JP2019191241A - Developing device and image forming apparatus including the same - Google Patents

Abstract

To provide a developing device that has developer conveyance chambers arranged up and down and can smoothly lift up a developer from the lower conveyance chamber to the upper conveyance chamber with a simple configuration, and an image forming apparatus including the developing device.SOLUTION: A developing device comprises: a developer container that has a first conveyance chamber and a second conveyance chamber arranged above the first conveyance chamber; a first stirring and conveying member that stirs and conveys a developer inside the first conveyance chamber in a first direction; a second stirring and conveying member that stirs and conveys a developer inside the second conveyance chamber in a second direction being an opposite direction to the first direction; and a developer carrier. The developer container has a first communication part communicating downstream side ends in the first direction of the first conveyance chamber and second conveyance chamber, and a second communication part communicating downstream side ends in the second direction of the first conveyance chamber and second conveyance chamber. The first stirring and conveying member has a rotation shaft and first spiral blades formed spirally at a constant pitch in the axial direction of the rotation shaft. A large-diameter part in which the outer diameter of a rotation shaft is larger than that of another portion is formed at a portion opposite to the first communication part of the first stirring and conveying member.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a developing device and an image forming apparatus including the developing device, and in particular, a first transport chamber in which a stirring transport member that stirs and transports a developer is disposed, and a first transport chamber disposed above the first transport chamber. The present invention relates to a developing device having two transfer chambers and an image forming apparatus including the developing device.

  In an image forming apparatus, a latent image formed on an image carrier made of a photoreceptor or the like is developed by a developing device and visualized as a toner image. As such a developing device, a developer container for containing a developer, a first agitating and conveying member for agitating and conveying the developer, a second agitating and conveying member, and a developer carrying the developer supplied from the second agitating and conveying member. A developing device including a roller (developer carrier) is known. The first agitating and conveying member conveys the developer to one side in the axial direction of the developing roller, and the second agitating and conveying member supplies the developer to the developing roller while conveying the developer to the other side (the side opposite to the one side). To do.

  Incidentally, in recent years, there has been an increasing demand for downsizing image forming apparatuses, and particularly in color machines, since a plurality of developing apparatuses are arranged, downsizing of developing apparatuses is required. Therefore, a first transfer chamber in which the first agitation transfer member is disposed, and a second transfer chamber in which the second agitation transfer member is disposed in the upper portion of the first transfer chamber are provided. A developing device is known. In this developing device, it is possible to downsize the developing device in the horizontal direction by arranging the first transfer chamber and the second transfer chamber vertically. For this reason, it is possible to reduce the arrangement space of the developing device, and thus it is possible to reduce the size of the image forming apparatus.

  For example, Patent Document 1 discloses a developing device including two augers (screws) arranged in parallel in the vertical direction so that the conveying directions are opposite to each other. In this developing device, the developer is circulated and transported between the stirring developer reservoir and the supply developer reservoir by two augers, and the developer carrier adjacent to the auger disposed in the supply developer reservoir. The developer is supplied to

  In the developing device in which the first transfer chamber and the second transfer chamber are arranged up and down as in Patent Document 1, the pumping of the developer from the lower screw to the upper screw is in a direction against gravity. Circulation is not performed smoothly and the developer tends to stay in the pumping section. For this reason, there has been a problem that the rotational torque of the screw increases to increase the driving torque, or mechanical stress is applied to the developer, causing deterioration such as adhesion.

  Therefore, a method for suppressing the stay of the developer in the pumping unit has been proposed. Patent Document 2 is arranged coaxially with the developing magnet roller, and is driven in accordance with the driving of the developing magnet roller. A developing device is disclosed in which a roller is placed in a lifting portion to ensure developer transportability. Further, Patent Document 3 includes first and second transport spaces, which are provided adjacent to each other in the gravity direction and in which a developer stirring and transporting member is disposed, and first and second transport spaces. A developing device provided with a communicating portion that is provided in the partitioning portion and serves as a developer delivery portion, and provided with a transfer conveying member that lifts and conveys the developer separately from the developer agitating and conveying member inside the communicating portion. It is disclosed.

