JP5061209B2 - Developing device and image forming apparatus including the same - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device mounted on an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and an image forming apparatus including the developing device, and more particularly to a developing device using a two-component developer composed of a magnetic carrier and toner. Is.

  Conventionally, as a development method using dry toner in an image forming apparatus using an electrophotographic process, a one-component development method using no carrier and a two-component developer charging a nonmagnetic toner using a magnetic carrier are used. In addition, a two-component development system is known in which an electrostatic latent image on an image carrier (photoconductor) is developed by a magnetic brush composed of toner and a carrier formed on a developing roller.

  The one-component development method is suitable for high image quality because the electrostatic latent image on the image carrier is not disturbed by the magnetic brush. On the other hand, the toner is charged by the charge roller, and the elastic regulating blade is used on the development roller. In order to regulate the layer thickness, the toner additive adheres to the charge roller, the charging ability is lowered, and it is difficult to stably maintain the charge amount of the toner. In addition, toner may adhere to the regulating blade, resulting in non-uniform layer formation and image defects.

  In the case of color printing in which color superposition is performed, since the color toner is required to be transparent, it needs to be a non-magnetic toner. Therefore, in a full-color image forming apparatus, a two-component development system in which toner is charged and conveyed using a carrier is often employed.

  By the way, in the two-component development system, a developer supply / recovery unit provided with a stirring and conveying screw for supplying the developer to the development roller and conveying the developer recovered from the development roller, and a developer supply / recovery unit 2. Description of the Related Art Generally, a biaxial transport type developing device having a stirring and transporting unit that replenishes toner to the developer transported from and stirs and transports the developer is generally used.

  However, in the above-described biaxial conveyance type, the developer having a low toner ratio (T / C) used for developing the electrostatic latent image on the photoconductor is recovered and immediately on the developing roller again. Since it is carried, there is a problem that a stable image density cannot be obtained.

  As countermeasures, for example, Patent Documents 1 and 2 disclose a developer supply / conveying section that supplies a developer to a developer carrying member (developing roller), and a developer collection that conveys the developer collected from the developer carrying member. A three-axis transport type developing device is disclosed in which a transport unit and a developer stirring and transport unit that replenishes toner and stirs and transports the developer transported from the developer recovery transport unit are separately provided.

  According to the methods of Patent Documents 1 and 2, all the developer having a lowered toner density (T / C) after development is collected by the developer collecting and conveying unit and is not immediately used for development. The concentration can be obtained.

JP 2007-147807 A JP 2009-58939 A

  In the methods of Patent Documents 1 and 2, the developer recovered from the developer carrier and transported in the developer recovery transport unit joins the developer in the developer supply transport unit at the end of the developer supply transport unit. . For this reason, particularly in a high-speed machine having a high developer conveyance speed, the stirring tends to be insufficient, and the toner concentration (T / C) in the developer becomes unstable, or the fluidity decreases to the developer supply and conveyance section. In some cases, the delivery of the developer is hindered.

  Further, in the configurations of Patent Documents 1 and 2, the developer amount in the developer supply / conveying portion decreases as the developer carrier moves toward the downstream side, and the bulk of the developer decreases. For this reason, there is a possibility that the developer pumping property at the downstream portion of the developer carrying member is insufficient and the image density is partially lowered.

  In addition, when a toner concentration sensor and a developer discharge unit are disposed near the downstream side of the developer merging point, excessive discharge of the developer may occur due to erroneous detection of the toner concentration or disturbance of the developer volume. is there.

  SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a three-axis conveyance type developing device capable of effectively suppressing a decrease in image density due to insufficient stirring of a two-component developer, and an image forming apparatus including the same. And

  In order to achieve the above object, the present invention provides a developer container that is divided into an agitating and conveying chamber, a supply and conveying chamber, and a collecting and conveying chamber that are arranged in parallel, and that contains a two-component developer containing a carrier and toner, A developer carrier that is rotatably supported by a developer container and carries a developer on a surface thereof, and is disposed in the supply and conveyance chamber and stirs and conveys the developer along the axial direction of the developer carrier and the developer. A supply / conveying member that supplies developer to the carrier, an agitating / conveying member that is disposed in the agitating / conveying chamber and that stirs and conveys the developer in a direction opposite to the supply / conveying member; A recovery transport member that stirs and transports the developer recovered from the developer carrier in the same direction as the supply transport member; and a communication section that transfers the developer from the recovery transport chamber to the supply transport chamber. For the conveying member Transport speed in at least one location upstream of the communicating portion with respect to the developer carrying direction is developing apparatus provided with a slower speed reduction portion than other portions.

  In this specification, “arranged substantially in parallel” means not only when the agitation transport chamber, the supply transport chamber, and the recovery transport chamber are parallel to each other, but also has a predetermined angle in the horizontal or vertical direction. Including cases.

