JP7467943B2 - Developing device and image forming apparatus - Google Patents

Description

The present invention relates to the discharge of developer in a developing device.

Conventionally, electrophotographic image forming devices are known that develop an electrostatic latent image formed on a photoconductor with toner to form a toner image, transfer the formed toner image to paper, and heat-fix the transferred toner image to form an image on paper.

The developing device that develops a toner image on the photoreceptor is composed of a developing roller (developer carrier) that is close to the photoreceptor, a screw for stirring and transporting, etc., that are arranged inside the developing tank, and the developer that contains the toner is stored in the developing container.

The developing device described in Patent Document 1 includes a supply screw that is arranged next to the developing roller to supply developer, and a stirring screw that is arranged parallel to the supply screw via a partition wall, and is configured so that the supply screw and the stirring screw feed the developer in opposite directions. Also, communication ports for circulating the developer are provided on the downstream and upstream sides of the partition wall in the transport direction of the supply screw, and the developer, in which the toner and carrier are stirred by the stirring screw, is supplied by the supply screw over almost the entire length of the developing roller.
In addition, this developing device is replenished with new developer through a supply port provided at the end of the supply screw on the downstream side in the transport direction, and developer that has deteriorated due to repeated use is discharged from a discharge port provided near the end of the supply screw on the downstream side in the transport direction and upstream of the supply port. The discharge port is provided with a shutter mechanism that controls opening and closing, and is disposed at a predetermined height, and is discharged when the developer increases to a level above the bottom end of the discharge port.

The developing device described in Patent Document 2, like the developing device in Patent Document 1, is equipped with a supply screw and an agitating screw separated by a partition, and the partition is provided with two communication ports through which the developer flows. In addition, this developing device is provided with another communication port with a low partition next to the communication port that sends developer from the agitating screw to the supply screw, preventing stagnation of the flow of developer from the agitating chamber to the supply chamber.

The developing device described in Patent Document 3, like the developing device in Patent Document 1, includes a supply screw and an agitating screw separated by a partition wall, and the partition wall is provided with two openings for allowing the developer to flow. This developing device also includes discharge ports for discharging the developer on the upstream and downstream sides of the conveying direction of the agitating screw in the agitating chamber, and the downstream discharge port is higher in height than the upstream discharge port.
As a result, the developer is discharged mainly from the upstream discharge port, and when the amount of developer increases too much, the developer is also discharged from the downstream discharge port.

Japanese Patent Application Laid-Open No. 11-231624 JP 2017-194645 A JP 2018-036537 A

None of the above developing devices took into consideration the possibility of developer unevenness on both sides of the screw longitudinal direction in the supply chamber and mixing chamber due to external factors such as tilt, the existence of developer with a low charge level due to insufficient mixing at stagnation points of the circulating developer, and the existence of toner aggregates caused by toner adhering to the walls peeling off when the toner supply section is replenished.
If the developer becomes unevenly distributed on both sides of the screw in the longitudinal direction in the supply chamber and the agitating chamber, an unexpected load may be generated on the rotation drive source of each screw.
Furthermore, if a developer with a low charge level is supplied to the developing roller, it can cause the toner to adhere to unintended locations on the recording medium (fogging), and if toner aggregates are present, this can result in toner stains, white spots, and other toner loss, which can degrade image quality.

The present invention has been made in consideration of the problems in the conventional technology described above, and an object of the present invention is to suppress uneven distribution of developer within an apparatus.
Another object of the present invention is to suppress the influence of developer and toner aggregates that are insufficiently stirred and have a low charge amount.

In order to solve the above problems, the developing device according to the present invention comprises:
A developer carrier;
a supplying and conveying member that conveys a developer and supplies the developer to the developer carrying member;
a stirring and conveying member that conveys the developer in a direction opposite to a developer conveying direction by the supply and conveying member;
a housing having a supply chamber for storing the supply transport member and a mixing chamber for storing the mixing transport member,
a stirring chamber side developer discharge port is provided in the housing for discharging the developer from an upstream region in the developer transport direction of the stirring transport member to the outside of the housing, and the developer that has reached the stirring chamber side developer discharge port is discharged toward the upstream side in the developer transport direction of the stirring transport member;
a reverse feed conveying member for conveying the developer in a direction opposite to the developer conveying direction of the supplying and conveying member is provided downstream of the developer conveying direction of the supplying and conveying member;
The housing is characterized in that a supply chamber side developer discharge port for discharging the developer from an upstream area in the developer transport direction of the reverse transport member to the outside of the housing is provided in the housing .
Further, another developing device according to the present invention is
A developer carrier;
a supplying and conveying member that conveys a developer and supplies the developer to the developer carrying member;
a stirring and conveying member that conveys the developer in a direction opposite to a developer conveying direction by the supply and conveying member;
a housing having a supply chamber for storing the supply transport member and a mixing chamber for storing the mixing transport member,
a stirring chamber side developer discharge port is provided in the housing for discharging the developer from an upstream region in the developer transport direction of the stirring transport member to the outside of the housing, and the developer that has reached the stirring chamber side developer discharge port is discharged toward the upstream side in the developer transport direction of the stirring transport member;
a supply chamber is provided extending from the mixing chamber toward an upstream side in a developer transport direction of the mixing and transporting member,
The supply chamber communicates with the mixing chamber without any boundary such as a partition or a step,
The developer discharge port on the mixing chamber side is opened downward from the inner bottom of the supply chamber.

The image forming device according to the present invention is characterized by being equipped with the above-mentioned developing device.

