JP2017191218A - Developing device and image forming apparatus including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of color points caused by a toner accumulated on a layer thickness regulation member in a developing device comprising a plurality of rollers that each have a magnet therein and deliver a developer to each other, and to provide an image forming apparatus including the developing device.SOLUTION: A developing device 23 comprises a developing roller 231, a conveyance roller 232 and a control part 50. The developing roller 231 includes a first magnet 231A and a first sleeve 231B. The conveyance roller 232 includes a second magnet 232A and a second sleeve 232B. The control part 50 reversely rotates the first sleeve 231B in a non-developing operation period to form a developer retention part around an opposite position TP, and reversely rotates the second sleeve 232B to bring the developer in the retention part into contact with a top face part of a layer thickness regulation member 235.SELECTED DRAWING: Figure 2A

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.

  Patent Documents 2 and 3 disclose techniques in which the transport roller is rotated in reverse in order to collect the toner deposited on the layer thickness regulating member facing the transport roller.

Japanese Patent Laid-Open No. 04-107586 Japanese Patent Laid-Open No. 03-103882 JP 2011-13248 A

  In the configuration of the developing device including two magnet rollers as described in Patent Document 1, even if the transport roller is reversely rotated as described in Patent Documents 2 and 3, the layer thickness is restricted. There is a problem that the toner deposited on the member cannot be sufficiently collected and a color point is generated on the image.

  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, the color caused by the toner deposited on the layer thickness regulating member. An object of the present invention is to provide an image forming apparatus provided with the developing device while suppressing occurrence of dots.

  A developing device according to an aspect of the present invention includes a first magnet that includes a plurality of magnetic poles fixed along a circumferential direction, and a developer that rotates around the first magnet and includes toner and a magnetic carrier on a circumferential surface. A developing sleeve for supplying the toner to the photoconductive drum, a developing roller disposed on a surface of the photoconductive drum on which an electrostatic latent image is formed and facing the photoconductive drum at a predetermined developing position. A second magnet that includes a plurality of magnetic poles fixed along the direction, and a second sleeve that rotates around the second magnet and carries the developer on a peripheral surface thereof, and has a predetermined facing to the developing roller A transport roller that is disposed so as to face each other, supplies the developer to the developing roller, a developer stirring unit that stirs the developer and supplies the developer to the transport roller, and the transport roller Arranged opposite to The developer layer supplied to the transport roller from the developer agitation unit, and a top surface portion that is connected to the tip surface so as to intersect the tip surface so as to intersect vertically. A layer thickness regulating member that regulates the thickness, a first drive unit that rotates the first sleeve of the developing roller in the forward and reverse directions, and a second drive unit that rotates the second sleeve of the transport roller in the forward and reverse directions. And a drive control unit that controls the first drive unit and the second drive unit, wherein the drive control unit is supplied with the electrostatic latent image on the photosensitive drum from the developing roller. During the developing operation that is manifested by the toner, the first sleeve of the developing roller is rotated in a first rotation direction, and the second sleeve of the transport roller is moved in the first rotation direction at the facing position. Opposite And the second sleeve is rotated in a second rotation direction in which the second sleeve moves from a lower side to an upper side in a region where the front end surface of the layer thickness regulating member is opposed to the developer position. And rotating the first sleeve of the developing roller in a third rotation direction opposite to the first rotation direction during a non-development operation different from that during the development operation. A developer retaining portion is formed on the upstream side in the three rotation directions, and the developer in the retaining portion is further rotated by rotating the second sleeve of the transport roller in a fourth rotation direction opposite to the second rotation direction. Is brought into contact with the upper surface portion of the layer thickness regulating member.

  According to this configuration, the toner accumulated on the layer thickness regulating member is stably recovered by the staying portion made of a developer larger than the amount of developer carried on the second sleeve of the transport roller during normal rotation. can do.

  In the above configuration, the drive control unit moves the first sleeve of the developing roller in the third rotation direction in a state in which the rotation of the second sleeve of the transport roller is stopped during the non-developing operation. It is desirable to form the staying portion by rotating.

  According to this configuration, a developer retention portion can be stably formed between the developing roller and the transport roller.

  In the above configuration, the drive control unit may be configured such that, during the non-development operation, the second sleeve of the transport roller is rotated in the fourth rotation direction at a first peripheral speed. It is desirable to form the stay portion by rotating one sleeve in the third rotation direction at a second peripheral speed larger than the first peripheral speed.

  According to this configuration, the toner accumulated on the layer thickness regulating member is stably recovered by the staying portion made of a developer larger than the amount of developer carried on the second sleeve of the transport roller during normal rotation. can do.

  In the above configuration, the drive control unit rotates the first sleeve of the developing roller at the second peripheral speed during the developing operation and during the non-developing operation, and during the developing operation, It is desirable that the second sleeve is rotated at a third peripheral speed that is twice the first peripheral speed.

