JP6428704B2 - Developing device and image forming apparatus having the same - Google Patents

Description

  The present invention relates to a developing device and an image forming apparatus including the developing device.

  Conventionally, image forming apparatuses such as printers and copiers that employ an electrophotographic method have a photosensitive drum carrying an electrostatic latent image, and toner is supplied to the photosensitive drum so that the electrostatic latent image becomes visible as a toner image. And a transfer device that transfers a toner image from the photosensitive drum to a sheet.

  Patent Document 1 discloses a developing roller that supplies toner to a photosensitive drum and a conveyance roller that supplies developer to the developing roller. Each of the developing roller and the transporting roller includes a magnet having a plurality of magnetic poles fixed and a sleeve that rotates around the magnet. The developer is supplied from the conveyance roller to the developing roller by a magnetic force generated between the first S pole on the conveyance roller side and the first N pole on the development roller side. The developer is collected from the developing roller to the transport roller by a magnetic force generated between the second N pole on the developing roller side and the second S pole on the transport roller side.

Japanese Patent Laid-Open No. 04-107586

  In recent years, a developing bias in which an AC bias is superimposed on a DC bias is applied to the developing roller in order to improve the image quality of the toner image and to suppress the toner fog generated on the background portion of the photosensitive drum. When such a developing bias is applied to the developing roller of Patent Document 1, toner is adsorbed on the sleeve surface of the developing roller, and a toner layer is easily formed. When such a toner layer is continuously laminated, the potential difference between the developing roller and the photosensitive drum fluctuates, and there is a problem that the image density is greatly lowered as it is used.

  The present invention has been made in view of the above problems, and in a developing device including a plurality of rollers each having a magnet therein and delivering a developer to each other, image density reduction caused by toner adhesion to the developing roller is reduced. An object of the present invention is to provide an image forming apparatus including the developing device.

  A developing device according to an aspect of the present invention includes a first magnet fixed including a plurality of magnetic poles along a circumferential direction, and the first rotation direction and the first rotation direction around the first magnet are opposite to each other. A first sleeve that is rotatable in the reverse rotation direction and carries a developer containing toner and a magnetic carrier on a peripheral surface thereof, and a photosensitive drum having an electrostatic latent image formed on the surface thereof at a predetermined development position. A developing roller for supplying the toner to the photosensitive drum, and a roller disposed so as to face the developing roller at a predetermined facing position, wherein a plurality of magnetic poles are provided along the circumferential direction. A second magnet that is included and fixed, and the periphery of the second magnet is rotated in a second rotation direction set to oppose the first rotation direction at the facing position, and the developer is carried on a peripheral surface. A second sleeve, and a front A transport roller that supplies the developer to the developing roller, a developer agitator that stirs the developer and supplies the developer to the transport roller, and the first rotation of the first sleeve of the developer roller. A first drive unit that rotates in the direction and the reverse rotation direction, a second drive unit that rotates the second sleeve of the transport roller in the second rotation direction, and the first drive unit and the second drive unit. A first magnetic pole disposed on the downstream side in the first rotational direction of the opposed position and a first magnetic pole disposed on the upstream side of the opposed position in the first rotational direction. A second magnetic pole disposed on the upstream side of the opposing position in the second rotational direction and a fourth magnetic pole disposed on the downstream side of the opposing position in the second rotational direction. And facing the A gap between the developing roller and the conveying roller in the setting is set to be narrower than a gap between the photosensitive drum and the developing roller at the developing position, and the electrostatic latent image on the photosensitive drum is the developing roller. During the developing operation of developing with the toner on the first sleeve, the control unit forms the developer supplied from the developer stirring unit to the transport roller by the third magnetic pole and the first magnetic pole. The developer is transferred from the transport roller to the developing roller by a magnetic field applied, and the developer passing through the developing position is transferred from the developing roller to the transport roller by a magnetic field formed by the second magnetic pole and the fourth magnetic pole. The first sleeve is rotated in the first rotational direction so that the second sleeve is transferred to the second sleeve. The control unit causes the developer on the first sleeve of the developing roller to pass through the opposing position during a non-developing operation different from the developing operation by rotating the tape in the second rotation direction. At the same time, the first sleeve is rotated in the reverse rotation direction and the second sleeve is rotated in the second rotation direction so as to be transferred from the developing roller to the transport roller.

  According to this configuration, during the developing operation, the first sleeve of the developing roller is rotated in the first rotation direction, and the second sleeve of the transport roller is rotated in the second rotation direction. As a result, the developer is supplied from the developer stirring unit to the conveyance roller, and the developer is supplied from the conveyance roller to the development roller. When a part of the toner is supplied from the developer to the photosensitive drum at the development position, the developer is collected from the development roller to the transport roller. At this time, a pair of developer delivery regions are formed so as to sandwich the facing position. On the other hand, during the non-development operation, the first sleeve of the developing roller is rotated in the reverse rotation direction, and the second sleeve of the transport roller is rotated in the second rotation direction. As a result, the developer on the first sleeve is collected by the transport roller while passing through the facing position. The gap at the opposite position is set narrower than the gap at the development position. For this reason, when the developer passes through the opposing position, the magnetic brush of the developer composed of toner and carrier polishes the toner layer attached on the first sleeve and the second sleeve. For this reason, the use of the developing device prevents the toner layer from being laminated on each sleeve, and prevents the density reduction in the image formed on the photosensitive drum.

  In the above configuration, the control unit rotates the first sleeve in the reverse rotation direction in a state in which the rotation of the second sleeve is stopped during the non-development operation, and then the first sleeve It is desirable that the second sleeve is rotated in the second rotation direction while being rotated in the reverse rotation direction.

  According to this configuration, a large amount of developer can be stored on the upstream side of the facing position by rotating the first sleeve reversely while the rotation of the second sleeve is stopped. Then, with the rotation of the second sleeve, it becomes possible to allow these developers to enter the opposing positions, and the polishing effect of the toner layer on the first sleeve and the second sleeve is promoted.

  In the above configuration, the control unit may set a rotation speed of the first sleeve in the reverse rotation direction during the non-development operation to be higher than a rotation speed of the first sleeve in the first rotation direction during the development operation. It is desirable to set a large value.

  According to this configuration, since the rotation speed at the time of reverse rotation of the first sleeve is set to be large, it becomes possible to allow a large amount of developer to enter the opposing position, and the toner layer on the first sleeve and the second sleeve The polishing effect is promoted.

  In the above configuration, it is preferable that the third magnetic pole is a magnetic pole different from the first magnetic pole, and the fourth magnetic pole is a magnetic pole having the same polarity as the first magnetic pole.

  According to this configuration, the developer can be stably transferred from the transport roller to the developing roller during the developing operation. Further, during the non-development operation, the developer that has passed through the facing position can be stably recovered to the transport roller side.