According to the present invention, when the developer inside the device begins to become uneven due to tilting of the developing device or other external factors, the developer that has reached the developer discharge outlet on the mixing chamber side against the transport force of the mixing transport member can be discharged outside the housing, making it possible to suppress uneven distribution of the developer inside the device.
In addition, according to the present invention, if the volume of developer inside the device increases due to uneven distribution, when the developer reaches the developer discharge port on the mixing chamber side and is discharged, it discharges the developer together with insufficiently stirred developer caused by stagnation and toner agglomerates generated during replenishment, making it possible to suppress the effects of insufficiently stirred developer with low charge and toner agglomerates.

1 is a block diagram showing a schematic configuration of an image forming apparatus according to a first embodiment; FIG. 2 is a vertical sectional view of the developing device according to the first embodiment. FIG. 2 is a horizontal cross-sectional view of the developing device as viewed from above. 4 is a cross-sectional view taken along line VV in FIG. 3. 4 is a cross-sectional view showing another example of a structure taken along the line VV in FIG. 3. 4 is a flowchart showing the operation of the developing device. FIG. 2 is a partial horizontal cross-sectional view of the developing device. FIG. 11 is a block diagram showing a schematic configuration of an image forming apparatus according to a second embodiment. FIG. 11 is a horizontal cross-sectional view of a developing device according to a second embodiment, as viewed from above. 10 is a cross-sectional view taken along line WW in FIG. 9. 4 is a flowchart showing the operation of the developing device.

[First embodiment]
A first embodiment of the present invention will be described below with reference to the drawings. The following is one embodiment of the present invention and is not intended to limit the present invention.

[Device Overview]
FIG. 1 is a block diagram showing a schematic configuration of an image forming apparatus 10 according to the first embodiment.
As shown in FIG. 1, the image forming apparatus 10 is an electrophotographic image forming apparatus, and is configured to include a control device 11, an image forming section 12, a storage device 18, an interface 19, a paper feed device 20, a paper discharge device 21, etc.
The image forming unit 12 is configured to include a photoconductor 13 as an electrostatic latent image carrier that carries an electrostatic latent image, an exposure device 14 that forms an electrostatic latent image on the photoconductor 13, a developing device 30 that develops the electrostatic latent image with toner to develop a toner image on the photoconductor, a transfer device 16 that transfers the toner image to paper, a fixing device 17 that fixes the toner image to the paper, as well as other devices such as a charging device and a cleaning device.

[Developing device]
2 is a vertical sectional view of the developing device 30, and FIG. 3 is a horizontal sectional view of the developing device 30 as viewed from above.
The developing device 30 is removably attached inside the image forming apparatus 10. The arrangement and orientation of each component of the developing device 30 described below are all based on the assumption that the developing device 30 is attached inside the image forming apparatus 10.
As shown in Figures 2 and 3, the developing device 30 includes a housing 31 that contains developer and supports the overall configuration of the device, a developing roller 32 as a developer carrier that develops a toner image on the photosensitive member 13, a supply screw 33 as a supply and transport member that supplies developer to the developing roller 32, and an agitating screw 34 as an agitating and transport member that transports the developer in the direction opposite to the developer transport direction by the supply screw 33.

The developer is a dry two-component developer containing toner and a carrier, and the toner can be charged by mixing and stirring the toner and carrier. The charged toner can be attached to the surface of the photoconductor 13 on which the electrostatic latent image is formed through the developing roller 32 to develop the toner image.

The housing 31 has an opening that is open toward the photoconductor 13, and a developing roller 32 is rotatably supported in a space formed in the vicinity of this opening.
The developing roller 32 as a developer carrier and the photoconductor 13 are both cylindrical, with their rotation axes parallel to each other and oriented horizontally. The outer circumferential surface of the developing roller 32 and the outer circumferential surface of the photoconductor 13 are disposed so as to form a predetermined development gap.
In the following description, the direction parallel to the rotation axis of the developing roller 32 may be referred to as the X-axis direction, the horizontal direction perpendicular to the X-axis direction may be referred to as the Y-axis direction, and the vertical direction perpendicular to both the X-axis direction and the Y-axis direction may be referred to as the Z-axis direction.

The housing 31 includes a supply chamber 311 housing the supply screw 33 and a mixing chamber 312 housing the mixing screw 34 .
In the housing 31, the developing roller 32, the supply screw 33, and the stirring screw 34 are all supported so that their rotational center lines are parallel to the X-axis direction, and are arranged side by side approximately in the Y-axis direction. The supply screw 33 and the supply chamber 311 are arranged next to the developing roller 32, on the opposite side of the photoconductor 13. The stirring screw 34 and the stirring chamber 312 are arranged next to the supply screw 33 and the supply chamber 311, on the opposite side of the developing roller 32.
The developing roller 32, the supply screw 33, and the stirring screw 34 are all rotated in the same direction in an interlocking manner using a motor 301 as a drive source via a power transmission mechanism (not shown).

The supply screw 33 includes a first shaft 331 rotatably supported within the housing 31 while facing the X-axis direction, and a spiral stirring blade 332 fixedly mounted on the first shaft 331 .
Supply chamber 311 has an inner bottom portion with a cross-sectional shape along the YZ plane that is convex downwardly in an arc shape, and its inner diameter is set to be slightly larger than the outermost diameter of stirring blade 332. The outer periphery of stirring blade 332 is disposed close to the inner bottom portion of supply chamber 311.
When the supply chamber 311 is filled with developer, the supply screw 33 is rotated in a specified forward rotation direction, whereby the developer can be transported while being stirred in the direction of the arrow H1 parallel to the X-axis direction within the supply chamber 311.
The supply screw 33 is disposed close to the developing roller 32 over the entire length in the X-axis direction, and can supply the toner contained in the developer over the entire outer circumferential surface of the developing roller 32 .

