WO2026009992A1 - Development device - Google Patents

Abstract

The maximum value of the absolute value of the magnetic flux density of a first development upstream pole (104) is greater than the maximum value of the absolute value of the magnetic flux density of a first development downstream pole (106). The maximum value of the absolute value of the magnetic flux density of a second development downstream pole (204) is greater than the maximum value of the absolute value of the magnetic flux density of a second development upstream pole (202). When the angle in the rotational direction of a second sleeve (34) from the position on an outer circumferential surface of the second sleeve (34) at which the absolute value of the magnetic flux density of the second development upstream pole (202) is at a maximum to the position on the outer circumferential surface of the second sleeve (34) at which the absolute value of the magnetic flux density of a second development pole (203) is at a maximum is θ1 (°) and the angle in the rotational direction of the second sleeve (34) from the position on the outer circumferential surface of the second sleeve (34) at which the absolute value of the magnetic flux density of the second development pole (203) is at a maximum to the position on the outer circumferential surface of the second sleeve (34) at which the absolute value of the magnetic flux density of the second development downstream pole (204) is at a maximum is θ2 (°), θ1>θ2.

Description

Developing device

The present invention relates to a developing device that develops an electrostatic latent image formed on an image carrier using a developer.

Developing devices that use a two-component developer made of toner and magnetic carrier typically have a configuration in which a magnet with multiple magnetic poles is installed inside a developing roller, and the developer is carried on the developing roller to develop an electrostatic latent image formed on an image carrier. To achieve higher image quality, a configuration using a magnet with seven or more magnetic poles has also been proposed (JP 2008-241997 A). In such a configuration, the distance between the developing pole facing the image carrier and the magnetic poles upstream and downstream of it is short, which increases the magnetic force and makes the magnetic brushes that come into contact with the image carrier near the developing pole denser, enabling higher image quality.

Furthermore, a developing device configuration has been proposed in which two developing rollers are arranged side by side in the direction of rotation of the image carrier (JP 2013-254107 A). In the developing device described in JP 2013-254107 A, of the two developing rollers, developer is supplied from a supply unit to the first developing roller, which is located vertically below, and developer is passed from the first developing roller, which is located vertically above, to the second developing roller, which is located vertically above.

In a configuration with two developing rollers as in JP 2013-254107 A, if magnets with seven or more magnetic poles as in Patent Document 1 are to be used for each developing roller, it is possible to configure the magnets as follows, for example. First, another magnetic pole (transport pole) is provided between the developing pole of the first developing roller and the delivery pole that transfers the developer from the first developing roller to the second developing roller. Also, another magnetic pole (transport pole) is provided between the developing pole of the second developing roller and the receiving pole that receives the developer from the first developing roller to the second developing roller. By adding a transport pole to each developing roller in this way, the effect of improving image quality can be further achieved.

However, when a new magnetic pole (transport pole) is placed between the development pole and the delivery pole or receiving pole of each development roller as described above, the transport pole of the first development roller and the transport pole of the second development roller will be composed of opposite poles. In other words, because the delivery pole and receiving pole are opposite poles, the transport poles of each adjacent development roller will also be opposite poles. This causes a magnetic field to be generated between the transport poles of each development roller. If this magnetic field between the transport poles causes developer to move between the transport poles, the developer moving between the transport poles will come into contact with the image carrier, causing streaky fogging on the output image. In order to prevent this streaky fogging, it is effective to reduce the magnetic flux density of the transport pole of each development roller, making it more difficult for a magnetic field to form between the transport poles.

When developing an electrostatic latent image on an image carrier, magnetic developer chains are formed on the surface of the developing roller, and toner is attached from these chains to the photosensitive drum, developing the electrostatic latent image with toner. During this process, carrier may adhere from the magnetic chains to the photosensitive drum (hereinafter referred to as "carrier adhesion"). When this carrier adhesion occurs, image defects such as small white areas appear on the output image occur. With regard to carrier adhesion, if the magnetic developer chains are in contact with the image carrier downstream of the portion facing the developing roller in the rotational direction, magnetic carrier is likely to remain on the image carrier, making carrier adhesion more likely.

As a result, the magnetic wires near the development pole are more likely to extend upstream, and on the downstream side, the magnetic wires are quickly folded, making contact less likely, and carrier adhesion is less likely to occur. To make it easier for the magnetic wires near the development pole to extend upstream, it is best to make the magnetic flux density of the magnetic pole downstream of the development pole greater than the magnetic flux density of the magnetic pole upstream of the development pole. In this way, the magnetic field lines from the development pole extend downstream while wrapping around upstream, making it easier for the magnetic wires near the development pole to extend upstream.

When applying this type of carrier adhesion countermeasure to a configuration in which a transport pole is provided between the development pole and the delivery pole or receiving pole of each developing roller, it is advisable to make the magnetic flux density of the transport pole downstream of the development pole in the first and second developing rollers greater than the magnetic flux density of the transport pole upstream of the development pole. However, in order to prevent the occurrence of the streaky fogging described above, it is desirable to make the magnetic flux density of the transport pole downstream of the development pole of the first developing roller as small as possible.

The present invention aims to provide a configuration that can simultaneously suppress streak-like fogging and carrier adhesion.

One aspect of the present invention is a developing container that contains a developer containing toner and a carrier; a first rotating body to which the developer contained in the developing container is supplied, the first rotating body rotating in the same direction as the rotating image carrier at a position on the outer surface of the first rotating body that is closest to the image carrier, and carrying and transporting the developer to a first developing position where an electrostatic latent image formed on the image carrier is developed; a first magnet that is fixedly arranged inside the first rotating body and does not rotate, the first magnet comprising: a first developing pole that is arranged facing the image carrier at the first developing position; a first upstream pole that is arranged adjacent to the first developing pole upstream of the first developing pole in the rotational direction of the first rotating body and has a polarity different from that of the first developing pole; and a first upstream pole that is arranged adjacent to the first developing pole downstream of the first developing pole in the rotational direction of the first rotating body and has a polarity different from that of the first developing pole. a first magnet having a first downstream pole having a polarity different from that of the first developing pole and a delivery pole arranged downstream of the first downstream pole and upstream of the first upstream pole in a rotational direction of the first rotating body; a second rotating body arranged opposite to the first rotating body and to which the developer is delivered from the first rotating body by a magnetic field generated by the first magnet, the second rotating body rotating in the same direction as the image carrier at a position on the outer circumferential surface of the second rotating body closest to the image carrier and carrying and transporting the developer to a second developing position where the electrostatic latent image is developed; a second magnet arranged inside the second rotating body and fixed so as not to rotate, the second developing pole arranged opposite to the image carrier at the second developing position; a second magnet having: a second upstream pole arranged downstream of the second developing pole with respect to the rotation direction of the second rotor and having a polarity opposite to that of the second developing pole; a second downstream pole arranged adjacent to the second developing pole downstream of the second developing pole with respect to the rotation direction of the second rotor and having a polarity opposite to that of the second developing pole; and a receiving pole arranged downstream of the second downstream pole and upstream of the second upstream pole with respect to the rotation direction of the second rotor and adjacent to the delivering pole with a polarity opposite to that of the delivering pole, wherein a maximum value of the absolute value of the magnetic flux density of the first upstream pole in a normal direction to the outer circumferential surface of the first rotor is greater than a maximum value of the absolute value of the magnetic flux density of the first downstream pole in a normal direction to the outer circumferential surface of the first rotor, and a maximum value of the absolute value of the magnetic flux density of the second downstream pole in a normal direction to the outer circumferential surface of the second rotor is greater than a maximum value of the absolute value of the magnetic flux density of the second downstream pole in a normal direction to the outer circumferential surface of the second rotor. The developing device satisfies θ1 > θ2, where θ1 [°] is the angle in the rotational direction of the second rotor from the position on the outer circumferential surface of the second rotor where the absolute value of the magnetic flux density of the second upstream pole in the normal direction to the outer circumferential surface of the second rotor is greatest and is greater than the maximum absolute value of the magnetic flux density of the second upstream pole, to the position on the outer circumferential surface of the second rotor where the absolute value of the magnetic flux density of the second development pole in the normal direction to the outer circumferential surface of the second rotor, and θ2 [°] is the angle in the rotational direction of the second rotor from the position on the outer circumferential surface of the second rotor where the absolute value of the magnetic flux density of the second development pole in the normal direction to the outer circumferential surface of the second rotor where the absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer circumferential surface of the second rotor.

One aspect of the present invention is a first magnet comprising: a developing container that contains a developer containing toner and a carrier; a first rotor to which the developer contained in the developing container is supplied, the first rotor rotating in the same direction as the rotating image carrier at a position on the outer circumferential surface of the first rotor closest to the image carrier, and carrying and transporting the developer to a first development position where an electrostatic latent image formed on the image carrier is developed; a first magnet fixedly disposed within the first rotor so as not to rotate, the first magnet comprising: a first developing pole disposed facing the image carrier at the first development position; a first upstream pole disposed adjacent to the first developing pole upstream of the first developing pole in the direction of rotation of the first rotor and having a polarity opposite to that of the first developing pole; a first downstream pole disposed adjacent to the first developing pole downstream of the first developing pole in the direction of rotation of the first rotor and having a polarity opposite to that of the first developing pole; and a delivery pole disposed downstream of the first downstream pole and upstream of the first upstream pole in the direction of rotation of the first rotor. a second rotor disposed opposite the first rotor and receiving the developer from the first rotor by a magnetic field generated by the first magnet, the second rotor rotating in the same direction as the image carrier at a position on the outer circumferential surface of the second rotor closest to the image carrier, and carrying and transporting the developer to a second development position where the electrostatic latent image is developed; a second magnet disposed inside the second rotor and fixed so as not to rotate, the second rotor having a second development pole disposed opposite the image carrier at the second development position; a second upstream pole disposed adjacent to the second development pole upstream of the second development pole in the rotation direction of the second rotor and having a polarity opposite to that of the second development pole; a second downstream pole disposed adjacent to the second development pole downstream of the second development pole in the rotation direction of the second rotor and having a polarity opposite to that of the second development pole; a receiving pole of an opposite polarity, and a second magnet having a receiving pole, wherein |Bθ1-1| is the maximum value of the absolute value of the magnetic flux density in a tangential direction to the outer circumferential surface of the first rotor in a section in the rotation direction of the first rotor from a position on the outer circumferential surface of the first rotor where the absolute value of the magnetic flux density of the first upstream pole in the normal direction to the outer circumferential surface of the first rotor is maximum to a position on the outer circumferential surface of the first rotor where the absolute value of the magnetic flux density of the first development pole in the normal direction to the outer circumferential surface of the first rotor is maximum, and |Bθ1-2| is the maximum value of the absolute value of the magnetic flux density in a tangential direction to the outer circumferential surface of the first rotor in a section in the rotation direction of the first rotor from the position on the outer circumferential surface of the first rotor where the absolute value of the magnetic flux density of the first development pole in the normal direction to the outer circumferential surface of the first rotor is maximum to a position on the outer circumferential surface of the first rotor where the absolute value of the magnetic flux density of the first downstream pole in the normal direction to the outer circumferential surface of the first rotor, ≧1.0, and |Bθ2-1| is the maximum value of the absolute value of the magnetic flux density in the tangential direction to the outer circumferential surface of the second rotor in a section in the rotation direction of the second rotor from a position on the outer circumferential surface of the second rotor where the absolute value of the magnetic flux density of the second upstream pole in the normal direction to the outer circumferential surface of the second rotor is maximum to a position on the outer circumferential surface of the second rotor where the absolute value of the magnetic flux density of the second development pole in the normal direction to the outer circumferential surface of the second rotor, When |Bθ2-2| is the maximum absolute value of the magnetic flux density in the tangential direction to the outer peripheral surface of the second rotor in a section in the rotational direction of the second rotor from the position on the outer peripheral surface of the second rotor where the absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer peripheral surface of the second rotor is maximum to the position on the outer peripheral surface of the second rotor where the absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer peripheral surface of the second rotor is maximum, this development device satisfies |Bθ2-2|/|Bθ2-1|≧1.1.

The present invention makes it possible to suppress both streaky fogging and carrier adhesion.

FIG. 1 is a cross-sectional view showing the schematic configuration of an image forming apparatus according to an embodiment.

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

Figure 3 shows the magnetic pole arrangement of the first developing roller according to the embodiment.

Figure 4 shows the magnetic pole arrangement of the second developing roller according to the embodiment.

Figure 5 shows the magnetic pole arrangement of the peeling roller according to the embodiment.

FIG. 6 shows the relationship between the magnetic pole arrangements of the first and second developing rollers according to the embodiment.

Figure 7 is a schematic diagram showing the magnetic field lines when the absolute value of the normal component of the magnetic flux density is greater for the magnetic pole located adjacent to the downstream side of the development pole than for the magnetic pole located adjacent to the upstream side of the development pole.

Figure 8 is a schematic diagram showing the magnetic field lines when the absolute value of the normal component of the magnetic flux density is greater for the magnetic pole located adjacent to the upstream side of the development pole than for the magnetic pole located adjacent to the downstream side of the development pole.

Figure 9 shows the relationship between the magnetic pole arrangements of the first and second developing rollers according to an embodiment, and illustrates the relationship between the transport poles of the first and second developing rollers.

Figure 10 shows (a) a graph showing the magnetic characteristics of the first developing roller and (b) a graph showing the magnetic characteristics of the second developing roller in Comparative Example 1.

Figure 11 shows (a) a graph showing the magnetic characteristics of the first developing roller and (b) a graph showing the magnetic characteristics of the second developing roller in Example 1.

Figure 12 shows (a) a graph showing the magnetic characteristics of the first developing roller and (b) a graph showing the magnetic characteristics of the second developing roller in Example 2.

Figure 13 is a graph showing the distribution of the normal component of the magnetic flux density of the second developing roller for Comparative Example 1 and Examples 1 and 2.

Figure 14 is a graph showing the distribution of the tangential component of the magnetic flux density of the second developing roller for Comparative Example 1 and Examples 1 and 2.

Figure 15 shows (a) a graph showing the magnetic characteristics of the first developing roller and (b) a graph showing the magnetic characteristics of the second developing roller in Example 3.

Figure 16 shows (a) a graph showing the magnetic characteristics of the first developing roller and (b) a graph showing the magnetic characteristics of the second developing roller in Comparative Example 2.

Figure 17 is a graph showing the distribution of the normal component of the magnetic flux density of the first developing roller for Examples 1 and 3 and Comparative Example 2.

Figure 18 is a graph showing the distribution of the tangential component of the magnetic flux density of the first developing roller for Examples 1 and 3 and Comparative Example 2.

Figure 19 shows (a) a graph showing the magnetic characteristics of the first developing roller and (b) a graph showing the magnetic characteristics of the second developing roller in Example 4.

Figure 20 is a graph showing the distribution of the normal component of the magnetic flux density of the first developing roller in Examples 1 and 4.

Figure 21 is a graph showing the distribution of the tangential component of the magnetic flux density of the first developing roller in Examples 1 and 4.

The embodiment will be described with reference to Figures 1 to 21. First, the schematic configuration of an image forming apparatus according to the present embodiment will be described with reference to Figure 1.
[Image forming apparatus]

Image forming apparatus 100 is a full-color image forming apparatus, and in this embodiment, for example, is an MFP (Multi-Function Peripheral) with copy, printer, and scan functions. As shown in Figure 1, image forming apparatus 100 has parallel image forming units PY, PM, PC, and PK that perform the image forming process for four colors of toner: yellow, magenta, cyan, and black.

The image forming units PY, PM, PC, and PK for each color each have 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. Image forming apparatus 100 also has a transfer device 2 and a fixing device 3. Because the image forming units PY, PM, PC, and PK for each color each have the same configuration, the following description will use image forming unit PY as a representative.

The photosensitive drum 28Y, which serves 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. In this embodiment, the linear speed of the surface of the photosensitive drum 28Y is set to 650 mm/s. The primary charger 21Y consists of a corona discharge electrode arranged around the photosensitive drum 28Y, and charges the surface of the photosensitive drum 28Y with the ions it generates.

