Developing device

Abstract

To provide a configuration capable of suppressing the occurrence of an image defect.SOLUTION: A second developing magnet 37 has a delivering pole 207, which is a magnetic pole for delivering developer from a second developing roller 31 to a peeling roller 32. A peeling magnet 38 has a receiving pole 303, which is a magnetic pole for receiving the developer from the second developing roller 31 by the peeling roller 32 and is different in a polarity from the delivering pole 207. A peak position P1, which is a position of the maximum value of the normal component of the magnetic flux density of the receiving pole 303 on a peeling sleeve 35 is positioned on a side downstream in a rotational direction of the peeling sleeve 35 with respect to a rectilinear line L1 connecting the rotation center of the second developing sleeve 34 and the rotation center of the peeling sleeve 35.SELECTED DRAWING: Figure 6

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 having a configuration including a peeling roller that peels off and collects developer from a developing roller that develops an electrostatic latent image formed on an image carrier with the developer (Patent Document 1). The developing roller includes a rotating developing sleeve and a non-rotating developing magnet arranged inside the developing sleeve, and the developer is carried on the surface of the developing sleeve by the magnetic force of the developing magnet. Similarly, the peeling roller also includes a rotating peeling sleeve and a non-rotating peeling magnet arranged inside the peeling sleeve, and the developer is carried on the surface of the peeling sleeve by the magnetic force of the peeling magnet. Then, the developer (used developer) that has been carried and transported by the developing sleeve and developed the electrostatic latent image on the image carrier is carried on the surface of the peeling sleeve, and the developer is collected from the developing roller by the peeling roller.

[0003] In the configuration described in Patent Document 1, the peeling sleeve rotates in the forward direction, that is, in such a way that the surface of the peeling sleeve moves in the same direction as the surface of the developing sleeve at the portion facing the developing sleeve. The developing magnet has a delivery pole that is a magnetic pole for delivering the developer from the developing roller to the peeling roller, and the peeling magnet has a receiving pole that is a magnetic pole for the peeling roller to receive the developer from the developing roller. In the configuration described in Patent Document 1, the peak position, which is the position of the maximum value of the normal component of the magnetic flux density of the receiving pole on the peeling sleeve, is located upstream of the rotation direction of the peeling sleeve with respect to the straight line connecting the rotation center of the developing sleeve and the rotation center of the peeling roller. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2003-149942 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the peak position of the receiving pole is located upstream of the line connecting the rotation center of the developing sleeve and the rotation center of the peeling roller in the rotation direction of the peeling sleeve, as in the configuration described in Patent Document 1, the following problem occurs. That is, the developer delivered to the peeling roller forms a magnetic brush along the magnetic field lines of the receiving pole, and the tip of the magnetic brush contacts the developing roller. At this time, since the peak position of the receiving pole is located upstream of the line connecting the rotation center of the developing sleeve and the rotation center of the peeling roller in the rotation direction of the peeling sleeve, the magnetic brush that contacts the developing roller advances while being compressed between the developing roller and the peeling roller. At this time, the magnetic brush breaks, and a part of it is left behind on the developing roller and moves toward the opposing part of the developing roller and the peeling roller.

[0006] In this opposing portion, the magnetic brush of the developer on the peeling roller lies between adjacent magnetic poles (between the poles), and the magnetic lines of force are formed in a direction along the surface of the peeling roller, so that the magnetic force that collects the developer left on the developing roller onto the peeling roller is difficult to work. The developer left on the developing roller is carried around the surface of the developing sleeve or falls downward, and is supplied to the developing roller again before being taken into the developer circulation path of the developing device. As a result, it affects the distribution of the TD ratio (T / D, the ratio of the toner weight to the total weight of the carrier and toner) of the developer carried on the developing sleeve, and causes image defects such as fluctuations in the color of the toner image after development.

[0007] An object of the present invention is to provide a configuration capable of suppressing the occurrence of image defects. [Means for solving the problem]

[0008] According to one aspect of the present invention, there is provided a developing roller having a rotating developing sleeve, a developing magnet that is non-rotatingly disposed inside the developing sleeve and that magnetically attracts a developer to a surface of the developing sleeve, the developing roller developing an electrostatic latent image formed on a rotating image carrier with the developer, a peeling sleeve that rotates in the same direction as the surface of the developing sleeve at an opposing portion that faces the developing sleeve, and a peeling magnet that is non-rotatingly disposed inside the peeling sleeve and that magnetically attracts the developer to the surface of the peeling sleeve, the developing roller developing the electrostatic latent image on the image carrier with the developer, the peeling magnet being disposed non-rotatingly inside the peeling sleeve and that magnetically attracts the developer to the surface of the peeling sleeve, the developing roller developing the electrostatic latent image on the image carrier with the developer, the peeling magnet being disposed a peeling roller which peels the developer off from the developing roller, wherein the developing magnet has a delivery pole which is a magnetic pole for transferring the developer from the developing roller to the peeling roller, and the peeling magnet has a receiving pole which is a magnetic pole for the peeling roller to receive the developer from the developing roller and has a polarity opposite to that of the delivery pole, and a peak position P1 which is the position of the maximum value of the normal component of the magnetic flux density of the receiving pole on the peeling sleeve is located downstream in the rotation direction of the peeling sleeve with respect to a straight line L1 which connects the rotation center of the developing sleeve and the rotation center of the peeling sleeve. Effect of the Invention

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

[0010] [Figure 1] 1 is a schematic cross-sectional view of an image forming apparatus according to a first embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view of the developing device according to the first embodiment. [Diagram 3] FIG. 4 is a diagram showing the arrangement of magnetic poles of a first developing roller according to the first embodiment. [Figure 4] FIG. 4 is a diagram showing the arrangement of magnetic poles of a second developing roller according to the first embodiment. [Diagram 5] FIG. 2 is a diagram showing the arrangement of magnetic poles of the peeling roller according to the first embodiment. [Figure 6] FIG. 4 is an enlarged view of the periphery of a second developing roller and a peeling roller according to the first embodiment. [Figure 7] FIG. 4 is a schematic diagram showing how developer is transferred between the second developing roller and the peeling roller according to the first embodiment. [Figure 8] FIG. 4 is a schematic diagram showing magnetic flux lines between a second developing roller and a peeling roller according to the first embodiment. [Figure 9] FIG. 4 is a diagram showing the arrangement of magnetic poles of a peeling roller according to Comparative Example 1. [Figure 10] FIG. 11 is a schematic diagram showing how developer is transferred between a second developing roller and a peeling roller according to Comparative Example 1. [Figure 11] FIG. 11 is a schematic diagram showing magnetic flux lines between a second developing roller and a peeling roller according to Comparative Example 1. [Figure 12] 5A and 5B are schematic diagrams showing the relationship between the falling of magnetic brushes of a developer and the friction between the magnetic brushes and a developing sleeve. [Figure 13] 5A and 5B are schematic diagrams showing the relationship between the adhesive force and the magnetic binding force between the magnetic brush of the developer and the developing sleeve. [Figure 14] FIG. 4 is an enlarged view of the periphery of the second developing roller and the peeling roller for explaining the positional relationship of the receiving pole according to the first embodiment. [Figure 15] FIG. 11 is an enlarged view of the periphery of the second developing roller and the peeling roller for explaining the positional relationship of the receiving pole according to Comparative Example 2. [Figure 16] FIG. 11 is a diagram showing the arrangement of magnetic poles of a second developing roller according to a second embodiment. [Figure 17] FIG. 13 is a diagram showing the arrangement of magnetic poles of a second developing roller according to a third embodiment. [Figure 18] FIG. 13 is a diagram showing the arrangement of magnetic poles of a second developing roller according to the fourth embodiment. [Figure 19] FIG. 13 is a diagram showing the arrangement of magnetic poles of a peeling roller according to a fourth embodiment. [Figure 20] FIG. 13 is an enlarged view of the periphery of a second developing roller and a peeling roller according to a fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] <First embodiment> The first embodiment will be described with reference to Figures 1 to 15. First, the schematic configuration of an image forming apparatus according to the present embodiment will be described with reference to Figure 1.

