JP5743570B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, and a developing device provided in the image forming apparatus.

  As a developing device used in a conventional image forming apparatus such as a copying machine, a printer, or a facsimile machine, a device using a magnetic brush developing method in which development is performed using a two-component developer as described in Patent Document 1 is used. is there.

  In the magnetic brush developing method, only toner particles are consumed for image formation, while the carrier particles are worn while circulating in the developing device. Therefore, a mechanism is provided for discharging a part of the developer as the developing device is driven and supplying a replenisher in which a carrier is mixed with toner at a predetermined ratio. Accordingly, it is possible to suppress the degree of wear of the carrier staying in the developing device within a certain range while supplementing the toner consumed with the image formation.

  In such a developer replenishment and discharge mechanism (auto carrier refresh mechanism: ACR), replenishment is usually performed as follows. That is, the toner / sensor carrier ratio is detected by a toner density sensor provided in the developing device, and the replenishment amount is adjusted so that the detection result becomes a desired mixture ratio. Usually, since the toner mixing ratio of the replenisher is larger than the toner mixing ratio of the developer in the developing device, the toner mixing ratio in the developing device increases with replenishment.

  On the other hand, from the viewpoint of the simplicity of the mechanism, as disclosed in Patent Document 2, a hole (discharge port) is simply provided at a predetermined position in the developing device, and the developer whose volume increases with replenishment overflows from there. The technique to make is common. If the bulk density of the developer is constant, this mechanism serves to determine the upper limit of the developer amount in the developing device, while the toner mixing ratio does not change if the developer is sufficiently stirred. Therefore, it is easy to assume the behavior.

  In Patent Document 3, a discharge port is provided at a position adjacent to the upstream side in the developer transport direction of the supply port for supplying the supply agent. This prevents the replenisher from being discharged from the discharge port when the toner mixing ratio is unstable due to insufficient agitation.

JP 59-15082 A Japanese Patent Publication No. 2-21591 Japanese Patent Laid-Open No. 10-186855

  It is desirable that the total amount of the developer staying in the developing device as shown in Patent Documents 1 to 3 is constant or at least within a predetermined range. If there is too much developer, it will cause overflow from the developing device with the change in the fluidity of the developer. On the other hand, when the amount of the developer is too small, a sufficient amount of developer is not supplied over the entire image area of the developing sleeve, and a part of the output image is lost. Therefore, it is ideal that the developer amount is not discharged at all until the developer amount reaches a constant value, and only the amount exceeding the threshold value is quickly discharged when the developer amount exceeds the threshold value.

  In reality, however, the developer discharge amount cannot be controlled well due to changes in the developer's bulk density and fluidity due to changes in developer wear, ambient temperature, and humidity. Further, when the atmospheric pressure in the developing device becomes negative with respect to the outside, an air flow that draws air in the vicinity of the discharge port into the developing device is generated, making it difficult to discharge the developer.

  Here, the positional relationship between the toner discharge port and the supply port of the developing device is such that the supplied toner is sufficiently agitated and discharged. The replenishment agent replenished from the replenishing port is conveyed to the developer circulation path by a conveying unit provided outside the developer circulation path before joining the developer circulation path in the developing device. That is, there is a transport means provided for transporting only the replenisher that has not yet been mixed with the developer circulating in the developing device.

  In such a system, when the replenishing port is completely sealed, the air near the replenishing port is sucked by the above-mentioned conveying means, and the vicinity of the junction with the developer circulation path becomes negative pressure. On the other hand, such a situation cannot occur if the supply port is open. As described above, the air pressure in the developing device depends on the airtightness of the supply port.

  When the vicinity of the joining point with the developer circulation path becomes negative pressure, the developer existing on the upstream side is drawn in the downstream direction. Usually, the discharge port is disposed upstream of the supply port in order to prevent the supply agent from being discharged without being stirred. For this reason, when the negative pressure is reached, the developer present in the vicinity of the discharge port is drawn in, and the discharge of the developer is hindered.

