JP6221813B2 - DEVELOPING DEVICE AND IMAGE FORMING DEVICE HAVING DEVELOPING DEVICE - Google Patents

Description

  The present invention relates to a developing device that develops an electrostatic latent image on an image carrier, and an image forming apparatus including the developing device.

  A developing device is mounted on an image forming apparatus such as a copying machine or a printer that forms an image on a sheet by electrophotography. The developing device develops an electrostatic latent image formed on an image carrier such as a photosensitive drum with toner. The developing device includes a developing roller disposed at a predetermined gap from the image carrier. As a developing method, the developer is magnetically pumped from the developer accommodating chamber to the surface of the developing roller, and the electric field generated by the developing bias applied to the developing roller causes the developing roller to transfer the electrostatic latent image on the image carrier. There is known a system in which toner is deposited by adhesion.

  This type of developing device is provided with an agitating member for conveying the developer to a position facing the developing roller while agitating the developer accommodated in the developer accommodating chamber. As the stirring member, for example, a screw rotating member in which a spiral wing member is attached to a rotating shaft, a paddle rotating member in which a paddle-shaped wing member is attached to a rotating shaft, and the like are known. Regardless of the stirring member, there is a difference between the thickness of the developer when the wing member faces the developing roller and the thickness of the developer when the region not having the wing member faces the developing roller. Depending on the difference, there may be a difference in the amount of developer pumped up by the developing roller. For example, the amount of developer pumped up when a region not having the blade member faces the developing roller is larger than the amount of developer pumped up when the blade member faces the developing roller. Such a difference in the amount of pumping causes density unevenness in a striped pattern corresponding to the pitch of the wing members in the image. As a conventional device for reducing the density unevenness, a device that presses the developer against the surface of the developing roller using a pressing member provided downstream of the developer pumping position in the rotation direction of the developing roller (see Patent Document 1) There is known an apparatus (see Patent Document 2) that improves the ability of pumping developer to a developing roller by interposing an auxiliary member made of a magnetic material.

JP 2002-258605 A Japanese Patent Laid-Open No. 2005-292301

  However, in the conventional apparatus, it is necessary to newly provide the pressing member and the auxiliary member, which increases the number of parts of the developing device and becomes a factor of increasing the size of the developing device. In addition, the pressing member gives extra stress to the developer, which reduces the life of the toner contained in the developer and reduces the charging characteristics. In addition, even if the pumping performance is improved by the auxiliary member and the density unevenness is reduced as a result, the difference in the pumping amount of the developer is not completely eliminated, so the auxiliary member prevents the density unevenness. I can't do it.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a developing device and an image forming device capable of uniformizing the amount of developer drawn up to the developing roller without applying stress to the developer. To provide an apparatus.

  A developing device according to one aspect of the present invention includes a storage portion, a stirring member, a developing roller, a cylindrical member, a first passage, and a second passage. The storage portion stores a developer. The agitating member is rotatably provided in the accommodating portion, and agitates the developer in the accommodating portion by being driven to rotate in a predetermined first rotation direction. The developing roller is rotatably provided above the stirring member, has a magnet for attracting the developer in the housing portion by magnetic force, and is driven to rotate in a predetermined second rotation direction. The said cylindrical member is formed in the cylinder shape with the nonmagnetic body which surrounds the outer peripheral surface of the said stirring member in a non-contact state. The first passage is formed on the outer peripheral wall of the cylindrical member at a position on the upstream side in the first rotation direction with respect to a position where the developing roller and the stirring member are opposed to each other. The second passage is formed on the outer peripheral wall of the tubular member at a position downstream of the facing position in the first rotation direction.

  An image forming apparatus according to another aspect of the present invention includes the developing device.

  According to the present invention, it is possible to make the amount of developer drawn up to the developing roller uniform without giving stress to the developer.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a vertical sectional view showing the configuration of the developing device according to the embodiment of the invention. FIG. 2 is a horizontal cross-sectional view illustrating a configuration of a developing device according to an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings as appropriate. The embodiment described below is merely an example embodying the present invention, and the embodiment of the present invention can be changed as appropriate without departing from the scope of the present invention.

