Developing device

Abstract

To provide a configuration that can prevent the occurrence of an image defect, while preventing a deterioration of developer.SOLUTION: The center of rotation of a second developing roller 31 is located above the center of rotation of a first developing roller 30 with respect to the vertical direction. A first pole position B1 of a delivery pole 107 is located on the upstream side of a first most proximity position A1 of a first sleeve 33 in the direction of rotation of the first sleeve 33. A second pole position B2 of a reception pole 201 is located on the downstream side of a second most proximity position A2 of a second sleeve 34 in the direction of rotation of the second sleeve 34. When the radius of the first sleeve 33 is defined as r1, the radius of the second sleeve 34 as r2, an angle formed by a line L1 connecting the first pole position B1 and the center of rotation O1 of the first sleeve 33 and a line L2 connecting the first most proximity position A1 and the center of rotation of the first sleeve as θ1, and an angle formed by a line L3 connecting the second pole position B2 and the center of rotation O2 of the second sleeve and a line L4 connecting the second most proximity position A2 and the center of rotation of the second sleeve as θ2, r1×θ1>r2×θ2 is satisfied.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 transfer of developer from the first developing roller to the second developing roller is performed against gravity. Here, the magnetic carrier contained in the developer on the first developing roller is subjected to a composite magnetic force of magnets respectively built into the first developing roller and the second developing roller, and gravity. Therefore, in order to transfer developer from the first developing roller to the second developing roller, it is required that the force obtained by adding gravity to the composite magnetic force is oriented in a direction away from the first developing roller (toward the second developing roller).

[0005] Regarding this point, if the magnetic flux density of the receiving pole of the magnet in the second developing roller, which is the magnetic pole that receives the developer from the first developing roller, is increased to a certain extent, it is possible to direct the magnetic force in the direction toward the second developing roller even when the effect of gravity is taken into account. However, if the magnetic flux density of the receiving pole of the magnet in the second developing roller is increased too much, the developer delivered to the second developing roller tends to accumulate near the receiving pole, which may cause developer deterioration or the generation of clumps due to shear forces acting on the developer. As a result, there is a risk of image defects occurring.

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

[0007] One aspect of the present invention is 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 magnetic carrier to a surface of the first sleeve, and develops 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 having a rotating second sleeve and a first magnet that is non-rotatingly disposed inside the first sleeve and that magnetically attracts 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 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 having a rotating second sleeve and a second magnet that is non-rotatably disposed inside a second sleeve and that attracts developer to a surface of the second sleeve by magnetic force, and a second developing roller that develops an electrostatic latent image formed on the image carrier with the developer, wherein the first magnet has a delivery pole that is a magnetic pole for delivering developer from the first developing roller to the second developing roller, and a first magnetic pole of the same polarity as the delivery pole that is located adjacent to the downstream side of the delivery pole in the rotation direction of the first sleeve, and the second magnet is a magnetic pole that is disposed inside the second sleeve and attracts developer from the first developing roller to the surface of the second sleeve by magnetic force, a receiving pole which is a magnetic pole for receiving a magnetic flux from a magnetic pole of the second sleeve, and a second magnetic pole of the same polarity as the receiving pole which is located adjacent to the upstream side of the receiving pole in the rotation direction of the second sleeve, a first pole position which is a position of a maximum value of a normal component of a magnetic flux density of the receiving pole is located upstream of a first closest position which is a closest position of the first sleeve to the second sleeve in the rotation direction of the first sleeve, and a second pole position which is a position of a maximum value of a normal component of a magnetic flux density of the receiving pole is located upstream of a first closest position which is a closest position of the second sleeve to the first sleeve in the rotation direction of the first sleeve, This developing device is located downstream of the closest position in terms of the rotation direction of the second sleeve, and is characterized in that, when the radius of the first sleeve is r1, the radius of the second sleeve is r2, the angle between a line connecting the first pole position and the rotation center of the first sleeve and a line connecting the first closest position and the rotation center of the first sleeve is θ1, and the angle between a line connecting the second pole position and the rotation center of the second sleeve and a line connecting the second closest position and the rotation center of the second sleeve is θ2, r1×θ1>r2×θ2 is satisfied. Effect of the Invention

[0008] According to the present invention, it is possible to suppress the occurrence of image defects while suppressing deterioration of the developer. [Brief description of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment. [Diagram 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a developing device according to the embodiment. [Diagram 3] FIG. 4 is a diagram showing the arrangement of magnetic poles of a first developing roller according to the embodiment. [Figure 4] FIG. 4 is a diagram showing the arrangement of magnetic poles of a second developing roller according to the embodiment. [Diagram 5] FIG. 4 is a diagram showing the arrangement of magnetic poles of the peeling roller according to the embodiment; [Figure 6] 4A and 4B are diagrams showing the relationship between the magnetic pole arrangements of a first developing roller and a second developing roller according to the embodiment. [Figure 7] FIG. 11 is a detailed view showing the relationship between the magnetic pole arrangements of the first developing roller and the second developing roller according to the comparative example. [Figure 8] 4A and 4B are detailed views showing the relationship between the arrangement of magnetic poles of a first developing roller and a second developing roller according to the embodiment. [Figure 9] 5 is a graph showing magnetic characteristics of a first developing roller according to the embodiment. [Figure 10] 6 is a graph showing magnetic characteristics of a second developing roller according to the embodiment. [Figure 11] 6 is a graph showing the force acting on the magnetic carrier on the first developing roller according to the embodiment. [Figure 12] 4 is a graph showing the force acting on the magnetic carrier on the first developing roller in accordance with Examples 1 and 2 and Comparative Examples 1 and 2. [Figure 13] 5 is a graph showing the force acting on the magnetic carrier on the first developing roller in accordance with Examples 1, 3, and 4. [Figure 14] 6 is a graph showing the force acting on the magnetic carrier on the first developing roller in accordance with Examples 1 and 5 and Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The embodiment will be described with reference to Figures 1 to 14. First, the schematic configuration of an image forming apparatus according to the present embodiment will be described with reference to Figure 1.

[0011] [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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] [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.

[0020] 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.

[0021] 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.

[0022] The first sleeve 33 is a non-magnetic cylindrical member with an outer diameter of 25 mm (radius r1 = 12.5 mm), 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.

