JP2011242451A - Developing device and image forming apparatus equipped with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device capable of suppressing generation of uneven image density even when an image having locally increased image density is printed, and to provide an image forming apparatus equipped with the developing device.SOLUTION: The developing device is mounted in an image forming apparatus employing an electrophotographic system and including a photoreceptor drum 3 for forming an electrostatic latent image on the surface thereof, and the developing device includes: a developer tank 111; a developing roller 114 disposed in the developer tank 111; first and second developer conveying passages P and Q, respectively; first and second developer conveying helical members 112 and 113, respectively, for circulating and conveying the developer in the first and second developer conveying passages P and Q; and a developer returning mechanism configured to distribute and return the developer on the developing roller 114 after supplying the toner to the photoreceptor drum 3, as a return developer to the first developer conveying passage P and to the second developer conveying passage Q.

Description

  The present invention relates to a developing device using a two-component developer and an image forming apparatus including the developing device.

2. Description of the Related Art In recent years, two-component developers (hereinafter simply referred to as “developers”) that are excellent in toner charging stability have been widely used in electrophotographic image forming apparatuses compatible with full color and high image quality.
The developer is composed of toner and carrier, and the toner and the carrier are rubbed by stirring them in the developer tank of the developing device, and a properly charged toner is obtained by this friction.
In the developing device, the charged toner is supplied to the surface of the developing roller, and is moved from the developing roller to the electrostatic latent image formed on the surface of the photosensitive drum by electrostatic attraction force.
As a result, a toner image based on the electrostatic latent image is formed on the photosensitive drum.

Further, such an image forming apparatus is required to be increased in speed and reduced in size, and it is necessary to quickly and sufficiently charge the developer and to quickly transport the developer.
In view of this, an image forming apparatus including a circulation type developing device has been proposed in order to instantly disperse the replenished toner in the developer and impart an appropriate charge amount (see, for example, Patent Document 1).
This circulation type developing device includes a developer conveyance path which is a path through which the developer is circulated and a conveyance screw which conveys the developer while stirring the developer in the developer conveyance path.

The developer transport path includes first and second developer transport paths that are formed by partitioning the interior of the developer transport path with partition walls, and first and second developer paths that communicate with both ends of the first and second developer transport paths. The first and second conveying screws are disposed in the first and second developer conveying paths.
The first developer transport path is supplied with toner from a toner cartridge mounted on the image forming apparatus, and the supplied toner is uniformly dispersed in the developer by rotating the first and second transport screws. The developer is supplied to the developing roller on the second developer conveyance path side while circulating in the first and second developer conveyance paths.
The toner in the developer on the developing roller is supplied to the photosensitive drum, and the developer on the developing roller thereafter is returned again into the second developer transport path.

JP-A-9-120201

However, if the toner in the developer on the developing roller is significantly consumed locally by printing an image with locally high image density, the toner concentration in the developer on the developing roller is locally increased. Lower.
If such a low-concentration developer is returned to the second developer conveyance path and supplied again to the developing roller before being sufficiently mixed with the other developer, it should be supplied to the photosensitive drum. The amount of toner locally decreases, and as a result, image density unevenness due to a decrease in the image density of the printed image occurs.

It is also conceivable to return the developer on the developing roller after supplying the toner to the photosensitive drum into the first developer conveying path on the side opposite to the developing roller.
However, in particular, when a developer having a low toner concentration is returned locally in the first developer conveyance path at a position where the conveyance distance to the second developer conveyance path is short, the developer having a low toner concentration is Since it is supplied to the developing roller as it is, it is difficult to suppress the occurrence of uneven image density of the printed image.
Even when the developer having a low toner concentration is locally returned to the first developer transport path at a position where the transport distance to the second developer transport path is far, the developer toner in the entire developer transport path In order to make the density uniform, the developer needs to be circulated and transported to some extent in the developer transport path (it takes time), so it is difficult to immediately suppress the occurrence of uneven image density in the printed image.

  The present invention has been made in view of such problems, and includes a developing device capable of suppressing the occurrence of uneven image density even when an image with locally high image density is printed. An object is to provide an image forming apparatus.

  Thus, according to the present invention, a developing device mounted on an electrophotographic image forming apparatus having a photosensitive drum on which an electrostatic latent image is formed, the developer including toner and a carrier is provided. An electrostatic latent image is formed while rotating with a developer tank accommodated therein, a toner replenishing port for replenishing toner in the developer tank, and a developer tank provided in the developer tank. A developing roller for supplying toner to the surface of the photosensitive drum, a developer transport path provided between the developer roller in the developer tank and a position where the toner is replenished, and the developer transport A developer conveying spiral member that is rotatably provided in the path and conveys the developer in the developer conveying path to the developing roller, and returns the developer on the developing roller after supplying the toner to the photosensitive drum. Return developer to the developer transport path as The developer transport path includes a first developer transport path on the toner supply port side and a second developer transport on the developer roller side defined by a partition wall parallel to the axial direction of the developing roller. And a first communication path and a second communication path that communicate the first developer transport path and the second developer transport path on both sides in the axial direction, and the developer transport spiral member includes: A first developer transport spiral member having a first developer transport spiral member disposed in the first developer transport path and a second developer transport spiral member disposed in the second developer transport path. And the second developer conveying spiral member convey the developer in opposite directions to circulate the developer between the first developer conveying path and the second developer conveying path, and The agent returning mechanism distributes and returns the return developer to the first developer conveying path and the second developer conveying path. It made a developing device is provided.

  According to another aspect of the present invention, a photosensitive member having a surface on which an electrostatic latent image is formed, a charging device for charging the surface of the photosensitive member, and an electrostatic latent image on the surface of the photosensitive member. An exposure device for forming, the developing device for supplying a toner to an electrostatic latent image on the surface of the photoconductor to form a toner image, a transfer device for transferring the toner image on the surface of the photoconductor to a recording medium, An image forming apparatus including a cleaning device for cleaning the surface of the photoreceptor and a fixing device for fixing a toner image on a recording medium is provided.

  According to the present invention, even when an image having a locally high image density is printed, the return developer whose toner density has been lowered by the developer return mechanism is used as the first developer transport path and the second developer. In order to distribute and return to the conveyance path, the developer having a low toner density is mixed with the developer in the first and second developer conveyance paths. As a result, the uniform toner density of the developer in the entire developer transport path is accelerated, and the occurrence of uneven image density in the printed image can be immediately suppressed.