JP-A-5-333691 Japanese Patent Laid-Open No. 11-24382 JP 2011-59605 A

  However, in the methods of Patent Documents 2 and 3, since it is necessary to provide a transfer magnet roller and a transfer transfer member, the cost of the developing device is increased. Further, it is necessary to extend the developing device in the longitudinal direction in order to secure an arrangement space for the conveying magnet roller and the transfer conveying member, which leads to an increase in the size of the developing device and the image forming apparatus on which the developing device is mounted.

  In view of the above problems, the present invention provides a developing device capable of smoothly pumping developer from a lower transfer chamber of a developing device in which developer transfer chambers are arranged vertically to an upper transfer chamber with a simple configuration, and An object of the present invention is to provide an image forming apparatus provided.

  In order to achieve the above object, a first configuration of the present invention is a developing device including a developing container, a first stirring and conveying member, a second stirring and conveying member, and a developer carrier. The developing container includes a first transport chamber and a second transport chamber disposed above the first transport chamber with the partition portion interposed therebetween, and stores a two-component developer including a carrier and toner. The first agitating and conveying member is rotatably supported in the first conveying chamber, and agitates and conveys the developer in the first conveying chamber in the first direction. The second agitating and conveying member is rotatably supported in the second conveying chamber in parallel with the first agitating and conveying member, and the developer in the second conveying chamber is agitated and conveyed in the second direction which is opposite to the first direction. To do. The developer carrying member is rotatably supported by the developing container and carries the developer in the second transport chamber on the surface. The developing container includes a first communicating portion that communicates downstream ends of the first transport chamber and the second transport chamber in the first direction, and downstream end portions of the first transport chamber and the second transport chamber in the second direction. A second communication portion that communicates with each other. The first stirring and conveying member includes a rotation shaft and first spiral blades that are provided integrally with the rotation shaft and are formed in a spiral shape at a constant pitch in the axial direction of the rotation shaft. A portion of the first stirring / conveying member facing the first communication portion is formed with a large-diameter portion having a larger outer diameter of the rotation shaft than other portions.

  According to the first configuration of the present invention, the large-diameter portion formed in the first agitating and conveying member reduces the protrusion amount of the first spiral blade at the portion facing the first communicating portion. The developer that is conveyed to the portion facing the first communication portion by the member is likely to stay. Further, since the volume around the large-diameter portion is reduced, the developer conveyed to the portion facing the first communication portion is easily directed upward. Accordingly, the developer can be smoothly pumped from the first transfer chamber to the second transfer chamber, and the amount of developer in the second transfer chamber is stabilized, so that uneven supply of the developer to the developer carrier does not occur. It is possible to maintain a stable image for a long time. In addition, since the compressing action of the developer at the end of the first transport chamber on the downstream side in the developer transport direction is also reduced, the aggregation of the developer and the accompanying increase in the driving torque of the first stirring transport member can be suppressed. it can.

Schematic sectional view showing the overall configuration of a color printer 100 including the developing devices 3a to 3d of the present invention. 1 is a longitudinal sectional view showing a structure of a stirring unit of a developing device 3a according to a first embodiment of the present invention. Side surface sectional view showing the structure around the first communication portion 22e of the developing device 3a of the first embodiment. The longitudinal cross-sectional view which cut | disconnected the 1st communication part 22e periphery of the developing device 3a of 1st Embodiment along the axial direction A longitudinal sectional view showing a structure of a stirring unit of a developing device 3a according to a second embodiment of the present invention. The longitudinal cross-sectional view which cut | disconnected the 1st communication part 22e periphery of the developing device 3a of 2nd Embodiment along the axial direction In the modification of the developing device 3a of the present invention, the vicinity of the first communication portion 22e of the developing device 3a in which the second transfer chamber 22d is disposed at a position shifted obliquely upward from the first transfer chamber 22c is along the axial direction. Sectional view cut

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a color printer 100 provided with developing devices 3a to 3d of the present invention, and here, a tandem color printer is shown. In the main body of the color printer 100, four image forming portions Pa, Pb, Pc, and Pd are arranged in the order of Pd to Pa from the upstream side in the conveyance direction (right side in FIG. 1). These image forming portions Pa to Pd are provided corresponding to images of four different colors (black, yellow, magenta, and cyan), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  These image forming portions Pa to Pd are provided with photosensitive drums 1a, 1b, 1c and 1d for carrying visible images (toner images) of the respective colors, and further rotate clockwise in FIG. An intermediate transfer belt 8 is provided adjacent to each of the image forming portions Pa to Pd.