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 area 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.

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 primary transfer rollers 23Y, 23M, 23C, and 23K and several other rollers and is supported so that it can run. From the top in Figure 1, the primary transfer rollers 23Y, 23M, 23C, and 23K correspond to the colors Y (yellow), M (magenta), C (cyan), and K (black). The secondary transfer roller 25 is positioned outside the intermediate transfer belt 24 and is configured to allow a recording material to pass between it and the intermediate transfer belt 24. The recording material is, for example, a sheet such as paper or a plastic sheet.

The toner images of each color formed on photosensitive drums 28Y, 28M, 28C, and 28K are transferred sequentially onto intermediate transfer belt 24 by 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 then transferred by secondary transfer roller 25 onto a recording material transported from a cassette or the like containing the recording material. Pressure and heat are applied to the recording material with the transferred toner image in fixing device 3. This melts the toner on the recording material, and the color image is fixed to the recording material.

Developer storage units 27Y, 27M, 27C, and 27K are provided corresponding to developing devices 1Y, 1M, 1C, and 1K, respectively, and are replaced with bottles containing developer corresponding to the respective colors of yellow, magenta, cyan, and black, from top to bottom. Developer storage units 27Y, 27M, 27C, and 27K are configured to transport (supply) developer to developing devices 1Y, 1M, 1C, and 1K corresponding to the color of developer stored therein.

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 amount consumed is replenished, and the toner weight ratio of the developer in the developing devices 1Y, 1M, 1C, and 1K is maintained constant.
[Developing device]

Next, developing devices 1Y, 1M, 1C, and 1K will be described in detail using Figures 2 to 5. Since developing devices 1Y, 1M, 1C, and 1K have the same configuration, the following description will focus on developing device 1Y as a representative. Figure 2 is a conceptual diagram explaining 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 within developing device 1Y.

As shown in Figure 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 housed in a developing container 60.

The first developing roller 30 is a rotatably driven developer carrier, and is positioned adjacent to the photosensitive drum 28Y so that its rotational axis is approximately parallel to the rotational axis of the photosensitive drum 28Y. The first developing roller 30 has a rotating first sleeve (first rotating body) 33 and a first magnet (fixed magnet, first magnet) 36 that is non-rotatingly positioned inside the first sleeve 33 and uses magnetic force to attract developer to the surface of the first sleeve 33. The first developing roller 30 uses magnetic force to attract (carry) the developer pumped up from the developer supply screw 42, and uses the developer to develop the electrostatic latent image formed on the rotating photosensitive drum 28Y (image carrier).

The first sleeve 33 of the developing device 1Y (and the second sleeve 34 described below) is applied with, for example, a DC developing bias of the same polarity as the charging polarity of the primary charger 21Y, or a developing bias in which a DC voltage of the same polarity as the charging polarity of the primary charger 21Y is superimposed on an AC voltage. As a result, reversal development is performed in which toner charged with the same polarity as the charging polarity of the primary charger 21Y adheres to the electrostatic latent image formed by the optical writing unit 22Y. In this embodiment, the charging polarity of the primary charger 21Y and the DC voltage of the developing bias are negative, and reversal development is performed in which negatively charged toner adheres to the electrostatic latent image.

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 the rotation axis 39. The rotation direction of the first sleeve 33 is clockwise as shown by the arrow in Figure 2, which in this embodiment is the opposite direction to the rotation direction of the photosensitive drum 28Y. Therefore, the first sleeve 33 and the photosensitive drum 28Y rotate in the same direction while facing each other. In this embodiment, the linear speed of the surface of the first sleeve 33 of the first developing roller 30 is set to be 1.0 times (= 650 mm/s) the linear speed of the surface of the photosensitive drum 28Y. It is advantageous in terms of toner degradation to keep the ratio of the linear speed of the surface of the first sleeve 33 to the linear speed of the surface of the photosensitive drum 28Y to approximately 1.0 times or more and 1.2 times or less. On the other hand, there are concerns about development performance as the amount of toner supplied to the photosensitive drum 28Y decreases, but in this embodiment, two developing rollers 30, 31 are provided, and the amount of toner supplied to the photosensitive drum 28Y can be maintained even if the linear velocity ratio is reduced.

The first magnet 36 is disposed inside the first sleeve 33 and has a plurality of magnetic poles 101-107, as shown in Figure 3. The solid lines of the magnetic poles 101-107 shown in Figure 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. A space is disposed between the inner circumference of the first sleeve 33 and the outer circumference of the first magnet 36 to allow rotation of the first sleeve 33.

The developer attracted to the first sleeve 33 (on the first sleeve) is carried and transported toward the photosensitive drum 28Y by the rotation of the first sleeve 33, and develops the latent image formed on the photosensitive drum 28Y at the first development position. 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 rotation of the first sleeve 33. Then, near the closest position between the first developing roller 30 and the second developing roller 31, the magnetic fields 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 cause the developer to be peeled off from the first sleeve 33 and transferred onto the second sleeve 34 (on the second sleeve).

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

The second developing roller 31 is a rotationally driven developer carrier, and is positioned downstream of the first developing roller 30 in the rotation direction of the photosensitive drum 28Y, with the center of rotation O2 of the second developing roller 31 positioned vertically above the center of rotation O1 of the first developing roller 30; developer is transferred from the first developing roller 30 by magnetic force (Figure 2). In this embodiment, the entire second developing roller 31 is positioned above the center of rotation O1 of the first developing roller 30. Like the first developing roller 30, the second developing roller 31 is positioned adjacent to the photosensitive drum 28Y with its rotational axis approximately parallel to the rotational axis of the photosensitive drum 28Y. Therefore, the rotational axes of the second developing roller 31 and the first developing roller 30 are approximately parallel to each other.

This second developing roller 31 has a rotating second sleeve (second rotating body) 34 and a second magnet (fixed magnet, second magnet) 37 that is non-rotatingly positioned inside the second sleeve 34 and uses magnetic force to attract developer to the surface of the second sleeve 34. The second developing roller 31 receives and attracts (carries) developer from the first developing roller 30 (first sleeve 33) using magnetic force, and uses the developer to develop the electrostatic latent image formed on the rotating photosensitive drum 28Y. A peeling roller 32, described below, is located to the side of the second developing roller 31.

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 Figure 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 when they are positioned opposite each other. Furthermore, the second sleeve 34 and the first sleeve 33 rotate in opposite directions when they are positioned opposite each other. In this embodiment, the linear speed of the surface of the second sleeve 34 of the second developing roller 31 is set to be 1.2 times (= 780 mm/s) the linear speed of the surface of the photosensitive drum 28Y.

The second magnet 37 is disposed inside the second sleeve 34 and has a plurality of magnetic poles 201-207, as shown in Figure 4. The solid lines of the magnetic poles 201-207 shown in Figure 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 is disposed between the inner circumference of the second sleeve 34 and the outer circumference of the second magnet 37 to allow rotation of the second sleeve 34.

The developer attracted to the second sleeve 34 is carried and transported toward the photosensitive drum 28Y by the rotation of the second sleeve 34, and develops the latent image formed on the photosensitive drum 28Y at the second development position. After the latent image formed on the photosensitive drum 28Y is developed, the developer remaining on the second sleeve 34 is transported to the vicinity of the peeling roller 32 by the rotation of the second sleeve 34. Then, near 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 fields generated by the second magnet 37 contained in the second developing roller 31 and the third magnet 38 contained in the peeling roller 32.

The peeling roller 32, which serves as a peeling unit, is positioned on the opposite side of the photosensitive drum 28Y from the center of rotation of the second sleeve 34, and peels the developer from the second developing roller 31 after the electrostatic latent image on the photosensitive drum 28Y has been developed by the second developing roller 31. Specifically, the peeling roller 32 is a developer carrier that is driven to rotate, and is positioned between the second developing roller 31 and the developer recovery screw 44 so that its center of rotation is above the center of rotation R of the second developing roller 31.

Furthermore, the peeling roller 32 is positioned so that its rotational axis is approximately parallel to the rotational axis of the second developing roller 31. Such a peeling roller 32 has a rotating third sleeve 35 and a third magnet (fixed magnet) 38 that is non-rotatingly positioned inside the third sleeve 35 and that uses magnetic force to attract developer to the surface of the third sleeve 35, and is configured to transfer developer from the second developing roller 31 based on magnetic force.

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 around the rotation axis 41. The rotation direction of the third sleeve 35 is counterclockwise as shown by the arrow in Figure 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 while facing each other.

The third magnet 38 is disposed inside the third sleeve 35 and has a plurality of magnetic poles 301-305, as shown in Figure 5. The solid lines of the magnetic poles 301-305 shown in Figure 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 is disposed between the inner circumference of the third sleeve 35 and the outer circumference of the third magnet 38 to allow rotation of the third sleeve 35.

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

The guide member 45 and developer recovery screw 44 constitute the developer recovery section 47, which serves as a recovery section for recovering 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 positioned so that its center of rotation is positioned lower than the center of rotation of the peeling roller 32 in the vertical direction, and transports the developer handed over (recovered) from the peeling roller 32 while stirring it.

The guide member 45, which serves as a guide, is positioned vertically below the peeling roller 32 and guides the developer peeled off by the peeling roller 32 toward the developer recovery screw 44. This guide member 45 has a slope 45a along which the developer slides down under its own weight, to more reliably guide the peeled developer toward the developer recovery screw 44. The slope 45a is inclined relative to the horizontal direction so that the developer recovery screw 44 side is lower than the position below the peeling roller 32.

The developer recovery screw 44, which serves as a recovery member and transport unit, transports the recovered developer to the developer circulation unit 46, which will be described next. In other words, 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 slope of the guide member 45.

The developer circulation unit 46 is a supply unit for supplying developer to the first developing roller 30, and includes a regulating member 50, a developer supply screw 42, and a developer stirring screw 43. In the developer circulation unit 46, the developer is stirred within the developer supply screw 42 and the developer stirring screw 43 while being transported in a substantially horizontal direction and supplied to the first developing roller 30. Also, as described above, the developer collected by the developer collection unit 47 falls under its own weight and is introduced into the developer circulation unit 46.

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. Furthermore, the developer supply screw 42, developer stirring screw 43, and developer recovery screw 44 are arranged so that their rotational axes are approximately parallel to each other. The rotational axis of each of these screws is also approximately parallel to the rotational axis of the first developing roller 30.

The developer supply screw 42 is located between the first developing roller 30 and the developer agitation screw 43, and the partition wall 48 of the developer container 60 is arranged between the developer supply screw 42 and the developer agitation screw 43. The partition wall 48 of the developer container 60 extends along the rotational axis of the developer supply screw 42 and the developer agitation screw 43. The partition wall 48 is provided with a communication opening (not shown) that connects the first transport path 61, through which the developer is transported by the developer supply screw 42, and the second transport path 62, through which the developer is transported by the developer agitation screw 43.

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

The position of the communication port through which the developer stirred by the developer recovery screw 44 falls under its own weight and is introduced into the developer circulation section 46 is preferably positioned to avoid the area where the developer is supplied toward the first developing roller 30 (the middle part in the direction of the rotational axis of the developer supply screw 42). In this embodiment, the communication port is positioned within 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 located.

The developer transport directions of the developer supply screw 42 and the developer agitation screw 43 are opposite to each other. The start side (upstream end in the developer transport direction) and end side (downstream end in the developer transport direction) of the first transport path 61 in which the developer supply screw 42 is arranged are connected to the end side and start side of the second transport path 62 in which the developer agitation 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 agitation screw 43 indicated by the arrows in Figure 2, and also in a substantially horizontal direction within the developing container 60, and a portion of it is supplied toward the first developing roller 30.

The developer supply port 51 (see Figure 2) is located above the developer stirring screw 43 in the developer container 60 and is connected to the developer storage unit 27Y (see Figure 1). The developer supply port 51 is configured to be able to supply 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 located.

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

The toner concentration detection sensor 49 (see Figure 2) is arranged to detect the toner concentration in the developer contained in the developer circulation unit 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 replenishment of developer from the developer storage unit 27Y. For example, when it is detected that the toner concentration has dropped below a predetermined value, developer is replenished from the developer storage unit 27Y. Note that the magnetic permeability of the developer changes depending on the toner concentration, so it is possible to detect the toner concentration using magnetic permeability.

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

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

As mentioned above, this embodiment uses a two-component development method, and the developer is a mixture of negatively charged non-magnetic toner and magnetic carrier. The non-magnetic toner becomes negatively charged due to friction with the magnetic carrier, while the magnetic carrier becomes positively charged. The non-magnetic toner is made by incorporating colorants, wax components, etc. into resins such as polyester or styrene acrylic, which are then ground or polymerized into powder, with fine powders such as titanium oxide or silica added to the surface. The magnetic carrier is made by coating the surface of a core made of resin particles kneaded with ferrite particles or magnetic powder. In this embodiment, the initial toner concentration in the developer (weight ratio of toner contained in the developer) is 8%.

It is preferable that the magnetic carrier have a magnetization amount per unit weight of 40 Am ² /kg or more and 80 Am ² /kg or less when an applied magnetic field of 1000 oersted (79577 A/m) is applied. Reducing the magnetization amount of the magnetic carrier has the effect of suppressing scavenging by the magnetic brush, but it also makes it difficult for the magnetic carrier to adhere to the non-magnetic sleeve due to the magnet inside the developing roller, which may result in image defects such as magnetic carrier adhesion to the photosensitive drum. 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 the pressure of the magnetic brush, as described above. In this embodiment, a magnetic carrier with a magnetization amount per unit weight of 63 Am ² /kg was used.

The magnetization amount of the magnetic carrier was measured using a vibration magnetic field type magnetic property automatic recording device BHV-30 manufactured by Riken Denshi Co., Ltd. The magnetic property value of the magnetic carrier was determined by creating an external magnetic field of 1000 oersted and determining the magnetization strength at that time. The magnetic carrier was packed in a cylindrical plastic container so that it was sufficiently dense. In this state, the magnetization moment was measured, and the actual weight when the sample was placed was measured to determine the magnetization strength ( ^Am2 /kg).

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

Generally, two-component development systems using toner and carrier charge both to a predetermined polarity through frictional contact between the toner and carrier, which means that the toner is subjected to less stress than single-component development systems using a single-component developer. However, over time, the amount of dirt (spent) adhering to the carrier surface increases, gradually reducing the carrier's ability to charge the toner. This results in problems such as fogging and toner scattering.
In order to extend the life of the two-component developing device, it is conceivable to increase the amount of carrier contained in the developing device, but this is not desirable because it would increase the size of the developing device.

To solve the above problems associated with two-component developers, this embodiment employs an ACR (Auto Carrier Refresh) system. The ACR system suppresses an increase in degraded carrier by gradually replenishing new developer from the developer storage unit 27Y into the developing device 1Y and gradually discharging developer with degraded charging performance from an outlet (not shown) of the developing device 1Y. This allows the degraded carrier in the developing device 1Y to be gradually replaced with new carrier, making it possible to maintain the charging performance of the carrier in the developing device 1Y at a substantially constant level.
[About the magnetic poles of each magnet]

Next, we will explain 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 Figures 3, 4, and 5.

As shown in Figure 3, the first magnet 36 contained within the first developing roller 30 has a total of seven poles: multiple magnetic poles 101, 102, 103, 104, 105, 106, and 107. Of these, magnetic pole 107 is a transfer pole for transferring developer from the first developing roller 30 to the second developing roller 31. The magnetic poles 101 to 107 are arranged in numerical order in the rotational direction of the first sleeve 33. As mentioned above, the solid lines of the magnetic poles 101 to 107 shown in Figure 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 relative to the surface of the first sleeve 33 (magnetic flux density Br in the normal direction relative to the outer peripheral surface of the first sleeve 33; hereinafter, this may be simply referred to as "magnetic flux density Br" or "normal component Br"). The same applies to the magnetic poles 201-207 of the second magnet 37 shown in Figure 4 and the magnetic poles 301-305 of the third magnet 38 shown in Figure 5.

