JP2008242256A - Developer supply apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developer supply device capable of stably supplying a developer just after the developing roller starts to rotate, and also, suppressing the heat generation by a bias voltage power source for applying a bias voltage to the developing roller. <P>SOLUTION: An AC frequency of the AC bias voltage to be applied to the developing roller 61 is reduced by an apparatus control part 9 that controls the bias voltage power source for applying the bias voltage to the developing roller 61 for supplying the developer on an electrostatic latent image formed on the surface of a photoreceptor drum 2, in accordance with the amount of the developer supplied to the photoreceptor drum 2 after the developing roller 61 starts to rotate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an apparatus for supplying a developer onto an electrostatic latent image on a photosensitive drum used in an image forming apparatus such as a printer, a copying machine, and a facsimile machine.

In a dry image forming apparatus using a one-component toner as a developer, a charged developer on the surface of a developing roller is supplied onto an electrostatic latent image formed on the surface of a photosensitive drum by a built-in developing device.
The developing roller is connected to a bias voltage power source, and a DC bias voltage and an AC bias voltage superimposed thereon are applied by the bias voltage power source.

During operation of the developing device, the developer is charged by friction received by the rotation of the developing roller. On the other hand, when the developing device stops and the developing roller does not rotate, the charged state of the developer on the surface of the developing roller becomes unstable.
Therefore, when the developing device is temporarily stopped and then restarted, immediately after the developing device is operated, the developer on the surface of the developing roller whose charging state has become unstable is supplied to the photosensitive drum. Cause. Therefore, by increasing the AC frequency of the AC bias voltage applied to the developing roller, the unstable charging state is improved, and the developer is stably supplied onto the electrostatic latent image on the surface of the photosensitive drum. (For example, Patent Document 1).
Japanese Patent Laid-Open No. 11-272048

However, the AC bias voltage needs to be about 900 V at the maximum. In such a bias voltage power source, the heat generation of the bias voltage power source increases as the AC frequency of the AC bias voltage applied to the developing roller increases. Due to such increased heat generation of the bias voltage power supply, the environmental temperature of other electronic components (for example, transformers) installed on the bias voltage power supply substrate may rise, and the characteristics of the electronic components may deteriorate.
Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to enable a stable supply of developer immediately after the start of rotation of the developing roller and to apply a bias voltage to the developing roller. It is an object of the present invention to provide a developer supply device that can suppress a temperature rise due to a bias voltage power supply.

  In order to achieve the above object, the present invention provides a developing roller for carrying a developer and supplying the developer onto the electrostatic latent image on the surface of the photosensitive drum, and in conjunction with the rotation of the developing roller. A developer supplying apparatus comprising a charging unit for charging a developer, and a bias voltage power source connected to the developing roller and for applying an AC bias voltage to the developing roller, and further from the bias voltage power source to the developing unit And a controller that reduces the AC frequency of the AC bias voltage applied to the roller in accordance with the amount of the developer supplied to the photosensitive drum after the rotation of the developing roller is started.

When the developing roller does not rotate, the developer is not newly frictionally charged by the charging unit, and immediately after starting the rotation of the developing roller, the charged state of the developer on the developing roller is unstable. It may be.
Therefore, according to the developer supply device of the present invention, immediately after the rotation of the developing roller is started, the developer charging state is stabilized by increasing the AC frequency of the AC bias voltage applied to the developing roller, It is supplied stably on the electrostatic latent image on the surface of the photosensitive drum. Further, after the rotation of the developing roller is started, the developer on the developing roller is supplied from the developing roller by being supplied onto the electrostatic latent image on the surface of the photosensitive drum. On the other hand, since the newly charged developer is supplied onto the developing roller by the rotation of the developing roller, the developer is applied to the developing roller according to the amount of the unstable charged developer consumed from the developing roller. Reduce the AC frequency of the AC bias voltage.
In this way, by setting the AC frequency of the AC bias voltage applied to the developing roller to the minimum necessary to stably supply the developer onto the electrostatic latent image on the surface of the photosensitive drum, the temperature by the bias voltage power supply is reduced. It is possible to suppress the rise and prevent the deterioration of characteristics due to the rise in the environmental temperature of the electronic components installed near the bias voltage power supply.