  According to this configuration, it is possible to form a stagnant portion made of a larger amount of developer than the amount of developer carried on the second sleeve of the transport roller during normal rotation as needed. Further, the peripheral speed of the developing roller during the developing operation and the non-developing operation can be made constant.

  In the above configuration, the drive control unit rotates the second sleeve of the transport roller at the first circumferential speed during the development operation and the non-development operation, and during the development operation, It is desirable that the first sleeve is rotated at a fourth peripheral speed that is a half speed of the second peripheral speed.

  According to this configuration, it is possible to form a stagnant portion made of a larger amount of developer than the amount of developer carried on the second sleeve of the transport roller during normal rotation as needed. Further, the peripheral speed of the transport roller during the developing operation and the non-developing operation can be made constant.

  In the above configuration, the first magnet is disposed on the downstream side in the first rotation direction of the facing position, and is disposed on the upstream side in the first rotation direction of the facing position and the first magnetic pole having a predetermined magnetic pole. A second magnetic pole having a different polarity from the first magnetic pole, wherein the second magnet is disposed to face the first magnetic pole on the upstream side in the second rotational direction of the facing position, and A third magnetic pole different in polarity from one magnetic pole, a fourth magnetic pole arranged opposite to the second magnetic pole on the downstream side in the second rotation direction of the opposing position, and a fourth magnetic pole different from the second magnetic pole, Preferably, the stagnant portion is formed by a magnetic field extending between the first magnetic pole and the third magnetic pole during the non-development operation.

  According to this configuration, the developer retaining portion can be more stably formed between the developing roller and the transport roller.

  In the above configuration, the second magnet is upstream in the second rotation direction with respect to the third magnetic pole, and further on the upstream side in the second rotation direction and below the tip surface of the layer thickness regulating member. And a fifth magnetic pole for regulating the layer thickness of the developer between the layer thickness regulating member and the layer thickness regulating member.

  According to this configuration, the developer that has contacted the upper surface portion of the layer thickness regulating member can be stably recovered in the developing device by the magnetic force of the fifth magnetic pole.

  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, the toner accumulated on the layer thickness regulating member is stably recovered by the staying portion made of a developer larger than the amount of developer carried on the second sleeve of the transport roller during normal rotation. can do. As a result, the generation of color points due to the toner deposited on the layer thickness regulating member is suppressed.

  According to the present invention, in a developing device including a plurality of rollers each having a magnet therein and delivering a developer to each other, generation of a color point due to toner deposited on the layer thickness regulating member is suppressed, and An image forming apparatus including a developing device is provided.

1 is a cross-sectional view showing an internal structure of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic cross-sectional view showing an internal structure of a developing device according to an embodiment of the present invention. It is a block diagram of a drive mechanism of a developing device according to an embodiment of the present invention. 5 is a flowchart illustrating a state in which a cleaning mode is executed in the developing device according to the first embodiment of the present invention. 6 is a timing chart showing how a cleaning mode is executed in the developing device according to the first embodiment of the present invention. FIG. 5 is a schematic diagram illustrating a state in which a cleaning mode is executed in the developing device according to the first embodiment of the present invention. FIG. 5 is a schematic diagram illustrating a state in which a cleaning mode is executed in the developing device according to the first embodiment of the present invention. FIG. 5 is a schematic diagram illustrating a state in which a cleaning mode is executed in the developing device according to the first embodiment of the present invention. FIG. 5 is a schematic diagram illustrating a state in which a cleaning mode is executed in the developing device according to the first embodiment of the present invention. 12 is a timing chart illustrating a state in which a cleaning mode is executed in the developing device according to the second embodiment of the present invention. 10 is a timing chart illustrating a state in which a cleaning mode is executed in a developing device according to a third embodiment of the present invention. It is a schematic diagram which shows a mode that cleaning mode is performed in the developing device which concerns on 2nd Embodiment of this invention. It is a schematic diagram which shows a mode that cleaning mode is performed in the developing device which concerns on 2nd Embodiment of this invention. It is a schematic diagram which shows a mode that cleaning mode is performed in the developing device which concerns on 2nd Embodiment of this invention. It is a schematic diagram which shows a mode that cleaning mode is performed in the developing device which concerns on 2nd Embodiment of this invention. 12 is a timing chart showing how a cleaning mode is executed in another developing device compared with the developing device according to the embodiment of the present invention. 6 is a graph showing the relationship between the number of printed sheets and the number of color points generated in an example of the present invention. 6 is a graph showing the relationship between the number of printed sheets and the number of color points generated in another embodiment of the present invention.

  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. 2A and 2B in addition to FIG. FIG. 2A is a schematic cross-sectional view showing the internal structure of the developing device 23 according to this embodiment. In FIG. 2A, the rotation direction of each rotating member of the developing device 23 is indicated by an arrow. FIG. 2B is a block diagram of the drive mechanism of the developing device 23 according to the present embodiment.