Magnetic pole 107, which serves as a transfer pole, transfers 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. Hereinafter, magnetic pole 107 may be referred to as transfer pole 107. Magnetic pole 101 is a north pole and is used to attract developer supplied from the developer supply screw 42 onto the first sleeve 33. Magnetic poles 102, 103, 104, 105, and 106 are south, north, south, north, and south poles and are used to transport the developer attracted by magnetic pole 101 upward as the first sleeve 33 rotates. Magnetic pole 107 is a north pole and, as described above, transfers developer from the first sleeve 33 to the second sleeve 34, which faces the first sleeve 33, by a magnetic field generated in cooperation with magnetic pole 201 in the second magnet 37 contained within the second developing roller 31.

Furthermore, in this embodiment, a low magnetic force portion 110 having a lower magnetic force than the delivery pole 107 is formed by a repulsive magnetic field generated in cooperation between the delivery pole 107 and the magnetic pole 101, which is disposed downstream of the delivery pole 107 in the rotational direction of the first sleeve 33 and has the same polarity as the delivery pole 107. This low magnetic force portion 110 promotes the transfer of developer from the first sleeve 33 to the second sleeve 34. Note that, while the low magnetic force portion 110 has almost no magnetic force in this embodiment, it may have a low magnetic force. For example, the magnetic force (normal component Br of the magnetic flux density) may be 5 mT or less. The same applies to 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.

As shown in Figure 4, the second magnet 37 contained within the second developing roller 31 has a total of seven poles: multiple magnetic poles 201, 202, 203, 204, 205, 206, and 207. Of these, magnetic pole 201 is a receiving pole that allows the second developing roller 31 to receive 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.

The magnetic pole 201 serving as a receiving pole is a magnetic pole that receives and attracts 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 hereafter may be referred to as the receiving pole 201. The magnetic pole 207 is a magnetic pole that transfers 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.

Furthermore, receiving pole 201 is an S pole, different in polarity from handover pole 107, and is used to attract developer from first developing roller 30 (first sleeve 33) onto second sleeve 34 as described above. Magnetic poles 202, 203, 204, 205, and 206 are N, S, N, S, and N poles, and are used to transport developer attracted by magnetic pole 201 upward as second sleeve 34 rotates. Magnetic pole 207 is an S pole, and transfers the developer after passing through the development area with photosensitive drum 28Y corresponding to magnetic pole 203 from second sleeve 34 to third sleeve 35, which faces second sleeve 34, by a magnetic field generated in cooperation with magnetic pole 303 in third magnet 38 contained within peeling roller 32.

Furthermore, in this embodiment, a low magnetic force portion 210 with a lower magnetic force than the magnetic pole 207 is formed by a repulsive magnetic field generated in cooperation between the magnetic pole 207, which is positioned upstream of the receiving pole 201 in the rotational 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 developer from the first sleeve 33 to the second sleeve 34. Furthermore, the low magnetic force portion 210 prevents developer from being attracted to the closest part of the first sleeve 33 and second sleeve 34, thereby reducing the pressure applied to the developer.

As shown in Figure 5, the third magnet 38 contained within the peeling roller 32 has multiple magnetic poles 301, 302, 303, 304, and 305. The magnetic poles 301 to 305 are arranged in numerical order in the rotational direction of the third sleeve 35.

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

Next, the positional relationship between the magnetic poles of the first magnet 36 arranged inside the first developing roller 30 and the magnetic poles of the second magnet 37 arranged inside the second developing roller 31 will be described with reference to FIG.
6 is a conceptual diagram illustrating the arrangement of the first developing roller 30, the second developing roller 31, and the photosensitive drum 28Y in this embodiment. The magnetic pole 105 of the first magnet 36 of the first developing roller 30 is an N pole and is positioned opposite the photosensitive drum 28Y across the first sleeve 33. This magnetic pole is used to develop the electrostatic latent image formed on the photosensitive drum 28Y. Hereinafter, the magnetic pole 105 may be referred to as the first developing pole 105. The delivery pole 107 is located downstream of the first developing pole 105 in the rotational direction of the first sleeve 33, has the same polarity as the first developing pole 105, and is used to deliver the developer from the first developing roller 30 to the second developing roller 31, as described above.

As mentioned above, the first magnet 36 of the first developing roller 30 has seven magnetic poles. This is intended to improve the quality of the output image. To achieve high quality output images, it is preferable that the magnetic chains of the developer formed by the magnetic force of the first developing pole 105, which is the magnetic pole facing the photosensitive drum 28Y via the first sleeve 33, are dense. To make the magnetic chains of the developer dense, the magnetic force of the first developing pole 105 is strengthened. By strengthening the magnetic force of the first developing pole 105, the magnetic carrier in the developer is more easily attracted to the surface of the first sleeve 33 of the first developing roller 30, making the magnetic chains denser.

In order to strengthen the magnetic force of the first development pole 105, either the absolute value of the magnetic flux density of the first development pole 105 is increased, or the change in magnetic flux density (differential with respect to distance) is increased. In this embodiment, the absolute value of the magnetic flux density Br of the first development pole 105 is increased to 150 mT or more, and the first magnet 36 has seven poles. This positions the magnetic poles (transport poles) 104 and 106 in a close area within 40° upstream and downstream of the first development pole 105 in the direction of rotation of the first sleeve 33, thereby increasing the change in magnetic flux density. As a result, the magnetic force of the first development pole 105 can be increased, the magnetic chains become denser, and higher quality output images can be achieved.

Therefore, in this embodiment, a magnetic pole (first developing downstream pole, first downstream pole) 106 is arranged adjacent to the first developing pole 105 between the first developing pole 105 and the delivery pole 107, downstream of the first developing pole 105 in the developer transport direction. Furthermore, a magnetic pole (first developing upstream pole, first upstream pole) 104 is arranged adjacent to the first developing pole 105 upstream of the first developing pole 105 in the developer transport direction. In other words, the magnetic pole 106 is located adjacent to the downstream side of the first developing pole 105 and adjacent to the upstream side of the delivery pole 107 in the rotation direction of the first sleeve 33, and is a magnetic pole of a different polarity from the first developing pole 105. Hereinafter, the magnetic pole 106 may be referred to as the first developing downstream pole 106. Furthermore, the magnetic pole 104 is located adjacent to the upstream side of the first developing pole 105 in the rotation direction of the first sleeve 33, and is a magnetic pole of a different polarity from the first developing pole 105. Hereinafter, the magnetic pole 104 may be referred to as the first development upstream pole 104.

Downstream in the rotation direction of the photosensitive drum 28Y from the portion where the first developing pole 105 of the photosensitive drum 28Y faces across the first sleeve 33, the magnetic pole 203 of the second magnet 37 of the second developing roller 31 is positioned approximately facing the photosensitive drum 28Y across the second sleeve 34. That is, the magnetic pole 203 of the second magnet 37 of the second developing roller 31 is an S pole, is positioned facing the photosensitive drum 28Y across the second sleeve 34, and is a magnetic pole for developing the electrostatic latent image formed on the photosensitive drum 28Y. Hereinafter, the magnetic pole 203 may be referred to as the second developing pole 203. The receiving pole 201 is positioned upstream of the second developing pole 203 in the rotation direction of the second sleeve 34, has the same polarity as the second developing pole 203 but is a magnetic pole of a different polarity from the delivery pole 107, and is a magnetic pole for the second developing roller 31 to receive developer from the first developing roller 30, as described above.

For the same reasons as the first magnet 36 of the first developing roller 30, to achieve high image quality, the absolute value of the magnetic flux density Br of the second developing pole 203 of the second magnet 37 of the second developing roller 31 is increased to 150 mT or more, and the second magnet 37 has seven poles. This allows the magnetic poles (transport poles) 202 and 204 to be positioned in a close area within 40° upstream and downstream of the second developing pole 203 in the direction of rotation of the second sleeve 34, thereby increasing the change in magnetic flux density. In this embodiment, the magnetic pole (second developing upstream pole, second upstream pole) 202 is positioned adjacent to the second developing pole 203 and the receiving pole 201, upstream of the second developing pole 203 in the developer transport direction. In addition, the magnetic pole (second developing downstream pole, second downstream pole) 204 is positioned adjacent to the second developing pole 203 downstream of the second developing pole 203 in the developer transport direction.

In other words, the magnetic pole 202 is located adjacent to the upstream side of the second developing pole 203 and adjacent to the downstream side of the receiving pole 201 in the rotation direction of the second sleeve 34, and is a magnetic pole of a different polarity from the second developing pole 203. Hereinafter, the magnetic pole 202 may be referred to as the second developing upstream pole 202. Furthermore, the magnetic pole 204 is located adjacent to the downstream side of the second developing pole 203 in the rotation direction of the second sleeve 34, and is a magnetic pole of a different polarity from the second developing pole 203. Hereinafter, the magnetic pole 204 may be referred to as the second developing downstream pole 204.

As mentioned above, if the first downstream developing pole 106 is provided between the first developing pole 105 and the delivery pole 107 of the first magnet 36 of the first developing roller 30, and the second upstream developing pole 202 is provided between the second developing pole 203 and the receiving pole 201 of the second magnet 37 of the second developing roller 31, there is a concern that image defects due to streaky fogging (abnormal images) may be more likely to occur. Streaky fogging (abnormal images) will now be explained. Typically, developer is transferred from the first developing roller 30 to the second developing roller 31 between the nearby delivery pole 107 of the first developing roller 30 and the receiving pole 201 of the second developing roller 31. In other words, because the delivery pole 107 and the receiving pole 201 have opposite polarities, a magnetic field is formed between the magnetic poles 107, 201, causing the developer to move and be transferred from the first developing roller 30 to the second developing roller 31.

However, as in this embodiment, when the first downstream developing pole 106 is positioned between the first developing pole 105 and the delivery pole 107 of the first developing roller 30, and the second upstream developing pole 202 is positioned between the second developing pole 203 and the delivery pole 201 of the second developing roller 31, the first downstream developing pole 106 of the first developing roller 30 and the second upstream developing pole 202 of the second developing roller 31 are composed of opposite poles, and a magnetic field is generated between the magnetic poles 106, 202. If the magnetic field between the magnetic poles 106, 202 causes the developer to move, the developer moving between the magnetic poles 106, 202 may come into contact with the photosensitive drum 28Y, potentially causing vertical streak-like fogging on the output image.

In order to prevent the occurrence of such streaky fogging (abnormal images), it is preferable to reduce the magnetic flux density of the first downstream developing pole 106 of the first developing roller 30 and the second upstream developing pole 202 of the second developing roller 31, making it difficult for a magnetic field to form between the two magnetic poles 106, 202.

Next, the magnetic pole configuration that is advantageous for carrier adhesion will be explained using Figures 7 and 8. Figures 7 and 8 are diagrams that schematically show the state of the magnetic field lines in the opposing area between the developing roller and photosensitive drum. In Figures 7 and 8, the photosensitive drum and developing roller rotate in the directions indicated by the arrows, with magnetic pole S1 located upstream of developing pole N in the direction of rotation of the developing roller, and magnetic pole S2 located downstream of developing pole N. The developing rollers shown in Figures 7 and 8 correspond to the first developing roller 30 or second developing roller 31.

Carrier adhesion is a phenomenon in which magnetic carrier adheres to the photosensitive drum 28Y and becomes apparent on the image. Carrier adhesion occurs when a negative charge is injected into the magnetic carrier in the developer due to the action of the development bias in the area where the first and second developing rollers 30, 31, and photosensitive drum 28Y face each other, causing the positively charged magnetic carrier to become negatively charged, the same polarity as the toner, and causing the magnetic carrier to fly to the photosensitive drum 28Y along with the toner.

For this reason, if the magnetic carrier remains for a long time in the opposing region between the first and second developing rollers 30 and 31 and the photosensitive drum 28Y, negative charge injection into the magnetic carrier is promoted, making carrier adhesion more likely to occur. As mentioned above, in this embodiment, in order to suppress toner degradation, the ratio of the surface linear speed of the first and second sleeves 33 and 34 of the first and second developing rollers 30 and 31 to the surface linear speed of the photosensitive drum 28Y is kept low at 1.0 to 1.2. As a result, the magnetic carrier remains for a long time in the opposing region between the first and second developing rollers 30 and 31 and the photosensitive drum 28Y, making negative charge injection into the magnetic carrier more likely to occur. For this reason, the configuration of this embodiment requires greater attention to addressing carrier adhesion.

In particular, when the surface linear velocity ratio is 1.4 or less, it is more important to address carrier adhesion.

According to the inventors' research, when the magnetic brush of the developer is in contact downstream in the direction of rotation of the photosensitive drum 28Y of the area where the photosensitive drum 28Y faces the first developing roller 30 and second developing roller 31, the magnetic carrier is more likely to remain on the photosensitive drum 28Y and carrier adhesion is more likely to occur. Therefore, by making the magnetic brush near each development pole of the first developing roller 30 and second developing roller 31 more likely to extend upstream and making the magnetic brush more likely to fold downstream, it is possible to make it less likely for the magnetic brush of the developer to come into contact downstream of the aforementioned facing area, making it less likely for carrier adhesion to occur.

The magnetic wires of the developer are formed when the magnetic carrier in the developer is connected along the magnetic field lines. Therefore, to make it easier for the magnetic wires near the development pole to extend upstream, it is preferable to make the magnetic field lines extend upstream of the development pole N, as shown in Figure 7. Figure 7 shows the magnetic field lines when the absolute value of the normal component Br of the magnetic flux density is greater for the magnetic pole S2 located adjacent to the downstream side of the development pole N than for the magnetic pole S1 located adjacent to the upstream side of the development pole N. In this case, the proportion of the magnetic field lines extending from the development pole N that extend to the downstream magnetic pole S2 increases. As a result, the magnetic field lines from the development pole N bend upstream before extending to the downstream magnetic pole S2, making it easier for the magnetic wires near the development pole N to extend upstream. When the magnetic wires extend upstream from the development pole N, they are more likely to come into contact with the photosensitive drum on the upstream side (the area surrounded by the dotted line in Figure 7) and less likely to come into contact on the downstream side, improving carrier adhesion.

On the other hand, Figure 8 shows the state of the magnetic field lines when the absolute value of the normal component Br of the magnetic flux density is greater for the magnetic pole S1 located adjacent to the upstream side of the development pole N than for the magnetic pole S2 located adjacent to the downstream side of the development pole N. In this case, the proportion of the magnetic field lines extending from the development pole N that extend to the upstream magnetic pole S1 increases. As a result, the magnetic field lines from the development pole N extend downstream while wrapping around to the upstream magnetic pole S1, making it easier for the magnetic brush near the development pole N to extend downstream.

If the magnetic brush extends downstream from the development pole N, it is likely to come into contact with the photosensitive drum on the downstream side (the area surrounded by the dotted line in Figure 8), raising concerns that carrier adhesion may be more likely to occur. One reason why carrier adhesion is more likely to occur when the magnetic brush comes into contact with the photosensitive drum on the downstream side of the photosensitive drum is that the distance between the photosensitive drum and the development roller gradually increases downstream of the photosensitive drum, weakening the magnetic force that pulls back the magnetic carrier that has adhered to the photosensitive drum. Another reason is that the magnetic brush spends more time in contact with the photosensitive drum. This is explained in more detail below.

As shown in Figure 8, even when the magnetic brush tends to extend downstream of the photosensitive drum, the distance between the photosensitive drum and the developing roller gradually narrows upstream of the photosensitive drum, causing developer to accumulate and making it easier for the magnetic brush to come into contact with the photosensitive drum even on the upstream side. As a result, the magnetic brush comes into contact with the photosensitive drum both upstream and downstream. As a result, the magnetic brush spends more time in contact with the photosensitive drum, which promotes the injection of negative charge into the magnetic carrier and is thought to make carrier adhesion more likely to occur. However, while a longer contact time between the magnetic brush and the photosensitive drum raises concerns about carrier adhesion as mentioned above, it also increases the time for toner to develop on the photosensitive drum, which is advantageous for developability.

