JP6460023B2 - 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 layer thickness of the developer on the conveyance roller is regulated by the layer thickness regulating member arranged to face the conveyance roller. The developer is supplied from the transport roller to the developing roller by a magnetic force generated between the first S pole on the transport 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. In such a developing device, the function of supplying the developer to the photosensitive drum and the function of regulating the transport amount (layer thickness) of the developer are separated, and the two rollers can have individual functions.

Japanese Patent Laid-Open No. 04-107586

  In recent years, toner for low-temperature fixing has been developed, and developer agglomerates are easily generated in a developing device. In the developing device as described above, a partial difference is likely to occur in the transport amount of the developer on the downstream side of the layer thickness regulating member due to aggregates clogged on the back side of the layer thickness regulating member. This difference in the transport amount remains even in the developer layer transferred from the transport roller to the developing roller, so that there is a problem that it appears as white stripes 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 provided with a magnet inside and delivering a developer to each other, while suppressing the occurrence of white stripes, An object is to provide an image forming apparatus provided.

  A developing device according to one aspect of the present invention includes a first magnet fixed including a plurality of magnetic poles along a circumferential direction, and a toner and a magnetic carrier on a circumferential surface rotating around the first magnet in a first rotation direction. And a first sleeve that carries a developer containing the toner, and is disposed to face a photosensitive drum on which an electrostatic latent image is formed at a predetermined development position, and supplies the toner to the photosensitive drum. A developing roller, a second magnet fixed including a plurality of magnetic poles along the circumferential direction, a second sleeve rotating around the second magnet in the second rotational direction and carrying the developer on the circumferential surface; A conveying roller that is arranged to face the developing roller at a predetermined facing position, supplies the developer to the developing roller, and agitates the developer, and supplies the developer to the conveying roller. A developer stirring section to A layer thickness regulating member that is disposed to face the conveyance roller and regulates a layer thickness of the developer supplied from the developer stirring unit to the conveyance roller, and includes the first rotation direction and the second rotation direction. The rotation direction is set to a direction opposite to each other at the facing position, and the first magnet is located on the first magnetic pole and the first magnetic pole disposed upstream of the facing position in the first rotation direction. A second magnetic pole arranged adjacent to the opposite position on the downstream side in the one rotation direction, and the second magnet is arranged on the upstream side in the second rotation direction from the opposite position, and A third magnetic pole disposed opposite to the second magnetic pole of the first magnet, and the third magnetic pole adjacent to the third magnetic pole on the downstream side in the second rotational direction with the opposing position interposed therebetween; and A first magnet disposed opposite to the first magnetic pole of the first magnet; And the second magnetic pole and the third magnetic pole are magnetic poles of the same polarity, and at least one of the first magnetic pole and the fourth magnetic pole is a magnetic pole of the same polarity as the second magnetic pole. The developer supplied from the developer stirring unit to the transport roller by the magnetic field formed by the third magnetic pole and the second magnetic pole is transferred from the transport roller to the development roller, and the first The developer passing through the developing position is transferred from the developing roller to the transport roller by a magnetic field formed by the magnetic pole and the fourth magnetic pole.

  According to this configuration, 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 developing position, the developer is collected from the developing roller to the transport roller. Further, a retentive portion in which the developer is partially retained on the second sleeve is formed by the repulsive force of the second magnetic pole and the third magnetic pole having the same polarity. Since the developer can move in the axial direction in the staying part, there is a partial difference in the layer amount in the developer layer after the layer thickness regulation due to developer aggregates or clogging of foreign matters. Even so, the difference in the layer amount is reduced by the movement of the developer. Further, since at least one of the first magnetic pole and the fourth magnetic pole is the same magnetic pole as the second magnetic pole, a repulsive magnetic field is stably formed by the second magnetic pole and the third magnetic pole, and the conveyance roller to the developing roller The delivery of the developer is stably realized.

  In the above configuration, one of the first magnetic pole and the fourth magnetic pole is the same magnetic pole as the second magnetic pole, and the other of the first magnetic pole and the fourth magnetic pole is the second magnetic pole. A magnetic pole with a different polarity is desirable.