  FIG. 1 is a schematic diagram showing a schematic configuration of an image forming apparatus 10 (an example of an image forming apparatus of the present invention) according to an embodiment of the present invention. As shown in FIG. 1, the image forming apparatus 10 is a so-called tandem color image forming apparatus, and includes a plurality of image forming units 1 to 4, an intermediate transfer belt 5, a driving roller 7A, and a driven roller 7B. , A secondary transfer device 15, a fixing device 16, a control unit (not shown), a paper feed tray 17, a paper discharge tray 18, and exposure devices 31 and 32. Note that the image forming apparatus 10 according to the embodiment of the present invention is not limited to a tandem color image forming apparatus, but is a printer, a copier, a facsimile machine, or a composite device having these functions that can form a color image or a monochrome image. It may be a machine.

  The image forming units 1 to 4 form images based on an electrophotographic system. The image forming units 1 to 4 form toner images of different colors on the plurality of photosensitive drums 11 to 14 arranged in parallel, and sequentially superimpose the toner images on the running (moving) intermediate transfer belt 5. And transcribe. In the example shown in FIG. 1, in order from the downstream side in the moving direction (arrow 19 direction) of the intermediate transfer belt 5, an image forming unit 1 for black, an image forming unit 2 for yellow, an image forming unit 3 for cyan, The magenta image forming units 4 are arranged in a line in that order.

  Each of the image forming units 1 to 4 includes photosensitive drums 11 to 14, charging devices 21 to 24, developing devices 41 to 44 (an example of the developing device of the present invention), primary transfer devices 51 to 54, and the like. That is, the image forming apparatus 10 includes developing devices 41 to 44. The photoconductive drums 11 to 14 carry toner images on their surfaces. The charging devices 21 to 24 charge the surfaces of the corresponding photosensitive drums 11 to 14 to a predetermined potential. The exposure devices 31 and 32 are devices that form an electrostatic latent image by exposing the surfaces of the photosensitive drums 11 to 14 and scanning the light. The exposure device 31 exposes the surfaces of the photosensitive drums 11 and 12, and the exposure device 32 exposes the surfaces of the photosensitive drums 13 and 14. The developing devices 41 to 44 develop the electrostatic latent images on the photosensitive drums 11 to 14 formed by the exposure devices 31 and 32 with toner. The primary transfer devices 51 to 54 transfer the toner images on the rotating photosensitive drums 11 to 14 to the intermediate transfer belt 5. Although not shown in FIG. 1, each of the image forming units 1 to 4 includes a cleaning device that removes the toner image remaining on the photosensitive drums 11 to 14.

  The intermediate transfer belt 5 is an endless belt made of a material such as rubber or urethane. The intermediate transfer belt 5 is supported by a driving roller 7A and a driven roller 7B so as to be rotationally driven. The driving roller 7A is disposed at a position close to the fixing device 16 (right side in FIG. 1), and the driven roller 7B is disposed at a position away from the fixing device 16 (left side in FIG. 1). The surface of the drive roller 7A is formed of a material such as rubber or urethane in order to increase the frictional force with the intermediate transfer belt 5. By being supported by the driving roller 7A and the driven roller 7B, the intermediate transfer belt 5 can move (run) while the surface thereof is in contact with the surface of each of the photosensitive drums 11-14. Then, when the surface of the intermediate transfer belt 5 passes between the photosensitive drums 11 to 14 and the primary transfer devices 51 to 54, the toner images are sequentially superimposed and transferred from the photosensitive drums 11 to 14. .