When the carrier adhesion countermeasures described using Figure 7 are applied to a configuration that includes two developing rollers that rotate in the same direction facing the photosensitive drum as described in Figure 6, and in which a transport pole is provided between the developing pole of each developing roller and the magnetic pole in the transfer area, it is advantageous to increase the magnetic flux density of the first developing downstream pole 106 of the first developing roller 30. Here, the magnetic poles in the transfer area are the transfer pole 107 of the first developing roller 30 and the receiving pole 201 of the second developing roller 31. Furthermore, the transport poles between the developing poles of each developing roller and the magnetic poles in the transfer area are the first developing downstream pole 106 located between the first developing pole 105 and the transfer pole 107 on the first developing roller 30, and the second developing upstream pole 202 located between the second developing pole 203 and the receiving pole 201 on the second developing roller 31. That is, when trying to take measures against carrier adhesion with the configuration described in FIG. 6, it is best to increase the magnetic flux density of the first downstream developing pole 106 downstream of the first developing pole 105 of the first developing roller 30, as described in FIG. 7. However, from the perspective of suppressing the above-mentioned streak-like fog (abnormal image), it is better for the magnetic flux density of the first downstream developing pole 106 of the first developing roller 30 to be as small as possible. For this reason, it is difficult to simultaneously suppress streak-like fog (abnormal image) and carrier adhesion with the configuration described in FIG. 6.

Therefore, in this embodiment, in a configuration having two developing rollers that rotate in the same direction facing the photosensitive drum and a transport pole provided between the developing pole of each developing roller and the magnetic pole in the transfer area, the following configuration is adopted to achieve both the suppression of streak-like fogging (abnormal images) and the suppression of carrier adhesion.
[First and second developing rollers]

Figure 9 shows a schematic configuration of the area surrounding the photosensitive drum 28Y where the first developing pole 105 of the first magnet 36 of the first developing roller 30 and the second developing pole 203 of the second magnet 37 of the second developing roller 31 face each other. Note that some of the magnetic poles have been omitted to avoid clutter.

As mentioned above, to address carrier adhesion, it is preferable to make the absolute value of the magnetic flux density Br of the first and second downstream developing poles 106, 204 greater than the absolute value of the magnetic flux density Br of the first and second upstream developing poles 104, 202 for the first developing pole 105 of the first developing roller 30 and the second developing pole 203 of the second developing roller 31. However, because the absolute value of the magnetic flux density Br of the first downstream developing pole 106 of the first developing roller 30 is large, a magnetic field is more likely to be formed between the first downstream developing pole 106 and the second upstream developing pole 202 of the second developing roller 31, raising concerns that streaky fogging may occur as the developer moves between the two magnetic poles 106, 202.

For this reason, this embodiment is configured as follows. First, the maximum absolute value of the normal component Br of the magnetic flux density of the first upstream developing pole 104 is made larger than the maximum absolute value of the normal component Br of the magnetic flux density of the first downstream developing pole 106. Furthermore, the maximum absolute value of the normal component Br of the magnetic flux density of the second downstream developing pole 204 is made larger than the maximum absolute value of the normal component Br of the magnetic flux density of the second upstream developing pole 202. Furthermore, in the second developing roller 31, the line connecting the position (peak position) on the second sleeve 34 where the absolute value of the normal component Br of the magnetic flux density of the second upstream developing pole 203 is maximum and the rotation center O2 of the second sleeve 34 is designated as line L2. The line connecting the position (peak position) on the second sleeve 34 where the absolute value of the normal component Br of the magnetic flux density of the second upstream developing pole 202 is maximum and the rotation center O2 of the second sleeve 34 is designated as line L21. The angle (acute angle) formed by line L2 and line L21 is defined as θ1 [°]. In other words, θ1 is the angle in the rotational direction of the second sleeve 34 from the position on the outer peripheral surface of the second sleeve 34 where the absolute value of the magnetic flux density of the second developing upstream pole 202 in the normal direction to the outer peripheral surface of the second sleeve 34 is maximum to the position on the outer peripheral surface of the second sleeve 34 where the absolute value of the magnetic flux density of the second developing pole 203 in the normal direction to the outer peripheral surface of the second sleeve 34 is maximum. Furthermore, line L22 is the line connecting the position (peak position) on the second sleeve 34 where the absolute value of the normal component Br of the magnetic flux density of the second developing downstream pole 204 is maximum and the rotation center O2 of the second sleeve 34. The angle (acute angle) formed by line L2 and line L22 is defined as θ2 [°]. In other words, θ2 is the angle in the rotation direction of the second sleeve 34 from the position on the outer circumferential surface of the second sleeve 34 where the absolute value of the magnetic flux density of the second developing pole 203 in the normal direction to the outer circumferential surface of the second sleeve 34 is maximum to the position on the outer circumferential surface of the second sleeve 34 where the absolute value of the magnetic flux density of the second developing downstream pole 204 in the normal direction to the outer circumferential surface of the second sleeve 34 is maximum. In this case, θ1 > θ2 is satisfied.

Let's explain this in more detail. First, with regard to the second developing roller 31, the absolute value of the magnetic flux density Br of the second developing downstream pole 204 is set to be greater than the absolute value of the magnetic flux density Br of the second developing upstream pole 202 of the second magnet 37. As a result, with regard to the second developing roller 31, the magnetic chains near the second developing pole 203 tend to extend toward the upstream side of the photosensitive drum 28Y, and as a result, carrier adhesion is less likely to occur.

On the other hand, in this embodiment, with respect to the first developing roller 30, the absolute value of the magnetic flux density Br of the first developing downstream pole 106 is set smaller than the absolute value of the magnetic flux density Br of the first developing upstream pole 104 of the first magnet 36. In this way, it is possible to keep the absolute values of the magnetic flux density Br of both the first developing downstream pole 106 and the second developing upstream pole 202 low. This makes it difficult for a magnetic field to be formed between the first developing downstream pole 106 of the first developing roller 30 and the second developing upstream pole 202 of the second developing roller 31, and reduces the occurrence of streaky fogging due to the movement of developer between the magnetic poles 106, 202.

However, with this configuration, there is a concern that the magnetic chains near the first developing pole 105 of the first developing roller 30 will tend to extend downstream of the photosensitive drum 28Y, making carrier adhesion more likely to occur. Regarding this point, the inventors' research has shown that, because the first developing roller 30 is positioned upstream of the second developing roller 31 in the rotation direction of the photosensitive drum 28Y, even if some carrier adhesion occurs on the first developing roller 30, it is possible to reset the carrier adhesion on the first developing roller 30 by taking proper measures to prevent carrier adhesion on the second developing roller 31.

Therefore, in this embodiment, with respect to the second developing roller 31, in addition to making the absolute value of the magnetic flux density Br of the second developing downstream pole 204 greater than the absolute value of the magnetic flux density Br of the second developing upstream pole 202, the angle θ2 between the peak positions of the magnetic flux density Br of the second developing pole 203 and the second developing downstream pole 204 is made smaller than the angle θ1 between the peak positions of the magnetic flux density Br of the second developing pole 203 and the second developing upstream pole 202. In this way, when angle θ2 is made smaller than angle θ1, the magnetic field lines extending from the second developing pole 203 extend more toward the second developing downstream pole 204, which is closer than the second developing upstream pole 202. As a result, the magnetic field lines extending from the second developing pole 203 extend downstream while winding around further upstream, making it easier for the magnetic wires formed by the second developing pole 203 to extend further upstream, making it less likely for these magnetic wires to come into contact downstream in the direction of rotation of the photosensitive drum 28Y.

Furthermore, if the angle θ2 between the peak positions of the second developing pole 203 and the second developing downstream pole 204 is small, the magnetic field lines extending from the second developing pole 203 will quickly move toward the second developing downstream pole 204 downstream of the second developing pole 203. As a result, the magnetic chain formed by the second developing pole 203 is quickly folded on the downstream side, making it more difficult for the magnetic chains to come into contact downstream in the direction of rotation of the photosensitive drum 28Y.

As described above, in this embodiment, with respect to the second developing roller 31, the absolute value of the magnetic flux density Br of the second downstream developing pole 204 is made greater than the absolute value of the magnetic flux density Br of the second upstream developing pole 202. In addition, the angle θ2 between the peak positions of the second downstream developing pole 204 and the second upstream developing pole 202 is made smaller than the angle θ1 between the peak positions of the second upstream developing pole 203 and the second downstream developing pole 204. While making the angle θ2 smaller than the angle θ1 is effective, it is preferable to make it smaller by 2° or more to achieve a greater effect, and even more preferably by 3° or more. That is, it is preferable to satisfy the relationship 2°≦θ1−θ2, and more preferably 3°≦θ1−θ2. However, it is preferable that the angle θ2 between the peak positions of the second downstream developing pole 204 be at least half the angle θ1 between the peak positions of the second upstream developing pole 202 and the second upstream developing pole 203 (θ2≧θ1/2). If the angle θ2 is too small, the peak position of the second developing downstream pole 204 becomes too close to the peak position of the second developing pole 203, and the volume of the magnet (piece of the second magnet 37) that contributes to the magnetic field formation of the second developing pole 203 becomes small, making it difficult to generate a magnetic field, which raises concerns that carrier adhesion may be more likely to occur due to the second developing roller 31. With the above-described configuration, this embodiment can achieve both suppression of streak-like fogging and suppression of carrier adhesion.
[Relationship between half-value widths]

A more preferable configuration is described below. In this embodiment, the half-width of the normal component Br of the magnetic flux density of the second downstream developing pole 204 is preferably larger than the half-width of the normal component Br of the magnetic flux density of the second upstream developing pole 202. Here, the half-width is the angle of the portion where the normal component Br of the magnetic flux density of each magnetic pole is half its peak value. To distinguish it from the half-width, it is sometimes called the full-width at half maximum, but in this specification, the half-width refers to the full-width at half maximum. This configuration can more reliably increase the proportion of the magnetic field lines extending from the second downstream developing pole 203 that extend to the second downstream developing pole 204, thereby improving carrier adhesion. Considering manufacturing variations, it is more preferable to make the half-width larger by 3° or more, and even more preferably by 5° or more. That is, the half-value width of the normal component Br of the magnetic flux density of the second developing downstream pole 204 is preferably 3° or more larger than the half-value width of the normal component Br of the magnetic flux density of the second developing upstream pole 202, and more preferably 5° or more larger.
[Relationship with Closest Position of Second Developing Roller]

Furthermore, in this embodiment, the peak position of the normal component Br of the magnetic flux density of the second developing pole 203 of the second developing roller 31 is set at a position approximately facing the photosensitive drum 28Y. More specifically, the peak position of the second developing pole 203 is positioned upstream in the rotation direction of the photosensitive drum 28Y from the facing position where the photosensitive drum 28Y and the second developing roller 31 are closest to each other (dashed line L23 connecting the center of the photosensitive drum 28Y and the center of the second developing roller 31 in Figure 9). In other words, the position on the second sleeve 34 where the absolute value of the normal component of the magnetic flux density of the second developing pole 203 is maximum (peak position) is located upstream in the rotation direction of the second sleeve 34 from the position where the second sleeve 34 is closest to the photosensitive drum 28Y.

This configuration allows the magnetic chains extending from the second developing pole 203 to extend further upstream of the photosensitive drum 28Y, more reliably improving carrier adhesion. However, because the magnetic force is strongest and the magnetic chains are dense near the peak position of the second developing pole 203, it is preferable for high image quality that the second developing pole 203 be positioned approximately facing the photosensitive drum 28Y. Therefore, it is preferable to position the peak position of the second developing pole 203 within 10°, preferably within 5°, and more preferably within 3° upstream of the opposing position of the photosensitive drum 28Y and the second developing roller 31. In other words, the angle (acute angle) formed by the line L2 connecting the peak position of the second developing pole 203 and the center of rotation O2 of the second sleeve and the line L23 connecting the closest position of the second sleeve 34 to the photosensitive drum 28Y and the center of rotation O2 of the second sleeve 34 is preferably 10° or less. Moreover, the angle (acute angle) formed by the line L2 and the line L23 is more preferably 5° or less, and even more preferably 3° or less.
[Sleeve surface linear speed]

Furthermore, as mentioned above, if the developer remains in the opposing area of the photosensitive drum 28Y for a long time, the injection of negative charge into the magnetic carrier in the developer due to the action of the development bias is promoted, making carrier adhesion more likely to occur. Therefore, in this embodiment, the ratio of the surface linear speed of the second sleeve 34 of the second developing roller 31 to the surface linear speed of the photosensitive drum 28Y is set to 1.2, which is larger than the ratio of the surface linear speed of the first sleeve 33 of the first developing roller 30 to the surface linear speed of the photosensitive drum 28Y, which is 1.0. In other words, in this embodiment, the surface linear speed of the second sleeve 34 is faster than the surface linear speed of the first sleeve 33.

The reason why the surface linear speed of the first sleeve 33 is suppressed to prevent toner degradation is as follows. As shown in Figure 2, a regulating member 50 faces the first sleeve 33, and when this regulating member 50 regulates the amount of developer coated on the first sleeve 33, shear is applied to the developer, leading to toner degradation. If the surface linear speed of the first sleeve 33 can be suppressed, the frequency with which the developer is subjected to shear can be reduced, making it possible to prevent toner degradation.

On the other hand, the second sleeve 34 of the second developing roller 31 receives developer from the first sleeve 33, and therefore does not face the regulating member 50 as does the first sleeve 33. For this reason, even if the surface linear speed of the second sleeve 34 is increased, toner degradation is less likely to occur as occurs when the linear speed of the first sleeve 33 is increased. Therefore, in this embodiment, the ratio of the surface linear speed of the second sleeve 34 to the surface linear speed of the photosensitive drum 28Y is set to 1.2, which is higher than the ratio of the surface linear speed of the first sleeve 33 to the surface linear speed of the photosensitive drum 28Y, which is 1.0. Increasing the surface linear speed of the second sleeve 34 suppresses the injection of negative charge into the magnetic carrier, making it possible to further improve carrier adhesion.

In this embodiment, the linear velocity ratio of the second sleeve 34 to the first sleeve 33 is set to 1.2 (=1.2/1.0), but to obtain the desired effect, it is preferable to set it to 1.1 or more.
On the other hand, if the linear velocity ratio of the second sleeve 34 to the first sleeve 33 is made greater than 1.3, the amount of developer coated per unit area of the second sleeve will decrease, and the magnetic chains will become too coarse, which may affect image quality, etc. For this reason, it is preferable that the linear velocity ratio of the second sleeve 34 to the first sleeve 33 be 1.3 or less.
[First Developing Roller]

As mentioned above, if sufficient measures are taken to prevent carrier adhesion on the second developing roller 31, which is positioned downstream in the rotation direction of the photosensitive drum 28Y, some carrier adhesion on the first developing roller 30 is acceptable. Therefore, in this embodiment, as mentioned above, the absolute value of the normal component Br of the magnetic flux density of the first developing downstream pole 106 is made smaller than the absolute value of the normal component Br of the magnetic flux density of the first developing upstream pole 104 of the first developing roller 30. This makes it easier for carrier adhesion caused by the first developing roller 30 to occur, but makes it less likely for streaky fogging to occur.

A more preferred configuration is described below. In this embodiment, the half-value width of the normal component Br of the magnetic flux density of the first downstream developing pole 106 is preferably smaller than the half-value width of the normal component Br of the magnetic flux density of the first upstream developing pole 104. This configuration further suppresses the magnetic field between the first downstream developing pole 106 and the second upstream developing pole 202, making it possible to further suppress the occurrence of streaky fogging. Taking into account manufacturing variations, it is more preferable to make it 3° or more smaller, and even more preferable to make it 5° or more smaller. In other words, the half-value width of the normal component Br of the magnetic flux density of the first downstream developing pole 106 is preferably 3° or more smaller, and more preferably 5° or more smaller than the half-value width of the normal component Br of the magnetic flux density of the first upstream developing pole 104.