As an example, the AC frequency of the AC bias voltage applied to the developing roller is changed in accordance with the rotation period of the developing roller.
For example, the AC frequency of the AC bias voltage may be changed every time the developing roller rotates, or the AC frequency is kept constant while the developing roller rotates a plurality of times and the unstable charged developer is consumed. May be retained.

  In a desirable configuration, the control unit is provided with a time counter capable of measuring a stop time from the last rotation of the developing roller until the rotation starts again, and the control unit is based on the stop time, An AC frequency of an AC bias voltage applied to the developing roller is determined immediately after rotation of the developing roller is started.

  Since the developer charging state increases instability with the progress of the development roller stop time, the longer the development roller stop time, the longer the AC bias voltage applied to the development roller immediately after the development roller starts rotating. Increase the frequency.

  As a specific configuration, the charging unit is provided between the supply member for supplying the developer to the surface of the developing roller and the developing roller, and downstream of the supply member in the rotation direction of the developing roller. Is formed between the regulating member provided on the developing roller and the developing roller.

  In such a configuration, the developer is charged by the frictional force received when it is supplied from the supply member to the developing roller and when it contacts the regulating member.

  The present invention as an image forming apparatus includes a photosensitive drum and the developer supply device according to any one of the above for supplying a charged developer onto an electrostatic latent image on the photosensitive drum.

  According to the developer supply device of the present invention, the developer can be stably supplied immediately after the start of rotation of the developing roller, and the temperature rise by the bias voltage power source for applying the bias voltage to the developing roller is suppressed. can do.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
FIG. 1 is an overall perspective view of the image forming apparatus according to the embodiment of the present invention, FIG. 2 is a block diagram showing a schematic configuration of the developer supply apparatus according to the embodiment of the present invention, and FIG. FIG. 4 is a diagram for explaining the relationship between the consumption amount of the developer and the AC frequency of the AC bias voltage applied to the developing roller. FIG. 4 shows the consumption amount of the developer and the AC bias applied to the developing roller in other cases. FIG. 5 is a flowchart for explaining the processing procedure of the apparatus control unit, for explaining the relationship between the voltage and the AC frequency.

1 is an example of the image forming apparatus 1 according to the present invention. In the image forming apparatus 1, a predetermined image is printed on the paper supplied from the paper feed cassette 11 by the dry one-component developing method, and the printed paper is conveyed to the paper discharge tray 13.
As shown in FIG. 2, the developing device D of the image forming apparatus includes a photosensitive drum 2, a charger 3 for charging the surface of the photosensitive drum 2, and a laser beam 4a for irradiating the surface of the photosensitive drum. And a laser light source 4.

The surface of the photosensitive drum 2 has a negative potential.
On the other hand, the laser light source 4 irradiates a predetermined portion of the surface of the photosensitive drum 2 charged to a uniform negative potential with a laser beam 4a based on an instruction from the CPU 90 of the apparatus control unit 9 having image information. As the negative potential of the portion irradiated with the laser beam 4a on the surface of the photosensitive drum 2 decreases, an electrostatic latent image is formed on the portion irradiated with the laser beam 4a.

The developing device D further includes a developer supply device S for supplying a developer composed of one-component toner and charged to a negative polarity on the electrostatic latent image formed on the surface of the photosensitive drum 2. .
The developer supply device S is more developed than the developing roller 61 installed near the photosensitive drum 2, the supply roller 62 (an example of a supply member) installed near the developing roller 61, and the supply roller 62. A regulation blade 64 (an example of a regulation member) is provided on the downstream side in the rotation direction of the roller 61 and installed in the vicinity of the developing roller 61.

  The developing roller 61 is connected to the bias voltage power source 7. The bias voltage power source 7 includes a DC voltage power source 72 and an AC voltage power source 71 connected in series to the DC voltage power source 72. The developing roller 61 receives a DC bias voltage and an AC bias voltage superimposed thereon. Apply. The bias voltage power supply 7 is connected to an AC frequency converter 70. As will be described later, the AC frequency converter 70 changes the AC frequency of the AC bias voltage applied to the developing roller 61 based on an instruction from the CPU 90 of the apparatus control unit 9.

  Further, the bias voltage power source 7 is also connected to the regulation blade 64 and the supply roller 62, and the regulation blade 64 and the supply roller 62 cut the AC bias voltage component from the bias voltage power source 7 through the diode 73. , The same bias voltage obtained by shifting the DC bias voltage component is applied.

