation direction of the second sleeve 34, and hereinafter, the magnetic pole 202 may be referred to as the second transport pole 202. The second developing pole 203 is located adjacent to the downstream side of the second transport pole 202 in the rotation direction of the second sleeve 33. The magnetic pole 207 is an S pole, and transfers the developer after passing through the development area with the photosensitive drum 28Y corresponding to the magnetic pole 203 from the second sleeve 34 to the third sleeve 35 facing the second sleeve 34 by a magnetic field generated in cooperation with the magnetic pole 303 in the third magnet 38 contained in the peeling roller 32.

[0062] Moreover, the magnetic pole 207 is disposed upstream of the receiving pole 201 in the rotation direction of the second sleeve 34, and has the same polarity as the receiving pole 201. The receiving pole 201 and the magnetic pole 207 form a low magnetic force portion 210 having a lower magnetic force than the magnetic pole 207 due to a repulsive magnetic field generated between them. This low magnetic force portion 210 causes the developer to peel off from the second sleeve 34 and promotes the transfer of the developer from the first sleeve 33 to the second sleeve 34. Furthermore, the low magnetic force portion 210 can prevent the developer from being attracted to the closest portion between the first sleeve 33 and the second sleeve 34, and can suppress the pressure applied to the developer.

[0063] 5, the third magnet 38 contained in the peeling roller 32 has a plurality of magnetic poles 301, 302, 303, 304, and 305. The magnetic poles 301 to 305 are arranged in numerical order in the rotation direction of the third sleeve 35.

[0064] The magnetic pole 303 is an N pole different from the magnetic pole 207, and is used to attract the developer peeled off from the second sleeve 34 to the third sleeve 35 as described above. The magnetic poles 301, 302, and 304 are an N pole, an S pole, and an S pole, and are used to transport the developer on the third sleeve 35 as the third sleeve 35 rotates. In particular, the magnetic pole 304 is used to transport the developer attracted by the magnetic pole 303 downward as the third sleeve 35 rotates. The magnetic pole 305 is an N pole, and is a peeling pole used to peel off the developer attracted to the third sleeve 35 from the third sleeve 35 by a repulsive magnetic field generated in cooperation with the magnetic pole 301 of the same polarity.

[0065] [Magnetic pole arrangement] Next, the arrangement of the magnetic poles of the first magnet 36 and the second magnet 37 arranged inside the first developing roller 30 and the second developing roller 31 will be described with reference to FIGS. 6 to 9. FIG. 6 is a conceptual diagram illustrating the arrangement of the first developing roller 30 and the second developing roller 31 of this embodiment, and in particular, shows the layout of the first conveying pole 105 and the handover pole 106 of the first magnet 36 of the first developing roller 30, and the receiving pole 201 and the second conveying pole 202 of the second magnet 37 of the second developing roller 31. Note that some of the magnetic poles are omitted from the illustration to avoid complication. Also, FIGS. 7 and 8 are graphs showing the magnetic characteristics of the first magnet 36 of the first developing roller 30. FIG. 9 is a conceptual diagram illustrating the magnetic field of the first developing roller 30 and the second developing roller 31 of this embodiment, and in particular, shows the absolute values ​​of the magnetic flux density of the handover pole 106, the first conveying pole 105, the receiving pole 201, and the second conveying pole 202, and the state of the magnetic flux lines formed thereby.

[0066] In this embodiment, as described above, the developer in the developing device 1Y moves from the first sleeve 33 to the second sleeve 34 of the second developing roller 31 by the magnetic fields of the delivery pole 106 in the first developing roller 30 and the receiving pole 201 in the second developing roller 31, and then moves onto the third sleeve 35 of the peeling roller 32 after being used in the developing process of the electrostatic latent image on the photosensitive drum 28Y.

[0067] The process (arrow F1) of transferring the developer from the first sleeve 33 of the first developing roller 30 to the second sleeve 34 of the second developing roller 31 will be described. As shown by the arrow F1 in Fig. 6 and Fig. 9, the developer moves downstream in the rotation direction 81 of the first sleeve 33 rotating around the rotation center R1 by the magnetic force along the magnetic flux lines extending from the first conveying pole 105 to the handover pole 106 of the first magnet 36. Then, the developer moves from the first sleeve 33 to the second sleeve 34 by the magnetic force along the magnetic flux lines extending from the handover pole 106 to the receiving pole 201. Furthermore, the developer moves downstream in the rotation direction 82 of the second sleeve 34 rotating around the rotation center R2 by the magnetic force along the magnetic pole lines extending from the receiving pole 201 to the second conveying pole 202.

[0068] Here, the position (peak position) of the maximum value (peak value) of the normal component of the magnetic flux density of the delivery pole 106 on the surface of the first sleeve 33 is defined as point T (FIG. 8). Also, among the half-value positions of the maximum value of the normal component of the magnetic flux density of the delivery pole 106, the downstream position in the rotation direction of the first sleeve 33 is defined as point Hd, and among the half-value positions of the maximum value of the normal component of the magnetic flux density of the delivery pole 106, the upstream position in the rotation direction of the first sleeve 33 is defined as point Hu. Also, straight lines L1, L2, L3, L4, L10, L11, and L12 shown by dashed lines in FIGS. 6 and 8 are defined as follows. L1: A horizontal line passing through the rotation center R1 of the first sleeve 33 L2: A horizontal line passing through the rotation center R2 of the second sleeve 34 L3: A vertical line passing through the rotation center R1 of the first sleeve 33 L4: A straight line passing through rotation centers R1 and R2 L10: A straight line connecting the center of rotation R1 and point T (peak position of magnetic flux density of the receiving pole 106) (Figure 8) L11: A straight line connecting the center of rotation R1 and point Hd (a downstream position in the direction of rotation 81 of the first sleeve 33 at half the peak value of the magnetic flux density of the transfer pole 106) (FIG. 8) L12: A straight line connecting the center of rotation R1 and point Hu (a position upstream of the rotation direction 81 of the first sleeve 33 at half the peak value of the magnetic flux density of the transfer pole 106) (FIG. 8)

[0069] The developer is transported from the first transport pole 105 of the first sleeve 33 to the delivery pole 106 by a force due to the rotation of the first sleeve 33 and a magnetic force along the magnetic flux line extending from the first transport pole 105 to the delivery pole 106. The peak value of the magnetic flux density of the delivery pole 106 is equal to or less than the peak value (maximum value of the normal component) of the magnetic flux density of the receiving pole 201. The magnetic field (delivery magnetic field) for delivering the developer from the first sleeve 33 to the second sleeve 34, which is formed by the delivery pole 106 and the receiving pole 201, is configured so that a repulsive force region is generated in which the magnetic force in the direction of the rotation center R1 in the vicinity of the outer circumferential surface of the first sleeve 33 is negative, in a range upstream of the intersection P1 (FIG. 6) of the straight line L4 and the first sleeve 33 and downstream of the peak position of the magnetic flux density of the first transport pole 105 (the position of the maximum value of the normal component on the surface of the first sleeve 33) with respect to the rotation direction 81 of the first sleeve 33.

[0070] The delivery magnetic field is configured so that an attractive region is generated in which the magnetic force in the direction of the rotation center R2 near the outer circumferential surface of the second sleeve 34 is positive, in a range downstream of an intersection P2 (FIG. 6) of the straight line L4 and the second sleeve 34 and upstream of a peak position of the magnetic flux density of the second transport pole 202 with respect to the rotation direction 82 of the second sleeve 34. The developer is delivered from the first sleeve 33 to the second sleeve 34 by such a magnetic force relationship.