If the absolute value of the magnetic flux density Br of the first downstream developing pole 106 is made smaller than the absolute value of the magnetic flux density Br of the first upstream developing pole 104, or if the half-width of the first downstream developing pole 106 is made smaller than the half-width of the first upstream developing pole 104, the proportion of the magnetic field lines extending from the first upstream developing pole 105 that extend to the first upstream developing pole 104 increases. Therefore, as shown in Figure 8, the magnetic brush is more likely to face downstream. As described above, when the magnetic brush faces downstream, the time the magnetic brush is in contact with the photosensitive drum 28Y increases, increasing the time for toner development on the photosensitive drum 28Y, which has the advantage of being beneficial to developability. The above configuration is effective when, as in this embodiment, there is a concern that reduced developability may result from suppressing the surface linear speed of the first sleeve 33 to prevent toner degradation.

Furthermore, in this embodiment, in the first developing roller 30, the line connecting the position (peak position) on the first sleeve 33 where the absolute value of the normal component Br of the magnetic flux density of the first developing pole 105 is maximum and the rotation center O1 of the first sleeve 33 is defined as line L1. The line connecting the position (peak position) on the first sleeve 33 where the absolute value of the normal component Br of the magnetic flux density of the first developing upstream pole 104 is maximum and the rotation center O1 of the first sleeve 33 is defined as line L11. The angle (acute angle) formed by lines L1 and L21 is defined as φ1 [°]. In other words, φ1 is the angle in the rotation direction of the first sleeve 33 from the position on the outer peripheral surface of the first sleeve 33 where the absolute value of the magnetic flux density of the first developing upstream pole 104 in the normal direction to the outer peripheral surface of the first sleeve 33 is maximum to the position on the outer peripheral surface of the first sleeve 33 where the absolute value of the magnetic flux density of the first developing pole 105 in the normal direction to the outer peripheral surface of the first sleeve 33 is maximum. Also, line L12 is the line connecting the position on the first sleeve 33 where the absolute value of the normal component Br of the magnetic flux density of the first developing downstream pole 106 is maximum (peak position) and the rotation center O1 of the first sleeve 33. The angle (acute angle) between line L1 and line L12 is φ2 [°]. In other words, φ2 is the angle in the rotation direction of the first sleeve 33 from the position on the outer circumferential surface of the first sleeve 33 where the absolute value of the magnetic flux density of the first developing pole 105 in the normal direction to the outer circumferential surface of the first sleeve 33 is maximum to the position on the outer circumferential surface of the first sleeve 33 where the absolute value of the magnetic flux density of the first developing downstream pole 106 in the normal direction to the outer circumferential surface of the first sleeve 33 is maximum. In this case, φ1 > φ2 is satisfied.

If a configuration were adopted in which φ1 < φ2 were satisfied, the effect of increasing the proportion of magnetic field lines extending from the first developing pole 105 that extend to the first developing upstream pole 104 would be achieved, but if φ1 were small, it would be difficult for the magnetic brush to contact the photosensitive drum 28Y on the upstream side, which could limit the effect of improving developability. Therefore, to increase the proportion of magnetic field lines extending from the first developing pole 105 that extend to the first developing upstream pole 104, it is preferable to achieve this by making the absolute value and half-width of the normal component Br of the magnetic flux density of the first developing downstream pole 106 smaller than the normal component Br of the magnetic flux density of the first developing upstream pole 104 of the first developing roller 30. For the above reasons, this embodiment adopts a configuration in which φ1 > φ2 is satisfied as a preferred example.

Specific explanation follows. With regard to the first developing roller 30, the angle φ2 between the peak positions of the magnetic flux densities Br of the first developing pole 105 and the first developing downstream pole 106 is smaller than the angle φ1 between the peak positions of the magnetic flux densities Br of the first developing pole 105 and the first developing upstream pole 104 of the first magnet 36. This configuration increases the distance between the first developing downstream pole 106 and the second developing upstream pole 202. This makes it difficult for a magnetic field to be generated between the magnetic poles 105 and 202, suppressing the movement of developer between the magnetic poles 105 and 202 and making it more difficult for streaky fogging to occur. Therefore, the angle φ2 between the peak positions of the magnetic flux densities Br of the first developing pole 105 and the first developing downstream pole 106 is preferably set to 40° or less (φ2≦40°), more preferably 35° or less (φ2≦35°). However, from the perspective of ensuring sufficient volume for the magnets (pieces of second magnet 37) that contribute to the formation of the magnetic field at each magnetic pole, angle φ2 is preferably set to 15° or greater (15°≦φ2), and more preferably 20° or greater (20°≦φ2). In summary, angle φ2 preferably satisfies 15°≦φ2≦40°, and more preferably satisfies 20°≦φ2≦35°.

On the other hand, from the perspective of ensuring the developability mentioned above, it is preferable that the angle φ1 between the peak positions of the magnetic flux densities Br of the first development pole 105 and the first development upstream pole 104 of the first magnet 36 not be too small. The angle φ1 between the peak positions of the magnetic flux densities Br of the first development pole 105 and the first development upstream pole 104 of the first magnet 36 is preferably 25° or greater (25°≦φ1), and more preferably 30° or greater (30°≦φ1). On the other hand, if the angle φ1 is made too large, there is a risk that the proportion of the magnetic field lines extending from the first development pole 105 that extend to the first development upstream pole 104 will decrease. For this reason, the angle φ1 is preferably 50° or less (φ1≦50°), and more preferably 45° or less (φ1≦45°). In summary, the angle φ1 preferably satisfies 25°≦φ1≦50°, and more preferably satisfies 30°≦φ1≦45°.

As in this embodiment, when the angle φ2 between the peak positions of the first developing downstream pole 106 and the first developing pole 105 becomes smaller, it becomes more difficult for a magnetic field to be generated between the first developing downstream pole 106 and the second developing upstream pole 202, while the magnetic field lines become more likely to extend between the first developing downstream pole 106 and the first developing pole 105. To achieve the effect of improving developability as described above, it is preferable to make it easier for the magnetic field lines to extend between the first developing pole 105 and the first developing upstream pole 104. Therefore, in this embodiment, the maximum absolute value of the normal component Br of the magnetic flux density of the first developing upstream pole 104 is set to be 10 mT or more larger than the maximum absolute value of the normal component Br of the magnetic flux density of the first developing downstream pole 106. It is more preferable to set it to be 15 mT or more larger, and even more preferable to set it to be 20 mT or more larger. That is, the maximum absolute value of the normal component Br of the magnetic flux density of the first upstream developing pole 104 is preferably 10 mT or more greater than the maximum absolute value of the normal component Br of the magnetic flux density of the first downstream developing pole 106, more preferably 15 mT or more greater, and even more preferably 20 mT or more greater. To prevent the magnetic poles 104 and 106 from affecting the developer transport performance, it is preferable to set the maximum absolute value of the normal component Br of the magnetic flux density of each of the magnetic poles 104 and 106 to 20 mT or more. Therefore, it is preferable to set the maximum absolute value of the normal component Br of the magnetic flux density of the first upstream developing pole 104 to 30 mT or more, thereby satisfying the above-mentioned relationship between the magnetic flux densities of the first upstream developing pole 104 and the first downstream developing pole 106.

However, in terms of the balance of magnetic flux densities, it is undesirable to increase the maximum absolute values of the normal components of the magnetic flux density of the first upstream developing pole 104 and the first downstream developing pole 106 to be greater than the maximum absolute value of the normal component of the magnetic flux density, |Br|, of the first upstream developing pole 104. For this reason, the absolute value of the difference between the maximum absolute value of the normal component Br of the magnetic flux density of the first upstream developing pole 104 and the maximum absolute value of the normal component Br of the magnetic flux density of the first downstream developing pole 106 is preferably kept within 100 mT, more preferably within 50 mT. Furthermore, in consideration of manufacturing stability and cost, it is preferable to keep the maximum absolute value of the normal component Br of the magnetic flux density of each of the magnetic poles 104, 105, and 106 to 200 mT or less, so as to satisfy the magnitude relationship between the magnetic flux densities of the first upstream developing pole 104 and the first downstream developing pole 106. In the following description, the maximum absolute value |Br| of the normal component of the magnetic flux density may be simply referred to as the absolute value |Br| of the normal component of the magnetic flux density.
[Comparative Examples and Examples]

Next, the configuration of this embodiment will be explained in more detail using the magnetic flux density distributions of Comparative Example 1 and Examples 1 and 2. Note that the Comparative Example has the same configuration as the Examples except for the items described below.

FIG. 10(a) is a graph showing the magnetic flux density distribution of the first developing roller 30 according to Comparative Example 1, and FIG. 10(b) is a graph showing the magnetic flux density distribution of the second developing roller 31 according to Comparative Example 1. FIG. 11(a) is a graph showing the magnetic flux density distribution of the first developing roller 30 according to Example 1, and FIG. 11(b) is a graph showing the magnetic flux density distribution of the second developing roller 31 according to Example 1. FIG. 12(a) is a graph showing the magnetic flux density distribution of the first developing roller 30 according to Example 2, and FIG. 12(b) is a graph showing the magnetic flux density distribution of the second developing roller 31 according to Example 2. 10(a), 11(a), and 12(a) schematically show, with a solid line, the distribution of the normal component Br of the magnetic flux density (magnetic flux density Br in the direction normal to the outer peripheral surface of the first sleeve 33) on the first sleeve 33 due to the first magnet 36, and with a dashed line, the distribution of the tangential component Bθ of the magnetic flux density (magnetic flux density Bθ in the direction tangential to the outer peripheral surface of the first sleeve 33). Also, in FIGS. 10(b), 11(b), and 12(b), the distribution of the normal component Br of the magnetic flux density on the second sleeve 34 due to the second magnet 37 is schematically shown with a solid line, and the distribution of the tangential component Bθ of the magnetic flux density is shown with a dashed line.

The normal component Br of the magnetic flux density, more precisely, refers to the component of the magnetic flux density B normal to the first sleeve 33 and the second sleeve 34 (magnetic flux density in the normal direction to the outer circumferential surfaces of the first and second rotating bodies). The normal component Br of the magnetic flux density of each magnet was measured using a magnetic field measuring device (F.W. BELL MS-9902) with the distance between the probe, a component of the magnetic field measuring device, and the surface of the first sleeve 33 and the second sleeve 34 set at approximately 100 μm.

Furthermore, the tangential component Bθ of the magnetic flux density refers to the tangential component of the magnetic flux density B with respect to the first sleeve 33 and the second sleeve 34 (the magnetic flux density in the tangential direction with respect to the outer circumferential surfaces of the first rotating body and the second rotating body). The tangential component Bθ of the magnetic flux density can be calculated from the following equation 1 using the value of the normal component Br of the magnetic flux density.

Table 1 below shows the absolute value |Br| and half-width of the normal component of the magnetic flux density of the first upstream developing pole 104, the first downstream developing pole 105, and the first magnet 36 of the first developing roller 30 in Comparative Example 1, Examples 1, and 2, the angle φ1 between the peak positions of the first upstream developing pole 104, and the angle φ2 between the peak positions of the first downstream developing pole 106 and the first magnet 36 of the first developing roller 36 in Comparative Example 1, Examples 1, and 2. The first magnet 36 used in each of the first developing rollers 30 in Comparative Example 1, Examples 1, and 2 is the same, and all values are the same.

Table 2 below shows the absolute value |Br| and half-width of the normal component of the magnetic flux density of the second development upstream pole 202, the second development pole 203, and the second development downstream pole 204 of the second magnet 37 of the second developing roller 31 in Comparative Example 1 and Examples 1 and 2, the angle θ1 between the peak positions of the second development pole 203 and the second development upstream pole 202, and the angle θ2 between the peak positions of the second development pole 203 and the second development downstream pole 204.

In order to clarify the differences in magnetic flux density of the second developing roller 31, Figure 13 shows the distribution of the normal component Br of the magnetic flux density for Comparative Example 1, Example 1, and Example 2. Furthermore, Figure 14 shows the distribution of the tangential component Bθ of the magnetic flux density for Comparative Example 1, Example 1, and Example 2.

In the magnetic flux density distribution of the first developing roller 30 of Comparative Example 1 shown in Figure 10(a) and Table 1, the absolute value |Br| of the normal component of the magnetic flux density of the first upstream developing pole 104 is greater than the absolute value |Br| of the normal component of the magnetic flux density of the first downstream developing pole 106. Also, in the magnetic flux density distribution of the second developing roller 31 of Comparative Example 1 shown in Figure 10(b) and Table 2, the absolute value |Br| of the normal component of the magnetic flux density of the second upstream developing pole 202 is smaller than the absolute value |Br| of the normal component of the magnetic flux density of the second downstream developing pole 204. Therefore, it is possible to keep the absolute value |Br| of the normal component of the magnetic flux density of each of the first downstream developing pole 106 and the second upstream developing pole 202 low, thereby preventing streaky fogging.

In this regard, the magnetic flux density distributions of the first developing roller 30 in Examples 1 and 2 shown in Figures 11(a), 12(a) and Table 1, and the magnetic flux density distributions of the second developing roller 31 in Examples 1 and 2 shown in Figures 11(b), 12(b) and Table 2, are similar to those in Comparative Example 1. Therefore, in Examples 1 and 2 as well, it is possible to keep low the absolute value |Br| of the normal component of the magnetic flux density of each of the first developing downstream pole 106 and the second developing upstream pole 202, thereby preventing streaky fogging.

In order to more reliably prevent the occurrence of streaky fogging, it is preferable to keep the absolute value |Br| of the normal component of the magnetic flux density of the first developing downstream pole 106 and the second developing upstream pole 202 at 100 mT or less, and more preferably 90 mT or less. However, since a value less than 20 mT may affect the transportability of the developer, it is preferable to keep it at 20 mT or more.

Continuing with the explanation of Comparative Example 1. As mentioned above, if the absolute value |Br| of the normal component of the magnetic flux density of the first upstream developing pole 104 of the first developing roller 30 is made larger than the absolute value |Br| of the normal component of the magnetic flux density of the first downstream developing pole 106, the occurrence of streak-like fogging is suppressed, but carrier adhesion to the first developing roller 30 becomes more likely to occur. For this reason, it is necessary for the second developing roller 31 to sufficiently recover carrier adhesion to the photosensitive drum 28Y on the first developing roller 30. However, the configuration of the second developing roller 31 in Comparative Example 1 is considered to be insufficient.

As already mentioned, to reduce the likelihood of carrier adhesion, it is preferable for the developer to contact the opposing portion of the developing pole facing the sleeve on the upstream side of the photosensitive drum 28Y, but not on the downstream side. To achieve this configuration, not only is the absolute value |Br| of the normal component of the magnetic flux density of the second upstream developing pole 202 made smaller than the absolute value |Br| of the normal component of the magnetic flux density of the second downstream developing pole 204, but the angle θ2 between the peak positions of the second downstream developing pole 204 and the second upstream developing pole 202 should be made smaller than the angle θ1 between the peak positions of the second downstream developing pole 204 and the second upstream developing pole 202. This increases the proportion of the magnetic field lines extending from the second downstream developing pole 204 that extend to the second downstream developing pole 204, and the magnetic field lines extend downstream while winding further upstream, making it easier for the magnetic brush to contact the opposing portion of the second downstream developing pole 203 on the upstream side of the photosensitive drum 28Y.

Furthermore, if the angle θ2 is reduced downstream of the photosensitive drum 28Y relative to the portion facing the second developing pole 203 via the second sleeve 34, the magnetic brush moves in a manner that quickly folds, making it less likely for the magnetic brush to come into contact downstream of the photosensitive drum 28Y. However, in the magnetic flux density distribution of the second developing roller 31 of Comparative Example 1 shown in Figure 10(b) and Table 2, the angle θ2 between the peak positions of the second developing pole 203 and the second developing downstream pole 204 is larger than the angle θ1 between the peak positions of the second developing pole 203 and the second developing upstream pole 202. For this reason, this is not necessarily sufficient to recover carrier adhesion on the first developing roller 30. As a result, while the configuration of Comparative Example 1 can suppress the occurrence of streaky fogging, it cannot sufficiently suppress the occurrence of carrier adhesion.