  Thus, the ease with which the developer is discharged varies depending on the airtightness of the supply port. Therefore, in order to keep the developer amount in the developing device stable, it is necessary to keep the airtightness of the replenishing port constant. Usually, the replenishing port is appropriately sealed so that the replenishing agent does not leak from the gap. However, since the developing device is detachable, it is difficult to maintain perfect airtightness, and the degree of sealing of the replenishing port varies depending on slight variation in the mounting position of the developing device. This produces variations in the ease with which the developer is discharged, produces variations in the amount of developer staying in the developing device, and leads to an image failure due to overflow of the developer or insufficient supply of the developer.

  Therefore, the present invention makes the developer replenishment port airtight by keeping constant the ease of discharging the developer, stabilizing the amount of developer staying in the developing device, and preventing the developer from overflowing. An object of the present invention is to provide a developing device and an image forming apparatus capable of suppressing image defects due to insufficient supply of developer.

In order to solve the above problems, a typical configuration of a developing device and an image forming apparatus according to the present invention is such that a developer carrying member carrying a developer, and the developer carrying member are opposed to each other so that the developer can be circulated. A first chamber and a second chamber that communicate with each other; a first developer transport member that is rotatably provided in the first chamber and transports the developer in the first chamber to the second chamber; and the second chamber. A second developer conveying member that is rotatably provided and conveys the developer in the second chamber to the first chamber; a replenishing port that is provided outside the developer circulation path and replenishes a new developer; A replenishment transport unit that is rotatably provided coaxially with the second developer transport member, transports the developer from the replenishment port to the second chamber, and the replenishment transport unit is disposed inside, Provided in the replenishment path for replenishment and in the developer circulation path of the first chamber, the excess developer is discharged. Wherein a discharge port, a developer circulation path out of the first chamber, the downstream side of the developer carrying direction than the discharge port, or to have a vent hole formed in the supply path to And

  According to the present invention, by making the developer replenishing port airtight, the developer can be easily discharged, the developer amount staying in the developing device is stabilized, and the developer overflows. And image defects due to insufficient supply of developer can be suppressed.

1A is a configuration diagram of an image forming apparatus according to a first embodiment. FIG. FIG. 2B is a configuration diagram of the developing device according to the first embodiment. (A) It is sectional drawing of the longitudinal direction of the developing device which concerns on 1st Embodiment. (B) A diagram expressing the flow of the developer according to the first embodiment. FIG. 5 is a diagram illustrating a relationship between a total developer amount and a developer discharge amount according to the first embodiment. It is sectional drawing of the longitudinal direction of the developing device which concerns on 2nd Embodiment. It is a block diagram of the conventional developing device.

[First embodiment]
A developing device and an image forming apparatus according to a first embodiment of the invention will be described with reference to the drawings. FIG. 1A is a configuration diagram of an image forming apparatus according to the present embodiment. As shown in FIG. 1A, in the image forming apparatus of this embodiment, the surface of a photosensitive drum (image carrier) 100 is uniformly charged by a primary charger 101, and image information is output by a laser exposure machine (not shown). By performing image exposure according to the above, an electrostatic latent image is formed on the surface of the photosensitive drum 100.

  The formed electrostatic latent image is developed as a toner image by the developing device 102 using a two-component developer containing a magnetic carrier and a non-magnetic toner. The developed toner image is transferred by the transfer roller 103 to the transfer material 110 conveyed to the transfer unit. The transfer material 110 onto which the toner image has been transferred is fixed to the toner image by the fixing device 105 and then discharged outside the apparatus main body. After the toner image is transferred, the transfer residual toner remaining on the photosensitive drum 100 is removed by the cleaner 104 and used for the next image formation.

(Developing device 102)
As shown in FIGS. 1B and 2A, the developing device 102 includes a developing container 200, a developing sleeve (developer carrying member) 201, a mag roll (magnetic field generating means) 202, a regulating blade (developer regulating means). ) 203 and screws (developer conveying members) 204 and 205. Further, the developing device 102 has a supply port 206, a discharge port 207, and a vent hole 208.

