JP2008299105A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device having a stirring section that is small, has less stress on developer and excels in view of an amount of conveyance and a charging amount, and to provide an image forming apparatus. <P>SOLUTION: The developing device includes: a developing means 10 for developing a latent image on an image carrier by using two-component developer; a stirring section 30 disposed separately from the developing means 10 and used for stirring developer and toner; and a circulation means for circulating the developer between the developing means 10 and stirring section 30. The stirring section 30 has a hollow stir cell 31 and a plurality of stirring vanes 32 fixed to the inside of the container 30, and stirs the developer and toner by rotating while keeping the axis of the stir cell 31 horizontal. Openings are made in both the ends of the stir cell 31 in the axial direction. Developer is supplied from one of the openings and the developer mixed with toner is discharged from the other opening. The number of revolutions of the stir cell 31 is changed during stirring. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a developing device and an image forming apparatus.

  In many printers, copiers, facsimiles, and image forming apparatuses having at least two functions, a two-component developing system is adopted as an apparatus for developing an electrostatic latent image formed on a photoreceptor. A developing device using this two-component developing system generally has a configuration in which the developer is stirred and conveyed by rotating two horizontally arranged screws.

  However, a device that stirs and conveys the developer by rotating these two screws cannot sufficiently stir the developer, and most of the charge imparted to the developer is slid at the doctor section. Depends on rubbing. As a result, the developer deterioration such as the embedding of the additive in the toner and the scraping of the carrier film has become a problem by applying a strong stress on the doctor portion to the developer.

  In view of this, development devices aimed at reducing stress in the doctor section have been studied. However, if the stress at the doctor portion is reduced, charging to the developer is not sufficiently performed, and uncharged toner is conveyed to the development area, and toner scattering and background contamination are likely to occur. In order to solve this, the developer charged sufficiently by the stirring unit may be supplied to the developing roller.

Japanese Patent No. 3349286 JP 2005-262156 A

  For example, as described in Patent Document 1, there is a method in which a developing unit and a stirring unit are separately provided, and a developer whose toner density and charge amount are appropriately controlled by the stirring unit is conveyed to the developing unit by a circulation unit. is there. With this configuration, the stress of the doctor portion can be reduced and sufficient charge can be imparted to the toner. However, there is a concern about the increase in stress due to the newly added stirring portion.

As a developer agitation method with less stress, there is a container rotation type agitation method in which agitation is performed by rotating a container provided with a stirring blade inside.
In the container rotation type stirring device, the conveyance amount increases as the rotation speed increases. However, when the critical rotational speed (centrifugal force acting on the agent = rotational speed at which gravity is applied) is exceeded, the transport amount rapidly decreases and becomes zero. Therefore, it is used at a relatively low rotational speed. For example, in patent document 2, it drives with the rotation speed of 0.5 to 5 rpm. Since the rotation is slow in this way, there has been a problem that the amount of conveyance is small for the size of the container when the input is continuously stirred and discharged.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device and an image forming apparatus having a stirring unit that solves the above-described conventional problems, is small in size, has little stress on the developer, and is excellent in both conveyance amount and charge amount. To do.

  In order to achieve the above object, the present invention provides a developing unit that develops a latent image on an image carrier using a two-component developer, and a stirring unit that is arranged separately from the developing unit and that stirs the developer and toner. And a developing device that circulates the developer between the developing unit and the stirring unit, the stirring unit includes a hollow stirring container and a plurality of stirring members fixed inside the container. An apparatus for performing stirring by rotating the axis of the stirring vessel horizontally, having openings at both ends in the axial direction of the stirring vessel, and supplying developer from one of the openings. The developing device is configured to discharge the mixed developer from the other opening, and changes the rotation speed of the stirring container during stirring.

In the present invention, it is effective to change the angular acceleration of the stirring container while stirring.
Furthermore, the present invention is effective when a developer accommodating portion that is provided in the vicinity of the discharge portion of the stirring portion and temporarily stores the developer discharged from the stirring portion is provided.

  Furthermore, the present invention is effective if the gravity acting on the developer is reduced to a rotational speed that is greater than the centrifugal force acting on the developer at least once during the rotation of the stirring container.

  Furthermore, in the present invention, when the stirring vessel is stirred at a rotational speed at which the centrifugal force acting on the developer is larger than the gravity acting on the developer, it is effective to temporarily stop the rotation when the stirring vessel is rotated halfway. It is.

Furthermore, the present invention is effective when the rotation stop time of the stirring vessel is √ (4 r / g), where rcm is the rotation radius of the stirring vessel and g is the acceleration of gravity.
Furthermore, the present invention is effective when the stirring member is a coil.

