JP5012403B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to a developing apparatus that visualizes an electrostatic latent image formed on a photoreceptor.

  2. Description of the Related Art Conventionally, an image forming apparatus such as an electrophotographic copying apparatus has been provided with a developing device that visualizes an electrostatic latent image formed on a photosensitive drum, and includes a toner and a carrier as the developing device. Those using a component developer are known. In this developing device, the developer whose toner has been consumed due to the completion of the developing process in the developing region is collected by a collecting member, mixed and stirred with new toner to be replenished from the toner replenishing device, and then used again for development. The The developer used here needs to maintain a constant toner concentration and charge amount in order to obtain a stable toner image. The toner density is adjusted by the amount of toner consumed by development and the amount of toner to be replenished, and the charge amount is given by frictional charging during mixing of the carrier and the toner. The developing device sufficiently stirs the two-component developer to uniformize the toner density distribution and charge the toner to stabilize the toner image.

  In a general developing device, the toner is dispersed and charged by using the stirring effect of the rotation of two screws during a short time until the replenished toner is pumped up to a developing roller as a developer carrier. Therefore, particularly when the toner balance is large, the replenished toner is pumped up to the developing roller without being sufficiently dispersed, and there is a problem that background contamination and toner scattering occur. .

  Therefore, a separate agitation unit is provided at a position away from the developing unit, and the developing unit and the agitation unit are connected by a developer circulation means, and the agitation unit performs agitation according to the state of the developer to thereby adjust the toner concentration and the charge amount. For example, “Patent Document 1”, “Patent Document 2”, and “Patent Document 3” disclose a developing device that supplies a developer with the developer adjusted appropriately to the developing unit.

Japanese Patent No. 3733496 Japanese Patent No. 3349286 JP-A-11-143196

  In each of the above-described technologies, the developer is continuously conveyed using air in the pipe, and the main components include a developer storage section, a developer supply section, a transport pipe, and an air supply source. In this configuration, the developer is transported using the air pressure (positive pressure) and the flow velocity, so that a differential pressure is generated between the air transport source and the transport destination (atmospheric pressure). Therefore, in order to transport the developer to the developing unit, it is necessary to seal the developer supplying unit so that the air from the air supply source does not leak into the developer containing unit. If air leaks, the pressure for transporting the developer will drop, and the transport amount will not be sufficient, and if the air flows back to the developer storage part (pressure is applied to the developer storage part), the developer will be stored. The developer entering the developer supply section from the section is hindered by the backflowing air, and the discharge amount decreases and varies.

  A rotary feeder is generally known as the developer supply unit. The rotary feeder has a rotor having a plurality of rotating blades and a stator that covers the rotor, and is a mechanism having excellent quantitativeness and controllability. However, if the sealing property is insufficient, the above-described air backflow occurs. As a method for ensuring the sealing performance, there is a method in which the blades of the rotor are used as elastic bodies to bite between the stators, but deterioration over time (rotation of the rotor and stator) becomes remarkable, which is not practical. In particular, since the carrier constituting the developer is iron or ferrite and has high hardness, it is difficult to obtain durability by this method.

  The present invention solves the above-mentioned problems and continuously reduces the amount of air entering the rotary feeder so that a developer having an appropriate toner concentration and charge amount is continuously developed as necessary for development. It is an object of the present invention to provide a developing device capable of stably supplying and an image forming apparatus including the developing device.

  According to the first aspect of the present invention, there is provided a developing unit that develops a latent image on a latent image carrier, a developer storage unit that is provided outside the developing unit and stores a part of the developer, and the developer storage unit. And a rotary feeder that quantitatively discharges the developer, and in the developing device that conveys the developer discharged from the rotary feeder to the developing unit by air pressure, the rotary feeder has an inflow hole through which the developer flows. All of the developer that has entered the rotor through the inflow hole, and has a discharge hole through which the developer is discharged, a rotatable rotor having a plurality of blades disposed between the inflow hole and the discharge hole. A part thereof is returned to the inflow hole side without being discharged from the discharge hole.

  According to a second aspect of the present invention, in the developing device according to the first aspect, the area of the discharge hole is smaller than the area of the inflow hole.

  According to a third aspect of the present invention, in the developing device according to the first or second aspect, the area of the discharge hole is a rectangular shape formed by the tips of two adjacent blades of the plurality of blades of the rotor. It is characterized by being formed smaller than the area.

  According to a fourth aspect of the present invention, in the developing device according to any one of the first to third aspects, each of the blades further includes a magnet at a tip portion thereof.