[0023] The first magnet 36 is disposed inside the first sleeve 33, and has a plurality of magnetic poles 101-107 as shown in Fig. 3. The solid lines of the magnetic poles 101-107 shown in Fig. 3 indicate the positions of the maximum values ​​(peak positions, pole positions) of the distribution of the normal component of the magnetic flux density of the first magnet 36. Between the inner circumference of the first sleeve 33 and the outer circumference of the first magnet 36, a space is disposed to allow the first sleeve 33 to rotate.

[0024] The developer attracted onto the first sleeve 33 is transported toward the photosensitive drum 28Y by the rotational movement 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 movement 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 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.

[0025] As described below, the second developing roller 31 of the developing device 1Y of this embodiment is disposed vertically above the first developing roller 30. Therefore, the developer must be transferred from the first sleeve 33 to the second sleeve 34 vertically from below to above against gravity. The first sleeve 33 and the second sleeve 34 are disposed with a gap of 3 mm between them at their closest portions.

[0026] The second developing roller 31 is a developer carrier that is driven to rotate, and is disposed downstream of the first developing roller 30 in the rotation direction of the photosensitive drum 28Y and such that the rotation center O2 of the second developing roller 31 is located above the rotation center O1 of the first developing roller 30 in the vertical direction, and the developer is transferred from the first developing roller 30 by magnetic force (FIG. 2). In this embodiment, the entire second developing roller 31 is located above the rotation center O1 of the first developing roller 30. The second developing roller 31, like the first developing roller 30, is disposed at a position adjacent to the photosensitive drum 28Y such that its rotation axis is substantially parallel to the rotation axis of the photosensitive drum 28Y. Therefore, the rotation axes of the second developing roller 31 and the first developing roller 30 are substantially parallel to each other.

[0027] 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.

[0028] The second sleeve 34 is a non-magnetic cylindrical member with an outer diameter of 25 mm (radius r2 = 12.5 mm) 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 positions facing each other. That is, the photosensitive drum 28 rotates from a vertically lower direction to a vertically upper direction at a position facing the second sleeve 34, which is forward development. Also, the second sleeve 34 and the first sleeve 33 rotate in opposite directions at positions facing each other.

[0029] The second magnet 37 is disposed inside the second sleeve 34, and has a plurality of magnetic poles 201-207 as shown in Fig. 4. The solid lines of the magnetic poles 201-207 shown in Fig. 4 indicate the positions of the maximum values ​​(peak positions, pole positions) of the distribution of the normal component of the magnetic flux density of the second magnet 37. A space that allows rotation of the second sleeve 34 is disposed between the inner circumference of the second sleeve 34 and the outer circumference of the second magnet 37.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] The third sleeve 35 is a non-magnetic cylindrical member with an outer diameter of 18 mm (radius 9 mm), and is driven to rotate about a rotation shaft 41. The rotation direction of the third sleeve 35 is counterclockwise as shown 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.

[0034] The third magnet 38 is disposed inside the third sleeve 35, and has a plurality of magnetic poles 301-305 as shown in Fig. 5. The solid lines of the magnetic poles 301-305 shown in Fig. 5 indicate the positions of the maximum values ​​(peak positions, pole positions) of the distribution of the normal component of the magnetic flux density of the third magnet 38. A space that allows rotation of the third sleeve 35 is disposed between the inner circumference of the third sleeve 35 and the outer circumference of the third magnet 38.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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 again from the second developing roller 31 to the peeling roller 32 on the side of the second developing roller 31 by magnetic force, and then 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 collection section 47, and is again introduced into the developer circulation section 46.

[0050] 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%.

[0051] In addition, the magnetic carrier has a magnetic field of 1000 oersted (79577A / m) and a magnetic field of 40Am 2 / kg or more 80Am 2 It is preferable that the magnetic carrier has a magnetization amount per unit weight of 63 Am / kg or less. Reducing the magnetization amount of the magnetic carrier has the effect of suppressing scavenging by the magnetic brush, but it becomes difficult for the magnetic carrier to adhere to the non-magnetic sleeve due to the magnet inside the developing roller, and image defects such as magnetic carrier adhesion to the photosensitive drum may occur. Scavenging is a phenomenon in which the developed toner is scraped off by the magnetic carrier once development has been completed. Furthermore, if the magnetization amount of the magnetic carrier is greater than the above range, image defects may occur due to scavenging by the magnetic brush as described above. In this embodiment, the magnetization amount per unit weight is 63 Am 2 / kg of magnetic carrier was used.

[0052] The magnetization amount of the magnetic carrier was measured using a vibration magnetic field type magnetic property automatic recorder BHV-30 manufactured by Riken Denshi Co., Ltd. The magnetic property value of the magnetic carrier is measured by creating an external magnetic field of 1000 oersteds and determining the magnetization strength at that time. The magnetic carrier is packed sufficiently densely in a cylindrical plastic container. In this state, the magnetization moment is measured, and the actual weight when the sample is placed inside is measured, and the magnetization strength (Am 2 / kg).

[0053] The true specific gravity of the magnetic carrier is measured using a dry automatic density type Accupyc 1330 manufactured by Shimadzu Corporation. In this embodiment, the true specific gravity (density) is 4.6 (g / cm 3 The magnetic carrier used had a weight average diameter of 35 μm (radius b=17.5 μm).

[0054] 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.

[0055] 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.

[0056] [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.

[0057] As shown in FIG. 3, the first magnet 36 contained in the first developing roller 30 has a plurality of magnetic poles 101, 102, 103, 104, 105, 106, and 107. Among them, the magnetic pole 107 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 sleeve 33. As described above, the solid lines of the magnetic poles 101 to 107 shown in FIG. 3 represent the positions (pole positions) of the peak values ​​(maximum values) of the magnitude of the normal component Br of the magnetic flux density of the first magnet 36 with respect to the surface of the first sleeve 33. This also applies to the magnetic poles 201 to 207 of the second magnet 37 shown in FIG. 4 and the magnetic poles 301 to 305 of the third magnet 38 shown in FIG. 5.

[0058] The magnetic pole 107 as a transfer pole is a magnetic pole for transferring 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 may be hereinafter referred to as the transfer pole 107. The magnetic pole 101 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, 104, 105, and 106 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 101 upward as the first sleeve 33 rotates. The magnetic pole 107 is an N pole, and transfers the developer from the first sleeve 33 to the second sleeve 34 facing the first sleeve 33 by a magnetic field generated in cooperation with the magnetic pole 201 in the second magnet 37 contained in the second developing roller 31 as described above.