The stirring screw 34 includes a second shaft 341 rotatably supported within the housing 31 while facing the X-axis direction, and a spiral stirring blade 342 fixedly mounted on the second shaft 341.
The cross-sectional shape of the inner bottom of the stirring chamber 312 along the YZ plane is an arc shape that is convex downward, and the inner diameter is set to be slightly larger than the outermost diameter of the stirring blade 342. The outer periphery of the stirring blade 342 is disposed close to the inner bottom of the stirring chamber 312.
The stirring blade 342 of the stirring screw 34 is formed in a spiral shape that winds in the opposite direction to the stirring blade 332 of the supply screw 33 .
As a result, when the stirring chamber 312 is filled with developer, the stirring screw 34 is rotated in the specified forward rotation direction, so that the developer can be stirred and transported within the stirring chamber 312 in the direction of arrow H2 (the opposite direction to arrow H1) parallel to the X-axis direction.

In addition, the supply chamber 311 and the stirring chamber 312 are separated by a partition 313 along the X-Z plane, and openings are provided at one end and the other end of the partition 313 in the X-axis direction, respectively, through which developer flows between the supply chamber 311 and the stirring chamber 312.
In Figure 3, the opening provided at the right end of the partition 313 is a first communication portion 314 that transfers developer from the supply screw 33 to the stirring screw 34, and the opening provided at the left end of the partition 313 is a second communication portion 315 that transfers developer from the stirring screw 34 to the supply screw 33.
That is, as described above, the supply screw 33 transports the developer in the direction of arrow H1, and the developer is forced into the mixing chamber 312 in the direction of arrow H3 from the first communication portion 314 located downstream in the transport direction of the forward rotation of the supply screw 33 in the supply chamber 311.
Similarly, as described above, the stirring screw 34 transports the developer in the direction of arrow H2, so that the developer is pushed into the supply chamber 311 in the direction of arrow H4 from the second communication portion 315, which is located downstream in the transport direction of the forward rotation of the stirring screw 34 in the stirring chamber 312.
That is, within the housing 31, the developer is transported along a circular circulation path indicated by the succession of arrows H1, H3, H2, and H4.

The agitating screw 34 is connected at one end to the supply screw 35. The supply screw 35 has a third shaft 351 rotatably supported in the housing 31 while facing the X-axis direction, and a spiral agitating blade 352 fixed to the third shaft 351. The third shaft 351 is connected concentrically to the second shaft 341 of the agitating screw 34 and rotates integrally with it. The developer transport direction of the agitating blade 352 is the same as that of the agitating blade 342 of the agitating screw 34.

The supply screw 35 is accommodated in a supply chamber 316 provided on one side of the mixing chamber 312 .
The cross-sectional shape of the supply chamber 316 along the YZ plane is set to be approximately the same as that of the mixing chamber 312, and the supply chamber 316 and the mixing chamber 312 are connected with each other without any boundary such as a partition or step.
The supply chamber 316 is provided with a developer supply port 317 for supplying developer to the housing 31 at a position near the mixing chamber 312 on the wall portion surrounding the supply screw 35 (e.g., above the supply screw 35) (shown by a dotted line in Figure 3).

A supply unit (not shown) including a supply toner storage unit in which toner is stored and a transport mechanism for transporting toner from the supply toner storage unit is disposed above the supply chamber 316. Toner is supplied to the supply screw 35 in the supply chamber 316 from above through a developer supply port 317.
As a result, the supplied toner moves in the same direction as the arrow H2 to join the developer circulating in the aforementioned circular circulation path inside the housing 31, and is agitated by the agitating screw .

The dry two-component developer consumes toner when forming an image, and therefore, in order to determine whether or not toner needs to be replenished, a toner amount detection device 302 (see FIG. 1 ) that detects the amount of toner contained in the developer is provided in the supply chamber 311 or the mixing chamber 312.
The toner amount detection device 302 consists of, for example, a magnetic permeability sensor, and detects the magnetic permeability in a direction penetrating the developer in the supply chamber 311 or the mixing chamber 312 (for example, the Z-axis direction), and the toner content in the developer can be determined from the detection result.
When the toner content based on the detection by toner amount detection device 302 falls below a predetermined threshold, the above-mentioned control device 11 operates the transport mechanism of the replenishing unit to supply a specified amount of toner.

In addition, instead of providing the toner amount detection device 302, the control device 11 may monitor the cumulative amount of image formation (e.g., the number of sheets of paper fed) in the image forming device 10, and control the supply of toner whenever a certain amount is exceeded.

A supply screw 35 is disposed over substantially the entire length in the X-axis direction in the supply chamber 316. A stirring chamber side developer discharge port 318 is provided on the wall surface surrounding the supply screw 35, which is upstream of a developer supply port 317 in the developer transport direction (which coincides with the transport direction of the stirring screw 34) caused by the forward rotation of the supply screw 35 in the supply chamber 316.
4, the mixing chamber side developer discharge port 318 opens downward from the inner bottom of the supply chamber 316. The developer discharged from the mixing chamber side developer discharge port 318 drops to a waste developer storage section (not shown) and is stored therein.

The developer discharge port 318 on the mixing chamber side provided in the supply chamber 316 is not limited to being directed downward as shown in FIG.
For example, as shown in Fig. 5, the stirring chamber side developer discharge port 318 may be provided facing to the side. In that case, the height of the lower end of the stirring chamber side developer discharge port 318 is set to a predetermined height from the inner bottom surface as shown. For example, it is preferable that the height is approximately the same as the height h of the upper end of the third shaft 351 of the supply screw 35. This height is a height that the developer does not reach when the developing device 30 is properly positioned without any inclination. At this height, the developer can be discharged by the transport and stirring action of the supply screw 35.