  A fifth aspect of the present invention is an image forming apparatus having the developing device according to any one of the first to fourth aspects.

  According to the present invention, the developer is left in the left portion of the rotor, and the remaining developer enters the clearance portion between the rotor and the stator, so that the air sealing effect works, and the air for transporting the developer is rotary. Since it is prevented from flowing into the feeder, it is possible to prevent a decrease in the developer conveyance amount due to a decrease in air pressure, reduce wasteful energy consumption, and further prevent an increase in the internal pressure of the developer storage unit. Accordingly, it is possible to prevent a decrease and variation in the amount of developer discharged from the developer storage portion.

  FIG. 1 shows an image forming apparatus employing one embodiment of the present invention. In FIG. 1, the image forming apparatus 1 has an intermediate transfer unit 5 having an intermediate transfer belt 3 and four primary transfer rollers 4 at a substantially central portion of the apparatus body 2. Image forming portions 6Y, 6M, 6C, and 6Bk corresponding to the respective colors of yellow, magenta, cyan, and black are arranged in parallel to the traveling direction of the intermediate transfer belt 3 at a position facing the lower surface of the intermediate transfer belt 3. Yes. Each of the image forming units 6Y, 6M, 6C, and 6Bk has the same structure except that the color of the toner used in the image forming process is different. The photosensitive drums 7Y, 7M, 7C, and 7Bk as latent image carriers are respectively provided. It has a charging means (not shown) disposed around the body drum 7, developing devices 8Y, 8M, 8C, and 8Bk, a cleaning means (not shown), and the like.

  The photosensitive drums 7Y, 7M, 7C, and 7Bk are rotated in the clockwise direction in the drawing by a driving unit (not shown), and the surface is uniformly charged by a charging unit (not shown), and then laser light emitted from an exposure unit (not shown). The electrostatic latent image based on the original image read by the image reading unit 9 provided on the upper part of the apparatus main body 2 is formed on the surface. The formed electrostatic latent images are developed by developing devices 8Y, 8M, 8C, and 8Bk to be visualized into desired toner images. The toner images are formed on the photosensitive drums 7Y, 7M, 7C, and 7Bk. When the surface reaches a portion facing each primary transfer roller 4 via the intermediate transfer belt 3, the primary transfer is performed on the intermediate transfer belt 3 by the action of each primary transfer roller 4.

  Each primary transfer roller 4 sandwiches the intermediate transfer belt 3 between the photosensitive drums 7Y, 7M, 7C, and 7Bk to form primary transfer nips. A transfer bias having a reverse polarity is applied. As the intermediate transfer belt 3 travels in the direction of the arrow in FIG. 1 and sequentially passes through the primary transfer nips of the primary transfer rollers 4, the toner images of the respective colors on the photosensitive drums 7Y, 7M, 7C, and 7Bk are obtained. The primary transfer is performed while being superimposed on the intermediate transfer belt 3. After the primary transfer, when the surface of the photosensitive drums 7Y, 7M, 7C, and 7Bk reaches a position facing a cleaning unit (not shown), it remains on the surface of the photosensitive drums 7Y, 7M, 7C, and 7Bk by the action of the cleaning unit. The untransferred toner thus collected is collected. After cleaning, the surface of the photoconductive drums 7Y, 7M, 7C, and 7Bk is initialized with a potential by a static eliminator (not shown), and a series of image forming processes is completed.

  Thereafter, the intermediate transfer belt 3 onto which the toner images of the respective colors are transferred in an overlapping manner reaches a position facing the secondary transfer roller 10. The color toner image formed on the intermediate transfer belt 3 is transferred onto a transfer paper P as a recording medium conveyed to the secondary transfer nip position, and a series of transfer processes is completed. A plurality of transfer sheets P are stored in a sheet feeding unit 11 disposed at the lower part of the apparatus main body 2, and the transfer sheets P are separated and fed one by one by a sheet feeding roller 12. The fed transfer paper P is temporarily stopped by the registration roller pair 13 and is fed toward the secondary transfer nip at a predetermined timing after correcting the oblique displacement. Then, a desired color image is transferred onto the transfer paper P at the secondary transfer nip position. The transfer paper P on which the color image has been transferred at the secondary transfer nip position is conveyed to the fixing device 14, and the color image transferred to the surface is fixed by heat and pressure by the heating roller and pressure roller. After the fixing, the transfer paper P is discharged and stacked on a paper discharge unit 16 formed on the upper surface of the apparatus main body by a paper discharge roller pair 15. In this way, a series of image forming processes in the image forming apparatus is completed.