[0071] Incidentally, the magnetic flux lines extending from the first transport pole 105 are connected not only to the delivery pole 106 but also to the second transport pole 202 of the second developing roller 31, which is configured with an N pole different from the first transport pole 105. When the magnetic field of the first transport pole 105 and the second transport pole 202 becomes dominant over the magnetic field between the first transport pole 105 and the delivery pole 106 with respect to the magnetic force acting on the developer on the first sleeve 33 near the first transport pole 105, the developer moves from the first transport pole 105 to the second transport pole 202 or from the second transport pole 202 to the first transport pole 105, as shown by the arrow F2 in FIG. 6. Then, the developer also comes into contact with the nearby photosensitive drum 28Y, causing a vertical streak-like fog image to occur on the photosensitive drum 28Y.

[0072] In order to suppress such movement of the developer in the direction of the arrow F2, the magnetic field between the first transport pole 105 and the second transport pole 202 may be weakened, and the magnetic field between the first transport pole 105 and the delivery pole 106 may be strengthened. One possible method for doing this is to increase the peak value of the magnetic flux density of the delivery pole 106. However, if the peak value of the magnetic flux density of the delivery pole 106 is increased, the force that binds the developer in the vicinity of the closest position between the first sleeve 33 and the second sleeve 34 becomes stronger, which applies pressure to the developer and accelerates deterioration of the developer. If the developer deteriorates, the charge amount of the toner decreases, and there is a risk that it will not be possible to develop an appropriate amount of toner on the photosensitive drum 28Y.

[0073] Furthermore, in the range upstream of the intersection P1 of the straight line L4 and the first sleeve 33 and downstream of the magnetic flux density peak position of the first transport pole 105 with respect to the rotation direction 81 of the first sleeve 33, the repulsive force region in which the magnetic force in the direction of the rotation center R1 in the vicinity of the outer circumferential surface of the first sleeve 33 becomes negative may become narrower or disappear, which may make it difficult to properly transfer the developer from the first sleeve 33 to the second sleeve 34. If such a developer transfer failure occurs, the developer may be dragged around on the first sleeve 33, causing unevenness in the toner concentration of the developer on the first sleeve 33, or the amount of developer remaining in the vicinity of the closest position between the first sleeve 33 and the second sleeve 34 may gradually increase, which may cause an overflow phenomenon in which the amount of developer supplied to the second sleeve 34 is excessive.

[0074] For the above reasons, it is not preferable to simply increase the peak value of the magnetic flux density of the delivery pole 106. Therefore, in this embodiment, the delivery pole 106 is configured as follows. First, as shown in FIG. 8, the angle formed by the straight lines L10 and L12 that are the width upstream of the peak position of the magnetic flux density of the delivery pole 106 in the half-width of the peak value of the magnetic flux density of the delivery pole 106 is set as angle w1, and the angle formed by the straight lines L10 and L11 that are the width downstream of the peak position of the magnetic flux density of the delivery pole 106 is set as angle w2. In addition, the angle difference (w1-w2) of the angle w2 with respect to the angle w1 is set as angle difference Δw, that is, Δw=w1-w2. In this case, the delivery pole 106 is configured to satisfy Δw≧0.

[0075] This weakens the magnetic field between the first transport pole 105 and the second transport pole 202, and strengthens the magnetic field between the first transport pole 105 and the delivery pole 106. This improves the transportability of the developer from the first transport pole 105 on the first sleeve 33 to the delivery pole 106. As a result, it is possible to suppress the movement of the developer between the first transport pole 105 of the first developing roller 30 and the second transport pole 202 of the second developing roller.

[0076] The magnetic characteristic distribution of the first magnet 36 of this embodiment is shown in Figs. 7 to 9. The graph shown in Fig. 7 shows the magnitude of magnetic flux density in the normal direction and the angular position of the first sleeve 33 of each of the magnetic poles 101 to 107 contained in the first magnet 36 shown in Figs. 3 and 6. The horizontal axis in Fig. 7 shows the angle in the rotation direction of the first sleeve 33 (shown by an arrow in Fig. 6) when the position on the photosensitive drum 28Y side with respect to the horizontal line L1 on the rotation center R1 of the first developing roller 30 is set to 0 degrees. The vertical axis shows the measurement result of the magnetic flux density in the normal direction of the first magnet 36 at the angle in the rotation direction of the first magnet 36.

[0077] FIG. 8 is an enlarged view of the first transport pole 105 and the vicinity of the delivery pole 106 in FIG. 7, in which the straight lines L1-L4 and L10-L12 on the first sleeve 33 are indicated by dashed lines, and the magnitudes of the angles w1 and w2 are added by arrows in the figure. In the first magnet 36 of this embodiment, the delivery pole 106 is set so that the angle w1=11 degrees, the angle w2=6 degrees, and the angle difference Δw=5 degrees. Here, the set values ​​adopted in this embodiment are only an example, and as described above, the angle difference Δw may have a relationship of Δw≧0, and more preferably Δw>0. By satisfying this relationship, the developer on the first sleeve 33 is easily transported from the first transport pole 105 to the delivery pole 106.

[0078] 9 is a schematic diagram showing an arrow F1 indicating the movement of the developer from the first transport pole 105 on the first sleeve 33 to the second transport pole 202 on the second sleeve 34, the state of the magnetic flux lines formed by the first transport pole 105, the handover pole 106, the receiving pole 201, and the second transport pole 202, and the absolute value of the magnitude of the magnetic flux density in the normal direction of each of these magnetic poles. In this embodiment, the first transport pole 105 and the receiving pole 201 are configured as S poles, and the handover pole 106 and the second transport pole 202 are configured as N poles. The magnetic flux lines connect with the first transport pole 105, which is an S pole, through the handover pole 106 and the second transport pole 202, which are N poles.

[0079] As described above, the shape of the magnetic flux density of the delivery pole 106 is set such that the upstream angle w1 of the half-width of the peak value of the magnetic flux density in the normal direction of the delivery pole 106 is set to be equal to or larger than the downstream angle w2. In this manner, by widening the upstream angle w1 of the half-width of the magnetic flux density of the delivery pole 106 close to the first transport pole 105, the magnetic field between the first transport pole 105 and the delivery pole 106 becomes stronger, and the magnetic field between the first transport pole 105 and the second transport pole 202 becomes weaker. This suppresses the movement of the developer between the first transport pole 105 and the second transport pole 202 as shown by the arrow F2, and suppresses the occurrence of abnormal images (images with vertical stripes) caused by this.

[0080] In order to weaken the magnetic field of the first transport pole 105 and the second transport pole 202, rather than simply increasing the peak value of the magnetic flux density in the normal direction of the delivery pole 106, the half-width of the magnetic flux density of the delivery pole 106 close to the first transport pole 105 is widened only on the upstream side to form an angle difference Δw≧0, thereby making it possible to suppress an increase in the force binding the developer in the vicinity of the closest position between the first sleeve 33 and the second sleeve 34. Furthermore, with respect to the rotation direction 81 of the first sleeve 33, in the range upstream of the intersection P1 of the straight line L4 and the first sleeve 33 and downstream of the peak position of the magnetic flux density of the first transport pole 105, there is no repulsive force region in which the magnetic force in the direction of the rotation center R1 in the vicinity of the outer circumferential surface of the first sleeve 33 becomes negative, and the developer is appropriately delivered from the first sleeve 33 to the second sleeve 34.

[0081] In addition, as described above, the distribution of magnetic flux density of the passing pole 106 may be made asymmetric by cutting out a portion of the circumferential direction of the magnet of the first magnet 36 that forms the passing pole 106, or by embedding a magnet with a different magnetic force in the cut-out portion.

[0082] Next, a comparative example to this embodiment will be described with reference to Fig. 10 to Fig. 12. In the comparative example, the distribution of the magnetic properties of the delivery pole 106A is set so that the angle difference Δw is Δw<0. Fig. 10 to Fig. 12 show the state of the magnetic field formed by the first delivery pole 105, the delivery pole 106A, the receiving pole 201, and the second delivery pole 202 in such a comparative example.