  2A, 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 regulating member 235. A developer conveying path 236 and a peeling member 237. 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 an electrostatic latent image is formed at a predetermined developing position NP (FIG. 2A), and supplies toner to the photosensitive drum 20. The developing roller 231 includes a first magnet 231A and a first sleeve 231B. 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, and carries a developer containing toner and a magnetic carrier on the peripheral surface. In the present embodiment, the first sleeve 231B is made of an aluminum circular pipe member (base material). The circumferential surface of the circular pipe member of the first sleeve 231B is subjected to sandblasting (blasting) and further includes a Ni plating layer applied on the circumferential surface. The surface of the Ni plating layer of the first sleeve 231B has a predetermined surface roughness. In the present embodiment, the surface roughness Rzjis 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.

  The transport roller 232 is disposed so as to face the developing roller 231 at a predetermined facing position TP (FIG. 2A), 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 and carries a developer including toner and a carrier on the peripheral surface. The second sleeve 232B of the transport roller 232 is rotatably supported by the housing 23H. The surface of the second sleeve 232B of the transport roller 232 has a known groove shape (knurled groove).

  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 shown in FIG. 2A, 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 to face each other at the facing position TP during the developing operation. (Counter direction)

  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. Further, the housing 23H includes a developer transport path 236 including a first stirring unit 236A in which the first screw 233A is disposed and a second stirring unit 236B in which the second screw 233B is disposed. The developer is circulated and conveyed between the first stirring unit 236A and the second stirring unit 236B. 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 unit 236A and the second stirring unit 236B along the axial direction of the first screw 233A and the second screw 233B. The first stirring unit 236A and the second stirring unit 236B communicate with each other at both ends of the partition plate 234. The toner replenished from the toner replenishing portion 15 flows into the housing 23H from one axial end side of the second agitating portion 236B and is agitated with 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. The layer thickness regulating member 235 is fixed to a support portion 235H provided in the housing 23H. In another embodiment, a magnetic member may be fixed to the upstream side surface of the layer thickness regulating member 235. The layer thickness regulating member 235 includes a front end surface disposed to face the transport roller 232 and an upper surface portion that is connected to the front end surface so as to intersect the front end surface and faces vertically upward. 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. Further, during the developing operation, the first screw 233A is rotated below the layer thickness regulating member 235 so that the outer peripheral portion thereof moves from the bottom to the top.

  Further, as shown in FIG. 2A, the axis of the transport roller 232 is disposed further below the axis of the developing roller 231. The developer composed of toner and carrier and circulated and conveyed by the agitating screw 233 is supplied to the conveying roller 232 from the first screw 233A. Thereafter, after the layer thickness of the developer is regulated by the layer thickness regulating member 235, the developer is supplied to the developing roller 231. When a part of the toner is supplied to the photosensitive drum 20 at the development position NP, the developer is collected from the development roller 231 to the transport roller 232. Thereafter, the developer collected by the transport roller 232 flows into the developer transport path 236 again.

  With reference to FIG. 2B, the developing device 23 includes a control unit 50 (drive control unit), a first drive unit 51, a second drive unit 52, and a clutch 53.

  The first drive unit 51 includes a motor and a gear (not shown), and the motor of the first drive unit 51 can rotate forward and backward. The first drive unit 51 moves the first sleeve 231B of the developing roller 231 in the first rotation direction (the direction of arrow D1 in FIG. 2A) and the third rotation direction opposite to the first rotation direction (see the direction of arrow D3 in FIG. 5B). Rotate to Similarly, the second drive unit 52 includes a motor and a gear (not shown). The motor of the second drive unit 52 can also rotate forward and reverse. The second drive unit 52 moves the second sleeve 232B of the transport roller 232 in the second rotation direction (the direction of arrow D2 in FIG. 2A) and the fourth rotation direction opposite to the second rotation direction (see the direction of arrow D4 in FIG. 5C). Rotate to Further, the second drive unit 52 rotates the first screw 233A and the second screw 233B of the stirring screw 233 in the arrow direction of FIG. 2A. When the second driving unit 52 rotates the second sleeve 232B of the transport roller 232 in the fourth rotation direction, the rotation of the stirring screw 233 is stopped by the action of the clutch 53. The control unit 50 controls the on / off timing of the first drive unit 51 and the second drive unit 52 and the rotation direction of the first drive unit 51 and the second drive unit 52.