[0012] [Image forming equipment] The image forming apparatus 100 is a full-color image forming apparatus, and in this embodiment, for example, it 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 of four colors of toner images of yellow, magenta, cyan, and black, respectively. In the image forming apparatus 100 of this embodiment, a document reading device connected to the image forming apparatus main body (apparatus main body) or a host device such as a personal computer is connected to the apparatus main body so as to be able to communicate with the image forming apparatus. Therefore, according to image information from the host device, a four-color full-color image of yellow (Y), magenta (M), cyan (C), and black (K) can be formed on a recording material (recording paper, plastic sheet, cloth, etc.) using an electrophotographic method.

[0013] The image forming units PY, PM, PC, and PK of the respective colors include primary chargers 21Y, 21M, 21C, and 21K, developing units 1Y, 1M, 1C, and 1K, exposure units 22Y, 22M, 22C, and 22K, photosensitive drums 28Y, 28M, 28C, and 28K, and cleaning units 26Y, 26M, 26C, and 26K. The image forming apparatus 100 also includes a transfer unit 2 and a fixing unit 3. Since the image forming units PY, PM, PC, and PK of the respective colors have the same configuration, the following description will be given using the image forming unit PY as a representative.

[0014] 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.

[0015] The exposure device 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 development 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.

[0016] 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 as primary transfer members correspond to the colors Y (yellow), M (magenta), C (cyan), and K (black) in order from the top in 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.

[0017] The toner images of each color formed on the photosensitive drums 28Y, 28M, 28C, and 28K are transferred (primary transfer) onto the intermediate transfer belt 24 by the action of a primary transfer bias applied to the primary transfer rollers 23Y, 23M, 23C, and 23K at a primary transfer portion (primary transfer nip) T1 where the intermediate transfer belt 24 and the photosensitive drums 28Y, 28M, 28C, and 28K come into contact with each other. For example, in the case of a four-color full-color image, the toner images are transferred onto the intermediate transfer belt 24 in order from the photosensitive drum 28Y, and a color toner image in which yellow, magenta, cyan, and black layers are superimposed is formed.

[0018] Meanwhile, the recording material S stored in a cassette 115 serving as a recording material storage section is conveyed toward the transfer device 2 via a pickup roller 111 and a registration roller 112. The recording material S is conveyed in synchronization with the toner image on the intermediate transfer belt 24 to a secondary transfer section (nip section) T2 where the intermediate transfer belt 24 and a secondary transfer roller 25 serving as a secondary transfer member come into contact with each other. Then, the toner image formed on the intermediate transfer belt 24 is secondarily transferred onto the recording material S at the secondary transfer section T2 by the action of a secondary transfer bias applied to the secondary transfer roller 25. Pressure and heat are applied to the recording material to which the toner image has been transferred in the fixing device 3. This melts the toner on the recording material, and the color image is fixed onto the recording material. Thereafter, the recording material S is discharged outside the machine.

[0019] When forming images on both sides of the recording material, the recording material S that has passed through the fixing device 3 is conveyed to a reversing conveying path 113, and the recording material S that has been turned over is conveyed to registration rollers 112 by conveying rollers 114, and in the secondary transfer portion T2, a toner image is transferred to the back side of the recording material S in the same manner as described above. Then, again in the fixing device 3, the toner image is fixed to the back side of the recording material S.

[0020] The toner and other deposits remaining on the photosensitive drums 28Y, 28M, 28C, and 28K after the primary transfer process are collected by the cleaning devices 26Y, 26M, 26C, and 26K. This prepares the photosensitive drums 28Y, 28M, 28C, and 28K for the next image forming process. In addition, the toner and other deposits remaining on the intermediate transfer belt 24 after the secondary transfer process are removed by the intermediate transfer belt cleaner 29.

[0021] The image forming apparatus 100 of this embodiment can form a single-color or multi-color image, such as a black single-color image, by using image forming units for a desired single color or several colors among four colors. In addition, in FIG. 1, the image forming units PY, PM, PC, and PK for each color are arranged vertically, but they may be arranged horizontally or diagonally. Furthermore, in this embodiment, the outer diameter of the photosensitive drums 28Y, 28M, 28C, and 28K is, for example, 80 [mm], and the image forming operation is performed while rotating at a peripheral speed of 513 mm / sec.

[0022] 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.

[0023] 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.

[0024] [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 developing magnet (first magnet) 36, the second developing magnet (second magnet) 37, and the peeling magnet (third magnet) 38 arranged in the developing device 1Y.

[0025] 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 members are contained in a developing container 60. The developing container 60 contains a two-component developer containing non-magnetic toner and a magnetic carrier.

[0026] 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 developing sleeve 33 and a first developing magnet (fixed magnet) 36 that is disposed inside the first developing sleeve 33 in a non-rotating manner and that attracts the developer to the surface of the first developing sleeve 33 by magnetic force. The first developing roller 30 attracts (carries) the developer pumped up from a 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.

[0027] The first developing sleeve 33 is a non-magnetic cylindrical member, and is driven to rotate around a rotation shaft 39. The rotation direction of the first developing 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 developing sleeve 33 and the photosensitive drum 28Y rotate in the same direction (forward direction) at a position where they face each other (facing portion). That is, the first developing sleeve 33 rotates such that the surface facing the photosensitive drum 28Y moves vertically from below toward above.

[0028] The first developing magnet 36 is disposed inside the first developing sleeve 33, and has a plurality of magnetic poles 101 to 107, as shown in Fig. 3. Between the inner periphery of the first developing sleeve 33 and the outer periphery of the first developing magnet 36, a space is disposed to allow the first developing sleeve 33 to rotate.

[0029] The developer attracted onto the first developing sleeve 33 is transported toward the photosensitive drum 28Y by the rotational movement of the first developing 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 developing sleeve 33 is transported to the vicinity of the second developing roller 31 by the rotational movement of the first developing 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 developing sleeve 33 and transferred onto the second developing sleeve 34 by the magnetic field generated by the first developing magnet 36 contained in the first developing roller 30 and the second developing magnet 37 contained in the second developing roller 31.

[0030] The second developing roller 31, which serves as a developing roller, 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 above the rotation center of the first developing roller 30 in the vertical direction, and receives the developer from the first developing roller 30 by magnetic force. Similar to the first developing roller 30, the second developing roller 31 is disposed adjacent to the photosensitive drum 28Y such that its rotation axis is substantially parallel to the rotation axis of the photosensitive drum 28Y. Therefore, the rotation axes of the second developing roller 31 and the first developing roller 30 are substantially parallel to each other.