  According to this configuration, the developer can be stably transferred from the transport roller to the developing roller.

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

  According to this configuration, the developer can be particularly stably transferred from the transport roller to the developing roller.

  In the above configuration, the fourth magnetic pole is preferably a magnetic pole having the same polarity as the second magnetic pole, and the first magnetic pole is preferably a magnetic pole having a different polarity from the second magnetic pole.

  According to this configuration, the developer can be particularly stably transferred from the transport roller to the developing roller.

  In the above configuration, when the peripheral speed of the developing roller is Vd (mm / sec) and the peripheral speed of the transport roller is Vc (mm / sec), a relationship of 0.2 ≦ Vc / Vd <1.0 is satisfied. It is desirable to satisfy.

  According to this configuration, since the peripheral speed Vc of the transport roller is slower than the peripheral speed Vd of the developing roller, the developer retention portion is stably formed. In addition, it is possible to suppress the occurrence of poor conveyance on the conveyance roller due to the large amount of developer in the developer layer after the layer thickness regulation, and there is a poor delivery of developer from the conveyance roller to the development roller. Occurrence is suppressed.

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

  According to this configuration, foreign substances and aggregates contained in the developer retention portion are prevented from being transferred to the developing roller side by the action of gravity.

  In the above configuration, the outer peripheral position of the second sleeve facing the peak position of the radial component of the magnetic force of the third magnetic pole is the first sleeve facing the peak position of the radial component of the magnetic force of the second magnetic pole. It is desirable to arrange below the outer peripheral position.

  According to this configuration, the foreign matter contained in the developer retention portion is further suppressed from being transferred to the developing roller side.

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

  According to this configuration, even when an oscillating electric field composed of an AC bias is formed at the development position and white streaks are likely to be manifested, the generation of white streaks is suppressed by the movement of the developer in the staying portion.

  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, there is provided an image forming apparatus that can suppress the occurrence of white stripes and can form a stable image.

  According to the present invention, there is provided a developing device that includes a magnet inside and includes a plurality of rollers that deliver developer to each other, and suppresses the occurrence of white streaks and provides an image forming apparatus that includes the developing device. .

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. FIG. 5 is a schematic diagram illustrating the periphery of a facing position in the developing roller and the transport roller 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 of a developing device and the conveyance roller which concern on the deformation | transformation embodiment of this invention. It is typical sectional drawing which shows magnetic pole arrangement | positioning of the developing roller of a developing device and the conveyance roller which concern on the deformation | transformation embodiment of this invention. It is typical sectional drawing which shows the structure of the housing of the developing device which concerns on deformation | transformation embodiment of this invention. It is typical sectional drawing which shows the magnetic pole arrangement | positioning of the developing roller of another developing device compared with 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 of 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. 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. In other embodiments, the circumferential surface of the first sleeve 231B may be provided with a known groove shape.

  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 toner and carrier on the peripheral surface. The second sleeve 232B of the transport roller 232 is rotatably supported by the housing 23H. A known groove shape is formed on the peripheral surface of the second sleeve 232 </ b> B of the transport roller 232.

  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 (FIG. 2). The layer thickness regulating member 235 is connected so as to have the same potential as the transport roller 232 through a conduction path (not shown). 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 so as to face each other at the facing position TP (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. 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. 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 upstream side surface 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.

  As shown in FIG. 2, the axis of the developing roller 231 is disposed below the axis of the photosensitive drum 20, and the axis of the transport roller 232 is further below the axis of the developing roller 231. Has been placed.

  Referring to FIG. 2, the developer composed of toner and carrier and circulated and conveyed by stirring screw 233 is supplied from first screw 233 </ b> A to conveying roller 232. 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 (FIG. 3), the developer is collected from the development roller 231 to the transport roller 232. Thereafter, the developer collected on the transport roller 232 again flows into the first stirring unit around the first screw 233A.

