JP2007241149A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device, equipped with a plurality of developer carriers and capable of stably keeping the coating state of developer on the developer carrier, and to provide an image forming apparatus equipped with the developing device. <P>SOLUTION: The developing device has a restricting member 11, arranged to be brought into contact with neither an image-forming region on an image carrier 21 nor image-forming regions on the first developer carrier 8 and the second developer carrier 10 in a region surrounded by a line segment A, linking the center of the first developer carrier 8 with the center of the second developer carrier 10; a line segment B that is the common tangent on the image carrier 21 side of the first developer carrier 8 and the second developer carrier 10, the surface of the first developer carrier 8 and the surface of the second developer carrier 10, and restricting the movement of the developer T from the first developer carrier 8 to the second developer carrier 10. The developer is delivered from the first developer carrier 8 to the second developer carrier 10, in a region nearer to the line segment A than to the restricting member 11. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a developing device that develops an electrostatic image formed on an image carrier and an image forming apparatus including the developing device. More specifically, the present invention relates to a developing device having a plurality of developer carriers and an image forming apparatus provided with the developing device.

  Conventionally, in an image forming apparatus such as a copying machine or a laser beam printer using an electrophotographic method or an electrostatic recording method, an electrostatic latent image formed on an image carrier such as a photosensitive drum can be used with a developer. Visualize. Of the developing devices used for such development, those using a two-component developer including a toner and a carrier as a developer are widely used. In order to cope with an increase in image output speed and the like, a developing device having a plurality of developer carriers that carry a developer and convey it toward the image carrier is known.

  FIG. 12 shows a schematic sectional configuration of a conventional developing device having a plurality of developing sleeves as a plurality of developer carriers. The developing device 1 in the illustrated example includes a developing container (developing device main body) 2, and the developing container 2 includes nonmagnetic toner particles (toner) and magnetic carrier particles (carrier) as the developer T. Contains a two-component developer. In the developing container 2, a first developing sleeve 8 as a first developer carrying member is disposed so as to be rotatable in the direction of the arrow in the drawing. Further, a regulating blade 9 is disposed as a developer regulating member that regulates the amount of developer T carried on the first developing sleeve 8 (the height of the developer spike). Further, in the developing container 2, a second developing sleeve 10 as a second developer carrying member is provided in the first developing sleeve 8 in a region facing the first developing sleeve 8 below the first developing sleeve 8. The sleeve 8 is arranged to be rotatable in the same direction.

  Further, the developing container 2 is vertically divided by a partition wall 7 into a developing chamber (first chamber) 3 on the upper side in the vertical direction and a stirring chamber (second chamber) 4 on the lower side. A first screw 5 and a second screw 6 as developer conveying members are arranged in the developing chamber 3 and the stirring chamber 4, respectively. The developer T is circulated in the developing chamber 3 and the stirring chamber 4 by the first and second screws 5 and 6.

  The first developing sleeve 8 is a cylindrical body made of a non-magnetic material, and a first magnet roller 8a as a first magnetic field generating means is installed in a non-rotating state inside the first developing sleeve 8. The first magnet roller 8a has a plurality of magnetic poles in the circumferential direction. In the illustrated example, the first magnet roller 8a includes a magnetic pole S2 that is a developing pole that causes a magnetic field to act on the developer T in the developing region, and magnetic poles S1, N1, N2, and N3 that are transport poles that transport the developer. 5 poles. Among these, the magnetic pole N3 and the magnetic pole N1, which are the same poles, are adjacent to each other, a repulsive magnetic field is formed between them, and a barrier is formed against the developer T. The magnetic pole N1 of the first magnet roller 8a is “first development pole”, the magnetic pole S1 is “regulation pole”, the magnetic pole N3 is “first repulsion pole” or “delivery pole”, and the magnetic pole N1 is “second repulsion”. Also called “pole”.

  Further, the second developing sleeve 10 is a cylindrical body made of a nonmagnetic material. Like the first developing sleeve 8, the second developing roller 10 has a second magnet roller 10a as a second magnetic field generating means. It is installed in a rotating state. The second magnet roller 10a has a plurality of magnetic poles in the circumferential direction. In the illustrated example, the second magnet roller 10a has three poles: a magnetic pole N4 that is a development pole and magnetic poles S3 and S4 that are transport poles that transport the developer. Among these, the magnetic poles S3 and S4 having the same polarity are adjacent to each other, a repulsive magnetic field is formed between them, and a barrier is formed against the developer T. The magnetic pole N4 of the second magnet roller 10a is also referred to as "second developing pole", the magnetic pole S3 is also referred to as "third repulsive pole" or "receiving pole", and the magnetic pole S4 is also referred to as "fourth repulsive pole".

  Next, an ideal flow of the developer T will be described with reference to FIG. FIG. 13 is an enlarged view of the vicinity of the first and second developing sleeves 8 and 10. The first and second developing sleeves 8 and 10 rotate in the same direction, and are attracted to the first and second developing sleeves 8 and 10 by the magnetic field generated by the first and second magnet rollers 8a and 10a. The developer T is transferred from the first developing sleeve 8 to the second developing sleeve.

  That is, the layer thickness of the developer T is regulated by the regulation blade 9 disposed in a non-contacting manner in the vicinity of the position corresponding to the regulation pole S1 on the first development sleeve 8, and the developer T is placed on the first development sleeve 8. A thin layer of developer T is formed. Then, the developer T that has been transported on the first developing sleeve 8 and passed through the developing region that is the region facing the image carrier 21 reaches the position of the first repulsive pole N3 of the first magnet 8a. .

  The developer T is caused by the repulsive magnetic field formed between the first repelling pole N3 and the second repelling pole N1 downstream from the first developing sleeve 8 as shown by an arrow e in the figure. It cannot pass through the closest position that is the portion facing the second developing sleeve 10. That is, the developer T cannot be rotated around the first developing sleeve 8.

  Then, the developer T that has reached the position of the first repulsive pole N3 on the first developing sleeve 8 is shown by an arrow in the drawing at the transfer portion between the first developing sleeve 8 and the second developing sleeve 10. As indicated by d, it moves to the second developing sleeve 10 side. At this time, the developer T follows the magnetic field lines extending from the position corresponding to the transfer pole N3 on the first developing sleeve 8 toward the position corresponding to the receiving pole S3 on the second developing sleeve 10. Move to the sleeve 10 side.

  In other words, the flow in which the developer T is delivered at the closest position between the first developing sleeve 8 and the second developing sleeve 10 is ideal.

  The developer T that has reached the fourth repulsion pole S4 is blocked by a repulsive magnetic field formed between the third repulsion pole S3 and the fourth repulsion pole S4. It is taken in by the screw 6.