  The secondary transfer device 15 transfers the toner image transferred to the intermediate transfer belt 5 onto the printing paper conveyed from the paper feed tray 17. The printing paper on which the toner image has been transferred is conveyed to the fixing device 16 by a conveying unit (not shown). The fixing device 16 includes a heating roller 16A heated to a high temperature, and a pressure roller 16B disposed to face the heating roller 16A. The printing paper conveyed to the fixing device 16 is conveyed while being sandwiched between the heating roller 16A and the pressure roller 16B, whereby the toner image is welded to the printing paper. Thereafter, the printing paper is discharged to the paper discharge tray 18.

  As described above, the image forming apparatus 10 transfers the color toner images on the intermediate transfer belt 5 by superimposing and transferring the toner images of the respective colors onto the running intermediate transfer belt 5 by the plurality of image forming units 1 to 4. Form on the surface. The color toner image is transferred from the intermediate transfer belt 5 to the printing paper by the secondary transfer device 15. Thereby, a color image is formed on the printing paper. A configuration in which the intermediate transfer belt 5 is used as a conveyance belt and a toner image is directly superimposed and transferred onto printing paper conveyed on the conveyance belt, or a roller-shaped intermediate transfer member is used instead of the intermediate transfer belt 5 The use of is also considered as another embodiment.

  FIG. 2 is a vertical cross-sectional view showing the configuration of the developing device 41 provided in the image forming unit 1. FIG. 3 is a horizontal sectional view showing the configuration of the developing device 41. Hereinafter, the configuration of the developing device 41 will be described with reference to FIGS. 2 and 3. Since the other developing devices 42 to 44 have the same configuration as the developing device 41, detailed description thereof is omitted.

  The developing device 41 is a device that develops the electrostatic latent image with toner by a developing method in which toner is electrostatically attached to the electrostatic latent image in a non-contact state with respect to the photosensitive drum 11. In general, the developer used for development includes a one-component developer mainly composed of magnetic toner or non-magnetic toner, and a two-component developer mainly composed of non-magnetic toner and magnetic carrier. In the present embodiment, a developing device 41 that performs development using a two-component developer is illustrated.

  As shown in FIG. 2, the developing device 41 includes a developing container 60 (an example of a storage unit of the present invention), a first stirring screw 61, a second stirring screw 62 (an example of a stirring member of the present invention), and a developing roller 63. (An example of the developing roller of the present invention), a shielding sleeve 160 (an example of the cylindrical member of the present invention), and the like.

  The developing container 60 contains a two-component developer containing toner (hereinafter also simply referred to as a developer). The developing container 60 contains a developer and also serves as a housing for the developing device 41. The developing container 60 is formed in a long shape in the longitudinal direction of the developing device 41 (direction perpendicular to the paper surface in FIG. 2). The developing container 60 is partitioned into a first stirring chamber 60B and a second stirring chamber 60C by a partition wall 60A. A developer is accommodated in each of the first stirring chamber 60B and the second stirring chamber 60C. The first agitation chamber 60B and the second agitation chamber 60C are not completely partitioned, but are connected to both ends in the longitudinal direction of the developing device 41 as shown in FIG. Passages 112 and 113 are provided.

  A first stirring screw 61 is rotatably provided in the first stirring chamber 60B. A second stirring screw 62 is rotatably provided in the second stirring chamber 60C. Both the first stirring screw 61 and the second stirring screw 62 are rotatably supported on the side wall 60E (see FIG. 3) of the developing container 60. The bottom wall 60 </ b> G of the first stirring chamber 60 </ b> B provided with the first stirring screw 61 is formed in an arc shape corresponding to the outer periphery of the first stirring screw 61. The bottom wall 60 </ b> H of the second stirring chamber 60 </ b> C provided with the second stirring screw 62 is formed in an arc shape corresponding to the outer periphery of the second stirring screw 62. A density detection sensor 97 for measuring the toner density of the developer is attached to the bottom wall 60G. A shielding sleeve 160 is fixed to the bottom wall 60H. The shielding sleeve 160 will be described later.