  With reference to FIG. 3 and FIG. 4, in the present embodiment, the first magnet 231 </ b> A of the developing roller 231 includes five magnetic poles along the circumferential direction. An N11 pole (second magnetic pole) is disposed on the downstream side in the first rotation direction (D1) from the facing position TP between the developing roller 231 and the transport roller 232. Further, the S11 pole is disposed downstream of the N11 pole in the first rotation direction. The S11 pole functions as a transport pole for transporting the developer received from the transport roller 232 to the photosensitive drum 20 side. Further, an N12 pole that functions as a main pole that supplies toner to the photosensitive drum 20 is disposed downstream of the S11 pole in the first rotation direction. The N12 pole is disposed in the vicinity of the development position NP.

  Furthermore, the first magnet 231A includes two magnetic poles (S12, N13) in the first region downstream of the developing position NP in the first rotational direction and upstream of the opposing position TP in the first rotational direction. Yes. The S12 pole is disposed downstream of the N12 pole in the first rotation direction. The N13 pole (first magnetic pole) is a magnetic pole that is adjacent to the S12 pole on the downstream side in the first rotation direction and is located upstream of the opposing position TP in the first rotation direction. The N11 pole described above is arranged adjacent to the N13 pole on the downstream side in the first rotation direction with the facing position TP interposed therebetween.

  Table 1 shows examples of the angles and magnetic forces (peak values of radial components) of five 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 that connects the facing position TP and the rotation axis of the developing roller 231 (a straight line that connects the rotation axis of the developing roller 231 and the rotation axis of the transport roller 232) is shown as the start point. .

  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. An S1 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 N1 pole is disposed downstream of the S1 pole in the second rotation direction. Further, the N2 pole is arranged at an interval on the downstream side of the N1 pole in the second rotation direction. The N1 pole functions as a peeling electrode for peeling the developer from the transport roller 232. The N2 pole functions as a pumping pole that pumps up the developer from the first screw 233A. The S2 pole and the N3 pole (third magnetic pole) are disposed downstream of the N2 pole in the second rotation direction. As shown in FIG. 5, the layer thickness regulating member 235 is spaced apart from the N3 pole by the second sleeve 232B of the transport roller 232 at a predetermined distance between the N2 pole and the S2 pole. It is arranged facing each other. In the present embodiment, the N2 pole also functions as a regulation pole. 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 N3 pole is disposed upstream of the opposing position TP in the second rotational direction, and the aforementioned S1 pole is disposed adjacent to the N3 pole downstream of the opposing rotational position in the second rotational direction. Yes. The N3 pole is disposed to face the N11 pole of the first magnet 231A, and the S1 pole is disposed to face the N13 pole of the first magnet 231A.

  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 transport roller 232) that connects the facing position TP and the rotation axis of the transport roller 232 is shown as the start point. ing.

  Further, the arrangement and function of four magnetic poles arranged around the opposing position TP among the first magnet 231A of the developing roller 231 and the second magnet 232A of the transport roller 232 will be additionally described. FIG. 7 is a schematic diagram illustrating a state around the facing position TP in the developing roller 231 and the transport roller 232 of the developing device 23 according to the present embodiment. The N11 pole and N13 pole of the first magnet 231A and the N3 pole of the second magnet 232A are magnetic poles of the same polarity, and the S1 pole of the second magnet 232A is a magnetic pole having a different polarity with respect to these magnetic poles. Then, the developer that has passed through the developing position NP is transferred from the developing roller 231 to the transport roller 232 by the magnetic field formed by the N13 pole and the S1 pole. The developer supplied from the first screw 233A of the stirring screw 233 to the conveyance roller 232 is regulated by the layer thickness regulating member 235 and then developed from the conveyance roller 232 by a magnetic field formed by the N3 pole and the N11 pole. Delivered to the roller 231.