[0059] In this embodiment, the magnetic pole 101, which is disposed downstream of the delivery pole 107 in the rotation direction of the first sleeve 33 and has the same polarity as the delivery pole 107, generates a repulsive magnetic field in cooperation with the delivery pole 107 to form a low magnetic force portion 110 having a magnetic force lower than that of the delivery pole 107. This low magnetic force portion 110 promotes the delivery of the developer from the first sleeve 33 to the second 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 magnet 37 shown in FIG. 4 and the low magnetic force portion 310 of the third magnet 38 shown in FIG. 5.

[0060] 4, the second magnet 37 contained in the second developing roller 31 has a plurality of 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.

[0061] 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 107 of the first magnet 36 of the first developing roller 30, and may hereinafter 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.

[0062] The receiving pole 201 is an S pole different from the delivery pole 107, 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 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 sleeve 34 rotates. The magnetic pole 207 is an S pole, and transfers the developer after passing through the development area with the photosensitive drum 28Y corresponding to the magnetic pole 203 from the second sleeve 34 to the third sleeve 35 facing the second sleeve 34 by a magnetic field generated in cooperation with the magnetic pole 303 in the third magnet 38 contained in the peeling roller 32.

[0063] 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 receiving pole 201 and the magnetic pole 207, which 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. This low magnetic force portion 210 promotes the transfer of the developer from the first sleeve 33 to the second sleeve 34. In addition, the low magnetic force portion 210 can prevent the developer from being attracted to the closest portion of the first sleeve 33 and the second sleeve 34, and can suppress the pressure applied to the developer.

[0064] 5, the third magnet 38 contained in the peeling roller 32 has a plurality of magnetic poles 301, 302, 303, 304, and 305. The magnetic poles 301 to 305 are arranged in numerical order in the rotation direction of the third sleeve 35.

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

[0066] [Magnetic pole arrangement] Next, the positional relationship between the magnetic pole of the first magnet 36 arranged inside the first developing roller 30 and the magnetic pole of the second magnet 37 arranged inside the second developing roller 31 will be described with reference to Figures 6 to 8. Figure 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 delivery pole 107 of the first magnet 36 of the first developing roller 30 and the receiving pole 201 of the second magnet 37 of the second developing roller 31. Note that some of the magnetic poles are omitted from the illustration to avoid complication.

[0067] 7 and 8 show a schematic configuration of the opposing region between the first developing roller 30 and the second developing roller 31, i.e., the vicinity region where the delivery pole 107 of the first magnets 36, 36A of the first developing roller 30 faces the receiving pole 201 of the second magnet 37 of the second developing roller 31. Fig. 7 shows the configuration of a comparative example, in which the first developing roller 30 has the first magnet 36A. Fig. 8 shows the configuration of the embodiment, in which the first developing roller 30 has the first magnet 36.

[0068] 7 and 8, the center O2 of the second developing roller 31 is located vertically above the center O1 of the first developing roller 30. As described above, this means that the developer is transferred from the first sleeve 33 to the second sleeve 34 from below to above against the force of gravity.

[0069] Additionally, the intersections A1, A2 of the line (dotted line in the figure) connecting the center O1 of the first developing roller 30 and the center O2 of the second developing roller 31 with the first sleeve 33 and the second sleeve 34 are the closest positions of the sleeves 33, 34. That is, the intersection A1 is the closest position (first closest position) of the first sleeve 33 to the second sleeve 34. Additionally, the intersection A2 is the closest position (second closest position) of the second sleeve 34 to the first sleeve 33.

[0070] Also, the pole position (the position of the maximum value of the normal component Br of the magnetic flux density (peak position, first pole position)) of the delivery pole 107 of the first magnet 36, 36A of the first developing roller 30 on the first sleeve 33 is defined as B1, and the pole position (the position of the maximum value of the normal component Br of the magnetic flux density (peak position, second pole position)) of the receiving pole 201 of the second magnet 37 of the second developing roller 31 on the second sleeve 34 is defined as B2. In this case, the first pole position B1 of the delivery pole 107 on the first sleeve 33 is located upstream of the first closest position A1 of the first sleeve 33 to the second sleeve 34 in the rotation direction of the first sleeve 33. Also, the second pole position B2 of the receiving pole 201 on the second sleeve 34 is located downstream of the second closest position A2 of the second sleeve 34 to the first sleeve 33 in the rotation direction of the second sleeve 34.

[0071] When the first pole position B1 of the delivery pole 107 and the second pole position B2 of the receiving pole 201 are arranged in this manner, the developer transported on the first sleeve 33 of the first developing roller 30 is delivered to the second sleeve 34 of the second developing roller 31 before reaching the closest positions A1, A2 of both sleeves 33, 34. Since the closest positions A1, A2 are spatially narrower than other positions of both sleeves 33, 34, when the developer passes the closest positions A1, A2, a large pressure is applied to the developer, which may cause deterioration of the developer due to shearing force or the like. For this reason, in this embodiment, the first pole position B1 and the second pole position B2 are arranged as described above.

[0072] Here, the angle formed by the pole position B1 of the receiving pole 107 of the first magnet 36 of the first developing roller 30 with respect to the first closest position A1 of the first sleeve 33 with respect to the second sleeve 34 is θ1. That is, the angle formed by the line L1 connecting the first pole position B1 and the rotation center O1 of the first sleeve 33 and the line L2 connecting the first closest position A1 and the rotation center O1 of the first sleeve 33 is θ1. Also, the angle formed by the pole position B2 of the receiving pole 201 of the second magnet 37 of the second developing roller 31 with respect to the second closest position A2 of the second sleeve 34 with respect to the first sleeve 33 is θ2. That is, the angle formed by the line L3 connecting the second pole position B2 and the rotation center O2 of the second sleeve 34 and the line L4 connecting the second closest position A2 and the rotation center O2 of the second sleeve 34 is θ2. In the comparative example shown in FIG. 7, θ1<θ2, whereas in this embodiment shown in FIG. 8, θ1>θ2.

[0073] Furthermore, if the radius of the first sleeve 33 is r1 and the radius of the second sleeve is r2, the circumferential distance between the first closest position A1 on the first sleeve 33 and the first pole position B1 of the handover pole 107 is r1×θ1, and the circumferential distance between the second closest position A2 on the second sleeve 34 and the second pole position B2 of the receiving pole 201 is r2×θ2. As described above, the radii r1 and r2 of the first sleeve 33 and second sleeve 34 of the developing device 1Y of this embodiment are both 12.5 mm and the same.