[0031] The second developing roller 31 has a rotating second developing sleeve 34 and a second developing magnet (fixed magnet) 37 that is non-rotatingly disposed inside the second developing sleeve 34 and attracts the developer to the surface of the second developing sleeve 34 by magnetic force. The second developing roller 31 receives the developer from the first developing roller 30 (first developing 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.

[0032] The second developing sleeve 34 is a non-magnetic cylindrical member, and is driven to rotate around the rotation shaft 40. The rotation direction of the second developing sleeve 34 is clockwise 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 developing sleeve 34 and the photosensitive drum 28Y rotate in the same direction (forward direction) at a position where they face each other (facing portion). That is, the second developing sleeve 34 rotates such that the surface facing the photosensitive drum 28Y moves from below to above in the vertical direction. Also, the second developing sleeve 34 and the first developing sleeve 33 rotate in opposite directions at a position where they face each other.

[0033] The second developing magnet 37 is disposed inside the second developing sleeve 34, and has, for example, a plurality of sector-shaped magnetic poles 201 to 207. Between the inner periphery of the second developing sleeve 34 and the outer periphery of the second developing magnet 37, a space is disposed to allow the second developing sleeve 34 to rotate.

[0034] The developer attracted onto the second developing sleeve 34 is transported toward the photosensitive drum 28Y by the rotational operation of the second developing 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 developing sleeve 34 is transported to the vicinity of the peeling roller 32 by the rotational operation of the second developing 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 developing sleeve 34 to the peeling sleeve 35 of the peeling roller 32 by the magnetic field generated by the second developing magnet 37 contained in the second developing roller 31 and the peeling magnet 38 contained in the peeling roller 32.

[0035] The peeling roller 32 is disposed on the opposite side to the photosensitive drum 28Y with respect to the rotation center of the second developing 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 of the second developing roller 31.

[0036] 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 peeling sleeve 35 and a peeling magnet (fixed magnet) 38 that is non-rotatingly disposed inside the peeling sleeve 35 and attracts the developer to the surface of the peeling sleeve 35 by magnetic force, and is configured to receive the developer from the second developing roller 31 based on the magnetic force.

[0037] The peeling sleeve 35 is a non-magnetic cylindrical member, and is driven to rotate around a rotation shaft 41. The rotation direction of the peeling sleeve 35 is counterclockwise as indicated by the arrow in Fig. 2, which is the opposite direction to the rotation direction of the second developing sleeve 34 in this embodiment. Therefore, the peeling sleeve 35 and the second developing sleeve 34 rotate in the same direction (forward direction) at positions where they face each other (facing portions).

[0038] The peeling magnet 38 is disposed inside the peeling sleeve 35, and has, for example, a plurality of magnetic poles 301 to 305. Between the inner periphery of the peeling sleeve 35 and the outer periphery of the peeling magnet 38, a space that allows the peeling sleeve 35 to rotate is disposed.

[0039] The developer attracted onto the peeling sleeve 35 is transported downstream in the rotation direction by the rotation of the peeling sleeve 35, and is peeled off from the peeling sleeve 35 by a peeling 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 a 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.

[0040] 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 peeling sleeve 35 on the peeling roller 32. In the developer recovery section 47, the developer recovery screw 44 is located below 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.

[0041] The guide member 45 as a guide portion is disposed vertically below the center of rotation of 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 lower position of the peeling roller 32.

[0042] 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.

[0043] 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. That is, the developer circulating section 46 is located lower than the developer collecting section 47 in the vertical direction.

[0044] 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 below the rotation center of the developer recovery screw 44 in the vertical direction. 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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 developing sleeve 33 of the first developing roller 30 and an end of the regulating member 50.

[0053] The developer circulation path in the developing container 60 is such that the developer is transported in a substantially horizontal direction while being stirred in the developer circulation section 46, and then supplied to the first developing roller 30, and is transferred from the first developing roller 30 to the second developing roller 31 above by magnetic force. Next, the developer is transferred from the second developing roller 31 to the peeling roller 32 on the side of the second developing roller 31 again by magnetic force, and then peeled off from the peeling roller 32 by a peeling magnet 38 contained in the peeling roller 32, and then collected in the developer collection section 47, and introduced again into the developer circulation section 46.

[0054] 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%.

[0055] 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.

[0056] 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.

[0057] In the developing device 1Y of the present embodiment thus configured, the developer in the first transport path 61 is supplied to the first developing sleeve 33 by the developer supply screw 42, and a predetermined amount of the developer supplied to the first developing sleeve 33 is carried on the first developing sleeve 33 by the magnetic field generated by the first developing magnet 36 to form a developer pool. As the first developing sleeve 33 rotates, the two-component developer on the first developing sleeve 33 passes through the developer pool and is coated in a thin layer on the surface of the first developing sleeve 33 by the regulating member 50, and is transported to a developing area facing the photosensitive drum 28Y. In the developing area, the developer on the first developing sleeve 33 stands up to form magnetic spikes.

[0058] In the first developing region where the first developing sleeve 33 and the photosensitive drum 28Y face each other, the electrostatic latent image formed on the photosensitive drum 28Y is visualized by the developing bias applied to the first developing sleeve 33. In this embodiment, the developing bias applied to the first developing sleeve 33 has a waveform in which both an AC electric field and a DC electric field are superimposed, but the developing bias may be a DC electric field only.

[0059] After the two-component developer is subjected to the developing process in the first developing region, it is transferred to the second developing sleeve 34 at a position close to the second developing sleeve 34 and transported to the second developing region where the second developing sleeve 34 faces the photosensitive drum 28Y. In the second developing region, the same developing bias as in the first developing region is applied, and the toner image is made uniform by developing and compensating for the lack of toner relative to the potential of the electrostatic latent image on the photosensitive drum 28Y and recovering the toner that has been developed in excess. Here, the developing bias applied to the first developing sleeve 33 and the developing bias applied to the second developing sleeve 34 may have different waveforms.

[0060] The developer that has passed through the second developing region is peeled off in a peeling magnetic field region formed by a second developing magnet 37 contained in the second developing sleeve 34. The developer peeled off from the second developing sleeve 34 is attracted to the surface of the peeling sleeve 35 by a magnetic field formed by a peeling magnet 38 contained in the peeling sleeve 35 of the peeling roller 32, and is transported along the rotation direction of the peeling sleeve 35. The developer is then detached from the surface of the peeling sleeve 35 by the peeling magnetic field formed by the peeling magnet 38, and is collected in a developer collecting section 47.

[0061] [About the magnetic poles of each magnet] Next, the magnetic pole configurations of the first developing magnet 36, the second developing magnet 37 and the peeling magnet 38 contained in the first developing roller 30, the second developing roller 31 and the peeling roller 32 shown in FIGS. 3, 4 and 5 will be described.

[0062] As shown in FIG. 3, the first developing magnet 36 contained in the first developing roller 30 has multiple magnetic poles 101 (S1), 102 (N2), 103 (S2), 104 (N3), 105 (S3), 106 (N4), and 107 (N1) (the S and N in parentheses indicate whether the magnetic pole is an S pole or an N pole, and the numbers are given to distinguish it from other magnetic poles. The same applies to FIGS. 4 and 5). Of these, the magnetic pole 106 is a transfer pole for transferring the developer from the first developing roller 30 to the second developing roller 31. The magnetic poles 101 to 107 are arranged in numerical order in the rotation direction of the first developing sleeve 33.

