JP5751799B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine and a laser beam printer using an electrophotographic method or an electrostatic recording method, and a developing device used therefor.

  As a conventional developing device, as shown in FIG. 8, there are ones in which two conveying screws 205 and 206 for agitating and conveying a developer are arranged up and down to reduce the occupied space in the horizontal direction. A color image forming apparatus such as a tandem system in which such developing devices are mounted in parallel in the horizontal direction can be downsized.

  Further, in such a vertical stirring type developing device, the developer recovered from the developing region is recovered to the stirring chamber 204 side and sufficiently stirred, and then conveyed to the developing chamber 203. For this reason, the developing sleeve 208 is supplied with a developer having a uniform concentration, and image unevenness in the thrust direction (image unevenness caused by insufficient stirring) and density difference (density difference caused by insufficient stirring). A uniform image can be obtained.

  As shown in FIG. 9, in the vertical stirring type developing device, the first conveying screw 205 is disposed substantially parallel to the bottom of the developing chamber 203 along the axial direction of the developing sleeve 208, and rotates by rotating. The developer in the developing chamber 203 is conveyed in one direction along the axial direction. The second conveying screw 206 is disposed at the bottom of the stirring chamber 204 substantially in parallel with the first conveying screw 205, and the developer in the stirring chamber 204 is placed in a direction opposite to the conveying direction of the first conveying screw 205. Transport. In this manner, the developer is conveyed between the developing chamber 203 and the agitating chamber 204 through the openings 211 and 212 at both ends of the partition wall 207 by the conveyance by the rotation of the first conveyance screw 205 and the second conveyance screw 206. Circulated between.

JP-A-5-333691 JP-A-6-51634 JP 2002-6599 A

  In the conventional developing device 201 described above, the developing chamber 203 and the stirring chamber 204 are arranged in the vertical direction. For this reason, as shown in FIG. 9, the developer from the developing chamber 203 to the stirring chamber 204 falls from top to bottom. On the other hand, the developer is delivered from the stirring chamber 204 to the developing chamber 203 so as to be pushed up from the bottom to the top by the pressure of the developer accumulated at the end. Not all of the developer transferred from the stirring chamber 204 to the developing chamber 203 reaches the downstream end of the first conveying screw 205 in the developing chamber 203. That is, as indicated by an arrow A in FIG. 9, there is a component that is supplied to the developing sleeve 208 halfway and is collected in the stirring chamber 204 after passing through the developing region. The developer is transferred to the developing sleeve 208 over substantially the entire width of the developing sleeve 208, and the amount of the developer conveyed by the first conveying screw 205 in the developing chamber 203 goes from the upstream end to the downstream end. It tends to decrease gradually. On the other hand, the amount of developer conveyed by the second conveying screw 206 in the stirring chamber 204 tends to gradually increase from the upstream end toward the downstream end. That is, there is a deviation in the developer distribution in the developing device 201.

  In particular, when the developer amount in the developing chamber 203 is shifted, the supply to the developing sleeve 208 becomes uneven, and the density of the formed image is not constant in the axial direction of the developing sleeve 208. That is, on the upstream side of the developing chamber conveyance path where the amount of developer is large, the amount of developer supplied to the developing sleeve 208 is stable and the image density is constant. However, on the downstream side of the developing chamber conveyance path with a small amount of developer, the amount of developer supplied to the developing sleeve 208 is small, resulting in density unevenness in the image and image defects.

  Therefore, there is a technique disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 5-333691). In this technique, the developer conveying ability of the first and second conveying screws is made sufficiently larger than the supply amount to the developing sleeve. Thereby, the offset effect is made relatively small, and the above-mentioned image defect is solved. However, if the developer conveyance amount is increased by increasing the rotation speed of the conveyance screw, there is an increase in stress on the developer and an increase in rotational torque, so the developer conveyance amount cannot be increased too much. Further, even when the conveying speed is increased by improving the pitch and shape of the conveying screw, the upper limit of the conveying speed is limited, so that it is not effective when the degree of deviation is severe.

  Further, as in the technique disclosed in Patent Document 2 (Japanese Patent Laid-Open No. 6-51634), a third conveying screw is provided between the developing sleeve and the second conveying screw provided in the stirring chamber, It may be possible to ease the deviation. However, in this case, the configuration of the developing device is complicated and expensive.

  Further, as in the technique disclosed in Patent Document 3 (Japanese Patent Application Laid-Open No. 2002-6599), a wall is provided at the opening side end of the partition wall, and a weir is provided at a portion falling from the developing chamber to the stirring chamber. There is also a method of ensuring a minimum amount of developer staying in the developing chamber. However, the periphery of the weir becomes a dead space, and the developer that enters the dam stays and does not circulate.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device and an image forming apparatus capable of improving the image quality by maintaining a good balance of the amount of developer staying between the developing chamber and the stirring chamber. To do.