[0074] Therefore, in the comparative example shown in FIG. 7, θ1<θ2, so (r1×θ1)<(r2×θ2). That is, the distance between the first closest position A1 and the first pole position B1 is shorter than the distance between the second closest position A2 and the second pole position B2. On the other hand, in the present embodiment shown in FIG. 8, θ1>θ2, so (r1×θ1)>(r2×θ2). That is, the distance between the first closest position A1 and the first pole position B1 is longer than the distance between the second closest position A2 and the second pole position B2. Note that, in the present embodiment, the case where the radii r1 and r2 of the first sleeve 33 and the second sleeve 34 are the same is described, but even if the radii are different, it is sufficient to satisfy (r1×θ1)>(r2×θ2).

[0075] As described above, ideal developer transfer is such that the developer on the first sleeve 33 is transported on the first sleeve 33 while receiving a force in a direction toward the center (O1) of the first sleeve 33 up to the first pole position B1 of the delivery pole 107, and after passing the first pole position B1 of the delivery pole 107, the developer receives a force in a direction away from the center (O1) of the first sleeve 33, i.e., in a direction toward the second sleeve 34, by the time it reaches the first closest position A1 with the second sleeve 34, so that the developer is smoothly transferred to the second sleeve 34. When the developer is smoothly transferred as described above, developer is less likely to stagnate between the two sleeves 33, 34, making it possible to suppress image defects caused by developer deterioration due to stagnation.

[0076] In the case of the pole arrangement as shown in the comparative example of Fig. 7, the following problem occurs when trying to achieve the smooth transfer of developer as described above. In the comparative example of Fig. 7, the distance r1 x θ1 from the first closest position A1 of the first sleeve 33 to the first pole position B1 of the delivery pole 107 is smaller than the distance r2 x θ2 from the second closest position A2 of the second sleeve 34 to the second pole position B2 of the receiving pole 201. For this reason, the developer is conveyed on the first sleeve 33 while receiving a force in the direction of the center (O1) of the first sleeve 33, and reaches the pole position B1 of the delivery pole 107 only after passing the opposing position of the second pole position B2 of the receiving pole 201 of the second sleeve 34.

[0077] As a result, in order for the developer on the first sleeve 33 to receive a force in a direction toward the second sleeve 34, overcoming gravity after being transported to the first pole position B1 of the delivery pole 107, it is necessary to increase the magnitude (peak value) of the magnetic flux density (normal component of) Br of the receiving pole 201 of the second magnet 37 of the second developing roller 31. If the magnitude of the magnetic flux density Br of the receiving pole 201 is increased, the developer becomes more likely to be confined to the position of the receiving pole 201, and there is an increased concern that the developer may deteriorate due to shear caused by the rotation of the second sleeve 34.

[0078] 8, the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first pole position B1 of the delivery pole 107 is greater than the distance r2×θ2 from the second closest position A2 of the second sleeve 34 to the second pole position B2 of the receiving pole 201. Therefore, the developer is transported on the first sleeve 33 to the pole position B1 of the delivery pole 107 while receiving a force in the direction of the center (O1) of the first sleeve 33, and then reaches a position facing the second pole position B2 of the receiving pole 201 of the second sleeve 34.

[0079] As a result, after the developer on the first sleeve 33 has been transported to the first pole position B1 of the delivery pole 107, the magnetic flux density originating from the delivery pole 107 of the first magnet 36 gradually decreases as it moves downstream, and the force on the developer toward the center (O1) of the first sleeve 33 gradually weakens. On the other hand, as it moves downstream, it approaches the opposing position of the receiving pole 201, so the magnetic flux density originating from the receiving pole 201 of the second magnet 37 gradually increases, and the force toward the second sleeve 34, that is, the force in the direction away from the center (O1) of the first sleeve 33, gradually increases.

[0080] Then, after the developer on the first sleeve 33 is transported to the first pole position B1 of the delivery pole 107, it receives a force in a direction toward the second sleeve 34, overcoming gravity, and it becomes easier to achieve smooth delivery of the developer. Therefore, in the case of this embodiment shown in Fig. 8, it is not necessary to forcibly increase the magnitude (peak value) of the magnetic flux density (normal component of) Br of the receiving pole 201 of the second magnet 37 of the second developing roller 31 as in the comparative example shown in Fig. 7, and it is also possible to suppress concerns about developer deterioration.

[0081] FIG. 9 is a diagram showing a schematic distribution of the normal component Br of the magnetic flux density on the first sleeve 33 by the first magnet 36 of this embodiment. FIG. 10 is a diagram showing a schematic distribution of the normal component Br of the magnetic flux density on the second sleeve 34 by the second magnet 37 of this embodiment. Note that the magnetic flux density Br is more precisely the component of the magnetic flux density B in the normal direction to the sleeve. Hereinafter, the "normal component Br of the magnetic flux density" may be simply called "magnetic flux density" according to convention. When simply referring to "magnetic flux density", it refers to the "normal component Br of the magnetic flux density". The magnetic flux density (normal component) Br of each magnet was measured using a magnetic field measuring device (FWBELL's "MS-9902") with the distance between the probe, which is a component of the magnetic field measuring device, and the surface of the sleeves 33 and 34 being about 100 μm.

[0082] 9, the positions corresponding to the first closest position A1 of the first sleeve 33 and the first pole position B1 of the delivering pole 107 are shown by dashed lines. Also, Fig. 10 shows the positions corresponding to the second closest position A2 of the second sleeve 33 and the second pole position B2 of the receiving pole 201. The angle θ1 formed by the first closest position A1 of the first sleeve 33 and the first pole position B1 of the delivering pole 107 is larger than the angle θ2 formed by the second closest position A2 of the second sleeve 34 and the second pole position B2 of the receiving pole 201.