[0063] The magnetic pole 106 is a magnetic pole for transferring the developer from the first developing sleeve 33 to the second developing sleeve 34 by a magnetic field generated in cooperation with the second developing magnet 37 of the second developing roller 31. 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 developing sleeve 33. The magnetic poles 101, 102, 103, 104, and 105 are an S pole, an N pole, an S pole, an N pole, and an S pole, and are used to transport the developer attracted by the magnetic pole 107 upward as the first developing sleeve 33 rotates. The magnetic pole 106 is an N pole, and transfers the developer from the first developing sleeve 33 to the second developing sleeve 34 facing the first developing sleeve 33 by a magnetic field generated in cooperation with the magnetic pole 201 in the second developing magnet 37 contained in the second developing roller 31 as described above.

[0064] In this embodiment, a low magnetic force portion 110 having a lower magnetic force than the magnetic pole 106 is formed by a repulsive magnetic field generated in cooperation between the magnetic pole 106 and the magnetic pole 107, which is disposed downstream of the magnetic pole 106 in the rotation direction of the first developing sleeve 33 and has the same polarity as the magnetic pole 106. This low magnetic force portion 110 promotes the transfer of the developer from the first developing sleeve 33 to the second developing sleeve 34. Note that, although the low magnetic force portion 110 has almost no magnetic force in this embodiment, it may have a low magnetic force, for example, it may be 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 developing magnet 37 shown in FIG. 4 and the low magnetic force portion 310 of the peeling magnet 38 shown in FIG. 5.

[0065] 4, the second developing magnet 37 contained in the second developing roller 31 has a plurality of magnetic poles 201 (S4), 202 (N5), 203 (S5), 204 (N6), 205 (S6), 206 (N7), and 207 (S7). Of these, the magnetic pole 201 is a receiving pole for the second developing roller 31 to receive the developer from the first developing roller 30. The magnetic poles 201 to 207 are arranged in numerical order in the rotation direction of the second developing sleeve 34.

[0066] The magnetic pole 201 is a magnetic pole for attracting the developer from the first developing sleeve 33 to the second developing sleeve 34 by a magnetic field generated in cooperation with the magnetic pole 107 of the first developing magnet 36 of the first developing roller 30. The magnetic pole 207 is a magnetic pole for transferring the developer from the second developing sleeve 34 to the peeling sleeve 35 by a magnetic field generated in cooperation with the peeling magnet 38 of the peeling roller 32, and hereinafter may be referred to as a transfer pole 207 (S7).

[0067] Moreover, the magnetic pole 201 is an S pole different from the magnetic pole 106, and is used to attract the developer from the first developing roller 30 (first developing sleeve 33) onto the second developing sleeve 34 as described above. The magnetic poles 202, 203, 204, 205, and 206 are an N pole, an S pole, an N pole, an S pole, and an N pole, and are used to transport the developer attracted by the magnetic pole 201 upward as the second developing sleeve 34 rotates. The magnetic pole 207 as a transfer pole 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 developing sleeve 34 to the peeling sleeve 35 facing the second developing sleeve 34 by a magnetic field generated in cooperation with the magnetic pole 303 in the peeling magnet 38 contained in the peeling roller 32.

[0068] In this embodiment, a low magnetic force portion 210 having a lower magnetic force than the magnetic pole 207 is formed by a repulsive magnetic field generated in cooperation between the magnetic pole 201 and the magnetic pole 207, which is disposed upstream of the magnetic pole 201 in the rotation direction of the second developing sleeve 34 and has the same polarity as the magnetic pole 201. This low magnetic force portion 210 promotes the transfer of the developer from the first developing sleeve 33 to the second developing sleeve 34. In addition, the low magnetic force portion 210 can prevent the developer from being attracted to the closest portion between the first developing sleeve 33 and the second developing sleeve 34, and can suppress the pressure applied to the developer.

[0069] 5, the peeling magnet 38 contained in the peeling roller 32 has a plurality of magnetic poles 301 (N8), 302 (S8), 303 (N9), 304 (S9), and 305 (N10). The magnetic poles 301 to 305 are arranged in numerical order in the rotation direction of the peeling sleeve 35.

[0070] The magnetic pole 303 as a receiving pole is a magnetic pole for attracting the developer from the second developing sleeve 34 to the peeling sleeve 35 by a magnetic field generated in cooperation with the magnetic pole 207 of the second developing magnet 37 of the second developing roller 31, and may be hereinafter referred to as the receiving pole 303 (S9). 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 developing sleeve 34 to the peeling 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 peeling sleeve 35 as the peeling sleeve 35 rotates. In particular, the magnetic pole 304 is used to transport the developer attracted by the magnetic pole 303 downward as the peeling 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 peeling sleeve 35 from the peeling sleeve 35 by a repulsive magnetic field generated in cooperation with the magnetic pole 301 of the same polarity. Between the magnetic pole 305 and the magnetic pole 301, a low magnetic force portion 310 having a magnetic force lower than that of the magnetic pole 305 is formed.

[0071] [Second developing roller and peeling roller] Next, the relationship between the second developing roller 31 and the peeling roller 32 will be described with reference to FIGS. 6 to 15. In order to form a high-quality image using the developing device 1Y having the above-mentioned configuration, it is required that the developer is not left behind on the second developing roller 31 when the developer is transferred from the second developing roller 31 to the peeling roller 32. If there is developer carried on the second developing roller 31 and not collected by the peeling roller 32, the developer left on the second developing roller 31 will be carried around on the surface of the second developing roller 31 or will fall downward and be supplied to the first developing roller 30 again before being taken into the developer circulation path. As a result, the T / D distribution of the developer carried by the first developing roller 30 and the second developing roller 31 will be affected, and there is a risk of density fluctuation occurring in the toner image after development.

[0072] Therefore, in this embodiment, the peak position P1, which is the position of the maximum value of the normal component of the magnetic flux density of the receiving pole 303 on the peeling sleeve 35, is positioned downstream in the rotation direction of the peeling sleeve 35 with respect to the straight line L1 connecting the rotation center of the second developing sleeve 34 and the rotation center of the peeling sleeve 35. In other words, the peak position P1 of the magnetic flux density of the receiving pole 303 (N9) formed by the peeling magnet 38 that receives the developer peeled off from the second developing sleeve 34 is positioned downstream in the rotation direction of the peeling roller 32 from the opposing portion where the developing roller 31 and the peeling roller 32 face each other. This will be described in detail below.

[0073] As described above, the developer is transferred from the first developing sleeve 33 to the second developing sleeve 34, and from the second developing sleeve 34 to the peeling roller 32 by the magnetic fields formed by the first developing magnet 36, the second developing magnet 37, and the peeling magnet 38. In this embodiment, the magnetic pole configuration and positional relationship of the second developing sleeve 34 and the peeling roller 32 are important.