  When image data is input from a host device such as a personal computer, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d. Next, the exposure device 5 irradiates the surfaces of the photosensitive drums 1a to 1d according to image data, and forms electrostatic latent images corresponding to the image data on the photosensitive drums 1a to 1d. Each of the developing devices 3a to 3d includes a two-component developer (hereinafter, also simply referred to as a developer) including toners of black, yellow, magenta, and cyan colors replenished from the toner containers 4a to 4d and a magnetic carrier. Fixed amount filling. The toner in the developer is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d, and electrostatically adheres. Thereby, a toner image corresponding to the electrostatic latent image formed by exposure from the exposure device 5 is formed.

  Then, the primary transfer rollers 6a to 6d apply an electric field at a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d, and black, yellow, magenta and the like on the photosensitive drums 1a to 1d are applied. A cyan toner image is primarily transferred onto the intermediate transfer belt 8. Toner remaining on the surfaces of the photosensitive drums 1a to 1d after the primary transfer is removed by the cleaning devices 7a to 7d.

  The transfer paper P onto which the toner image is transferred is accommodated in a paper cassette 16 disposed at the lower part of the color printer 100. The transfer paper P passes through a paper feed roller 12a and a registration roller pair 12b at a predetermined timing at a nip portion (secondary transfer nip) between the secondary transfer roller 9 and the intermediate transfer belt 8 provided adjacent to the intermediate transfer belt 8. Part). The transfer sheet P on which the toner image is secondarily transferred is conveyed to the fixing unit 13.

  The transfer paper P conveyed to the fixing unit 13 is heated and pressurized by passing through the nip portion between the fixing belt and the pressure roller, and the toner image is fixed on the surface of the transfer paper P, and a predetermined full-color image is formed. It is formed. The transfer paper P on which the full-color image is formed is discharged to the discharge tray 17 by the discharge roller pair 15 as it is (or after being distributed to the reverse conveyance path 18 by the branching unit 14 and the image is formed on both sides).

  FIG. 2 is a longitudinal cross-sectional view showing the structure of the stirring unit of the developing device 3a according to the first embodiment of the present invention mounted on the color printer 100. Here, the developing device 3a disposed in the image forming unit Pa of FIG. 1 will be described, but the configuration of the developing devices 3b to 3d disposed in the image forming units Pb to Pd is basically the same, and thus described. Is omitted.

  As shown in FIG. 2, the developing device 3 a includes a developing roller (developer carrier) 20, a stirring and conveying member 42, and a developing container 22. The developing container 22 constitutes the outline of the developing device 3a, and is formed with a partition 22b, a first transfer chamber 22c, a second transfer chamber 22d, a first communication portion 22e, and a second communication portion 22f. Yes. A two-component developer composed of a carrier and toner is accommodated in the first transfer chamber 22c and the second transfer chamber 22d. Further, the developing container 22 holds the stirring and conveying member 42 and the developing roller 20 rotatably. Further, the developing container 22 is formed with an opening 22a (see FIG. 3) that exposes the developing roller 20 toward the photosensitive drum 1a.

  The partition portion 22b extends in the longitudinal direction of the developing container 22 and partitions the first transfer chamber 22c and the second transfer chamber 22d in parallel. The first communication part 22e and the second communication part 22f are respectively formed on one side and the other side (the A1 direction downstream side and the A2 direction downstream side) of the partition part 22b in the longitudinal direction. The first communication portion 22e communicates the downstream end portions in the A1 direction (first direction) of the first transfer chamber 22c and the second transfer chamber 22d. The second communication portion 22f communicates the downstream end portions in the A2 direction (second direction) of the first transfer chamber 22c and the second transfer chamber 22d. Note that the second communication portion 22f is formed in a sufficient size so that the developer conveyed to the second spiral 44 does not stay. The developer circulates through the first transfer chamber 22c, the first communication portion 22e, the second transfer chamber 22d, and the second communication portion 22f.