FIG. 1 is an explanatory diagram showing the overall configuration of an image forming apparatus including a developing device (Embodiment 1) according to the present invention. FIG. 2 is a schematic enlarged sectional view of the developing device shown in FIG. 3 is a cross-sectional view taken along line AA in FIG. 4 is a cross-sectional view taken along line BB in FIG. 5 is a cross-sectional view taken along the line CC of FIG. FIG. 6 is an operation explanatory view showing a developer returning mechanism in the developing device of the first embodiment. FIG. 7 is a schematic cross-sectional view showing a toner replenishing device in the developing device of the first embodiment. 8 is a cross-sectional view taken along the line DD of FIG. FIG. 9 is a front view illustrating a partition wall in the developer tank of the developing device according to the second embodiment. FIG. 10 is a front view showing a partition wall in the developer tank of the developing device according to the third embodiment. FIG. 11A is an operation explanatory view showing the developer return mechanism in the developing device of Embodiment 4, and FIG. 11B is a plan view showing the upper end portion of the partition wall of the developer return mechanism of Embodiment 4. is there. FIG. 12 is an operation explanatory view showing a developer returning mechanism in the developing device of the fifth embodiment.

As described above, the developing device of the present invention includes the developer tank, the toner replenishing port, the developing roller, the first and second developer transport paths, the first and second developer transport spiral members, and the developer. This is a circulation type developing device provided with a return mechanism, and is mounted on an electrophotographic image forming apparatus such as a monochrome or full-color copying machine, printer, facsimile machine, and a multifunction machine having these functions.
The developer returning mechanism of the developing device can be configured like the following first or second developer returning mechanism.

(First developer return mechanism)
The first developer return mechanism includes a return developer flow member that removes the return developer from the photosensitive drum and slides it down to the developer transport path, and an upper end portion of the partition wall. The return developer sliding down on the return developer flow member falls to the upper end portion of the partition wall and is distributed in two directions of the first developer conveyance path and the second developer conveyance path.
That is, the first developer return mechanism is configured to distribute the return developer in two directions by cooperation of the return developer flow member and the upper end portion of the partition wall. It can be configured as follows.

(A) The upper end portion of the partition wall portion is formed in an uneven shape in which a concave portion and a convex portion in the height direction are repeated in the longitudinal direction,
The developer return mechanism is configured such that the return developer sliding down on the return developer flow member returns to the first developer conveyance path through each concave portion at the upper end portion of the partition wall and hits each convex portion. By returning to the second developer conveyance path, the return developer is distributed in two directions.
The configuration (A) corresponds to Embodiments 1 and 2 described later.

(B) The upper end portion of the partition wall portion has a plurality of through holes formed at predetermined intervals in the longitudinal direction and a plurality of shielding portions located between the plurality of through holes.
The developer return mechanism is configured such that the return developer sliding down on the return developer flow member returns to the first developer conveyance path through each through hole in the upper end portion of the partition wall, and to each shielding portion. By returning to the second developer conveyance path, the return developer is distributed in two directions.
The configuration (B) corresponds to a third embodiment described later.

(C) The upper end portion of the partition wall portion is formed in a meandering shape in which first and second bent portions that swing toward the first and second developer transport paths are repeated in the longitudinal direction of the developer transport path. Become
The developer return mechanism is configured such that the return developer sliding down on the return developer flow member jumps over each second bent portion of the upper end portion of the partition wall and returns to the first developer transport path, and By returning to the second developer conveyance path by hitting one bent portion, the return developer is distributed in two directions.
The configuration (C) corresponds to a fourth embodiment described later.

The first developer return mechanism returns a part of the return developer sliding down on the return developer flow member to the second developer conveyance path by applying a part of the return developer to the upper end portion of the partition wall, and partitions the remainder of the return developer. It is configured so as to return to the first developer transport path by passing without passing the upper end of the wall, and the configurations (A) to (C) are specific examples.
Although these have a simple structure, the return developer can be reliably distributed to the first and second developer transport paths.

(Second developer return mechanism)
The second developer return mechanism removes the return developer from the photosensitive drum, slides it down to the developer transport path, and distributes it in the two directions of the first developer transport path and the second developer transport path. It has a configured return developer sink member.
That is, the second developer return mechanism is configured to distribute the return developer in two directions mainly by the return developer flow member. Specifically, the second developer return mechanism can be configured as follows.

(D) the return developer sink member has a lower end in a sliding direction of the return developer;
The lower end portion is formed in a concavo-convex shape in which a concave portion and a convex portion are repeated in the longitudinal direction of the developer conveyance path,
The developer return mechanism is configured such that the return developer sliding down on the return developer flow member returns to the second developer transport path through each recess at the lower end and slides down onto each projection. The return developer is distributed in two directions by jumping over the partition wall and returning to the first developer transport path.
The configuration (D) corresponds to Embodiment 5 described later.

(E) the return developer sink member has a lower end in a sliding direction of the return developer;
The lower end portion includes a plurality of through holes formed at predetermined intervals in the longitudinal direction of the developer transport path, and a plurality of shielding portions positioned between the plurality of through holes.
The developer return mechanism is configured such that the return developer sliding down on the return developer flow member returns to the second developer conveyance path through each through hole in the lower end portion and slides down onto each shielding portion. The return developer is distributed in two directions by jumping over the partition wall and returning to the first developer transport path.
Configuration (E) corresponds to Embodiment 6 described later.

  The second developer return mechanism drops a part of the return developer sliding down on the return developer flow member and returns it to the second developer conveyance path, and jumps the remaining part of the return developer over the upper end of the partition wall. By doing so, it is configured to return to the first developer conveyance path, and configurations (D) and (E) are specific examples.

  Hereinafter, embodiments of a developing device and an image forming apparatus including the same according to the present invention will be described in detail with reference to the drawings.

<Embodiment 1>
FIG. 1 is an explanatory diagram showing the overall configuration of an image forming apparatus including a developing device (Embodiment 1) according to the present invention.
The image forming apparatus 100 includes a developing device accommodating portion 100A in which a plurality of developing devices 2a to 2d are accommodated in a casing, and a fixing device accommodating portion in which the fixing device 12 is accommodated above the developing device accommodating portion 100A in the casing. And a printer capable of forming a multicolor or single color image on a sheet-like recording medium (recording paper) according to image data transmitted from the outside.
The upper surface of the developing device housing portion 100A located beside the fixing device housing portion 100B is a paper discharge tray 15.

  In this embodiment, a printer is exemplified as the image forming apparatus. However, the image forming apparatus can also be used as a recording medium according to image data transmitted from the outside and / or image data read from a document by a scanner. It may be a copier, a facsimile machine, or a multifunction machine having these functions capable of forming a multicolor or single color image.