The developer is supplied to the surface of the supply roller 62 from a storage portion (not shown) in which the developer is stored, and is supplied from the surface of the supply roller 62 to the surface of the development roller 61.
When the developer is supplied from the supply roller 62 to the development roller 61, the developer is negatively charged due to friction received between the supply roller 62 and the development roller 61, and then developed on the downstream side of the rotation of the development roller 61. When passing between the roller 61 and the regulating blade 64, the thickness is regulated to a predetermined thickness, and further charged to a negative polarity due to friction received by contact with the regulating blade 64.

  The surface potential of the developing roller 61 oscillates on the negative side due to the application of an AC bias voltage. When the surface potential of the developing roller 61 becomes a negative potential as compared with the potential of the electrostatic latent image on the surface of the photosensitive drum 2, the developer charged to the negative polarity is caused by the electrostatic force. To the electrostatic latent image on the surface of the photosensitive drum 2 and developed on the surface of the photosensitive drum 2. The developer developed on the surface of the photosensitive drum 2 is then transferred to a sheet P, and the sheet P after the image transfer passes through a fixing unit (not shown), and then is discharged from the image forming apparatus 1 shown in FIG. 13 is conveyed.

In this way, while the developer supply device S shown in FIG. 2 is operated and the developing roller 61 and the supply roller 62 are rotating, the developer moves from the supply roller 62 to the development roller 61. In addition, due to the friction received when contacting the regulating blade 64, the negative polarity is sufficiently charged. Further, the developer that has not been supplied from the developing roller 61 to the photosensitive drum 2 is scraped off by a cleaning blade (not shown) provided in contact with the developing roller 61 and returned to the storage unit. Such a circulation also stabilizes the charged state of the developer.
At this time, the AC frequency of the AC bias voltage applied to the developing roller 61 is maintained at a constant steady value.

  On the other hand, when the developer supply device S is stopped and the developing roller 61 and the supply roller 62 do not rotate, the developer is not newly frictionally charged. While the developing device D is stopped, the charged state of the developer is unstable due to factors such as the length of the stop time of the developer supplying device S and the ambient humidity of the image forming device due to discharge to the ambient air. It becomes.

Therefore, when the developer supply device S that has been stopped is operated, immediately after the operation of the developer supply device S, the surface of the developing roller 61 is in an unstable charging state while the developer supply device S is stopped. The developed developer remains.
According to the developer in an unstable charged state, the electrostatic latent image portion on the surface of the photosensitive drum 2 may not be developed, or the portion other than the electrostatic latent image on the surface of the photosensitive drum 2 may be developed. is there. Therefore, immediately after the operation, the developer supply device S adjusts the AC frequency of the AC bias voltage applied to the developing roller 61 to make it higher than the steady value, so that the developer is transferred from the developing roller 61 to the photosensitive drum 2. The number of times of moving onto the electrostatic latent image on the surface and the number of times of returning the developer other than the electrostatic latent image portion on the surface of the photosensitive drum 2 to the developing roller 61 are increased. The developer is stably supplied onto the electrostatic latent image on the surface of the photosensitive drum 2.

Immediately after the operation of the developer supply device S, the increment from the steady value of the AC frequency of the AC bias voltage applied to the developing roller 61 is determined by the CPU 90 of the device control unit 9 based on the stop time of the developer supply device S. The longer the stop time, the larger it becomes. The AC frequency converter 70 adjusts the AC frequency of the AC bias voltage applied to the developing roller 61 based on an instruction from the CPU 90 of the apparatus control unit 9.
For this purpose, the device control unit 9 includes a time counter 91, counts the time from when the developer supply device S stops to the current time, stores it in the memory 92, and develops based on this stop time. The AC frequency of the AC bias voltage applied to the developing roller 61 immediately after the operation of the agent supply device S is determined.
Further, by further connecting a sensor capable of detecting the ambient humidity of the image forming apparatus to the apparatus control unit 9, the CPU 90 of the apparatus control unit 9 increases the increase range from the steady value of the AC frequency to the developer supply apparatus S. In addition to the stop time, it can also be determined by the ambient humidity.