[0083] The graph shown in Fig. 10 is a magnetic characteristic showing the angular position and the magnitude of magnetic flux density in the normal direction of each magnetic pole contained in the first magnet 36 shown in Figs. 3 and 6 in the comparative example, and is the same as Fig. 7 described above, except for the delivery pole 106A. Fig. 11 is an enlarged view of the part near the delivery pole 106A and the first conveying pole 105 in Fig. 10, in which the straight lines L1 to L4 and L10 to L12 on the first sleeve 33 described above are shown by dashed lines, and the magnitudes of the angles w1 and w2 are added by arrows in the figure. The delivery pole 106A of the first magnet 36 in the comparative example has the same peak value of magnetic flux density as the delivery pole 106 described above, and is configured so that the width on the downstream side of the half-value width is wide Δw<0, and the angles are set to w1=6 degrees and w2=11 degrees.

[0084] Like FIG. 9, FIG. 12 is a schematic diagram showing an arrow F1 indicating the movement of developer from the first transport pole 105 on the first sleeve 33 to the second transport pole 202 on the second sleeve 34, the state of the magnetic flux lines formed by the first transport pole 105, the handover pole 106A, the receiving pole 201, and the second transport pole 202, and the absolute value of the magnitude of the magnetic flux density in the normal direction of each of these magnetic poles.

[0085] As described above, the shape of the magnetic flux density of the delivery pole 106A in the comparative example is set such that the angle w1 is smaller than the angle w2. In this configuration in which the angle w1 on the upstream side of the half-width of the delivery pole 106A close to the first transport pole 105 is narrow, the magnetic field between the first transport pole 105 and the delivery pole 106A is weak, and the magnetic field between the first transport pole 105 and the second transport pole 202 cannot be sufficiently weakened. For this reason, the developer moves between the first transport pole 105 and the second transport pole 202, and the above-mentioned vertical stripe-like fog image occurs. That is, the developer coating state on the second sleeve 34 becomes uneven, and an uneven image occurs on the output image. In contrast, in this embodiment, the magnetic field characteristics of the first magnet 36 are as shown in FIG. 8 and FIG. 9, so that it is possible to suppress the occurrence of unevenness and vertical stripe-like images in the output image as in the comparative example.

[0086] [experiment] Next, an experiment was conducted to investigate the occurrence of streaky fogged images (abnormal images) in the above-mentioned configuration. In the experiment, angles w1 and w2 in the magnetic flux density distribution were set on the delivery pole 106, and images were output using an image forming apparatus incorporating a developing device under various conditions. Then, the occurrence of streaky fogged images on the output images was investigated.

[0087] In the experiment, the occurrence of streaky fog images in output images was evaluated as follows. Ten A3 solid white images were printed and the number of vertical streaks on the output images was measured. If no vertical streaks were found among the 10 A3 solid white images, 100 A3 solid white images were printed and checked for vertical streaks.

[0088] The results of this experiment are shown in Tables 1 and 2. [Table 1] [Table 2]

[0089] The symbols in the abnormal image columns of Tables 1 and 2 indicate the results of evaluating the occurrence of streaky fog images (abnormal images), and the meanings of each symbol are as follows: ×: 10 or more vertical streaks were found in one A3 image. △: Approximately one vertical line was found in one A3 image. ○: Approximately one vertical line was found among 10 A3 images. Among the above evaluations, a rating of ◯ indicates a level at which abnormal images hardly occur in practical use.

[0090] The configurations of the first developing roller 30 and the second developing roller 31 used in the experiment are as shown in Fig. 6. For the magnetic characteristics, the peak value of the magnetic flux density of the delivery pole 106 was fixed at approximately 36 mT, and the shape of the magnetic flux density near the delivery pole 106 with respect to the rotation angle of the first sleeve 33 was changed. The magnetic flux density can be changed by changing the conditions for magnetizing the delivery pole 106 supported by the first magnet 36, or by cutting out part of the shape of the magnet. The magnetic poles other than the delivery pole 106 are as shown in Figs. 7 to 10.

[0091] Table 1 shows the results when only the angle w1 is increased and when only the angle w2 is increased, with the angle w1 and the downstream angle w2 both being equal at 6 degrees. It was found that when the angle difference Δw, which is the difference between the angle w1 and the angle w2, is <0, that is, when the angle w1 is smaller than the angle w2, the occurrence of abnormal images cannot be suppressed. This is because, as in the comparative example shown in FIG. 12, the angle w1 adjacent to the first transport pole 105 is small, and the magnetic field between the first transport pole 105 and the delivery pole 106 cannot sufficiently weaken the magnetic field between the first transport pole 105 and the second transport pole 202, and the developer moves between the first transport pole 105 and the second transport pole 202. In addition, even if the angle w2 not adjacent to the first transport pole 105 is increased, the magnetic field between the first transport pole 105 and the delivery pole 106 cannot be strengthened, and the magnetic field between the first transport pole 105 and the second transport pole 202 cannot be sufficiently weakened.

[0092] On the other hand, it was found that the occurrence of abnormal images can be suppressed when the angle difference Δw≧0, that is, when the angle w1 is equal to or larger than the angle w2. This is because, as explained in FIG. 9, the angle w1 adjacent to the first transport pole 105 is large, so that the magnetic field between the first transport pole 105 and the handover pole 106 becomes stronger and the magnetic field between the first transport pole 105 and the second transport pole 202 can be weakened. As a result, the movement of the developer between the first transport pole 105 and the second transport pole 202 as indicated by the arrow F2 can be suppressed, and the occurrence of abnormal images can be suppressed.

[0093] Table 2 shows the results when only the angle w1 is increased and when only the angle w2 is increased, with the angle w1 and the downstream angle w2 both being equal at 4 degrees. As with the results of Table 1, it was found that the occurrence of abnormal images can be suppressed when the angle difference Δw ≧ 0. However, it was confirmed that under the conditions of Table 2, the occurrence of abnormal images cannot be sufficiently suppressed when the angle difference Δw = 0, compared to the results of Table 1. This is because the half-width of the delivery pole 106 when the angle difference Δw = 0 in Table 1 is 12 degrees, whereas the half-width of the delivery pole 106 when the angle difference Δw = 0 in Table 2 is narrow at 8 degrees. If the half-width is narrow, the magnetic field between the delivery pole 106 and the first conveying pole 105 may change in a weakening direction due to the assembly tolerance of the first magnet 36 and the second magnet 37, or a slight change in the magnetic pole position due to the influence of variations in magnetization. In this case, the effect of weakening the magnetic field of the first transport pole 105 and the second transport pole 202 is reduced, and the effect of suppressing the movement of the developer between the first transport pole 105 and the second transport pole 202 is weakened. Therefore, when the half-width is narrow, it is more preferable to satisfy the angle difference Δw>0. It is even more preferable to satisfy Δw≧2.5 degrees.

[0094] As described above, according to this embodiment, the occurrence of image defects can be suppressed. That is, in the developing device 1Y of this embodiment, the developer is transported from the first transport pole 105 to the delivery pole 106 on the first sleeve 33, is delivered to the second sleeve 34 based on the magnetic force between the delivery pole 106 and the receiving pole 201, and is transported on the second sleeve 34 from the receiving pole 201 to the second transport pole 202. In such a configuration, the developer may move due to the magnetic force along the magnetic field between the first transport pole 105 and the second transport pole 202. In contrast, in this embodiment, since the delivery pole 106 satisfies Δw≧0 as described above, the magnetic field of the first transport pole 105 and the delivery pole 106 weakens the magnetic field of the first transport pole 105 and the second transport pole 202, and the movement of the developer between the first transport pole 105 and the second transport pole 202 can be suppressed. Therefore, the occurrence of the above-mentioned streaky fog image can be suppressed.