  Next, the developing device which is a characteristic part of the present invention will be described. Although only the developing device 8Y will be described here, the other developing devices 8M, 8C, and 8Bk have the same configuration except that the color of the developer used is different. In this description, each member constituting the developing device 8Y will be described with the letter “Y”, which is an acronym of yellow, at the end. The other developing devices 8M, 8C, and 8Bk are replaced with “M” and “C”. , Bk characters are added.

  As shown in FIG. 2, the developing device 8Y has a casing 17Y constituting a developing device. As shown in FIG. 3, the casing 17Y has conveying screws 18Y and 19Y having spiral fins and a developing roller 20Y. And are rotatably provided. A yellow developer is accommodated in the casing 17Y, and this developer is conveyed from the front side to the rear side in FIG. 3 by the rotation of the conveyance screw 18Y, and a part of the developer is contained in the developing roller 20Y. It is sucked and attracted to the surface of the developing roller 20Y by a provided magnet (not shown). The developer adsorbed on the surface of the developing roller 20Y is made uniform by the doctor blade 21Y, and is then brought into contact with the photosensitive drum 7Y to form an electrostatic latent image formed on the photosensitive drum 7Y. To visualize. The casing 17Y, the conveying screws 18Y and 19Y, the developing roller 20Y, and the doctor blade 21Y constitute a developing unit 22Y.

  The developed developer is conveyed to a developer accommodating portion 24Y through a circulation path 23Y from a hole (not shown) provided at an end portion of the conveying screw 19Y. A toner concentration detection unit (not shown) is disposed at the most downstream position in the developer conveyance direction of the conveyance screw 19Y, and toner is supplied from the toner cartridge 25Y based on a detection signal from the toner concentration detection unit. Toner supply from the toner cartridge 25Y is performed by rotating a shaftless screw (not shown) provided in the toner supply path 27Y by the motor 26Y. The toner is replenished in the developer circulation path at a position immediately before the developer storage unit 24Y. In the developer storage unit 24Y, the developed developer and the replenished toner are mixed, and an appropriate toner concentration and charge amount are mixed. A developer having is formed.

  The developer in the developer storage unit 24 is conveyed into the rotary feeder 28Y via a discharge port disposed in the lower part of the developer storage unit 24. The developer conveyed into the rotary feeder 28Y is discharged downward by the rotation of the rotor 29Y (both see FIG. 4) provided in the stator 41Y constituting the rotary feeder 28Y, and again through the circulation path 30Y. It is supplied to the casing 17Y. An air pump 31Y is used as the developer circulating means, and the developer is conveyed by air pressure.

  As shown in FIG. 4, the developer accommodating portion 24Y includes a first space 32Y into which the developer flows first, a second space 33Y in which the screw 35Y is disposed, and a third space 34Y in which the screw 36Y is disposed. Divided into three spaces. The collected developer and newly replenished toner are lifted upward by the rotation of the screw 35Y in the second space 33Y, and at this time, the developer that is about to fall by its own weight and the development that is lifted by the screw 35Y. By rubbing against the developer, the developer is dispersed and charged. Next, the developer proceeds into the third space 34Y through the opening 37Y, is conveyed downward by the rotation of the screw 36Y, and enters the rotary feeder 28Y. In the figure, reference numeral 38Y denotes a motor for driving the screws 35Y and 36Y, and the rotational driving force from the motor 38Y is transmitted to the screws 35Y and 36Y via the gears 39Y and 40Y.

  As shown in FIG. 5, the rotary feeder 28Y has a clearance of about 0.01 mm to 0.2 mm between the tip of the blade of the rotor 29Y and the inner wall of the stator 41Y. As described in the section “Problems to be Solved by the Invention”, if there is a gap between the rotor 29Y and the stator 41Y, a part of the air sent from the air pump 31Y passes through this gap and enters the rotary feeder 28Y. The air pressure for transporting the developer decreases. On the other hand, since the developer appropriately enters the clearance portion between the two, it is possible to reduce the inflow of air by optimizing the size of the clearance.

  However, even when the clearance is miniaturized, the rotor 29Y after the developer is discharged downward is almost empty as shown in FIG. 5 (the left half of FIG. 5), and therefore enters the clearance portion. Therefore, the amount of the developing agent or the developer existing near the tip of the blade of the rotor 29Y becomes extremely small, and the effect of preventing the inflow of air into the rotary feeder 28Y is reduced.