  In the above configuration, a straight line connecting the peak position of the magnetic force of the first magnetic pole and the rotation axis of the developing roller, and a straight line connecting the rotation axis of the developing roller and the rotation axis of the transport roller are: A straight line connecting the peak position of the magnetic force of the second magnetic pole and the rotation axis of the developing roller, and a straight line connecting the rotation axis of the developing roller and the rotation axis of the transport roller. And a straight line connecting the peak position of the magnetic force of the third magnetic pole and the rotation axis of the transport roller, a rotation axis of the developing roller, and a rotation axis of the transport roller. And the rotation angle of the developing roller and the rotation of the conveying roller is a third angle, and the straight line connecting the peak position of the magnetic force of the fourth magnetic pole and the rotation axis of the conveying roller. Connect the axis When the angle formed by the line is the fourth angle, the first angle, the second angle, the third angle, and the fourth angle are all 20 degrees or more and 40 degrees or less, so that It is desirable that the positions of the magnetic poles of the first magnet and the second magnet are set.

  According to this configuration, during a developing operation, a large amount of developer is prevented from entering the closest position between the developing roller and the transport roller, and an increase in rotational torque of the first sleeve and the second sleeve is suppressed. Further, toner scattering is reduced when the developer is transferred between the developing roller and the transport roller.

  In the above configuration, the peak magnetic force of the first magnetic pole is M1 (mT), the peak magnetic force of the second magnetic pole is M2 (mT), the peak magnetic force of the third magnetic pole is M3 (mT), and the peak of the fourth magnetic pole is When the magnetic force is M4 (mT), it is desirable that the relationship of M3 <M1 <M4 and M2 <M4 is satisfied.

  According to this configuration, delivery of the developer between the developing roller and the transport roller is stably realized during the developing operation. Further, during the non-development operation, the developer that has passed through the facing position can be stably recovered to the transport roller side.

  In the above configuration, it is desirable that the relationship of M1 <M4-10, M2 <M4-10, and M3 <M4-10 is further satisfied.

  According to this configuration, during the non-development operation, the developer that has passed through the facing position can be strongly drawn toward the transport roller, and the developer can be stably recovered.

  In the above configuration, the rotation axis of the developing roller is disposed below the rotation axis of the photosensitive drum, and the rotation axis of the transport roller is disposed below the rotation axis of the developing roller. It is desirable that

  According to this configuration, during the non-development operation, the recovery of the developer that has passed through the facing position to the conveyance roller side is promoted by gravity.

  In the above configuration, a developing bias in which an AC bias is superimposed on a DC bias may be applied to the developing roller.

  According to this configuration, even when the toner layer is easily formed on the first sleeve by the action of the AC bias during the developing operation, the toner layer can be polished by the flow of the developer during the non-developing operation. It becomes possible.

  An image forming apparatus according to another aspect of the present invention includes the developing device according to any one of the above, the photosensitive drum that is supplied with the toner from the developing device and carries a toner image on the peripheral surface, And a transfer unit that transfers the toner image from the photosensitive drum to a sheet.

  According to this configuration, an image forming apparatus capable of suppressing a decrease in image density due to toner adhesion to the developing roller is provided.

  According to the present invention, in a developing device that includes a plurality of rollers each having a magnet therein and delivering developer to each other, the image density reduction due to toner adhesion to the developing roller is suppressed, and the developing device is provided. An image forming apparatus is provided.

1 is a cross-sectional view illustrating an internal structure of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing the internal structure of the developing device according to the embodiment of the present invention. It is typical sectional drawing which shows magnetic pole arrangement | positioning of the developing roller which concerns on embodiment of this invention, and a conveyance roller. It is a typical sectional view showing magnetic pole arrangement of a development roller concerning an embodiment of the present invention. It is typical sectional drawing which shows magnetic pole arrangement | positioning of the conveyance roller which concerns on embodiment of this invention. It is a typical sectional view showing the structure of the housing of the developing device concerning the embodiment of the present invention. In the developing device according to the embodiment of the present invention, it is a schematic diagram showing the rotation direction of the developing roller and the transport roller during the non-developing operation. In the developing device according to the embodiment of the present invention, it is a schematic diagram for explaining the magnetic pole arrangement of the first magnet and the second magnet. 6 is a graph showing the relationship between the number of printed sheets and the image density in an example of the present invention. It is typical sectional drawing which shows the magnetic pole arrangement | positioning of the developing roller which concerns on deformation | transformation embodiment of this invention, and a conveyance roller.

  Hereinafter, an image forming apparatus 10 according to an embodiment of the present disclosure will be described in detail with reference to the drawings. In this embodiment, a tandem color printer is illustrated as an example of an image forming apparatus. The image forming apparatus may be, for example, a copying machine, a facsimile machine, and a complex machine of these.

  FIG. 1 is a cross-sectional view showing the internal structure of the image forming apparatus 10. The image forming apparatus 10 includes an apparatus main body 11 having a box-shaped housing structure. In the apparatus main body 11, a sheet feeding unit 12 that feeds the sheet P, an image forming unit 13 that forms a toner image to be transferred to the sheet P fed from the sheet feeding unit 12, and the toner image are primarily transferred. Intermediate transfer unit 14, secondary transfer roller 145, toner replenishing unit 15 for replenishing toner to the image forming unit 13, and fixing unit for performing a process of fixing an unfixed toner image formed on the sheet P to the sheet P 16 are decorated. Further, a discharge unit 17 that discharges the sheet P that has been subjected to the fixing process by the fixing unit 16 is provided on the upper portion of the apparatus main body 11.

  In the apparatus main body 11, a sheet conveying path 111 extending in the vertical direction is further formed on the right side of the image forming unit 13. The sheet conveyance path 111 is provided with a conveyance roller pair 112 that conveys a sheet to an appropriate position. A registration roller pair 113 that corrects the skew of the sheet and feeds the sheet to a nip portion of secondary transfer described later at a predetermined timing is also provided on the upstream side of the nip portion in the sheet conveyance path 111. The sheet conveyance path 111 is a conveyance path that conveys the sheet P from the paper feeding unit 12 to the paper discharge unit 17 via the image forming unit 13 (secondary transfer nip unit) and the fixing unit 16.

  The paper feed unit 12 includes a paper feed tray 121, a pickup roller 122, and a paper feed roller pair 123. The sheet feeding tray 121 is detachably mounted at a lower position of the apparatus main body 11 and stores a sheet bundle P1 in which a plurality of sheets P are stacked. The pickup roller 122 feeds the uppermost sheet P of the sheet bundle P1 stored in the sheet feeding tray 121 one by one. The pair of paper feed rollers 123 sends out the sheet P fed out by the pickup roller 122 to the sheet conveyance path 111.