[0095] In particular, even in an image forming apparatus with a high image formation speed (process speed), it is possible to suppress the movement of developer between the first transport pole 105 and the second transport pole 202, thereby suppressing the occurrence of the above-mentioned streaky fog image. It is then possible to provide a developing device 1Y and an image forming apparatus 100 that stably circulate the developer from the first developing roller 30 to the second developing roller 31, the peeling roller 32, and the developer circulating section 46, thereby performing stable image output.

[0096] <Second embodiment> The second embodiment will be described with reference to Figures 13 to 16. This embodiment differs from the first embodiment in the configuration of the delivery pole 106B of the first magnet 36 of the first developing roller 30. Since the other configurations and functions are similar to those of the first embodiment described above, the same reference numerals are used for similar configurations, and explanations and illustrations are omitted or simplified. The following description will focus on the points that are different from the first embodiment.

[0097] 8, in the case of the first embodiment described above, the magnetic flux density of the delivery pole 106 in the first magnet 36 contained in the first developing roller 30 satisfies the angle difference Δw≧0. Since the angle w1 close to the first transport pole 105 is large, the magnetic fields of the first transport pole 105 and the delivery pole 106 can weaken the magnetic field between the first transport pole 105 and the second transport pole 202.

[0098] On the other hand, in this embodiment, as shown in Figures 13 and 14, a delivery pole 106B is disposed at the position of the delivery pole 106 of the first magnet 36 employed in the first embodiment. The peak value of the magnetic flux density of this delivery pole 106B is the same as that of the delivery pole 106. Meanwhile, the shape of the peak value of the magnetic flux density is made to be flat.

[0099] This flat shape will now be described. Fig. 15 shows the results of measuring the magnetic flux density in the normal direction of the delivery pole 106B with the rotation direction of the first sleeve 33 as the horizontal axis in this embodiment. That is, Fig. 15 is a graph showing the normal component of the magnetic flux density of the delivery pole 106B on the surface of the first sleeve 33, with the magnetic flux density on the vertical axis and the angle of the rotation direction of the first sleeve 33 on the horizontal axis. Here, the values ​​Lt, Lh, the straight line HLt, the straight line HLh, the straight line VL11, and the straight line VL12 are defined as follows. Lt: Peak value of magnetic flux density of the delivery pole 106B on the surface of the first sleeve 33 (maximum value of the normal component) Lh: Half the peak value Lt of the magnetic flux density of the receiving pole 106B HLt: A straight line (dashed line) that passes through the position of value Lt and is parallel to the horizontal axis HLh: A straight line (dashed line) that passes through the position of value Lh and is parallel to the horizontal axis VL11: A straight line (dash line) that passes through point Hd and is parallel to the vertical axis VL12: A straight line (dash line) that passes through point Hu and is parallel to the vertical axis

[0100] As in the first embodiment, Hd is a downstream position in the rotation direction of the first sleeve 33 among half-maximum positions of the normal component of the magnetic flux density of the delivery pole 106B. As in the first embodiment, Hu is an upstream position in the rotation direction of the first sleeve 33 among half-maximum positions of the normal component of the magnetic flux density of the delivery pole 106B.

[0101] Furthermore, the rectangular area enclosed by the lines VL11, VL12, HLt, and HLh is defined as area S, and in the graph of Figure 15, the area obtained by integrating the normal component of the magnetic flux density of the handover pole 106B from the line VL11 to the line VL12 with respect to the angle of the rotational direction of the first sleeve 33 (shaded area) is defined as area Sa.

[0102] As described above, in order to suppress the movement of developer by weakening the magnetic field from the first transport pole 105 to the second transport pole 202, it is effective to strengthen the magnetic field between the first transport pole 105 and the delivery pole 106B. For this reason, it is conceivable to increase the peak value of the magnetic flux density of the delivery pole 106B, which makes it possible to strengthen the magnetic field between the delivery pole 106B and the first transport pole 105. However, this would also significantly change the magnetic field that contributes to the delivery of developer from the first sleeve 33 to the second sleeve 34, which may lead to the drag phenomenon and developer deterioration.

[0103] Therefore, in this embodiment, the peak value of the magnetic flux density of the delivery pole 106B is not increased, but the area Sa, which is an integral value of at least half the peak value of the magnetic flux density of the delivery pole 106B, is increased. Specifically, the vicinity of the peak value of the magnetic flux density of the delivery pole 106B is formed in a flat shape so that the area ratio Sa / S of the area Sa to the area S is 75% or more (Sa / S≧75%). As a result, the magnetic field between the first transport pole 105 and the delivery pole 106B can be strengthened and the magnetic field between the first transport pole 105 and the second transport pole 202 can be weakened, and the movement of the developer between the first transport pole 105 and the second transport pole 202 can be suppressed.

[0104] The flat magnetic flux density near the peak value of the passing pole 106B does not necessarily mean a single peak, but may mean that there are multiple peaks, and may be configured to satisfy the area ratio Sa / S≧75%. Also, the flat magnetic flux density like the passing pole 106B may be formed by cutting out a part of the circumferential direction of the magnet forming the passing pole 106B of the first magnet 36, or by embedding a magnet with a different magnetic force in the cut-out portion.

[0105] In addition, the delivery pole 106B of the present embodiment has a flat shape in which the magnetic flux density in the normal direction is wider not only on the upstream side but also on the downstream side than the peak value of the magnetic flux density in the normal direction of the delivery pole 106 in the first embodiment. Therefore, a wide magnetic field is formed between the delivery pole 106B and the receiving pole 201, and the influence of the magnetization variation of the first magnet 36 and the second magnet 37 and the assembly tolerance on the magnetic field change of the delivery pole 106B and the receiving pole 201 is reduced. In other words, in the present embodiment, compared to the first embodiment, the latitude of the delivery of the developer from the first sleeve 33 to the second sleeve 34 in response to the variation in the magnetic pole arrangement of the first magnet 36 and the second magnet 37 is widened, while the movement of the developer between the first transport pole 105 and the second transport pole 202 can be suppressed.

[0106] [experiment] Next, an experiment to investigate the occurrence of streaky fog images (abnormal images) in the above-mentioned configuration will be described. In the experiment, the areas S and Sa were varied by adjusting the magnetic flux density of the delivery pole 106B, and images were output by image forming apparatuses incorporating developing devices under various conditions. Then, the occurrence of streaky fog images on the output images was investigated. The other conditions and the evaluation of the experiment were the same as those of the experiment described in the first embodiment. The results of this experiment are shown in Table 3. [Table 3]

[0107] The configurations of the first developing roller 30 and the second developing roller 31 in the experiment are as shown in Fig. 6. As for the magnetic characteristics, as shown in Fig. 16, the peak value of the magnetic flux density of the handover pole 106B was fixed at approximately 36 mT, and the shape of the magnetic flux density in the vicinity of the handover pole 106B was changed in stages from an area ratio Sa / S of 60% to 78%. Note that Fig. 16 shows the magnetic characteristics when Sa / S is 60%, 70%, and 78% as representatives. The magnetic poles other than the handover pole 106B are as shown in Fig. 13.

[0108] As is clear from Table 3, the occurrence of abnormal images could be suppressed when the area ratio Sa / S was 75% or more. This is because the vicinity of the peak value of the magnetic flux density of the delivery pole 106B approached the first delivery pole 105, strengthening the magnetic field between the first delivery pole 105 and the delivery pole 106B and weakening the magnetic field between the first delivery pole 105 and the second delivery pole 202. On the other hand, when the area ratio Sa / S was smaller than 75%, the effect of the magnetic flux of the delivery pole 106B in weakening the magnetic field between the first delivery pole 105 and the second delivery pole 202 was low, and the developer moved between the first delivery pole 105 and the second delivery pole 202, resulting in insufficient suppression of abnormal images.