  In the present embodiment, the first magnet 231A of the developing roller 231 includes six magnetic poles along the circumferential direction (FIG. 2A). The N21 pole (first magnetic pole) is arranged downstream of the opposing position TP between the developing roller 231 and the transport roller 232 in the first rotation direction (D1). Further, the S21 pole is disposed downstream of the N21 pole in the first rotation direction. The S21 pole functions as a transport pole for transporting the developer received from the transport roller 232 to the photosensitive drum 20 side. Further, an N22 pole that functions as a main pole for supplying toner to the photosensitive drum 20 is disposed downstream of the S21 pole in the first rotation direction. The N22 pole is disposed in the vicinity of the development position NP.

  Furthermore, the first magnet 231A includes three magnetic poles (S22, N23, S23) on the downstream side in the first rotation direction from the development position NP and on the upstream side in the first rotation direction from the facing position TP. The S22 pole is disposed on the downstream side of the N22 pole in the first rotation direction, and is a magnetic pole different from N22. The N23 pole is disposed downstream of the S22 pole in the first rotation direction, and is a magnetic pole different from the S22 pole. Further, the S23 pole (second magnetic pole) is disposed downstream of the N23 pole in the first rotation direction, and is a magnetic pole different from the N23 pole. In addition, the S23 pole is disposed on the upstream side of the opposing position TP in the first rotation direction, and is a magnetic pole different from the N21 pole.

  On the other hand, the second magnet 232A of the transport roller 232 includes five magnetic poles along the circumferential direction. An N11 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 S11 pole is disposed downstream of the N11 pole in the second rotation direction. Furthermore, the S12 pole is arranged at an interval on the downstream side in the second rotation direction of the S11 pole. The S11 pole functions as a peeling pole for peeling the developer from the transport roller 232. In addition, the plate-shaped peeling member 237 (FIG. 2A) is arranged at an interval with respect to the transport roller 232 so as to face the S11 pole. The S12 pole functions as a pumping pole that pumps up the developer from the first screw 233A. An N12 pole and an S13 pole are disposed downstream of the S12 pole in the second rotation direction. As shown in FIG. 2A, the layer thickness regulating member 235 is disposed on the second sleeve 232B of the transport roller 232 on the upstream side in the second rotational direction from the S13 pole and on the downstream side in the second rotational direction of the N12 pole. They are arranged facing each other at a predetermined interval. For this reason, the developer layer thickness can be stably regulated before the developer is transferred from the transport roller 232 to the developing roller 231. The N12 pole is disposed upstream and below the second rotation direction of the front end surface of the layer thickness regulating member 235, and functions as a regulating electrode that regulates the layer thickness of the developer with the layer thickness regulating member 235. . Further, the above-described S13 pole is disposed on the upstream side in the second rotation direction of the facing position TP.

  Table 1 shows the angle and magnetic force (peak value of the radial component) of each magnetic pole as an example of the first magnet 231A of the developing roller 231 and the second magnet 232A of the transport roller 232 according to this embodiment. . The angle of each magnetic pole shown in Table 1 starts from a straight line CL connecting the rotation axis of the developing roller 231 and the rotation axis of the conveying roller 232, and the developing roller 231 is in the first rotation direction. Roller 232 is shown along the second rotational direction.

  Referring to FIG. 2A, during the developing operation in which the electrostatic latent image on the photosensitive drum 20 is made visible by the toner supplied from the developing roller 231, the control unit 50 moves the first sleeve 231 </ b> B of the developing roller 231 to the first position. An area in which the second sleeve 232B of the transport roller 232 is rotated in one rotation direction (D1) and is opposed to the first rotation direction at the opposed position TP, and the tip surface of the layer thickness regulating member 235 is opposed to the area. The second sleeve 232B is rotated in the second rotation direction (D2) that moves from the lower side toward the upper side. As a result, the developer that has passed through the layer thickness regulating member 235 is supplied to the development position NP. At this time, the developer is transferred from the transport roller 232 to the developing roller 231 by a magnetic field formed by the S13 pole of the second magnet 232A and the N21 pole of the first magnet 231A. On the other hand, in the present embodiment, the upper surface portion of the layer thickness regulating member 235 is disposed at a predetermined angle with respect to the horizontal direction or the horizontal direction so as to face at least vertically upward. Therefore, the toner scattered from the developer that has passed through the layer thickness regulating member 235 with the rotation of the second sleeve 232B is likely to accumulate on the upper surface portion of the layer thickness regulating member 235. The toner deposited in this manner is unstable in charging and forms toner aggregates. During the developing operation of the developing device 23, when toner aggregates are reattached to the second sleeve 232 </ b> B and then supplied from the developing roller 231 to the photosensitive drum 20, a color point is generated on the image.

  In this embodiment, in order to solve such a problem, the control unit 50 executes the cleaning mode during a non-development operation different from the development operation. Next, the cleaning mode according to the first embodiment of the present invention will be described. FIG. 3 is a flowchart showing how the cleaning mode is executed in the developing device 23 according to the present embodiment. FIG. 4 is a timing chart showing how the cleaning mode is executed in the developing device 23. 5A to 5D are schematic diagrams illustrating a state in which the cleaning mode is executed in the developing device 23. FIG.