  In the developing apparatus 1 having the plurality of developing sleeves 8 and 10 as described above, the second developing sleeve 8 downstream from the first developing sleeve 8 in the conveying direction of the developer T at the portion facing the photosensitive drum 21. Delivery of the developer T to the developing sleeve 10 is important. If the delivery of the developer T occurs on the photosensitive drum side with respect to the facing portion, the delivery will be incomplete. Hereinafter, this phenomenon is referred to as “icicle phenomenon”. This “icicle phenomenon” will be described later.

  As a countermeasure against the above problems, the development on the developing sleeve is improved by improving the magnetic force pattern in the transfer portion between the first developing sleeve 8 on the upstream side and the second developing sleeve 10 on the downstream side. It is conceivable to keep the coating state of the agent stable. The following proposal has been made as the method.

  Patent Document 1 discloses a first magnetic pole in a first developing roller, a delivery magnetic pole for delivering developer to the second development roller, and a first peeling pole having the same polarity as the delivery magnetic pole. It is disclosed that at least one second separation electrode having the same polarity as the first separation electrode is disposed between the two electrodes. In the invention of Patent Document 1, the developer is completely peeled off at the closest position (transfer section) between the first developing roller and the second developing roller by the magnetic force pattern as described above.

  Patent Document 2 discloses that the half-value width of the normal magnetic flux density of the developing pole in the developing sleeve on the downstream side in the electrostatic latent image moving direction is greater than the half-value width of the normal magnetic flux density on the developing pole in the upstream developing sleeve. Narrowing is disclosed. In the invention of Patent Document 2, the lines of magnetic force extending from the developing pole to the developing pole are to be reduced by the magnetic force pattern as described above.

  Patent Document 3 describes a configuration in which a limiting member is disposed in the gap between the upstream and downstream developing rollers and the photosensitive drum as a countermeasure against toner cloud and fogging. However, in Patent Document 3, since the toner is not transferred from the upstream roller to the downstream roller, the above-described icicle phenomenon does not occur.

Patent Document 4 describes a configuration in which a partition plate is inserted and removed between two developing rollers in order to switch between the case where the developer is transferred between the two developing rollers and the case where the developer is not transferred.
JP 11-327308 A JP 2002-268386 A Japanese Patent Laid-Open No. 1-142759 Japanese Patent Laid-Open No. 11-219022

  However, in the case of using a developing sleeve having a small diameter having a magnetic force capable of lubricatingly transporting the developer in response to the downsizing of the developing device, a magnetic pole is provided at a desired position as in the invention of the above prior art document. In some cases, the magnetic pole cannot be arranged, or the desired magnetic pole size cannot be achieved. Further, when the absolute distance between the developing poles between the plurality of developing sleeves is shortened, the magnetic lines of force from the developing pole to the developing pole are likely to be extended, and the above-described “icicle phenomenon” is likely to occur. The “icicle phenomenon” of the developer will be described below with reference to FIG.

  Referring to the developing device 1 described above, the “icicle phenomenon” of the developer means that the first developing electrode (main electrode) S2 and the second developing electrode 8 on the first developing sleeve 8 side, as shown in FIG. This is a phenomenon in which the developer T is connected to the second developing electrode (main electrode) N4 on the developing sleeve 10 side. When such a series of the developer T occurs, the developer T is conveyed as shown by an arrow f in the drawing. More specifically, as a main factor of the “icicle phenomenon”, interference of magnetic force between the first magnet roller 8a and the second magnet roller 10a can be considered. That is, when the first developing pole S2 on the first developing sleeve 8 side and the second developing pole N4 on the second developing sleeve 10 side are different polarities, the first developing pole S2 to the second developing pole By generating a magnetic line of force to the development pole N4, the developer T is connected between the first and second development poles S2 and N4.

  In the above description, the case where the “icicle phenomenon” occurs due to the magnetic interference between the developing poles has been described. However, the “icicle phenomenon” is also caused by the magnetic pole interference between the conveying pole and the developing pole and between the conveying pole and the conveying pole. May occur.

  When the developing operation is performed in a state where the “icicle phenomenon” is occurring, the developer T contributing to the “icicle phenomenon” has a weak magnetic restraint force, so that many carriers adhere to the image carrier 21.

  For this reason, it is difficult to collect all the carriers adhering to the image carrier with the developing sleeve 10 on the downstream side in the developer transport direction from the location where the developer T is connected in the “icicle phenomenon”. Accordingly, when the developer T jumps out of the developing container 2, the capacity of the developer T in the developing container 2 decreases.

  Further, when the carrier adheres on the image carrier 21, a cleaning failure, a bias leak, a carrier adhesion image, or the like occurs. Further, if the toner is conveyed to the fixing device, the rollers of the fixing device may be damaged. Therefore, it is desired to prevent the occurrence of the “icicle phenomenon”.

  In the “icicle phenomenon”, the development pole S2 of the first magnet roller 8a and the development pole N4 of the second magnet roller 10a approach each other, causing interference between the development poles (magnetic lines extend between the development pole and the development pole). Sometimes prone to occur. Further, the “icicle phenomenon” occurs when the transfer pole N3 of the upstream first magnet roller 8a and the receive pole S3 of the second magnet roller 10a on the downstream side are moved to the development pole side, respectively. It's easy to do. This is because the developer T becomes a path along the vicinity of the image carrier 21.

  The ideal developer flow in the developing device having a plurality of developer carriers has been described above. The flow of the developer T in which the “icicle phenomenon” does not occur can be said to be that the developer T is delivered on the image carrier 21 so as not to induce carrier adhesion.

  As described above, for example, in the case where a small-diameter developing sleeve having a magnetic force capable of lubricatingly transporting the developer is used in response to the downsizing of the developing device, the conventional method coats the developer on the developing sleeve. It has become difficult to stabilize the state.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a developing device including a plurality of developer carriers, and a developing device capable of maintaining a stable coating state of the developer on the developer carrier, and an image forming apparatus including the same. Is to provide.

  The above object is achieved by the developing device and the image forming apparatus according to the present invention. In summary, the first aspect of the present invention develops an electrostatic image using a developer that is disposed opposite to an image carrier that carries an electrostatic image formed in an image forming area and that includes magnetic particles. A developing device, which carries the developer and transports the developer to a developing area facing the image carrier, and the first and second developer carriers disposed adjacent to each other; And a first magnetic field generating means for generating a magnetic field acting on the developer, the first and second developer carriers being the same as each other. In the developing device that rotates in the direction and delivers the developer from the first developer carrier to the second developer carrier, the center of the first developer carrier and the second development Line A connecting the center of the developer carrier, the first developer carrier and the second developer carrier Of the image carrier in a region surrounded by a line segment B which is a common tangent line on the image carrier side, the surface of the first developer carrier, and the surface of the second developer carrier. In the image forming region, the first developer carrying member, and the second developer carrying member without contact with any of the image forming regions, and from the first developer carrying member to the first developer carrying member. And a transfer member that restricts movement of the developer to the second developer carrier, and the delivery of the developer from the first developer carrier to the second developer carrier is surrounded by In the developing device, the developing device is performed in a region closer to the line segment A than the limiting member.