[Developing device container]
As shown in FIG. 1, the developing device housing portion 100A includes four photosensitive drums 3a, 3b, 3c, and 3d and four chargers (charging devices) 5a that charge the surfaces of the photosensitive drums 3a to 3d. 5b, 5c, 5d, an exposure unit (exposure apparatus) 1 that forms an electrostatic latent image on the surface of each of the photosensitive drums 3a to 3d, and black, cyan, magenta, and yellow toners are individually accommodated. Four developing devices 2a, 2b, 2c, and 2d that develop electrostatic latent images on the surfaces of the photosensitive drums 3a to 3d to form toner images, and the surfaces of the photosensitive drums 3a to 3d after development and image transfer Cleaner units (cleaning devices) 4a, 4b, 4c, and 4d for removing residual toner remaining on the toner, and four toner replenishing devices 22a, 22b, and 22 for individually replenishing the developing devices 2a to 2d with the four color toners. , And 22 d, the intermediate transfer belt unit (transfer unit) 8 for transferring to a recording medium the toner image on the surface of the photosensitive drum 3 a to 3 d, such as an intermediate transfer belt cleaning unit 9 is accommodated.

Further, the developing device accommodating portion 100A includes a paper feed tray 10 that accommodates a plurality of recording media arranged at the bottom thereof, a manual feed tray 20 that is arranged on one side surface and on which an irregular-sized recording medium is set, A sheet transport path S for transporting a recording medium from the paper feed tray 10 or the manual feed tray 20 to an intermediate transfer belt unit (transfer device) 8 is provided.
In each of the members indicated by reference numerals having a to d, a is a member for forming a black image, b is a member for forming a cyan image, c is a member for forming a magenta image, and d is a member for forming a yellow image. It is a member.

That is, the image forming apparatus 100 has a black toner image, a cyan toner image, a magenta toner image, and a magenta toner image on the surface of each of the photosensitive drums 3a to 3d based on the image data for each color component of black, cyan, magenta, and yellow. A yellow toner image is selectively formed, and the formed toner images are superimposed on the intermediate transfer belt unit 8 to form a color image on a recording medium.
Since the photosensitive drums 3a to 3d corresponding to the respective colors have the same configuration, in the description of the configuration, the reference numeral is unified to 3. Similarly, the developing device has the reference numeral 2, the charger has the reference numeral 5, the cleaner The unit will be described with the reference numeral 4 and the toner replenishing device with the reference numeral 22.

(Photosensitive drum and its peripheral members)
The photosensitive drum 3 is a cylindrical member that is composed of a conductive substrate and a photosensitive layer formed on the surface thereof, and is responsible for forming a latent image by charging and exposure. An electrical image called an electrostatic latent image is formed.
The photosensitive drum 3 is supported by a driving unit (not shown) so that it can be driven to rotate about its axis.

As the charger 5, a charger such as a contact roller type, a contact brush type or a non-contact charger type is used, and the surface of the photosensitive drum 3 is uniformly charged to a predetermined potential.
The exposure unit 1 passes light between the charger 5 and the developing device 2 and irradiates the surface of the charged photosensitive drum 3 with light corresponding to the image data, thereby exposing the photosensitive drum 3. An electrostatic latent image corresponding to the image data is formed on the surface.
In this embodiment, the case where a laser scanning unit (LSU) provided with a laser irradiation unit and a reflection mirror is used as the exposure unit 1 is illustrated, but EL (electroluminescence) in which light emitting elements are arranged in an array. Alternatively, an LED write head can be used.

(Developer)
2 is a schematic enlarged sectional view of the developing device shown in FIG. 1, FIG. 3 is a sectional view taken along line AA in FIG. 2, and FIG. 4 is a sectional view taken along line BB in FIG. FIG. 5 is a sectional view taken along the line CC of FIG. In these drawings, the developer accommodated in the developer tank 111 is not shown.

  As shown in FIGS. 2 to 5, the developing device 2 includes a developer tank 111 having a substantially rectangular container shape in which a developer containing toner and a carrier is accommodated, and a toner tank for replenishing the developer tank 111. Toner replenishing port 115a, developing roller 114 provided in developer tank 111, and first and second developers provided between developer roller 114 and a position where toner is supplied in developer tank 111. First and second developer passages a and b, which are provided on both ends of the conveyance paths P and Q, and are connected to both ends of the first and second developer conveyance paths P and Q, and the first and second developer conveyances The first and second developer conveying spiral members 112 and 113 rotatably provided in the paths P and Q, and the developer on the developing roller 114 after supplying the toner to the photosensitive drum 3 are used as return developers. Return developer that flows to the first and second developer transport paths P and Q And a toner density detection sensor (magnetic permeability sensor) 118. The toner is supplied to the surface of the photosensitive drum 3 by the developing roller 114, and is formed on the surface of the photosensitive drum 3. The apparatus develops (develops) the electrostatic latent image.

The interior of the developer tank 111 is divided into two rooms by a partition wall 117 parallel to the axial direction of the developing roller 114, and the toner replenishing port 115 a side of the two rooms is the first developer transport path P. Yes, the developing roller 114 side is the second developer transport path Q.
Further, the first developer conveyance path P and the second developer conveyance path Q are communicated with each other by the first communication path a and the second communication path b on both sides in the axial direction.
Therefore, the first and second developer transport paths P and Q and the first and second communication paths a and b form one annular developer transport path.

Further, the developer tank 111 has a removable developer tank cover 115 that constitutes an upper wall thereof.
The developer tank cover 115 is formed with a toner replenishing port 115a for replenishing unused toner on the upstream side of the first developer transport path P in the developer transport direction (arrow X direction).
The developer tank 111 has an opening between the side wall on the second developer transport path Q side and the lower edge of the developer tank cover 115, and the developing roller 114 rotates at the position of the opening. A predetermined developing nip is provided between the photosensitive drum 3 and the photosensitive drum 3.

A first developer conveying spiral member 112 (hereinafter, referred to as “first conveying member 112”) has two spiral blades 112a ₁ and 112a having the same spiral pitch on a shaft 112b rotatably supported by the developer tank 111 at both ends. ₂ is a double screw shaft attached.
The second developer conveying spiral member 113 (hereinafter referred to as “second conveying member 113”) is the same double screw shaft as the first conveying member 112, and includes a shaft 113b and two helical blades 113a attached thereto. ₁ and 113a ₂ .
The first and second transport members 112 and 113 may be single screw shafts.