By the way, the developer on the surface of the developing roller 61 is consumed from the surface of the developing roller 61 by being supplied onto the electrostatic latent image on the surface of the photosensitive drum 2 after the operation of the developer supplying device S is started. Go. On the other hand, a newly charged developer is supplied from the supply roller 62 to the surface of the developing roller 61.
As described above, as the developer supply to the photosensitive drum 2 by the developer supply device S proceeds, the developer on the surface of the developing roller 61 is changed from an unstable charged state to a newly charged one. It will be replaced.

Therefore, the CPU 90 of the apparatus control unit 9 starts electrostatic operation on the surface of the photosensitive drum 2 after the start of the operation of the developer supply device S based on image forming information for forming an electrostatic latent image on the surface of the photosensitive drum 2. The amount of the developer supplied and consumed on the latent image is calculated, and the AC frequency of the AC bias voltage applied to the developing roller 61 according to the amount of developer consumed is immediately after the operation of the developer supply device S. From a high value to a steady value.
As described above, the developer supply device S can stably supply the developer onto the electrostatic latent image on the surface of the photosensitive drum 2 by increasing the AC frequency of the AC bias voltage applied to the developing roller 61. By making the minimum necessary, it is possible to suppress the temperature rise due to the bias voltage power supply 7 and to prevent the deterioration of characteristics due to the environmental temperature rise of the electronic components (transformers and the like) installed on the substrate of the bias voltage power supply 7.

As an example of a method of reducing the AC frequency of the AC bias voltage applied to the developing roller 61 according to the amount of developer supplied and consumed on the electrostatic latent image on the surface of the photosensitive drum 2, the developing roller It is conceivable to change the AC frequency of the AC bias voltage applied to the developing roller 61 in accordance with the rotation period of the developing roller 61 based on the amount of developer consumed during one rotation of the 61.
For example, when a solid image (an image with a large amount of developer consumption) is printed by the image forming apparatus, the developer on the surface of the developing roller 61, that is, the developer, while the developing roller 61 rotates in the first round. Most of the developer that has become unstablely charged during the stop time of the supply device S is consumed by being supplied onto the electrostatic latent image on the surface of the photosensitive drum 2 (see FIG. 3A). .
In this case, in the rotation after the second turn of the developing roller 61, most of the developer on the surface of the developing roller 61 is in a stable charged state newly supplied from the supply roller 62. Therefore, the developing roller 61 As shown in FIG. 3B, the AC frequency of the AC bias voltage applied to is set to a steady value after the second rotation of the developing roller.

On the other hand, when printing an image such as a character (an image with a small amount of developer consumption) by the image forming apparatus, while the developing roller 61 shown in FIG. Only a part of the developer, that is, a part of the developer that is in an unstable charged state during the stop time of the developer supply device S is relatively supplied by being supplied onto the electrostatic latent image on the surface of the photosensitive drum 2. It is consumed slowly (see FIG. 4 (a)).
In this case, when the developing roller 61 rotates for the second turn, the developer charged in an unstable state remaining on the surface of the developing roller 61 from the rotation of the first turn of the developing roller 61 and the supply roller 62 Newly supplied developer in a stable charged state is mixed. Therefore, when the developing roller 61 rotates on the second round, the AC frequency of the AC bias voltage applied to the developing roller 61 is changed from the rotation of the first round of the developing roller as shown in FIG. Is lower and higher than the steady value.
Similarly, with respect to the rotation of the developing roller after the third rotation, the AC frequency of the AC bias voltage applied to the developing roller is decreased gradually from the previous rotation until the steady value is reached. To go.

  As shown in FIG. 4, the developer shown in FIG. 2 is smaller when the amount of developer consumed for printing by the image forming apparatus is smaller than when the developer is consumed as shown in FIG. It is also possible to increase the AC frequency of the AC bias voltage applied to the developing roller 61 after the operation of the supply device S is started.

  Further, when the AC frequency of the AC bias voltage applied to the developing roller 61 is changed for each rotation of the developing roller 61 as described above, an unnatural density change occurs at the boundary portion of the rotating period of the developing roller 61 in the printed image. It is also possible to continuously change the frequency of the AC frequency at finer intervals so that there is no such thing.

Note that, as described above, the method of changing the AC frequency of the AC bias voltage applied to the developing roller 61 for each rotation of the developing roller 61 is an example. The AC frequency may be kept constant while the agent is consumed.
In the above embodiment, the AC frequency of the AC bias voltage applied to the developing roller 61 is adjusted by the device control unit 9 of the image forming apparatus main body. However, a dedicated control unit is provided, and the AC frequency is controlled by the control unit. May be adjusted.