[Developing Operation of Developing Device]
The operation of the developing device 30 is controlled by the control device 11. Fig. 6 is a flow chart showing the operation control of the developing device 30 during image formation by the control device 11. The operation of the developing device 30 will be described with reference to Fig. 6.

The control device 11 can perform control to switch the motor 301 that drives the supply screw 33, the stirring screw 34, and the replenishment screw 35 of the developing device 30 between forward and reverse rotation.
During image formation, in normal developing operation, the control device 11 drives the motor 301 in a direction to rotate the supply screw 33, the mixing screw 34, and the replenishment screw 35 forward (step S1). As a result, the developer in the supply chamber 311 and the mixing chamber 312 is transported along the circular circulation path indicated by the arrows H1, H3, H2, and H4 while the toner and carrier are mixed.
In addition, the supply screw 33 supplies the toner in the developer that has been charged by stirring to the outer circumferential surface of the developing roller 32 located adjacent to it in the supply chamber 311. This allows the developing roller 32 to develop a toner image on the outer circumferential surface of the photoconductor 13 that faces it outside the housing 31.

Then, the control device 11 continuously or periodically detects the magnetic permeability in the supply chamber 311 or the mixing chamber 312 using the toner amount detection device 302, and determines from the detection result whether the toner content in the developer is below a specified threshold value (step S3).
If the toner content is equal to or greater than the specified threshold, the process proceeds to step S7, and if the toner content is less than the threshold, the control device 11 executes control to operate the transport mechanism of the replenishing unit to replenishing a specified amount of toner (step S5). The toner replenishing may be performed for a specified period of time, or may be continued until the toner content indicated by the magnetic permeability detected by the toner amount detection device 302 reaches a target value at the time of replenishing.

When toner is replenished, the toner is supplied from developer replenishment port 317 into replenishment chamber 316, and the toner is transported by replenishment screw 35 in the direction of arrow H5 toward mixing chamber 312, and is transported while being stirred by mixing screw 34 together with the developer in mixing chamber 312. Therefore, the developer to which the toner has been replenished is transported to supply chamber 311.
In addition, within the supply chamber 316, the supply screw 35 transports toner toward the mixing chamber 312. Therefore, in the proper developer transport state, the toner and developer are not transported upstream in the forward rotation transport direction of area A1 shown in Figure 3, and the toner and developer are not discharged from the mixing chamber side developer discharge port 318.

On the other hand, due to some reason, such as the developing device 30 being attached to the image forming device 10 in an inclined state, the developer may become biased at both ends in the X-axis direction within the housing 31, and the developer may increase at one end of the supply chamber 311 or the mixing chamber 312.
When such developer unevenness occurs, the volume of developer rises in the mixing chamber 312 and the supply chamber 316, and the toner and developer retreat to area A2 shown in Fig. 3. As a result, the toner and developer are discharged from the mixing chamber side developer discharge port 318 to the waste developer storage section, and the uneven state can be eliminated.

In addition, when the toner is supplied, the toner merges with the flow of developer that is already circulating. As a result, as shown in FIG. 7, the toner flow may stagnate near the junction R, causing insufficient stirring and resulting in the accumulation of developer with a low charge amount.
As described above, when developer unevenness occurs and the volume of the developer increases, developer with a low charge amount is mixed into the flow of circulating developer, which can cause deterioration in image quality, such as fogging.
In addition, toner agglomerates may occur on the housing wall around the developer supply port 317 due to toner peeling off from the wall. When the volume of the developer increases, the toner agglomerates may become mixed into the flow of circulating developer, which may cause degradation of image quality, such as toner stains, white spots, and other toner loss.
However, when the volume of the developer rises, the toner and developer are discharged from the stirring chamber side developer discharge port 318, which prevents developer with a low charge amount or toner aggregates from mixing into the flow of circulating developer, thereby reducing the occurrence of degradation in image quality.

Furthermore, in consideration of the occurrence of uneven distribution of developer, the control device 11 performs control to rotate the motor 301 in the reverse direction periodically or when the driving torque of the motor 301 increases. The increase in the driving torque of the motor 301 can be detected by monitoring the driving current to the motor 301.
That is, when the control device 11 detects, for example, the arrival of a regular period or an increase in motor torque, and thus satisfies the condition for executing reverse rotation of the motor 301 (step S7), it executes reverse rotation of the motor 301 (step S9).

By the reverse rotation of the motor 301, in the supply chamber 311, the mixing chamber 312 and the replenishing chamber 316, as shown by the two-dot chain line arrow G1 in FIG.
At the aforementioned confluence R, the circulating developer stagnates, resulting in insufficient stirring and developer with a low charge level remaining there, and toner agglomerates may also occur around the developer supply port 317 when the developer is transported in the reverse direction.
Since the developer is transported along the arrow G1, developer and toner aggregates that are insufficiently stirred and have a low charge level can be discharged to a waste developer storage section outside the housing 31 from the stirring chamber side developer discharge outlet 318, which is located at the downstream end point of the reverse rotation transport direction.

The time for which the motor 301 rotates in the reverse direction is set to at least the time required to transport the developer from the circular circulation path (near the junction R) formed by the arrows H1, H3, H2, and H4 to the mixing chamber side developer discharge port 318. This allows developer that is insufficiently mixed and has a low charge amount that is accumulated at the junction R and toner aggregates that have formed around the developer supply port 317 to be discharged from the mixing chamber side developer discharge port 318. It is desirable to actually measure the time required to transport the developer from this circular circulation path to the mixing chamber side developer discharge port 318 in advance, for example by testing, and record the required time in the storage device 18.