  The developing container 200 contains a two-component developer t composed of toner and carrier. The developing sleeve 201 is rotatably provided in the arrow b direction at a position facing the photosensitive drum 100 of the developing container. The mag roll 202 is installed inside the developing sleeve 201. The surface of the developing sleeve 201 rotates along the outer periphery of the mag roll 202. The regulating blade 203 is arranged so that the closest contact point is located at a predetermined distance from the developing sleeve 201.

  The screws 204 and 205 are disposed inside the developing device 102 and circulate the two-component developer t between the stirring chamber and the developing chamber. The two-component developer t spiked by the magnetic force of the mag roll 202 in the developing unit comes into contact with the surface of the photosensitive drum 100, and only the toner is formed on the surface of the photosensitive drum 100 by the developing bias applied to the developing sleeve 201. Transfers to an electrostatic latent image to form a toner image.

  The two-component developer t remaining on the developing sleeve 201 after development passes through the developing unit as the developing sleeve 201 rotates, is returned to the developing container, and is peeled off from the surface of the developing sleeve 201 by receiving a magnetic repulsive force. . Then, it is conveyed by a screw 205 provided below the developing sleeve 201 and transferred to the screw 204.

  The replenishment agent is replenished from the replenishing port 206, and the toner consumed in the developing process is replenished. The replenisher is a mixture of toner and carrier so that the weight ratio is 9: 1, and is filled in a hopper (not shown) connected to the replenishment port 206.

  The average magnetic permeability of the developer is detected by a magnetic permeability sensor (not shown) provided in the developing container 200, and the weight ratio of the toner occupying the developer is calculated from the detected value. When the value is less than 8%, replenishment is performed. I do. Replenishment is performed by transferring a replenisher in the hopper to the replenishing port 206 by rotating a screw provided inside the hopper. The replenishing agent replenished from the replenishing port 206 is conveyed by a replenishing agent conveying unit 209 that only plays a role of conveying the replenishing agent in the screw 205, and enters a circulation path of another developer circulating in the developing container 200. Join. The replenishment agent transport unit 209 is below the replenishment port 206 in the vertical direction and is outside the circulation path of other circulating developer.

  Since the replenishment agent includes a carrier, the total amount of developer increases even if replenishment is performed to supplement the consumed toner. For this reason, the powder level of the developer rises, and when the developer reaches the lower end of the discharge port 207, the developer is discharged out of the developing container 200 through the discharge port 207. The discharge port 207 is provided on the downstream side in the developer conveying direction by the screw 204 in the developing chamber and above the developing chamber.

  The developer discharged from the discharge port 207 is discarded into a waste toner box (not shown) through a discharge path (not shown). As a result, it is possible to prevent the developer from overflowing from a gap between the developing sleeves 201 due to an excessive increase in the developer amount.

(Vent hole 208)
The vent hole 208 is provided vertically above the opening 210 for transferring the developer from the screw 204 to the screw 205 and downstream of the discharge port 207 and the opening 210 in the developer conveying direction by the screw 204. Yes. The vent hole 208 is provided outside the developer circulation path constituted by the screws 204 and 205. Therefore, the developer does not reach the position of the vent hole 208, and the developer does not overflow from the vent hole 208. The vent hole 208 allows the inside and the outside of the developing container 200 to communicate with each other.

  As shown in FIG. 5, the conventional developing device is not provided with the vent hole 208. For this reason, due to variations in the mounting position of the developing device, the airtightness at the joint between the replenishing port 206 and a hopper (not shown) connected thereto becomes unstable. Then, the airflow near the discharge port 207 is disturbed, and the developer is sucked into the discharge port 207.

  Specifically, when the screw 205 is driven, the air around the replenisher transport unit 209 is sucked toward the downstream side in the replenisher transport direction by the replenisher transport unit 209 of the screw 205. Then, in order to compensate for the air around the replenisher transport unit 209 that has become negative pressure, the air near the discharge port 207 located on the upstream side in the developer transport direction is sucked in the direction toward the replenisher transport unit 209.