  Referring to FIG. 3, when the print job is completed in image forming apparatus 1 (step S1), control unit 50 determines whether or not the number of printed sheets PV printed after the previous cleaning mode is 50 or more. Determine (step S2). Here, when PV ≧ 50 (YES in step S2), the control unit 50 executes the cleaning mode of the layer thickness regulating member 235 (step S3). Thereafter, the control unit 50 performs Ready display on a display unit (not shown) provided in the image forming apparatus 1 (step S4), and notifies that the next print job can be executed. If PV <50 in step S2, the controller 50 proceeds to step S4 without executing the cleaning mode.

  Next, details of the cleaning mode executed in step S3 will be further described. When the cleaning mode is executed, the control unit 50 rotates the first sleeve 231B of the developing roller 231 and the second sleeve 232B of the transport roller 232 in the first direction and the second direction, respectively, for T11 hours (see FIG. 5A). . At this time, the scattered toner TF is deposited on the upper surface portion of the layer thickness regulating member 235. In another embodiment, the rotation for the time T11 may be applied by the rotation in the immediately preceding print job. As described above, the first sleeve 231B and the second sleeve 232B are forwardly rotated in advance, so that the chargeability of the toner on each sleeve is stabilized.

  Next, the control unit 50 rotates the first sleeve 231B of the developing roller 231 in the third rotation direction for T12 time (FIG. 4) in a state where the rotation of the second sleeve 232B of the transport roller 232 is stopped (FIG. 4). 5B). As a result, a developer retention portion TD is formed on the upstream side in the third rotational direction of the facing position TP (FIG. 2). At this time, the staying portion TD is stably formed by the magnetic lines of force (magnetic field) extending between the S13 pole of the first magnet 231A and the N21 pole of the second magnet 232A.

  Next, the control unit 50 rotates the first sleeve 231B in the third rotation direction and the second sleeve 232B in the fourth rotation direction for T13 hours, respectively (see FIG. 4). As a result, the developer in the staying portion TD flows into the housing 23H below the layer thickness regulating member 235 while moving so as to wipe the upper surface portion of the layer thickness regulating member 235 (FIG. 5C). At this time, the scattered toner accumulated on the upper surface portion of the layer thickness regulating member 235 is collected in the housing 23H along with the flow of the developer (see FIG. 5D). After that, the control unit 50 rotates the first sleeve 231B and the second sleeve 232B in the first rotation direction and the second rotation direction for T14 time, respectively (FIG. 4). As a result, the developer layer is formed again on the developing roller 231 and the preparation for the next print job is completed.

  As described above, the control unit 50 rotates the first sleeve 231B of the developing roller 231 in the third rotation direction opposite to the first rotation direction during a non-development operation that is different from the development operation. A developer retention portion TD is formed on the upstream side in the third rotation direction of TP. Furthermore, the control unit 50 rotates the second sleeve 232 </ b> B of the transport roller 232 in the fourth rotation direction opposite to the second rotation direction so that the developer in the staying portion TD contacts the upper surface portion of the layer thickness regulating member 235. Let For this reason, the toner deposited on the layer thickness regulating member 235 can be stably recovered by the staying portion TD made of a developer larger than the amount of developer carried on the second sleeve 232B during normal rotation. it can.

  In addition, the controller 50 stays by rotating the first sleeve 231B of the developing roller 231 in the third rotation direction while the rotation of the second sleeve 232B of the transport roller 232 is stopped during the non-developing operation. A portion TD is formed. For this reason, the stay part TD of the developer can be stably formed between the developing roller 231 and the transport roller 232.

  In the present embodiment, the N12 pole that regulates the layer thickness of the developer with respect to the layer thickness regulating member 235 is arranged on the upstream side in the second rotational direction and below the tip surface of the layer thickness regulating member 235. Yes. Therefore, in the cleaning mode, the developer that has come into contact with the upper surface portion of the layer thickness regulating member 235 can be stably recovered inside the housing 23H by the magnetic force of the N12 pole. At this time, the rotation of the first screw 233A is stopped by the action of the clutch 53 (FIG. 2B), so that the developer that has entered the housing 23H is pushed upward by the rotational force of the first screw 233A. Deterred.

  Further, in the present embodiment, the developer is stably supplied from the developing roller 231 to the transport roller 232 during the developing operation by the magnetic field formed by the S23 pole of the first magnet 231A and the N11 pole of the second magnet 232A having different polarities. Can be handed over. Further, the axis of the transport roller 232 is disposed below the axis of the developing roller 231. For this reason, coupled with the action of gravity, the developer is stably delivered from the developing roller 231 to the transport roller 232.