  The agitating / conveying member 42 is composed of a first spiral (first agitating / conveying member) 43 and a second spiral (second agitating / conveying member) 44. The first spiral 43 is rotatably supported in the first transfer chamber 22c. The second spiral 44 is rotatably supported in the second transfer chamber 22d.

  The first spiral 43 disposed in the first transfer chamber 22c is provided integrally with the rotation shaft 43b and the rotation shaft 43b, and is formed in a spiral shape at a constant pitch in the axial direction of the rotation shaft 43b. And a spiral blade 43a. The rotation shaft 43b is rotatably supported by the developing container 22. The first spiral blade 43a rotates in a predetermined direction (counterclockwise direction in FIG. 3), thereby stirring the developer in the first transfer chamber 22c in the A1 direction (one side in the axial direction of the developing roller 20). Transport to.

  A toner replenishing port 23 for replenishing toner into the developing container 22 is provided on the end surface of the first transfer chamber 22c in the A2 direction. A toner supply path 24 connected to the toner container 4a (see FIG. 1) is connected to the toner supply port 23. The rotating shaft 43 b passes through the toner supply port 23 and is disposed in the toner supply path 24. A replenishment blade 43c formed in a spiral shape at a constant pitch in the axial direction of the rotation shaft 43b is integrally formed in a portion of the rotation shaft 43b arranged in the toner supply path 24. The supply blades 43c are formed by spiral blades facing in the same direction (in the same phase) as the first spiral blades 43a, and have a smaller pitch and a smaller diameter than the first spiral blades 43a.

  The second spiral 44 disposed in the second transfer chamber 22d is provided integrally with the rotation shaft 44b and the rotation shaft 44b, and has a spiral shape with blades facing in the opposite direction (reverse phase) to the first spiral blade 43a. The second spiral blade 44a is formed. The rotation shaft 44b is disposed in parallel with the rotation shaft 43b and is rotatably supported by the developing container 22. The second spiral blade 44a rotates in the same direction (counterclockwise direction in FIG. 3) as the first spiral blade 43a, thereby causing the developer in the second transfer chamber 22d to move in the A2 direction (the direction opposite to the A1 direction). The developer is supplied to the developing roller 20 while being stirred and conveyed.

  The first spiral 43 and the second spiral 44 stir the developer to charge the toner in the developer to a predetermined level. As a result, the toner is held on the carrier. When the first spiral 43 and the second spiral 44 rotate, the developer is transported from the one communication portion (first communication portion 22e) provided in the partition portion 22b to the second spiral 44, and the other communication portion (second communication portion). Part 22f) is transported to the first spiral 43 and the developer circulates between the first transport chamber 22c and the second transport chamber 22d. Then, the developer is supplied from the second spiral 44 to the developing roller 20, and a magnetic brush is formed on the developing roller 20.

  The developing roller 20 includes a developing sleeve 20a that is rotatably supported by the developing container 22, and a magnetic pole member 20b that is fixed to a fixed shaft (not shown) and has a plurality of magnetic poles. In the vicinity of the developing sleeve 20a, a regulating blade 21 is provided that is disposed at a predetermined distance from the developing sleeve 20a and regulates the layer thickness of the magnetic brush on the surface of the developing sleeve 20a. The developing sleeve 20a is rotated in the direction of the arrow in FIG. 3 (counterclockwise direction) by a drive mechanism including a motor and a gear (not shown). Further, a developing bias in which an AC voltage is superimposed on a DC voltage is applied to the developing sleeve 20a.

  In the developing device 3a, as shown in FIG. 2, the developer in the first transfer chamber 22c is stirred and transferred in the A1 direction (first communication portion 22e side) by the first spiral 43, and the developer in the first transfer chamber 22c. It gradually accumulates on one side. On one side of the first transfer chamber 22c, the developer is pushed by the subsequent developer and is pushed up to the second transfer chamber 22d via the first communication portion 22e. The developer in the second transport chamber 22d is supplied to the developing roller 20 while being stirred and transported in the A2 direction (second communication portion 22f side) by the second spiral 44.