  The image forming unit 13 forms a toner image to be transferred to the sheet P, and includes a plurality of image forming units that form toner images of different colors. As this image forming unit, in this embodiment, a magenta (M) color which is sequentially arranged from the upstream side to the downstream side in the rotation direction of the intermediate transfer belt 141 described later (from the left side to the right side in FIG. 1). A magenta unit 13M using a developer, a cyan unit 13C using a cyan (C) developer, a yellow unit 13Y using a yellow (Y) developer, and a black (Bk) developer are used. A black unit 13Bk is provided. Each of the units 13M, 13C, 13Y, and 13Bk includes a photosensitive drum 20, and a charging device 21, a developing device 23, and a cleaning device 25 disposed around the photosensitive drum 20. An exposure device 22 common to the units 13M, 13C, 13Y, and 13Bk is disposed below the image forming unit.

  The photosensitive drum 20 is driven to rotate about its axis, and an electrostatic latent image and a toner image are formed on its peripheral surface. As this photosensitive drum 20, a photosensitive drum using an amorphous silicon (a-Si) material can be used. The photosensitive drums 20 are arranged corresponding to the image forming units of the respective colors. The charging device 21 uniformly charges the surface of the photosensitive drum 20. The charging device 21 includes a charging roller and a charging cleaning brush for removing toner attached to the charging roller. The exposure device 22 has various optical system devices such as a light source, a polygon mirror, a reflection mirror, and a deflection mirror, and irradiates light that has been modulated based on image data onto the circumferential surface of the uniformly charged photoreceptor drum 20. Thus, an electrostatic latent image is formed. The cleaning device 25 cleans the peripheral surface of the photosensitive drum 20 after the toner image is transferred.

  The developing device 23 supplies toner to the peripheral surface of the photosensitive drum 20 in order to develop the electrostatic latent image formed on the photosensitive drum 20. The developing device 23 is for a two-component developer composed of toner and carrier. In this embodiment, the toner has a characteristic of being charged to a positive polarity.

  The intermediate transfer unit 14 is disposed in a space provided between the image forming unit 13 and the toner supply unit 15. The intermediate transfer unit 14 includes an intermediate transfer belt 141, a driving roller 142, a driven roller 143, and a primary transfer roller 24.

  The intermediate transfer belt 141 is an endless belt-like rotating body, and is stretched between the driving roller 142 and the driven roller 143 so that the circumferential surface side thereof is in contact with the circumferential surface of each photosensitive drum 20. The intermediate transfer belt 141 is driven to circulate in one direction, and carries the toner image transferred from the photosensitive drum 20 on the surface.

  The drive roller 142 stretches the intermediate transfer belt 141 on the right end side of the intermediate transfer unit 14 and drives the intermediate transfer belt 141 to rotate. The driving roller 142 is a metal roller. The driven roller 143 stretches the intermediate transfer belt 141 on the left end side of the intermediate transfer unit 14. The driven roller 143 applies tension to the intermediate transfer belt 141.

  The primary transfer roller 24 forms a primary transfer nip portion with the photosensitive drum 20 with the intermediate transfer belt 141 interposed therebetween, and primarily transfers the toner image on the photosensitive drum 20 onto the intermediate transfer belt 141. A primary transfer roller 24 is disposed to face the photosensitive drum 20 of each color.

  The secondary transfer roller 145 is disposed to face the driving roller 142 with the intermediate transfer belt 141 interposed therebetween. The secondary transfer roller 145 is pressed against the peripheral surface of the intermediate transfer belt 141 to form a secondary transfer nip portion. The toner image primarily transferred onto the intermediate transfer belt 141 is secondarily transferred to the sheet P supplied from the paper feeding unit 12 at the secondary transfer nip portion. The intermediate transfer unit 14 and the secondary transfer roller 145 of this embodiment constitute a transfer unit of the present invention. The transfer unit transfers the toner image from the photosensitive drum 20 to the sheet P.

  The toner replenishing unit 15 stores toner used for image formation, and includes a magenta toner container 15M, a cyan toner container 15C, a yellow toner container 15Y, and a black toner container 15Bk in this embodiment. The toner containers 15M, 15C, 15Y, and 15Bk replenish toner of each color to the developing devices 23 of the image forming units 13M, 13C, 13Y, and 13Bk corresponding to the respective colors of MCYBk through a toner transport unit (not shown).

  The sheet P supplied to the fixing unit 16 is heated and pressed by passing through the fixing nip. As a result, the toner image transferred to the sheet P at the secondary transfer nip is fixed to the sheet P.

  The paper discharge unit 17 is formed by recessing the top of the apparatus main body 11, and a paper discharge tray 171 for receiving the discharged sheet P is formed at the bottom of the concave portion. The sheet P on which the fixing process has been performed is discharged toward the discharge tray 151 via the sheet conveyance path 111 extending from the upper part of the fixing unit 16.

  Next, the developing device 23 according to the present embodiment will be described in more detail with reference to FIGS. 2 to 6 in addition to FIG. FIG. 2 is a schematic cross-sectional view showing the internal structure of the developing device 23 according to this embodiment. In FIG. 2, the rotation direction of each rotation member of the developing device 23 is indicated by an arrow. FIG. 3 is a schematic cross-sectional view showing the magnetic pole arrangement of the developing roller 231 and the transport roller 232 according to this embodiment. FIG. 4 is a schematic cross-sectional view showing the magnetic pole arrangement of the developing roller 231. FIG. 5 is a schematic cross-sectional view showing the magnetic pole arrangement of the transport roller 232. FIG. 6 is a schematic cross-sectional view showing the structure of the housing 23H in the developing device 23 according to the present embodiment.

  1 to 6, the developing device 23 includes a housing 23H, a developing roller 231, a transport roller 232, two stirring screws 233 (developer stirring unit), a partition plate 234, and a layer thickness. A restricting member 235. The housing 23H is a housing portion that supports each member of the developing device 23.

  The developing roller 231 is arranged to face the photosensitive drum 20 on which the electrostatic latent image is formed at a predetermined developing position NP (FIG. 3), and supplies toner to the photosensitive drum 20. The developing roller 231 includes a first magnet 231A and a first sleeve 231B (FIG. 3). In the present embodiment, the development position NP includes the closest position between the photosensitive drum 20 and the development roller 231. The first magnet 231A is a columnar magnet including a plurality of magnetic poles along the circumferential direction and fixed to the housing 23H. The first sleeve 231B rotates around the first magnet 231A in the first rotation direction (the direction of arrow D1 in FIGS. 2 and 3), and carries a developer containing toner and a magnetic carrier on the peripheral surface. As will be described later, the first sleeve 231B can rotate around the first magnet 231A in the reverse rotation direction (the direction of arrow D3 in FIG. 7) opposite to the first rotation direction. In the present embodiment, the first sleeve 231B is made of an aluminum circular pipe member (base material). Sandblasting (blasting) is performed on the circumferential surface of the circular pipe member of the first sleeve 231B. The surface of the first sleeve 231B has a predetermined surface roughness. In the present embodiment, the surface roughness Rz of the first sleeve 231B is set in the range of 4.0 μm to 14.0 μm. The first sleeve 231B of the developing roller 231 is rotatably supported by the housing 23H. Note that a known groove shape may be formed on the first sleeve 231B instead of the sandblasting process.