[0109] As described above, according to this embodiment, the occurrence of image defects can be suppressed. That is, in the developing device 1Y of this embodiment, the developer is transported from the first transport pole 105 to the delivery pole 106B on the first sleeve 33, and is delivered to the second sleeve 34 based on the magnetic force from the delivery pole 106B to the receiving pole 201, and is transported on the second sleeve 34 from the receiving pole 201 to the second transport pole 202. In such a configuration, the developer may move due to the magnetic force along the magnetic field between the first transport pole 105 and the second transport pole 202. In contrast, in this embodiment, the magnetic field of the first transport pole 105 and the delivery pole 106B is configured to be flat in the vicinity of the peak value of the magnetic flux density so that the area ratio Sa / S≧75% is satisfied as described above, and therefore the magnetic field of the first transport pole 105 and the delivery pole 106B weakens the magnetic field of the first transport pole 105 and the second transport pole 202, and the movement of the developer between the first transport pole 105 and the second transport pole 202 can be suppressed. Therefore, the occurrence of the above-mentioned streaky fogged image can be suppressed.

[0110] <Third embodiment> The third embodiment will be described with reference to Figures 17 and 18. This embodiment differs from the first embodiment in the configuration of the delivery pole 106C of the first magnet 36 of the first developing roller 30. Since the other configurations and functions are similar to those of the first embodiment described above, the same reference numerals are used for similar configurations, and explanations and illustrations are omitted or simplified. The following description will focus on the points that are different from the first embodiment.

[0111] In the case of the second embodiment described above, as shown in FIG. 15, the integral value Sa of at least half the peak value of the magnetic flux density of the delivery pole 106B in the first magnet 36 contained in the first developing roller 30 is increased and the area ratio Sa / S is made 75% or more, thereby strengthening the magnetic field between the first conveying pole 105 and the delivery pole 106B and weakening the magnetic field between the first conveying pole 105 and the second conveying pole 202.

[0112] On the other hand, in this embodiment, as shown in Fig. 17, a delivery pole 106C is arranged at the position of the delivery pole 106 of the first magnet 36 employed in the first embodiment. The peak value of the magnetic flux density of this delivery pole 106C is the same as that of the delivery pole 106. On the other hand, it is characterized in that the shape of the peak value of the magnetic flux density is nearly flat.

[0113] This flat shape will now be described. Fig. 18 shows the results of measuring the magnetic flux density in the normal direction of the delivery pole 106C in this embodiment, with the rotation direction of the first sleeve 33 as the horizontal axis. Here, values ​​C, D, points Cd, Cu, Dd, Du, lines L11C, L12C, L11D, L12D, angles Wc, and Wd are defined as follows. Note that value Lt is the peak value of the magnetic flux density of the delivery pole 106C, as in the second embodiment. C: 10% of value Lt D: 90% of value Lt Cd: among the positions where the normal component of the magnetic flux density of the delivery pole 106C has value C, the downstream position in the rotation direction of the first sleeve 33 Cu: Among the positions where the normal component of the magnetic flux density of the receiving pole 106C has a value C, the upstream position in the rotation direction of the first sleeve 33 Dd: a downstream position in the rotation direction of the first sleeve 33 among the positions where the normal component of the magnetic flux density of the delivery pole 106C has a value D Du: among the positions where the normal component of the magnetic flux density of the delivery pole 106C has a value D, the upstream position in the rotation direction of the first sleeve 33 L11C: A straight line (dotted line) connecting the rotation center R1 of the first sleeve 33 and point Cd L12C: A straight line (dotted line) connecting the center of rotation R1 and point Cu L11D: A straight line (dotted line) connecting the center of rotation R1 and point Dd L12D: A straight line (dotted line) connecting the center of rotation R1 and point Du Wc: The angle between lines L11C and L12C Wd: The angle between lines L11D and L12D

[0114] As described above, in order to weaken the magnetic field from the first transport pole 105 to the second transport pole 202 and suppress the movement of the developer between the first transport pole 105 and the second transport pole 202, it is effective to strengthen the magnetic field between the first transport pole 105 and the delivery pole 106C. For this reason, it is conceivable to increase the peak value of the magnetic flux density of the delivery pole 106C, which makes it possible to strengthen the magnetic field with the first transport pole 105. However, this would also significantly change the magnetic field that contributes to the delivery of the developer from the first sleeve 33 to the second sleeve 34, which may lead to the drag phenomenon and developer deterioration.

[0115] Therefore, in this embodiment, the peak value of the magnetic flux density of the delivery pole 106C is not increased, but the angle Wd, which is the 90% width of the peak value of the magnetic flux density of the delivery pole 106C, is increased. Specifically, the vicinity of the peak value of the magnetic flux density of the delivery pole 106C is formed in a flat shape so that the angle ratio Wd / Wc of the angle Wd to the angle Wc, which is the 10% width of the peak value of the magnetic flux density of the delivery pole 106C, is 45% or more (Wd / Wc≧45%). As a result, the magnetic field between the first conveying pole 105 and the delivery pole 106C can be strengthened, and the magnetic field between the first conveying pole 105 and the second conveying pole 202 can be weakened, and the movement of the developer between the first conveying pole 105 and the second conveying pole 202 can be suppressed.

[0116] The flat magnetic flux density near the peak value of the passing pole 106C does not necessarily mean a single peak, but may mean multiple peaks, as long as the angular ratio Wd / Wc ≧ 45% is satisfied. A flat magnetic flux density like that of the passing pole 106C may be formed by cutting out a part of the circumferential direction of the magnet forming the passing pole 106C of the first magnet 36, or by embedding a magnet with a different magnetic force in the cut-out portion.

[0117] In addition, the delivery pole 106C of this embodiment has a flat shape in which the magnetic flux density in the normal direction is wider not only on the upstream side but also on the downstream side than the peak value of the magnetic flux density in the normal direction of the delivery pole 106 in the first embodiment. Therefore, a wide magnetic field is formed between the delivery pole 106C and the receiving pole 201, and the influence of the magnetization variation of the first magnet 36 and the second magnet 37 and the assembly tolerance on the magnetic field change of the delivery pole 106C and the receiving pole 201 is reduced. In other words, in this embodiment, compared to the first embodiment, the latitude of the delivery of the developer from the first sleeve 33 to the second sleeve 34 in response to the variation in the magnetic pole arrangement of the first magnet 36 and the second magnet 37 is widened, while the movement of the developer between the first transport pole 105 and the second transport pole 202 can be suppressed.

[0118] [experiment] Next, an experiment to investigate the occurrence of streaky fog images (abnormal images) in the above-mentioned configuration will be described. In the experiment, the angles Wc and Wd were varied by adjusting the magnetic flux density of the delivery pole 106C, and images were output using image forming apparatuses incorporating developing devices under various conditions. Then, the occurrence of streaky fog images on the output images was investigated. The other conditions and the evaluation of the experiment were the same as those in the experiment described in the first embodiment. The results of this experiment are shown in Table 4. [Table 4]

[0119] The configurations of the first developing roller 30 and the second developing roller 31 in the experiment are as shown in Figure 6. Regarding the magnetic characteristics, the peak value of the magnetic flux density of the delivery pole 106C was fixed at approximately 36 mT, and the shape of the magnetic flux density of the delivery pole 106C was changed stepwise from an angle ratio Wd / Wc of 22% to 51%. The magnetic poles other than the delivery pole 106C are as shown in Figure 13.