  When the developing sleeve 20a to which the developing bias is applied rotates counterclockwise in FIG. 3, the developing sleeve 20a is carried on the magnetic brush on the surface of the developing sleeve 20a due to the potential difference between the developing bias potential and the potential of the exposed portion of the photosensitive drum 1a. The toner moves to the photosensitive drum 1a. The toner sequentially adheres to the exposed portion on the photosensitive drum 1a that rotates in the clockwise direction, and the electrostatic latent image on the photosensitive drum 1a is developed.

  The developer on the developing sleeve 20a that has not been used for development is peeled off from the developing sleeve 20a at the same pole portion of the magnetic pole member 20b and collected in the second transfer chamber 22d. And it falls to the 1st conveyance chamber 22c via the 2nd communicating part 22f.

  FIG. 3 is a side cross-sectional view (cross-sectional view taken along the line XX ′ in FIG. 2) showing the configuration around the first communication portion 22e of the developing device 3a of the first embodiment. FIG. 4 is a longitudinal sectional view in which the periphery of the first communication portion 22e of the developing device 3a of the first embodiment is cut along the axial direction. 3 shows a state in which the developing device 3a is viewed from the back side of FIG. 1, and the arrangement of each member in the developing device 3a is opposite to that in FIG.

  As shown in FIG. 3, the first communication portion 22 e is formed at a substantially central portion of the partition portion 22 b in the width direction (arrow Y direction) of the developing container 22. A portion of the first spiral 43 facing the first communication portion 22e is formed with a large diameter portion 45 in which the outer diameter of the rotating shaft 43b is larger than the other portions. The large-diameter portion 45 has a cylindrical shape whose outer diameter is constant over the entire area in the axial direction, and the downstream edge of the rotating shaft 43b with respect to the developer transport direction (A1 direction) in the first transport chamber 22c (see FIG. 4 to the upstream side (the right side in FIG. 4) beyond the upstream side edge of the first communication portion 22e.

  Further, in the vicinity of the downstream edge of the rotation shaft 43b with respect to the developer conveyance direction (A1 direction) in the first conveyance chamber 22c, the reverse spiral blade is directed in the opposite direction (in reverse phase) to the first spiral blade 43a. One turn (one pitch) 46 is formed. The reverse spiral blade 46 restricts the entry of the developer into the bearing portion 47 of the rotating shaft 43b.

  In the developing device 3a of the present embodiment, the second transfer chamber 22d is disposed above the first transfer chamber 22c. That is, the first transfer chamber 22c and the second transfer chamber 22d are arranged vertically. Thereby, the developing device 3a can be reduced in size in the horizontal direction. In the color printer 100, since the four developing devices 3a to 3d are arranged in the horizontal direction, downsizing the developing devices 3a to 3d is particularly effective for downsizing the color printer 100.

  In the present embodiment, a large-diameter portion 45 is formed on the rotation shaft 43b of the first spiral 43 so as to face the first communication portion 22e from which the developer is pumped from the first transfer chamber 22c to the second transfer chamber 22d. Yes. As a result, the protruding amount of the first spiral blade 43a at the portion facing the first communication portion 22e is reduced, so that the developer conveyed by the first spiral 43 is likely to stay at the portion facing the first communication portion 22e. Become. In addition, since the volume of the first transfer chamber 22c around the large-diameter portion 45 is reduced, the developer transferred to the portion facing the first communication portion 22e can easily move upward. As a result, the developer can be smoothly pumped from the first transfer chamber 22c to the second transfer chamber 22d.

  Accordingly, since the amount of developer in the second transfer chamber 22d is stabilized, uneven supply of the developer to the developing roller 20 does not occur, and a stable image can be maintained for a long period. In addition, since the compressing action of the developer at the end of the first transport chamber 22c on the downstream side in the developer transport direction (A1 direction) is also reduced, the developer agglomerates and the drive torque of the first spiral 43 is increased accordingly. Can be suppressed.