  According to a second aspect of the present invention, in an image forming apparatus for forming and outputting an image on a transfer material, the image has an image carrier that carries an electrostatic image and the developing device of the present invention. A forming apparatus is provided.

  According to the present invention, in a developing device including a plurality of developer carriers, the coat state of the developer on the developer carrier can be kept stable.

  Hereinafter, the developing device and the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Example 1
[Overall Configuration and Operation of Image Forming Apparatus]
First, the overall configuration and operation of an embodiment of an image forming apparatus according to the present invention will be described. FIG. 1 shows a schematic cross-sectional configuration of an image forming apparatus 100 of the present embodiment. The image forming apparatus 100 of this embodiment is an electrophotographic full color image forming apparatus capable of forming a full color image according to an image information signal. The image information signal is sent to the apparatus main body from an external device such as a document reading apparatus or a personal computer connected to the image forming apparatus main body (apparatus main body). In this embodiment, the image forming apparatus 100 employs a well-known tandem method, direct transfer method, and heating / pressure fixing method. Further, in the image forming apparatus 100 of this embodiment, the charging polarity of the image carrier that carries the electrostatic image (latent image) is negative, the charging polarity of the toner of the developer is also negative, and the reversal development method. To develop the electrostatic image.

  The image forming apparatus 100 includes first, second, third, and fourth image forming units PY, PM, PC, and PK as a plurality of image forming units. The first, second, third, and fourth image forming units PY, PM, PC, and PK form yellow (Y), magenta (M), cyan (C), and black (K) images, respectively. Is to do. In this embodiment, the configurations and operations of the image forming units PY, PM, PC, and PK are substantially the same except that the color of the toner used is different. Therefore, in the following, unless there is a particular distinction, the subscripts Y, M, C, and K given to the reference numerals to indicate that they are elements provided for any color are omitted, and generally explain.

  In the image forming portion P, a drum-shaped electrophotographic photosensitive member as an image carrier, that is, a photosensitive drum 21 is rotatably provided. The photosensitive drum 21 is usually a drum having a diameter of 30 to 150 mm. In this embodiment, the photosensitive drum 21 having a diameter of 108 mm is used. Around the photosensitive drum 21, there are a primary charger 22 as primary charging means, an exposure device (laser exposure optical system) 23 as exposure means, a transfer charger 25 as transfer means, a cleaning device 26 as cleaning means, and the like. Has been placed. Further, a conveyance belt (transfer material conveyance sheet) 28 serving as a transfer material carrier is disposed so as to face the photosensitive drums 21Y, 21M, 21C, and 21K of the image forming units PY, PM, PC, and PK. The conveying belt 28 is wound around two supporting rollers, a driving roller 28a and a driven roller 28b, as a plurality of supporting members, and a rotational driving force is transmitted to the driving roller 28a, whereby an arrow direction in the figure. Move around (rotate). The transfer charger 25 of each image forming unit P is disposed on the inner peripheral surface side of the conveyance belt 28 so as to face the photosensitive drum 21. The transfer charger 26 presses the conveyance belt 28 toward the photosensitive drum 21 to form a transfer portion (transfer nip) N where the conveyance belt 28 and the photosensitive drum 21 are in contact with each other.

  During image formation, the rotating photosensitive drum 21 is uniformly charged by the primary charger 22. Next, the surface of the charged photosensitive drum 21 is exposed with light modulated in accordance with an image information signal by an exposure device 23 having a light emitting element (laser in this embodiment). Thereby, an electrostatic image is formed on the photosensitive drum 21. Thereafter, the electrostatic image on the photosensitive drum 21 is visualized by the developing device 1 as a developer image (toner image). The developing device 1 will be described in detail later.

  Next, the toner image on the photosensitive drum 21 is transferred to a transfer material (recording paper, plastic sheet, etc.) 29 conveyed by the conveying belt 28 by the action of the transfer charger 25. At this time, a predetermined transfer bias having a polarity opposite to the charging polarity of the toner is applied to the transfer charger 25 from a transfer bias power source (not shown) as a transfer bias output unit.

  The transfer material 29 is conveyed from the transfer material supply unit (not shown) to the conveyance belt 28 at a predetermined timing in accordance with the image forming operation in the image forming unit P, and is adsorbed and supported on the conveyance belt 28 to be transferred to the transfer unit. To N.

  For example, when a full-color image is formed, the above-described operation is sequentially performed in each of the first to fourth image forming units PY to PK. As a result, a multiple toner image is formed on the transfer material 29 conveyed by the conveyance belt 28 by superimposing the toner images of each color of Y, M, C, and K. Of course, it is also possible to drive only the desired image forming portion P and transfer only the desired color toner image onto the transfer material 29.

  After the transfer of the toner image, the transfer material 29 is separated from the conveyor belt 28 and conveyed to a fixing device 27 as a fixing unit. The fixing device 27 heats and pressurizes the transfer material 29 to fix the unfixed toner image on the transfer material 29 to obtain a permanent image. Thereafter, the transfer material 29 on which the image is fixed is discharged out of the apparatus main body.

  The toner (transfer residual toner) remaining on the photosensitive drum 21 after the toner image is transferred to the transfer material 29 is removed and collected by the cleaning device 26.

  In this embodiment, an amount of toner corresponding to the toner consumed in image formation is replenished to the developing device 1 from the toner replenishing tank 24 provided on the upper portion of the developing device 1 as needed.

[Developer]
Next, the developing device 1 will be described with reference to FIG. FIG. 2 shows the developing device 1 used in the image forming apparatus 100 of this embodiment in more detail.

  The developing device 1 of the present embodiment includes a developing container (developing device main body) 2, and the developing container 2 includes nonmagnetic toner particles (toner) and magnetic carrier particles (carrier) as the developer T. Contains a two-component developer. In the developing container 2, a first developing sleeve 8 as a first developer carrying member is disposed so as to be rotatable in the direction of the arrow in the drawing. The developing container 2 is provided with a regulating blade 9 as a developer regulating member that regulates the amount of the developer T carried on the first developing sleeve 8 (the height of the spike of the developer). . Further, in the developing container 2, a second developing sleeve 10 as a second developer carrying member is provided in a region facing the first developing sleeve 8 below the first developing sleeve 8. 8 is arranged so as to be rotatable in the same direction.

  The first and second developing sleeves 8 and 10 usually have a diameter of 12 mm or more. In this embodiment, the first and second developing sleeves 8 and 10 have a relatively small diameter of 20 mm.

  Further, the developing container 2 is vertically divided by a partition wall 7 into a developing chamber (first chamber) 3 on the upper side in the vertical direction and a stirring chamber (second chamber) 4 on the lower side. A first screw 5 and a second screw 6 as developer conveying members are arranged in the developing chamber 3 and the stirring chamber 4, respectively.