[0120] As is clear from Table 4, the occurrence of abnormal images could be suppressed when the angle ratio Wd / Wc was 45% or more. This is because the vicinity of the peak value of the magnetic flux density of the delivery pole 106C approaches the first transport pole 105, strengthening the magnetic field between the first transport pole 105 and the delivery pole 106C, and weakening the magnetic field between the first transport pole 105 and the second transport pole 202. On the other hand, when the angle ratio Wd / Wc is smaller than 45%, the effect of the magnetic flux of the delivery pole 106C in weakening the magnetic field between the first transport pole 105 and the second transport pole 202 is low, and the developer moves between the first transport pole 105 and the second transport pole 202, resulting in insufficient suppression of abnormal images.

[0121] As described above, according to this embodiment, the occurrence of image defects can be suppressed. That is, in the developing device 1Y of this embodiment, the developer is transported from the first transport pole 105 to the delivery pole 106C on the first sleeve 33, is delivered to the second sleeve 34 based on the magnetic force between the delivery pole 106C and the receiving pole 201, and is transported on the second sleeve 34 from the receiving pole 201 to the second transport pole 202. In such a configuration, the developer may move due to the magnetic force along the magnetic field between the first transport pole 105 and the second transport pole 202. In contrast, in this embodiment, as described above, the delivery pole 106C is configured so that the magnetic flux density is flat near the peak value so as to satisfy the angle ratio Wd / Wc≧45%, and therefore the magnetic field between the first transport pole 105 and the delivery pole 106C weakens the magnetic field between the first transport pole 105 and the second transport pole 202, and therefore the movement of the developer between the first transport pole 105 and the second transport pole 202 can be suppressed. Therefore, the occurrence of the above-mentioned streaky fogged image can be suppressed.

[0122] <Fourth embodiment> The fourth embodiment will be described with reference to Fig. 19. This embodiment differs from the first embodiment in the configuration of the delivery pole 106D of the first magnet 36 of the first developing roller 30. Since the other configurations and functions are similar to those of the first embodiment described above, the same reference numerals are used for similar configurations, and explanations and illustrations are omitted or simplified. The following description will focus on the points that are different from the first embodiment.

[0123] In this embodiment, as shown in FIG. 19, a delivery pole 106D is disposed at the position of the delivery pole 106 of the first magnet 36 employed in the first embodiment. The peak value of the magnetic flux density of this delivery pole 106D is the same as that of the delivery pole 106. On the other hand, the shape of the peak value of the magnetic flux density of the delivery pole 106D is nearly flat, and the upstream width of the half value is wider than the downstream width. Specifically, the configuration is such that the angle difference Δw≧0 described in the first embodiment and the area ratio Sa / S≧70% described in the second embodiment are satisfied. In this embodiment, unlike the second embodiment, Δw≧0 is satisfied, so that the area ratio Sa / S only needs to satisfy Sa / S≧65%. However, it is preferable to satisfy Sa / S≧70%.

[0124] In this embodiment, the magnetic flux density upstream of the peak value of the magnetic flux density of the delivery pole 106D, which is a range close to the first delivery pole 105, is larger than the magnetic flux density in the same range in the first and second embodiments. Therefore, the magnetic field between the first delivery pole 105 and the delivery pole 106D is stronger than in the first and second embodiments, and the effect of weakening the magnetic field between the first delivery pole 105 and the second delivery pole 202 is greater. Therefore, the effect of suppressing the movement of the developer between the first delivery pole 105 and the second delivery pole 202 is greater.

[0125] [experiment] Next, an experiment to investigate the occurrence of streaky fog images (abnormal images) in the above-mentioned configuration will be described. In the experiment, the angle difference Δw and the area ratio Sa / S were varied by adjusting the magnetic flux density of the delivery pole 106B, and images were output using image forming apparatuses incorporating developing devices under various conditions. Then, the occurrence of streaky fog images on the output images was investigated. The other conditions and the evaluation of the experiment were the same as those in the experiment described in the first embodiment. The results of this experiment are shown in Table 5. [Table 5]

[0126] The configurations of the first developing roller 30 and the second developing roller 31 in the experiment are as shown in Figure 6. For the magnetic characteristics, the peak value of the magnetic flux density of the handover pole 106D was fixed at approximately 36 mT, and the angle difference Δw was changed from -3 degrees to 3 degrees, while the area ratio Sa / S was changed stepwise from 61% to 74% to change the shape of the magnetic flux density of the handover pole 106D. The magnetic poles other than the handover pole 106D are as shown in Figure 7.

[0127] As is clear from Table 5, the occurrence of abnormal images could be suppressed when the angle difference Δw was 0 degrees or more and the area ratio Sa / S was 70% or more. This is because the vicinity of the peak value of the magnetic flux density of the passing pole 106D approaches the first carrier pole 105, which strengthens the magnetic fields of the first carrier pole 105 and the passing pole 106D and weakens the magnetic fields of the first carrier pole 105 and the second carrier pole 202.

[0128] Furthermore, the effect of suppressing the occurrence of abnormal images was also observed when the angle difference Δw=-1 degree and the area ratio Sa / S=65%. However, under these conditions, slight changes in the magnetic pole positions due to the influence of assembly tolerances of the first magnet 36 and the second magnet 37 and variations in magnetization may cause the magnetic field between the handover pole 106D and the first conveyor pole 105 to weaken, and the effect of weakening the magnetic field between the first conveyor pole 105 and the second conveyor pole 202 may become smaller. For this reason, it is preferable to satisfy Δw≧0, and in this case, it is sufficient if Sa / S≧65%. However, it is more preferable to satisfy the angle difference Δw≧0 and the area ratio Sa / S≧70%.

[0129] As described above, according to this embodiment, the occurrence of image defects can be suppressed. That is, in the developing device 1Y of this embodiment, the developer is transported on the first sleeve 33 from the first transport pole 105 to the delivery pole 106D, delivered to the second sleeve 34 based on the magnetic force between the delivery pole 106D and the receiving pole 201, and transported on the second sleeve 34 from the receiving pole 201 to the second transport pole 202. In such a configuration, the developer may move due to the magnetic force along the magnetic field between the first transport pole 105 and the second transport pole 202. In contrast, in this embodiment, as described above, by configuring the magnetic flux density of the delivery pole 106D to satisfy the angle difference Δw≧0 and the area ratio Sa / S≧65%, more preferably Sa / S≧70%, the magnetic field between the first delivery pole 105 and the delivery pole 106D weakens the magnetic field between the first delivery pole 105 and the second delivery pole 202, thereby suppressing the movement of developer between the first delivery pole 105 and the second delivery pole 202. As a result, the occurrence of the above-mentioned streaky fog image can be suppressed.

[0130] <Fifth embodiment> The fifth embodiment will be described with reference to Fig. 20. This embodiment differs from the first embodiment in the configuration of the delivery pole 106E of the first magnet 36 of the first developing roller 30. Since the other configurations and functions are similar to those of the first embodiment described above, the same reference numerals are used for similar configurations, and explanations and illustrations are omitted or simplified. The following description will focus on the points that are different from the first embodiment.

[0131] In this embodiment, as shown in FIG. 20, a delivery pole 106E is disposed at the position of the delivery pole 106 of the first magnet 36 employed in the first embodiment. The peak value of the magnetic flux density of this delivery pole 106E is the same as that of the delivery pole 106. On the other hand, the shape of the peak value of the magnetic flux density of the delivery pole 106E is nearly flat, and the width of the upstream side of the half value is wider than the width of the downstream side. Specifically, the configuration is such that the angle difference Δw≧0 described in the first embodiment and the angle ratio Wd / Wc≧35% described in the third embodiment are satisfied. In this embodiment, unlike the third embodiment, since Δw≧0 is satisfied, it is sufficient that the angle ratio Wd / Wc satisfies Wd / Wc≧30%. However, it is preferable to satisfy Wd / Wc≧35%.