On the other hand, in the magnetic flux density distribution of the second developing roller 31 of Example 1 shown in Figures 11(b), 13, and Table 2, the angle θ2 between the peak positions of the second developing pole 203 and the second developing downstream pole 204 is smaller than the angle θ1 between the peak positions of the second developing pole 203 and the second developing upstream pole 202. As a result, a greater proportion of the magnetic field lines extending from the second developing pole 203 extend to the second developing downstream pole 204, making it easier for the magnetic wires to contact the opposing portion of the second developing pole 203 facing the second sleeve 34 on the upstream side of the photosensitive drum 28Y. Meanwhile, the magnetic wires quickly fold on the downstream side of the photosensitive drum 28Y, making it more difficult for them to contact the opposing portion on the downstream side of the photosensitive drum 28Y. Therefore, in Example 1, carrier adhesion on the first developing roller 30 can be sufficiently recovered by the second developing roller 31. As a result, the configuration of Example 1 is able to simultaneously suppress the occurrence of streak-like fogging and carrier adhesion.

To more reliably suppress carrier adhesion, it is preferable to limit the angle θ2 between the peak positions of the second developing pole 203 and the second downstream developing pole 204 to 30° or less (θ2≦30°), and more preferably 28° or less (θ2≦28°). This configuration effectively prevents contact of the magnetic brush on the downstream side of the photosensitive drum 28Y with the opposing portion of the second developing pole 203 facing the second sleeve 34. However, if the angle θ2 is less than 15°, it becomes difficult to ensure sufficient volume for the magnets (pieces of the second magnet 37) that contribute to the magnetic field formation of each magnetic pole, raising concerns that sufficient magnetic flux density may not be ensured. For this reason, it is preferable to set the angle θ2 to 15° or more (15°≦θ2), and more preferably 20° or more (20°≦θ2). In summary, it is preferable for the angle θ2 to satisfy 15°≦θ2≦30°, and even more preferable for it to satisfy 20°≦θ2≦28°.

On the other hand, if the angle θ1 between the peak positions of the second developing pole 203 and the second developing upstream pole 202 is made too large, the second developing upstream pole 202 will move closer to the first developing downstream pole 106, which is unfavorable for the occurrence of streaky fogging. For this reason, it is preferable to keep the angle θ1 between the peak positions of the second developing pole 203 and the second developing upstream pole 202 to 35° or less (θ1≦35°), and more preferably 30° or less (θ1≦30°). However, from the perspective of ensuring sufficient volume for the magnets (pieces of the second magnet 37) that contribute to the formation of the magnetic field at each magnetic pole, it is preferable to set the angle θ1 to 15° or more (15°≦θ1), and more preferably 20° or more (20°≦θ1). In summary, it is preferable for the angle θ1 to satisfy 15°≦θ1≦35°, and even more preferably 20°≦θ1≦30°.

Next, we will discuss Example 2. The magnetic flux density distribution of the second developing roller 31 in Example 2, shown in Figures 12(b), 13, and Table 2, has a larger absolute value |Br| of the normal component of the magnetic flux density of the second developing downstream pole 204 compared to Example 1. As a result, the proportion of the magnetic field lines extending from the second developing pole 203 that extend to the second developing downstream pole 204 is greater than in Example 1, making it easier for the magnetic wires to contact the opposing portion of the second developing pole 203 facing the second sleeve 34 on the upstream side of the photosensitive drum 28Y, thereby further suppressing the occurrence of carrier adhesion. To achieve a greater effect in suppressing carrier adhesion, it is preferable to make the absolute value |Br| of the normal component of the magnetic flux density of the second developing downstream pole 204 10 mT or more greater than the absolute value |Br| of the normal component of the magnetic flux density of the second developing upstream pole 202, more preferably 15 mT or more, and even more preferably 20 mT or more. That is, the maximum absolute value of the normal component Br of the magnetic flux density of the second downstream developing pole 204 is preferably 10 mT or more, more preferably 15 mT or more, and even more preferably 20 mT or more, greater than the maximum absolute value of the normal component Br of the magnetic flux density of the second upstream developing pole 202. To prevent the magnetic poles 202, 204 from affecting the developer transport performance, it is preferable to set the maximum absolute value of the normal component Br of the magnetic flux density of each magnetic pole 202, 204 to 20 mT or more. Therefore, it is preferable to set the maximum absolute value of the normal component Br of the magnetic flux density of the second downstream developing pole 204 to 30 mT or more, thereby satisfying the above-mentioned relationship between the magnetic flux densities of the second upstream developing pole 202 and the second downstream developing pole 204.

In Example 2, as shown in Table 2, the absolute value |Br| of the normal component of the magnetic flux density of the second developing downstream pole 204 is set to be 20 mT or more greater than the absolute value |Br| of the normal component of the magnetic flux density of the second developing upstream pole 202. However, it is not desirable in terms of the balance of magnetic flux densities to make the maximum absolute values of the normal components of the magnetic flux density of the second developing upstream pole 202 and the second developing downstream pole 204 greater than the maximum absolute value |Br| of the normal component of the magnetic flux density of the second developing pole 203. For this reason, the absolute value of the difference between the maximum absolute value of the normal component Br of the magnetic flux density of the second developing upstream pole 202 and the maximum absolute value of the normal component Br of the magnetic flux density of the second developing downstream pole 204 is preferably kept within 100 mT, and more preferably within 50 mT. Furthermore, considering manufacturing stability and costs, it is preferable to limit the maximum absolute value of the normal component Br of the magnetic flux density of each magnetic pole 202, 203, 204 to 200 mT or less, and to satisfy the magnitude relationship between the magnetic flux densities of the second upstream developing pole 202 and the second downstream developing pole 204 described above.

As mentioned above, to address carrier adhesion on the second developing roller 31, it is important to increase the proportion of magnetic field lines extending from the second developing pole 203 that extend to the second developing downstream pole 204 rather than the second developing upstream pole 202, and to have the magnetic brush contact the photosensitive drum 28Y as upstream as possible. The proportion of magnetic field lines extending from the second developing pole 203 that extend to each of the second developing upstream pole 202 and the second developing downstream pole 204 is primarily determined by the relationship between the maximum absolute value |Br| of the normal component of the magnetic flux density of the second developing upstream pole 202 and the second developing downstream pole 204, the half-width, and the angles θ1 and θ2 between the peak positions with the second developing pole 203.

In the configurations of Examples 1 and 2, the maximum value |Br| of the absolute value of the normal component of the magnetic flux density of the second developing downstream pole 204 is set larger than the maximum value |Br| of the absolute value of the normal component of the magnetic flux density of the second developing upstream pole 202. Also, the angle θ2 between the peak positions of the second developing pole 203 and the second developing downstream pole 204 is set smaller than the angle θ1 between the peak positions of the second developing pole 203 and the second developing upstream pole 202. Furthermore, the half-width of the normal component Br of the magnetic flux density of the second developing downstream pole 204 is set larger than the half-width of the normal component Br of the magnetic flux density of the second developing upstream pole 202.

The proportion of the magnetic field lines extending from the second developing pole 203 to the second developing upstream pole 202 and the second developing downstream pole 204 can be predicted from the distribution of the tangential component Bθ of the magnetic flux density. Figures 10(b), 11(b), 12(b), 13 and 14 show the magnetic flux density distribution of the second developing roller 31. Between the peak positions of the normal component Br between the second developing pole 203 and the second developing upstream pole 202 and the second developing downstream pole 204, there are peaks (maximum values) Bθ2-1 and Bθ2-2 of the tangential component Bθ. It is believed that the larger the peak of the tangential component Bθ, the more magnetic field lines there are. Therefore, by comparing the magnitude (absolute value) of the peaks Bθ2-1 and Bθ2-2 of the tangential component Bθ of the magnetic flux density upstream and downstream of the second developing pole 203, it is possible to predict the proportion of the magnetic field lines extending from the second developing pole 203 to the second developing upstream pole 202 and the second developing downstream pole 204.

The right side of Table 3 below shows the absolute values |Bθ2-1| and |Bθ2-2| of the peaks of the tangential component Bθ of the magnetic flux density upstream and downstream of the second developing pole 203 for Comparative Example 1, Example 1, and Example 2. Table 3 also shows the ratio |Bθ2-2|/|Bθ2-1| of the absolute value of the downstream peak to the absolute value of the upstream peak. |Bθ2-1| is the maximum absolute value of the magnetic flux density in the tangential direction to the outer peripheral surface of the second sleeve 34 in the section in the rotational direction of the second sleeve 34 from the position on the outer peripheral surface of the second sleeve 34 where the absolute value of the magnetic flux density of the second developing upstream pole 202 in the normal direction to the outer peripheral surface of the second sleeve 34 is maximum to the position on the outer peripheral surface of the second sleeve 34 where the absolute value of the magnetic flux density of the second developing pole 203 in the normal direction to the outer peripheral surface of the second sleeve 34 is maximum. Furthermore, |Bθ2-2| is the maximum absolute value of the magnetic flux density in the tangential direction to the outer peripheral surface of the second sleeve 34 in the section in the rotational direction of the second sleeve 34 from the position on the outer peripheral surface of the second sleeve 34 where the absolute value of the magnetic flux density of the second developing pole 203 in the normal direction to the outer peripheral surface of the second sleeve 34 is maximum to the position on the outer peripheral surface of the second sleeve 34 where the absolute value of the magnetic flux density of the second developing pole 204 in the normal direction to the outer peripheral surface of the second sleeve 34 is maximum. It can be said that the larger this value, the greater the proportion of the magnetic field lines extending from the second developing pole 203 that extend toward the second developing pole downstream 204 rather than toward the second developing pole upstream 202. Note that information regarding the first developing roller 30 is also listed on the left side of Table 3, which will be described later.

In Comparative Example 1, |Bθ2-2|/|Bθ2-1| was 1.08. From this, it can be said that in Comparative Example 1 as well, a greater proportion of the magnetic lines of force extending from the second developing pole 203 extend to the second developing downstream pole 204 than to the second developing upstream pole 202. However, as mentioned above, there is concern that the configuration of Comparative Example 1 may make carrier adhesion more likely to occur. This is thought to be because |Bθ2-2|/|Bθ2-1| in Comparative Example 1 was small at 1.08 times, leaving concerns that carrier adhesion caused by the first developing roller 30 may not be sufficiently recovered.

On the other hand, according to Figure 14 and Table 3, in Example 1, |Bθ2-1| decreased slightly and |Bθ2-2| increased compared to Comparative Example 1, and |Bθ2-2|/|Bθ2-1| was 1.15. As a result, it is thought that in Example 1, the proportion of magnetic field lines extending from the second developing pole 203 that extended toward the second developing downstream pole 204 rather than the second developing upstream pole 202 was higher than in Comparative Example 1. This is thought to have made carrier adhesion less likely to occur, as described above.

According to Figure 14 and Table 3, in Example 2, |Bθ2-1| was further reduced and |Bθ2-2| was further increased compared to Example 1, with |Bθ2-2|/|Bθ2-1| being 1.34. As a result, it is believed that in Example 2, the proportion of the magnetic field lines extending from the second developing pole 203 that extend toward the second developing downstream pole 204 rather than the second developing upstream pole 202 was further increased compared to Example 1. For this reason, it is believed that, as mentioned above, carrier adhesion was even less likely to occur.

From the above, it is preferable to adjust the relationship between the absolute value |Br| of the normal component of the magnetic flux density of the second upstream developing pole 202 and the second downstream developing pole 204, the half-width, and the angle θ between the peak positions with the second developing pole 203 so that |Bθ2-2|/|Bθ2-1| is 1.10 or greater, more preferably 1.15 or greater, and even more preferably 1.30 or greater. That is, on the second sleeve 34, the absolute value of the magnitude at which the tangential component of the magnetic flux density between the second upstream developing pole 202 and the second upstream developing pole 202 reaches its maximum (peak) in the direction of rotation of the second sleeve 34 is defined as |Bθ2-1|. Furthermore, the absolute value of the magnitude at which the tangential component of the magnetic flux density between the second downstream developing pole 203 and the second downstream developing pole 204 reaches its maximum (peak) in the direction of rotation of the second sleeve 34 is defined as |Bθ2-2|. In this case, the relationship |Bθ2-2|/|Bθ2-1|≧1.1 should be satisfied. It is also preferable to satisfy |Bθ2-2|/|Bθ2-1|≧1.15, and it is even more preferable to satisfy |Bθ2-2|/|Bθ2-1|≧1.30. The larger |Bθ2-2|/|Bθ2-1| is, the greater the effect of suppressing carrier adhesion, but it is not preferable for it to be 10.0 or more in terms of developer transport balance. Therefore, it is preferable to satisfy |Bθ2-2|/|Bθ2-1|<10.0.

Next, Example 3 and Comparative Example 2 will be described using Figures 15(a) to 16(b). Figure 15(a) is a graph showing the magnetic flux density distribution of the first developing roller 30 according to Example 3, and Figure 15(b) is a graph showing the magnetic flux density distribution of the second developing roller 31 according to Example 3. Figure 16(a) is a graph showing the magnetic flux density distribution of the first developing roller 30 according to Comparative Example 2, and Figure 16(b) is a graph showing the magnetic flux density distribution of the second developing roller 31 according to Comparative Example 2.

In Figures 15(a) and 16(a), the distribution of the normal component Br of the magnetic flux density on the first sleeve 33 due to the first magnet 36 is shown schematically by a solid line, and the distribution of the tangential component Bθ of the magnetic flux density is shown schematically by a dashed line. In Figures 15(b) and 16(b), the distribution of the normal component Br of the magnetic flux density on the second sleeve 34 due to the second magnet 37 is shown schematically by a solid line, and the distribution of the tangential component Bθ of the magnetic flux density is shown schematically by a dashed line.

Furthermore, Table 4 below, like Table 1, shows the absolute value |Br| and half-width of the normal component of the magnetic flux density of the first development upstream pole 104, the first development pole 105, and the first development downstream pole 106 of the first magnet 36 of the first developing roller 30 in Example 3 and Comparative Example 2, the angle φ1 between the peak positions of the first development pole 105 and the first development upstream pole 104, and the angle φ2 between the peak positions of the first development pole 105 and the first development downstream pole 106.

In order to clarify the differences in magnetic flux density of the first developing roller 30, Figure 17 shows the distribution of the normal component Br of the magnetic flux density for Example 1, Example 3, and Comparative Example 2. Furthermore, Figure 18 shows the distribution of the tangential component Bθ of the magnetic flux density for Example 1, Example 3, and Comparative Example 2.

Similar to Table 2, Table 5 below shows the absolute value |Br| and half-width of the normal component of the magnetic flux density of the second upstream developing pole 202, second downstream developing pole 203, and second magnet 37 of the second developing roller 31 in Example 3 and Comparative Example 2, the angle θ1 between the peak positions of the second upstream developing pole 202, and the angle θ2 between the peak positions of the second downstream developing pole 204. Note that the second magnet 37 used in each second developing roller 31 in Example 3 and Comparative Example 2 is the same as that in Example 1, and all values are the same.

Figures 15(a) and 16(a) show the magnetic flux density distribution of the first developing roller 30.