  The transport roller 232 is disposed so as to face the developing roller 231 at a predetermined facing position TP (FIG. 3), and supplies the developer to the developing roller 231. In the present embodiment, the facing position TP includes the closest position between the transport roller 232 and the developing roller 231. The transport roller 232 includes a second magnet 232A and a second sleeve 232B. The second magnet 232A includes a plurality of magnetic poles along the circumferential direction, and is fixed to the housing 23H. The second sleeve 232B rotates around the second magnet 232A in the second rotation direction (the direction of arrow D2 in FIGS. 2 and 3), and carries a developer containing nonmagnetic toner and a magnetic carrier on the peripheral surface. As shown in FIG. 3, the first rotation direction D1 in which the developing roller 231 rotates and the second rotation direction D2 in which the transport roller 232 rotates are set in directions opposite to each other at the counter position TP (counter direction). ). The second sleeve 232B of the transport roller 232 is rotatably supported by the housing 23H.

  The gap between the developing roller 231 and the transport roller 232 at the facing position TP is set to be narrower than the gap between the photosensitive drum 20 and the developing roller 231 at the developing position NP. As an example, the gap (development position NP) between the developing roller 231 and the photosensitive drum 20 is set to be larger than 0.25 mm and equal to or smaller than 0.40 mm. On the other hand, the gap (opposing position TP) between the developing roller 231 and the transport roller 232 is set to 0.18 mm or more and 0.25 mm or less.

  The developing roller 231 and the transport roller 232 are applied with a developing bias in which an AC bias is superimposed on a DC bias. Furthermore, the layer thickness regulating member 235 is set to the same potential as the second sleeve 232B of the transport roller 232 via a conduction path (not shown).

  The stirring screw 233 charges the toner by circulating and conveying the two-component developer while stirring. The stirring screw 233 includes a first screw 233A and a second screw 233B. Although not shown in FIG. 2, the housing 23H includes a first agitation unit (not shown) in which the first screw 233A is arranged and a second agitation unit (not shown) in which the second screw 233B is arranged. Provided (see developing device 23 in FIG. 1). The developer is circulated and conveyed between the first screw 233A and the second screw 233B. Then, the first screw 233 </ b> A supplies the developer to the transport roller 232. The partition plate 234 is a plate-like member provided in the housing 23H. The partition plate 234 partitions the first stirring portion and the second stirring portion along the axial direction of the first screw 233A and the second screw 233B. At both end portions of the partition plate 234, the first stirring unit and the second stirring unit communicate with each other. Further, the toner replenished from the toner replenishing portion 15 flows into the housing 23H from one end side in the axial direction of the second screw 233B, and is agitated with the other developer.

  The layer thickness regulating member 235 is a plate-like member made of a nonmagnetic metal that is disposed so as to face the peripheral surface of the transport roller 232. In another embodiment, a magnetic member may be fixed to the tip of the layer thickness regulating member 235. The layer thickness regulating member 235 regulates the layer thickness of the developer supplied from the first screw 233 </ b> A of the stirring screw 233 to the transport roller 232.

  The first drive unit 51 includes a motor and a gear (not shown), and moves the first sleeve 231B of the developing roller 231 in the first rotation direction (arrow D1 in FIG. 3) or the reverse rotation direction (arrow D3 in FIG. 7). Rotate. Similarly, the second drive unit 52 includes a motor and a gear (not shown). The motor of the second drive unit 52 rotates the second sleeve 232B of the transport roller 232 in the second rotation direction (arrow D2 in FIG. 3). Further, the second drive unit 52 rotates the first screw 233A and the second screw 233B of the stirring screw 233. The control unit 50 controls the first drive unit 51 and the second drive unit 52 to control the on / off timing and the rotation direction of the first sleeve 231B in the rotation of the first sleeve 231B and the second sleeve 232B. To do.

  Further, as illustrated in FIG. 2, the rotation axis of the developing roller 231 is disposed below the rotation axis of the photosensitive drum 20, and the rotation axis of the transport roller 232 is from the rotation axis of the developing roller 231. Is further disposed below.

  With reference to FIG. 3 and FIG. 4, in the present embodiment, the first magnet 231 </ b> A of the developing roller 231 includes six magnetic poles along the circumferential direction. An S2 pole (first magnetic pole) is disposed on the downstream side in the first rotational direction (D1) of the facing position TP where the developing roller 231 and the transport roller 232 face each other. Further, the N3 pole is disposed downstream of the S2 pole in the first rotation direction. The N3 pole functions as a transport pole for transporting the developer received from the transport roller 232 to the photosensitive drum 20 side. Further, an S3 pole that functions as a main pole that supplies toner to the photosensitive drum 20 is disposed downstream of the N3 pole in the first rotation direction. The S3 pole is disposed in the vicinity of the development position NP.

  Further, the first magnet 231A has three magnetic poles (N4 pole, S4 pole, S4 pole, in the first region R downstream of the development position NP in the first rotation direction and upstream of the facing position TP in the first rotation direction). N5 pole). The N4 pole is disposed adjacent to the S3 pole on the downstream side in the first rotation direction, and is a magnetic pole different from S3. The S4 pole is disposed adjacent to the N4 pole downstream in the first rotation direction, and is a magnetic pole different from N4. Further, the N5 pole (second magnetic pole) is arranged adjacent to the downstream side of the S4 pole in the first rotation direction, and is arranged upstream of the opposing position TP in the first rotation direction. The N5 pole is a magnetic pole different from the S4 pole and the S2 pole. As shown in FIG. 3, the S2 pole and the N5 pole are arranged adjacent to each other so as to sandwich the facing position TP in the circumferential direction.

  Table 1 shows examples of angles and peak magnetic forces of six magnetic poles as the first magnet 231A according to the present embodiment. In addition, the angle of each magnetic pole shown in Table 1 is shown along the 1st rotation direction from the opposing position TP of FIG. 4 as a starting point (angle 0 degree). In FIG. 4, a straight line CL (a straight line connecting the rotation axis of the developing roller 231 and the rotation axis of the transport roller 232) connecting the facing position TP and the rotation axis of the developing roller 231 is shown.