  According to the present invention, in the developing device configured as described above, a gap is provided above the partition wall that divides the collection conveyance chamber and the supply conveyance chamber along the longitudinal direction of the collection conveyance member. .

  According to the present invention, in the developing device configured as described above, the collecting and conveying member includes a rotating shaft and a spiral blade formed on an outer peripheral surface of the rotating shaft, and the speed reduction portion is formed between the spiral blades. And a rib protruding substantially parallel to the rotation axis is formed.

  In the developing device having the above-described configuration, the collecting and conveying member includes a rotation shaft and a spiral blade formed on an outer peripheral surface of the rotation shaft. It is characterized in that at least one of is partially reduced.

  According to the present invention, in the developing device configured as described above, the collection transfer chamber is arranged at a position higher than the supply transfer chamber.

  According to the present invention, in the developing device configured as described above, the communication portion is provided upstream of a developer passage that transfers the developer from the supply conveyance chamber to the agitation conveyance chamber in the developer conveyance direction. It is a feature.

  According to the present invention, in the developing device configured as described above, a developer discharge portion for discharging excess developer is provided at the downstream end of the supply transfer chamber in the developer transfer direction.

  The present invention also provides an image forming apparatus equipped with the developing device having the above-described configuration.

  According to the first configuration of the present invention, by providing the recovery conveyance member with the speed reducing portion, the developer recovered from the developer carrying member and having a reduced toner concentration is supplied in a state dispersed in the conveyance direction. Returned to the transfer chamber. Accordingly, it is possible to effectively suppress the variation in the toner concentration and the toner charge amount in the developing container and the development history.

  Further, according to the second configuration of the present invention, in the developing device of the first configuration, by providing a gap above the partition wall that divides the collection transfer chamber and the supply transfer chamber, not only the communication portion, Since the developer is gradually returned to the supply / conveying chamber from a wide area on the upstream side, the developer amount in the supply / conveying chamber can be easily controlled, and the stability of the developer balance can be improved.

  Further, according to the third configuration of the present invention, in the developing device having the above first or second configuration, the recovery transport member is formed with ribs substantially parallel to the rotation shaft and provided with the speed reduction unit, thereby simplifying the operation. With the configuration, the developer can be retained. Further, since the force in the direction perpendicular to the transport direction is applied to the developer by the rotation of the rib, the developer can be smoothly returned from the collection transport chamber to the supply transport chamber.

  Further, according to the fourth configuration of the present invention, in the developing device having the first or second configuration, at least one of the pitch or the outer diameter of the spiral blades of the recovery conveyance member is partially reduced to reduce the speed reduction unit. By providing it, the retention of the developer can be generated with a simple configuration.

  According to the fifth configuration of the present invention, in the developing device having any one of the first to fourth configurations, the recovery transport chamber is formed at a position higher than the supply transport chamber, so that the recovery transport member can The developer that has been transported in the collection transport chamber is merged while dropping from the communication portion and the speed reduction portion to the supply transport chamber, and the developer in the developer container can be smoothly circulated.

  According to the sixth configuration of the present invention, in the developing device having any one of the first to fifth configurations, the communication section is connected to the developer passage path that transfers the developer from the supply conveyance chamber to the stirring conveyance chamber. Since the developer having a low toner concentration recovered from the developer carrying member is transported to the stirring transport chamber in a state of being sufficiently mixed with the developer in the supply transport chamber, the upstream side of the developer carrying member is newly provided in the stirring transport chamber. After the toner is replenished, the toner concentration in the developer can be stabilized until the toner is again supplied to the developer carrying member in the supply conveyance chamber.

  According to the seventh configuration of the present invention, in the developing device having any one of the first to sixth configurations, excess developer is discharged to the downstream end of the supply transport chamber in the developer transport direction. By providing the developer discharging section, a long-life developing device capable of supplying a new carrier together with the toner and discharging the deteriorated carrier as an excess can be obtained. In addition, the toner concentration and developer balance in the developer container can be stabilized, and the developer discharge amount from the developer discharge portion is also kept constant.

  Further, according to the eighth configuration of the present invention, by mounting the developing device having any one of the first to seventh configurations, the unevenness of the image density due to the variation in the toner concentration or the developer balance in the developing device. An image forming apparatus capable of forming a high-quality image that does not occur over a long period of time.

1 is a schematic diagram showing the overall configuration of an image forming apparatus of the present invention. Side surface sectional drawing which shows the structure of the image development apparatus concerning 1st Embodiment of this invention. Plan sectional drawing which shows the structure of the developing device of 1st Embodiment. The figure which shows an example of the bias waveform applied to a developing roller and a magnetic roller 1 is a schematic perspective view showing a developer recovery chamber of a developing device according to a first embodiment. Plan sectional drawing which shows the structure of the image development apparatus concerning 2nd Embodiment of this invention. Side surface sectional drawing which shows the structure of the developing device which concerns on 3rd Embodiment of this invention. Plan sectional drawing which shows the structure of the image development apparatus of 3rd Embodiment. Side surface sectional drawing which shows the other structural example of the developing device which concerns on 1st Embodiment. Plan sectional drawing which shows the other structural example of the developing device which concerns on 1st Embodiment.