[0132] In this embodiment, the magnetic flux density upstream of the peak value of the magnetic flux density of the delivery pole 106E, which is a range close to the first delivery pole 105, is larger than the magnetic flux density in the same range in the first and third embodiments. Therefore, the magnetic field between the first delivery pole 105 and the delivery pole 106E is stronger than in the first and third embodiments, and the effect of weakening the magnetic field between the first delivery pole 105 and the second delivery pole 202 is greater. Therefore, the effect of suppressing the movement of the developer between the first delivery pole 105 and the second delivery pole 202 is greater.

[0133] [experiment] Next, an experiment to investigate the occurrence of streaky fog images (abnormal images) in the above-mentioned configuration will be described. In the experiment, the angle difference Δw and the angle ratio Wd / Wc were varied by adjusting the magnetic flux density of the delivery pole 106E, and images were output using image forming apparatuses incorporating developing devices under various conditions. Then, the occurrence of streaky fog images on the output images was investigated. The other conditions and the evaluation of the experiment were the same as those of the experiment described in the first embodiment. The results of this experiment are shown in Table 6. [Table 6]

[0134] The configurations of the first developing roller 30 and the second developing roller 31 in the experiment are as shown in Figure 6. For the magnetic characteristics, the peak value of the magnetic flux density of the handover pole 106E was fixed at approximately 36 mT, and the angle difference Δw was changed from -3 degrees to 3 degrees, while the angle ratio Wd / Wc was changed stepwise from 25% to 46% to change the shape of the magnetic flux density of the handover pole 106E. The magnetic poles other than the handover pole 106E are as shown in Figure 7.

[0135] As is clear from Table 6, the occurrence of abnormal images could be suppressed when the angle difference Δw was 0 degrees or more and the angle ratio Wd / Wc was 35% or more. This is because the vicinity of the peak value of the magnetic flux density of the handover pole 106E approaches the first carrier pole 105, which strengthens the magnetic fields of the first carrier pole 105 and the handover pole 106E and weakens the magnetic fields of the first carrier pole 105 and the second carrier pole 202.

[0136] In addition, the effect of suppressing the occurrence of abnormal images was also observed when the angle difference Δw=-1 degree and the angle ratio Wd / Wc=30%. However, under these conditions, slight changes in the magnetic pole position due to the influence of the assembly tolerance of the first magnet 36 and the second magnet 37 and the variation in magnetization may cause the magnetic field between the handover pole 106E and the first conveyor pole 105 to weaken, and the effect of weakening the magnetic field between the first conveyor pole 105 and the second conveyor pole 202 may become smaller. For this reason, it is preferable to satisfy Δw≧0, and in this case, it is sufficient if Wd / Wc≧30%. However, it is more preferable to satisfy the angle difference Δw≧0 and the angle ratio Wd / Wc≧35%.

[0137] As described above, according to this embodiment, the occurrence of image defects can be suppressed. That is, in the developing device 1Y of this embodiment, the developer is transported from the first transport pole 105 to the delivery pole 106E on the first sleeve 33, delivered to the second sleeve 34 based on the magnetic force between the delivery pole 106E and the receiving pole 201, and transported from the receiving pole 201 to the second transport pole 202 on the second sleeve 34. In such a configuration, the developer may move due to the magnetic force along the magnetic field between the first transport pole 105 and the second transport pole 202. In contrast, in this embodiment, as described above, by configuring the magnetic flux density of the delivery pole 106E to satisfy the angle difference Δw≧0 and the angle ratio Wd / Wc≧30%, more preferably Wd / Wc≧35%, the magnetic field between the first delivery pole 105 and the delivery pole 106E weakens the magnetic field between the first delivery pole 105 and the second delivery pole 202, thereby suppressing the movement of developer between the first delivery pole 105 and the second delivery pole 202. As a result, the occurrence of the above-mentioned streaky fog image can be suppressed.

[0138] <Other embodiments> The present invention is not limited to the configurations of the above-mentioned embodiments. For example, the image forming apparatus 100 is not limited to an MFP, and may be a copier, a printer, or a facsimile machine. In addition, the configurations of the developer supply screw 42, the developer stirring screw 43, and the developer recovery screw 44 are not particularly limited as long as they can transport the developer, and for example, a spiral blade or a paddle-shaped blade can be applied.

[0139] In the above embodiment, the first sleeve 33 and the photosensitive drum 28Y rotate in the same direction at positions facing each other, and the second sleeve 34 and the photosensitive drum 28Y rotate in the same direction at positions facing each other, but the present invention is not limited to this. The rotation center R2 of the second developing roller 31 may be disposed vertically above the rotation center R1 of the first developing roller 30, and the first sleeve 33 and the photosensitive drum 28Y may rotate in opposite directions at positions facing each other, and the second sleeve 34 and the photosensitive drum 28Y may rotate in opposite directions at positions facing each other. That is, the photosensitive drum 28 may rotate from the upper side in the vertical direction to the lower side in the vertical direction at a position facing the first developing roller 30, and the photosensitive drum 28 may rotate from the upper side in the vertical direction to the lower side in the vertical direction at a position facing the second developing roller 31. The present invention may be applied to such a configuration. Furthermore, in the case where three or more developing rollers are provided, the present invention can be applied to any two of the developing rollers. [Explanation of symbols]

[0140] 1Y, 1M, 1C, 1K... Developing device 28Y, 28M, 28C, 28K...Photosensitive drum (image carrier) 30...First developing roller 31 Second developing roller 33...First sleeve 34...Second sleeve 35···Third sleeve 36... First magnet 37 Second magnet 105 1st conveying pole (1st magnetic pole) 106, 106B, 106C, 106D, 106E... Delivery pole 201 Receiving pole 202 Second carrying pole (second magnetic pole)

Claims

1. a first developing roller including a rotating first sleeve, a first magnet disposed inside the first sleeve in a non-rotating manner and configured to attract a developer containing toner and a magnetic carrier to a surface of the first sleeve by magnetic force, and which develops an electrostatic latent image formed on a rotating image carrier with the developer; a second developing roller having a rotation center located above the rotation center of the first developing roller in a vertical direction and receiving a developer from the first developing roller by magnetic force, the second developing roller having a second sleeve rotating in a direction opposite to the first sleeve at a position facing the first sleeve, and a second magnet disposed non-rotatingly inside the second sleeve and attracting the developer to a surface of the second sleeve by magnetic force, the second developing roller developing an electrostatic latent image formed on the image carrier with the developer, the first magnet has a transfer pole which is a magnetic pole for transferring developer from the first developing roller to the second developing roller, and a first magnetic pole located adjacent to and upstream of the transfer pole in a rotation direction of the first sleeve, the second magnet has a receiving pole which is a magnetic pole for the second developing roller to receive the developer from the first developing roller, and a second magnetic pole located adjacent to the receiving pole on the downstream side with respect to the rotation direction of the second sleeve, The receiving pole is A position where a normal component of the magnetic flux density of the transfer pole on the surface of the first sleeve is maximum is defined as point T, Among the half-maximum positions of the normal component of the magnetic flux density of the delivery pole, a position downstream in the rotation direction of the first sleeve is defined as point Hd, Among the positions of half the maximum value of the normal component of the magnetic flux density of the transfer pole, a position on the upstream side in the rotation direction of the first sleeve is defined as point Hu, A straight line connecting the rotation center R1 of the first sleeve and the point T is defined as a straight line L10, A straight line connecting the rotation center R1 and the point Hd is defined as a straight line L11. A straight line connecting the rotation center R1 and the point Hu is defined as a straight line L12, The angle between the straight line L10 and the straight line L12 is w1. The angle between the straight line L10 and the straight line L11 is w2, When Δw=w1-w2, Δw≧0 A developing device characterized by satisfying the above.