A drive gear is provided at one end of each of the shafts 112b and 113b of the first and second transport members 112 and 113, and the first transport member 112 is rotated in the reverse direction synchronously by a drive unit (not shown). In the developer transport path P, the developer is transported while stirring in the direction of arrow X away from the toner replenishing port 115a, and the second transport member 113 is in the second developer transport path Q, which is opposite to the arrow X direction. The developer is conveyed in the direction.
The developer sent downstream in the transport direction of the first and second developer transport paths P and Q is pushed by the upstream developer and passes through the first and second communication paths a and b to be second. The first developer transport paths Q and P are sent to the second and first developer transport paths Q and P, and thus the developer circulates in the developer tank 111. At this time, the toner of the developer is sufficiently charged by friction with the carrier.

The first and second developer transport paths P and Q have arc-shaped bottom portions along the spiral blades of the first and second transport members 112 and 113, and the arc shape of the first and second transport members 112 and 113. A partition wall 117 is formed at the bottom contact position.
The partition wall 117 has a concavo-convex upper end portion in which a concave portion 117a and a convex portion 117b in the height direction are repeated at regular intervals in the longitudinal direction.
In the case of the first embodiment, the concave portion 117a and the convex portion 117b are formed in a square shape, and a slope inclined downward toward the first developer transport path P is formed at the lower end edge of the concave portion 117a, and the upper end of the convex portion 117b. At the edge, a slope inclined downward toward the second developer transport path Q is formed.
The upper end portion of the partition wall 117 and the return developer flow member 128 return the first developer transport path P and the second developer using the developer on the developing roller 114 after the toner is supplied to the photosensitive drum 3 as the return developer. A developer returning mechanism for distributing and returning the developer to the developer transport path Q is configured. The developer return mechanism will be described in detail later.

The developing roller 114 includes a developing sleeve 119 and a magnet roller 120 provided in the developing sleeve 119.
The developing sleeve 119 is a cylindrical member made of a nonmagnetic material such as aluminum or stainless steel that constitutes the outer peripheral portion of the developing roller 114.
A driving shaft 128 having a driving gear 129 and a fixed shaft 126 are disposed on the axial center of the developing sleeve 119, and an outer end of the driving shaft 128 is rotatably supported by the developer tank 111. The outer end of 126 is fixed to the developer tank 111.
Both ends of the developing sleeve 119 are attached to the fixed shaft 126 via bearings 130, and one end of the developing sleeve 119 is connected to the driving shaft 128 to transmit the rotational force of the driving shaft 128.

The magnet roller 120 has seven magnetic poles (a first magnetic pole 120a to a fifth magnetic pole 120g), which are fixed to a fixed shaft 126 and configured integrally.
The first magnetic pole 120a is composed of an N pole, and is positioned opposite to the developer stirred and transported in the developer tank 111, specifically, a second developer transport spiral member 113 (hereinafter referred to as “second transport”). This magnetic pole is provided at a position opposite to the member 113 ”) and pumps up the developer stirred and transported by the second transport member 113.
During the normal image forming operation, the developer in the developing tank 111 is pumped onto the surface of the developing roller 114 by the magnetic lines formed by the first magnetic pole 120a.

The second magnetic pole 120b is composed of an S pole, and is provided next to the first magnetic pole 120a on the downstream side in the rotation direction of the developing sleeve 119 (clockwise in FIG. 2).
The developer pumped up on the surface of the developing sleeve 119 is made a constant layer thickness by the doctor blade 116 at the position of the magnetic force peak on the magnetic force line formed by the second magnetic pole 120b.
The third magnetic pole 120c is composed of an N pole, and is provided next to the second magnetic pole 120b on the downstream side in the rotation direction of the developing sleeve 119.
The developer having a constant layer thickness formed on the developing sleeve 119 is stabilized in the direction of the fourth magnetic pole 120d on the downstream side in the rotation direction of the developing sleeve 119 of the third magnetic pole 120c by the magnetic force lines formed by the third magnetic pole 120c. Then transported.

The fourth magnetic pole 120d is composed of an S pole, is provided next to the third magnetic pole 120c on the downstream side in the rotation direction of the developing sleeve 119, and functions as a main magnetic pole for forming an image.
The developer fed from the third magnetic pole 120c becomes a magnetic brush by the magnetic lines of force of the fourth magnetic pole 120d and rubs the surface of the photosensitive drum 3.
The fifth magnetic pole 120e is composed of an N pole, and is provided next to the fourth magnetic pole 120d on the downstream side in the rotation direction of the developing sleeve 119.
The developer fed from the fourth magnetic pole 120d is carried on the developing sleeve 119 by the magnetic force lines formed by the fifth magnetic pole 120e, and is collected into the developer tank 111.

The sixth magnetic pole 120f is composed of an S pole, and is provided next to the fifth magnetic pole 120e on the downstream side in the rotation direction of the developing sleeve 119.
The developer fed from the fifth magnetic pole 120e is carried on the developing sleeve 119 by the magnetic lines of force formed by the sixth magnetic pole 120f and is subsequently collected into the developer tank 111.
The seventh magnetic pole 120g is composed of an N pole, and is provided next to the sixth magnetic pole 120f on the downstream side in the rotation direction of the developing sleeve 119.
The developer fed from the sixth magnetic pole 120f is carried on the developing sleeve 119 by the magnetic force lines formed by the seventh magnetic pole 120g and is subsequently collected into the developer tank 111.

A gap 127 is provided between the seventh magnetic pole 120g and the first magnetic pole 120a.
The return developer flow member 128 is disposed at a position opposed to the gap portion 127 via the developing sleeve 119.
The magnetic pole on the developing sleeve 119 side of the first magnetic pole 120a and the magnetic pole on the developing sleeve 119 side of the seventh magnetic pole 120g are the same magnetic pole (N pole in this embodiment). The magnetic field lines are not formed in the portion 127. Therefore, the developer carried on the seventh magnetic pole 120g returns from the developing sleeve 119 and moves onto the developer flow member 128.

A return developer flow member 128 (hereinafter referred to as “flow member 128”) is opposed to the gap 127 of the developing roller 114 and is disposed on the partition wall 117 side on the second developer conveyance path Q. It is a substantially triangular tubular member.
The flow member 128 has a triangular top portion 128 a disposed close to the surface of the developing roller 114, and has an inclined surface 128 b inclined downward from the top portion 128 a toward the partition wall 117.
As described above, the return developer moved from the developing roller 114 to the flow member 128 slides down the inclined surface 128b and falls to the upper end portion of the partition plate 117.