  The rotational driving force from the motor is transmitted to the rotation shafts 61A and 62A of the first stirring screw 61 and the second stirring screw 62, respectively. Thereby, the 1st stirring screw 61 and the 2nd stirring screw 62 rotate in a predetermined direction. Specifically, the first stirring screw 61 and the second stirring screw 62 rotate in the counterclockwise rotation direction (an example of the first rotation direction of the present invention) indicated by arrows 93 and 94 in FIG.

  The developing container 60 has a replenishing port 60D. The supply port 60D is formed in the upper wall 60F that forms a flat wall surface on the upper side of the first stirring chamber 60B. The supply port 60D is a through hole that guides the toner supplied from a toner container (not shown) to the developing container 60.

  As shown in FIG. 3, the first stirring screw 61 has a spiral wing member 66 around its axis. The second stirring screw 62 has a spiral wing member 67 around its axis. As a result, when rotationally driven by the rotational driving force from the motor, the first stirring screw 61 and the second stirring screw 62 magnetize the toner supplied from the toner container (not shown) to the developing container 60 through the supply port 60D. It is mixed with the carrier and conveyed in the axial direction while stirring. Further, the developer is agitated by the first agitation screw 61 and the second agitation screw 62, whereby a charge is imparted to the toner. In the present embodiment, the developer is indicated by an arrow 96 (see FIG. 3) between the first stirring chamber 60B and the second stirring chamber 60C via the communication paths 112 and 113 (see FIG. 3) formed in the partition wall 60A. It is circulated and conveyed in the direction shown.

  As shown in FIG. 2, a developing roller 63 is rotatably provided in the developing container 60. Specifically, the developing roller 63 is provided above the second stirring screw 62 in the second stirring chamber 60C. Specifically, the developing roller 63 is provided on the photosensitive drum 11 side with respect to the second stirring screw 62 and in parallel with the second stirring screw 61. The developing roller 63 is disposed so as to face the second stirring screw 62 with a predetermined gap therebetween.

  The developing roller 63 includes a cylindrical developing sleeve 63A. The developing sleeve 63A is rotatably supported in the second stirring chamber 60C. The developing sleeve 63A is composed of an aluminum tube.

  The developing roller 63 faces the photosensitive drum 11 on the opening 64 side (right side in FIG. 2) of the developing container 60. That is, the developing roller 63 is arranged to face the outer peripheral surface of the photosensitive drum 11 with a predetermined gap therebetween. The developing roller 63 receives a rotational driving force from a motor (not shown) and is rotated in the counterclockwise direction (an example of the second rotational direction of the present invention) indicated by an arrow 91 in FIG. That is, the rotation direction of the developing roller 63 and the rotation direction of the second stirring screw 62 are the same rotation direction, and the developing roller 63 is rotated in the same rotation direction as the second stirring screw 62.

  The developing roller 63 includes a magnet unit 63B having a plurality of magnetic poles. The magnet unit 63B is provided inside the developing sleeve 63A. The magnet unit 63B is fixed in the developing sleeve 63A. In the present embodiment, the magnet unit 63 </ b> B has five magnetic poles, that is, a main pole 75, a transport pole 76, a peeling pole 77, a scooping pole 78, and a transport pole 79. Each magnetic pole 75-79 is comprised with the permanent magnet which generate | occur | produces magnetic force, for example.

  The main pole 75 is a magnetic pole that generates a peak magnetic force at a position facing the photosensitive drum 11. The main pole 75 is attached to the magnet unit 63B with its magnetic pole surface facing the photosensitive drum 11 side.

  The transport pole 76 is a magnetic pole having a different polarity from the main pole 75, generates a magnetic field in the circumferential direction of the developing sleeve 63A, holds the developer on the developing sleeve 63A, and transports it in the circumferential direction.

  The peeling pole 77 is a magnetic pole that forms a peeling area 89 having substantially zero magnetic flux density on the opposite side of the developing sleeve 63A from the photosensitive drum 11. When the developer is carried to the peeling area 89, the force for magnetically attracting the developer is lost, and the developer is peeled from the peeling area 89. The peeled developer falls on the second stirring screw 62 located below, is returned to the second stirring chamber 60C, and is conveyed while being stirred again by the second stirring screw 62. Then, after being stirred and transported by the first stirring screw 61 and the second stirring screw 62, the developer is uniformly pumped again onto the developing sleeve 63A by the pumping pole 78 as a uniformly charged developer with an appropriate toner concentration.