  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 S12 pole and the N13 pole, and extends along the peripheral surface of the first sleeve 231B of the developing roller 231 from the developing position NP to a position facing the N13 pole. The second inner wall portion 23H2 is connected to the first inner wall portion 23H1, is opposed to the S1 pole and the N1 pole, and extends along the peripheral surface of the second sleeve 232B of the transport roller 232. Similarly, the third inner wall portion 23H3 opposes the S11 pole and the N11 pole on the side opposite to the first inner wall portion 23H1, and the first sleeve 231B of the developing roller 231 from the developing position NP to a position facing the N11 pole. It is extended so that the surrounding surface of this may be followed. 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 N3 pole and the S2 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.

  In recent years, considering the influence on the environment and the like, toner for low-temperature fixing is often used in the image forming apparatus 10. In this case, toner aggregates are likely to be generated in the developing device 23 and the toner replenishing unit 15. When the aggregate is clogged between the layer thickness regulating member 235 (FIG. 2) of the developing device 23 and the conveyance roller 232, a partial conveyance failure of the developer occurs, and an image such as a white stripe on the printed image. Defects occur. In particular, when a developing bias in which an AC bias is superimposed on a DC bias is applied to the developing roller 231, such an image defect is likely to appear remarkably.

  In the present embodiment, in the developing device 23 provided with two magnetic rollers (developing roller 231 and transport roller 232), one developing roller 231 is disposed to face the photosensitive drum 20. Further, the layer thickness regulating member 235 is disposed so as to face the transport roller 232. In order to suppress the partial conveyance failure of the developer as described above from being formed on the developing roller 231 and to suppress the generation of the white streak image, the developing device 23 is arranged around the opposite position TP. The magnetic pole arrangement is characterized.

  That is, with reference to FIG. 6 and FIG. 7, in the developer transport path of the developing roller 231 and the transport roller 232, the same polarity magnetic pole is applied from the N3 pole of the transport roller 232 toward the N11 pole of the developing roller 231. The developer is delivered. Note that it is not easy to move the developer between magnetic poles of the same polarity. In the present embodiment, the movement (delivery) of the developer is promoted by the S1 pole and the N13 pole that are located on the opposite sides across the facing position TP. Normally, the developer around the N3 pole is easily transported toward the S1 pole. However, in the present embodiment, since the N13 pole having a different polarity is arranged in the S1 pole, most of the magnetic force lines generated from the S1 pole are formed toward the N13 pole. As a result, the lines of magnetic force connecting the S1 pole and the N3 pole are very few.

  Further, since the N11 pole of the same polarity is opposed to the N3 pole, most of the magnetic lines of force from the N3 pole are affected by the N11 pole and are directed to the S2 pole upstream in the second rotation direction (FIG. 6). It is formed. Similarly, many of the magnetic field lines of the N11 pole are formed toward the S11 pole downstream of the first rotation direction due to the influence of the N3 pole. As a result, the developer transported on the second sleeve 232B of the transport roller 232 stays at the N3 pole (stagnation part TD in FIG. 6), and a part of the developer flies to the N11 pole. The N11 pole having the same polarity is arranged downstream of the N13 pole in the first rotation direction. For this reason, a magnetic shield MS (FIG. 7) is formed between the N13 pole and the N11 pole by a repulsive magnetic field. As a result, the developer that has passed through the developing nip NP and conveyed on the developing roller 231 is prevented from turning around to the N11 pole side.