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

  The image forming portions Pa to Pd are provided with photosensitive drums 1a, 1b, 1c, and 1d that carry visible images (toner images) of the respective colors, and are further driven by a driving unit (not shown). The intermediate transfer belt 8 that rotates clockwise is provided adjacent to the image forming portions Pa to Pd. The toner images formed on the photosensitive drums 1a to 1d are sequentially primary-transferred and superimposed on the intermediate transfer belt 8 that moves while contacting the photosensitive drums 1a to 1d, and then the secondary transfer roller. 9 is secondarily transferred onto a transfer paper P as an example of a recording medium, and further fixed on the transfer paper P in the fixing unit 13 and then discharged from the apparatus main body. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d counterclockwise in FIG.

  The transfer paper P onto which the toner image is transferred is accommodated in a paper cassette 16 at the lower part of the apparatus, and drives a secondary transfer roller 9 and an intermediate transfer belt 8 described later via a paper feed roller 12a and a registration roller pair 12b. It is conveyed to the nip portion with the roller 11. A sheet made of dielectric resin is used for the intermediate transfer belt 8, and a (seamless) belt having no seam is mainly used. A blade-like belt cleaner 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed downstream of the secondary transfer roller 9.

  Next, the image forming units Pa to Pd will be described. There are chargers 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d that are rotatably arranged. The exposure device 5 for exposing the toner, the developing devices 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and the developer (toner) remaining on the photosensitive drums 1a to 1d are removed. Cleaning parts 7a, 7b, 7c and 7d are provided.

  When image data is input from a host device such as a personal computer, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d, and then light is irradiated according to the image data by the exposure device 5. The electrostatic latent images corresponding to the image data are formed on the respective photosensitive drums 1a to 1d. Each of the developing devices 3a to 3d is filled with a predetermined amount of a two-component developer containing toner of each color of cyan, magenta, yellow, and black. In addition, when the ratio of the toner in the two-component developer filled in each developing device 3a to 3d falls below a specified value due to the formation of a toner image described later, each developing device 3a to 3d is transferred from the toner container 4a to 4d. Toner is replenished. The toner in the developer is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d and electrostatically adheres to the electrostatic latent image formed by the exposure from the exposure device 5. A toner image is formed.

  Then, by applying a predetermined transfer voltage to the primary transfer rollers 6 a to 6 d, yellow, cyan, magenta, and black toner images on the photosensitive drums 1 a to 1 d are primarily transferred onto the intermediate transfer belt 8. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning units 7a to 7d in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 8 is stretched between an upstream conveyance roller 10 and a downstream drive roller 11, and the intermediate transfer belt 8 rotates clockwise as the drive roller 11 is rotated by a drive motor (not shown). When the rotation starts, the transfer paper P is conveyed from the registration roller 12b to the nip portion (secondary transfer nip portion) between the drive roller 11 and the secondary transfer roller 9 provided adjacent thereto at a predetermined timing. The full color image on the intermediate transfer belt 8 is transferred onto the transfer paper P. The transfer paper P onto which the toner image is transferred is conveyed to the fixing unit 13.

  The transfer paper P conveyed to the fixing unit 13 is heated and pressurized by the fixing roller pair 13a, and the toner image is fixed on the surface of the transfer paper P, so that a predetermined full color image is formed. The transfer paper P on which the full-color image is formed is distributed in the transport direction by the branching portion 14 that branches in a plurality of directions. When an image is formed only on one side of the transfer paper P, it is discharged as it is onto the discharge tray 17 by the discharge roller 15.

  On the other hand, when forming images on both sides of the transfer paper P, the transfer paper P that has passed through the fixing unit 13 is once transported in the direction of the discharge roller 15, and the discharge roller after the rear end of the transfer paper P has passed through the branching unit 14. 15 is rotated in the reverse direction and the conveyance direction of the branching portion 14 is switched, so that the paper is distributed from the rear end of the transfer paper P to the paper conveyance path 18 and re-conveyed to the secondary transfer nip portion with the image surface reversed. . Then, after the next image formed on the intermediate transfer belt 8 is transferred by the secondary transfer roller 9 to the surface of the transfer paper P where the image is not formed and conveyed to the fixing unit 13 and the toner image is fixed. , And discharged to the discharge tray 17.

  FIG. 2 is a side sectional view of the developing device according to the first embodiment of the present invention, and FIG. 3 is a plan sectional view of the developing device according to the first embodiment (a sectional view taken along line AA ′ in FIG. 2). . 2 shows a state viewed from the back side of FIG. 1, and the arrangement of each member in the developing device is opposite to that in FIG. Further, the developing device 3a disposed in the image forming unit Pa in FIG. 1 will be described here, but the configuration of the developing devices 3b to 3d disposed in the image forming units Pb to Pd is basically the same, and thus described. Is omitted.