The control device 11 measures the elapsed time from the start of reverse rotation of the motor 301, and determines whether or not a predetermined execution time has elapsed (step S11).
If the execution time has not elapsed, the motor 301 continues to rotate in the reverse direction, and if the execution time has elapsed, the motor 301 is switched back to rotating in the forward direction (step S13).
Thereafter, the control device 11 determines whether image formation is complete (step S15), and if not, returns to step S1 to continue the developing operation, and when image formation is complete, stops the motor 301 (step S17) to end the developing operation.

[Technical effect of the first embodiment]
As described above, the developing device 30 of the image forming apparatus 10 is provided with the stirring chamber side developer discharge port 318 in the housing 31 for discharging the developer from the supply chamber 316, which is the area upstream in the developer transport direction of the forward rotation of the stirring screw 34, to the outside. Therefore, during normal transport, the developer is not discharged from the stirring chamber side developer discharge port 318, but if the developer becomes unevenly distributed in the housing 31, the developer can be discharged from the stirring chamber side developer discharge port 318 due to an increase in the volume of the developer. With this simple configuration, it is possible to reduce the load on the motor 301 caused by an increase in the torque due to the uneven distribution of the developer.
In addition, when low-charge developer is generated due to insufficient stirring caused by stagnation at the confluence R, which is a position outside the developer circulation path, if the developer becomes uneven, the low-charge developer may enter the developer circulation path due to an increase in volume. Even in such a case, when the excess developer due to the increase in volume is discharged from the stirring chamber side developer discharge port 318, the low-charge developer can be discharged together, making it possible to suppress the effects of the low-charge developer.

In addition, the mixing chamber side developer discharge port 318 is located upstream of the developer supply port 317, which supplies the developer, in the developer transport direction when the mixing screw 34 is rotating in the forward direction. Therefore, when developer bias occurs, toner aggregates generated around the developer supply port 317 can be discharged from the mixing chamber side developer discharge port 318, making it possible to improve the image quality of the images formed in the image forming device 10.

In addition, the developing device 30 is equipped with a control device 11 as a control unit, and can switch between forward and reverse feed by controlling the motor 301 that is the driving source for the supply screw 33 and the stirring screw 34, so that unevenness in the developer can be reduced when it occurs.
In addition, when the motor 301 rotates in reverse, developer that has been insufficiently stirred and has a low charge amount generated at the junction R and toner aggregates that have generated around the developer supply port 317 can be effectively discharged from the stirring chamber side developer discharge port 318, making it possible to further improve the image quality of the images formed in the image forming apparatus 10.

In addition, the control device 11 controls the motor 301 to drive the supply screw 33 and the stirring screw 34 in the reverse direction for at least the time it takes for the developer to move from the developer circulation path to the stirring chamber side developer discharge port 318 by transport. This makes it possible to more effectively discharge from the stirring chamber side developer discharge port 318 the developer that has been insufficiently stirred and has a low charge amount generated at the junction R and the toner aggregates that have been generated around the developer supply port 317, thereby making it possible to further improve the image quality of the images formed in the image forming device 10.

In addition, the housing 31 of the developing device 30 has a partition 313 separating the supply chamber 311 and the stirring chamber 312, and is provided with a first communication section 314 that transfers the developer from the supply screw 33 to the stirring screw 34 and a second communication section 315 that transfers the developer from the stirring screw 34 to the supply screw 33. This allows the developer to circulate, and sufficiently stirred developer can be supplied to the developing roller 32 through the supply screw 33.

In addition, if the mixing chamber side developer discharge port 318 is provided with its lower end spaced a certain height from the inner bottom surface of the housing 31, as shown in FIG. 5, it becomes possible to adjust whether developer is discharged depending on the height of the mixing chamber side developer discharge port 318 and the height at which the volume of developer inside the housing 31 reaches.

[Second embodiment]
The second embodiment will be described with reference to the drawings. Image forming apparatus 10A according to the second embodiment is different from image forming apparatus 10 described above mainly in the configuration of developing device 30A. Therefore, the differences between developing device 30A and developing device 30 will be mainly described, and the same components as those of image forming apparatus 10A and image forming apparatus 10 will be denoted by the same reference numerals and will not be described again.
Fig. 8 is a block diagram showing a schematic configuration of image forming apparatus 10A, Fig. 9 is a horizontal cross-sectional view of developing device 30A seen from above, and Fig. 10 is a cross-sectional view taken along line W-W in Fig. 9. This developing device 30A is also detachable from the inside of the image forming apparatus, and the arrangement and orientation of each component of developing device 30A described below are all based on the assumption that it is installed inside the image forming apparatus.

The developer used in developing device 30A is also a dry two-component developer containing toner and carrier. However, in the case of developing device 30A, taking into consideration the deterioration of the carrier due to use, the toner is mixed with a small amount of new carrier when the toner is replenished.
When the carrier is contained in the toner and replenished, the developer inside the housing 31 gradually increases, so the developing device 30A is provided with a mechanism for discharging the developer and maintaining the content amount constant.

As shown in FIG. 8, the developing device 30A is provided with a developer amount detection device 303A for detecting the volume (content) of the developer in the supply chamber 311 or the mixing chamber 312. As shown in FIG.
This developer amount detection device 303A is, for example, a magnetic permeability sensor. For example, the magnetic permeability is detected in the horizontal direction (for example, the X-axis direction or the Y-axis direction) at a predetermined height in the supply chamber 311 or the stirring chamber 312, and it is possible to detect that the developer has increased to the predetermined height based on the magnetic permeability detection result.
The developer amount detection device 303A is not limited to a magnetic permeability sensor, and may detect an increase in developer by optically detecting the developer height using a photointerrupter or the like.