Furthermore, the present invention is effective when the stirring member is a wing having an angle.
Furthermore, the present invention is effective when a screw for forcibly feeding the agent is provided on the inlet side of the stirring unit.

Furthermore, the present invention is effective when the inner wall of the stirring vessel is formed of a charge imparting member.
In order to achieve the above object, the present invention proposes an image forming apparatus using the developing device according to any one of claims 1 to 10.

  According to the present invention, the amount of conveyance can be ensured by intermittently performing the stirring operation at a rotational speed equal to or higher than the critical rotational speed, which contributes to downsizing of the stirring apparatus. Further, a developer having a high charge amount can be obtained.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a perspective view showing the overall structure of the developing device of the present invention.
In FIG. 1, reference numeral 1 denotes a photosensitive drum as an image carrier, and an electrostatic latent image is formed on the surface by a charger and an optical writing device (not shown). Reference numeral 10 denotes a developing means, and as shown in FIG. 2, the developing means 10 is disposed so as to face the photosensitive drum 1 and a developing case 11 containing a dry two-component developer D having toner and a carrier. The developing roller 12 that rotates, the screws 13 and 14 that convey the developer D while stirring, and the developing roller 13 are sucked and adsorbed by the magnetic force, and the doctor blade 15 uniforms the thickness uniformly. The toner image is formed by developing the electrostatic latent image on the photosensitive member with toner by contacting the photosensitive member.
Further, reference numeral 20 in FIG. 1 denotes a circulation forward path as a developer discharge path, and discharges the developer circulating inside the developing device toward an external stirring unit 30. The agitating unit 30 agitates the developer and the toner and adjusts them to an appropriate charge amount and toner density. The adjusted developer is conveyed again to the developing means 10 via a circulation return path 21 as a developer circulation path.
The stirring unit 30 is configured as a unit separate from the developing unit 10 and is disposed at a different position, and has a function of adjusting the toner density and the charge amount of the developer to be constant. Further, immediately before the agitating part of the circulation path 20, a toner cartridge 16 for replenishing new toner is connected to the agitating part 30 via the toner replenishing path 17.

  As shown in FIG. 3, the stirring unit 30 is a cylindrical stirring container 31 provided with a plurality of stirring blades 32 as stirring members inside, and has a rotating shaft 40 whose axis is in the horizontal direction. 41 is supported on both sides. The base 41 is provided with a motor 42 for rotating the stirring container. The motor 42 and the stirring vessel 31 are drivingly connected via a gear 43, and the rotation speed of the motor 42 can be arbitrarily adjusted. An inlet opening 33 and an outlet opening 34 are provided at both ends of the stirring container 31, and developer and toner are replenished from the inlet opening 33, and the toner density and charge amount are optimized by stirring from the outlet opening 34. Developer is discharged.

  Note that a screw 35 is installed in the inlet opening 33 of the stirring unit 30 so that the developer and toner are forcibly fed into the stirring unit 30 using the screw. Since the amount of the developer that can be taken in by the rotating operation of the stirring unit 30 is small, the supply amount can be increased by forcibly taking in as described above, and the size of the stirring unit 30 can be reduced.

  The circulation path 20 connected from the developing means 10 to the stirring unit 30 utilizes free fall due to gravity. The circulation path 20 is a hollow pipe, and the developer after development is automatically sent to the agitation unit 30 and taken into the interior by the screw 35 through the inlet opening 33. A circulation return path 21 from the stirring unit 30 to the developing unit 10 conveys the developer to the developing unit 10 by an auger. In addition, the conveyance with an air pump, a powder pump, etc. can be utilized instead of an auger.

  On the outlet side of the stirring unit 30, a developer storage unit 44 that temporarily stores the developer discharged from the stirring unit is provided. By providing the developer storage unit 44, the developer unit 10 is always fixed to the developing unit 10. An amount of developer can be delivered. That is, when the developer accommodating portion 44 is provided, even when the discharge amount from the stirring portion 30 fluctuates, the fluctuation can be absorbed, so that a constant amount of developer can always be supplied to the developing means 10. Moreover, the developer immediately after being discharged from the agitating unit 30 contains air, and the density is not constant. However, when such a developer containing unit 44 is provided, the developer containing air also becomes a developer containing unit 44. Since the bulk is reduced while staying inside, there is an effect of calming the bulk density of the developer.

  If image formation is repeated, there is a possibility that the developer in the developer accommodating portion 44 is emptied. In this case, the image formation is temporarily stopped, and only the developer is circulated and the developer is stored in the buffer. Thereafter, image formation is started again after confirming that it has accumulated to some extent in the developer container 44. Normally, control may be performed so that only the developer is circulated while the image is not formed and the developer is stored in the buffer.