[0083] 11 shows an outline of the magnetic attraction force Fr that attracts the magnetic carrier of the developer on the first sleeve 33 toward the center (O1) of the first sleeve 33. Hereinafter, the "magnetic attraction force Fr in the center (O1) of the first sleeve" may be simply referred to as the "magnetic attraction force." When simply referred to as the "magnetic attraction force," it refers to the "magnetic attraction force Fr in the center (O1) of the first sleeve 33." The magnetic attraction force Fr of the first sleeve 33 can be derived from the normal component Br of the magnetic flux density, and is expressed by the following Equation 1.

number

[0084] In formula 1, μ is the magnetic permeability of the magnetic carrier, μ0 is the magnetic permeability of a vacuum, and b is the radius of the magnetic carrier. The tangential component Bθ of the magnetic flux density is calculated from formula 2 below using the value of the normal component Br of the magnetic flux density.

number

[0085] Regarding the magnetic attraction force Fr that the magnetic carrier on the first sleeve 33 receives, it is necessary to consider the influence of the second magnet 37 in addition to the influence of the first magnet 36. For this reason, when calculating the magnetic attraction force Fr in the above formula 1, the normal component Br of the magnetic flux density and the tangential component Bθ of the magnetic flux density must be the combined influences of both the first magnet 36 and the second magnet 37. In addition, the influence of gravity on the magnetic carrier must be taken into consideration. Thus, FIG. 11 shows an outline of the force (=magnetic attraction force Fr+gravity) that attracts the magnetic carrier of the developer on the first sleeve 33 toward the center (O1) of the first sleeve 33, after combining the influences of both the first magnet 36 and the second magnet 37 and adding the influence of gravity. The gravity of the magnetic carrier is expressed as the product Mg of the weight M of the magnetic carrier and the gravitational acceleration g, and the weight M of the magnetic carrier is the volume (4πb 3 / 3) and the true specific gravity (density). Note that the graph shows an enlarged portion related to the transfer of the developer, and also shows the positions corresponding to the first closest position A1 of the first developing roller 30 and the first pole position B1 of the transfer pole 107 with dotted lines.

[0086] 11, it can be seen that the force (magnetic attractive force Fr+gravity) that the magnetic carrier on the first sleeve 33 receives in the direction toward the center (O1) of the first sleeve 33 is an attractive force until it reaches the first pole position B1 of the delivery pole 107, and then changes to a repulsive force against gravity while being transported and reaches the first closest position A1. That is, of the force that acts on the carrier contained in the developer on the first sleeve 33, which is the magnetic attractive force by both the first magnet 36 and the second magnet 37 plus gravity, the component in the direction toward the rotation center O1 of the first sleeve 33 is an attractive force at the first pole position B1, and changes from an attractive force to a repulsive force between the first pole position B1 and the first closest position A1 in the rotation direction of the first sleeve 33. The repulsive force refers to a force in the direction away from the center (O1) of the first sleeve 33. For this reason, it is believed that the magnetic carrier on the first sleeve 33 is transported on the first sleeve 33 until it reaches the first pole position B1 of the transfer pole 107, and then the developer is smoothly transferred from the first sleeve 33 to the second sleeve 34 vertically above on the way to the first closest position A1.

[0087] 12 shows the force (magnetic attraction force Fr + gravity) that the magnetic carrier on the first sleeve 33 receives in the direction of the center (O1) of the first sleeve 33 when the angle θ1 between the first pole position B1 and the first closest position A1 of the delivery pole 107 is varied while the angle θ2 between the second pole position B2 and the second closest position A2 of the receiving pole 201 is fixed under the condition that the magnetic flux density Br of the delivery pole 107 of the first developing roller 30 is 40 mT and the magnetic flux density Br of the receiving pole 201 of the second developing roller 31 is 50 mT. Each condition is shown in Table 1. [Table 1]

[0088] In the first and second embodiments, the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first pole position B1 of the delivery pole 107 is greater than the distance r2×θ2 from the second closest position A2 of the second sleeve 34 to the second pole position B2 of the receiving pole 201. At this time, when the distribution of the magnetic attraction force Fr+gravity in the first and second embodiments in FIG. 12 is seen, a repulsive force is generated up to the upstream of the first closest position A1. Therefore, it is considered that the developer transported to the first pole position B1 of the delivery pole 107 on the first sleeve 33 is smoothly delivered to the second sleeve 34 against gravity on the way to the first closest position A1. In fact, in the study by the inventors, in these configurations, the deterioration of the developer due to idling was suppressed. In addition, idling refers to the operation of rotating the first developing roller 30, the second developing roller 31, the peeling roller 32, the developer supply screw 42, the developer stirring screw 43 and the developer recovery screw 44 of the developing device while developer is contained in the developing container 60, without performing the developing operation of developing the electrostatic latent image on the photosensitive drum with developer.

[0089] On the other hand, in Comparative Example 2, the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first pole position B1 of the delivery pole 107 is smaller than the distance r2×θ2 from the second closest position A2 of the second sleeve 34 to the second pole position B2 of the receiving pole 201. At this time, looking at the distribution of the magnetic attraction force Fr+gravity in Comparative Example 2 in FIG. 12, a repulsive force sufficient to counter gravity is not generated. Therefore, it is considered that the delivery of the developer that has been transported to the first pole position B1 of the delivery pole 107 on the first sleeve 33 to the second sleeve 34 is delayed, and retention is likely to occur. In fact, in the study by the inventors, in the case of the configuration of Comparative Example 2, developer deterioration due to idle rotation occurred.

[0090] In Comparative Example 1, the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first pole position B1 of the delivery pole 107 is the same as the distance r2×θ2 from the second closest position A2 of the second sleeve 34 to the second pole position B2 of the receiving pole 201. At this time, looking at the distribution of the magnetic attraction force Fr+gravity in Comparative Example 1 in FIG. 12, a repulsive force against gravity is generated, but the magnitude of the repulsive force is small. In addition, the timing of the generation of the repulsive force is just before the upstream of the first closest position A1 or the timing of reaching the first closest position A1. Therefore, the transfer of the developer that has been transported to the first pole position B1 of the delivery pole 107 on the first sleeve 33 to the second sleeve 34 is somewhat lacking in smoothness, and it is considered that stagnation begins to occur near the first closest position A1. In fact, according to the inventors' study, in the configuration of Comparative Example 1, developer deterioration due to idle rotation was suppressed more than in Comparative Example 2, but occurred more than in Examples 1 and 2.

[0091] From the above, deterioration of the developer can be suppressed by making the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first pole position B1 of the handover pole 107 larger than the distance r2×θ2 from the second closest position A2 of the second sleeve 34 to the second pole position B2 of the receiving pole 201, in other words, by satisfying r1×θ1>r2×θ2. Furthermore, if deterioration of the developer can be suppressed, the occurrence of image defects can be suppressed.

[0092] The pole position of the magnet varies slightly due to manufacturing. When this is taken into consideration, it is preferable that the relationship between the pole position and the closest position is increased by a distance equivalent to 3°, that is, r1×(θ1-3°)≧r2×θ2 is satisfied. It is more preferable that the pole position is increased by a distance equivalent to 5°, that is, r1×(θ1-5°)≧r2×θ2 is satisfied. It is even more preferable that the pole position is increased by a distance equivalent to 7°, that is, r1×(θ1-7°)≧r2×θ2 is satisfied. By adopting the above-mentioned configuration, it is possible to suppress deterioration of the developer even if the pole position of the magnet varies due to manufacturing.