As described above, the developer return mechanism includes the concavo-convex upper end portion of the partition wall 117 and the return developer flow member 128.
The height of the upper end portion of the partition wall 117 is lower than the lower limit of the height range of the return developer falling from the inclined surface 128b of the developer flow member 128 toward the upper end portion of the partition wall 117. What is necessary is just to set the lowest position and to set the highest position of the convex part 117b higher than the upper limit of the said height range.
Further, the partition wall 117 has a length corresponding to the length range of the magnet roller 120, and in the upper end portion having this length, the width in the longitudinal direction of the concave portion 117a and the convex portion 117b is substantially the same. And the recessed part 117a and the convex part 117b are uniformly arrange | positioned in the same ratio in the longitudinal direction.
In the case of the first embodiment, the width of the concave portion 117a and the convex portion 117b is about half of one pitch of the spiral of the double screw, and the interval between the concave portion 117a and the convex portion 117b is approximately equal to the pitch of the spiral of the double screw. equal.

FIG. 6 is an operation explanatory view showing a developer returning mechanism in the developing device of the first embodiment. In FIG. 6, the arrow indicates the direction of return developer movement.
According to the developer return mechanism configured as described above, as shown in FIGS. 2 to 6, the return developer that has slid down the inclined surface 128 b of the flow member 128 from the developing roller 114 is applied to the upper end portion of the partition plate 117. It falls toward each concave part 117a and each convex part 117b.
The return developer dropped toward each recess 117a jumps over each recess 117a and falls into the first developer transport path P, and the return developer dropped toward each projection 117b hits each projection 117b. To the second developer transport path Q.
At this time, the return developer sliding down the flow member 128 is uniformly distributed to the first developer transport path P and the second developer transport path Q in an approximately equal amount in the longitudinal direction.

By the way, when the toner in the developer on the developing roller 114 is significantly consumed locally by printing an image having a locally high image density, the toner concentration in the returning developer on the developing roller is locally increased. Lower.
For example, when the toner concentration of the developer carried on the intermediate portion 114 a (see FIG. 6) in the longitudinal direction of the developing roller 114 becomes low, the return developer having a low toner concentration is moved to the middle portion in the longitudinal direction of the upper end of the partition wall 117. The developer returned to the first and second developer transport paths P and Q is dropped in two directions, and returned to the first and second developer transport paths P and Q.

That is, the return developer having a low toner concentration flows dispersedly into the first developer transport path P and the second developer transport path Q. As a result, the toner concentration of the developer in the entire developer transport path is reduced. Uniformity is accelerated and the occurrence of uneven image density in the printed image can be immediately suppressed.
In other words, the return developer having a low toner concentration locally flows into the second developer conveyance path Q, and the return developer having a low toner concentration is sufficiently mixed with other developers in the second developer conveyance path Q. Before the toner image is supplied onto the developing roller 114, a problem that the image density unevenness of the printed image occurs is suppressed.

The toner concentration detection sensor 118 is mounted on the bottom surface of the developer tank 111 immediately below the second transport member 113 and in the substantially central portion of the second developer transport path Q. It is exposed inside the agent conveyance path Q.
The toner concentration detection sensor 118 is electrically connected to a toner concentration control means (not shown).
The toner density control means rotates and drives a toner discharge member 122 of a toner replenishing device 22 (see FIG. 8), which will be described later, in accordance with the measured toner density value detected by the toner density detection sensor 118, so that the toner is discharged from the toner discharge port 123. Control is performed so that the toner is discharged and supplied into the first developer transport path P of the developing device 2.

When the toner density control means determines that the measured toner density value is lower than the toner density setting value, a control signal is transmitted to the driving means for driving the toner discharge member 122 to rotate, and the toner discharge member 122 rotates.
As the toner concentration detection sensor 118, for example, a general toner concentration detection sensor such as a transmitted light detection sensor, a reflected light detection sensor, or a magnetic permeability detection sensor can be used, and among these, the magnetic permeability detection sensor is preferable. .

A power supply (not shown) is connected to the magnetic permeability detection sensor (toner concentration detection sensor 118).
The power supply applies a drive voltage for driving the magnetic permeability detection sensor and a control voltage for outputting a detection result of the toner density to the control means.
Application of a voltage to the magnetic permeability detection sensor by the power source is controlled by the control means.
The permeability detection sensor is a type of sensor that receives the control voltage and outputs the toner density detection result as an output voltage value. Basically, the sensitivity near the median value of the output voltage is good. It is used by applying a control voltage to obtain a voltage.
Such type of magnetic permeability detection sensors are commercially available, and examples thereof include trade names TS-L, TS-A, and TS-K manufactured by TDK.

(Toner supply device)
FIG. 7 is a schematic cross-sectional view showing a toner replenishing device in the developing device of Embodiment 1, and FIG. 8 is a cross-sectional view taken along the line DD in FIG.
As shown in FIGS. 7 and 8, the toner replenishing device 22 includes a toner container 121 having a toner discharge port 123, a toner stirring member 125, and a toner discharge member 122, in which unused toner is contained. Be contained.
The toner replenishing device 22 is disposed above the developer tank 111 (see FIG. 1), and the toner discharge port 123 and the toner replenishing port 115a (see FIG. 2) of the developing device 2 are connected to the toner transport pipe 102. Connected at.

The toner container 121 is a substantially semi-cylindrical container member having an internal space, and a toner discharge port 123 is disposed at a lateral position in the circumferential direction of the semi-cylindrical portion.
The toner stirring member 125 is rotatably disposed at a substantially central position of the semi-cylindrical portion of the toner container 121, and the toner discharge member 122 is rotatably disposed at a position near the toner discharge port 123.

  The toner agitating member 125 is a plate-like member that rotates about the rotating shaft 125a, and a sheet-like toner made of a flexible resin (for example, polyethylene terephthalate) at both ends spaced apart from the rotating shaft 125a. A pumping member 125b is provided. The rotating shaft 125a is rotatably supported on the side walls on both sides in the longitudinal direction of the toner container 121, and one end of the rotating shaft 125a passes through the side wall, and a gear that meshes with a driving gear of a driving unit (not shown). It is fixed.

The toner stirring member 125 pumps up the toner stored in the toner storage container 121 while stirring the toner pumping member 125b as it rotates in the arrow Z direction from the lower side to the upper side with respect to the toner discharge port 123. The toner is conveyed to the toner discharge member 122.
At this time, the toner scooping member 125b rotates and slides along the inner wall of the toner container 121 due to its flexibility, and supplies the toner to the toner discharge member 122 side.
A toner discharge member partition wall 124 is provided between the toner discharge member 122 and the toner stirring member 125 so that the toner pumped up by the toner stirring member 125 can hold an appropriate amount of toner around the toner discharge member 122. It has been.