In order to solve the above problems, a typical configuration of the developing device and the image forming apparatus according to the present invention is provided with a developing chamber for supplying the developer to the developer carrying member, and below the developing chamber in the direction of gravity, A stirring chamber for stirring the developer supplied to the developing chamber; a partition partitioning the developing chamber and the stirring chamber; and a partition provided for moving the developer from the stirring chamber to the developing chamber. In a developing device having an opening and a shutter member capable of changing an opening amount of the opening, the opening amount of the opening is increased in accordance with an increase in the number of images formed from the initial stage of the developer. And a controller for controlling the position of the shutter member.

  According to the present invention, by changing the opening amount of the opening communicating the developing chamber and the stirring chamber in accordance with the deterioration of the developer, the amount of developer moving from the stirring chamber to the developing chamber is optimized and developed. The amount of the developer in the room can be kept constant, and the image quality can be stabilized.

It is a perspective view of the developing device according to the present embodiment. It is sectional drawing of the developing device which concerns on this embodiment. It is a flowchart figure of the shutter drive which concerns on this embodiment. It is a block diagram of the control part concerning this embodiment. It is a block diagram of the developing device according to the present embodiment. 1 is a configuration diagram of an image forming apparatus according to an exemplary embodiment. It is a figure explaining the relationship between the movement amount of a developing agent, and the amount of partition opening. It is typical sectional drawing of the developing device which concerns on a prior art. It is typical sectional drawing of the developing device which concerns on a prior art.

  Embodiments of a developing device and an image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 6 is a configuration diagram of the image forming apparatus according to the present embodiment. As shown in FIG. 6, the image forming apparatus according to the present embodiment includes yellow (Y), magenta (M), cyan (C), and black (Bk) stations.

  The photosensitive drum (image carrier) 10 (10Y, 10M, 10C, 10K) is rotatably provided. The surface of the photosensitive drum 10 is uniformly charged by a primary charger 21 (21Y, 21M, 21C, 21K), and is modulated by a light emitting element 22 (22Y, 22M, 22C, 22K) according to an image information signal. Are exposed to form an electrostatic latent image. The electrostatic latent image is visualized as a toner image using a developer by the developing device 1 (1Y, 1M, 1C, 1K).

  The toner image is transferred onto the sheet S conveyed by the sheet conveying belt 24 by the transfer charger 23 (23Y, 23M, 23C, 23K), and is fixed by being heated and pressurized by the fixing device 25. Further, the transfer residual toner on the photosensitive drum 10 is removed by the cleaning device 26 (26Y, 26M, 26C, 26K). The toner supply tank 20 (20Y, 20M, 20C, 20K) supplies toner to the developing device 1.

  FIG. 5 is a configuration diagram of the developing device according to the present embodiment. As shown in FIG. 5, the developing device 1 includes a developing sleeve (developer carrying member) 8 and a panning member 9 in the developing container 2. The developing container 2 contains a two-component developer containing a nonmagnetic toner and a magnetic carrier. The developing sleeve 8 performs development by applying a developer to the developing region. The ear cutting member 9 restricts the ears of the developer carried on the developing sleeve 8. A substantially central portion in the vertical direction in the developing container 2 is partitioned into a developing chamber 3 and an agitating chamber 4 by a partition wall 7 extending in an axial direction perpendicular to the vertical direction. It is accommodated in the chamber 4.

  A first conveying screw (developer stirring / conveying member) 5 is disposed in the developing chamber 3. A second conveying screw (developer stirring / conveying member) 6 is disposed in the agitating chamber 4. The first conveying screw 5 is disposed substantially in parallel along the axial direction of the developing sleeve 8 at the bottom of the developing chamber 3 and rotates to allow the developer in the developing chamber 3 to move in one direction along the axial direction. Transport. The second conveying screw 6 is disposed at the bottom of the stirring chamber 4 substantially in parallel with the first conveying screw 5, and conveys the developer in the stirring chamber 4 in the direction opposite to the conveying direction of the first conveying screw 5. .

  The developer is transported by the rotation of the first and second transport screws 5 and 6, and the developer passes through the opening (first communication portion) 11 and the opening (second communication portion) 12 provided at both ends of the partition wall 7. It is circulated between the developing chamber 3 and the stirring chamber 4. The developer supplied from the agitating chamber 4 to the developing chamber 3 is developed by the conveying force of the second conveying screw 6 in the opening 11 of the partition wall 7 provided between the agitating chamber 4 and the developing chamber 3. The developer is pushed up from the bottom to the top by the agent pressure.