  As shown in FIGS. 2 and 3, the developing device 3a includes a developing container 20 in which a two-component developer (hereinafter simply referred to as a developer) is stored. The developing container 20 is separated by partition walls 20a and 20b. The agitating and conveying chamber 21, the supply and conveying chamber 22, and the recovery and conveying chamber 23 are partitioned. In the agitating / conveying chamber 21 and the supply / conveying chamber 22, the agitating / conveying screw 25 a for supplying toner (positively charged toner) supplied from the toner container 4 a (see FIG. 1) with the carrier, agitating and charging, and the supplying and conveying Each screw 25b is rotatably arranged. Further, a collection conveyance screw 25c for conveying the developer peeled off from a magnetic roller 30 (described later) is rotatably disposed in the collection conveyance chamber 23.

  Then, the developer is agitated by the agitating and conveying screw 21a and the supply and conveying screw 21b while being conveyed in the axial direction (the direction of arrows B and C in FIG. 3), and the developer passage 26a formed at both ends of the partition wall 20a, It circulates between the stirring conveyance chamber 21 and the supply conveyance chamber 22 via 26b. Further, the developer peeled off from the magnetic roller 30 (described later) is conveyed in the axial direction (arrow C direction) by the recovery conveying screw 25c, and is supplied from the communication portion 27 formed at one end of the partition wall 20b into the supply stirring chamber 22. To the developer. That is, a developer circulation path is formed in the developer container 20 by the agitation transport chamber 21, the supply transport chamber 22, the recovery transport chamber 23, the developer passage paths 26 a and 26 b, and the communication portion 27.

  The developing container 20 extends obliquely upward to the right in FIG. 2, and the magnetic roller 30 is disposed above the second stirring screw 21 a in the developing container 20, and the developing roller 31 is disposed obliquely upward to the right of the magnetic roller 30. Are arranged opposite to each other. The developing roller 31 faces the photosensitive drum 1a (see FIG. 1) on the opening side (right side in FIG. 2) of the developing container 20, and the magnetic roller 30 is rotated clockwise in FIG. The developing roller 31 rotates counterclockwise in the figure.

  A toner concentration sensor 33 is disposed in the agitating and conveying chamber 21 so as to face the agitating and conveying screw 21a, and in the vicinity of the toner replenishing port 20c, toner is replenished at a predetermined speed from the toner container 4a (see FIG. 1). A toner replenishing motor (not shown) is provided. As shown in FIG. 3, the toner replenishing port 20c is disposed at the upstream end of the agitating / conveying chamber 20c in the developer circulation direction when seen in a plan view, and the toner concentration sensor 33 is disposed in the developer circulation direction. It arrange | positions in the downstream of the supply port 20c.

  As the toner concentration sensor 33, a magnetic permeability sensor that detects the magnetic permeability of a two-component developer composed of toner and magnetic carrier in the developing container 20 is used. Here, the toner concentration is the ratio (T / C) of the toner to the magnetic carrier in the developer. In this embodiment, the toner permeability is detected by the toner concentration sensor 33, and the detection result is as follows. Is output to a control unit (not shown), and the toner density is determined from the output value of the toner density sensor 33. The control unit transmits a control signal to the toner supply motor in accordance with the determined toner concentration, and supplies a predetermined amount of toner into the developing container 20 from the toner supply port 20c.

  The sensor output value changes according to the toner concentration. The higher the toner concentration, the higher the ratio of toner to the magnetic carrier, and the higher the ratio of toner that does not pass magnetism, the lower the output value. On the other hand, the lower the toner concentration, the lower the ratio of toner to carrier, and the higher the ratio of carrier that passes magnetism, the higher the output value.

  The magnetic roller 30 is composed of a non-magnetic rotating sleeve that rotates clockwise in FIG. 2 and a fixed magnet body having a plurality of magnetic poles contained in the rotating sleeve.

  The developing roller 31 includes a cylindrical developing sleeve that rotates counterclockwise in FIG. 2 and a developing roller-side magnetic pole fixed in the developing sleeve. The magnetic roller 30 and the developing roller 31 face each other. It faces with a predetermined gap at (opposite position). The developing roller side magnetic pole has a different polarity from the opposing magnetic pole (main pole) of the fixed magnet body.

  Further, a spike cutting blade 35 is attached to the developing container 20 along the longitudinal direction of the magnetic roller 30 (the front and back direction in FIG. 2), and the spike cutting blade 35 is rotated in the direction of rotation of the magnetic roller 30 (clockwise in the figure). Around the opposite position between the developing roller 31 and the magnetic roller 30. A slight gap (gap) is formed between the tip of the ear cutting blade 35 and the surface of the magnetic roller 30.