  The first screw 5 is disposed substantially parallel to the bottom of the developing chamber 3 along the axial direction (developing width direction) of the developing sleeve 8. In this embodiment, the first screw 5 has a screw structure in which a blade member made of a nonmagnetic material is provided in a spiral shape around a rotating shaft made of a ferromagnetic material. The first screw 5 rotates to convey the developer T in the developing chamber 3 along the axial direction of the developing sleeve 8 at the bottom of the developing chamber 3.

  In the present embodiment, the second screw 6 is also provided with a blade member made of a nonmagnetic material in a spiral shape around the rotating shaft made of a ferromagnetic material, like the first screw 5. Screw structure. However, the blade member of the second screw is provided around the rotating shaft in the opposite direction to the blade member of the first screw 5. The second screw 6 is arranged at the bottom of the stirring chamber 4 substantially parallel to the first screw 5, that is, substantially parallel to the axial direction (developing width direction) of the developing sleeve 8. The second screw 6 rotates in the same direction as the first screw 5 and transports the developer T in the stirring chamber 4 in the opposite direction to the first transport screw 5.

  The developer T is circulated between the developing chamber 3 and the stirring chamber 4 by such rotation of the first and second screws 5 and 6. In the developing device 1 of this embodiment, the developing chamber 3 and the stirring chamber 4 are vertically arranged, and the developer from the developing chamber 3 to the stirring chamber 4 is from top to bottom, and from the stirring chamber 4 to the developing chamber. Developer to 3 moves from bottom to top. In particular, the developer T is transferred from the stirring chamber 4 to the developing chamber 3 so as to be pushed up from the bottom to the top by the pressure of the developer T accumulated at the end.

  A position corresponding to the developing region of the developing container 2 facing the photosensitive drum 21 is open, and the first and second developing sleeves 8 and 10 are positioned in the opening, and the photosensitive drum 21 in the image forming apparatus. It is rotatably arranged so as to be partially exposed in the direction in which it is installed. The first and second developing sleeves 8 and 10 rotate in a direction that passes from the top to the bottom in the developing region, which is a portion facing the photosensitive drum 21. Therefore, the first and second developing sleeves 8 and 10 are rotated in such a direction that the developer is supplied from the upper developing chamber 3 in the vertical direction and the developed developer is returned to the lower stirring chamber 4. . In this embodiment, the photosensitive drum 21 also rotates in the direction passing through the development area from the top to the bottom in the vertical direction. That is, in the present embodiment, each of the first and second developing sleeves 8 and 10 and the photosensitive drum 21 are rotated so that the surface movement direction is the same direction at the facing portion.

  Here, with respect to the first and second developing sleeves 8 and 10, the developer transport direction at the portion facing the photosensitive drum 21 is the developer T supplied to the first developing sleeve 8 in the developing chamber 3. 2 is a direction that is transferred to the developing sleeve 10 and returned to the stirring chamber 4. In the present embodiment, the developer transport direction is such that the photosensitive drum 21 and the first and second developing sleeves 8 are disposed at the opposing portions of the photosensitive drum 21 and the first and second developing sleeves 8 and 10. 10 in the same direction as the surface movement direction. The first developing sleeve 8 is also referred to as “upstream developing sleeve”, and the second developing sleeve 10 is also referred to as “downstream developing sleeve”.

  The first developing sleeve 8 is a cylindrical body made of a non-magnetic material such as aluminum or stainless steel, and a first magnet roller 8a serving as a first magnetic field generating means is not rotated (fixed) inside the first developing sleeve 8. It is installed in a state. The first magnet roller 8a has a plurality of magnetic poles in the circumferential direction. In the present embodiment, the first magnet roller 8a includes a magnetic pole S2 that is a development pole that causes a magnetic field to act on the developer T in the development area, and magnetic poles S1, N1, N2, and N3 that are transport poles that transport the developer. 5 poles. Among these, the magnetic pole N3 and the magnetic pole N1, which are the same poles, are adjacent to each other, a repulsive magnetic field is formed between them, and a barrier is formed against the developer T. In the present embodiment, the magnetic pole N1 of the first magnet roller 8a is the "first developing pole", the magnetic pole S1 is the "regulating pole", the magnetic pole N3 is the "first repulsive pole" or "delivery pole", and the magnetic pole N1 is Also called “second repulsion pole”.

  The regulating blade 9 is made of a nonmagnetic member such as aluminum or stainless steel, and is disposed upstream of the photosensitive drum 21 (that is, the developing region) in the rotation direction of the first developing sleeve 8. Then, the developer T containing toner and carrier passes between the tip of the regulating blade 9 and the first developing sleeve 8 and is sent to the developing region.

  Incidentally, by adjusting the distance between the regulating blade 9 and the surface of the first developing sleeve 8, the amount of magnetic brush (earing) by the developer T carried on the first developing sleeve 8 is regulated. The amount of developer T conveyed to the development area is adjusted.

  The second developing sleeve 10 is a cylindrical body made of a non-magnetic material such as aluminum or stainless steel. Like the first developing sleeve 8, the second developing sleeve 10 includes a second developing sleeve 10 as a second magnetic field generating means. The magnet roller 10a is installed in a non-rotating (fixed) state. The second magnet roller 10a has a plurality of magnetic poles in the circumferential direction. In the present embodiment, the second magnet roller 10a has three poles: a magnetic pole N4 that is a development pole and magnetic poles S3 and S4 that are transport poles that transport the developer. Among these, the magnetic poles S3 and S4 having the same polarity are adjacent to each other, a repulsive magnetic field is formed between them, and a barrier is formed against the developer T. Of the magnetic poles S3 and S4 forming the repulsive magnetic field, the magnetic pole S3 upstream in the rotation direction of the second developing sleeve 10 is connected to the magnetic pole N3 of the first magnet 8a by the first and second developing members. The sleeves 8 and 10 face each other in the vicinity of the closest position. In the present embodiment, the magnetic pole N4 of the second magnet roller 10a is referred to as “second developing pole”, the magnetic pole S3 as “third repulsive pole” or “receiving pole”, and the magnetic pole S4 as “fourth repelling pole”. Say.

  Each of the first and second developing sleeves 8 and 10 is connected to a developing bias power source (not shown) as developing bias output means. During the developing operation, a developing bias in which a DC voltage component and an AC voltage component are superimposed as a developing bias is applied to the first and second developing sleeves 8 and 10 from a developing bias power source. The developing bias power supply for the first and second developing sleeves 8 and 10 may be shared or provided separately.

  In the developing device 1 of the present embodiment, as will be described in detail later, a restricting member (an icicle phenomenon preventing member, an icicle restricting member, a continuous preventing member) 11 includes a first developing sleeve 8 and a second developing sleeve 10. Is disposed in the vicinity of the transfer portion of the developer T. That is, in this embodiment, a series (conveyance) of the developer T that induces carrier adhesion on the photosensitive drum 21 between the adjacent first developing sleeve 8 and the second developing sleeve 10 is prevented. Further, the limiting member 11 is disposed. As will be described in detail later, in this embodiment, the limiting member 11 does not contact any of the regions surrounded by the photosensitive drum 21, the first developing sleeve 8, and the second developing sleeve 10. Be placed. The restricting member 11 restricts at least a part of the movement of the developer T from the first developing sleeve 8 to the second developing sleeve 10.