  In the present embodiment, the developer is stably supplied from the transport roller 232 to the developing roller 231 during the developing operation by the magnetic field formed by the S13 pole of the second magnet 232A and the N21 pole of the first magnet 231A. Can be supplied. Therefore, a developer transfer area between the developing roller 231 and the transport roller 232 is stably formed in a different direction at a position sandwiching the facing position TP. In this embodiment, 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. In other words, 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. Then, the developer is transferred between the developing roller 231 and the transport roller 232 so as to sandwich the opposing 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 if the gap at the facing position TP is set narrow as described above, the developer is prevented from sticking to the facing position TP due to the presence of the developer. Further, the developer in the staying portion TD formed in the cleaning mode is prevented from aggregating at the facing position TP. 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, a second embodiment and a third embodiment of the present invention will be described. 6 and 7 are timing charts showing how the cleaning mode is executed in the developing devices according to the second and third embodiments of the present invention, respectively. 8A to 8D are schematic views showing a state where the cleaning mode is executed in the developing device according to the second embodiment of the present invention. Since the second embodiment and the third embodiment are different in step S3 in FIG. 3 as compared with the first embodiment, the difference will be mainly described. In the second embodiment and the third embodiment, the first drive unit 51 and the second drive unit 52 can change the peripheral speeds of the first sleeve 231B and the second sleeve 232B. In the cleaning mode, the control unit 50 (FIG. 2B) moves the first sleeve 231B of the developing roller 231 in the state where the second sleeve 232B of the transport roller 232 is rotated in the fourth rotation direction at the first peripheral speed. The stay part TD is formed by rotating in the third rotation direction at a second peripheral speed larger than the peripheral speed of 1.

  With reference to FIG. 6, in the second embodiment, the control unit 50 moves the first sleeve 231B of the developing roller 231 and the second sleeve 232B of the transport roller 232 in the first rotation direction and the second rotation direction, respectively, for T21 hours. Rotate (see FIG. 8A). Then, the control unit 50 rotates the first sleeve 231B of the developing roller 231 and the second sleeve 232B of the transport roller 232 in the third rotation direction and the fourth rotation direction, respectively, for T22 time (see FIG. 8B). At this time, the control unit 50 rotates the first sleeve 231B in the third rotation direction at a peripheral speed (fourth peripheral speed) that is double the peripheral speed (second peripheral speed) during the normal developing operation. On the other hand, the control unit 50 rotates the second sleeve 232B in the fourth rotation direction at the same peripheral speed as the peripheral speed (first peripheral speed) during the normal developing operation. As a result, a speed difference is generated between the first sleeve 231B and the second sleeve 232B around the facing position TP. Accordingly, the developer staying part TD is always in contact with the upper surface of the layer thickness regulating member 235 while the developer staying part TD is formed near the upstream side in the third rotation direction of the facing position TP ( FIG. 8C). As a result, the developer in the retention portion TD flows into the housing 23H (FIG. 2) below the layer thickness regulating member 235 while moving so as to wipe the upper surface portion of the layer thickness regulating member 235. At this time, the scattered toner accumulated on the upper surface portion of the layer thickness regulating member 235 is collected in the housing 23H together with the flow of the developer (see FIG. 8D). Thereafter, the control unit 50 rotates the first sleeve 231B and the second sleeve 232B in the first rotation direction and the second rotation direction for T23 time (FIG. 6), respectively. As a result, the developer layer is formed again on the developing roller 231 and the preparation for the next print job is completed.

  On the other hand, referring to FIG. 7, in the third embodiment, the control unit 50 moves the first sleeve 231 </ b> B of the developing roller 231 and the second sleeve 232 </ b> B of the transport roller 232 to T <b> 31 in the first rotation direction and the second rotation direction, respectively. Rotate for hours. Then, the control unit 50 rotates the first sleeve 231B of the developing roller 231 and the second sleeve 232B of the transport roller 232 in the third rotation direction and the fourth rotation direction, respectively, for T32 hours. At this time, the control unit 50 rotates the first sleeve 231B in the third rotation direction at the peripheral speed (second peripheral speed) during the normal developing operation. On the other hand, the control unit 50 rotates the second sleeve 232B in the fourth rotation direction at a peripheral speed (first peripheral speed) that is half the peripheral speed (third peripheral speed) during the normal developing operation. As a result, a speed difference is generated between the first sleeve 231B and the second sleeve 232B around the facing position TP. Accordingly, the developer staying portion TD is always in contact with the upper surface portion of the layer thickness regulating member 235 while the developer staying portion TD is formed near the upstream side in the third rotation direction of the facing position TP. The scattered toner deposited on the upper surface portion of the layer thickness regulating member 235 is collected in the housing 23H together with the developer flow. Thereafter, the control unit 50 rotates the first sleeve 231B and the second sleeve 232B in the first rotation direction and the second rotation direction for T33 time (FIG. 7), respectively. As a result, the developer layer is formed again on the developing roller 231 and the preparation for the next print job is completed.