  A DC voltage (hereinafter referred to as Vslv (DC)) and an AC voltage (hereinafter referred to as Vslv (AC)) are applied to the developing roller 31, and a DC voltage (hereinafter referred to as Vmag (DC)) is applied to the magnetic roller 30. And an alternating voltage (hereinafter referred to as Vmag (AC)) is applied. These DC voltage and AC voltage are applied to the developing roller 31 and the magnetic roller 30 from a developing bias power source via a bias control circuit (both not shown).

  As described above, the developer is agitated by the agitating / conveying screw 25a and the supply / conveying screw 25b, and the toner is charged by circulating through the agitating / conveying chamber 21 and the supplying / conveying chamber 22 in the developing container 20, and the supply / conveying screw 25b The developer is conveyed to the magnetic roller 30. Then, a magnetic brush (not shown) is formed on the magnetic roller 30, and the layer thickness of the magnetic brush on the magnetic roller 30 is regulated by the earbrushing blade 35, and then the opposite portion between the magnetic roller 30 and the developing roller 31. A thin toner layer is formed on the developing roller 31 by the potential difference ΔV between the Vmag (DC) conveyed and applied to the magnetic roller 30 and the Vslv (DC) applied to the developing roller 31 and a magnetic field.

  The toner layer thickness on the developing roller 31 varies depending on the resistance of the developer and the difference in rotational speed between the magnetic roller 30 and the developing roller 31, but can be controlled by ΔV. When ΔV is increased, the toner layer on the developing roller 31 is thickened, and when ΔV is decreased, the toner layer is thinned. The range of ΔV at the time of development is generally about 100V to 350V.

  FIG. 4 is a diagram illustrating an example of a bias waveform applied to the developing roller 31 and the magnetic roller 30. As shown in FIG. 4A, a composite waveform Vslv (solid line) in which a rectangular wave Vslv (AC) having a peak-to-peak value of Vpp1 is superimposed on Vslv (DC) is applied to the developing roller 31. The magnetic roller 30 is applied with a combined waveform Vmag (broken line) in which Vmag (DC) is superimposed on a rectangular wave Vmag (AC) having a peak-to-peak value of Vpp2 and a phase different from Vslv (AC). The

  Therefore, the voltage applied between the magnetic roller 30 and the developing roller 31 (hereinafter referred to as MS) is a composite waveform Vmag−Vslv having Vpp (max) and Vpp (min) as shown in FIG. Become. Note that Vmag (AC) is set so that the duty ratio is larger than Vslv (AC). Actually, an AC voltage having a partially distorted shape is applied instead of a complete rectangular wave as shown in FIG.

  The toner thin layer formed on the developing roller 31 by the magnetic brush is conveyed to a portion facing the developing roller 31 by the rotation of the developing roller 31. Since Vslv (DC) and Vslv (AC) are applied to the developing roller 31, the toner flies due to a potential difference with the photosensitive drum 1a, and the electrostatic latent image on the photosensitive drum 1a is developed. .

  The remaining toner that is not used for development is conveyed again to the opposite portion between the developing roller 31 and the magnetic roller 30 and is collected by the magnetic brush on the magnetic roller 30. Then, the magnetic brush is peeled off from the magnetic roller 30 at the same pole portion of the fixed magnet roller body, and then falls into the collection conveyance chamber 23. The developer in the collection conveyance chamber 23 is conveyed in the axial direction by the collection conveyance screw 25c, and merges with the developer in the supply conveyance chamber 22 from the communication portion 27. As shown in FIG. 5, the communication portion 27 is formed by notching the downstream end portion of the partition wall 20 b in the developer circulation direction (white arrow in the figure).

  Thereafter, a predetermined amount of toner is replenished from the toner replenishing port 20 c based on the output of the toner concentration sensor 33, and the toner is uniformly charged again with an appropriate toner concentration while circulating through the supply transport chamber 22 and the stirring transport chamber 21. Becomes a component developer. This developer is again supplied onto the magnetic roller 30 by the supply stirring screw 25 b to form a magnetic brush, and is conveyed to the ear cutting blade 35.

  As shown in FIG. 2, the collection transfer chamber 23 is formed at a position higher than the supply transfer chamber 22. For this reason, the developer that has been transported in the recovery transport chamber 23 by the recovery transport screw 25c is merged while falling from the communication portion 27 to the supply transport chamber 22, and the developer can be smoothly circulated.

  Further, when the developer transport speed in the collection transport chamber 23 is slow, the amount of developer in the supply transport chamber 22 decreases, and the developer balance in the developer container 20 is deteriorated, affecting the developability. On the other hand, if a large amount of the developer having a lowered toner concentration in the collection transport chamber 23 is merged into the supply transport chamber 22 at a time, the developer is not sufficiently stirred until the developer is transported to the toner supply port 20c. As a result, variations in toner concentration occur in the developing container 20.