  Further, the developer pumping performance can be improved only by changing the shape of the rotating shaft 43b of the first spiral 43, and there is no space restriction compared to a configuration in which a pumping member is separately provided, so that the developing device can be downsized. It also contributes to cost reduction.

  If the large-diameter portion 45 is formed too long in the direction of the rotation axis, the range in which the developer stays in the first transfer chamber 22c becomes longer, and the developer stays in the first transfer chamber 22c and the second transfer chamber 22d. There is a risk that it will not be able to circulate smoothly. For this reason, the formation range of the large diameter portion 45 is limited to the range corresponding to one pitch of the first spiral blade 43a.

If the outer diameter of the large-diameter portion 45 is too large, the amount of protrusion of the first spiral blade 43a at the large-diameter portion 45 is reduced, and the developer pumping force is reduced. Therefore, when the outer diameter of the first spiral blade 43a is R1, and the outer diameter of the rotating shaft 43b is R2, the outer diameter R3 of the large diameter portion 45 is expressed by the following equation (1).
R3 ≦ (R1 + R2) / 2 (1)
It is preferable to satisfy. For example, when the outer diameter of the first spiral wing portion 43a is 16 mm and the outer diameter of the rotating shaft 43b is 6 mm, the outer diameter of the large diameter portion 45 is (16 + 6) / 2 = 11 mm or less.

  FIG. 5 is a side sectional view showing a configuration around the first communication portion 22e of the developing device 3a according to the second embodiment of the present invention. FIG. 6 is a longitudinal sectional view of the developing device 3a according to the second embodiment, in which the periphery of the first communication portion 22e is cut along the axial direction. In the present embodiment, the outer diameter of the rotating shaft 43b is located downstream of the developer conveying direction (A1 direction) of the first conveying chamber 22c at the portion of the first spiral 43 facing the first communicating portion 22e (in FIG. 5). A tapered portion 50 is formed which increases conically toward the left side. The configuration of other parts of the developing device 3a is the same as that of the first embodiment. In the present embodiment, the tapered portion 50 restricts the developer from entering the bearing portion 47, so the reverse spiral blade 46 provided in the first embodiment is unnecessary.

  According to the configuration of the present embodiment, the tapered portion 50 is formed on the rotation shaft 43b of the first spiral 43 so as to face the first communication portion 22e where the developer is pumped from the first transfer chamber 22c to the second transfer chamber 22d. Has been. As a result, the volume of the first transfer chamber 22c around the taper portion 50 is reduced, and the drag vector acting on the developer from the taper portion 50 causes the developer to move obliquely upward due to the inclination of the outer peripheral surface of the taper portion 50 (see FIG. 6), the developer conveyed to the portion facing the first communication portion 22e can easily be directed upward. As a result, the developer can be smoothly pumped from the first transfer chamber 22c to the second transfer chamber 22d.

  Accordingly, as in the first embodiment, since the amount of developer in the second transfer chamber 22d is stabilized, uneven supply of the developer to the developing roller 20 does not occur, and a stable image can be maintained over a long period of time. Can do. In addition, since the compressing action of the developer at the end of the first transport chamber 22c on the downstream side in the developer transport direction (A1 direction) is also reduced, the developer agglomerates and the drive torque of the first spiral 43 is increased accordingly. Can be suppressed.

  Note that when the tapered portion 50 is formed upstream of the first communication portion 22e in the developer transport direction (A1 direction) of the first transport chamber 22c, the developer is pushed back in the reverse direction in the first transport chamber 22c. As a result, the developer may not be able to circulate smoothly in the first transfer chamber 22c and the second transfer chamber 22d. Therefore, the formation range of the taper portion 50 in the direction of the rotation shaft 43b is set within the range of the opening width of the first communication portion 22e in the direction of the rotation shaft 43b. Further, as the outer diameter (maximum diameter) at the downstream end of the tapered portion 50 in the developer conveyance direction (A1 direction) increases, the force that pushes the developer obliquely upward increases, so the maximum diameter of the tapered portion 50 is increased. It is preferable to have the same diameter as that of one spiral blade 43a.