[0074] FIG. 6 shows the magnetic pole configuration and positional relationship of the second developing roller 31 and the peeling roller 32 in this embodiment. R1 in FIG. 6 is the radius of the second developing roller 31, and is the distance from the rotation center of the second developing sleeve 34 to the surface of the second developing sleeve 34. R2 is the radius of the peeling roller 32, and is the distance from the rotation center of the peeling roller 32 to the surface of the peeling sleeve 35. d1 is the closest distance between the developing roller 31 and the peeling roller 32, and is the distance between the surface of the second developing sleeve 34 and the surface of the peeling roller 32. L1 is a straight line connecting the rotation center of the second developing sleeve 34 and the rotation center of the peeling sleeve 35 in FIG. 6. L2 is a straight line connecting the peak position P1 of the magnetic flux density on the surface of the peeling sleeve 35 formed by the receiving pole 303 (N9) of the peeling magnet 38 and the rotation center of the peeling sleeve 35. Θ1 is the angle made by the straight lines L1 and L2. In this embodiment, R1=12.5 mm, R2=12.5 mm, d1=2.6 mm, and Θ1=10°.

[0075] 6, the manner in which the developer is transferred from the second developing roller 31 to the peeling roller 32 will be described. The developer carried on the second developing sleeve 34 of the second developing roller 31 is transported as the second developing sleeve 34 rotates in the direction of the arrow a in the figure. In the second developing region where the second developing roller 31 faces the photosensitive drum 28Y, toner is scattered and collected from the magnetic brush formed by the magnetic pole 203 (S5) of the second developing magnet 37 by the applied developing bias, and the toner image on the photosensitive drum 28Y is uniformly arranged.

[0076] Thereafter, the developer carried on the second developing sleeve 34 is transported with the rotation of the second developing sleeve 34 and reaches the vicinity of the magnetic pole 207 (S7) of the second developing magnet 37. As described above, the magnetic pole 207 (S7) of the second developing magnet 37 in the second developing sleeve 34 and the magnetic pole 201 (S4) downstream of the magnetic pole 207 in the rotation direction of the second developing sleeve 34 have the same polarity, and the magnetic force attracting the developer to the second developing sleeve 34 is weakened between the magnetic pole 207 and the magnetic pole 201 (low magnetic force portion 210).

[0077] On the other hand, in the peeling magnet 38 in the peeling roller 32 facing the second developing sleeve 34, a magnetic pole 303 (N9) having a polarity different from that of the magnetic pole 207 (S7) is arranged downstream in the rotation direction of the second developing sleeve 34 from the opposing portion between the second developing roller 31 and the peeling roller 32. Therefore, the developer, which is being transported with the rotation of the second developing sleeve 34 but whose magnetic force attracting it to the second developing sleeve 34 is weakened, is transferred from the second developing roller 31 to the peeling roller 32 by the magnetic field formed by the magnetic pole 303 of the peeling magnet 38.

[0078] The developer that has moved to the peeling roller 32 is transported as the peeling sleeve 35 rotates in the direction of the arrow b in the figure, and reaches the vicinity of the magnetic pole 305 (N10) of the peeling magnet 38. The magnetic pole 305 of the peeling magnet 38 and the magnetic pole 301 (N8) arranged downstream of the magnetic pole 305 in the rotation direction of the peeling sleeve 35 have the same polarity, and the magnetic force that attracts the developer to the peeling roller 32 is weak between the magnetic pole 305 and the magnetic pole 301 (low magnetic force portion 310). When the developer tries to be transported from the magnetic pole 305 as the peeling sleeve 35 rotates, gravity acts on the developer in a direction that pulls the developer off the peeling roller 32, and the developer is collected in the developer collecting section 47.

[0079] The manner in which the developer is transferred from the second developing sleeve 34 to the peeling sleeve 35 will be described in more detail with reference to Fig. 7. The developer t in the figure forms a magnetic brush m along the magnetic flux lines formed by the magnetic poles of the second developing magnet 37 and the peeling magnet 38. Fig. 8 shows a schematic diagram of the magnetic flux lines formed by the magnetic poles of the second developing magnet 37 and the peeling magnet 38.

[0080] 7, the magnetic brush m formed on the second developing sleeve 34 by the magnetic pole 207 (S7) of the second developing magnet 37 is conveyed to the opposing portion (position where the straight line L1 passes) of the second developing sleeve 34 and the peeling roller 32 while collapsing along the magnetic flux line. Since the magnetic force attracting the second developing sleeve 34 is weak at the opposing portion, the magnetic brush m moves from the second developing sleeve 34 onto the peeling sleeve 35 by the magnetic field formed by the magnetic pole 303 (N9) of the peeling magnet 38 in the peeling roller 32.

[0081] Here, in Comparative Example 1 shown in FIG. 9, the magnetic pole configuration of the peeling magnet 38A inside the peeling roller 32A is configured as follows. That is, as shown in FIG. 9 and FIG. 10, the peak position P1 of the magnetic flux density on the surface of the peeling sleeve 35 formed by the magnetic pole 303 (N9) of the peeling magnet 38A is located upstream in the rotation direction of the second developing sleeve 34 from the opposing portion (position where the straight line L1 passes) between the second developing sleeve 34 and the peeling roller 32A. In the case of such a configuration, as shown in FIG. 10, when the developer is transferred from the second developing sleeve 34 onto the peeling sleeve 35, the amount of developer remaining on the second developing sleeve 34 is larger than that of the configuration of this embodiment. The reason for this will be explained below.

[0082] In Comparative Example 1, the developer transferred from the surface of the second developing sleeve 34 onto the peeling sleeve 35 by the magnetic field formed by the magnetic pole 303 of the peeling magnet 38A in the peeling roller 32A forms a magnetic brush m by the magnetic field formed by the magnetic pole 303 as shown in FIG. 11, and moves toward the opposing portion of the second developing sleeve 34 and the peeling roller 32A (the position where the straight line L1 passes). In the case of Comparative Example 1, compared to the position where the developer transferred onto the peeling sleeve 35, the downstream in the rotation direction of the peeling sleeve 35 is closer to the opposing portion, which is the closest position between the second developing sleeve 34 and the peeling sleeve 35. Therefore, the distance between the surface of the second developing sleeve 34 and the surface of the peeling sleeve 35 becomes closer. Then, the magnetic brush m enters a narrower area, and the tip of the magnetic brush m carried by the peeling roller 32A and the surface of the second developing sleeve 34 are easily compressed.

[0083] When the tip of the magnetic brush m carried by the peeling roller 32A and the surface of the second developing sleeve 34 are compressed, a frictional force Ffr acts between the tip of the magnetic brush m and the surface of the second developing sleeve 34 in the opposite direction to a force Fv that causes the magnetic brush m to fall along the magnetic flux lines, as shown in Fig. 12. When the frictional forces Ffr and Fv become larger than the magnetic binding force Fmg acting on the developer at the tip of the magnetic brush m, the magnetic brush m separates midway, and the developer at the tip of the magnetic brush m tends to remain on the surface of the second developing sleeve 34.

[0084] In addition, the magnetic field formed by the magnetic pole 303 of the peeling magnet 38 in the peeling roller 32 has a strong force attracting the developer, so downstream of the magnetic pole 303, a force acts against the rotation of the peeling roller 32 to try to remain on the magnetic pole 303, which makes it easy for the developer to stagnate. When the developer stagnates and the developer density on the surface of the peeling roller 32 increases, the magnetic brush m formed by the magnetic pole 303 becomes longer. Then, the tip of the magnetic brush m carried by the peeling roller 32 and the surface of the second developing sleeve 34 become more easily compressed, and the amount of developer remaining on the surface of the second developing sleeve 34 increases.