The toner discharging member 122 includes a rotating shaft 122b that is rotatably supported on both side walls in the longitudinal direction of the toner container 121, first and second spiral blades 122a ₁ fixed to the outer peripheral surface of the rotating shaft 122b, 122a _2, and one end of the rotating shaft 122b passing through the side wall of the toner container 121 is connected to the shaft of the motor 134.
The spiral winding directions of the first spiral blade 122a ₁ and the second spiral blade 122a ₂ are relatively opposite to each other, and the toner discharge port 123 is disposed between them.
As the toner discharge member 122 rotates, the toner supplied to the toner discharge member 122 side is transferred from the both ends in the axial direction of the toner discharge member 122 to the toner discharge port 123 side by the first spiral blade 122a ₁ and the second spiral blade 122a ₂ . And is supplied from the toner discharge port 123 to the upstream side of the first developer transport path P in the developer tank 111 through the toner transport pipe 102.
The toner replenished into the first developer transport path P is uniformly dispersed in the developer while being circulated and transported through the first and second developer transport paths P and Q.

(Intermediate transfer belt unit and intermediate transfer belt cleaning unit)
As shown in FIG. 1, the intermediate transfer belt unit 8 disposed above each photoconductive drum 3 stretches the intermediate transfer belt 7 and the intermediate transfer belt 7 and rotates in the direction of arrow B in FIG. Intermediate transfer rollers 6 a, 6 b, 6 c, 6 d (hereinafter referred to as a unified reference numeral 6), a driving roller 71, a driven roller 72, and a belt tension mechanism (not shown), close to the driving roller 71. The transfer roller 11 is arranged. Each intermediate transfer roller 6 is rotatably supported by a roller mounting portion in a belt tension mechanism.
Further, an intermediate transfer belt cleaning unit 9 is disposed on the side of the driven roller 72 of the intermediate transfer belt unit 8.

The driving roller 71 and the driven roller 72 are arranged outside the photosensitive drums 3 on both sides of the four photosensitive drums 3 so that the intermediate transfer belt 7 is in contact with each photosensitive drum 3.
The intermediate transfer belt 7 is formed endlessly using a film having a thickness of about 100 to 150 μm, for example, and the toner images of the respective color components formed on the respective photosensitive drums 3 are sequentially formed on the outer surface thereof. A color toner image (multicolor toner image) is formed by being transferred in a superimposed manner.

Transfer of the toner image from each photosensitive drum 3 to the intermediate transfer belt 7 is performed by each intermediate transfer roller 6 in contact with the inner surface of the intermediate transfer belt 7.
The intermediate transfer roller 6 is covered with a metal shaft (for example, made of stainless steel) having a diameter of, for example, 8 to 10 mm, and a conductive elastic material layer that covers the outer peripheral surface of the metal shaft.
Examples of the material of the conductive elastic material layer include ethylene-propylene-diene terpolymer (EPDM) containing a conductive agent such as carbon black, urethane foam, and the like.
A high-voltage transfer bias (a high voltage having a polarity (+) opposite to the toner charging polarity (−)) is applied to the metal shaft of the intermediate transfer roller 6 in order to transfer the toner image. 6 can uniformly apply a high voltage to the intermediate transfer belt 7.
In the present embodiment, the intermediate transfer roller 6 is used as a transfer electrode, but a brush or the like can also be used.

The toner images stacked on the outer surface of the intermediate transfer belt 7 move to the position (transfer portion) of the transfer roller 11 as the intermediate transfer belt 7 rotates.
On the other hand, the recording medium is also conveyed through the sheet conveying path S to the transfer unit, and the recording medium is pressed toward the intermediate transfer belt 7 by the transfer roller 11, whereby the toner image on the intermediate transfer belt 7 is transferred onto the recording medium. Is done.
In this case, the intermediate transfer belt 7 and the transfer roller 11 are pressed against each other at a predetermined nip, and the transfer roller 11 has a polarity (+) opposite to the toner charging polarity (−) for transferring the toner image to the recording medium. ) Is applied.
Also, one of the transfer roller 11 and the drive roller 71 is made of a hard material such as metal so that the nip between the intermediate transfer belt 7 and the transfer roller 11 can be constantly obtained, and the other is made of rubber, foamed resin, or the like. Formed from a soft material.

The toner remaining on the intermediate transfer belt 7 without being transferred from the intermediate transfer belt 7 to the recording medium may cause toner color mixture when a new toner image is stacked on the intermediate transfer belt 7. It is removed and collected by the transfer belt cleaning unit 9.
The intermediate transfer belt cleaning unit 9 includes a cleaning blade that contacts the intermediate transfer belt 7 and removes residual toner, and a toner collection unit that collects the removed toner. A portion of the intermediate transfer belt 7 that is in contact with the cleaning blade is supported by a driven roller 72.

(Sheet conveyance path and its peripheral members)
As shown in FIG. 1, the sheet conveyance path S leads from the paper feed tray 10 and the manual feed tray 20 to the paper discharge tray 15 through a fixing device 12 described later, and pickup rollers 16 a, 16 b, Conveying rollers 25a to 25h (which will be described with reference to 25), a registration roller 14, a transfer roller 11, a fixing device 12, and the like are arranged.
The conveyance rollers 25 are small rollers for promoting and assisting conveyance of the sheet, and a plurality of pairs are provided along the sheet conveyance path S.
The pickup roller 16 a is a pull-in roller that is provided at the end of the paper feed tray 10 and supplies sheet-like recording media (recording paper) from the paper feed tray 10 to the sheet transport path S one by one.
The pickup roller 16 b is a drawing roller that is provided near the manual feed tray 20 and supplies the recording medium from the manual feed tray 20 to the sheet conveyance path S one by one.
The registration roller 14 temporarily holds the recording medium conveyed in the sheet conveyance path S, and conveys the recording medium to the transfer unit at a timing when the leading edge of the toner image on the intermediate transfer belt 7 and the leading edge of the recording medium are aligned. Is.