[0093] In this manner, in this embodiment, the effect of suppressing deterioration of the developer is obtained by making the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first pole position B1 of the delivery pole 107 larger than the distance r2×θ2 from the second closest position A2 of the second sleeve 34 to the second pole position B2 of the receiving pole 201. However, the effect of suppressing deterioration of the developer can be further obtained by adopting the following configuration.

[0094] In the magnetic flux density (normal component) Br distribution on the first sleeve 33 by the first magnet 36 of the first developing roller 30 in FIG. 9, the angle x of the downstream side of the first pole position B1 with respect to the rotation direction of the first sleeve 33 is shown in the half-width of the normal component of the magnetic flux density of the delivery pole 107. For reference, FIG. 9 also shows the opposing position of the second pole position B2 of the receiving pole 201 of the second sleeve 34. In this case, it is preferable that the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first pole position B1 of the delivery pole 107 is larger than the distance r2×θ2 from the second closest position A2 of the second sleeve 34 to the second pole position B2 of the receiving pole 201 by the distance equivalent to the angle x of the half-width of the magnetic flux density Br distribution of the delivery pole 107 downstream in the rotation direction of the first sleeve 33, that is, it is preferable to satisfy r1×(θ1-x)≧r2×θ2.

[0095] In the above configuration, the developer transported on the first sleeve 33 reaches the position facing the second pole position B2 of the receiving pole 201 of the second sleeve 34 after the magnetic flux density Br of the delivery pole 107 has dropped by more than half. Therefore, the developer after passing the first pole position B1 of the delivery pole 107 on the first sleeve 33 can receive the magnetic attraction force from the magnetic flux density Br of the receiving pole 201 at a stage where the magnetic flux density Br of the delivery pole 107 has sufficiently weakened. As a result, the developer transported to the first pole position B1 of the delivery pole 107 on the first sleeve 33 is smoothly delivered to the second sleeve 34 against gravity on the way to the first closest position A1.

[0096] In the above-mentioned Example 1 and Example 2, the angle x of the half-width of the magnetic flux density Br distribution of the delivery pole 107 of the first magnet 36 on the downstream side of the rotation direction of the first sleeve 33 was 7°. In Example 2, the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first pole position B1 of the delivery pole 107 is larger than the distance r2×θ2 from the second closest position A2 of the second sleeve 34 to the second pole position B2 of the receiving pole 201 by the downstream angle of 7° of the half-width of the delivery pole (r1×(θ1-7°)=r2×θ2). In Example 1, it is even larger, but as shown in FIG. 12, the repulsive force does not differ greatly between Example 1 and Example 2. This is thought to be because Example 2 has already increased the downstream angle of the half-width of the delivery pole by the equivalent of 7°, and therefore a sufficient effect has been obtained at that stage.

[0097] From the above, by making the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first pole position B1 of the delivery pole 107 larger than the distance r2×θ2 from the second closest position A2 of the second sleeve 34 to the second pole position B2 of the receiving pole 201 by a distance equivalent to the angle x downstream of the rotation direction of the first sleeve 33 of the half-width of the magnetic flux density Br distribution of the delivery pole 107 (r1×(θ1-x)≧r2×θ2), it is possible to more effectively suppress deterioration of the developer while ensuring smooth transfer of the developer from the first sleeve 33 to the second sleeve 34.

[0098] FIG. 8 shows the third pole position B3 on the second sleeve 34 of the magnetic pole 202 downstream of the receiving pole 201 in the rotation direction of the second sleeve 34. The magnetic pole 202 corresponds to the third magnetic pole of the second magnet 37, which is adjacent to the receiving pole 201 downstream in the rotation direction of the second sleeve 34 and has a different polarity from the receiving pole 201. The position of the maximum value of the normal component of the magnetic flux density of the magnetic pole 202 (peak position) is set as the third pole position B3. The angle between the magnetic pole 202 and the second closest position A2 is set as θ3. That is, the angle between the line L5 connecting the third pole position B3 and the rotation center O2 of the second sleeve 34 and the line L4 connecting the second closest position A2 and the rotation center O2 of the second sleeve 34 is set as θ3. The angle θ3 is also shown in FIG. 8.

[0099] It is not preferable that the first pole position B1 of the delivery pole 107 from the first closest position A1 of the first sleeve 33 faces the magnetic pole 202 downstream in the rotation direction of the second sleeve 34 of the receiving pole 201. This is because, since the delivery pole 107 and the magnetic pole 202 are like poles, a repulsive magnetic field is generated when like poles face each other, and it is likely to hinder the delivery of the developer. For this reason, it is preferable to make the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first pole position B1 of the delivery pole 107 smaller than the distance r2×θ3 from the second closest position A2 of the second sleeve 34 to the third pole position B3 of the magnetic pole 202, that is, to satisfy r1×θ1 < r2×θ3. In this embodiment, θ3 = 47°, which is sufficiently larger than θ1 of this embodiment. Also, in this embodiment, r1 = r2 = 12.5 mm. For this reason, as shown also in FIG. 8, r1×θ1 < r2×θ3 holds.

[0100] As in Examples 1 and 2, when the distance r1×θ1 from the first closest position A1 of the first sleeve 33 to the first pole position B1 of the delivery pole 107 is made larger than the distance r2×θ2 from the second closest position A2 of the second sleeve 34 to the second pole position B2 of the receiving pole 201, as shown in FIG. 12, a sufficient repulsive force is generated up to the upstream of the first closest position A1 in the distribution of the magnetic attraction force Fr + gravity. For this reason, in the case of such a configuration, even if the magnitude of the magnetic flux density (normal component) Br of the receiving pole 201 is reduced, it is possible to obtain a sufficient repulsive force. If the magnitude of the magnetic flux density (normal component) Br of the receiving pole 201 can be reduced, the developer is less likely to be constrained at the position of the receiving pole 201, and further suppression of developer deterioration due to shear accompanying the rotation of the second sleeve 34 can be achieved.