Peaks (maximum values) Bθ1-1 and Bθ1-2 of the tangential component Bθ are present between the peak positions of the normal component Br between the first developing pole 105 and the first developing upstream pole 104 and the first developing downstream pole 106. The left side of Table 3 and the following Table 6 show the absolute values |Bθ1-1| and |Bθ1-2| of the peaks of the tangential component Bθ of the magnetic flux density upstream and downstream of the first developing pole 105 in Comparative Examples 1 and 2 and Examples 1, 2 and 3. |Bθ1-1| is the maximum absolute value of the magnetic flux density in the tangential direction to the outer surface of the first sleeve 33 in the section in the rotational direction of the first sleeve 33 from the position on the outer surface of the first sleeve 33 where the absolute value of the magnetic flux density of the first developing upstream pole 104 in the normal direction to the outer surface of the first sleeve 33 is maximum to the position on the outer surface of the first sleeve 33 where the absolute value of the magnetic flux density of the first developing pole 105 in the normal direction to the outer surface of the first sleeve 33 is maximum. Furthermore, |Bθ1-2| is the maximum absolute value of the magnetic flux density in the tangential direction to the outer peripheral surface of the first sleeve 33 in the section in the rotational direction of the first sleeve 33 from the position on the outer peripheral surface of the first sleeve 33 where the absolute value of the magnetic flux density of the first developing pole 105 in the normal direction to the outer peripheral surface of the first sleeve 33 is maximum to the position on the outer peripheral surface of the first sleeve 33 where the absolute value of the magnetic flux density of the first developing pole downstream 106 in the normal direction to the outer peripheral surface of the first sleeve 33 is maximum. Tables 3 and 6 also show the ratio of the absolute value of the upstream peak to the absolute value of the downstream peak, |Bθ1-1|/|Bθ1-2|. Based on the same considerations as those described above for the second developing roller 31, it can be said that the larger this value, the greater the proportion of the magnetic field lines extending from the first developing pole 105 that extend toward the first developing pole upstream 104 rather than the first developing pole downstream 106. As in Table 3, the right side of Table 6 also shows the absolute values |Bθ2-1|, |Bθ2-2| of each peak of the tangential component Bθ of the magnetic flux density upstream and downstream of the second development pole 203 in Example 3 and Comparative Example 2, and the ratio |Bθ2-2|/|Bθ2-1| of the absolute value of the downstream peak to the absolute value of the upstream peak.

In the first developing roller 30 of Example 3 shown in Figures 15(a), 17, and Table 4, the absolute value |Br| of the normal component of the magnetic flux density of the first developing downstream pole 106 is larger than in Example 1 (Table 1). This increases the concern about the occurrence of streak-like fogging. However, in Example 3, the absolute value |Br| of the normal component of the magnetic flux density of the first developing upstream pole 104 is maintained to be larger than the absolute value |Br| of the normal component of the magnetic flux density of the first developing downstream pole 106, so it is possible to just barely achieve both the suppression of streak-like fogging and the suppression of carrier adhesion.

However, according to the inventors' investigations, it was found that Example 3 had slightly inferior developability compared to Example 1, although the practical impact was small. This is thought to be due to the following reason. The |Bθ1-1|/|Bθ1-2| ratio for Example 3 shown in Figure 18 and Table 6 is 1.00. This means that the ratio of magnetic field lines extending from the first developing pole 105 to the first developing upstream pole 104 and the magnetic field lines extending to the first developing downstream pole 106 is approximately the same.

On the other hand, |Bθ1-1|/|Bθ1-2| for Example 1 shown in Figure 18 and Table 3 is 1.09. This means that the proportion of magnetic field lines extending from the first developing pole 105 to the first developing upstream pole 104 is greater than the proportion of magnetic field lines extending to the first developing downstream pole 106. As a result, in the configuration of Example 1, the magnetic brush extends toward the downstream side of the photosensitive drum 28Y. As mentioned above, when the magnetic brush faces downstream, the time that the magnetic brush is in contact with the photosensitive drum 28Y increases, increasing the time for toner development on the photosensitive drum 28Y, which has the advantage of being beneficial to developability. This advantage is no longer available in the configuration of Example 3, and it is therefore believed that developability is inferior to that of Example 1.

In the first developing roller 30 of Comparative Example 2 shown in Figures 16(a), 17, and Table 4, the absolute value |Br| of the normal component of the magnetic flux density of the first developing downstream pole 106 is even larger than in Examples 1 and 3. This further increases concerns about the occurrence of streaky fog, and when images are actually formed with the configuration of Comparative Example 2, streaky fog sometimes occurred. The configuration of Comparative Example 2 does not maintain a configuration in which the absolute value |Br| of the normal component of the magnetic flux density of the first developing upstream pole 104 is larger than the absolute value |Br| of the normal component of the magnetic flux density of the first developing downstream pole 106. Furthermore, the absolute value |Br| of the normal component of the magnetic flux density of the first developing downstream pole 106 is greater than 100 mT. This is thought to be why streaky fog occurred in Comparative Example 2.

Furthermore, the configuration of Comparative Example 2 was less likely to cause carrier adhesion compared to Examples 1 and 3, but the developability was reduced. The |Bθ1-1|/|Bθ1-2| ratio for Comparative Example 2 shown in Figure 18 and Table 6 is 0.96. This means that the proportion of magnetic field lines extending to the first downstream developing pole 106 is greater than the proportion of magnetic field lines extending from the first upstream developing pole 104 to the first downstream developing pole 105. This is thought to be why the magnetic chains tend to extend upstream of the photosensitive drum 28Y, preventing the developability benefits of the magnetic chains extending downstream, resulting in reduced developability.

From the above, the ratio |Bθ1-1|/|Bθ1-2|, which is the ratio of the absolute value of the upstream peak of the tangential component Bθ of the magnetic flux density of the first developing roller 30 to the absolute value of the downstream peak of the first developing pole 105, is preferably 1.00 or greater as in Example 3, and more preferably 1.05 or greater as in Example 1. That is, it is preferable to satisfy |Bθ1-1|/|Bθ1-2|≧1.0, and it is even more preferable to satisfy |Bθ1-1|/|Bθ1-2|≧1.05. However, while the greater the effect, the greater the increase in |Bθ1-1|/|Bθ1-2|, it is not preferable to set it to 10.0 or greater due to the balance of development and transport. Therefore, it is preferable to satisfy |Bθ1-1|/|Bθ1-2|<10.0.

Next, Example 4 will be described using Figures 19(a) and (b). Figure 19(a) is a graph showing the magnetic flux density distribution of the first developing roller 30 according to Example 4, and Figure 19(b) is a graph showing the magnetic flux density distribution of the second developing roller 31 according to Example 4. Figure 19(a) schematically shows the distribution of the normal component Br of the magnetic flux density on the first sleeve 33 due to the first magnet 36 using a solid line, and the distribution of the tangential component Bθ of the magnetic flux density using a dashed line. Figure 19(b) also schematically shows the distribution of the normal component Br of the magnetic flux density on the second sleeve 34 due to the second magnet 37 using a solid line, and the distribution of the tangential component Bθ of the magnetic flux density using a dashed line.

In addition, Table 7 below, similar to Tables 1 and 4, shows the absolute value |Br| and half-width of the normal component of the magnetic flux density of the first developing upstream pole 104, the first developing pole 105, and the first developing downstream pole 106 of the first magnet 36 of the first developing roller 30 in Example 4, the angle φ1 between the peak positions of the first developing pole 105 and the first developing upstream pole 104, and the angle φ2 between the peak positions of the first developing pole 105 and the first developing downstream pole 106.

In order to clarify the difference in magnetic flux density of the first developing roller 30, Figure 20 shows the distribution of the normal component Br of the magnetic flux density in Examples 1 and 4. Furthermore, Figure 21 shows the distribution of the tangential component Bθ of the magnetic flux density in Examples 1 and 4.

Similar to Tables 2 and 5, Table 8 below shows the absolute value |Br| and half-width of the normal component of the magnetic flux density of the second upstream developing pole 202, the second downstream developing pole 203, and the second magnet 37 of the second developing roller 31 in Example 4, the angle θ1 between the peak positions of the second upstream developing pole 202, and the angle θ2 between the peak positions of the second downstream developing pole 204. The second magnet 37 of the second developing roller 31 in Example 4 is the same as that in Examples 1 and 3, and all values are the same. Therefore, similar to Examples 1 and 3, carrier adhesion is less likely to occur.

Similar to Tables 3 and 6, Table 9 below shows the absolute values |Bθ1-1|, |Bθ1-2| of each peak of the tangential component Bθ of the magnetic flux density upstream and downstream of the first developing pole 105 in Example 4, and the ratio |Bθ1-1|/|Bθ1-2| of the absolute value of the upstream peak to the absolute value of the downstream peak. Table 9 also shows the absolute values |Bθ2-1|, |Bθ2-2| of each peak of the tangential component Bθ of the magnetic flux density upstream and downstream of the second developing pole 203 in Example 4, and the ratio |Bθ2-2|/|Bθ2-1| of the absolute value of the downstream peak to the absolute value of the upstream peak.

As shown in Figure 20 and Table 7, the configuration of Example 4 reduces the angle φ2 between the peak positions of the first developing pole 105 and the first developing downstream pole 106 of the first developing roller 30 compared to Example 1 (see Tables 1 and 7). In this case, the angle φ2 between the peak positions of the first developing pole 105 and the first developing downstream pole 106 of the first developing roller 30 is smaller than the angle θ2 between the peak positions of the second developing pole 203 and the second developing downstream pole 204 of the second developing roller 31 (θ2 > φ2). As a result, in Example 4, the first developing downstream pole 106 is positioned away from the second developing upstream pole 202 compared to Example 1, which has the advantage of weakening the magnetic field between the two poles and further suppressing the occurrence of streaky fogging.

On the other hand, if the angle φ2 between the peak positions of the first developing pole 105 and the first developing downstream pole 106 of the first developing roller 30 is reduced, the magnetic field lines will be more likely to extend from the first developing pole 105 to the first developing downstream pole 106. For this reason, reducing the angle φ2 between the peak positions of the first developing pole 105 and the first developing downstream pole 106 of the first developing roller 30 can be a disadvantage in terms of developability.

However, as shown in Figure 20 and Table 7, in the first developing roller 30 of Example 4, the absolute value |Br| of the normal component of the magnetic flux density of the first upstream developing pole 104 is greater than the absolute value |Br| of the normal component of the magnetic flux density of the first downstream developing pole 106 by 15 mT or more. Therefore, as shown in Table 9, |Bθ1-1|/|Bθ1-2| in Example 4 is 1.0 or greater, maintaining a state in which the proportion of magnetic field lines extending from the first developing pole 105 to the first upstream developing pole 104 is greater than the proportion of magnetic field lines extending from the first developing pole 105 to the first downstream developing pole 106. By adopting this configuration, Example 4 also maintains the developability benefits of the magnetic brush extending downstream of the photosensitive drum 28Y.

As in Example 4, even if the angle φ2 between the peak positions of the first developing pole 105 and the first developing downstream pole 106 of the first developing roller 30 is made smaller than the angle θ2 between the peak positions of the second developing pole 203 and the second developing downstream pole 204 of the second developing roller 31, as long as |Bθ1-1|/|Bθ1-2| is made 1.0 or greater, it is possible to suppress both carrier adhesion and the occurrence of streaky fogging, and also to obtain the benefit of improved developability.
<Other Embodiments>

The present invention is not limited to the configurations of the above-described embodiments. For example, the image forming apparatus 100 is not limited to an MFP, but may also be a copier, printer, or facsimile machine. Furthermore, the configurations of the developer supply screw 42, developer stirring screw 43, and developer recovery screw 44 are not particularly limited as long as they are capable of transporting developer; for example, spiral blades or paddle-shaped blades can be applied.

Furthermore, in the above embodiment, the first developing roller 30 is positioned upstream and the second developing roller 31 is positioned downstream with respect to the rotation direction of the photosensitive drum 28Y, but the same effect can be obtained even if the second developing roller 31 is positioned upstream and the first developing roller 30 is positioned downstream.

The present invention provides a developing device that can simultaneously suppress streak-like fogging and carrier adhesion.

The present invention is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the present invention. Therefore, the following claims are appended to clarify the scope of the present invention.

This application claims priority based on Japanese Patent Application No. 2024-107390, filed July 3, 2024, and Japanese Patent Application No. 2025-067174, filed April 16, 2025, the entire contents of which are incorporated herein by reference.

Claims (43)