In the developing device 30A, a reverse winding screw 36A as a reverse feed conveying member is connected to the downstream side in the forward conveying direction of the supply screw 33, and further, a discharge screw 37A is connected to the downstream side in the forward conveying direction.
The reverse winding screw 36A includes a fourth shaft 361A rotatably supported within the housing 31 while facing the X-axis direction, and a spiral stirring blade 362A fixedly mounted on the fourth shaft 361A. The discharge screw 37A includes a fifth shaft 371A rotatably supported within the housing 31 while facing the X-axis direction, and a spiral stirring blade 372A fixedly mounted on the fifth shaft 371A.
The fourth shaft 361A and the fifth shaft 371A are concentrically connected to the first shaft 331 of the supply screw 33 and rotate integrally with each other.
The agitating blade 362A of the reverse-winding screw 36A is a spiral blade that is wound in the opposite direction to the agitating blade 332 of the supply screw 33 , and the developer transport direction of the forward rotation is opposite to the developer transport direction by the supply screw 33 .
The stirring blade 372A of the discharge screw 37A is a spiral blade that is oriented in the same direction as the stirring blade 332 of the supply screw 33 , and the developer transport direction during forward rotation is the same as that of the supply screw 33 .

The reverse winding screw 36A and the discharge screw 37A are accommodated in a discharge chamber 319A provided on the downstream side of the supply chamber 311 in the conveying direction of the forward rotation of the supply screw 33.
The cross-sectional shape of the discharge chamber 319A along the YZ plane is set to be approximately the same as that of the supply chamber 311, and the discharge chamber 319A and the supply chamber 311 are connected with each other without any boundary such as a partition or step.
In the discharge chamber 319A, the reverse winding screw 36A or the discharge screw 37A is disposed over almost the entire length in the X-axis direction. A supply chamber side developer discharge port 319B is provided on the wall surface surrounding the discharge screw 37A at the end on the downstream side in the conveying direction of the forward rotation of the supply screw 33 of the discharge chamber 319A.
9, this supply chamber side developer discharge port 319B opens downward from the inner bottom of the discharge chamber 319A. The developer discharged from this supply chamber side developer discharge port 319B drops to and is stored in a waste developer storage unit (not shown).

In addition, the supply chamber 316 of the developing device 30A is not provided with a mixing chamber side developer discharge port 318 directly connected to a waste developer storage section, but instead is provided with a mixing chamber side developer discharge port 318A consisting of a communication port that communicates with the discharge chamber 319A from the upstream end of the supply screw 35 in the supply chamber 316 in the forward rotation transport direction.
As shown in Fig. 10, the stirring chamber side developer discharge port 318A is provided horizontally along the Y-axis direction, and it is preferable that the height of the lower end of the stirring chamber side developer discharge port 318A is approximately the same as the height h of the upper end of the third shaft 351 of the supply screw 35. This height is a height that the developer does not reach when the developing device 30 is properly positioned without any inclination. At this height, the developer can be discharged by the transport and stirring operation of the supply screw 35. In addition, the stirring chamber side developer discharge port 318A may be provided with a downward gradient toward the discharge chamber 319A side.

[Developing Operation of Developing Device]
The operation of the developing device 30A is controlled by the control device 11. Fig. 11 is a flow chart showing the operation control of the developing device 30A during image formation by the control device 11. The operation of the developing device 30A will be described with reference to Fig. 11.

During image formation, in a normal developing operation, the control device 11 drives the motor 301 in a direction to rotate the supply screw 33, the reverse winding screw 36A, the discharge screw 37A, the stirring screw 34, and the replenishing screw 35 in the forward direction (step S21). As a result, the developer in the supply chamber 311 and the stirring chamber 312 is transported along the circular circulation path indicated by the arrows H1, H3, H2, and H4 while the toner and carrier are being stirred.
In addition, the supply screw 33 supplies the toner in the developer that has been charged by stirring to the outer circumferential surface of the developing roller 32 located adjacent to it in the supply chamber 311. This allows the developing roller 32 to develop a toner image on the outer circumferential surface of the photoconductor 13 that faces it outside the housing 31.

Then, the control device 11 continuously or periodically detects the magnetic permeability in the supply chamber 311 or the mixing chamber 312 using the toner amount detection device 302, and determines from the detection result whether the toner content in the developer is below a specified threshold value (step S23).
If the toner content is equal to or greater than the specified threshold, the process proceeds to step S27, and if the toner content is less than the threshold, the control device 11 executes control to operate the conveying mechanism of the replenishing unit to replenish toner containing a specified amount of carrier (hereinafter, referred to as toner, etc.) (step S25). The replenishing of toner, etc. may be performed for a specified period of time, or may be continued until the toner content indicated by the magnetic permeability detected by the toner amount detection device 302 reaches a target value at the time of replenishing.

When toner or the like is replenished, the toner or the like is supplied from the developer replenishment port 317 into the supply chamber 316, and the toner or the like is transported toward the mixing chamber 312 by the supply screw 35, and is transported while being stirred by the mixing screw 34 together with the developer in the mixing chamber 312. Therefore, the developer to which the toner or the like has been replenished is transported to the supply chamber 311.
In addition, within the supply chamber 316, the supply screw 35 transports toner toward the mixing chamber 312. Therefore, under normal developer transport conditions, the toner and developer are not transported upstream in the forward rotation transport direction of area A1 shown in Figure 9, and the toner and developer are not discharged from the mixing chamber side developer discharge port 318A.

Next, the control device 11 continuously or periodically detects an increase in the amount of developer in the supply chamber 311 or the mixing chamber 312 by the developer amount detection device 303A, and determines whether the amount of developer has increased to a specified amount (step S27).
If the developer has not increased to the specified amount, the process proceeds to step S35. If the developer has increased to the specified amount, control is performed to rotate the motor 301 in the reverse direction (step S29).