[Fixing device housing]
As shown in FIG. 1, the fixing device 12 accommodated in the fixing device accommodating portion 100 </ b> B includes a heat roller 81 and a pressure roller 82 that rotate in opposite directions with a recording medium onto which a toner image has been transferred interposed therebetween, A roller 25b and a paper discharge roller 25c are provided.
The heat roller 81 is controlled by a control unit (not shown) so as to have a predetermined fixing temperature. This control unit controls the temperature of the heat roller 81 based on a detection signal from a temperature detector (not shown).
The heat roller 81 and the pressure roller 82 that have been heated to the fixing temperature press the recording medium and melt the toner, thereby fixing the toner image on the recording medium.
The recording medium on which the toner image is fixed is transported to the reverse paper discharge path of the sheet transport path S by the transport roller 25b and the paper discharge roller 25c, and discharged in a reversed state (the toner image is directed downward). It is discharged onto the tray 15.

[Description of sheet transport operation]
In the case of single-sided printing, the sheet conveyed from the sheet feeding tray 10 is conveyed to the registration roller 14 by the conveyance roller 25a in the sheet conveyance path S, and is stacked on the leading edge of the sheet and the intermediate transfer belt 7 by the registration roller 14. The toner image is conveyed to a transfer portion (a contact position between the transfer roller 11 and the intermediate transfer belt 7) at a timing when the leading end of the toner image is aligned. In the transfer portion, a toner image is transferred onto the sheet, and this toner image is fixed on the sheet by the fixing unit 12. Thereafter, the sheet is discharged onto the discharge tray 15 from the discharge roller 25c via the conveyance roller 25b.
Further, the sheet conveyed from the manual feed tray 20 is conveyed to the registration roller 14 by a plurality of conveying rollers 25f, 25e, and 25d. Subsequent sheet conveyance operations are discharged to the sheet discharge tray 15 through a process similar to that for the sheets supplied from the sheet feed tray 10 described above.
On the other hand, in the case of double-sided printing, the sheet on which single-sided printing has been completed passes through the fixing unit 12 and then the rear end of the sheet is chucked by the paper discharge roller 25c. Next, the sheet is guided to the conveying rollers 25g and 25h by the reverse rotation of the paper discharge roller 25c, and after the back side printing is performed again through the registration roller 14, it is discharged to the paper discharge tray 15.

<Embodiment 2>
FIG. 9 is a front view illustrating a partition wall in the developer tank of the developing device according to the second embodiment.
In the developing device of Embodiment 2, the upper end portion constituting the developer return mechanism of the partition wall 217 is formed in a triangular uneven shape in which a concave portion 217a and a convex portion 217b in the height direction are repeated in the longitudinal direction, Other configurations are the same as those of the developing device of the first embodiment.
Similarly to the first embodiment, the upper end portion of the triangular concave-convex shape in the partition wall 217 is lower than the lower limit of the height range of the return developer falling from the inclined surface of the flow member toward the upper end portion of the partition wall 217. The lowest position of the concave portion 217a and the highest position of the convex portion 217b higher than the upper limit of the height range may be set. The intermediate height of the convex portion 217b is set to the intermediate height of the height range. It is preferable to make them substantially coincide.
Further, at the upper end portion of the partition wall 217, the interval between the concave portion 217a and the convex portion 217b is substantially equal to the spiral 1 pitch of the double screw.

<Embodiment 3>
FIG. 10 is a front view showing a partition wall in the developer tank of the developing device according to the third embodiment.
In the developing device of the third embodiment, the upper end portion constituting the developer returning mechanism of the partition wall 317 also falls from the inclined surface of the flow member toward the upper end portion of the partition wall 317 as in the first embodiment. The lower end position of the through hole 317a may be set lower than the lower limit of the height range of the return developer, and the upper end position of the shielding portion 317b may be set lower than the upper limit of the height range. It is preferable that the intermediate height of the through-hole 317a is substantially matched.
Further, at the upper end portion of the partition wall 317, the interval between the through hole 317a and the shielding portion 317b is substantially equal to the spiral 1 pitch of the double screw.

<Embodiment 4>
FIG. 11A is an operation explanatory view showing the developer return mechanism in the developing device of Embodiment 4, and FIG. 11B is a plan view showing the upper end portion of the partition wall of the developer return mechanism of Embodiment 4. is there. In FIG. 11A, the arrow indicates the moving direction of the return developer, and the same elements as those in FIG.
In the developing device of the fourth embodiment, the upper end of the partition wall 417 is repeated in the longitudinal direction of the developer conveying path, with the first and second developer conveying paths P and the first and second bent portions that swing to the Q side being repeated. The other configuration is the same as that of the first embodiment.
In the fourth embodiment, the upper end portion of the partition wall 417 is formed in a wave shape when seen in a plan view, but may have an uneven shape (see FIG. 6) seen in a plan view.

In the developer return mechanism of the fourth embodiment having the upper end portion of the partition wall 417, the return developer sliding down on the flow member 128 jumps over the second bent portions 417b of the upper end portion of the partition wall 417 and performs the first development. By returning to the agent transport path P and returning to the second developer transport path Q by hitting each first bent portion 417a, the return developer is distributed in two directions.
In this case, at the upper end portion of the partition wall 417, the interval between the first bent portion 417a and the second bent portion 417b is substantially equal to the spiral 1 pitch of the double screw.
Note that only the upper end of the partition wall 417 is formed in a meandering shape, and the portion below the upper end (at least the portion below the axis of the first and second conveying members) is a vertical wall.

<Embodiment 5>
FIG. 12 is an operation explanatory view showing a developer returning mechanism in the developing device of the fifth embodiment. In FIG. 12, the arrow indicates the moving direction of the return developer, and the same elements as those in FIG.
In the case of Embodiments 1 to 4, the return developer is distributed in two directions by the developer return mechanism by the cooperation of the flow member and the partition wall, but in the case of Embodiment 5, the developer return mechanism. The returning developer in two directions is mainly performed only by the flow member.
Therefore, the upper end of the partition wall 517 in the developer tank in Embodiment 5 has a normal linear shape.

In the developing device according to the fifth embodiment, the flow member 528 constituting the developer returning mechanism has a lower end portion in the sliding direction of the return developer, and the lower end portion has the concave portion 528c ₁ and the convex portion 528c ₂ as the developer. It is formed in the uneven | corrugated shape repeated in the longitudinal direction of the conveyance path.
The return mechanism the developer is returned developer sliding down on the inclined surface 528b of the flow member 528, back through the respective recesses 528c ₁ of the lower end portion to the second developer conveying path Q, and each convex portion 528c By sliding down ₂ and jumping over the partition wall 517 and returning to the first developer transport path P, the return developer is distributed in two directions.
In this case, the inclination angle of the inclined surface 528b, height, etc. of the lower part can be returned developer sliding down on the inclined surface 528b of the flow member 528 jump over the partition wall 517 from the protrusion 528c ₂ of the lower end portion It is set as follows.
In the fifth embodiment, other configurations are the same as those in the first embodiment.