Next, the processing procedure of the apparatus control unit for adjusting the AC frequency of the AC bias voltage applied to the developing roller will be described based on the flowchart of FIG. 5 with reference to FIG. In addition, S1-S11 shown below represents the identification code of the processing procedure (step).
The device controller 9 starts counting the stop time by the time counter 91 from the time when the developer supply device S stops (NO in S1), that is, from the time when the rotation of the developing roller 61 stops (S2), The result is stored in the memory 92 (S3).
On the other hand, when the operation of the developer supply device S is instructed by pressing the copy start button (not shown) or the like (YES in S1), stop time data is acquired from the memory 92 (S4), and the length of the stop time is obtained. An AC bias voltage corresponding to is applied to the developing roller 61 (S5). For this purpose, the device control unit 9 refers to a storage unit (not shown) that stores the correspondence between the stop time and the value of the AC bias voltage.

  When the operation of the developer supply device S is started (S6), the AC bias applied to the developing roller 61 according to the amount of developer consumed by the first rotation of the developing roller 61 (YES in S7). The AC frequency of the voltage is decreased (S8). After that, the AC frequency of the AC bias voltage is decreased according to the consumption amount of the developer, and from when the AC frequency becomes a steady value (YES in S9), until there is an instruction to stop the developer supply device S, The AC frequency is held at a steady value (S10). Then, from the time point when the developer supply device S stops (YES in S11), the time counter 91 starts counting the stop time again.

  Note that the amount of developer consumed varies depending on the type of document image (solid image, text, halftone, etc.) to be imaged. These types of images are detected by the apparatus control unit 9 based on the image density measured by a known method. The apparatus control unit 9 can change the AC frequency of the AC bias voltage applied to the developing roller 61 in accordance with the type of document thus obtained, that is, in accordance with the consumption of the developer.

  The present invention is applicable to printers, copiers, facsimiles, and the like.

1 is an overall perspective view of an image forming apparatus according to an embodiment of the present invention. 1 is a block diagram illustrating a schematic configuration of a developer supply apparatus according to an embodiment of the present invention. The figure for demonstrating the relationship between the consumption amount of a developer, and the alternating current frequency of the alternating current bias voltage applied to a developing roller. The figure for demonstrating the relationship between the consumption of a developer and the alternating current frequency of the alternating current bias voltage applied to a developing roller in other cases. The flowchart showing the process sequence of an apparatus control part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 2 ... Photosensitive drum 7 ... Bias voltage power supply 9 ... Apparatus control part 61 ... Developing roller 62 ... Supply roller 64 ... Regulation blade 71 ... AC voltage power supply 72 ... DC voltage power supply 90 ... CPU
91 ... Clock counter 92 ... Memory D ... Developing device S ... Developer supply device

Claims (5)

A developing roller for carrying the developer and supplying the developer onto the electrostatic latent image on the surface of the photosensitive drum; a charging unit for charging the developer in conjunction with rotation of the developing roller; In a developer supply apparatus that is connected to a roller and includes a bias voltage power source for applying an AC bias voltage to the developing roller.
A controller that reduces an AC frequency of an AC bias voltage applied to the developing roller from the bias voltage power supply in accordance with an amount of the developer supplied to the photosensitive drum after the developing roller starts rotating; A developer supply device comprising: a developer supply device;   The developer supply device according to claim 1, wherein the AC frequency of the AC bias voltage applied to the developing roller is changed in accordance with a rotation period of the developing roller.   The control unit is provided with a time counter capable of measuring a stop time from the last rotation of the developing roller until the rotation starts again, and the control unit rotates the developing roller based on the stop time. 3. The developer supply device according to claim 1, wherein an AC frequency of an AC bias voltage to be applied to the developing roller is determined immediately after starting the operation.   The charging unit includes a regulating member provided between the supply member for supplying the developer to the surface of the developing roller and the developing roller, and downstream of the supply member in the rotation direction of the developing roller. The developer supply device according to claim 1, wherein the developer supply device is formed between the developing roller and the developing roller. A photosensitive drum;
An image forming apparatus comprising the developer supply device according to any one of claims 1 to 4 for supplying a charged developer onto an electrostatic latent image on the photosensitive drum.

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