  As described above, in the present embodiment, the developer retention portion TD is located downstream of the layer thickness regulating member 235 in the second rotation direction and immediately before the developer is transferred from the transport roller 232 to the developing roller 231. It is formed. In the staying part TD, the developer stays while slipping on the second sleeve 232B, so that the developer can be slightly moved along the axial direction in the rotation of the transport roller 232. For this reason, developer aggregates are sandwiched between the layer thickness regulating member 235 and the second sleeve 232B of the conveying roller 232, and the developer conveyance amount is streaked downstream of the layer thickness regulating member 235 in the second rotation direction. Even in the case of a drop in the shape, the difference in the transport amount of the developer in the staying part TD is alleviated. As a result, the developer flying from the staying portion TD and delivered to the first sleeve 231B of the developing roller 231 can obtain a more uniform transport amount along the axial direction of the developing roller 231. Become. As a result, the occurrence of white streak images on the photosensitive drum 20 and the printed sheet P is suppressed. In addition, when the same-polarity magnetic poles are disposed opposite to each other between the two rollers as in this embodiment, and the staying portion TD is formed in the developer delivery portion, the same-polarity magnetic poles are adjacent to each other on the circumference of one roller. Compared with the case where it arrange | positions, the following effects are expressed. That is, in the present embodiment, the developer moves along the substantially radial direction of the transport roller 232 when the developer flies from the staying portion TD. Therefore, the developer that has passed through the layer thickness regulating member 235 reaches the staying portion TD along the circumferential direction of the second sleeve 232B, and after staying in the staying portion TD, moves along the substantially radial direction. By such movement of the developer, a partial difference in the layer amount of the developer is preferably complemented. On the other hand, since the developer that has reached the staying portion along the circumferential direction moves again along the circumferential direction on one roller, movement in the axial direction is limited.

  In order to promote the flying movement of the developer between the N3 pole and the N11 pole, the peripheral speed of the transport roller 232 (second sleeve 232B) is the peripheral speed of the developing roller 231 (first sleeve 231B). It is desirable to be slower. In such a speed relationship, the gap between the layer thickness regulating member 235 and the second sleeve 232B is set wide in order to obtain a desired developer conveyance amount. As a result, when the transport roller 232 and the developing roller 231 are rotated at a constant speed or when the developing roller 231 is rotated slower than the transport roller 232, the amount of developer in the staying portion TD is increased. Is done. For this reason, the complementation effect by retention increases and it becomes possible to suppress generation | occurrence | production of a white stripe. When the peripheral speed of the developing roller 231 is Vd (mm / sec) and the peripheral speed of the transport roller 232 is Vc (mm / sec), the relationship of 0.2 ≦ Vc / Vd <1.0 is satisfied. Is desirable.

  In this embodiment, as shown in FIG. 6, the axis of the developing roller 231 is disposed below the axis of the photosensitive drum 20, and the axis of the transport roller 232 is higher than the axis of the developing roller 231. It is arranged below. The N11 pole is disposed above the N3 pole. In other words, the outer peripheral position of the second sleeve 232B facing the peak position of the radial component of the magnetic force of the N3 pole is more than the outer peripheral position of the first sleeve 231B facing the peak position of the radial component of the magnetic force of the N11 pole. It is arranged below. Therefore, the developer flying from the staying portion TD moves upward toward the N11 pole (the magnetic field line between the N11 pole and the S11 pole). At this time, toner agglomerates and foreign matters that are not easily restrained by the magnetic force fall without reaching the developing roller 231 due to the action of gravity. For this reason, it is suppressed that these aggregates and foreign substances appear on an image.

  Further, in the present embodiment, a developer delivery region between the developing roller 231 and the transport roller 232 is stably formed in different directions at a position across the facing position TP. In particular, the developer is delivered from the transport roller 232 to the developing roller 231 by magnetic poles of the same polarity, and the developer is delivered from the development roller 231 to the transport roller 232 by magnetic poles of different polarities. 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, 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.

  Referring to FIG. 6, in the present embodiment, the first inner wall portion 23 </ b> H <b> 1 and the second inner wall portion 23 </ b> H <b> 2 are connected to each other while being formed along the peripheral surfaces of the developing roller 231 and the transport roller 232. For this reason, the developer can be smoothly transferred from the developing roller 231 to the transport roller 232. Similarly, in the developer transfer region from the transport roller 232 to the developing roller 231, the developer can be smoothly transferred from the transport roller 232 to the developing roller 231 by the third inner wall portion 23H3 and the fourth inner wall portion 23H4. it can.