  As a result, an air flow is generated such that the developer to be discharged from the discharge port 207 is pulled back into the developing container 200, and the discharge of the developer is hindered. The degree of this inhibition depends on the atmospheric pressure around the replenisher transport unit 209, and the atmospheric pressure depends on the airtightness in the vicinity of the unstable replenishment port 206.

  As shown in FIG. 2A, the developing device 102 of the present embodiment has a vent hole 208 in the vicinity of the discharge port 207. For this reason, when the pressure around the replenisher transport unit 209 becomes negative, the air drawn from the upstream side in the developer transport direction to compensate for the negative pressure is positively applied from the outside of the developing container 200 through the vent hole 208 communicating with the replenishment port 206. Supplied. For this reason, the effect of drawing air from the discharge port 207 may still remain, but at least the airflow generated in the vicinity of the discharge port 207 is reduced by the influence of the air holes 208, and the instability of the developer discharge amount is greatly improved. . That is, the air hole 208 stabilizes the developer discharge amount by adjusting the airflow in the vicinity of the discharge port 207.

  As can be seen from the comparison between FIG. 2A and FIG. 5, in this embodiment, the developing container 200 is expanded by the space for providing the vent hole 208. This is to establish the positional relationship between the supply port 206, the discharge port 207, and the vent hole 208 as described above. That is, if the vent hole 208 exists outside the developer circulation path and is provided at a position communicating with the replenishing port 206, the developing container 200 does not necessarily need to be expanded.

  FIG. 2B is a diagram expressing the flow of the developer in the present embodiment. A straight line in FIG. 2B represents a path having a conveyance capability, and a wavy line represents a path that does not have a conveyance capability but communicates. Of the straight lines, a solid line represents a developer circulation path, and a dotted line represents a replenisher passage path through which only the replenisher passes. The present invention is not limited to the configuration of the present embodiment, and may be any developing device or image forming apparatus that embodies the diagram of FIG.

(Amount of developer staying in developer container 200)
As described above, the developing device 102 according to the present embodiment is provided with the air holes 208 so that the air tightness of the replenishing port 206 is made constant, the ease of discharging the developer is kept constant, and the developer stays in the developing container 200. The amount of developer (total amount of developer) is stabilized.

  The total amount of developer is determined by the amount of developer discharged from the discharge port 207 and the amount of toner consumed for image formation. The developer discharge amount depends on the developer total amount itself, and the developer discharge amount per unit time increases as the developer total amount increases. The amount of toner consumed depends on the output image.

  In the present embodiment, the developer is replenished so that the same amount of toner as the amount of consumed toner is supplemented. Here, since the replenisher contains a carrier in addition to the toner, the total amount of developer increases by the amount of the carrier as replenishment is performed. When the solid image is continuously output, the replenishment is performed with the maximum efficiency, and the total amount of the developer gradually approaches the maximum value. On the other hand, when the white solid image is continuously output, the supply is hardly performed, and the total amount of the developer gradually approaches the minimum value. In addition, in order to discharge the deteriorated toner, even when white solid images are continuously output, the toner is consumed to the same extent as when a solid image is assumed to be formed in an area where the area ratio of the image area is 1%. It has come to be.

  In the present embodiment, “the total developer amount so that the developer discharge amount per unit time is 0.05 g / s” is the maximum value of the total developer amount. Further, “the total developer amount so that the developer discharge amount per unit time is 0.0005 g / s” is the minimum value of the total developer amount.

(Experiment for quantifying fluctuations in total developer amount)
FIG. 3 is a diagram illustrating the relationship between the total developer amount and the developer discharge amount. In FIG. 3, when the vent hole 208 is not provided as in the conventional developing device, the case where the supply port 206 is sealed is shown as (A), and the case where the supply port 206 is opened is shown as (B). On the other hand, in the case where the vent hole 208 is provided as in the developing device 102 of this embodiment, the case where the supply port 206 is sealed is (C), and the case where the supply port 206 is opened is (D). For each of (A) to (D), the horizontal axis is the total developer amount, and the vertical axis is the developer discharge amount per second. The variation in the total amount of developer was defined as the difference between the maximum value and the minimum value described above.