  Therefore, in the present invention, as shown in FIG. 6, the developer in the rotor 29Y does not fall down and remains in the left half of the figure, so that the developer is present in the clearance portion to seal the air. It is configured to work. In order to leave the developer in the left half of the stator 41Y, specifically, the area of the developer discharge hole 42Y (hole diameter φC) provided on the lower side of the stator 41Y is set to the upper side of the stator 41Y. It is configured to be smaller than the area (diameter φD of the hole) of the inflow hole 43Y provided in (see FIG. 7C).

  With the above configuration, since the amount of developer discharged from the rotary feeder 28Y is smaller than the amount of developer flowing into the rotary feeder 28Y, the developer remains on the left side portion of the rotor 29Y as shown in FIG. Since the remaining developer enters the clearance portion between the rotor 29Y and the stator 41Y, an air sealing effect works and air for conveying the developer is prevented from flowing into the rotary feeder 28Y. It is possible to prevent a decrease in the developer conveyance amount due to the decrease, reduce wasteful energy consumption, and further prevent an increase in the internal pressure of the developer storage unit 24Y to discharge the developer from the developer storage unit 24Y. Can be prevented from decreasing and varying.

  In the above-described configuration, as shown in FIG. 7, the area of the discharge hole 42Y, that is, a rectangular area A × B formed by the tips of two adjacent blades of the rotor 29Y is set to a value of C × C × π / 4. It is good also as a structure made smaller than this value. With this configuration, even if the developer filled in the rotor 29Y reaches a position corresponding to the discharge hole 42Y, it does not fall down, and the developer can be left in the left portion of the rotor 29Y. As a method of leaving the developer on the left side portion of the rotor 29Y, the rotor 29Y having the developer passes through the discharge hole 42Y before all the developer falls from the discharge hole 42Y by increasing the rotational speed of the rotor 29Y. A method may be adopted.

  In the above embodiment, as shown in FIG. 8, a configuration in which the magnet 44Y is arranged at the tip of each blade of the rotor 29Y may be adopted. With this configuration, the developer remaining in the rotor 29Y is attracted by the magnetic force of the magnet 44Y, the developer stays at the tip of the blade, and the air sealing effect can be made to act reliably.

  In each of the above-described embodiments, an example in which a tandem type electrophotographic color copying apparatus is used as an image forming apparatus has been described. However, an image forming apparatus to which the present invention can be applied is not limited to this, and a printer, a facsimile, a plotter, The present invention is also applicable to other image forming apparatuses such as a multi-function machine that combines these.

1 is a schematic front view of a main part of an image forming apparatus employing an embodiment of the present invention. 1 is a schematic perspective view of a developing device adopting an embodiment of the present invention. It is the schematic of the image development part used for one Embodiment of this invention. FIG. 3 is a schematic view of a developer storage unit and a rotary feeder used in an embodiment of the present invention. It is the schematic explaining the behavior of the developer in the conventional rotary feeder. It is the schematic explaining the behavior of the developer in the rotary feeder in one Embodiment of this invention. It is the schematic explaining the dimension of the rotary feeder used for one Embodiment of this invention. It is the schematic explaining the behavior of the developer in the rotary feeder in other embodiment of this invention.

Explanation of symbols

1 Image forming device 7 Latent image carrier (photosensitive drum)
8 Developing Device 22 Developing Section 24 Developer Storage Section 28 Rotary Feeder 29 Rotor 42 Discharge Hole 43 Inflow Hole 44 Magnet

Claims (5)

A developing unit that develops the latent image on the latent image carrier, a developer storage unit that is provided outside the developing unit and stores a part of the developer, and quantitatively discharges the developer in the developer storage unit. A developing device that conveys the developer discharged from the rotary feeder to the developing unit by air pressure,
The rotary feeder has an inflow hole into which developer flows, a discharge hole through which developer is discharged, and a rotatable rotor having a plurality of blades disposed between the inflow hole and the discharge hole, A developing device characterized in that a part of the developer that has entered the rotor from the inflow hole is returned to the inflow hole side without being discharged from the discharge hole. The developing device according to claim 1,
The developing device according to claim 1, wherein an area of the discharge hole is smaller than an area of the inflow hole. The developing device according to claim 1 or 2,
2. The developing device according to claim 1, wherein an area of the discharge hole is smaller than a rectangular area formed by tips of two adjacent blades of the plurality of blades of the rotor. The developing device according to any one of claims 1 to 3,
Each of the blades has a magnet at the tip thereof.   An image forming apparatus comprising the developing device according to claim 1.

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