  The pumping pole 78 is a magnetic pole that generates a peak magnetic force at a position facing the second stirring screw 62. Specifically, the pumping pole 78 generates the peak magnetic force in the direction of a line segment connecting the rotation shaft 62A of the second stirring screw 62 and the rotation shaft of the developing roller 63. The developer is attracted by the magnetic force onto the surface of the developing sleeve 63A by the upper electrode 78 and is attracted by the magnetic force. As a result, the developer is carried on the surface of the developing sleeve 63A. In this state, the developing sleeve 63 </ b> A is rotated, so that the developer is carried to a position facing the photosensitive drum 11.

  The developing container 60 is provided with a regulating blade 65 (an example of a regulating member of the present invention). The regulating blade 65 is made of a magnetic material, and is a metal plate member having magnetism, for example. The regulating blade 65 is attached along the longitudinal direction of the developing container 60 (direction perpendicular to the paper surface of FIG. 2). The regulating blade 65 is arranged on the downstream side in the rotation direction of the developing roller 63 with respect to the position where the developing roller 63 and the second stirring screw 62 are opposed in the rotating direction of the developing roller 63 (see arrow 91). A slight gap (gap) is formed between the leading end portion 65 </ b> A of the regulating blade 65 and the roller surface of the developing roller 63. The developer attached to the developing roller 63 is regulated to a thickness corresponding to the gap by the regulating blade 65. The transport pole 79 is a magnetic pole that holds the developer on the developing sleeve 63A and carries it in the circumferential direction while generating a peak magnetic force at a position on the developing sleeve 63A facing the regulating blade 65.

  In the developing device 41 configured as described above, the developer unevenness in thickness corresponding to the pitch in the axial direction of the blade member 67 of the second stirring screw 62 occurs on the developing sleeve 63A. This uneven thickness is not necessarily made uniform uniformly by the regulating blade 65, and may be conveyed to a position facing the photosensitive drum 11 with the uneven thickness remaining. In this case, the thickness unevenness appears in the image as density unevenness. Specifically, the density unevenness of the stripe pattern corresponding to the pitch appears in the image. In order to prevent such density unevenness, the developing device 41 of the present embodiment is provided with a shielding sleeve 160.

  Hereinafter, the configuration of the shielding sleeve 160 will be described with reference to FIGS. 2 and 3.

  As shown in FIG. 2, the shielding sleeve 160 is formed of a cylindrical member having a hollow inside. The shielding sleeve 160 is a cylindrical member made of a non-magnetic material. Specifically, the shielding sleeve 160 is a sleeve-shaped member formed of a synthetic resin having no magnetism. The shielding sleeve 160 may be formed of any material as long as it is a non-magnetic material, and the material is not limited to synthetic resin. The shielding sleeve 160 is formed in a long shape in the longitudinal direction of the developing container 60 (direction perpendicular to the paper surface of FIG. 2). The shielding sleeve 160 is provided in the second stirring chamber 60C. Specifically, the shielding sleeve 160 is provided in the second stirring chamber 60C so as to surround the outer peripheral surface of the second stirring screw 62 in a non-contact state. Further, the outer peripheral wall of the shielding sleeve 160 on the developing roller 63 side is not in contact with the developing roller 63 and is disposed at a position where the developing roller 63 and the second stirring screw 62 face each other. The shielding sleeve 160 is fixed to an arc-shaped bottom wall 60H that constitutes an outer wall on the bottom side of the second stirring chamber 60C. Specifically, the lower part of the shielding sleeve 160 is fixed to the bottom wall 60H. Various fixing methods such as adhesion, screwing, pressure bonding, and welding can be applied.