[0101] 13 shows the force (magnetic attraction force Fr+gravity) that the magnetic carrier on the first sleeve 33 receives in the direction of the center (O1) of the first sleeve 33 when the magnetic flux density Br of the receiving pole 201 of the second developing roller 31 is varied while the magnetic flux density Br of the receiving pole 201 of the second developing roller 31 is fixed and the magnetic flux density Br of the receiving pole 201 of the second developing roller 31 is fixed at 40 mT. Table 2 shows the respective conditions. For comparison, FIG. 13 also shows the results of Example 1 in Table 1. [Table 2]

[0102] 13, even if the magnitude of the magnetic flux density Br of the receiving pole 201 is set equal to or smaller than the magnitude of the magnetic flux density Br of the delivery pole 107 as in the third and fourth embodiments, a repulsive force is generated up to the upstream of the first closest position A1. For this reason, it is considered that the developer transported to the first pole position B1 of the delivery pole 107 on the first sleeve 33 is smoothly delivered to the second sleeve 34 against gravity on the way to the first closest position A1. In fact, the inventors' study showed that in these configurations, developer deterioration due to idle rotation is suppressed, and is suppressed more than when the magnitude of the magnetic flux density Br of the receiving pole 201 of the first embodiment is 50 mT.

[0103] This is believed to be because the developer is less likely to be confined to the position of the receiving pole 201 by reducing the magnitude of (the normal component of) the magnetic flux density Br of the receiving pole 201, and deterioration of the developer due to shearing caused by the rotation of the second sleeve 34 is further suppressed. For this reason, as long as a repulsive force is generated up to the upstream of the first closest position A1 in the distribution of the magnetic attractive force Fr+gravity, by reducing the magnitude of (the normal component of) the magnetic flux density Br of the receiving pole 201, the developer is less likely to be confined to the position of the receiving pole 201, and deterioration of the developer due to shearing caused by the rotation of the second sleeve 34 can be further suppressed.

[0104] In addition, the magnitude of the magnetic flux density (normal component) Br of the receiving pole 201 is smaller in Example 4 than in Example 3. However, the developer deterioration due to idle rotation in Example 3 and Example 4 was almost the same. This is because the magnitude of the magnetic flux density (normal component) Br of the receiving pole 201 is smaller in Example 4, but as shown in FIG. 13, the repulsive force generated up to the upstream of the first closest position A1 is also smaller. Therefore, the developer binding force at the receiving pole 201 is small, which is advantageous for suppressing deterioration of the developer due to idle rotation, while the developer moving force to the second sleeve 34 is small, which is disadvantageous for suppressing deterioration of the developer due to idle rotation. For this reason, it is considered that the developer deterioration is almost the same in Examples 3 and 4. From the above, it is not preferable to reduce the magnitude of the magnetic flux density (normal component) Br of the receiving pole 201 to such an extent that no repulsive force is generated up to the upstream of the first closest position A1 in the distribution of the magnetic attraction force Fr + gravity.

[0105] The magnitude of the magnetic flux density (normal component) Br of the receiving pole 201 is preferably 0.5 times or more the magnitude of the magnetic flux density (normal component) Br of the delivering pole 107. Moreover, the magnitude of the magnetic flux density (normal component) Br of the receiving pole 201 is more preferably 0.75 times or more the magnitude of the magnetic flux density (normal component) Br of the delivering pole 107 as in the fourth embodiment, and further preferably 1.0 times or more.

[0106] On the other hand, as described above, if the magnitude of the magnetic flux density (normal component) Br of the receiving pole 201 is increased too much, the developer may be easily restricted to the position of the receiving pole 201, and developer deterioration may occur due to shearing caused by the rotation of the second sleeve 34. For this reason, the magnitude of the magnetic flux density (normal component) Br of the receiving pole 201 is preferably 1.5 times or less, and more preferably 1.25 times or less, of the magnetic flux density (normal component) Br of the delivering pole 107.

[0107] 14 shows the magnetic attraction force Fr (+gravity) that the magnetic carrier on the first sleeve 33 receives in the direction of the center (O1) of the first sleeve 33 under the condition that the magnetic flux density Br of the delivery pole 107 of the first developing roller 30 is 40 mT and the magnetic flux density Br of the receiving pole 201 of the second developing roller 31 is 50 mT, as in Examples 1 and 2 and Comparative Examples 1 and 2, while the angle θ1 between the first pole position B1 and the first closest position A1 of the delivery pole 107 is the same as in Comparative Example 1, and the angle θ2 between the second pole position B2 and the second closest position A2 of the receiving pole 201 is changed. The conditions are shown in Table 3. FIG. 14 also shows the results of Example 1 and Comparative Example 1. [Table 3]

[0108] 14, in Example 5, a repulsive force is generated up to the upstream of the first closest position A1. In fact, in the study by the inventors, in these configurations, developer deterioration due to idle rotation was suppressed.

[0109] In comparison with Comparative Example 1, Example 1 achieves r1×θ1>r2×θ2 by varying the angle θ1 between the first pole position B1 and the first closest position A1 of the delivering pole 107, and Example 5 achieves r1×θ1>r2×θ2 by varying the angle θ2 between the second pole position B2 and the second closest position A2 of the receiving pole 201, respectively, and produces a similar effect. This shows that the relative positional relationship between the first pole position B1 of the delivering pole 107 and the second pole position B2 of the receiving pole 201 is important, and the means for achieving this is not important.

[0110] <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.

[0111] In the above embodiment, the first sleeve 33 and the photosensitive drum 28Y rotate in the same direction at positions facing each other, and the second sleeve 34 and the photosensitive drum 28Y rotate in the same direction at positions facing each other, but the present invention is not limited to this. The rotation center O2 of the second developing roller 31 may be disposed vertically above the rotation center O1 of the first developing roller 30, and the first sleeve 33 and the photosensitive drum 28Y may rotate in opposite directions at positions facing each other, and the second sleeve 34 and the photosensitive drum 28Y may rotate in opposite directions at positions facing each other. That is, the photosensitive drum 28 may rotate from the upper side in the vertical direction to the lower side in the vertical direction at a position facing the first developing roller 30, and the photosensitive drum 28 may rotate from the upper side in the vertical direction to the lower side in the vertical direction at a position facing the second developing roller 31. The present invention may be applied to such a configuration. Furthermore, in the case where three or more developing rollers are provided, the present invention can be applied to any two of the developing rollers. [Explanation of symbols]

[0112] 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 101...Magnetic pole (1st magnetic pole) 107 Delivery pole 201 Receiving pole 202...Magnetic pole (3rd magnetic pole) 207...Magnetic pole (second magnetic pole)