  As shown in FIGS. 3A and 3B, when the vent hole 208 is not provided, the relationship between the total developer amount and the developer discharge amount differs greatly depending on the sealing property of the replenishing port 206. In this case, the upper limit and the lower limit of the total amount of developer are 400 g and 200 g, respectively, with a variation of twice. When the total amount of developer is 400 g, the developer overflows from the developing container 200. On the other hand, when the total amount of developer was 200 g, the developer supply was insufficient and the output image was missing.

  On the other hand, as shown in FIGS. 3C and 3D, when the vent hole 208 is provided, the relationship is almost constant regardless of the sealing property of the supply port 206. In this case, the upper limit and the lower limit of the total developer amount are 320 g and 280 g, respectively. That is, by providing the vent hole 208, the fluctuation range of the total developer amount is 280 g to 320 g, and the total developer amount can be stabilized. Thereby, it is possible to avoid image defects due to overflow of the developer and insufficient supply of the developer.

[Second Embodiment]
Next, a second embodiment of the developing device and the image forming apparatus according to the present invention will be described with reference to the drawings. The same parts as those in the first embodiment will be denoted by the same reference numerals and the description thereof will be omitted. FIG. 4 is a longitudinal sectional view of the developing device 102 according to this embodiment.

  As shown in FIG. 4, the developing device 102 of the present embodiment is obtained by providing a developer returning screw (developer returning member) 701 in the developing device 102 of the first embodiment. The developer return screw 701 is provided in a path that branches from the developer circulation path to the vent hole 208 and rotates to push the developer back to the developer circulation path side. This prevents the developer from overflowing from the vent hole 208.

  Thereby, for example, when the developer reaches the vent hole 208 side without being transferred from the opening 210 to the screw 205 due to a change in the fluidity of the developer accompanying a change in the atmospheric temperature or humidity. However, the developer is pushed back toward the opening 210 again by the action of the developer return screw 701 and returns to the developer circulation path.

t ... two-component developer 100 ... photosensitive drum (image carrier)
DESCRIPTION OF SYMBOLS 101 ... Primary charger 102 ... Developing device 103 ... Transfer roller 104 ... Cleaner 105 ... Fixing device 110 ... Transfer material 200 ... Developing container 201 ... Developing sleeve 202 ... Mag roll 203 ... Restricting blades 204, 205 ... Screw (developer conveying member)
206 ... supply port 207 ... discharge port 208 ... vent hole 209 ... replenisher transport unit 210 ... opening 701 ... developer return screw (developer return member)

Claims (4)

A developer carrying member carrying the developer;
A first chamber and a second chamber facing the developer carrier and communicating with the developer in a circulatory manner;
A first developer transport member rotatably provided in the first chamber and transporting the developer in the first chamber to the second chamber;
A second developer transport member rotatably provided in the second chamber and transporting the developer in the second chamber to the first chamber;
A replenishment port provided outside the developer circulation path for replenishing a new developer;
A replenishment transport unit that is rotatably provided coaxially with the second developer transport member, and transports the developer from the replenishment port to the second chamber;
A replenishment path for replenishing the developer, wherein the replenishment transport unit is disposed inside;
A discharge port provided in the developer circulation path of the first chamber for discharging excess developer;
A vent hole formed outside the developer circulation path of the first chamber and downstream of the discharge port in the developer transport direction, or in the supply path;
A developing device comprising:   The developing device according to claim 1, wherein the vent hole is provided in the vicinity of the discharge port. 3. The developing device according to claim 1, further comprising a developer returning member that is disposed outside the developer circulation path and that pushes the developer back into the developing device from the air hole. An image carrier for carrying an electrostatic latent image;
An image forming apparatus, comprising a developing device according to any one of claims 1 to 3 develop the electrostatic latent image formed on said image bearing member.

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