  In the second embodiment and the third embodiment as described above, the layer thickness regulating member 235 is also formed by the staying portion TD made of a developer larger than the amount of developer carried on the second sleeve 232B during normal rotation. The toner deposited thereon can be recovered stably. In the second embodiment, the peripheral speed of the transport roller 232 during the developing operation and the non-developing operation (in the cleaning mode) can be made constant. In the third embodiment, the peripheral speed of the developing roller 231 can be constant during the developing operation and the non-developing operation (in the cleaning mode).

Next, based on an Example, this invention is further demonstrated. Each experiment was performed under the following experimental conditions.
<Experimental conditions>
Photosensitive drum 20: Amorphous silicon photosensitive member (a-Si), diameter φ30 mm, surface potential Vo = 270 V, peripheral speed = 165 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
Toner: 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 φ16mm
・ Linear speed of developing roller 231: 298 mm / sec
A gap between the developing roller 231 and the photosensitive drum 20: 350 μm
Development bias: DC bias = 170 V, AC bias = Vpp 1.4 kV, frequency f4.7 kHz, Duty 50%, rectangular wave (note that the development bias of the transport roller 232 is also at the same potential)
-Surface condition of the first sleeve 231B: sand blast (Rzjis 8 μm)
The magnetic pole distribution of the developing roller 231 used in the experiment is shown in Table 1 above. In addition, the magnetic force measurement of the developing roller 231 and the conveyance roller 232 was performed using Japan Electromagnetic Instrument Co., Ltd. GAUSS METER Model GX-100.

Moreover, the conditions of the conveyance roller 232 used for experiment are as follows.
・ Conveying roller 232: Diameter φ16mm
-Surface condition of the second sleeve 232B: Knurled V groove (groove depth 80 μm, groove width 0.2 mm, number of grooves 120)
・ Linear speed of transport roller 232: 298 mm / sec
-Gap between transport roller 232 and developing roller 231: 300 μm
The magnetic pole distribution of the transport roller 232 used in the experiment is shown in Table 1 above.

<Experiment 1>
In Experiment 1, 50 image charts each having a printing rate of 20% for each color were printed continuously under one of the above conditions, and repeated 100 JOBs. In Example 1, the cleaning mode of the first embodiment is executed at the end of each JOB, and in the comparative example, the cleaning mode consisting of the timing chart shown in FIG. 9 is executed. That is, in the comparative example, the first sleeve 231B of the developing roller 231 and the second sleeve 232B of the transport roller 232 are reversely rotated in synchronization only during the time T02. FIG. 10 is a graph showing the relationship between the number of printed sheets and the number of generated color points in Example 1 and Comparative Example in Experiment 1. In either case, the number of color points generated in the image is counted until 5000 sheets are printed. When an image pattern with a large amount of scattered toner continues to be printed such as a printing rate of 20%, in the comparative example, a color point was randomly generated on a blank paper portion on the image after printing 1000 sheets. On the other hand, in Example 1, generation of color points was suppressed up to 5000 sheets.

<Experiment 2>
In Experiment 2, as in Experiment 1, 50 image charts with a printing rate of 20% for each color were printed continuously per JOB, and 100 JOBs were repeated. In Example 2, the cleaning mode of the previous second embodiment is executed at the end of each JOB, and in Example 3, the cleaning mode of the previous third embodiment is executed at the end of each JOB. Compared. FIG. 11 is a graph showing the relationship between the number of printed sheets and the number of generated color points in Example 2, Example 3, and Comparative Example in Experiment 2. Even when an image pattern with a large amount of scattered toner continues to be printed such as a printing rate of 20%, in Example 2 and Example 3, the generation of color points was suppressed to 3000 sheets. Further, even in the range of 3000 to 5000 sheets, Examples 2 and 3 resulted in greatly suppressing the generation of color points as compared with the comparative example.

As for the condition of the first sleeve 231B of the developing roller 231, the same evaluation as in Experiment 1 and Experiment 2 was performed in the range of Rzjis 4 μm or more and 14 μm or less, and it was found that the same result as above was obtained. Further, in each of Experiment 1 and Experiment 2, the gap (blade gap) between the layer thickness regulating member 235 and the second sleeve 232B is adjusted, and the toner conveyance amount on the first sleeve 231B is 100 g / m ² or more and 400 g / m ² or more. ^When the same evaluation was performed within a range of ² or less, similar results were obtained with respect to the effect of suppressing the color point. Further, in each of Experiment 1 and Experiment 2, when the same evaluation as described above was performed in a toner concentration range of 5% to 12%, similar results were obtained with respect to the effect of suppressing the color point. Further, when the same evaluation is performed in the range where the diameter of the developing roller 231 and the transport roller 232 is 12 m or more and 35 mm or less and the peripheral speed of the photosensitive drum 20 is 100 mm / sec or more and 400 mm / sec or less, the color point Similar results were obtained with respect to the inhibitory effect.