  The shielding sleeve 160 includes a first passage 162A (an example of the first passage of the present invention), a second passage 162B (an example of the second passage of the present invention), and a shielding portion 163.

  The first passage 162A is located on the outer peripheral wall of the shielding sleeve 160 on the upstream side of the rotation direction of the second stirring screw 62 (the direction of the arrow 94 in FIG. 2) with respect to the position where the developing roller 63 and the second stirring screw 62 face each other. Placed in position. The first passage 162 </ b> A is an opening that penetrates the outer peripheral wall of the shielding sleeve 160. The first passage 162 </ b> A is an opening elongated in the longitudinal direction of the developing container 60. The developer stirred by the second stirring screw 62 is guided to the surface of the developing roller 63 through the passage 162A.

  The second passage 162B is located on the outer peripheral wall of the shielding sleeve 160 on the downstream side of the rotation direction of the second stirring screw 62 (the direction of the arrow 94 in FIG. 2) relative to the position where the developing roller 63 and the second stirring screw 62 are opposed to each other. Placed in position. Specifically, the second passage 162 </ b> B is formed at a position spaced from the first passage 162 </ b> A to the downstream side in the rotation direction of the second stirring screw 62 by a predetermined interval. The second passage 162 </ b> B is an opening that penetrates the outer peripheral wall of the shielding sleeve 160. The second passage 162 </ b> B is an opening that is elongated in the longitudinal direction of the developing container 60. In the present embodiment, the second passage 162B is located below the peeling region 89 in the developing sleeve 63A. For this reason, the developer peeled from the developing roller 63 in the peeling region 89 falls downward, and is guided to the second stirring screw 62 of the first stirring chamber 60C through the second passage 162B. Then, after being stirred again by the second stirring screw 62, the developer is guided to the surface of the developing roller 63.

  The outer wall portion between the first passage 162A and the second passage 162B is a shielding portion 163. The shielding part 163 is disposed at a position where the developing roller 63 and the second stirring screw 62 are opposed to each other. The shielding portion 163 is disposed so as to intersect the path of the shortest distance from the second stirring screw 62 to the developing roller 63, that is, a path passing through a line segment connecting the rotation shaft 62A and the rotation axis of the developing roller 63. Yes. Since the shielding portion 163 is provided, even if the developer is attracted to the facing position by the magnetic force of the scooping pole 78, the developer cannot move further to the developing roller 63 side by the shielding portion 163.

  In the present embodiment, a stay space 99 is formed in a path from the first passage 162 </ b> A of the shielding sleeve 160 to the roller surface of the developing roller 63. The retention space 99 is a space for retaining the developer that has passed through the passage 102. This staying space 99 is a space formed between the second stirring screw 62 and the regulating blade 65. By arranging the regulating blade 65 at a position separated from the second stirring screw 62 toward the downstream side in the rotation direction of the developing roller 63, a stay space 99 is formed between the second stirring screw 62 and the regulating blade 65. Therefore, the developer that has moved to the staying space 99 through the first passage 162A so as to bypass the shielding portion 163, moves to the surface side of the developing roller 63 in the staying space 99 and stays there. The developer slowly moves toward the developing roller 63 while staying in the stay space 99. During this gentle movement, the difference in the developer pumping amount corresponding to the pitch of the wing members 67 that causes the unevenness of the developer thickness is made uniform.

  As described above, in the developing device 41 of the present embodiment, the shielding sleeve 160 is provided so that the shielding portion 163 is located at a position where the developing roller 63 and the second stirring screw 62 are opposed to each other. Therefore, even when the developer is attracted by the drawing upper pole 78, the shortest distance path from the second stirring screw 62 to the developing roller 63, that is, the path passing through the line segment connecting the rotation shaft 62A and the rotation shaft of the developing roller 63. Therefore, the developer is not supplied to the developing roller 63 through the path. On the other hand, since the first passage 162A is formed in the shielding sleeve 160, the developer is attracted by the magnetic force of the scooping pole 78, bypasses the shielding portion 163, passes through the first passage 162A, and the second stirring screw 62. To the developing roller 63. That is, the developer is guided to the developing roller 63 through the first passage 162A so as to bypass the facing position without passing through the facing position between the developing roller 63 and the second stirring screw 62. Thereby, the path | route until a developing agent reaches the developing roller 63 becomes long, and the cause of the thickness nonuniformity of a developing agent is eliminated while moving the path | route. As a result, the amount of developer pumped up to the developing roller 63 can be made uniform without giving stress to the developer.