  Therefore, in the present embodiment, the diameter of the spiral blade of the recovery conveyance screw 25c arranged in the recovery conveyance chamber 23 is made smaller than that of the supply conveyance screw 25b arranged in the supply conveyance chamber 22, and the recovery conveyance screw 25c The number of rotations per unit time is set to be larger than that of the supply conveying screw 25b. As a result, the developer having a lowered toner concentration in the collection conveyance chamber 23 can be quickly and gradually returned to the supply conveyance chamber 22, and the developer balance and toner concentration in the developing container 20 can be maintained constant. Become.

  In the present embodiment, the shaft diameter of the agitating and conveying screw 25a and the supply and conveying screw 25b is 8 mm, the outer diameter of the spiral blade is 20 mm, the pitch is 15 mm, and the number of rotations per unit time is 500 rpm. Further, the shaft diameter of the collecting and conveying screw 25c is 4 mm, the outer diameter of the spiral blade is 10 mm, the pitch is 10 mm, and the rotation speed per unit time is 510 rpm.

  As shown in FIG. 3, the communication unit 27 that transfers the developer from the collection transfer chamber 23 to the supply transfer chamber 22 is connected to the stirring transfer chamber from the supply transfer chamber 22 in the developer transfer direction (arrow C direction). 21 is provided on the upstream side of the developer passage 26 b for delivering the developer to 21. According to this configuration, the developer in the collecting and transporting chamber 23 in which the toner concentration has been lowered is transported to the toner replenishing port 20c in a state of being sufficiently mixed with the developer in the supply and transporting chamber 22, and new toner is replenished. Before, the toner concentration in the developer becomes substantially uniform. Therefore, the toner concentration in the developer can be stabilized before the toner is supplied in the agitating and conveying chamber 21 and supplied again to the magnetic roller 30 in the supply and conveying chamber 22.

  Further, the partition wall 20b protruding from the bottom surface of the developing container 20 does not completely partition the supply transport chamber 22 and the recovery transport chamber 23 in the vertical direction, and there is a gap above the partition wall 20b as shown in FIG. S is formed. As shown in FIG. 3, ribs 40 that are substantially parallel to the rotation axis are provided between the spiral blades at three locations on the rotation axis of the recovery conveying screw 25c.

  According to this configuration, a force in the developer transport direction (arrow C direction) is not applied to the developer in the collection transport chamber 23 at the portion where the rib 40 is provided, and the developer stays and becomes bulky. In other words, the portion where the rib 40 is provided functions as a deceleration portion having a lower conveyance speed than the other portions. Further, a force in a direction perpendicular to the transport direction is applied to the staying developer by the rotation of the rib 40. Accordingly, the developer transported in the collection transport chamber 23 joins the supply transport chamber 22 from the communication portion 27 as indicated by the white arrow in the figure, and a part of the developer is transported in the transport direction (arrow C direction). On the other hand, the vehicle passes over the partition wall 20b from three locations (locations where the ribs 40 are formed) on the upstream side of the communication portion 27, passes through the gap S, and falls into the supply transfer chamber 22.

  Accordingly, the distance from the time when the developer in the collection conveyance chamber 23 joins the supply conveyance chamber 22 to the conveyance to the toner supply port 20c becomes long. As a result, the toner in the supply and transfer chamber 22 is sufficiently agitated and uniformed to supply toner, so that the toner concentration in the developer can be further stabilized.

  Further, since the developer is gradually returned to the supply conveyance chamber 22 not only from the communication portion 27 but also from a wide area upstream, the control of the developer amount in the supply conveyance chamber 22 is facilitated, and the developer balance is improved. Stability can be improved.

  By the way, when the developer peeled off from the magnetic roller 30 and collected in the collection conveyance chamber 23 is returned to the developer in the supply conveyance chamber 22 at a time, the toner concentration is increased in the developer in the supply conveyance chamber 22. Low parts tend to occur. As a result, particularly when a high-density image is printed partially such as a patch image, the developer having a reduced toner density used for development is directly supplied onto the magnetic roller 30, and the immediately preceding There was a problem that the image appeared as a history.

  In the configuration of the present embodiment, the developer collected from the magnetic roller 22 and having a reduced toner concentration once stays in the vicinity of the rib 40, then passes over the partition wall 20 b little by little and is returned to the supply conveyance chamber 22. Therefore, the occurrence of the development history as described above can be suppressed.

  Note that the wider the region in which the developer is returned from the collection conveyance chamber 23 to the supply conveyance chamber 22, the more advantageous the stabilization of the developer balance in the supply conveyance chamber 22 is. The risk of being carried again on 30 increases. For this reason, the width of the region where the developer is returned from the collection conveyance chamber 23 to the supply conveyance chamber 22 in the conveyance direction and the amount of the developer to be returned are set in consideration of the influence on the developer balance and the image density. It is preferable to adjust according to the size, shape, number, etc. of the sheath 40.