  A toner concentration detection member 22 is provided at one end of the circulation forward path 20 for conveying the developer from the developing means 10 to the stirring unit 30 and detects the toner concentration of the developer after development. An appropriate amount of new toner is supplied from the toner cartridge 16 via the toner supply path 17 in accordance with the detected toner density. By adjusting the number of revolutions of the stirring unit according to the replenishment amount, a developer having an appropriate charge amount of toner density can be supplied to the developing unit.

In the stirring unit 30 shown in FIG. 3, the shape of a plurality of stirring blades 32 provided on the inner wall of the stirring container 31 is coiled. Thus, in the case of the coil-shaped stirring blade 32, the ability to move the developer up and down is low, but the transport amount of the developer is stabilized.
4 (a), 4 (b), and 4 (c), the stirring unit 60 according to another embodiment of the present invention has four angles on the inner wall of the stirring vessel 61 that rotates with the axis line in the horizontal direction. A stirring member composed of twisted stirring blades 62a to 62d is provided. The four stirring blades 62a to 62d are twisted and attached to positions rotated 90 degrees in the same direction on the inlet side and the outlet side.

  In the case of the stirring unit 60 that twists the plate as the stirring blades 62a to 62d in this way, the developer is placed on the blades as it rotates, is lifted up to the top of the container, and repeats the movement of dropping. FIGS. 5A, 5B, and 5C are diagrams illustrating the movement of the developer D when the stirring unit 60 rotates. As the stirring unit 60 rotates, the entire developer D inside is slowly lifted and then dropped. By this movement, the developer D and the toner are mixed.

  The direction in which the developer slides down can be changed by adjusting the angles of the stirring blades 62a to 62d. When the angle is small, the distance transported by one rotation becomes long, so that the agitation performance decreases. On the other hand, if the angle is increased, the agitation is high because the distance conveyed by one rotation is small. Therefore, the angle may be determined based on the necessary conveyance amount and stirring ability.

The twist angle of the stirring blade 62 is suitably 30 degrees to 90 degrees.
3 and FIG. 4 is preferably composed of a charge imparting member, it is desirable that the toner can be imparted with charge by friction between the inner wall of the container and the developer during rotation.

In the present embodiment, the stirring method for rotating the entire container has a rotation speed of stirring of 300 rpm or less, and is slower than a screw.
Therefore, this is a stirring method in which the stress on the developer due to the collision between the developers at the time of stirring is small and the developer is hardly deteriorated. Therefore, there is an advantage that there is almost no increase in stress due to the newly provided stirring section.

  In such a container rotating type stirring device, the transport amount and the charge amount depend on the number of rotations. The faster the rotation, the greater the centrifugal force acting on the internal developer, and the higher the developer is lifted. Therefore, the larger the number of revolutions, the more the developer moves inside and the greater the triboelectric charge.

  The carry amount increases as the rotation speed increases. However, when the critical rotational speed (centrifugal force acting on the agent = rotational speed at which gravity is applied) is exceeded, the centrifugal force causes the agent to stick to the stirring vessel, and the conveyance amount rapidly decreases to zero in the worst case. In order to avoid the influence of centrifugal force, it is sufficient to control at a relatively low rotational speed, but there is a drawback that there are many gaps and the conveyance amount is small for the size of the container. Further, when the rotational speed is low, mixing is sufficiently performed, but there may be a case where a charge amount necessary for development cannot be secured.

Therefore, the inventors examined from experimental results and the like, and when stirring at a rotational speed higher than the critical rotational speed, by carrying out the rotation discontinuously, the transport amount does not decrease so much and an agent with a high charge amount can be obtained. It has been found. The critical rotational speed is the centrifugal force acting on the agent = gravity. At this time, the balance of the force acting on the agent is mr (2πN / 60) ^ 2 = mg to N = 10 ^ 4√ (1118 × r) rpm. It is.
Here, r is the rotation radius (cm) of the stirring container, m is the mass of the developer, and Ng is the number of rotations per minute.

  N is a coastal rotation number indicating whether or not the developer can be discharged from the stirring vessel, and the developer is discharged when the developer is rotated below this rotation number. Therefore, when the developer is rotating at a rotation speed of N rpm or higher where the developer cannot be discharged from the stirring container, the transportability is reduced due to centrifugal force by reducing the rotation speed to N rpm or less at least once during the rotation of the stirring container. Therefore, it is possible to secure a desired conveyance amount and a charge amount necessary for development.

  Moreover, the time for the container to rotate half is 30 / N. When the rotation operation is interrupted at this interval and controlled to rotate again, the internal developer is transported to the top of the stirring vessel and repeats the falling motion. By controlling in this way, frictional charging due to the collision of the developer is efficiently performed, and it is effective to supply a developer having a high charge amount. Therefore, it was found that the time for interrupting rotation is preferably √ (4r / g).