  The shielding sleeve 160 has a second passage 162B. For this reason, the developer peeled in the peeling region 89 falls to the second stirring screw 62 side through the second passage 162B. Thereby, the separated developer is guided to the second stirring screw 62 side without being obstructed by the shielding sleeve 160.

  Further, since the staying space 99 is formed in the developing container 60, the movement of the developer that has entered the staying space 99 through the first passage 162A can be moderated. As a result, the developer becomes a uniform amount in the longitudinal direction of the staying space 99, and the amount of the developer pumped up to the developing roller 63 becomes uniform. Further, since the developer staying in the stay space 99 comes into contact with the roller surface of the developing roller 63, the developer is easily pumped up to the roller surface of the developing roller 63.

  In the above-described embodiment, the second agitating screw 62 having the spiral wing member 67 is exemplified. For example, the second stirring screw 62 extends in the axial direction of the rotating shaft 62A, and is perpendicular to the axial direction from the rotating shaft 62A. The present invention can be applied even to a stirring member having a paddle-shaped wing extending to the top.

10: Image forming apparatuses 11-14: Photoconductor drums 41-44: Developing apparatus 61: First stirring screw 62: Second stirring screw 63: Developing roller 63A: Developing sleeve 63B: Magnet unit 160: Shielding sleeve 162A: First Passage 162B: Second pass 163: Shielding part

Claims (7)

An accommodating portion for accommodating a developer mainly composed of a non-magnetic toner and a magnetic carrier;
An agitation member that is rotatably provided in the accommodating part, has a spiral wing member around an axis, and agitates the developer in the accommodating part by being driven to rotate in a predetermined first rotation direction;
A pumping magnet is provided rotatably above the stirring member, and generates a peak magnetic force in a direction from the inside toward the facing position at a position facing the stirring member, and attracts the developer in the housing portion by the magnetic force. A developing roller that is rotationally driven in a predetermined second rotational direction;
Provided below the developing roller, is fixed to the outer wall of the housing part, Ri Do a nonmagnetic material surrounding the outer peripheral surface of the stirring member in a non-contact state, and the cylindrical member inside the hollow cylindrical ,
A first passage which is formed at a position on the upstream side of the first rotation direction with respect to the position where the developing roller and the stirring member are opposed to each other on the outer peripheral wall of the cylindrical member, and is an opening penetrating the outer peripheral wall;
A second passage that is formed at a position downstream of the facing position in the outer peripheral wall of the cylindrical member in the first rotation direction and is an opening penetrating the outer peripheral wall;
A developing device, comprising: an arcuate shielding portion provided between the first passage and the second passage on an outer peripheral wall of the cylindrical member and disposed at the facing position.   The developing device according to claim 1, wherein the shielding portion is disposed so as to intersect a path passing through a straight line connecting a rotation axis of the stirring member and a rotation axis of the developing roller.   The developing device according to claim 2, wherein the shielding portion is disposed so as to be orthogonal to the path.   4. The developing device according to claim 1, wherein a retention space for retaining the developer is formed in a path from the first passage to a roller surface of the developing roller. A regulating member that is provided on the downstream side in the second rotation direction and regulates the thickness of the developer on the developing roller;
The developing device according to claim 4, wherein the staying space is a gap formed between the stirring member and the regulating member.   The developing device according to claim 1, wherein the first rotation direction and the second rotation direction are the same rotation direction. An image forming apparatus comprising the developing device according to claim 1.

Images