Next, based on an Example, this invention is further demonstrated. In addition, this invention is not limited to a following example. In each experiment described later, the experiment was performed under the following experimental conditions.
<Experimental conditions>
Print speed: 55 sheets / min Photoconductor drum 20: Amorphous silicon photoconductor (a-Si), diameter φ30 mm, surface potential Vo (white background portion, background portion) = + 270 V, VL (image portion) = + 20 V, peripheral speed = 300mm / sec
A gap between the layer thickness regulating member 235 and the second sleeve 232B: 200 to 600 μm
-Developer conveyance amount (after layer thickness regulation) on the conveyance roller 232 and the developing roller 231: 100 to 300 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%, positive chargeability

The conditions of the developing roller 231 are as follows.
・ Developing roller 231: Diameter φ20 mm
-Peripheral speed ratio of the developing roller 231 to the photosensitive drum 20: 1.8 (same direction at the opposite position, with direction)
A gap between the developing roller 231 and the photosensitive drum 20: 300 μm
Development 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).
-Surface condition of the first sleeve 231B: sandblast (Rzjis 7 μm), Ni plating treatment.
Further, the magnetic pole distribution of the developing roller 231 used in the experiment is the condition 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 the transport roller 232 to the developing roller 231: Variable from 0.18 to 1.0 (reverse direction at counter position, counter direction)
-Gap between transport roller 232 and developing roller 231: 250 μm
Further, the magnetic pole distribution of the transport roller 232 used in the experiment is shown in Table 2 above.

  Table 3 shows the results of evaluating each image quality by changing the peripheral speed of the transport roller 232 and the arrangement of each roller under the above experimental conditions.

  Regarding the roller arrangement, the arrangement of the developing device 23 in the image forming apparatus 10 is changed on a trial basis so that the vertical relationship between the N11 pole on the developing roller 231 side and the N3 pole on the conveying roller 232 side is reversed. The experiment was conducted.

  Among the image quality evaluations, white streak elimination evaluates whether or not white streaks are generated in the halftone image on the printed image. ○ indicates no white streaks and Δ indicates slightly. It shows a state where white stripes are generated. Even when the result of white stripes is Δ, there is no problem in actual use. Further, the uneven transport is a phenomenon in which a developer slip on the transport roller 232 occurs due to an excessive amount of developer on the transport roller 232, and a transport failure occurs. In Table 3, ○ indicates that no conveyance unevenness occurs, and x indicates a state where conveyance unevenness occurs. Furthermore, in the evaluation of aggregate recoverability, it is evaluated whether the aggregate that has passed between the layer thickness regulating member 235 and the transport roller 232 moves to the developing roller 231 side and appears as a color point on the image. It is what. In Table 3, “◯” indicates a state where no color point is generated, and “×” indicates a state where a color point is generated.

  As shown in Table 3, the relationship between the magnetic poles of the developing roller 231 and the transport roller 232 according to the present invention, particularly the N13 pole and N11 pole on the developing roller 231 side, the N3 pole on the transport roller 232 side, and the S1 pole must be satisfied. As a result, the white streak resolution was good. From Table 3, when the peripheral speed of the developing roller 231 is Vd (mm / sec) and the peripheral speed of the transport roller 232 is Vc (mm / sec), the relationship of Vc / Vd <1.0 is satisfied. Thus, it is possible to obtain a result in which no white stripes are generated.

  On the other hand, when the peripheral speed of the transport roller 232 is reduced without changing the amount of developer supplied to the developing roller 231 side, it is necessary to increase the developer transport amount per unit area on the transport roller 232. In this case, the adjustment gap between the layer thickness regulating member 235 and the transport roller 232 is enlarged. However, if the developer transport amount on the transport roller 232 increases too much, the transport of the developer on the transport roller 232 may be poor or the developer may be unevenly transferred from the transport roller 232 to the developing roller 231. . As a result, as shown in Table 3, the peripheral speed of the developing roller 231 is Vd and the peripheral speed of the transport roller 232 is Vc satisfying the relationship of 0.2 ≦ Vc / Vd. became. Further, when the N11 pole is arranged above the N3 pole, the aggregates fall while the developer flies from the transport roller 232 to the developing roller 231, so that an image defect such as a color point does not occur. became.