  On the other hand, referring to FIGS. 3 and 5, second magnet 232 </ b> A of transport roller 232 includes five magnetic poles along the circumferential direction. The S5 pole (fourth magnetic pole) is disposed downstream of the opposing position TP between the developing roller 231 and the transport roller 232 in the second rotation direction (D2). Further, the N6 pole is disposed downstream of the S5 pole in the second rotation direction. Further, the N1 pole is arranged at an interval on the downstream side in the second rotation direction of the N6 pole. The N6 pole functions as a peeling electrode that peels the developer from the transport roller 232. The N1 pole functions as a pumping pole that pumps up the developer from the first screw 233A. The S1 pole and the N2 pole (third magnetic pole) are arranged downstream of the N1 pole in the second rotation direction. As shown in FIG. 5, the layer thickness regulating member 235 is spaced apart from the N2 pole by the second sleeve 232B of the transport roller 232 at a predetermined interval between the S1 pole and the N1 pole. It is arranged facing each other. For this reason, in this embodiment, before the developer is transferred from the transport roller 232 to the developing roller 231, the layer thickness of the developer can be stably regulated. Note that the N2 pole is disposed upstream of the facing position TP in the second rotational direction. The N2 pole and the S5 pole are arranged adjacent to each other so as to sandwich the facing position TP in the circumferential direction.

  Table 2 shows angles and magnetic forces (peak values of radial components) of five magnetic poles as an example of the second magnet 232A according to the present embodiment. The angles of the magnetic poles shown in Table 2 are shown along the second rotation direction with the opposing position TP in FIG. 5 as the starting point (angle 0 °). In FIG. 5, a straight line CL (a straight line connecting the rotation axis of the developing roller 231 and the rotation axis of the conveyance roller 232) connecting the facing position TP and the rotation axis of the conveyance roller 232 is shown.

  With reference to FIG. 6, the housing 23 </ b> H includes a plurality of inner wall portions facing the developing roller 231 and the transport roller 232. Specifically, the housing 23H includes a first inner wall portion 23H1, a second inner wall portion 23H2, a third inner wall portion 23H3, and a fourth inner wall portion 23H4. The first inner wall portion 23H1 faces the N4 pole, the S4 pole, and the N5 pole, and extends along the peripheral surface of the first sleeve 231B of the developing roller 231. The second inner wall portion 23H2 is connected to the first inner wall portion 23H1, is opposed to the S5 pole and the N6 pole, and extends along the peripheral surface of the second sleeve 232B of the transport roller 232. Similarly, the third inner wall portion 23H3 faces the N3 pole and the S2 pole on the opposite side of the first inner wall portion 23H1, and extends along the peripheral surface of the first sleeve 231B of the developing roller 231. . Between the first inner wall portion 23H1 and the third inner wall portion 23H3, the first sleeve 231B of the developing roller 231 is partially exposed and arranged to face the photosensitive drum 20. The fourth inner wall portion 23H4 is connected to the third inner wall portion 23H3, faces the N2 pole and the S1 pole, and extends along the peripheral surface of the second sleeve 232B of the transport roller 232. As shown in FIG. 6, a substantially uniform gap H (developer transport path) is formed between each inner wall and the first sleeve 231B of the developing roller 231 and the second sleeve 232B of the transport roller 232. Has been. In this embodiment, the height of the gap H is smaller than the radii of the developing roller 231 and the transport roller 232, and is set in the range of 0.5 mm to 2.0 mm.

  With reference to FIG. 3, the arrangement and function of the magnetic poles of the first magnet 231A of the developing roller 231 and the second magnet 232A of the transport roller 232 will be further described. The N2 pole (third magnetic pole) of the second magnet 232A is disposed opposite to the S2 pole (first magnetic pole) of the first magnet 231A, and is a magnetic pole different from the S2 pole. In addition, the S5 pole is disposed on the downstream side in the second rotation direction of the N2 pole, and is the same pole as the S2 pole.

  Referring to FIG. 2, during the developing operation in which the electrostatic latent image on the photoconductive drum 20 is developed by the toner on the first sleeve 231B of the developing roller 231, the control unit 50, as shown in FIG. The first sleeve 231B is rotated in the first rotation direction, and the second sleeve 232B is rotated in the second rotation direction. As a result, the developer composed of toner and carrier and circulated and conveyed by the stirring screw 233 is first supplied from the first screw 233A to the conveyance roller 232. Thereafter, after the layer thickness of the developer is regulated by the layer thickness regulating member 235, the developer is transferred from the transport roller 232 to the developing roller 231 by a magnetic field formed by the N2 pole and the S2 pole. When a part of the toner is supplied to the photosensitive drum 20 at the development position NP (FIG. 3), the developer that has passed through the development position NP is removed from the development roller 231 by the magnetic field formed by the N5 pole and the S5 pole. It is delivered to the conveyance roller 232. Thereafter, the developer collected on the transport roller 232 is peeled off by the N6 pole and flows again into the first stirring unit around the first screw 233A. As described above, in the present embodiment, during the developing operation for developing the electrostatic latent image on the photosensitive drum 20, a pair of developer delivery areas are formed so as to sandwich the facing position TP.

  As described above, in the developing operation, a developing bias in which an AC bias is superimposed on a DC bias is applied to the developing roller 231 and the transport roller 232. As a result, an oscillating electric field due to an AC bias is formed at the development position NP (development nip), so that the fog toner adhered to the background portion on the photosensitive drum 20 can be collected. However, such an oscillating electric field attracts toner also onto the first sleeve 231B of the developing roller 231. As a result, a thin toner layer (toner film) is likely to be formed on the first sleeve 231B at the root of the magnetic brush made of toner and carrier.

  When the toner layer as described above is formed on the first sleeve 231B of the developing roller 231, the potential difference between the first sleeve 231B and the photosensitive drum 20 is partially equal to the charge of the toner remaining on the first sleeve 231B. Shift. As a result, as the image forming apparatus 10 is used, the image density of the printed image is reduced. In particular, when there is no adjacent homopolar magnetic pole in the first magnet 231A of the developing roller 231, the surface of the first sleeve 231B cannot be cleaned, and the above-described density reduction tends to occur.

  In the present embodiment, a toner layer is formed on the developing roller 231 that is one roller facing the photosensitive drum 20 in the developing device 23 in which two magnetic rollers (the developing roller 231 and the transport roller 232) are arranged. Thus, the occurrence of a decrease in density as described above is preferably suppressed. That is, in order to suppress a decrease in image density due to toner adhesion to the developing roller 231, the control unit 50 performs the first sleeve 231 </ b> B of the developing roller 231 and the transport roller 232 during a non-developing operation different from the developing operation. The rotation of the second sleeve 232B is controlled (cleaning mode). Specifically, the control unit 50 reversely rotates the first sleeve 231B so that the developer on the first sleeve 232B of the developing roller 231 passes through the facing position TP and is transferred from the developing roller 231 to the transport roller 232. And the second sleeve 232B is rotated in the second rotation direction. The cleaning mode performed by the control unit 50 may be performed before or after the print job, or may be performed when the power of the image forming apparatus 10 is turned on. FIG. 7 is a schematic diagram showing the rotation directions of the developing roller 231 and the transport roller 232 in the cleaning mode executed during such a non-developing operation.