  In the developing device 1 having the above-described configuration, the surface of the first developing sleeve 8 and the second developing sleeve 10 facing the photosensitive drum 21 is a region where the developing operation is performed. In this region, a developing electric field is formed by the difference between the latent image potential formed on the photosensitive drum 21 and the DC voltage applied to the first and second developing sleeves 8 and 10. Due to the electric field and the latent image potential, the toner moves from the developer T on the first and second developing sleeves 8 and 10 to the photosensitive drum 21, and a toner image is formed on the photosensitive drum 21. Further, in order to improve the developing efficiency (that is, the toner application rate to the latent image formed on the photosensitive drum 21), the first and second developing sleeves 8 and 10 are connected to the developing bias power source as described above. The developing operation is performed by applying a developing bias in which a DC voltage and an AC voltage are superimposed.

[Flow of developer in developing device]
In the present embodiment, the first developing pole (main pole) S2 of the first magnet roller 8a included in the first developing sleeve 8 and the second magnet roller 10a included in the second developing sleeve 10 are included. The second developing electrode (main electrode) N4 is different from each other. For this reason, the lines of magnetic force tend to extend between the first development pole S2 and the second development pole N4, and the “icicle phenomenon” is likely to occur.

  By the way, in order to prevent the “icicle phenomenon”, it is conceivable to make the developing electrode of the upstream developing sleeve and the developing electrode of the downstream developing sleeve the same. However, in order to make both the developing poles the same in this way, three or more magnetic poles (odd number of poles) must be arranged between the developing pole and the developing pole. Therefore, increasing the number of magnetic poles leads to an increase in cost.

  Further, when a plurality of relatively small developing sleeves are used, there are many cases where three or more magnetic poles cannot be inserted between the developing pole and the developing pole without deteriorating the transportability of the developer. From the above, in this embodiment, the developing electrodes of the first and second developing sleeves 8 and 10 are different from each other.

  Next, the flow of the developer T in this embodiment will be described with reference to FIG. FIG. 3 is an enlarged view of the vicinity of the first and second developing sleeves 8 and 10.

  The layer thickness of the developer T is regulated by a regulating blade 9 that is disposed in a non-contacting manner in the vicinity of the position corresponding to the regulating electrode S <b> 1 on the first developing sleeve 8, and the developer is placed on the first developing sleeve 8. A thin layer of T is formed. Then, the developer T that has been transported on the first developing sleeve 8 and passed through the developing region reaches the position of the first repulsive pole N3 of the first magnet 8a.

  The developer T has a first repelling pole N3 and a second repelling pole N1 downstream from the first developing sleeve 8 and the first developing sleeve 8 as shown by an arrow e in the drawing. It is impossible to pass through the closest position that is the portion facing the second developing sleeve 10. That is, the developer T cannot be rotated around the first developing sleeve 8.

  In this embodiment, the restricting member 11 is disposed in the vicinity of the developer delivery portion of the first developing sleeve 8 and the second developing sleeve 10. As a result, as will be described in detail later, the developer T continues from a position corresponding to the development pole S2 on the first development sleeve 8 toward a position corresponding to the development pole N4 on the second development sleeve 10. This prevents the occurrence of the “icicle phenomenon”.

  Therefore, in the developing device 1 of the present embodiment, the flow of the developer T along the first and second developing sleeves 8 and 10 can be realized as indicated by an arrow d in FIG. That is, a flow in which the developer T is delivered at the closest position between the first developing sleeve 8 and the second developing sleeve 10 is realized.

  That is, as indicated by an arrow d in FIG. 3, the developer T that has reached the position of the first repulsive magnetic pole N <b> 3 on the first developing sleeve 8 is between the first developing sleeve 8 and the second developing sleeve 10. In the intermediate transfer portion, it moves to the second developing sleeve 10 side. At this time, the developer T follows the magnetic field lines extending from the position corresponding to the transfer pole N3 on the first developing sleeve 8 toward the position corresponding to the receiving pole S3 on the second developing sleeve 10. Move to the developing sleeve 10 side.

  Thereafter, the developer T on the second developing sleeve 10 is formed between the fourth repulsive pole S4 and the third repelling pole S3 of the second magnet roller 10a included in the second developing sleeve 10. It is blocked by the repulsive magnetic field and is taken into the second screw 6 in the stirring chamber 4.

  In this way, the developer T is supplied from the developing chamber 3 on the upper side in the vertical direction to the first developing sleeve 8 on the upstream side, and is transferred from the first developing sleeve 8 to the second developing sleeve 10 on the downstream side. It is. Finally, the developed developer T is returned to the stirring chamber 4 on the lower side in the vertical direction. As described above, the developing device 1 according to the present embodiment adopts a function-separated stirring configuration.

  In addition, since the restricting member 11 is disposed, the design of the magnetic force pattern of the transfer portion can be prioritized so as not to cause a developer coating failure on the developing sleeve. Further, even if the magnetic pattern causes the occurrence of the “icicle phenomenon” in the prior art, the presence of the limiting member 11 does not cause the “icicle phenomenon”, and the image defect as described above. Can be prevented. That is, by arranging the limiting member 11, it is possible to ensure a design margin for the magnetic pattern of the transfer portion.

[Restricted members]
Next, with reference to FIGS. 4 and 5, the restricting member (icicle phenomenon preventing member, icicle regulating member, continuous preventing member) 11 will be described in more detail.

  First, as shown in FIG. 4, when the first and second developing sleeves 8 and 10, which are a plurality of adjacent developer carrying members, are viewed in the axial direction, the center (rotation center) of the first developing sleeve 8. A straight line connecting the center of the second developing sleeve 10 (the center of rotation) is defined as a line segment A. A common tangent line on the photosensitive drum 21 side of the first developing sleeve 8 and the second developing sleeve 10 is defined as a line segment B. At this time, the restricting member 11 is a region surrounded by at least the line segment A, the line segment B, and the surfaces of the first and second developing sleeves 8 and 10 (hatched portion in FIG. 4; hereinafter, “arrangement region”). ") Is arranged in Z. As will be described later, the limiting member 11 may partially protrude from the arrangement region Z.