Claims

1. A developing device, A first rotating body to which a developer containing toner and a carrier is supplied, the first rotating body carrying and transporting the developer to a first developing position, A first magnet is fixedly and non-rotatingly disposed inside the first rotating body, and the first magnet has a first magnetic pole and a second magnetic pole which is disposed downstream of the first magnetic pole with respect to the rotational direction of the first rotating body and adjacent to the first magnetic pole and has the same pole as the first magnetic pole. A second rotating body is positioned opposite the first rotating body, and the developer is transferred from the first rotating body by the magnetic field generated by the first magnet, the second rotating body carrying and transporting the developer to a second developing position, A second magnet is fixedly positioned in a non-rotating manner inside the second rotating body, the second magnet having a third magnetic pole that is positioned opposite to the first magnetic pole and is of the opposite pole to the first magnetic pole, A regulating member is positioned opposite the first rotating body and regulates the amount of developer supported on the first rotating body, and the system comprises: With respect to the vertical direction, the axis of rotation of the second body of revolution is above the axis of rotation of the first body of revolution. The direction of rotation of the first rotating body at the first nearest-neighbor position on the outer surface of the first rotating body, where the first rotating body is closest to the second rotating body, is opposite to the direction of rotation of the second rotating body at the second nearest-neighbor position on the outer surface of the second rotating body, The position on the outer surface of the first rotating body where the regulating member faces is downstream of the first nearest-neighbor position and upstream of the first developing position with respect to the rotational direction of the first rotating body. The first maximum position where the magnetic flux density of the first magnetic pole is maximum in the direction normal to the outer surface of the first rotating body is located downstream of the first development position and upstream of the first nearest-neighbor position with respect to the rotational direction of the first rotating body. The second maximum position where the magnetic flux density of the third magnetic pole is maximum in the direction normal to the outer surface of the second rotating body is located downstream of the second nearest-neighbor position and upstream of the second developing position with respect to the rotational direction of the second rotating body. Let the radius of the first solid of revolution be r1. Let the radius of the second solid of revolution be r2. With respect to the rotation direction of the first rotating body, let θ1 be the angle from the first maximum position to the first nearest tangential position. With respect to the rotation direction of the second rotating body, if the angle from the second nearest point to the second maximum point is θ2, Satisfying r1 × θ1 > r2 × θ2 A developing apparatus characterized by the following features.

2. The second magnet is positioned downstream of the third magnetic pole and adjacent to the third magnetic pole with respect to the rotation direction of the second rotating body, and further has a fourth magnetic pole that is opposite to the third magnetic pole. The third maximum position where the magnetic flux density of the fourth magnetic pole is maximum in the direction normal to the outer surface of the second rotating body is located downstream of the second maximum position and upstream of the second developing position with respect to the rotational direction of the second rotating body. With respect to the rotation direction of the second rotating body, if the angle from the second nearest point to the third maximum point is θ3, r1 × θ1 < r2 × θ3 satisfies The developing apparatus according to feature 1.

3. If x is the angle downstream of the first maximum position with respect to the rotational direction of the first rotating body, among the full width at half maximum of the magnetic flux density of the first magnetic pole in the direction normal to the outer surface of the first rotating body, r1×(θ1-x)≧r2×θ2 satisfies The developing apparatus according to claim 1 or 2.

4. r1×(θ1-3°)≧r2×θ2 satisfies The developing apparatus according to claim 1 or 2.

5. r1×(θ1-5°)≧r2×θ2 satisfies The developing apparatus according to claim 1 or 2.

6. r1×(θ1-7°)≧r2×θ2 satisfies The developing apparatus according to claim 1 or 2.

7. The absolute value of the maximum magnetic flux density of the third magnetic pole in the direction normal to the outer surface of the second rotating body is 0.5 times or more the absolute value of the maximum magnetic flux density of the first magnetic pole in the direction normal to the outer surface of the first rotating body. The developing apparatus according to claim 1 or 2.

8. The absolute value of the maximum magnetic flux density of the third magnetic pole in the direction normal to the outer surface of the second rotating body is 0.75 times or more the absolute value of the maximum magnetic flux density of the first magnetic pole in the direction normal to the outer surface of the first rotating body. The developing apparatus according to claim 1 or 2.

9. The absolute value of the maximum magnetic flux density of the third magnetic pole in the direction normal to the outer surface of the second rotating body is 1.0 times or more the absolute value of the maximum magnetic flux density of the first magnetic pole in the direction normal to the outer surface of the first rotating body. The developing apparatus according to claim 1 or 2.

10. The absolute value of the maximum magnetic flux density of the third magnetic pole in the direction normal to the outer surface of the second rotating body is 1.5 times or less the absolute value of the maximum magnetic flux density of the first magnetic pole in the direction normal to the outer surface of the first rotating body. The developing apparatus according to claim 1 or 2.

11. The absolute value of the maximum magnetic flux density of the third magnetic pole in the direction normal to the outer surface of the second rotating body is 1.25 times or less the absolute value of the maximum magnetic flux density of the first magnetic pole in the direction normal to the outer surface of the first rotating body. The developing apparatus according to claim 1 or 2.

12. The radius of the second solid of revolution is the same as the radius of the first solid of revolution. The developing apparatus according to claim 1 or 2.

13. The radius of the second body of revolution is different from the radius of the first body of revolution. The developing apparatus according to claim 1 or 2.

14. The second magnet is positioned upstream of the third magnetic pole and adjacent to the third magnetic pole with respect to the rotational direction of the second rotating body, and further has a fifth magnetic pole which is the same pole as the third magnetic pole. The developing apparatus according to claim 1 or 2.

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

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

17. The developing container further comprises a developing container for containing the developer, The developer contained in the developing container is supplied to the first rotating body. The first development position is the position for developing the electrostatic latent image formed on the image carrier. The second development position is the position in which the electrostatic latent image is developed. The developing apparatus according to claim 1 or 2.

18. A third rotating body is positioned opposite the second rotating body, and the developer is transferred from the second rotating body by the magnetic field generated by the second magnet, The third rotating body comprises a third magnet fixedly and non-rotatingly positioned inside the third rotating body, The developing container includes a supply chamber for supplying the developer to the first rotating body, and a recovery chamber separated from the supply chamber by a partition wall, for recovering the developer after developing the electrostatic latent image. The third rotating body carries and transports the developer in order to recover the developer in the recovery chamber after developing the electrostatic latent image. The developing apparatus according to feature 17.

Images