  In addition, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, in each of the above-described embodiments, the developing devices 3a to 3d in which the second transfer chamber 22d is formed immediately above the first transfer chamber 22c have been described. However, as illustrated in FIG. 7, obliquely above the first transfer chamber 22c. The present invention can be applied in exactly the same manner to the developing device 3a in which the second transfer chamber 22d is disposed at a position deviated.

  In each of the above embodiments, an example in which the developer is supplied from the second spiral 44 to the developing roller 20 has been described, but the present invention is not limited to this. A developer carrier such as a magnetic roller is further provided between the second spiral 44 and the developing roller 20, and after supplying the developer from the second spiral 44 to the magnetic roller or the like, toner is supplied from the magnetic roller or the like to the developing roller 20. You may supply.

  The present invention is not limited to the tandem color printer 100 shown in FIG. 1, and is disposed above the first transfer chamber and the first transfer chamber of a digital or analog monochrome copying machine, color copying machine, facsimile, or the like. The present invention can be applied to various image forming apparatuses provided with a developing device including a second transfer chamber.

  The present invention is applicable to a developing device having a first transfer chamber and a second transfer chamber disposed above the first transfer chamber. By utilizing the present invention, it is possible to provide a developing device capable of smoothly pumping the developer from the first transfer chamber to the second transfer chamber, and an image forming apparatus including the same.

3a to 3d Developing device 20 Developing roller (developer carrier)
20a Development sleeve 20b Magnet member 22 Developer container 22b Partition 22c First transport chamber 22d Second transport chamber 22e First communication section 22f Second communication section 23 Toner replenishment port 42 Stirring transport member 43 First spiral (first stirring transport member) )
44 2nd spiral (2nd stirring conveyance member)
43a First spiral blade (conveying blade)
44a Second spiral blade (conveying blade)
43b, 44b Rotating shaft 45 Large diameter part 50 Taper part (large diameter part)
100 color printer (image forming device)

Claims (8)

A first transport chamber and a second transport chamber disposed above the first transport chamber across the partition, and a developer container containing a two-component developer containing a carrier and toner;
A first agitating and conveying member that is rotatably supported in the first conveying chamber and agitates and conveys the developer in the first conveying chamber in a first direction;
The second conveying chamber is parallel to the first agitating / conveying member and is rotatably supported, and secondly agitates and conveys the developer in the second conveying chamber in a second direction opposite to the first direction. An agitating and conveying member;
A developer carrying member rotatably supported by the developing container and carrying a developer in the second transfer chamber on a surface;
In a developing device comprising:
The developing container includes a first communication portion that communicates downstream ends of the first transfer chamber and the second transfer chamber in the first direction, and the first transfer chamber and the second transfer chamber. A second communicating portion that communicates the two downstream end portions in two directions,
The first agitating and conveying member includes a rotating shaft and first spiral blades that are provided integrally with the rotating shaft and formed in a spiral shape at a constant pitch in the axial direction of the rotating shaft. The developing device, wherein a portion of the agitating / conveying member facing the first communication portion is formed with a large-diameter portion having an outer diameter of the rotating shaft larger than that of other portions.   The developing device according to claim 1, wherein the large-diameter portion has a cylindrical shape whose outer diameter is constant over the entire axial direction.   The large diameter portion is formed from a downstream edge of the rotating shaft to a range corresponding to one pitch of the first spiral blade with respect to a developer transport direction in the first transport chamber. 2. The developing device according to 2. When the outer diameter of the first spiral blade is R1, the outer diameter of the rotating shaft is R2, and the outer diameter of the large diameter portion is R3, the following formula (1)
R3 ≦ (R1 + R2) / 2 (1)
The developing device according to claim 2, wherein:   The developing device according to claim 1, wherein the large-diameter portion has a conical shape whose outer diameter increases toward the downstream side with respect to the developer conveyance direction in the first conveyance chamber.   The developing device according to claim 5, wherein the large diameter portion is formed within a range of an opening width of the first communication portion in the rotation axis direction.   The developing device according to claim 5, wherein a maximum diameter of the large-diameter portion is the same as an outer diameter of the first spiral blade.   An image forming apparatus comprising the developing device according to claim 1.

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