  In addition, the delivery of the developer at the same polarity magnetic pole (N3 pole, N11 pole) has an action of suppressing the unevenness of the developer conveyance according to the groove shape (knurl groove) of the second sleeve 232B of the conveyance roller 232. Yes. In particular, when the peripheral speed of the transport roller 232 becomes slow, a difference occurs in the transport amount of the developer according to the unevenness of the groove portion on the transport roller 232. However, the change in the transport amount can be reduced by the retention of the developer in the retention portion TD.

  In order to increase the developer transport amount on the transport roller 232 when the peripheral speed of the transport roller 232 is decreased, it is desirable to use a nonmagnetic material for the layer thickness regulating member 235. Compared to the magnetic material, the non-magnetic material has a weaker regulating force of the developer, and thus the driving torque of the transport roller 232 becomes smaller. As a result, it is possible to suppress heat generation of a motor (not shown) that rotates the transport roller 232 due to a decrease in torque and a decrease in the number of rotations.

  In the experiment described above, the surface condition of the first sleeve 231B was evaluated in the range of 4 to 14 μm in Rzjis. As a result, it was found that the same result as above was obtained. Further, when the same evaluation as described above was performed in a toner concentration range of 5% to 12%, the same results were obtained with respect to white streak suppression effect, developer delivery, transport unevenness, and aggregate recovery. . Further, the same results are obtained when the same evaluation is performed in the range where the diameter of the developing roller 231 and the transport roller 232 is 16 mm or more and 35 mm or less and the peripheral speed of the photosensitive drum 20 is 200 mm / sec or more and 400 mm / sec or less. was gotten.

  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 and the second magnet 232A have been described in the case where the three same-polarity poles are the N3 pole, the N11 pole, and the N13 pole. However, the present invention is not limited to this. It is not something. The same magnetic pole may be composed of the S pole. In this case, other magnetic poles around the opposing position TP may be reversed between the S pole and the N pole.

  (2) In the above embodiment, as shown in FIGS. 6 and 7, the N13 pole, the N11 pole, and the N3 pole are magnetic poles having the same polarity, and the S1 pole is a magnetic pole having a different polarity from these magnetic poles. However, the present invention is not limited to this. FIG. 8 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. In the present modified embodiment, the developing roller 231M includes a first magnet 231AM and a first sleeve 231BM. Further, the transport roller 232M includes a second magnet 232AM and a second sleeve 232BM. The N11 pole of the first magnet 231AM, the N1 pole and the N4 pole of the second magnet 232AM are magnetic poles of the same polarity, and the S2 pole of the second magnet 232AM is a magnetic pole different from these magnetic poles. Even in such a case, the generation of white stripes is suppressed by the staying portion of the developer formed around the N4 pole in FIG.

  FIG. 9 is a schematic cross-sectional view showing the magnetic pole arrangement of the developing roller 231N and the conveying roller 232N of the developing device 23N according to a modified embodiment of the present invention. In the present modified embodiment, the developing roller 231N includes a first magnet 231AN and a first sleeve 231BN. Further, the transport roller 232N includes a second magnet 232AN and a second sleeve 232BN. The N13 pole and N11 pole of the first magnet 231AN and the N1 pole and N4 pole of the second magnet 232AM are magnetic poles of the same polarity. Even in such a case, the generation of white stripes is suppressed by the staying portion of the developer formed around the N4 pole in FIG. FIG. 11 is a schematic cross-sectional view showing the magnetic pole arrangement of the developing roller 231Z and the conveying roller 232Z of another developing device 23Z compared with the present invention. As described above, when the two N poles and the two S poles are arranged to face each other across the opposing position TP, that is, when the S13 pole and the S1 pole are different in magnetic force from the N11 pole and the N3 pole. , Strong magnetic field lines are formed between the N13 pole and the S1 pole, and between the N11 pole and the S13 pole. For this reason, the developer on the transport roller 232 is unlikely to fly to the opposing developing roller 231 side and is easily transported from the N3 pole to the S1 pole side. For this reason, at least one of the magnetic poles of the first magnet 231A upstream of the opposing position TP in the first rotational direction or the magnetic poles of the second magnet 232A downstream of the opposing position TP in the second rotational direction is shown in FIG. It is desirable that the magnetic poles have different polarities (S poles) from the N3 pole and the N11 pole. In the modified embodiment, each magnetic pole may be inverted between the N pole and the S pole.