[0085] The developer left on the second developing sleeve 34 is carried around on the surface of the second developing sleeve 34 or falls downward and is supplied again to the first developing roller 30 before being taken into the developer circulation path. This causes uneven distribution of the developer T / D carried by the first developing roller 30 and the second developing roller 31, resulting in density fluctuation.

[0086] For this reason, in this embodiment, the magnetic pole (receiving pole) 303 (N9) of the peeling magnet 38 is disposed downstream in the rotation direction of the second developing sleeve 34 from the opposing portion at the closest position between the second developing sleeve 34 and the peeling roller 32. Here, in this embodiment, the downstream in the rotation direction of the peeling sleeve 35 is farther from the opposing portion at the closest position between the second developing sleeve 34 and the peeling sleeve 35 than the position where the developer has moved onto the peeling sleeve 35. For this reason, the distance between the surface of the second developing sleeve 34 and the surface of the peeling roller 32 at the position where the magnetic brush m formed by the magnetic pole 303 contacts the second developing sleeve 34 is greater than the distance at the opposing portion between the second developing sleeve 34 and the peeling roller 32.

[0087] Then, the magnetic brush m formed by the magnetic pole 303 moves toward a wider area as the peeling sleeve 35 rotates, so that the contact pressure between the tip of the magnetic brush m carried by the peeling sleeve 35 and the surface of the second developing sleeve 34 is reduced compared to Comparative Example 1. Therefore, the amount of developer remaining on the surface of the second developing sleeve 34 can be reduced compared to Comparative Example 1.

[0088] In addition, the configuration of this embodiment can suppress the amount of developer remaining on the surface of the second developing sleeve 34 from the following point of view. When the magnetic brush m moves from the second developing sleeve 34 onto the peeling sleeve 35 by the magnetic field formed by the magnetic pole 303 of the peeling magnet 38 in the peeling roller 32, as shown in FIG. 13, an electrostatic and non-electrostatic adhesive force Fad is generated between the developer at the base of the magnetic brush m that was in contact with the second developing sleeve 34 and the second developing sleeve 34. Normally, the adhesive force Fad is smaller than the magnetic binding force Fmg generated between the developer constituting the magnetic brush m, but when a distance is generated between the developer due to the effect of the magnetic brush m colliding with each other, the binding force Fmg is suddenly reduced. As a result, the adhesive force Fad may exceed the binding force Fmg, and the developer may remain on the surface of the second developing sleeve 34.

[0089] In such a case, when the tip of the magnetic brush m carried on the peeling sleeve 35 passes near the developer remaining on the surface of the second developing sleeve 34, a magnetic force is generated between the remaining developer and the tip of the magnetic brush m carried on the peeling sleeve 35, and the developer remaining on the surface of the second developing sleeve 34 can be collected at the tip of the magnetic brush m.

[0090] Therefore, in this embodiment, by positioning the magnetic pole 303 of the peeling magnet 38 in the peeling roller 32 downstream in the rotation direction of the second developing sleeve 34 from the opposing portion between the second developing sleeve 34 and the peeling sleeve 35, the amount of developer remaining on the surface of the second developing sleeve 34 can be reduced.

[0091] In addition, it is preferable that the position of the magnetic pole (receiving pole) 303 (N9) of the peeling magnet 38 in the peeling roller 32 of this embodiment satisfies the following formula. (R1+R2+d1)×sin(Θ1) <R1

[0092] The reason will be explained below with reference to FIG. 14 and FIG. 15. FIG. 14 shows the magnetic pole configuration and positional relationship of the second developing roller 31 and the peeling roller 32 when the above formula is satisfied. The length of L1 in the figure can be expressed as L1=R1+R2+d1. The length of the line indicated by L3 in the figure can be expressed as L3=(R1+R2+d1)×sin(Θ1) using sin(Θ1). If this L3 is smaller than the radius R1 of the second developing sleeve 34, the straight line L2 has a point where it intersects with the surface of the second developing sleeve 34. The straight line L2 is a straight line that connects the peak position P1 of the magnetic flux density in the rotation direction of the peeling sleeve 35 on the surface of the peeling sleeve 35 in the magnetic field formed by the magnetic pole 303 of the peeling magnet 38 and the rotation center of the peeling sleeve 35.

[0093] The magnetic force acting on the magnetic brush is strongest at the peak position P1 of the magnetic flux density, and therefore this is also the position where the tip of the magnetic brush m formed by the magnetic pole 303 has the strongest ability to collect the developer remaining on the surface of the second developing sleeve 34.

[0094] On the other hand, FIG. 15 shows the configuration of Comparative Example 2 having a peeling magnet 38B that does not satisfy the above formula. FIG. 15 shows Comparative Example 2 having the magnetic pole configuration and positional relationship of the second developing sleeve 34 and the peeling roller 32B in Comparative Example 2. In the case of Comparative Example 2, L3=(R1+R2+d1)×sin(Θ1) is larger than the radius R1. Therefore, at the position where the tip of the magnetic brush m formed by the magnetic pole 303 should have the strongest ability to collect the developer remaining on the surface of the second developing sleeve 34, the magnetic brush m does not face the surface of the second developing sleeve 34, and the ability to collect the developer remaining on the surface of the second developing sleeve 34 decreases. Therefore, by satisfying the above formula as in this embodiment, it becomes possible to better collect the developer remaining on the surface of the second developing sleeve 34 by the tip of the magnetic brush m formed by the magnetic pole 303.

[0095] [Distance between the second developing sleeve and the peeling sleeve] Here, the closest distance d1 between the surface of the second developing sleeve 34 and the surface of the peeling sleeve 35 is preferably 0.2 mm or more and not more than 3 mm. If d1 is too large, the distance between the tip of the magnetic brush carried by the peeling sleeve 35 and the developer remaining on the surface of the second developing sleeve 34 becomes large, and the magnetic force acting from the tip of the magnetic brush to the residual developer becomes weak. As a result, the ability of the tip of the magnetic brush to collect the developer remaining on the surface of the second developing sleeve 34 decreases.

[0096] On the other hand, if d1 is too small, the space between the surface of the second developing sleeve 34 and the surface of the peeling sleeve 35 becomes narrower than the volume of the developer, and part of the developer cannot pass the closest point between the surface of the second developing sleeve 34 and the surface of the peeling sleeve 35, and remains upstream in the rotation direction from the closest point. The developer that remains upstream in the rotation direction from the closest point is rubbed against the surface of the second developing sleeve 34 and the surface of the peeling sleeve 35, and toner spent, in which toner is fused to the carrier, is likely to occur.

[0097] [Speed ​​of the second developing sleeve and peeling sleeve] Here, the relationship between the speeds of the second developing sleeve 34 and the stripping sleeve 35 will be described. As described above, the stripping sleeve 35 and the second developing sleeve 34 rotate in the same direction (forward direction) at a position where they face each other (facing portion). When the surface movement speed (linear speed) of the second developing sleeve 34 is v1 and the surface movement speed of the stripping sleeve 35 is v2, it is preferable that v1≦v2 is satisfied. In other words, the linear speed of the surface of the second developing sleeve 34 may be equal to or slower than the linear speed of the stripping sleeve 35.