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 Stir Screw (Developer Stirrer)
233A First screw 233B Second screw 234 Partition plate 235 Layer thickness regulating member 23H Housing 24 Primary transfer roller 50 Control unit (drive control unit)
51 1st drive part 52 2nd drive part 53 Clutch NP Development position TP Opposite position

Claims (8)

A first magnet that includes a plurality of magnetic poles fixed along the circumferential direction, and a first sleeve that rotates around the first magnet and carries a developer containing toner and a magnetic carrier on the circumferential surface, A developing roller that is disposed to face a photosensitive drum on which an electrostatic latent image is formed at a predetermined developing position, and supplies the toner to the photosensitive drum;
A second magnet that is fixed including a plurality of magnetic poles along the circumferential direction, and a second sleeve that rotates around the second magnet and carries the developer on a circumferential surface thereof, and the developing roller has a predetermined A transport roller that is arranged to face at a facing position and supplies the developer to the development roller;
A developer agitating unit for agitating the developer and supplying the developer to the transport roller;
A front end surface disposed facing the transport roller, and an upper surface portion connected to the front end surface so as to intersect the front end surface and facing vertically upward, from the developer stirring unit to the transport roller A layer thickness regulating member for regulating the layer thickness of the supplied developer;
A first drive unit that rotates the first sleeve of the developing roller in forward and reverse directions;
A second drive unit that rotates the second sleeve of the transport roller in forward and reverse directions;
A drive control unit for controlling the first drive unit and the second drive unit;
Have
The drive control unit
During the developing operation in which the electrostatic latent image on the photosensitive drum is made visible by the toner supplied from the developing roller, the first sleeve of the developing roller is rotated in a first rotation direction, and the The second sleeve of the transport roller is in a direction facing the first rotation direction at the facing position, and the region where the second sleeve faces the tip end surface of the layer thickness regulating member is directed from below to above. The developer is supplied to the development position by rotating in the second rotational direction of movement,
By rotating the first sleeve of the developing roller in a third rotation direction opposite to the first rotation direction during a non-development operation different from the development operation, the upstream position in the third rotation direction of the opposite position is increased. A developer retaining portion is formed on the side, and the second sleeve of the transport roller is rotated in a fourth rotational direction opposite to the second rotational direction, thereby causing the developer in the retaining portion to have the layer thickness. A developing device which is brought into contact with the upper surface portion of the regulating member.   The drive control unit rotates the first sleeve of the developing roller in the third rotation direction in a state where the rotation of the second sleeve of the transport roller is stopped during the non-developing operation. The developing device according to claim 1, wherein the staying portion is formed.   In the non-development operation, the drive control unit moves the first sleeve of the developing roller in the state in which the second sleeve of the transport roller is rotated in the fourth rotation direction at a first peripheral speed. 2. The developing device according to claim 1, wherein the staying portion is formed by rotating in the third rotation direction at a second peripheral speed larger than a peripheral speed of one. The drive control unit
Rotating the first sleeve of the developing roller at the second peripheral speed during the developing operation and the non-developing operation;
4. The developing device according to claim 3, wherein, during the developing operation, the second sleeve of the transport roller is rotated at a third peripheral speed that is double the first peripheral speed. 5. The drive control unit
During the developing operation and the non-developing operation, the second sleeve of the transport roller is rotated at the first peripheral speed,
4. The developing device according to claim 3, wherein, during the developing operation, the first sleeve of the developing roller is rotated at a fourth peripheral speed that is a half speed of the second peripheral speed. 5. The first magnet is
A first magnetic pole disposed on the downstream side of the opposing position in the first rotation direction and having a predetermined magnetic pole;
A second magnetic pole disposed on the upstream side of the opposing position in the first rotation direction, and having a different polarity from the first magnetic pole;
With
The second magnet is
A third magnetic pole disposed opposite to the first magnetic pole on the upstream side of the opposing position in the second rotational direction, and having a different polarity from the first magnetic pole;
A fourth magnetic pole disposed opposite to the second magnetic pole on the downstream side in the second rotational direction of the opposing position, and having a different polarity from the second magnetic pole;
With
6. The developing device according to claim 1, wherein the staying portion is formed by a magnetic field extending between the first magnetic pole and the third magnetic pole during the non-development operation.   The second magnet is disposed upstream of the third magnetic pole in the second rotation direction, further upstream and below the second rotation direction of the tip surface of the layer thickness regulating member, The developing device according to claim 6, further comprising a fifth magnetic pole for regulating a layer thickness of the developer between the layer thickness regulating member. A developing device according to any one of claims 1 to 7,
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:

Images