2. The transfer pole is Δw>0 2. The developing device according to claim 1, wherein the above formula is satisfied.

3. The transfer pole is Δw≧2.5 degrees.

2. The developing device according to claim 1, wherein the above formula is satisfied.

4. The receiving pole is The maximum value of the normal component of the magnetic flux density of the transfer pole on the surface of the first sleeve is defined as a value Lt, Half the value of the value Lt is set as a value Lh, When the normal component of the magnetic flux density of the delivery pole on the surface of the first sleeve is graphed with the magnetic flux density on the vertical axis and the angle in the rotational direction of the first sleeve on the horizontal axis, a straight line parallel to the horizontal axis passing through the position of the value Lt is a straight line HLt, a straight line parallel to the horizontal axis passing through the position of the value Lh is a straight line HLh, a straight line parallel to the vertical axis passing through the point Hd is a straight line VL11, and a straight line parallel to the vertical axis passing through the point Hu is a straight line VL12, A rectangular area surrounded by the straight lines VL11, VL12, HLt, and HLh is defined as an area S, In the graph, when the area obtained by integrating the normal component of the magnetic flux density of the transfer pole from the straight line VL11 to the straight line VL12 with respect to the angle in the rotational direction of the first sleeve is defined as an area Sa, Sa / S≧65% 2. The developing device according to claim 1, wherein the above formula is satisfied.

5. The receiving pole has Sa / S≧70% 5. The developing device according to claim 4, wherein the above formula is satisfied.

6. The receiving pole is The maximum value of the normal component of the magnetic flux density of the transfer pole on the surface of the first sleeve is defined as a value Lt, A value that is 10% of the value Lt is set as a value C, A value that is 90% of the value Lt is a value D, Among the positions where the normal component of the magnetic flux density of the delivery pole is the value C, a position downstream in the rotation direction of the first sleeve is defined as point Cd, Among the positions where the normal component of the magnetic flux density of the delivery pole is the value C, a position on the upstream side in the rotation direction of the first sleeve is defined as point Cu, Among the positions where the normal component of the magnetic flux density of the delivery pole is the value D, a position downstream in the rotation direction of the first sleeve is defined as point Dd, Among the positions where the normal component of the magnetic flux density of the delivery pole is the value D, a position on the upstream side in the rotation direction of the first sleeve is defined as point Du, A straight line connecting the rotation center R1 of the first sleeve and the point Cd is defined as a straight line L11C, A straight line connecting the rotation center R1 and the point Cu is defined as a straight line L12C, A straight line connecting the rotation center R1 and the point Dd is a straight line L11D, A straight line connecting the rotation center R1 and the point Du is a straight line L12D, The angle between the straight line L11C and the straight line L12C is Wc, When the angle between the straight lines L11D and L12D is Wd, Wd / Wc≧30% 2. The developing device according to claim 1, wherein the above formula is satisfied.

7. The receiving pole is Wd / Wc≧35% 7. The developing device according to claim 6, wherein the above formula is satisfied.

8. a first developing roller including a rotating first sleeve, a first magnet disposed inside the first sleeve in a non-rotating manner and configured to attract a developer containing toner and a magnetic carrier to a surface of the first sleeve by magnetic force, and which develops an electrostatic latent image formed on a rotating image carrier with the developer; a second developing roller having a rotation center located above the rotation center of the first developing roller in a vertical direction and receiving a developer from the first developing roller by magnetic force, the second developing roller having a second sleeve rotating in a direction opposite to the first sleeve at a position facing the first sleeve, and a second magnet disposed non-rotatingly inside the second sleeve and attracting the developer to a surface of the second sleeve by magnetic force, the second developing roller developing an electrostatic latent image formed on the image carrier with the developer, the first magnet has a transfer pole which is a magnetic pole for transferring developer from the first developing roller to the second developing roller, and a first magnetic pole located adjacent to and upstream of the transfer pole in a rotation direction of the first sleeve, the second magnet has a receiving pole which is a magnetic pole for the second developing roller to receive the developer from the first developing roller, and a second magnetic pole located adjacent to the receiving pole on the downstream side with respect to the rotation direction of the second sleeve, The receiving pole is The maximum value of the normal component of the magnetic flux density of the transfer pole on the surface of the first sleeve is defined as a value Lt, Half the value of the value Lt is set as a value Lh, Among the half-maximum positions of the normal component of the magnetic flux density of the delivery pole, a position downstream in the rotation direction of the first sleeve is defined as point Hd, Among the positions of half the maximum value of the normal component of the magnetic flux density of the transfer pole, a position on the upstream side in the rotation direction of the first sleeve is defined as point Hu, When the normal component of the magnetic flux density of the delivery pole on the surface of the first sleeve is graphed with the magnetic flux density on the vertical axis and the angle in the rotational direction of the first sleeve on the horizontal axis, a straight line parallel to the horizontal axis passing through the position of the value Lt is a straight line HLt, a straight line parallel to the horizontal axis passing through the position of the value Lh is a straight line HLh, a straight line parallel to the vertical axis passing through the point Hd is a straight line VL11, and a straight line parallel to the vertical axis passing through the point Hu is a straight line VL12, A rectangular area surrounded by the straight lines VL11, VL12, HLt, and HLh is defined as an area S, In the graph, when the area obtained by integrating the normal component of the magnetic flux density of the transfer pole from the straight line VL11 to the straight line VL12 with respect to the angle in the rotational direction of the first sleeve is defined as an area Sa, Sa / S≧75% A developing device characterized by satisfying the above.

9. a first developing roller including a rotating first sleeve, a first magnet disposed inside the first sleeve in a non-rotating manner and configured to attract a developer containing toner and a magnetic carrier to a surface of the first sleeve by magnetic force, and which develops an electrostatic latent image formed on a rotating image carrier with the developer; a second developing roller having a rotation center located above the rotation center of the first developing roller in a vertical direction and receiving a developer from the first developing roller by magnetic force, the second developing roller having a second sleeve rotating in a direction opposite to the first sleeve at a position facing the first sleeve, and a second magnet disposed non-rotatingly inside the second sleeve and attracting the developer to a surface of the second sleeve by magnetic force, the second developing roller developing an electrostatic latent image formed on the image carrier with the developer, the first magnet has a transfer pole which is a magnetic pole for transferring developer from the first developing roller to the second developing roller, and a first magnetic pole located adjacent to and upstream of the transfer pole in a rotation direction of the first sleeve, the second magnet has a receiving pole which is a magnetic pole for the second developing roller to receive the developer from the first developing roller, and a second magnetic pole located adjacent to the receiving pole on the downstream side with respect to the rotation direction of the second sleeve, The receiving pole is The maximum value of the normal component of the magnetic flux density of the transfer pole on the surface of the first sleeve is defined as a value Lt, A value that is 10% of the value Lt is set as a value C, A value that is 90% of the value Lt is a value D, Among the positions where the normal component of the magnetic flux density of the delivery pole is the value C, a position downstream in the rotation direction of the first sleeve is defined as point Cd, Among the positions where the normal component of the magnetic flux density of the delivery pole is the value C, a position on the upstream side in the rotation direction of the first sleeve is defined as point Cu, Among the positions where the normal component of the magnetic flux density of the delivery pole is the value D, a position downstream in the rotation direction of the first sleeve is defined as point Dd, Among the positions where the normal component of the magnetic flux density of the delivery pole is the value D, a position on the upstream side in the rotation direction of the first sleeve is defined as point Du, A straight line connecting the rotation center R1 of the first sleeve and the point Cd is defined as a straight line L11C, A straight line connecting the rotation center R1 and the point Cu is defined as a straight line L12C, A straight line connecting the rotation center R1 and the point Dd is a straight line L11D, A straight line connecting the rotation center R1 and the point Du is a straight line L12D, The angle between the straight line L11C and the straight line L12C is Wc, When the angle between the straight lines L11D and L12D is Wd, Wd / Wc≧45% A developing device characterized by satisfying the above.

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