[0098] Even if the linear speed of the surface of the second developing sleeve 34 is slower than that of the peeling sleeve 35, the tip of the magnetic brush m carried by the peeling sleeve 35 can pass near the developer remaining on the surface of the second developing sleeve 34 downstream of the opposing portion between the second developing sleeve 34 and the peeling sleeve 35. Therefore, it is possible to collect the developer remaining on the surface of the second developing sleeve 34 by the magnetic force from the tip of the magnetic brush m. However, the number of tips of the magnetic brush m passing near the developer remaining on the surface of the second developing sleeve 34 decreases as the linear speed of the second developing sleeve 34 becomes slower relative to the linear speed of the peeling sleeve 35, and therefore the amount of developer remaining on the surface of the second developing sleeve 34 that the tips of the magnetic brush m collect also decreases.

[0099] In this embodiment, the first developing sleeve 33 has a surface movement speed (linear speed) of 513 mm / sec, the same as the photosensitive drum 28Y, the surface movement speed v1 of the second developing sleeve 34 is 616 mm / sec, and the surface movement speed v2 of the peeling roller 32 is 740 mm / sec.

[0100] [Surface shape of peeling sleeve] The surface of the peeling roller 32 of this embodiment preferably has an uneven shape. The uneven shape may be, for example, a shape formed so that a plurality of grooves are arranged in the circumferential direction, or may be a shape formed by blasting. By having an uneven shape on the surface of the peeling sleeve 35, the developer on the peeling sleeve 35 can be transported more reliably downstream as the peeling sleeve 35 rotates. In addition, the magnetic brush carried on the peeling sleeve 35 can pass more in the vicinity of the developer remaining on the surface of the second developing sleeve 34. As a result, the amount of developer remaining on the surface of the second developing sleeve 34 that the tip of the magnetic brush collects can be increased, and the amount of developer remaining on the surface of the second developing sleeve 34 can be further suppressed.

[0101] As described above, in this embodiment, the receiving pole 303 formed by the peeling magnet 38 that receives the developer peeled off from the second developing roller 31 is disposed downstream in the rotation direction of the peeling sleeve 35 from the opposing portion between the second developing sleeve 34 and the peeling sleeve 35. This allows the peeling sleeve 35 to sufficiently peel off the developer from the second developing sleeve 34, and reduces density unevenness caused by the developer being carried around to the second developing sleeve 34. As a result, the occurrence of image defects can be suppressed.

[0102] <Second embodiment> The second embodiment will be described with reference to Fig. 16. In this embodiment, the peak position P2 of the magnetic flux density of the delivery pole 207 of the second developing magnet 37A is changed from that of the first embodiment. Since other configurations and functions are similar to those of the first embodiment described above, the same reference numerals are used to designate 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.

[0103] 16 shows the magnetic pole arrangement of the second developing magnet 37A in the second developing roller 31A of this embodiment. In this embodiment, the peak position P2, which is the maximum value of the normal component of the magnetic flux density of the delivery pole 207 (S7) on the second developing sleeve 34, is located downstream in the rotation direction of the second developing sleeve 34 from the closest position P3 of the second developing sleeve 34 to the peeling sleeve 35. Note that in the first embodiment, the peak position, which is the maximum value of the normal component of the magnetic flux density of the delivery pole 207 (S7) on the second developing sleeve 34, is located upstream in the rotation direction of the second developing sleeve 34 from the closest position of the second developing sleeve 34 to the peeling sleeve 35.

[0104] In this embodiment, similarly to the first embodiment, the receiving pole 303 (N9) of the peeling magnet 38 is disposed downstream in the rotation direction of the peeling sleeve 35 from the opposing portion between the second developing sleeve 34 and the peeling sleeve 35. In addition, the handover pole 207 (S7) of the second developing magnet 37A in the second developing sleeve 34 is disposed downstream in the rotation direction of the second developing sleeve 34 from the opposing portion between the second developing sleeve 34 and the peeling sleeve 35 (closest position P3).

[0105] Even in this embodiment, the downstream side in the rotation direction of the peeling sleeve 35 is farther from the opposing portion of the second developing sleeve 34 and the peeling sleeve 35 than the position where the developer has moved onto the peeling sleeve 35, so the distance between the surface of the second developing sleeve 34 and the surface of the peeling sleeve 35 becomes greater. Then, the magnetic brush heads toward a wider area, so the contact pressure between the tip of the magnetic brush carried by the peeling sleeve 35 and the surface of the second developing sleeve 34 is reduced.

[0106] Therefore, in this embodiment as well, it is possible to suppress the amount of developer remaining on the surface of the second developing sleeve 34. Meanwhile, in this embodiment, compared to the first embodiment, the distance that the tip of the magnetic brush carried by the peeling roller 32 stays near the surface of the second developing sleeve 34 is shorter. Therefore, the ability of the tip of the magnetic brush to collect the developer remaining on the surface of the second developing sleeve 34 is reduced compared to the first embodiment.

[0107] <Third embodiment> The third embodiment will be described with reference to Fig. 17. In this embodiment, the peak position P2 of the magnetic flux density of the delivery pole 207 of the second developing magnet 37B is changed from that of the first embodiment. Since other configurations and functions are similar to those of the first embodiment described above, the same reference numerals are used to designate 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.

[0108] 17 shows the magnetic pole arrangement of the second developing magnet 37B in the second developing roller 31B of this embodiment. In this embodiment, the peak position P2, which is the position of the maximum value of the normal component of the magnetic flux density of the delivery pole 207 (S7) on the second developing sleeve 34, is located upstream of the rotation direction of the second developing sleeve 34 from the vertical top position P4 of the second developing sleeve 34. Note that in the first embodiment, the peak position, which is the position of the maximum value of the normal component of the magnetic flux density of the delivery pole 207 (S7) on the second developing sleeve 34, is located downstream of the vertical top position of the second developing sleeve 34 in the rotation direction of the second developing sleeve 34.

[0109] In this embodiment, similarly to the first embodiment, the receiving pole 303 (N9) of the peeling sleeve 38 is disposed downstream in the rotation direction of the peeling sleeve 35 from the opposing portion between the second developing sleeve 34 and the peeling sleeve 35. In addition to this, the peak position P2 of the magnetic flux density on the surface of the second developing sleeve 34 formed by the delivery pole 207 of the second developing magnet 37B in the second developing sleeve 34 is located upstream in the rotation direction of the opposing portion between the second developing sleeve 34 and the peeling sleeve 35 from the vertical top position P4 on the surface of the second developing sleeve 34.

[0110] In the case of this embodiment, as in the first embodiment, the contact pressure between the tip of the magnetic brush supported on the peeling sleeve 35 and the surface of the second developing sleeve 34 is reduced, so that the amount of developer remaining on the surface of the second developing sleeve 34 can be suppressed. On the other hand, the developer that is transported on the second developing sleeve 34 and reaches the peak position P2 is subjected to gravity in a direction that pushes it back to the peak position P2 when it reaches position P4. The force with which the second developing sleeve 34 transports the developer is about 5 to 10 times the gravity acting on the developer, so gravity cannot be ignored. Therefore, the developer is more likely to remain at the peak position P2 compared to the configuration of the first embodiment, and the contact between the second developing sleeve 34 and the developer increases between the peak position P2 and position P4, which makes it easier for toner spent, in which the toner is fused to the carrier, to occur.