  Further, in the above embodiment, the gap S is provided above the partition wall 20b, and the developer staying in the vicinity of the rib 40 gets over the partition wall 20b and returns into the supply conveyance chamber 22, but this is not a limitation. For example, one or more openings may be provided in the partition wall 20b.

  FIG. 6 is a plan sectional view (a sectional view taken along the line AA ′ in FIG. 2) of the developing device according to the second embodiment of the present invention. The side sectional view of the developing device 3a is the same as FIG. In the present embodiment, narrow pitch portions 41 where the pitch of the spiral wings is narrower than the other portions are provided at three locations of the recovery conveying screw 25c in place of the ribs 40 as speed reducing portions.

  According to this configuration, the developer conveying force in the narrow pitch portion 41 is smaller than the conveying force in the other portions of the recovery conveying screw 25c, so that the developer stays in the narrow pitch portion 41 and the developer The bulk increases. As a result, the developer transported in the collection transport chamber 23 joins the supply transport chamber 22 from the communication portion 27 as shown by the white arrow in the figure, and communicates with the developer transport direction (arrow C direction). The vehicle passes over the partition wall 20b from three locations upstream of the portion 27 (where the narrow pitch portion 41 is formed), passes through the gap S, and falls into the supply transfer chamber 22.

  Therefore, similarly to the first embodiment, the toner concentration in the developer can be further stabilized. Further, it becomes easy to control the amount of developer in the supply transfer chamber 22 and the stability of the developer balance can be improved. Furthermore, since the developer in the collection and transfer chamber 23 once stays in the vicinity of the narrow pitch portion 41 and then returns to the supply and transfer chamber 22 little by little, the development history can be suppressed. Also in the present embodiment, the area where the developer is returned from the collection conveyance chamber 23 to the supply conveyance chamber 22 by changing the height of the partition wall 20b, the number of the narrow pitch portions 41, the pitch width of each narrow pitch portion 41, and the like. Width and developer return amount can be adjusted.

  Here, the narrow pitch portion 41 is provided to cause the developer to stay, but instead of providing the narrow pitch portion 41, the developer stays by providing a small diameter portion in which the diameter of the spiral blade is partially reduced. It is also possible to generate Further, both the pitch and the diameter of the spiral wing may be partially reduced.

  FIG. 7 is a side sectional view of the developing device according to the third embodiment of the present invention, and FIG. 8 is a plan sectional view of the developing device according to the third embodiment (a sectional view taken along the line AA ′ in FIG. 7). In this embodiment, unlike the above embodiments, the magnetic roller 30 rotates counterclockwise in FIG. 7, and the developing roller 31 rotates clockwise in FIG. Therefore, the developer peeled off from the magnetic roller 30 falls to the inside of the supply conveyance chamber 22. Therefore, the recovery transfer chamber 23 is provided above the vicinity of the boundary between the supply transfer chamber 22 and the stirring transfer chamber 21.

  In addition, the configuration of the present embodiment is a developing device of a type in which a new carrier is supplied together with toner, and excess developer including a deteriorated carrier is discharged. That is, toner and a new carrier are supplied into the developing container 20 from the toner containers 4a to 4d (see FIG. 1) and the carrier container (not shown) through the toner supply port 20c. Further, a developer discharge section 50 for discharging excess developer (corresponding to the amount of developer replenished from the toner replenishing port 20c) is provided at the downstream end of the supply transport chamber 22 with respect to the developer transport direction. Yes. Since the configuration of other parts is the same as that of the first embodiment, description thereof is omitted.

  According to this method, since a new carrier is supplied together with the toner, and the deteriorated carrier is gradually discharged from the developer discharge unit 50 as an excess developer, the carrier in the developing container 20 can be replaced, and the development can be performed. The life of the device 3a can be extended.

  Also in the third embodiment, since the collection conveyance chamber 23 is provided at a position higher than the supply conveyance chamber 22, the developer conveyed in the collection conveyance chamber 23 is transferred from the communication portion 27 to the supply conveyance chamber 22. The developer flows together while falling, and the developer can be circulated smoothly. The communication portion 27 is provided on the upstream side of the developer passage 26b with respect to the developer transport direction (arrow C direction). As a result, the developer in the collecting and transporting chamber 23 in which the toner concentration has decreased is transported to the toner replenishing port 20c in a state of being sufficiently mixed with the developer in the supply and transporting chamber 22, and before the new toner and carrier are replenished. In addition, the toner concentration in the developer can be made substantially uniform.

  Since the recovery conveyance screw 25c is provided with the rib 40 as in the first embodiment, the developer can be gradually returned to the supply conveyance chamber 22 not only from the communication portion 27 but also from a wide area upstream. The bias of the developer balance in the developing container 20 can be suppressed. Accordingly, it is possible to prevent the occurrence of uneven density and to maintain the discharge amount from the developer discharge portion 50 at a constant amount.