  Referring to FIG. 7, the second sleeve 232B of the transport roller 232 is rotated in the second rotation direction, and the first sleeve 231B of the development roller 231 is rotated in the reverse rotation direction, whereby the development roller 231 is driven by the magnetic force of the S5 pole. The developer can be separated from the toner and collected on the transport roller 232. At this time, the developer passes between the developing roller 231 and the transport roller 232 at the facing position TP set narrower than the developing position NP, thereby cleaning the surfaces of both rollers. Therefore, the toner layer formed on the first sleeve 231B of the developing roller 231 can be polished by the developer magnetic brush.

  In particular, in the present embodiment, one developing roller 231 is disposed to face the photosensitive drum 20 and develops the electrostatic latent image on the photosensitive drum 20. Therefore, it is necessary to stably expose the electrostatic latent image at one development position NP as compared with other development devices in which a plurality of development rollers are arranged adjacent to each other along the circumferential surface of the photosensitive drum 20. There is. In other words, when a plurality of developing rollers are arranged along the rotation direction of the photosensitive drum 20 as described above, the downstream developing roller corrects the density-decreasing portion of the image formed by the upstream developing roller. can do. On the other hand, in the present embodiment, it is difficult to correct the density if the toner layer formed on the first sleeve 231B of the developing roller 231 causes a decrease in density. Therefore, the toner layer is prevented from being stacked on the first sleeve 231B by executing the cleaning mode. As a result, the structure of the developing device 23 is prevented from becoming complicated, and the cost of the developing device 23 is prevented from increasing.

  In addition, according to the present embodiment, even when a toner layer is likely to be formed on the first sleeve 231B due to the action of an AC bias during the developing operation, the above toner layer is generated by the developer flow during the non-developing operation. Can be polished.

  FIG. 8 is a schematic diagram for explaining the magnetic pole arrangement of the first magnet 231A and the second magnet 232A in the developing device 23 according to the present embodiment. In FIG. 8, for the sake of explanation, the notation positions of the S2, N5, N2, and S5 poles are slightly shifted. Referring to FIG. 8, the straight line connecting the peak position of the magnetic force (vertical component) of the S2 pole and the rotation axis of the developing roller 231, the rotation axis of the developing roller 231, and the rotation axis of the transport roller 232 The angle formed by the connecting straight line CL is defined as β (first angle). Further, a straight line connecting the peak position of the magnetic force (vertical direction component) of the N5 pole and the rotation axis of the developing roller 231; a straight line CL connecting the rotation axis of the developing roller 231 and the rotation axis of the transport roller 232; Is defined as γ (second angle). Further, a straight line connecting the peak position of the magnetic force (vertical component) of the N2 pole and the rotation axis of the transport roller 232, and a straight line CL connecting the rotation axis of the developing roller 231 and the rotation axis of the transport roller 232, Is defined as α (third angle). Furthermore, a straight line connecting the peak position of the magnetic force (vertical component) of the S5 pole and the rotation axis of the transport roller 232, and a straight line connecting the rotation axis of the developing roller 231 and the rotation axis of the transport roller 232 are: The angle formed is defined as σ (fourth angle). In this case, the positions of the magnetic poles of the first magnet 231A and the second magnet 232A are set so that all of β, γ, α, and σ are 20 degrees or more and 40 degrees or less.

  In particular, when the above four angles are set to be less than 20 degrees, during the developing operation, the developer enters up to the position closest to the closest position between the transport roller 232 and the developing roller 231, and the first sleeve 231B and the second sleeve 232B. Rotational torque increases. For this reason, by setting the above four angles to 20 degrees or more, a large amount of developer is prevented from entering the closest position between the developing roller 231 and the transport roller 232 during the developing operation. An increase in rotational torque of the sleeve 231B and the second sleeve 232B is suppressed. Further, if the above four angles exceed 40 degrees, the flying distance of the developer flying between the transport roller 232 and the developing roller 231 increases during the developing operation, and thus toner scattering is likely to occur. Therefore, when the four angles are set to 40 degrees or less, toner scattering is reduced when the developer is transferred between the developing roller 231 and the transport roller 232.

  In the present embodiment, the N2 pole of the second magnet 232A is a magnetic pole having a different polarity from the S2 pole of the first magnet 231A, and the S5 pole is a magnetic pole having the same polarity as the S2 pole. For this reason, the developer can be stably delivered from the transport roller 232 to the developing roller 231 during the developing operation. Further, during the non-development operation, the developer that has passed through the facing position TP can be stably recovered to the transport roller 232 side.

In the present embodiment, the peak magnetic force of the S2 pole of the first magnet 231A is M1 (mT), the peak magnetic force of the N5 pole is M2 (mT), the peak magnetic force of the N2 pole of the second magnet 232A is M3 (mT), When the peak magnetic force of the S5 pole is M4 (mT), it is desirable that the relationship of the following formula 1 is satisfied.
M3 <M1 <M4 and M2 <M4 (Formula 1)
In this case, during the developing operation, the delivery of the developer between the developing roller and the transport roller is stably realized. Further, during the non-development operation, the developer that has passed through the facing position TP can be stably recovered to the transport roller 232 side.

Furthermore, the peak magnetic force M1 (mT) of the S2 pole, the peak magnetic force M2 (mT) of the N5 pole, the peak magnetic force M3 (mT) of the N2 pole, and the peak magnetic force M4 (mT) of the S5 pole are It is more desirable to satisfy the relationship.
M1 <M4-10, M2 <M4-10, and M3 <M4-10 (Formula 2)
In this case, the magnetic force of the S5 pole is set to be larger by 10 mT or more than the other three magnetic poles. By satisfying such a relationship, when the first sleeve 231B is rotated in the reverse rotation direction during the non-development operation, the developer can smoothly pass through the narrow facing position TP. This is because the S5 pole disposed on the downstream side of the facing position TP attracts the developer with a strong magnetic force. As a result, the developer on the first sleeve 231B can be stably recovered to the second sleeve 232B side.