  In this embodiment, the position corresponding to the transfer pole N3 on the first developing sleeve 8 and the position corresponding to the receiving pole S3 on the second developing sleeve 10a are the first developing sleeve 8 and the second developing sleeve 8a. It is arranged near the closest position to the developing sleeve 10. This portion is a delivery portion for the developer T. Therefore, in this embodiment, the transfer portion for the developer T is in the arrangement region Z. In other words, in this embodiment, the delivery of the developer T from the first developing sleeve 8 to the second developing sleeve 10 is within the arrangement region Z and is closer to the line segment A than the limiting member 11. Done in

  In this embodiment, the position corresponding to the first developing pole S2 on the first developing sleeve 8 and the position corresponding to the second developing pole N4 on the second developing sleeve 10 are respectively photosensitive. It is disposed at a position closest to the drum 21.

  Here, it is preferable that the limiting member 11 is disposed so as to contact the line segment B or straddle the line segment B. As a result, the limiting member 11 is disposed so as to fall within a region where there is a magnetic force line extending from the position of the developing pole S2 on the first developing sleeve 8 to the position of the developing pole N4 on the second developing sleeve 10. In addition, the occurrence of the “icicle phenomenon” can be prevented.

  The restricting member 11 is perpendicular to a line segment A connecting the center of the first developing sleeve 8 and the center of the second developing sleeve 10 and is closest to the first developing sleeve 8 and the second developing sleeve. A straight line passing through the midpoint between the first and second developing sleeves 8 and 10 at the position is defined as a line segment C. At this time, it is preferable that the limiting member 11 is disposed so as to contact the line segment C or straddle the line segment C. More preferably, the limiting member 11 is arranged so as to intersect the line segment C. As a result, the limiting member 11 is disposed so as to fall within a region where there is a magnetic force line extending from the position of the developing pole S2 on the first developing sleeve 8 to the position of the developing pole N4 on the second developing sleeve 10. In addition, the occurrence of the “icicle phenomenon” can be prevented.

  The limiting member 11 is made of a nonmagnetic material. As a material of the limiting member 11, for example, a plastic material such as ABS resin or PBT resin can be suitably used. Since the limiting member 11 is made of a nonmagnetic material, interference with the first and second magnet rollers 8a and 10a inside the first and second developing sleeves 8 and 10 does not occur, and the limiting member 11 is magnetized. Thus, the developer T can be prevented from collecting in the vicinity of the limiting member 11. Further, since a high voltage in which a DC voltage and an AC voltage are superimposed is applied as the developing bias to the first and second developing sleeves 8 and 10, the limiting member 11 is electrically floated.

  Next, the shape and arrangement method of the limiting member 11 will be described in more detail.

  As shown in more detail in FIG. 5A, the restricting member 11 has at least an image forming area (the maximum size in the apparatus) in the longitudinal direction (rotational axis direction) of the photosensitive drum 21 and the first and second developing sleeves 8 and 10. An area where an electrostatic image is formed). In this region, the other members, typically, the first and second developing sleeves 8 and 10 and the photosensitive drum 21 are disposed so as not to contact. FIG.5 (b) expands and shows the cross section of the limiting member 11 shown to Fig.5 (a).

  In the present embodiment, the restricting member 11 has a triangular shape having vertices α, β, and γ as viewed in the longitudinal direction. And the opposing surface (side βγ) of the limiting member 11 with respect to the photosensitive drum 21 is arranged so as to contact the line segment B or straddle the line segment B. Thereby, as described above, the limiting member 11 is arranged so as to block the magnetic field lines extending from the position of the developing pole S2 on the first developing sleeve 8 to the developing pole N4 on the second developing sleeve 10, and more. The occurrence of the “icicle phenomenon” can be prevented well.

  Preferably, the distance (interval) D1 between the first developing sleeve 8 and the limiting member 11 and the distance (interval) D2 between the second developing sleeve 10 and the limiting member 11 are each 1.0 mm or more. Set. When the distances D1 and D2 are less than 1 mm, the transportability of the developer T between the limiting member 11 and the first and second developing sleeves 8 and 10 is deteriorated. The developer T may stay between the two developing sleeves 8 and 10.

  On the other hand, the distances D1 and D2 are usually set to 3.0 mm or less in consideration of, for example, maximizing the effect of preventing the continuous developer T (icicle phenomenon) by the limiting member 11. In this embodiment, the distances D1 and D2 are set to 1.0 mm.

  The distance (interval) D3 between the limiting member 11 and the photosensitive drum 21 is the closest distance between the first developing sleeve 8 and the photosensitive drum 21, and the closest distance between the second developing sleeve 10 and the photosensitive drum 21. Set equal to one or both. Preferably, this distance D3 is set to 400 μm or less. Thereby, it is possible to satisfactorily prevent the developer T connected to each other between the limiting member 11 and the photosensitive drum 21 from entering. In the example shown in FIG. 5, the distance D <b> 3 is set to 300 μm, which is the closest distance between each of the first and second developing sleeves 8 and 10 and the photosensitive drum 21.

  It is effective to set the distance D3 to 200 μm or less in order to more reliably prevent the developer T connected to each other from entering between the limiting member 11 and the photosensitive drum 21.

  On the other hand, the distance D3 is usually set to 20 μm or more, more preferably 50 μm or more in consideration of interference with the toner image on the photosensitive drum 1.

  That is, the distance D3 is preferably set to 20 μm or more and 400 μm or less, more preferably 50 μm or more and 200 μm or less.

  In addition, the angles ∠αβγ and ∠αγβ of the limiting member 11 are preferably set to 20 degrees or more and 60 degrees or less, respectively. Thereby, it is possible to better prevent the developer T from spilling on the side of the restricting member 11 facing the photosensitive drum 21 (side βγ). If this angle is less than 20 degrees, the effect of preventing the series of the developer T (icicle phenomenon) is weakened. On the other hand, if the angle exceeds 60 degrees, the developer T may spill on the side of the restricting member 11 facing the photosensitive drum 21 (side βγ).

  Alternatively, as shown in FIG. 6A, the restricting member 11 has a surface facing the first developing sleeve 8 (side αβ) and a surface facing the second developing sleeve 10 (side αγ). One or both of them may have a curvature. FIG. 6B shows an enlarged cross section of the limiting member 11 shown in FIG. The curvature of the limiting member 11 is preferably provided in accordance with the curvatures of the first developing sleeve 8 and the second developing sleeve 10. That is, the curvature of the limiting member 11 is preferably substantially equal to the curvature of the surface of the first developing sleeve 8 or the second developing sleeve 10 facing each other. Accordingly, it is possible to make the developer T less likely to stay between the limiting member 11 and each of the first and second developing sleeves 8 and 10 than the limiting member 11 having a triangular cross section shown in FIG. .

  In the above description, the limiting member 11 has been described as having a triangular shape (or a triangular shape having curvatures on the side αβ and the side αγ). However, the present invention is not limited to this, and the occurrence of the “icicle phenomenon” is prevented. Any shape can be used. For example, other shapes as shown in FIG. 7 may be used.

  The limiting member 11 shown in FIG. 7A is a member having a V-shaped cross section in which the opposing surface (side βγ) of the limiting member 11 having the triangular cross section shown in FIG. 5B facing the photosensitive drum 21 is not provided. It is. In the limiting member 11, the side αβ and the side αγ form a surface facing the first developing sleeve 8 and the second developing sleeve 10, respectively. In the limiting member 11, the angles ∠αβγ and ∠αγβ can be set to angles when the line segment βγ is assumed.

  The limiting member 11 shown in FIGS. 7B and 7C has a shape in which protrusions are formed on the first and second developing sleeves 8 and 10 side of a substantially plate-like member that forms a surface facing the photosensitive drum 21. Have. In the limiting member 11 in FIG. 7B, the skirt of the protrusion is relatively wide compared to the limiting member 11 in FIG. In the limiting member 11 shown in FIG. 7B, the protrusion has a curvature on the surface facing each of the first and second developing sleeves 8 and 10. The width and curvature of the skirt of the protrusion are the effect of preventing the developer T from staying between the limiting member 11 and each of the first and second developing sleeves 8 and 10, and between the limiting member 11 and the photosensitive drum 21. It can be set appropriately so as to adjust the effect of preventing the developer T from entering the toner. In these restricting members 11 as well, the angles ∠αβγ and ∠αγβ can be the angles when the line segment αβ and the line segment αγ are assumed.

  Next, the arrangement of the limiting member 11 in the longitudinal direction will be described with reference to FIG. FIG. 8 is a partial cross-sectional view of the developing device 1 showing the restriction member 11 as seen from the photosensitive drum 21 side.

  Support for supporting the limiting member 11 in the vicinity of both ends of the limiting member 11 on both ends in the longitudinal direction of the developing device 1 (on both ends of the developing device 1 from the first and second developing sleeves 8 and 10). Members 40a and 40b are provided. The support members 40 a and 40 b support the restriction member 11 so as to be pressed against the developing container 1. The support members 40a and 40b are fixed to the developing device 1 with screws 41 as fixing means. The support members 40a and 40b are not limited to this, but can be suitably formed using a plastic material such as ABS resin.

  In addition, it is desirable for the limiting member 11 to have strength and rigidity so as not to bend and deform in the longitudinal direction. Further, the length in the longitudinal direction may be equal to or slightly longer than the first and second developing sleeves 8 and 10. That is, the limiting member 11 has at least a length in the longitudinal direction that is equal to or longer than the length of the image forming region in the longitudinal direction (rotational axis direction) of the photosensitive drum 21 and the first and second developing sleeves 8 and 10. It is preferable. In this example, the longitudinal dimension of the limiting member 11 was 70 cm.

  As described above, according to this embodiment, it is possible to suppress the “icicle phenomenon” of the developer T that tends to become noticeable when the developing device 1 is downsized, for example. That is, according to the present embodiment, in the developing device 1 using the plurality of developing sleeves 8 and 10, by arranging the limiting member 11, the coating state of the developer T on the developing sleeves 8 and 10 is stably maintained. It becomes possible. As a result, it is possible to prevent image defects due to carrier adhesion to the photosensitive drum 21 and stably form a high-quality image. Further, according to the present embodiment, by arranging the limiting member 11, it is not always necessary to design a magnetic pattern giving priority to preventing the “icicle phenomenon”, so that the magnetic pattern can be designed relatively freely. It becomes possible. As a result, the degree of freedom in designing the developing device 1 and, in turn, the image forming apparatus 100 is increased.

Example 2
Next, another embodiment of the present invention will be described. FIG. 9 shows a schematic cross-sectional configuration of the image forming apparatus 200 of the present embodiment. In FIG. 9, elements having the same functions or configurations as those of the image forming apparatus 100 of the first embodiment are denoted by the same reference numerals.

  In the image forming apparatus 200 of this embodiment, the electrophotographic photosensitive member as the image carrier is not a drum shape as in the first embodiment but a belt shape.

  That is, in this embodiment, the belt-shaped electrophotographic photosensitive member, that is, the photosensitive belt 21, is provided with three supporting rollers, that is, a driving roller 30, first and second driven rollers 31, 32 as a plurality of supporting members. It is laid around. The photosensitive belt 21 is rotated (rotated) in the direction of the arrow in the figure when a rotational driving force is transmitted to the driving roller 30.

  A charging device 22 as a primary charging unit is disposed opposite to the photosensitive belt 21 at the position of the second driven roller 32. Then, along the moving direction of the surface of the photosensitive belt 21 formed between the driving roller 30 and the second driven roller 32, the first to fourth image forming units PY, PM, PC, and PK are arranged. In this embodiment, each of the image forming portions PY, PM, PC, and PK is formed on the photosensitive belt 21 by the exposure device 23 as an exposure unit that exposes the photosensitive belt 21 according to the image information signal. And a developing device 1 for developing an electrostatic image. A transfer belt 33 is disposed so as to face the driving roller 30 of the photosensitive belt 21. The transfer belt 33 is wound around a transfer roller 34 as a transfer unit and a drive roller 35. Further, a cleaning device 26 for cleaning the photosensitive belt 21 is disposed at a position facing the first driven roller 31. The transfer belt 33 rotates (rotates) in the direction of the arrow in the figure when a rotational driving force is transmitted to the drive roller 35.

  For example, when forming a full-color image, each process of exposure on the photosensitive belt 21 charged by the charging device 22 and development of the electrostatic image formed by the exposure is performed in accordance with the movement of the photosensitive belt 21. This is performed sequentially in the parts PY, PM, PC, PK. As a result, a multiple toner image in which the toner images of the respective colors are superimposed on the photosensitive belt 21 is formed. The multiple toner image is transferred onto the transfer material 29 by applying a transfer bias to the transfer roller 34. The transfer material P is conveyed to a transfer portion (transfer nip) N via a paper feed roller 36, a transfer material guide 37, and the like. In the transfer portion N, the transfer roller 34 contacts the photosensitive belt 21 via the transfer belt 33. The transfer material P onto which the toner image has been transferred is conveyed by a conveyance belt 33 to a fixing device 27 as a fixing unit. The fixing device 27 fixes the toner image transfer material 29 on the transfer material 29 to make a permanent image.

  As the developing device 1 provided in the image forming apparatus 200 of the present embodiment, substantially the same one as described in the first embodiment can be used.

  FIG. 10A shows an enlarged view of the vicinity of the first and second developing sleeves 8 and 10 of the developing device 1. FIG. 10B shows an enlarged cross section of the limiting member 11 shown in FIG. In this embodiment, the pole arrangement of the developing device 1 and the flow of the developer T are the same as those in the first embodiment. Also in this embodiment, the developing device 1 has the limiting member 11 substantially the same as that described in the first embodiment. FIGS. 10A and 10B show an example in which the restricting member 11 has a curvature on the facing surface of each of the first and second developing sleeves 8 and 10.

  As described above, even when the electrophotographic photosensitive member has a belt shape as in the present embodiment, the same effect as in the first embodiment can be obtained.

  In addition, although this invention was demonstrated according to the specific Example, this invention is not limited to the above-mentioned embodiment.

  For example, in each of the above-described embodiments, the first developing sleeve 8 and the second developing sleeve are arranged above and below in the direction of gravity. However, as shown in FIG. May be arranged in a crossing direction (typically a vertical direction). The present invention can be equally applied to such a developing apparatus. In FIG. 11, elements that are the same as or equivalent to those of the image forming apparatuses of the above embodiments are given the same reference numerals.

  Further, in each of the above embodiments, the case where two of the first and second developing sleeves 8 and 10 are used as a plurality of developer carrying bodies, that is, the case where there is one developer carrying body on the downstream side is taken as an example. explained. However, the present invention is not limited to this, and there may be a plurality of downstream developer carriers. That is, the present invention can be equally applied if a limiting member is provided between two adjacent developer carriers, that is, in the above-described arrangement region Z (FIG. 4) in the same manner as in the above embodiments. it can. However, also in this case, the restriction member is not limited to being provided in all of the plurality of arrangement regions Z, and the restriction member can be provided in any or all of the plurality of arrangement regions Z.

  In the first embodiment, the image forming apparatus 100 that employs a method (direct transfer method) in which a toner image is directly transferred from the photosensitive drum 21 to the transfer material 29 conveyed by the conveyance belt 28 has been described. However, an intermediate transfer member is provided instead of the conveyance belt 28 described in the first embodiment, and after each toner image of each color is primarily transferred from each photosensitive drum 21 to the intermediate transfer member, a composite toner image of each color is transferred onto the transfer material 29. An intermediate transfer type image forming apparatus that performs secondary transfer at once is well known. As the intermediate transfer member, an endless moving intermediate transfer belt or the like is used. The present invention can be equally applied to such an intermediate transfer type image forming apparatus.

1 is a schematic cross-sectional view of an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a schematic cross-sectional view showing an enlarged image forming unit in the image forming apparatus of FIG. 1. FIG. 3 is an enlarged cross-sectional view of the vicinity of first and second developing sleeves in the developing device of FIG. 2 as viewed in the longitudinal direction of a photosensitive drum, first and second developing sleeves, and a limiting member. It is explanatory drawing for demonstrating the arrangement | positioning method of the limiting member according to this invention. It is explanatory drawing for demonstrating an example of arrangement | positioning and a shape of a limiting member according to this invention. It is explanatory drawing for demonstrating the other example of arrangement | positioning and a shape of the limiting member according to this invention. It is sectional drawing which looked at the limiting member for demonstrating the other example of the shape of the limiting member according to this invention to the longitudinal direction. FIG. 6 is a partial cross-sectional view of a developing device for explaining the arrangement of the restricting members in the longitudinal direction when viewed from the photosensitive drum side. FIG. 5 is a schematic cross-sectional view of another embodiment of an image forming apparatus according to the present invention. FIG. 10 is an explanatory diagram for explaining a method of arranging the limiting member in the developing device of the image forming apparatus of FIG. 9. It is a schematic sectional drawing of the image forming part for demonstrating the other example of the arrangement | positioning method of a developing device. It is a schematic sectional drawing of an example of the conventional developing device. FIG. 10 is an enlarged cross-sectional view in the vicinity of first and second developing sleeves for explaining an ideal flow of developer in a conventional developing device. FIG. 4 is an enlarged cross-sectional view of the vicinity of first and second developing sleeves for explaining a “icicle phenomenon” of a developer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Developing apparatus 2 Developer container 8 1st developing sleeve (1st developer carrier)
8a First magnet roller (first magnetic field generating means)
9 Regulating blade (developer regulating member)
10 Second developing sleeve (second developer carrier)
10a Second magnet roller (second magnetic field generating means)
21 Photosensitive drum (image carrier)
11 Limiting member 20 Toner supply tank

Claims (14)

A developing device that is disposed to face an image carrier that carries an electrostatic image formed in an image forming region and that develops the electrostatic image using a developer having magnetic particles, Adjacently disposed first and second developer carriers that are carried and conveyed to a development area facing the image carrier, and disposed inside the first and second developer carriers, respectively. First and second magnetic field generating means for generating a magnetic field acting on the developer, wherein the first and second developer carriers rotate in the same direction, and the developer is moved to the first In a developing device for transferring from one developer carrier to the second developer carrier,
A line segment A connecting the center of the first developer carrier and the center of the second developer carrier, the image carrier side of the first developer carrier and the second developer carrier The image forming region of the image carrier is within a region surrounded by a line segment B, which is a common tangent line, and the surface of the first developer carrier and the surface of the second developer carrier. The first developer carrier and the second developer carrier are disposed without contacting any of the image forming regions, and the second developer carrier is disposed from the first developer carrier. Having a restricting member that restricts the movement of the developer to the body,
The delivery of the developer from the first developer carrier to the second developer carrier is performed in a region closer to the line segment A than the limiting member. A developing device.   The developing device according to claim 1, wherein the restricting member is disposed so as to contact with or straddle the line segment B.   The restricting member is perpendicular to the line segment A, and is located between the first and second developer carriers at the closest position between the first developer carrier and the second developer carrier. 3. The developing device according to claim 1, wherein the developing device is disposed so as to be in contact with or across the line segment C passing through the point.   One or both of the surface of the restricting member facing the first developer carrier and the surface of the restricting member facing the second developer carrier have a curvature. The developing device according to the item.   The curvature of the surface of the restricting member that faces the first developer carrier or the surface that faces the second developer carrier is the curvature of the surface of the opposing first or second developer carrier. The developing device according to claim 4, wherein the developing device is substantially equal to:   The developing device according to claim 1, wherein a distance between the limiting member and each of the first and second developer carriers is 1 mm or more.   The developing device according to claim 1, wherein an interval between the limiting member and the image carrier is 20 μm or more and 400 μm or less.   The first and second magnetic field generating units each have a plurality of magnetic poles, and are fixedly disposed inside the first and second developer carriers. 8. The developing device according to any one of items 7.   9. The developing device according to claim 8, wherein magnetic poles that generate a magnetic field acting on the developer in the developing area provided in each of the first and second magnetic field generating units are different from each other. .   A magnetic pole for generating a magnetic field acting on the developer at the nearest position between the first developer carrier and the second developer carrier provided in each of the first and second magnetic field generators, The developing device according to claim 8, wherein the developing devices are different from each other.   The developing device according to claim 1, wherein the developer is a two-component developer including nonmagnetic toner particles and magnetic carrier particles.   12. The developing device according to claim 1, wherein the image carrier and the first and second developer carriers are moved in the same direction in the development region.   An image forming apparatus for forming and outputting an image on a transfer material, comprising: an image carrier that carries an electrostatic image; and the developing device according to any one of claims 1 to 12. Image forming apparatus.   The image forming apparatus according to claim 13, wherein the image carrier has a drum shape or a belt shape.

Images