  An opening is provided at a position corresponding to the developing area of the developing container 2 facing the photosensitive drum 10. The developing sleeve 8 is rotatably disposed in the opening so as to be partially exposed in the direction of the photosensitive drum 10. The developing sleeve 8 rotates during development, carries a two-component developer whose layer thickness is regulated by the cutting of the magnetic brush by the cutting member 9, and transports this to the developing region facing the photosensitive drum 10 for photosensitivity. A developer is supplied to the latent image formed on the drum 10 to develop the latent image.

(Change in opening amount of opening 11)
In this embodiment, the opening amount of the opening portion 11 is changed in accordance with the change in the viscosity of the developer so that the amount of developer pumped through the opening portion 11 becomes a constant amount. Thereby, a decrease in the developer in the developing chamber 3 is suppressed. Hereinafter, a detailed description will be given with reference to FIGS.

  FIG. 1 is a perspective view of a developing device according to this embodiment. FIG. 2 is a sectional view of the developing device according to this embodiment. As shown in FIGS. 1 and 2, the developing device 1 according to the present embodiment moves a partition shutter (shutter member) 13 at the end of the partition by a stepping motor 14, so that the space between the stirring chamber 4 and the developing chamber 3 is moved. The opening amount of the opening 11 at the end of the partition wall 7 is changed.

  In order to obtain a good image, the amount of developer on the developing sleeve 8 must be constant. For this purpose, it is necessary that a sufficient amount of developer always stays in the developing chamber 3. For this reason, it is important to supply an appropriate amount of developer corresponding to the amount carried out by the developing sleeve 8 to the developing chamber 3 to ensure a certain amount or more of the developing chamber 3.

  FIG. 7 is a diagram showing the relationship between the opening amount of the opening 11 and the moving amount of the developer. In FIG. 7, the vertical axis represents the amount of developer moved from the stirring chamber 4 to the developing chamber 3, and the horizontal axis represents the opening amount of the opening 11. A solid line a represents a fresh developer, and a broken line b represents the developer when the durability has deteriorated. A region c indicated by oblique lines indicates an optimum opening amount of the opening 11 in the fresh developer. A region d indicated by hatching indicates an optimum opening amount of the opening 11 in the developer whose durability has deteriorated.

  As shown in FIG. 7, the moving amount of the developer depends on the opening amount of the opening 11. While the opening amount of the opening portion 11 is small, the opening amount and the moving amount of the developer are in a proportional relationship. When the opening amount further increases, the relationship in which the developer movement amount does not increase even when the opening amount increases continues. When the opening amount is further increased, the developer once moved to the developing chamber 3 falls by its own weight into the stirring chamber 4, so that the moving amount of the developer decreases.

  From the above, it can be seen that the optimum opening amount is the regions c and d where the movement amount does not increase with respect to the opening amount and the movement amount is maximum, and the optimum opening amount increases due to the durability of the developer. As the developer circulates with the operation of the image forming apparatus, the developer deteriorates and the viscosity increases. Since the durable developer having an increased viscosity has poor fluidity as compared with a fresh developer, the optimum opening amount is increased.

  As shown in FIG. 7, there may be no common optimum opening amount that satisfies all of the developer life (from a fresh developer to a durable developer). In this case, the developer distribution between the agitating chamber 4 and the developing chamber 3 cannot be kept constant during the developer life and gradually changes (the developer amount in the developing chamber 3 decreases), and the amount of the agent in the developing chamber is insufficient. There was a problem of causing a change in image quality caused by. Therefore, in the present embodiment, as shown by an arrow E, the opening amount of the opening 11 is increased in accordance with the durability of the developer (= deterioration of the developer). In the present embodiment, the optimum opening amount of the opening portion 11 in the initial stage of the developer is 26 mm, and thereafter increases by 1 mm for every 100,000 sheets, and is 33.5 mm at the maximum for a developer life of 750,000 sheets.

  FIG. 3 is a flowchart for driving the partition shutter 13 according to the present embodiment. FIG. 4 is a block diagram of the control unit according to the present embodiment. As shown in FIG. 4, the image forming apparatus according to the present exemplary embodiment includes a controller (control unit) 500 and a counter (endurance detection unit) 506. A counter 506 counts the number of sheets processed (number of images formed) accompanying the operation of the apparatus.