  When the stirring container is rotated halfway and the developer falls from the top of the stirring container, the time taken to completely drop is √ (4 r / g). After waiting for √ (4r / g) after stopping the rotation, all the developer stuck to the container is considered to fall.

Then, if it controls to start rotation again, it can stir efficiently.
A control example of the rotation speed is shown in FIG.
FIG. 6A shows an example of control when the rotational speed is intermittently made zero, b is when the rotational speed is made intermittently less than N, and c is an example of control when the angular acceleration is changed. In any case, the number of rotations is once less than N during one rotation of the stirring vessel. When the control for stopping the rotation is performed as in a, the charge amount of the developer increases. In addition, when the rotation is not stopped as in b, there is little decrease in the transport amount. When the angular acceleration is changed as in c, the control becomes complicated, but the temporal change in the transport amount is small. In addition, although the rotation speed is periodically changed in FIG. 6, it is not necessarily required to be periodic.

With respect to the stirring unit 60 having a length of 90 mm, an outer diameter of 40 mm, and four wings twisted 60 degrees inside, the rotation amount dependence of the transport amount and the charge amount was examined.
FIG. 7 is a diagram showing the relationship between the rotation speed and the carry amount.

In FIG. 7, □ is a comparative example driven at a constant rotational speed. ● is an example in the case of intermittent rotation by the method of FIG.
As in the comparative example, when driven at a constant rotation speed, the conveyance amount becomes zero when the rotation speed exceeds 210 rpm. On the other hand, when it rotates by intermittent operation like a present Example, the conveyance amount can be maintained.

FIG. 8 is a diagram showing the relationship between the rotational speed and the charge amount when the rotational operation is intermittently performed at intervals of 0.5 s. It can be seen that the charge amount increases as the rotational speed increases.
In the configuration of this embodiment, by intermittently rotating at a rotation speed of 210 rpm or more, a developer having a high charge amount can be sufficiently supplied as compared with the case of stirring at a constant rotation speed less than that. It becomes possible.

1 is a vertical sectional view showing an example of an image forming apparatus according to the present invention. FIG. 3 is an explanatory cross-sectional view showing a developing device. It is sectional explanatory drawing which shows an example of the stirring part of this invention. a, b, and c are the left-right sectional view and sectional explanatory drawing which show another stirring part of this invention. It is explanatory drawing which shows a motion of the developer in a stirring container. It is a graph which shows the example of control of the rotation speed of a stirring container. It is a graph which shows the relationship between this invention and the conventional rotation speed, and flow volume. It is a graph which shows the relationship between the rotation speed of a stirring container, and a charge amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Developing means 30, 60 Stirring part 31, 61 Stirring container 32, 62a-62d Stirring blade

Claims (11)

Developing means for developing a latent image on the image carrier using a two-component developer;
An agitation part that is arranged separately from the developing means and agitates the developer and toner;
In the developing device having a circulating means for circulating the developer between the developing means and the stirring unit,
The stirring unit includes a hollow stirring container and a plurality of stirring members fixed to the inside of the container, and is a device that performs stirring by rotating the stirring container in the horizontal direction.
It has an opening at both ends in the axial direction of the stirring vessel, is configured to replenish the developer from one of the openings, and discharge the mixed developer from the other opening,
A developing device, wherein the number of rotations of the stirring container is changed during stirring.   2. The developing device according to claim 1, wherein the angular acceleration of the stirring container is changed during stirring.   3. The developing device according to claim 1, further comprising a developer accommodating portion that is provided in the vicinity of the discharging portion of the stirring portion and temporarily stores the developer discharged from the stirring portion. .   4. The developing device according to claim 1, wherein the gravitational force acting on the developer is lowered to a rotational speed that is greater than the centrifugal force acting on the developer at least once while the stirring container rotates once. A developing device.   5. The developing device according to claim 4, wherein when the stirring container is stirred at a rotational speed at which a centrifugal force acting on the developer is larger than a gravity acting on the developer, the rotation is temporarily stopped when the stirring container is rotated halfway. A developing device.   6. The developing device according to claim 5, wherein the rotation stop time of the stirring vessel is √ (4r / g), where rcm is the rotation radius of the stirring vessel and g is the acceleration of gravity.   7. The developing device according to claim 4, wherein the stirring member is a coil.   7. The developing device according to claim 4, wherein the stirring member is a wing having an angle.   The developing device according to claim 7 or 8, wherein a screw for forcibly feeding the agent is provided on the inlet side of the stirring unit.   The developing device according to claim 9, wherein an inner wall of the stirring container is formed of a charge imparting member.   An image forming apparatus using the developing device according to claim 1.

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