[0111] <Fourth embodiment> The fourth embodiment will be described with reference to Figures 18 to 20. In this embodiment, the arrangement of the second developing roller 31C and the peeling roller 32C is changed compared to the first embodiment. 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.

[0112] 18 and 19 are conceptual diagrams illustrating the magnetic pole configuration of the second developing magnet 37C in the second developing sleeve 34 and the peeling magnet 38C in the peeling sleeve 35 in this embodiment. FIG. 20 shows the magnetic pole configuration and positional relationship of the second developing roller 31C and the peeling roller 32C in this embodiment. In this embodiment, the peak position P1, which is the position of the maximum value of the normal component of the magnetic flux density of the receiving pole 303 (N9) on the peeling sleeve 35, is positioned vertically above the peak position P2, which is the position of the maximum value of the normal component of the magnetic flux density of the delivery pole 207 on the second developing sleeve 34. In the first embodiment, the peak position P1, which is the position of the maximum value of the normal component of the magnetic flux density of the receiving pole 303 (N9) on the peeling sleeve 35, is positioned vertically below the peak position, which is the position of the maximum value of the normal component of the magnetic flux density of the delivery pole 207 on the second developing sleeve 34.

[0113] In this embodiment, similarly to the first embodiment, the receiving pole 303 (N9) of the peeling magnet 38C is disposed downstream in the rotation direction of the peeling sleeve 35 from the opposing portion between the second developing sleeve 34 and the peeling sleeve 35. In addition, the peak position P2 of the magnetic flux density on the surface of the second developing sleeve 34 formed by the delivery pole 207 (S7) of the second developing magnet 37C is located lower in the direction of gravity than the peak position P1 of the magnetic flux density on the surface of the peeling sleeve 35 formed by the receiving pole 303 (N9) of the peeling magnet 38C. For this reason, in this embodiment, the peeling roller 32C is located vertically higher than the second developing roller 31C.

[0114] In this embodiment, the magnetic force acting on the developer from the receiving pole 303 of the peeling magnet 38C is about 10 times larger than the gravity acting on the developer, so the developer is collected from the second developing sleeve 34 to the peeling sleeve 35. At this time, as in the first embodiment, the contact pressure between the tip of the magnetic brush supported on the peeling sleeve 35 and the surface of the second developing sleeve 34 is reduced, so that the amount of developer remaining on the surface of the second developing sleeve 34 can be suppressed.

[0115] However, since the direction of the magnetic force acting on the developer from the receiving pole 303 of the peeling magnet 38C is different from the direction of gravity acting on the developer, the force recovering the developer from the second developing sleeve 34 to the peeling sleeve 35 is weaker, and more developer remains on the surface of the second developing sleeve 34 compared to the configuration of the first embodiment.

[0116] <Other embodiments> In the above-described embodiments, the developing device has two developing rollers, but the present invention can be applied to a configuration with one developing roller. That is, the present invention can be applied to a configuration with one developing roller for developing an electrostatic latent image on an image carrier such as a photosensitive drum, and a peeling roller for peeling the developed image from the developing roller.

[0117] 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. [Explanation of symbols]

[0118] 1Y, 1M, 1C, 1K... Developing device 28Y, 28M, 28C, 28K...Photosensitive drum (image carrier) 30...First developing roller 31, 31A, 31B, 31C: Second developing roller 32, 32C: Peeling roller 33 First developing sleeve 34 Second developing sleeve 35 Peeling sleeve 36...First developing magnet 37, 37A, 37B, 37C...Second developing magnet 38, 38C... Peel-off magnet 46 Developer circulation section (supply section) 47 Developer recovery section (recovery section) 100 Image forming apparatus 207 Magnetic pole (delivery pole) 303 Magnetic pole (receiving pole)

Claims

1. a developing roller including a rotating developing sleeve, a developing magnet disposed non-rotatingly inside the developing sleeve and for attracting a developer to a surface of the developing sleeve by magnetic force, and for developing an electrostatic latent image formed on a rotating image carrier with the developer; a peeling sleeve that rotates in the same direction as the surface of the developing sleeve at an opposing portion facing the developing sleeve, and a peeling magnet that is non-rotatingly disposed inside the peeling sleeve and that attracts the developer to the surface of the peeling sleeve by magnetic force, and a peeling roller that peels off the developer from the developing roller after the electrostatic latent image on the image carrier is developed by the developing roller, the developing magnet has a transfer pole which is a magnetic pole for transferring the developer from the developing roller to the peeling roller, the peeling magnet is a magnetic pole for the peeling roller to receive the developer from the developing roller, and has a receiving pole that is a different polarity from the delivery pole; A developing device characterized in that a peak position P1, which is the position of the maximum value of the normal component of the magnetic flux density of the receiving pole on the peeling sleeve, is located downstream in the rotation direction of the peeling sleeve with respect to a straight line L1 connecting the rotation center of the developing sleeve and the rotation center of the peeling sleeve.

2. When the radius of the developing roller is R1, the radius of the peeling roller is R2, the closest distance between the developing roller and the peeling roller is d1, the line connecting the peak position and the rotation center of the peeling sleeve is L2, and the angle between the line L1 and the line L2 is Θ1, (R1+R2+d1)×sin(Θ1)<R1 2. The developing device according to claim 1, wherein the above formula is satisfied.

3. 2. The developing device according to claim 1, wherein a peak position P2, which is a position of a maximum value of a normal component of the magnetic flux density of the transfer pole on the developing sleeve, is located downstream in the rotation direction of the developing sleeve from a closest position P3 of the developing sleeve to the peeling sleeve.

4. 2. The developing device according to claim 1, wherein a peak position P2, which is a position of a maximum value of a normal component of the magnetic flux density of the transfer pole on the developing sleeve, is located upstream of a vertical top position P4 of the developing sleeve in a rotation direction of the developing sleeve.

5. 2. The developing device according to claim 1, wherein the peak position P1 is located vertically above a peak position P2 which is a position of a maximum value of a normal component of the magnetic flux density of the transfer pole on the developing sleeve.

6. When the surface moving speed of the developing sleeve is v1 and the surface moving speed of the peeling sleeve is v2, v1≦v2 2. The developing device according to claim 1, wherein the above formula is satisfied.

7. 2. The developing device according to claim 1, wherein the surface of the stripping sleeve has an uneven shape.

8. 2. The developing device according to claim 1, wherein a closest distance d1 between said developing roller and said peeling roller is in the range of 0.2 mm to 3 mm.

9. a first developing roller including a rotating first developing sleeve, a first developing magnet disposed inside the first developing sleeve in a non-rotating manner and adapted to attract a developer onto a surface of the first developing sleeve by magnetic force, and which develops an electrostatic latent image formed on the rotating image carrier with the developer; a supply section for supplying a developer to the first developing roller, the developing sleeve is a second developing sleeve, the developing magnet is a second developing magnet, and the developing roller is a second developing roller; The developing device according to claim 1, characterized in that the second developing roller is positioned downstream of the first developing roller in the rotation direction of the image carrier and above the center of rotation of the first developing roller in the vertical direction, and developer is transferred from the first developing roller by magnetic force.

Images