By the reverse rotation of the motor 301, within the mixing chamber 312 and the supply chamber 316, as shown by the two-dot chain line arrow G2 in FIG. 9, a flow of the developer in the direction opposite to that during normal operation is generated.
The developer with low charge due to insufficient mixing occurring at the confluence R (see FIG. 7) and toner aggregates occurring around the developer supply port 317 are transported along the arrow G2 together with the developer, so the toner, etc. and the developer retreat to the area A2 shown in FIG. 9.
When the toner or developer in the supply chamber 316 reaches a predetermined height, it flows into the discharge chamber 319A through the mixing chamber side developer discharge port 318A.

In addition, as the motor 301 rotates in the reverse direction, the developer in the discharge chamber 319A is transported by the reverse winding screw 36A along the arrow G3 toward the downstream side of the transport direction when the supply screw 33 rotates in the forward direction. As a result, the developer that had increased in the supply chamber 311 is also transported to the discharge chamber 319A side.

The time for which the motor 301 rotates in the reverse direction is set to at least the time required to transport the developer from the circular circulation path (near the junction R) indicated by the arrows H1, H3, H2, and H4 to the mixing chamber side developer discharge port 318A. This allows developer that is insufficiently mixed and has a low charge level, which occurs at the junction R, and toner aggregates that occur around the developer supply port 317, to be transported from the mixing chamber side developer discharge port 318A to the discharge chamber 319A.

In addition, even if the developing device 30A is tilted or the like, causing the developer to become unevenly distributed in the supply chamber 311 or the mixing chamber 312 and increase in volume, the developer amount detection device 303A detects an increase in the amount of developer in the supply chamber 311 or the mixing chamber 312, and the motor 301 is controlled to rotate in the reverse direction to suppress or eliminate the uneven distribution of developer.

The control device 11 measures the elapsed time from the start of reverse rotation of the motor 301, and determines whether or not a predetermined execution time has elapsed (step S31).
If the execution time has not elapsed, the motor 301 continues to rotate in the reverse direction, and if the execution time has elapsed, the motor 301 is switched back to rotating in the forward direction (step S33).
As a result, the developer transported into the discharge chamber 319A by the reverse-winding screw 36A and the toner, etc. and developer transported into the discharge chamber 319A through the stirring chamber side developer discharge port 318A are discharged to the waste developer storage section from the supply chamber side developer discharge port 319B by the discharge screw 37A.

Then, the control device 11 determines whether image formation is complete (step S35), and if not, returns to step S21 to continue the developing operation, and when image formation is complete, stops the motor 301 (step S37) to end the developing operation.

In the control of this developing device 30A, the control to reverse rotation of the motor 301 due to an increase in developer has been exemplified, but as in the case of the developing device 30, control to perform reverse rotation periodically or when the driving torque of the motor 301 increases may also be performed.

[Technical effect of the second embodiment]
As described above, the image forming apparatus 10A has the same technical effects as the image forming apparatus 10.
Furthermore, in the developing device 30A, a reverse-winding screw 36A is provided downstream in the developer transport direction of the forward rotation of the supply screw 33, and a supply chamber side developer discharge port 319B is provided in the housing 31 for discharging developer to the outside of the housing 31 from the upstream area in the developer transport direction when the reverse-winding screw 36A rotates forward. This makes it possible to discharge excess developer in response to an increase in developer inside the housing 31.
Therefore, it is possible to perform good development by replenishing new carrier, thereby improving the image quality of the image forming apparatus 10A.
Even if the developer increases on one side in the X-axis direction due to an inclined arrangement of the developing device 30A with respect to the X-axis direction, the excess developer can be discharged.

The mixing chamber side developer discharge port 318A is configured as a communication port that leads from the supply chamber 316, which is the area upstream in the developer transport direction when the mixing screw 34 rotates forward, to the discharge chamber 319A, which is the area upstream in the developer transport direction when the reverse-winding screw 36A rotates forward. This allows developer with insufficient mixing and low charge at the developer confluence point R and toner aggregates generated around the developer supply port 317 to be discharged from the mixing chamber side developer discharge port 318A through the discharge chamber 319A and the supply chamber side developer discharge port 319B, making it possible to improve the quality of images formed in the image forming device 10A.

The stirring chamber side developer discharge port 318A is illustrated as being a communication port leading from the supply chamber 316 to the discharge chamber 319A, but the stirring chamber side developer discharge port 318A may also be configured to be directly connected to a waste developer storage unit (not shown).

[Comparative Test 1]
An image forming apparatus 10 including the developing device 30 having the above-mentioned configuration is taken as a first embodiment, and an image forming apparatus 10A including the developing device 30A having the above-mentioned configuration is taken as a second embodiment.
In addition, an image forming apparatus having a developing device in which the stirring chamber side developer discharge port 318 is removed from the developing device 30 is referred to as Comparative Example 1, and an image forming apparatus having a developing device in which the stirring chamber side developer discharge port 318A is removed from the developing device 30A is referred to as Comparative Example 2.
Then, the following Comparative Test 1 was carried out for the above-mentioned Examples 1 and 2 and Comparative Examples 1 and 2.
That is, each developing device was installed with an inclination of 3° so that the developer supply port side was facing downward, and image formation with a coverage of 10% in A4 size was performed continuously on multiple recording media, and the change in the driving torque of each internal screw was measured.
As a result, in Comparative Examples 1 and 2, due to the pressure of the developer biased toward the developer supply port side, the torque increased by 1.5 times when the number of images formed was approximately 100, and by 2.5 times when the number of images formed was approximately 300, exceeding the rated value of the motor that serves as the driving source and leading to mechanical failure.
In contrast to this, in Examples 1 and 2, the uneven developer is discharged from the supply chamber side developer discharge outlet 319B via the mixing chamber side developer discharge outlet 318 or the mixing chamber side developer discharge outlet 318A, so even when images are formed on 300 recording media, the driving torque of each screw does not increase.
In this way, it was found that in the image forming apparatus 10, 10A equipped with the developing device 30, 30A which is an embodiment of the present invention, developer can be effectively discharged in the event of developer being biased due to the inclination of the developing device 30, 30A, etc., and image formation can be continued stably without placing excessive load on the motor 301.