  The controller 500 controls the rotation operation of the stepping motor 14 via the driver 505 based on the value of the counter 506 (detection result). The controller 500 includes a CPU 501, a program storage ROM 503, a temporary data storage RAM 502, and a communication I / O 504. The controller 500 also controls the entire image forming apparatus.

  When the image forming apparatus is powered on, first, the motor 14 is rotated for a predetermined time via a driver 505 in accordance with a command from the controller 500. Then, the partition shutter 13 opens (or closes) until it hits the operating area, and the RAM 502 recognizes the position as the home position (FIG. 3, S1, S2).

  Next, the CPU 501 calculates the optimum opening amount of the opening 11 in the current developer state from the “conversion table” stored in the RAM 502 and the “number of sheets passed from the initial developer” (FIG. 3, FIG. 3). S3). The “conversion table” indicates the relationship between the number of sheets passed (change in developer viscosity due to developer deterioration) and the optimum opening amount of the opening 11. “Number of sheets passed from the initial stage of the developer” is obtained by subtracting the counter value at the time of developer replacement from the current counter value of the counter 506. As the conversion table, different conversion tables are used depending on the temperature and humidity.

  The required number of pulses from the home position to the opening position is calculated from the obtained optimum opening amount (S4 in FIG. 3), and the motor 14 is driven via the driver 505 to make the partition shutter 13 the optimum opening. 11 to the position where the opening amount is 11 (FIG. 3, S5 to S7).

  Thereafter, the counter 506 is monitored, and whenever the count-up amount exceeds a preset sheet passing number interval, the motor 14 is rotated by the necessary number of pulses, and the position of the partition shutter 13 is gradually moved to widen the opening amount ( FIG. 3, S8 to S10). This operation loop is repeated until the preset number of developer lifetimes (FIG. 3, S7 to S12), and when the lifetime is reached, the controller 500 issues a replacement alarm to the display device 507 (FIG. 3, S13).

  As described above, in this embodiment, the opening amount of the opening 11 is gradually increased in consideration of the fluidity of the developer that has been lowered due to the viscosity change accompanying the developer deterioration. As a result, the amount of developer in the developing chamber can be kept constant, and image defects such as density unevenness can be prevented.

  In the present embodiment, the configuration in which the opening amount of the opening portion 11 is adjusted based on the number of sheets to be passed has been described. However, the present invention is not limited to this configuration, and the opening portion 11 is based on the deterioration of the developer. It is only necessary to adjust the opening amount. For example, the developer viscosity may be detected from a change in rotational torque obtained from a torque converter (viscosity measuring means) attached to the first conveying screw 5 instead of the number of sheets passed. In such a configuration, the opening amount of the partition shutter 13 corresponding to the torque change is calculated from a conversion table determined in advance.

  Further, the operation of the partition shutter 13 is not limited to the operation by the stepping motor 14, but may be performed using a voltage change to the piezoelectric element or an artificial muscle. Further, the configuration for changing the opening amount of the opening 11 is not limited to the partition shutter 13, and any configuration that can change the opening amount of the opening 11 may be used.

S ... sheet 1 ... developing device 2 ... developing container 3 ... developing chamber 4 ... stirring chamber 5 ... first conveying screw 6 ... second conveying screw 7 ... partition wall 8 ... developing sleeve (developer carrier)
9 ... Hot cutting member 10 ... Photosensitive drum 11 ... Opening portion 12 ... Opening portion 13 ... Bulk shutter
DESCRIPTION OF SYMBOLS 14 ... Stepping motor 20 ... Toner replenishing tank 21 ... Primary charger 22 ... Light emitting element 23 ... Transfer charger 24 ... Sheet conveyance belt 25 ... Fixing device 26 ... Cleaning device 500 ... Controller (control part)
501 ... CPU
502 ... RAM
503 ... ROM
504 ... I / O
505 ... Driver 506 ... Counter (endurance detection means)
507 ... Display device

Claims (3)

A developing chamber for supplying the developer to the developer carrying member;
A stirring chamber provided below the developing chamber in the direction of gravity and stirring the developer supplied to the developing chamber;
A partition partitioning the developing chamber and the stirring chamber;
An opening provided in the partition for moving the developer from the stirring chamber to the developing chamber;
A developing device having a shutter member capable of changing an opening amount of the opening,
And a controller that controls the position of the shutter member so as to increase the opening amount of the opening in accordance with an increase in the number of images formed from the initial stage of the developer. The control unit moves the shutter member based on a conversion table indicating the opening amount of the opening,
The developing device according to claim 1, wherein the conversion table uses different conversion tables depending on temperature and humidity. An image carrier;
An image forming apparatus having the developing device according to claim 1, wherein the image bearing member is developed.

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