  (3) Furthermore, FIG. 10 is a schematic cross-sectional view showing the structure of the housing 23H of the developing device 23 according to a modified embodiment of the present invention. In the present modified embodiment, the collection unit 50 is provided in a region located below the N11 pole. According to such a configuration, it is possible to collect the agglomerates and foreign matters that have fallen due to gravity after being lifted upward together with the other developer from the retention portion TD.

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 (6)

A first magnet including a plurality of magnetic poles fixed along the circumferential direction; a first sleeve that rotates around the first magnet in a first rotational direction and carries a developer containing toner and a magnetic carrier on the circumferential surface; A developing roller that is arranged opposite to a photosensitive drum on which an electrostatic latent image is formed at a predetermined development position and supplies the toner to the photosensitive drum;
A second magnet that includes a plurality of magnetic poles fixed along the circumferential direction, and a second sleeve that rotates around the second magnet in a second rotational direction and carries the developer on the circumferential surface, A transport roller that is arranged to face the developing roller at a predetermined facing position, and that supplies the developer to the developing roller;
A developer agitating unit for agitating the developer and supplying the developer to the transport roller;
A layer thickness regulating member that is arranged to face the conveyance roller and regulates the layer thickness of the developer supplied from the developer stirring unit to the conveyance roller;
With
The first rotation direction and the second rotation direction are set in directions facing each other at the facing position,
The first magnet is
A first magnetic pole disposed on the upstream side in the first rotational direction of the opposing position; and a second magnetic pole disposed adjacent to the first magnetic pole on the downstream side in the first rotational direction with the opposing position interposed therebetween. ,
With
The second magnet is
A third magnetic pole disposed upstream of the opposed position in the second rotational direction and disposed opposite the second magnetic pole of the first magnet; and downstream in the second rotational direction with respect to the third magnetic pole A fourth magnetic pole disposed adjacent to the opposite position on the side and disposed opposite the first magnetic pole of the first magnet;
With
The second magnetic pole and the third magnetic pole are magnetic poles of the same polarity, and at least one of the first magnetic pole and the fourth magnetic pole is a magnetic pole of the same polarity as the second magnetic pole;
The fourth magnetic pole is a magnetic pole having the same polarity as the second magnetic pole, the first magnetic pole is a magnetic pole different from the second magnetic pole,
By the magnetic field formed by the third magnetic pole and the second magnetic pole, the developer supplied from the developer stirring unit to the transport roller is transferred from the transport roller to the developing roller,
The developing device, wherein the developer passing through the developing position is transferred from the developing roller to the transport roller by a magnetic field formed by the first magnetic pole and the fourth magnetic pole. When the peripheral speed of the developing roller is Vd (mm / sec) and the peripheral speed of the transport roller is Vc (mm / sec), the relation of 0.2 ≦ Vc / Vd <1.0 is satisfied. The developing device according to claim 1 . The axial center of the developing roller is disposed below the axial center of the photosensitive drum,
The axis of the conveying roller, a developing device according to claim 1 or 2, characterized in that it is disposed below the axis of the developing roller. The outer peripheral position of the second sleeve facing the peak position of the radial component of the magnetic force of the third magnetic pole is more than the outer peripheral position of the first sleeve facing the peak position of the radial component of the magnetic force of the second magnetic pole. The developing device according to claim 3 , wherein the developing device is disposed below. Wherein the developing roller, a developing apparatus according to any one of claims 1 to 4, characterized in that developing bias AC bias on a DC bias is superposed is applied. A developing device according to any one of claims 1 to 5 ,
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