[Comparative Test 2]
The following Comparative Test 2 was carried out for the above-mentioned Examples 1 and 2 and Comparative Examples 1 and 2.
In order to increase the frequency of toner replenishment, image formation was performed on 10,000 sheets of A4 size recording media at a somewhat high coverage of 50%. After the above image formation, each screw of the developing device was rotated in reverse for 5 seconds, and then image formation was resumed.
As a result, in Comparative Examples 1 and 2, stains due to toner aggregates occurred on the recording medium immediately after restarting, and deterioration of image quality due to fogging was observed for about 50 sheets thereafter.
In contrast to this, in Examples 1 and 2, the reverse rotation of each screw caused both the toner aggregates and stagnant developer (developer that was insufficiently stirred and had a low charge amount) to be discharged from the supply chamber side developer discharge outlet 319B via the stirring chamber side developer discharge outlet 318 or the stirring chamber side developer discharge outlet 318A, so that good image formation was achieved on the recording medium immediately after reverse rotation was resumed, just as on the recording medium before reverse rotation.
In this way, it was found that in the image forming apparatus 10, 10A equipped with the developing device 30, 30A which is an embodiment of the present invention, stagnant developer and toner aggregates which are easily mixed into the supplied developer during reverse rotation can be effectively discharged from the mixing chamber side developer discharge port 318 or the supply chamber side developer discharge port 319B, and stable, high-quality image formation can be performed.

10, 10A Image forming apparatus 11 Control device 12 Image forming section 13 Photoconductor 30, 30A Developing device 31 Housing 32 Developing roller (developer carrier)
33 Supply screw (supply conveying member)
34 Stirring screw (stirring and conveying member)
35 Supply screw 36A Reverse winding screw 37A Discharge screw 301 Motor (drive source)
302 toner amount detection device 303A developer amount detection device 311 supply chamber 312 mixing chamber 313 partition wall 314 first communication portion 315 second communication portion 316 supply chamber 317 developer supply port 318, 318A mixing chamber side developer discharge port 319A discharge chamber 319B supply chamber side developer discharge port R junction

Claims (9)

A developer carrier;
a supplying and conveying member that conveys a developer and supplies the developer to the developer carrying member;
a stirring and conveying member that conveys the developer in a direction opposite to a developer conveying direction by the supply and conveying member;
a housing having a supply chamber for storing the supply transport member and a mixing chamber for storing the mixing transport member,
a stirring chamber side developer discharge port is provided in the housing for discharging the developer from an upstream region in the developer transport direction of the stirring transport member to the outside of the housing, and the developer that has reached the stirring chamber side developer discharge port is discharged toward the upstream side in the developer transport direction of the stirring transport member;
a reverse feed conveying member for conveying the developer in a direction opposite to the developer conveying direction of the supplying and conveying member is provided downstream of the developer conveying direction of the supplying and conveying member;
a supply chamber side developer discharge port for discharging the developer from an upstream area in a developer transport direction of the reverse feed transport member to the outside of the housing, the supply chamber side developer discharge port being provided in the housing. The mixing chamber side developer discharge port is
2. The developing device according to claim 1, further comprising a communication port extending from an upstream region of said agitating and transporting member in the developer transport direction to an upstream region of said reverse transporting member in the developer transport direction. The developing device according to claim 1 or 2, characterized in that the lower end of the developer discharge port on the mixing chamber side is spaced a certain height from the inner bottom surface of the housing. A developer carrier;
a supplying and conveying member that conveys a developer and supplies the developer to the developer carrying member;
a stirring and conveying member that conveys the developer in a direction opposite to a developer conveying direction by the supply and conveying member;
a housing having a supply chamber for storing the supply transport member and a mixing chamber for storing the mixing transport member,
a stirring chamber side developer discharge port is provided in the housing for discharging the developer from an upstream region in the developer transport direction of the stirring transport member to the outside of the housing, and the developer that has reached the stirring chamber side developer discharge port is discharged toward the upstream side in the developer transport direction of the stirring transport member;
a supply chamber is provided extending from the mixing chamber toward an upstream side in a developer transport direction of the mixing and transporting member,
The supply chamber communicates with the mixing chamber without any boundary such as a partition or a step,
a mixing chamber-side developer discharge port that opens downward from an inner bottom of the supply chamber; The housing has a partition wall that separates the supply chamber and the mixing chamber,
5. The developing device according to claim 1, wherein the partition is provided with a first communicating portion for transferring the developer from the supply and transport member to the agitating and transport member, and a second communicating portion for transferring the developer from the agitating and transport member to the supply and transport member. The developing device according to any one of claims 1 to 5, characterized in that the mixing chamber side developer discharge port is provided upstream in the developer transport direction of the mixing transport member with respect to a developer supply port through which the developer is replenished into the housing. A drive source for the stirring and conveying member;
a control device for the driving source,
7. The developing device according to claim 1, wherein the control device controls the drive source so as to switch between forward and reverse feeding of the agitating and conveying member. a circulation path for the developer is formed by driving the supply transport member and the agitation transport member,
the mixing chamber side developer discharge port is provided at a position outside the circulation path,
The developing device according to claim 7, wherein the control device controls the drive source so as to drive the stirring and transporting member in the reverse direction for a time period longer than the time it takes for the developer to move from the circulation path to the stirring chamber side developer discharge port. An image forming apparatus comprising the developing device according to any one of claims 1 to 8.

Images