a developer container containing a developer containing toner and a carrier;
a first rotating body to which the developer contained in the developing container is supplied, the first rotating body rotating in the same direction as the rotating image carrier at a position on the outer circumferential surface of the first rotating body closest to the image carrier, and carrying and transporting the developer to a first developing position where an electrostatic latent image formed on the image carrier is developed;
a first magnet disposed inside the first rotating body so as to be fixed and non-rotatable, the first magnet having: a first developing pole disposed facing the image carrier at the first developing position; a first upstream pole disposed adjacent to the first developing pole upstream of the first developing pole in the rotational direction of the first rotating body and having a polarity opposite to that of the first developing pole; a first downstream pole disposed adjacent to the first developing pole downstream of the first developing pole in the rotational direction of the first rotating body and having a polarity opposite to that of the first developing pole; and a delivery pole disposed downstream of the first downstream pole and upstream of the first upstream pole in the rotational direction of the first rotating body;
a second rotating body that is disposed opposite the first rotating body and to which the developer is transferred from the first rotating body by a magnetic field generated by the first magnet, the second rotating body rotating in the same direction as the image carrier at a position on the outer circumferential surface of the second rotating body that is closest to the image carrier, and that carries and transports the developer to a second developing position where the electrostatic latent image is developed;
a second magnet disposed inside the second rotating body so as to be fixed and non-rotatable, the second magnet having: a second developing pole disposed facing the image carrier at the second developing position; a second upstream pole disposed adjacent to the second developing pole upstream of the second developing pole in the rotational direction of the second rotating body and having a polarity opposite to that of the second developing pole; a second downstream pole disposed adjacent to the second developing pole downstream of the second developing pole in the rotational direction of the second rotating body and having a polarity opposite to that of the second developing pole; and a receiving pole disposed downstream of the second downstream pole and upstream of the second upstream pole in the rotational direction of the second rotating body and adjacent to the delivering pole and having a polarity opposite to that of the delivering pole;
Equipped with
a maximum absolute value of the magnetic flux density of the first upstream pole in a normal direction to the outer circumferential surface of the first rotor is greater than a maximum absolute value of the magnetic flux density of the first downstream pole in a normal direction to the outer circumferential surface of the first rotor,
a maximum absolute value of the magnetic flux density of the second downstream pole in a normal direction to the outer circumferential surface of the second rotor is greater than a maximum absolute value of the magnetic flux density of the second upstream pole in a normal direction to the outer circumferential surface of the second rotor,
an angle in the rotation direction of the second rotor from a position on the outer circumferential surface of the second rotor at which the absolute value of the magnetic flux density of the second upstream pole in the normal direction to the outer circumferential surface of the second rotor is maximum to a position on the outer circumferential surface of the second rotor at which the absolute value of the magnetic flux density of the second development pole in the normal direction to the outer circumferential surface of the second rotor is maximum is defined as θ1 [°];
When the angle in the rotation direction of the second rotor from the position on the outer circumferential surface of the second rotor where the absolute value of the magnetic flux density of the second developing pole in the normal direction to the outer circumferential surface of the second rotor is maximum to the position on the outer circumferential surface of the second rotor where the absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer circumferential surface of the second rotor is maximum is θ2 [°],
θ1>θ2
A developing device that meets these requirements. 2°≦θ1−θ2
2. The developing device according to claim 1, further satisfying the following: 3°≦θ1−θ2
2. The developing device according to claim 1, further satisfying the following: θ2≧θ1/2
2. The developing device according to claim 1, further satisfying the following: 15°≦θ2≦30°
2. The developing device according to claim 1, further satisfying the following: 15°≦θ1≦35°
2. The developing device according to claim 1, further satisfying the following: A developing device as described in claim 1, wherein the half-value width of the magnetic flux density of the second downstream pole in the normal direction to the outer peripheral surface of the second rotating body is greater than the half-value width of the magnetic flux density of the second upstream pole in the normal direction to the outer peripheral surface of the second rotating body. A developing device as described in claim 7, wherein the half-width of the magnetic flux density of the second downstream pole in the normal direction to the outer peripheral surface of the second rotating body is 3° or more larger than the half-width of the magnetic flux density of the second upstream pole in the normal direction to the outer peripheral surface of the second rotating body. The developing device described in claim 7, wherein the half-width of the magnetic flux density of the second downstream pole in the normal direction to the outer peripheral surface of the second rotating body is 5° or more larger than the half-width of the magnetic flux density of the second upstream pole in the normal direction to the outer peripheral surface of the second rotating body. With respect to the rotation direction of the second rotating body, the position on the outer circumferential surface of the second rotating body at which the absolute value of the magnetic flux density of the second developing pole in the normal direction to the outer circumferential surface of the second rotating body becomes maximum is
2. A developing device as described in claim 1, wherein the second rotating body is located upstream of the position on the outer surface of the second rotating body that is closest to the image carrier, and downstream of the position on the outer surface of the second rotating body where the absolute value of the magnetic flux density of the second upstream pole in the direction normal to the outer surface of the second rotating body is maximum. The developing device described in claim 10, wherein the angle in the rotational direction of the second rotating body from the position on the outer circumferential surface of the second rotating body where the absolute value of the magnetic flux density of the second developing pole in the normal direction to the outer circumferential surface of the second rotating body is maximum to the position on the outer circumferential surface of the second rotating body where the second rotating body is closest to the image carrier is 10° or less. A developing device as described in claim 1, wherein the maximum absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer circumferential surface of the second rotating body is 10 mT or more greater than the maximum absolute value of the magnetic flux density of the second upstream pole in the normal direction to the outer circumferential surface of the second rotating body. a maximum absolute value of the magnetic flux density of the second upstream pole in a normal direction to the outer circumferential surface of the second rotor is 20 mT or more and 200 mT or less,
13. The developing device according to claim 12, wherein the maximum absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer circumferential surface of the second rotating body is 30 mT or more and 200 mT or less. A developing device as described in claim 1, wherein the maximum absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer peripheral surface of the second rotating body is 15 mT or more greater than the maximum absolute value of the magnetic flux density of the second upstream pole in the normal direction to the outer peripheral surface of the second rotating body. A developing device as described in claim 1, wherein the half-value width of the magnetic flux density of the first downstream pole in the normal direction to the outer peripheral surface of the first rotating body is smaller than the half-value width of the magnetic flux density of the first upstream pole in the normal direction to the outer peripheral surface of the first rotating body. A developing device as described in claim 15, wherein the half-width of the magnetic flux density of the first downstream pole in the normal direction to the outer peripheral surface of the first rotating body is smaller by 3° or more than the half-width of the magnetic flux density of the first upstream pole in the normal direction to the outer peripheral surface of the first rotating body. A developing device as described in claim 15, wherein the half-width of the magnetic flux density of the first downstream pole in the normal direction to the outer peripheral surface of the first rotating body is smaller by 5° or more than the half-width of the magnetic flux density of the first upstream pole in the normal direction to the outer peripheral surface of the first rotating body. With respect to the rotation direction of the first rotating body, the position on the outer circumferential surface of the first rotating body at which the absolute value of the magnetic flux density of the first developing pole in the normal direction to the outer circumferential surface of the first rotating body becomes maximum is
2. A developing device as described in claim 1, wherein the first rotating body is located upstream of the position on the outer surface of the first rotating body that is closest to the image carrier, and downstream of the position on the outer surface of the first rotating body where the absolute value of the magnetic flux density of the first upstream pole in the direction normal to the outer surface of the first rotating body is maximum. an angle in the rotation direction of the first rotor from a position on the outer circumferential surface of the first rotor at which the absolute value of the magnetic flux density of the first upstream pole in the normal direction to the outer circumferential surface of the first rotor is maximum to a position on the outer circumferential surface of the first rotor at which the absolute value of the magnetic flux density of the first development pole in the normal direction to the outer circumferential surface of the first rotor is maximum is defined as φ1 [°];
When the angle in the rotation direction of the first rotor from the position on the outer circumferential surface of the first rotor where the absolute value of the magnetic flux density of the first development pole in the normal direction to the outer circumferential surface of the first rotor is maximum to the position on the outer circumferential surface of the first rotor where the absolute value of the magnetic flux density of the first downstream pole in the normal direction to the outer circumferential surface of the first rotor is set to φ2 [°],
φ1>φ2
2. The developing device according to claim 1, wherein the above formula (1) is satisfied. 15°≦φ2≦40°
20. The developing device according to claim 19, further satisfying the following: 20°≦φ2≦35°
20. The developing device according to claim 19, further satisfying the following: 25°≦φ1≦50°
20. The developing device according to claim 19, further satisfying the following: 30°≦φ1≦45°
20. The developing device according to claim 19, further satisfying the following: θ2>φ2
20. The developing device according to claim 19, further satisfying the following: When the angle in the rotation direction of the first rotor from the position on the outer circumferential surface of the first rotor where the absolute value of the magnetic flux density of the first development pole in the normal direction to the outer circumferential surface of the first rotor is maximum to the position on the outer circumferential surface of the first rotor where the absolute value of the magnetic flux density of the first downstream pole in the normal direction to the outer circumferential surface of the first rotor is set to φ2 [°],
θ2>φ2
2. The developing device according to claim 1, wherein the above formula (1) is satisfied. The developing device described in claim 1, wherein the maximum absolute value of the magnetic flux density of the first upstream pole in the normal direction to the outer peripheral surface of the first rotating body is 10 mT or more greater than the maximum absolute value of the magnetic flux density of the first downstream pole in the normal direction to the outer peripheral surface of the first rotating body. The developing device described in claim 1, wherein the maximum absolute value of the magnetic flux density of the first upstream pole in the normal direction to the outer peripheral surface of the first rotating body is 15 mT or more greater than the maximum absolute value of the magnetic flux density of the first downstream pole in the normal direction to the outer peripheral surface of the first rotating body. The developing device described in claim 1, wherein the surface linear speed of the second rotating body is faster than the surface linear speed of the first rotating body. a developer container containing a developer containing toner and a carrier;
a first rotating body to which the developer contained in the developing container is supplied, the first rotating body rotating in the same direction as the rotating image carrier at a position on the outer circumferential surface of the first rotating body closest to the image carrier, and carrying and transporting the developer to a first developing position where an electrostatic latent image formed on the image carrier is developed;
a first magnet disposed inside the first rotating body so as to be fixed and non-rotatable, the first magnet having: a first developing pole disposed facing the image carrier at the first developing position; a first upstream pole disposed adjacent to the first developing pole upstream of the first developing pole in the rotational direction of the first rotating body and having a polarity opposite to that of the first developing pole; a first downstream pole disposed adjacent to the first developing pole downstream of the first developing pole in the rotational direction of the first rotating body and having a polarity opposite to that of the first developing pole; and a delivery pole disposed downstream of the first downstream pole and upstream of the first upstream pole in the rotational direction of the first rotating body;
a second rotating body that is disposed opposite the first rotating body and to which the developer is transferred from the first rotating body by a magnetic field generated by the first magnet, the second rotating body rotating in the same direction as the image carrier at a position on the outer circumferential surface of the second rotating body that is closest to the image carrier, and that carries and transports the developer to a second developing position where the electrostatic latent image is developed;
a second magnet disposed inside the second rotating body so as to be fixed and non-rotatable, the second magnet having: a second developing pole disposed facing the image carrier at the second developing position; a second upstream pole disposed adjacent to the second developing pole upstream of the second developing pole in the rotational direction of the second rotating body and having a polarity opposite to that of the second developing pole; a second downstream pole disposed adjacent to the second developing pole downstream of the second developing pole in the rotational direction of the second rotating body and having a polarity opposite to that of the second developing pole; and a receiving pole disposed downstream of the second downstream pole and upstream of the second upstream pole in the rotational direction of the second rotating body and adjacent to the delivering pole and having a polarity opposite to that of the delivering pole;
Equipped with
|Bθ1-1| is the maximum value of the absolute value of the magnetic flux density in the tangential direction to the outer peripheral surface of the first rotor in a section in the rotation direction of the first rotor from a position on the outer peripheral surface of the first rotor where the absolute value of the magnetic flux density of the first upstream pole in the normal direction to the outer peripheral surface of the first rotor is maximum to a position on the outer peripheral surface of the first rotor where the absolute value of the magnetic flux density of the first development pole in the normal direction to the outer peripheral surface of the first rotor,
When the maximum value of the absolute value of the magnetic flux density in the tangential direction to the outer peripheral surface of the first rotor in a section in the rotation direction of the first rotor from a position on the outer peripheral surface of the first rotor where the absolute value of the magnetic flux density of the first development pole in the normal direction to the outer peripheral surface of the first rotor is maximum to a position on the outer peripheral surface of the first rotor where the absolute value of the magnetic flux density of the first downstream pole in the normal direction to the outer peripheral surface of the first rotor is maximum is defined as |Bθ1-2|,
|Bθ1-1|/|Bθ1-2|≧1.0
Fulfilling
and,
|Bθ2-1| is the maximum value of the absolute value of the magnetic flux density in the tangential direction to the outer peripheral surface of the second rotor in a section in the rotation direction of the second rotor from a position on the outer peripheral surface of the second rotor where the absolute value of the magnetic flux density of the second upstream pole in the normal direction to the outer peripheral surface of the second rotor is maximum to a position on the outer peripheral surface of the second rotor where the absolute value of the magnetic flux density of the second development pole in the normal direction to the outer peripheral surface of the second rotor,
When the maximum value of the absolute value of the magnetic flux density in the tangential direction to the outer peripheral surface of the second rotating body in a section in the rotation direction of the second rotating body from a position on the outer peripheral surface of the second rotating body where the absolute value of the magnetic flux density of the second developing pole in the normal direction to the outer peripheral surface of the second rotating body is maximum to a position on the outer peripheral surface of the second rotating body where the absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer peripheral surface of the second rotating body is maximum is defined as |Bθ2-2|,
|Bθ2-2|/|Bθ2-1|≧1.1
A developing device that meets these requirements. |Bθ1-1|/|Bθ1-2|≧1.05
30. The development device of claim 29, further satisfying the following: |Bθ2-2|/|Bθ2-1|≧1.15
30. The development device of claim 29, further satisfying the following: |Bθ2-2|/|Bθ2-1|≧1.30
30. The development device of claim 29, further satisfying the following: an angle in the rotation direction of the second rotor from a position on the outer circumferential surface of the second rotor at which the absolute value of the magnetic flux density of the second upstream pole in the normal direction to the outer circumferential surface of the second rotor is maximum to a position on the outer circumferential surface of the second rotor at which the absolute value of the magnetic flux density of the second development pole in the normal direction to the outer circumferential surface of the second rotor is maximum is defined as θ1 [°];
When the angle in the rotation direction of the second rotor from the position on the outer circumferential surface of the second rotor where the absolute value of the magnetic flux density of the second developing pole in the normal direction to the outer circumferential surface of the second rotor is maximum to the position on the outer circumferential surface of the second rotor where the absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer circumferential surface of the second rotor is maximum is θ2 [°],
θ1>θ2
30. The developing device according to claim 29, wherein the above formula satisfies the above formula. an angle in the rotation direction of the first rotor from a position on the outer circumferential surface of the first rotor at which the absolute value of the magnetic flux density of the first upstream pole in the normal direction to the outer circumferential surface of the first rotor is maximum to a position on the outer circumferential surface of the first rotor at which the absolute value of the magnetic flux density of the first development pole in the normal direction to the outer circumferential surface of the first rotor is maximum is defined as φ1 [°];
When the angle in the rotation direction of the first rotor from the position on the outer circumferential surface of the first rotor where the absolute value of the magnetic flux density of the first development pole in the normal direction to the outer circumferential surface of the first rotor is maximum to the position on the outer circumferential surface of the first rotor where the absolute value of the magnetic flux density of the first downstream pole in the normal direction to the outer circumferential surface of the first rotor is set to φ2 [°],
φ1>φ2
34. The developing device according to claim 33, wherein the above formula satisfies the above formula. A developing device as described in claim 29, wherein the maximum absolute value of the magnetic flux density of the first upstream pole in the normal direction to the outer peripheral surface of the first rotating body is greater than the maximum absolute value of the magnetic flux density of the first downstream pole in the normal direction to the outer peripheral surface of the first rotating body. A developing device as described in claim 29, wherein the maximum absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer peripheral surface of the second rotating body is greater than the maximum absolute value of the magnetic flux density of the second upstream pole in the normal direction to the outer peripheral surface of the second rotating body. A developing device as described in claim 29, wherein the half-value width of the magnetic flux density of the second downstream pole in the normal direction to the outer peripheral surface of the second rotating body is greater than the half-value width of the magnetic flux density of the second upstream pole in the normal direction to the outer peripheral surface of the second rotating body. A developing device as described in claim 29, wherein the half-width of the magnetic flux density of the first downstream pole in the normal direction to the outer peripheral surface of the first rotating body is smaller than the half-width of the magnetic flux density of the first upstream pole in the normal direction to the outer peripheral surface of the first rotating body. With respect to the rotation direction of the second rotating body, the position on the outer circumferential surface of the second rotating body at which the absolute value of the magnetic flux density of the second developing pole in the normal direction to the outer circumferential surface of the second rotating body becomes maximum is
30. A developing device as described in claim 29, wherein the second rotating body is located upstream of the position on the outer peripheral surface of the second rotating body that is closest to the image carrier, and downstream of the position on the outer peripheral surface of the second rotating body where the absolute value of the magnetic flux density of the second upstream pole in the normal direction to the outer peripheral surface of the second rotating body is maximum. With respect to the rotation direction of the first rotating body, the position on the outer circumferential surface of the first rotating body at which the absolute value of the magnetic flux density of the first developing pole in the normal direction to the outer circumferential surface of the first rotating body becomes maximum is
A developing device as described in claim 29, wherein the first rotating body is located upstream of the position on the outer surface of the first rotating body that is closest to the image carrier, and downstream of the position on the outer surface of the first rotating body where the absolute value of the magnetic flux density of the first upstream pole in the direction normal to the outer surface of the first rotating body is maximum. an angle in the rotation direction of the first rotor from a position on the outer circumferential surface of the first rotor at which the absolute value of the magnetic flux density of the first upstream pole in the normal direction to the outer circumferential surface of the first rotor is maximum to a position on the outer circumferential surface of the first rotor at which the absolute value of the magnetic flux density of the first development pole in the normal direction to the outer circumferential surface of the first rotor is maximum is defined as φ1 [°];
When the angle in the rotation direction of the first rotor from the position on the outer circumferential surface of the first rotor where the absolute value of the magnetic flux density of the first development pole in the normal direction to the outer circumferential surface of the first rotor is maximum to the position on the outer circumferential surface of the first rotor where the absolute value of the magnetic flux density of the first downstream pole in the normal direction to the outer circumferential surface of the first rotor is set to φ2 [°],
φ1>φ2
30. The developing device according to claim 29, wherein the above formula satisfies the above formula. When the angle in the rotation direction of the second rotor from the position on the outer circumferential surface of the second rotor where the absolute value of the magnetic flux density of the second developing pole in the normal direction to the outer circumferential surface of the second rotor is maximum to the position on the outer circumferential surface of the second rotor where the absolute value of the magnetic flux density of the second downstream pole in the normal direction to the outer circumferential surface of the second rotor is maximum is defined as θ2 [°], and the angle in the rotation direction of the first rotor from the position on the outer circumferential surface of the first rotor where the absolute value of the magnetic flux density of the first developing pole in the normal direction to the outer circumferential surface of the first rotor is maximum to the position on the outer circumferential surface of the first rotor where the absolute value of the magnetic flux density of the first downstream pole in the normal direction to the outer circumferential surface of the first rotor is maximum,
θ2>φ2
30. The developing device according to claim 29, wherein the above formula satisfies the above formula. A developing device as described in claim 29, wherein the surface linear speed of the second rotating body is faster than the surface linear speed of the first rotating body.