  In addition, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, the present invention is not limited to the developing device provided with the magnetic roller 30 and the developing roller 31 as shown in the above embodiments, but various types using a two-component developer composed of a toner component and a magnetic carrier. It can be applied to the developing device.

  FIG. 9 is a side sectional view showing another configuration example of the developing device according to the first embodiment of the present invention, and FIG. 10 is a plan sectional view of the developing device (a cross-sectional view taken along line AA ′ in FIG. 9). In FIG. 9, the developing roller 31 on which the toner thin layer is formed is not provided, and the magnetic brush formed on the magnetic roller 30 is directly brought into contact with the photosensitive drum 1a to be developed in a two-component developing type developing device. The configuration of the first embodiment in which the transfer chamber 23 is provided at a position higher than the supply transfer chamber 22 and the communication portion 27 is provided on the upstream side of the developer passage 26b is applied.

  As shown in FIG. 10, the communication portion 27 is provided at substantially the same position as the developer passage 26b in the developer transport direction (arrow C direction).

  Also in the developing device 3a shown in FIGS. 9 and 10, the same operational effects as those of the developing device 3a shown in FIG. 2 can be obtained. Of course, the same effect can be obtained by providing a narrow pitch portion 41 as in the second embodiment in place of the ribs 40 to cause the developer to stay.

  The present invention is not limited to the tandem color printer shown in FIG. 1, but can be applied to various image forming apparatuses such as a digital or analog monochrome copying machine, a monochrome printer, a color copying machine, and a facsimile.

  The present invention can be used in a three-axis conveyance type developing device using a two-component developer, and is provided with at least one speed reduction portion on the upstream side of a communication portion that transfers the developer from the collection conveyance chamber to the supply conveyance chamber. It is a thing. Accordingly, it is possible to provide a developing device in which the developer is smoothly circulated and the toner concentration in the developer and the developer balance are stable.

  Further, by mounting the developing device of the present invention, it is possible to provide an image forming apparatus that forms a high-quality image without image defects such as uneven image density.

Pa to Pd Image forming section 1a to 1d Photosensitive drum 3a to 3d Developing device 20 Developing container 20a, 20b Partition wall 20c Toner replenishment port 21 Stirring transport chamber 22 Supply transport chamber 23 Recovery transport chamber 25a Stirring transport screw (stirring transport member)
25b Supply conveyance screw (supply conveyance member)
25c Recovery conveying screw (recovery conveying member)
26a, 26b Developer passage 27 Communication portion 30 Magnetic roller (developer carrier)
31 Developing Roller 33 Toner Concentration Sensor 35 Panicle Blade 40 Rib (Decelerator)
41 Narrow pitch part (reduction part)
50 Developer discharge section 100 Color printer

Claims (7)

A developer container containing a two-component developer including a carrier and a toner, which is partitioned into an agitation transport chamber, a supply transport chamber, and a recovery transport chamber disposed substantially in parallel with each other;
A developer carrying member rotatably supported by the developing container and carrying a developer on the surface;
A supply / conveying member that is disposed in the supply / conveying chamber, stirs and conveys the developer along the axial direction of the developer-carrying member, and supplies the developer to the developer-carrying member;
An agitating and conveying member disposed in the agitating and conveying chamber and agitating and conveying the developer in a direction opposite to the supply and conveying member;
A recovery transport member disposed in the recovery transport chamber and stirring and transporting the developer recovered from the developer carrier in the same direction as the supply transport member;
A communication section for transferring the developer from the collection transfer chamber to the supply transfer chamber;
In a developing device comprising:
The recovery conveyance member is provided with a speed reduction portion whose conveyance speed is slower than other portions at at least one location upstream of the communication portion with respect to the developer conveyance direction ,
A developing device , wherein a gap is provided above a partition wall that divides the collection conveyance chamber and the supply conveyance chamber along a longitudinal direction of the collection conveyance member . The collection conveyance member includes a rotation shaft and a spiral wing formed on an outer peripheral surface of the rotation shaft, and a rib that protrudes substantially parallel to the rotation shaft is formed between the spiral wings on the speed reduction portion. the developing device according to claim 1, characterized in that it is. The collection conveyance member includes a rotation shaft and a spiral wing formed on an outer peripheral surface of the rotation shaft, and at the speed reduction portion , at least one of the pitch or the outer diameter of the spiral wing is partially reduced. The developing device according to claim 1 . The collection conveying chamber, a developing device according to any one of claims 1 to 3, characterized in that it is arranged at a position higher than the supply conveyance chamber. 5. The communication device according to claim 1, wherein the communication portion is provided on an upstream side of a developer passage that transfers the developer from the supply conveyance chamber to the agitation conveyance chamber in the developer conveyance direction. The developing device according to any one of the above. The developing device according to claim 1 , further comprising a developer discharge portion that discharges excess developer at a downstream end of the supply transfer chamber with respect to a developer transfer direction. . An image forming apparatus on which the developing device according to claim 1 is mounted .

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