<Embodiment 6>
In the case of Embodiment 6, the lower end portion of the flow member has a plurality of through holes formed at predetermined intervals in the longitudinal direction of the developer transport path and a plurality of shielding portions located between the plurality of through holes. (Not shown).
In the developer return mechanism of Embodiment 6 having this sink member, the return developer sliding down on the sink member returns to the second developer transport path through each through-hole in the lower end portion, and to each shield portion. By jumping over the sliding partition wall and returning to the first developer conveyance path, the return developer is distributed in two directions.
That is, the sixth embodiment is different from the fifth embodiment in that each recess 528c ₁ (see FIG. 12) of the flow member 528 of the fifth embodiment is changed to a through hole.

DESCRIPTION OF SYMBOLS 1 Exposure apparatus 2 (2a-2d) Development apparatus 3 (3a-3d) Photosensitive drum 4 (4a-4d) Cleaning apparatus 5 (5a-5d) Charging apparatus 8 Transfer apparatus 12 Fixing apparatus 100 Image forming apparatus 111 Developer tank 112 First developer transport spiral member 113 Second developer transport spiral member 114 Developing roller 115a Toner replenishment port 117, 217, 317, 417, 517 Partition wall 117a, 217a, 528c ₁ concave portion 117b, 217b, 528c ₂ convex portion 128 528 Return developer flow member 317a Through hole 317b Shielding portion 417a First bent portion 417b Second bent portion P First developer transport path Q Second developer transport path a First communication path b Second communication path

Claims (9)

A developing device mounted on an electrophotographic image forming apparatus having a photosensitive drum on which an electrostatic latent image is formed,
A developer tank containing a developer containing toner and a carrier, a toner replenishing port for replenishing toner in the developer tank, and a developer tank provided in the developer tank and rotating in a state of carrying the developer. A developing roller for supplying toner to the surface of the photosensitive drum on which the electrostatic latent image is formed, and a development provided between the developing roller and a position in the developer tank where the toner is supplied. A developer conveying path, a developer conveying spiral member that is rotatably provided in the developer conveying path and conveys the developer in the developer conveying path to the developing roller, and development after toner supply to the photosensitive drum A developer return mechanism that returns the developer on the roller to the developer transport path as a return developer,
The developer conveying path includes a first developer conveying path on the toner supply port side, a second developer conveying path on the developing roller side, and a first developer defined by a partition wall parallel to the axial direction of the developing roller. A first communication path and a second communication path for communicating the developer conveyance path and the second developer conveyance path on both sides in the axial direction;
The developer transport spiral member includes a first developer transport spiral member disposed in the first developer transport path and a second developer transport spiral member disposed in the second developer transport path. The first developer transport spiral member and the second developer transport spiral member transport the developer in opposite directions, and circulate the developer between the first developer transport path and the second developer transport path. Configured to let
The developing device, wherein the developer return mechanism is configured to distribute and return the return developer to a first developer transport path and a second developer transport path.   The developer return mechanism includes a return developer flow member that removes the return developer from the photosensitive drum and slides it down to the developer transport path, and an upper end portion of the partition wall. The return developer sliding down on the agent flow member falls to the upper end portion of the partition wall and is distributed in two directions of the first developer transport path and the second developer transport path. The developing device described. The upper end portion of the partition wall portion is formed in an uneven shape in which a concave portion and a convex portion in the height direction are repeated in the longitudinal direction,
The developer return mechanism is configured such that the return developer sliding down on the return developer flow member returns to the first developer conveyance path through each concave portion at the upper end portion of the partition wall and hits each convex portion. The developing device according to claim 2, wherein the return developer is distributed in two directions by returning to the second developer conveyance path. The upper end portion of the partition wall portion includes a plurality of through holes formed at predetermined intervals in the longitudinal direction, and a plurality of shielding portions positioned between the plurality of through holes.
The developer return mechanism is configured such that the return developer sliding down on the return developer flow member returns to the first developer conveyance path through each through hole in the upper end portion of the partition wall, and to each shielding portion. The developing device according to claim 2, wherein the return developer is distributed in two directions by returning to the second developer conveyance path. The upper end portion of the partition wall portion is formed in a meandering shape in which first and second bent portions that swing toward the first and second developer transport paths are repeated in the longitudinal direction of the developer transport path,
The developer return mechanism is configured such that the return developer sliding down on the return developer flow member jumps over each second bent portion of the upper end portion of the partition wall and returns to the first developer transport path, and The developing device according to claim 2, wherein the return developer is distributed in two directions by hitting one bent portion and returning to the second developer conveyance path.   The developer return mechanism is configured to remove the return developer from the photosensitive drum, slide it down to the developer transport path, and distribute it in two directions, a first developer transport path and a second developer transport path. The developing device according to claim 1, further comprising a returning developer flow member. The return developer sink member has a lower end in the sliding direction of the return developer,
The lower end portion is formed in a concavo-convex shape in which a concave portion and a convex portion are repeated in the longitudinal direction of the developer conveyance path,
The developer return mechanism is configured such that the return developer sliding down on the return developer flow member returns to the second developer transport path through each recess at the lower end and slides down onto each projection. The developing device according to claim 6, wherein the return developer is distributed in two directions by jumping over the partition wall and returning to the first developer conveyance path. The return developer sink member has a lower end in the sliding direction of the return developer,
The lower end portion includes a plurality of through holes formed at predetermined intervals in the longitudinal direction of the developer transport path, and a plurality of shielding portions positioned between the plurality of through holes.
The developer return mechanism is configured such that the return developer sliding down on the return developer flow member returns to the second developer conveyance path through each through hole in the lower end portion and slides down onto each shielding portion. The developing device according to claim 6, wherein the return developer is distributed in two directions by jumping over the partition wall and returning to the first developer transport path.   A photosensitive member having a surface on which an electrostatic latent image is formed; a charging device for charging the surface of the photosensitive member; an exposure device for forming an electrostatic latent image on the surface of the photosensitive member; A developing device according to any one of claims 1 to 8, wherein a toner image is formed by supplying toner to the electrostatic latent image, a transfer device for transferring the toner image on the surface of the photoreceptor to a recording medium, An image forming apparatus comprising: a cleaning device that cleans the surface of the photoreceptor; and a fixing device that fixes a toner image on a recording medium.

Images