  Furthermore, in this embodiment, as shown in FIG. 6, the S5 pole, which is different from the N5 pole, is arranged to face the N5 pole, so that the developer is stably from the developing roller 231 to the transport roller 232. Can be handed over. At this time, since the first inner wall portion 23H1 and the second inner wall portion 23H2 are connected to each other while being formed along the peripheral surfaces of the developing roller 231 and the conveying roller 232, the developer is supplied from the developing roller 231 to the conveying roller 232. It can be delivered smoothly. 6, the rotation axis of the developing roller 231 is disposed below the rotation axis of the photosensitive drum 20, and the rotation axis of the transport roller 232 is below the rotation axis of the developing roller 231. Is arranged. For this reason, during the non-development operation, the collection of the developer that has passed through the facing position TP to the transport roller 232 side is promoted by gravity.

  Further, in the present embodiment, during the developing operation, a developer delivery region between the developing roller 231 and the transport roller 232 is stably formed in a different direction at a position across the facing position TP. The gap between the developing roller 231 and the transport roller 232 is set to be narrower than the gap between the developing roller 231 and the photosensitive drum 20. The developer is transferred between the developing roller 231 and the transport roller 232 so as to sandwich the opposed position TP set so narrow. As described above, the peak position of any magnetic pole does not face the facing position TP. For this reason, even when the gap at the facing position TP is set narrow as described above, it is possible to prevent the developer from sticking to the facing position TP during the developing operation. Further, since two magnetic brushes for the developer to be transferred are formed so as to sandwich the facing position TP in the circumferential direction, even when the toner is scattered at the facing position TP, the toner can be contained.

Next, based on an Example, this invention is further demonstrated. In addition, this invention is not limited to a following example.
In the experiment described later, the experiment was performed under the following experimental conditions.
<Experimental conditions>
・ Printing speed: 55ppm
Photosensitive drum 20: amorphous silicon photosensitive member (a-Si), diameter φ30 mm, surface potential Vo (white background portion) = 270 V, VL (image portion) = 20 V, peripheral speed = 300 mm / sec
A gap between the layer thickness regulating member 235 and the second sleeve 232B: 200 to 600 μm
-Developer transport amount on developing roller 231 (after regulation of layer thickness): 250 g / m ²
Carrier: Volume average particle size 35 μm, magnetic force 80 emu / g, ferrite resin coated carrierToner: Volume average particle size 6.8 μm, toner concentration 7%

The conditions of the developing roller 231 used in the experiment are as follows.
・ Developing roller 231: Diameter φ20 mm
-Peripheral speed ratio of developing roller 231 to photosensitive drum 20: 1.8 (trailing direction at developing position NP)
A gap between the developing roller 231 and the photosensitive drum 20: 350 μm
Developing bias: DC bias = 170 V, AC bias = Vpp 1.4 kV, frequency f3.7 kHz, duty 50%, rectangular wave (note that the transport roller 232 and the layer thickness regulating member 235 are also at the same potential as the developing roller 231)
・ Surface condition of the first sleeve 231B: Sandblast Rzjis 7 μm
Further, the magnetic pole distribution of the developing roller 231 used in Experiment 1 is the magnet shown in Table 1 above. In addition, the magnetic force measurement of the following developing roller 231 and the conveyance roller 232 was performed using the Japan Electromagnetic Instrument Co., Ltd.

Moreover, the conditions of the conveyance roller 232 used for experiment are as follows.
・ Conveyance roller 232: Diameter φ20mm
-Surface condition of the second sleeve 232B: Knurled V groove (groove depth 80 μm, groove width 0.2 mm, number of grooves 120)
-Peripheral speed ratio of transport roller 232 to developing roller 231: 1.4 (counter direction at opposite position TP)
-Gap between transport roller 232 and developing roller 231: 300 μm
Further, the magnetic pole distribution of the transport roller 232 used in the experiment is shown in Table 2 above.

  In the experiment, 30000 sheets were printed under the above experimental conditions, and the transition of the image density was evaluated. FIG. 9 is a graph showing the relationship between the number of printed sheets and the image density. In the embodiment, the above-described cleaning mode is executed every 5000 sheets. In the comparative example, the above cleaning mode is not executed. As shown in FIG. 9, in the example, compared with the comparative example, the image density is saturated in a region. This is because the toner layer on the first sleeve 231B is polished by the cleaning mode, and the development electric field at the development position NP is stably formed.

  The developing device 23 and the image forming apparatus 10 including the developing device 23 according to an embodiment of the present invention have been described in detail above, but the present invention is not limited to this. The present invention can take, for example, the following modified embodiments.

  (1) In the above embodiment, the first magnet 231A is provided with the S2 pole and the N5 pole, and the second magnet 232A is provided with the N2 pole and the S5 pole in the vicinity of the facing position TP. Is not limited to this. Each of the above magnetic poles may be inverted between the S pole and the N pole. FIG. 10 is a schematic cross-sectional view showing the magnetic pole arrangement of the developing roller 231M and the conveying roller 232M of the developing device 23M according to a modified embodiment of the present invention. The developing device 23M is mainly different from the developing device 23 according to the previous embodiment in that the N5 pole of the first magnet 231A (FIG. 3) is the S4 pole. Even in such a configuration, the first sleeve 231BM is rotated in a direction opposite to the first rotation direction D1 during the non-development operation, and the developer passes through the opposing position, so that the toner layer on the first sleeve 231BM is removed. Can be polished. Further, in the developing device 23M of FIG. 10, when the first sleeve 231BM rotates in the reverse direction, the developer that has passed between the developing roller 231M and the transport roller 232M easily moves to the transport roller 232M side. This is because strong magnetic field lines are formed between the S5 pole and the N2 pole, but the S4 pole has the same polarity as the adjacent S2 pole and the opposite S5 pole, and therefore repulsion between these poles. A magnetic field is formed. For this reason, the developer that has passed between the developing roller 231M and the conveying roller 232M is easily conveyed toward the S5 pole to which a strong magnetic field line is connected.

  (2) In the above embodiment, the first sleeve 231B of the developing roller 231 is reversely rotated while the second sleeve 232B of the transport roller 232 is rotated in the second rotation direction during the non-development operation. However, the present invention is not limited to this. The controller 50 (FIG. 2) rotates the first sleeve 231B in the reverse rotation direction while the rotation of the second sleeve 232B is stopped during the non-development operation, and then the first sleeve 231B moves in the reverse rotation direction. The second sleeve 232B may be rotated in the second rotation direction in the rotated state. In this case, when the rotation of the second sleeve 232B is stopped, the first sleeve 231B is reversely rotated, so that a large amount of developer can be stored upstream of the facing position TP. As the second sleeve 232B rotates, these developers can enter the facing position TP, and the polishing effect of the toner layer on the first sleeve 231B and the second sleeve 232B is promoted.

  Further, the control unit 50 may set the rotation speed of the first sleeve 231B in the reverse rotation direction during the non-development operation higher than the rotation speed of the first sleeve 231B during the development operation. In this case, since the rotation speed at the time of reverse rotation of the first sleeve 231B is set large, it becomes possible to allow a large amount of developer to enter the facing position TP, and the toner on the first sleeve 231B and the second sleeve 232B. The polishing effect of the layer is promoted. Furthermore, it is possible to increase the amount of developer per unit time that moves from the first sleeve 231B to the second sleeve 232B. Therefore, the cleaning mode can be executed in a short time.

  (3) In the above-described embodiment, the layer thickness regulating member 235 has been described as being disposed so as to face the transport roller 232, but the present invention is not limited to this. The layer thickness regulating member 235 may be disposed to face the periphery of the S1 pole of the developing roller 231 and the like. In this case, another magnetic pole for transporting the developer may be added to the first magnet 231A.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 11 Apparatus main body 13 Image forming part 14 Intermediate transfer unit (transfer part)
145 Secondary transfer roller (transfer section)
20 Photosensitive drum (image carrier)
23 Developing device 231 Developing roller 231A First magnet 231B First sleeve 232 Conveying roller 232A Second magnet 232B Second sleeve 233 Stirring screw 233A First screw 233B Second screw 234 Partition plate 235 Layer thickness regulating member 23H Housing 23H1 First inner wall Part 23H2 Second inner wall part 23H3 Third inner wall part 23H4 Fourth inner wall part 24 Primary transfer roller NP Development position TP Opposite position

Claims (10)

A first magnet including a plurality of magnetic poles fixed along a circumferential direction, and a periphery of the first magnet capable of rotating in a first rotational direction and a reverse rotational direction opposite to the first rotational direction. And a first sleeve carrying a developer containing toner and a magnetic carrier, and disposed at a predetermined development position so as to face a photosensitive drum having an electrostatic latent image formed on the surface thereof. A developing roller for supplying the toner;
A roller disposed so as to face the developing roller at a predetermined facing position; a second magnet fixed including a plurality of magnetic poles along a circumferential direction; and a periphery of the second magnet at the facing position A transport roller that rotates in a second rotation direction that is set to face the first rotation direction and carries the developer on a peripheral surface thereof, and supplies the developer to the development roller When,
A developer agitating unit for agitating the developer and supplying the developer to the transport roller;
A first drive unit that rotates the first sleeve of the developing roller in the first rotation direction and the reverse rotation direction;
A second drive unit that rotates the second sleeve of the transport roller in the second rotation direction;
A control unit for controlling the first drive unit and the second drive unit;
With
The first magnet is
A first magnetic pole disposed downstream of the opposing position in the first rotational direction; a second magnetic pole disposed upstream of the opposing position in the first rotational direction;
With
The second magnet is
A third magnetic pole disposed upstream of the opposing position in the second rotational direction; a fourth magnetic pole disposed downstream of the opposing position in the second rotational direction;
With
The gap between the developing roller and the transport roller at the facing position is set to be narrower than the gap between the photosensitive drum and the developing roller at the developing position,
During the developing operation in which the electrostatic latent image on the photosensitive drum is developed by the toner on the first sleeve of the developing roller, the control unit is supplied from the developer stirring unit to the transport roller. The developer is transferred from the transport roller to the developing roller by a magnetic field formed by the third magnetic pole and the first magnetic pole, and the developer that has passed through the developing position is transferred to the second magnetic pole and the first magnetic pole. The first sleeve is rotated in the first rotation direction and the second sleeve is rotated in the second rotation direction so as to be transferred from the developing roller to the transport roller by a magnetic field formed by four magnetic poles. Let
During a non-development operation different from the development operation, the control unit transfers the developer on the first sleeve of the development roller from the development roller to the transport roller while passing through the facing position. The developing device is configured to rotate the first sleeve in the reverse rotation direction and rotate the second sleeve in the second rotation direction.   The control unit rotates the first sleeve in the reverse rotation direction while the rotation of the second sleeve is stopped during the non-development operation, and then the first sleeve rotates in the reverse rotation direction. 2. The developing device according to claim 1, wherein the second sleeve is rotated in the second rotation direction in a state of being applied.   The control unit sets the rotation speed of the first sleeve in the reverse rotation direction during the non-development operation to be larger than the rotation speed of the first sleeve during the development operation in the first rotation direction. The developing device according to claim 1 or 2, characterized in that The third magnetic pole is a magnetic pole different from the first magnetic pole;
The developing device according to claim 1, wherein the fourth magnetic pole is a magnetic pole having the same polarity as the first magnetic pole. An angle formed by a straight line connecting the peak position of the magnetic force of the first magnetic pole and the rotation axis of the developing roller and a straight line connecting the rotation axis of the developing roller and the rotation axis of the transport roller is a first angle. Angle and
An angle formed by a straight line connecting the peak position of the magnetic force of the second magnetic pole and the rotation axis of the developing roller and a straight line connecting the rotation axis of the developing roller and the rotation axis of the transport roller is a second angle. Angle and
An angle formed by a straight line connecting the peak position of the magnetic force of the third magnetic pole and the rotation axis of the conveyance roller and a straight line connecting the rotation axis of the developing roller and the rotation axis of the conveyance roller is a third angle. Angle and
An angle formed by a straight line connecting the peak position of the magnetic force of the fourth magnetic pole and the rotation axis of the transport roller and a straight line connecting the rotation axis of the developing roller and the rotation axis of the transport roller is a fourth angle. If it is an angle,
The positions of the magnetic poles of the first magnet and the second magnet are set so that all of the first angle, the second angle, the third angle, and the fourth angle are 20 degrees or more and 40 degrees or less. The developing device according to claim 4, wherein the developing device is provided. The peak magnetic force of the first magnetic pole is M1 (mT), the peak magnetic force of the second magnetic pole is M2 (mT), the peak magnetic force of the third magnetic pole is M3 (mT), and the peak magnetic force of the fourth magnetic pole is M4 (mT). )
M3 <M1 <M4 and M2 <M4
The developing device according to claim 4, wherein the relationship is satisfied. M1 <M4-10, M2 <M4-10, and M3 <M4-10
The developing apparatus according to claim 6, wherein the relationship is further satisfied. The rotation axis of the developing roller is disposed below the rotation axis of the photosensitive drum,
The developing device according to claim 1, wherein a rotation axis of the transport roller is disposed below a rotation axis of the developing roller.   The developing device according to claim 1, wherein a developing bias in which an AC bias is superimposed on a DC bias is applied to the developing roller. A developing device according to any one of claims 1 to 9,
The photosensitive drum that is supplied with the toner from the developing device and carries a toner image on the peripheral surface;
A transfer unit for transferring the toner image from the photosensitive drum to a sheet;
An image forming apparatus comprising: