JP2008096688A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus designed so as to prevent deterioration in the quality of a formed image, by performing a developer refresh process such that all deteriorating developer remaining on a developer carrier is transferred to an image carrier and ejected. <P>SOLUTION: The image forming apparatus X has the function of performing the toner refresh process such that a developing roller 21 is rotated by a drum motor 2 without performing the process of forming images on recording paper, thereby toner is transferred from the developing roller 21 to a photoreceptor drum 11 and the toner on the photoreceptor drum 11 is removed. During the toner refresh process, the image forming apparatus drives the developing roller 21 by means of the drum motor 2 so that the peripheral speed of the developing roller 21 is equal to or lower than that of the photoreceptor drum 11. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus having a function of executing a developer refresh process for periodically discharging a deteriorated developer on a developer carrying member.

In a conventional general image forming apparatus using a one-component magnetic toner that includes a magnetic material and is a developer of only one type of toner, the toner carried on the developing roller provided in the image forming apparatus is It is charged by a layer thickness regulating member that makes the layer thickness of the toner carried on the roller uniform. The charged toner is used for image formation, but the overcharged toner may be aggregated or may remain on the developing roller without being developed due to strong adhesion to the developing roller.
In addition, the toner that is not charged due to deterioration and has no uncharged charge that is charged in the opposite polarity remains on the developing roller without being used for image formation.
If the ratio of the toner having no charge on the developing roller increases due to repeated image formation, the toner adheres to the background other than the image formation area and causes so-called fogging. Reduce image quality.
Further, the quality of the formed image is also lowered by the above-mentioned aggregation toner adhering to the developing roller.
In the image forming apparatus described in Patent Document 1, in order to prevent the quality of an image formed due to the generation of the toner that has no such poorly charged charge or the aggregation toner from being deteriorated, a predetermined value is set. When the specified condition is satisfied, a toner refresh process for updating the toner in the developing device is executed.
In the toner refresh process, a voltage is applied to the developing roller and the photosensitive drum to rotate the image without forming an image, whereby the toner carried on the developing roller is transformed into a solid black electrostatic latent image. The developing device is moved to the applied photosensitive drum and the toner transferred to the photosensitive drum is removed by a cleaning means provided on the photosensitive drum without transferring (image forming). Update the toner inside.
JP 2000-310909 A

However, even if the toner refresh process as described above is performed, the toner carried on the outermost side of the thin layer of toner formed on the developing roller easily moves to the photosensitive drum, but is close to the surface of the developing roller. There is a tendency that the toner carried on the inner layer portion does not easily transfer to the photosensitive drum.
Further, conventionally, the toner transfer from the developing roller to the photosensitive drum is not stopped even during the toner refresh process, and the peripheral speed of the developing roller at that time is the same as in the normal image formation. It is set faster than the peripheral speed of the drum, and toner is always supplied excessively to the photosensitive drum. As described above, in the conventional toner refresh process, the toner on the developing roller may be reduced or the thickness of the toner layer may be reduced no matter how much toner transferred to the photosensitive drum is cleaned. However, the effect of reducing the developing roller layer thickness due to the toner refreshing process and renewing the toner in the inner layer portion of the toner layer on the peripheral surface of the developing roller is limited.
Therefore, in the present invention, during the toner refresh process, the peripheral speed of the developing roller is made slower than the peripheral speed of the photosensitive drum, that is, the ratio of the peripheral speed of the developing roller to the peripheral speed of the photosensitive drum exceeds zero. By setting the ratio to 1.0 or less, the toner carried on the inner side closest to the developing roller is also easily exposed to the electrical influence of the photosensitive drum. As a result, it is possible to execute a toner refresh process in which all of the toner carried on the developing roller can be transferred to the photosensitive drum. Therefore, it is possible to provide an image forming apparatus in which the toner in the developing device can be updated and the quality of the formed image does not deteriorate.

As described above, in the conventional image forming apparatus that forms the basis of the present invention, the developer carrier that carries the developer, the image carrier that carries the original image, and the developer carrier and the image carrier that are driven. Driving means for driving the developer carrying body by the driving means without performing image forming processing on the recording material, whereby the developer is transferred from the developer carrying body to the image carrying body. And a function of executing a developer refresh process for removing the developer on the image carrier.
In such a conventional image forming apparatus, as in the image formation, the developer carrier is driven in a state where the peripheral speed of the developer carrier is higher than the peripheral speed of the image carrier. , Developer refresh processing has been executed. For this reason, even when the developer refresh process is executed, the developer carried on the inner layer portion close to the surface of the developer carrying body is unlikely to move to the image carrying body, and the developer carrying body is overcharged. In some cases, the ratio of the developer and the developer that has become uncharged remains large. In this case, the developer aggregated due to the overcharged developer adheres to the developer carrier, or the developer that has become uncharged occasionally moves to the image carrier. Therefore, there is a problem that the quality of the formed image is deteriorated.
In order to solve this problem, at the time of developer refresh, the developer carried on the inner side near the developer carrying member must be transferred to the image carrying member.
That is, at the development position where the developer carried on the developer carrying body moves to the image carrying body, the developer carried on the inner side near the developer carrying body also has an electrical influence by the image carrying body. It must be easy to receive.
For this purpose, at the time of the developer refreshing process, it is necessary that the driving means drive the developer carrying member so that its peripheral speed is equal to or lower than the peripheral speed of the image carrier.
In particular, it is desirable that the ratio of the peripheral speed of the developer carrier to the peripheral speed of the image carrier during the developer refresh process driven by the driving means exceeds 1.0 and is 1.0 or less.
With such a configuration, when the developer is refreshed, consumption of the developer on the developer carrier is promoted, so that all the deteriorated developer remaining on the developer carrier is transferred to the image carrier. Therefore, it is possible to provide an image forming apparatus that can prevent the deterioration of the quality of the formed image.

  According to the present invention, image formation that prevents deterioration in image quality to be formed is performed by executing a developer refresh process for transferring all the deteriorated developer remaining on the developer carrier to the image carrier and discharging it. An apparatus can be provided.

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 a schematic sectional view of an image forming unit G of the image forming apparatus X according to the embodiment of the present invention. FIG. 2 is a block diagram of a control system of the image forming apparatus X according to the embodiment of the present invention. FIG. 3 is a graph showing the image density formed when the peripheral speed of the developing roller 21 is changed in the image forming apparatus X according to the embodiment of the present invention.

An image forming apparatus X according to an embodiment of the present invention is an image forming apparatus that uses a one-component magnetic toner that includes a magnetic material and is a developer of only one type of toner. For example, the toner includes an internal additive of 51.2% styrene acrylic binder resin, 46.1% magnetic powder, 2.6% hydrocarbon wax, 0.4% hydrophobic silica, abrasive (oxidizing agent). Titanium) and 0.2% external additive.
The image forming apparatus X according to the embodiment of the present invention can be broadly divided into an image forming unit G that forms (transfers) a toner image on a recording paper, and a paper feeding unit (not configured) that supplies the recording paper to the image forming unit G. And a fixing unit (not shown) for heating and fixing the toner image on the recording paper on which the toner image is formed by the image forming unit G.
First, the schematic configuration of the image forming unit G will be described with reference to the cross-sectional view of FIG.
As shown in FIG. 1, the image forming unit G includes a photosensitive drum 11 (an example of an image carrier) that carries an image, a charging roller 12 that charges the surface of the photosensitive drum 11, and the photosensitive drum 11. An exposure unit 13 for forming an electrostatic latent image by irradiating a laser beam on the developing unit 20; a developing device 20 for forming a toner image on the surface of the photosensitive drum 11 by attaching toner to the electrostatic latent image; A transfer position at which a toner image is transferred from the photosensitive drum 11, an endless transfer belt 16 transported to the fixing unit (not shown), and a toner image developed on the photosensitive drum 11 are transferred by the transfer belt 16. A transfer roller 17 to be transferred onto the conveyed recording paper, a cleaning unit 14 for cleaning the photoconductor drum 11 after transfer, and a charge removal unit 15 for removing a potential remaining on the photoconductor drum 11 after transfer. It is configured to include a etc.. In FIG. 1, a transfer belt 16 described later is partially omitted.

Next, referring to the block diagram shown in FIG. 2, the storage unit 1, the drum motor 2, the developing roller voltage applying unit 3, the charging roller voltage applying unit 4, the transfer roller voltage applying unit 5, the developing roller motor 6 and the control The unit 10 will be described.
As shown in the block diagram of FIG. 2, the image forming apparatus X includes a storage unit 1 that is a memory for storing various data, a drum motor 2 that is a drive source of devices included in the photosensitive drum 11 and the developing device 20 ( An example of driving means), a developing roller voltage applying unit 3 for applying a voltage to the developing roller 21 described later, a charging roller voltage applying unit 4 for applying a voltage to the charging roller 12, and a transfer roller for applying a voltage to the transfer roller 17 A voltage application unit 5, a developing roller motor 6 for exclusively driving the developing roller 21, and a control unit 10 for comprehensively controlling them are provided.
The storage unit 1 stores the rotational speed of the developing roller motor 6 corresponding to the peripheral speed for rotating the developing roller 21 described later at the time of image formation and the peripheral speed for rotating the developing roller 21 described later during the toner refresh process. ing.
Based on the information stored in the storage unit 1, the drum motor 2 rotates each roller including a photosensitive drum other than the developing device 20 including the developing roller 21 described later.
That is, the developing roller motor 6 changes and rotates the peripheral speed of the developing roller 21 described later according to the number of rotations stored in the storage unit 1 during image formation and toner refresh processing. In this case, the developing roller motor 6 has a peripheral speed ratio, which is a ratio of a peripheral speed of the developing roller 21 to a peripheral speed of the photosensitive drum 11 described later, between 0 and 2.0. In addition, the peripheral speed of the developing roller 21 can be changed and rotated. Details will be described later.
As an example, the drum motor 2 rotates the photosensitive drum 11 at a peripheral speed of 220 mm / second.
For example, the developing roller voltage application unit 3 applies a voltage obtained by superimposing a DC voltage and an AC voltage of a DC voltage of 150 V, an AC voltage of 1.5 kV, a frequency of 2.7 kHz, and a duty of 40% to the developing roller 21 described later. Apply.

Next, a schematic configuration of the developing device 20 will be described with reference to FIG.
As shown in FIG. 1, the developing device 20 includes a developing roller 21 (an example of a developer carrier) that carries toner on the surface, a supply roller 22 that stirs the toner and supplies the toner to the developing roller 21, An agitation roller 23 that agitates and supplies toner to the supply roller 22, contains each of these rollers 21 to 23, a developer tank 24 that contains toner, and a toner supply tank that contains toner for replenishment to the developer tank 24 27, replenishing rollers 25 and 26 for replenishing the toner stored in the toner replenishing tank 27 to the developing tank 24, a layer thickness regulating member 28 for regulating the layer thickness of the toner carried on the developing roller 21 substantially uniformly, and the like. It is configured with.
The developing roller 21 is, for example, a φ20 roller.
The developing roller motor 6 drives each roller including the developing roller 21 provided in the developing device 20.

Next, an image forming process executed by the image forming apparatus X will be briefly described focusing on functions in the image forming unit G.
An image information signal transmitted from a predetermined reading device (not shown) or the like is transmitted to the control unit 10 of the image forming apparatus X, and the control unit 10 performs predetermined image processing. Data (image data) that has undergone predetermined image processing is input to the exposure unit 13 by the control unit 10. Thereafter, the exposure unit 13 emits a laser beam (laser beam for writing an electrostatic latent image) whose light amount and blinking state are adjusted according to the data subjected to the predetermined image processing to the surface of the photosensitive drum 11. The
Then, an electrostatic latent image is written on the surface of the photosensitive drum 11 charged by the charging roller 12. The photosensitive drum 11 is rotated at a peripheral speed of 220 mm / second in a predetermined direction by the drum motor 2, and the developing roller voltage application unit is at a developing position facing the developing roller 21 provided in the developing device 20. 3, the toner carried on the developing roller 21 to which a voltage obtained by superimposing a DC voltage and an AC voltage of a DC voltage of 150 V, an AC voltage of 1.5 kV, a frequency of 2.7 kHz, and a duty of 40% is applied is the photosensitive drum. 11 is transferred to an electrostatic latent image on the surface, and a toner image is formed.
At the time of this image formation, the developing roller 21 has a peripheral speed ratio of 1.64 relative to the peripheral speed at the time of image formation stored in the storage unit 1, for example, the peripheral speed of the photosensitive drum 11. Is rotated by the developing roller motor 6 at such a peripheral speed. The rotation of the developing roller motor 6 for obtaining the peripheral speed ratio is stored in the storage unit 1 as described above, and the developing roller motor 6 is driven by the control unit 10 with reference to the stored information. . In general, at the time of image formation, the drum motor 2 causes the developing roller to have a higher peripheral speed than the photosensitive drum, that is, the peripheral speed ratio of the developing roller 21 to the peripheral speed of the photosensitive drum 11 is 1. It is rotated at a peripheral speed that is greater than zero.
The photosensitive drum 11 is continuously rotated by the drum motor 2, and the toner image formed on the photosensitive drum 11 is transferred by the transfer roller 17 to which a voltage is applied by the transfer roller voltage application unit 5. The image is transferred to the recording paper conveyed by the transfer belt 16. The cleaning unit 14 is disposed downstream of the transfer roller 17 in the rotation direction of the photosensitive drum 11, and toner and other deposits remaining on the surface of the photosensitive drum 11 are removed. . The neutralization unit 15 is provided downstream of the cleaning unit 14 in the rotation direction of the photosensitive drum 11, and the potential remaining on the photosensitive drum 11 is removed. The toner image transferred to the recording paper is fixed to the recording paper by applying heat of 195 degrees by a heating roller (not shown) having a φ29.7, fluororesin tube, for example, in the fixing unit.

The image forming apparatus X has a function of executing a toner refresh process for preventing the toner from remaining on the developing roller 21 for a long time, like the general image forming apparatus described above.
When the toner refresh process is executed in the state where the peripheral speed of the developing roller 21 is higher than the peripheral speed of the photosensitive drum 11 as in the conventional image formation, as in the conventional case, the image is close to the developing roller. Since the toner carried on the inside remains on the developing roller 21, there are cases where the ratio of the overcharged toner or the toner that has become uncharged remains large. Aggregated toner caused by the overcharged toner and toner that has become uncharged have an adverse effect on the formed image. Therefore, it is necessary to perform a toner refresh process in which not only the outermost toner layer adhered to the developing roller 21 but also the inner toner layer is transferred to the photosensitive drum 11.
Therefore, in the present invention, during the toner refresh process, the peripheral speed of the developing roller 21 is made slower than the peripheral speed of the photosensitive drum 11 to promote the transfer of toner from the developing roller 21 to the photosensitive drum 11, thereby developing the toner. Provided is an image forming apparatus that performs a toner refresh process in which not only the outermost toner layer adhered to the roller 21 but also the inner toner layer is transferred to the photosensitive drum 11.
Details are described below.

A toner refresh process executed by the image forming apparatus X will be described.
The toner refresh process is not yet performed when predetermined conditions such as the printing rate, which is the ratio of drawing pixels in the image data read and input by a reading device (not shown), and the number of prints are satisfied. Even if image data for which printing processing has not been executed remains, the remaining printing processing is temporarily interrupted and executed.
When a predetermined condition is satisfied, such as when a predetermined number of image forming processes with a low printing rate are executed, first, the developing device 20 first develops the developing from the toner replenishing tank 27 by the replenishing rollers 25 and 26. The toner conveyed to the tank 24 is supplied to the supply roller 22 when the stirring roller 23 is rotationally driven by the developing roller motor 6 in a predetermined direction (for example, in the direction of arrow P1 in FIG. 1). The supply roller 22 is driven to rotate in a predetermined direction (for example, an arrow P2 direction in FIG. 1) by the developing roller motor 6 to supply toner to the developing roller 21.
Subsequently, the developing roller 21 is rotated in a predetermined direction (for example, an arrow P3 direction in FIG. 1) by the developing roller motor 6. The peripheral speed of the developing roller 21 at this time will be described later.
By this rotation, the toner supplied by the supply roller 22 is carried by the developing roller 21. Subsequently, the developing roller 21 is rotated by the developing roller motor 6, and the toner carried by the developing roller 21 is charged by the layer thickness regulating member 28 and a substantially uniform toner layer is formed.
On the other hand, the photosensitive drum 11 is rotated in a predetermined direction (for example, the direction of arrow P4 in FIG. 1) by the drum motor 2, so that the charging roller 12 to which a voltage is applied by the charging roller voltage application unit 4 is used. Charged.
In the developing device 20, the developing roller 21 is continuously rotated in the predetermined direction by the developing roller motor 6, and a thin layer of toner formed on the surface of the developing roller 21 faces the surface of the photosensitive drum 11. Contact. The photosensitive drum 11 is rotated in the predetermined direction by the drum motor 2 in synchronization with the rotation of the developing roller 21. By applying to the developing roller 21 a voltage obtained by superimposing a DC voltage and an AC voltage of a DC voltage of 150 V, an AC voltage of 1.5 kV, a frequency of 2.7 kHz, and a duty of 40% by the developing roller voltage application unit 3. The toner carried on the developing roller 21 in contact with the photosensitive drum 11 is transferred onto the surface of the photosensitive drum 11.
At this time, the amount of toner transferred from the developing roller 21 to the photosensitive drum 11 varies depending on the ratio of the peripheral speed of the developing roller 21 to the peripheral speed of the photosensitive drum 11. Of the toner carried on the developing roller 21, not only the toner carried on the outside of the developing roller 21 but also the toner carried on the inner layer portion near the developing roller 21 is transferred to the photosensitive drum 11. In order to investigate the optimum peripheral speed ratio of the developing roller 21 with respect to the peripheral speed of the photosensitive drum 11, the following experiment was conducted.

FIG. 3 shows the case where the toner refresh process is executed by changing the peripheral speed ratio of the developing roller 21 with respect to the peripheral speed of the photosensitive drum 11 during the image forming process for a predetermined number of times, and the peripheral speed ratio is changed. FIG. 6 is a graph showing a change in image density formed on a recording sheet when a toner refresh process is performed without performing a toner refresh process and when a toner refresh process is not performed.
The measuring instrument used for measuring the image density is a reflection densitometer RD918 manufactured by Macbeth.
As in the above example, the image forming apparatus X used in the experiment is rotated by the drum motor 2 at a peripheral speed of the photosensitive drum 11 of 220 mm / second. At the time of image formation, the peripheral speed ratio of the developing roller 21 with respect to the peripheral speed of the photosensitive drum 11 is 1.64.
Using this image forming apparatus X, a predetermined number of image forming processes are performed, and under the same conditions except for the peripheral speed ratio of the developing roller 21 to the peripheral speed of the photosensitive drum 11 during the toner refresh process executed during that time. An experiment was conducted to examine the density of the formed image.
As a result of the experiment, when the toner refresh process is not executed (Z1 in FIG. 3), the number of printed sheets is about 20000, and the formed image density is lowered.
Then, as in the conventional image forming apparatus, when the developing roller 21 is rotated at the same peripheral speed as during image formation during toner refresh processing (the peripheral speed of the developing roller 21 relative to the peripheral speed of the photosensitive drum 11). The ratio is 1.64.Z2) in FIG.3 is about 50000 printed sheets, and the formed image density is lowered.
On the other hand, during the toner refresh process, the peripheral speed of the developing roller 21 and the peripheral speed of the photosensitive drum 11 are the same (the peripheral speed ratio of the developing roller 21 to the peripheral speed of the photosensitive drum 11 is 1. 0 (Z3 in Fig. 3) or during toner refresh processing, when the peripheral speed of the developing roller 21 is less than the peripheral speed of the photosensitive drum 11 (the developing roller 21 has a peripheral speed relative to the peripheral speed of the photosensitive drum 11). The peripheral speed ratio was 0.5, and it was found by experiment that Z4) in FIG.
Thus, during the toner refresh process, it is desirable to drive the developing roller 21 by the drum motor 2 so that its peripheral speed is equal to or lower than the peripheral speed of the photosensitive drum 11.
In particular, the peripheral speed ratio of the developing roller 21 with respect to the peripheral speed of the photosensitive drum 11 during the toner refresh process driven by the drum motor 2 is preferably 0.5 to 1.0. .
In such a toner refresh process, when the peripheral speed of the developing roller 21 is 0, that is, when the peripheral speed ratio is 0, no refresh is performed. Therefore, although the peripheral speed ratio is excluded, if there is a slight peripheral speed for the developing roller 21, even if there is a problem that the refresh speed is slow, a practical refresh is possible. Accordingly, it is considered that the peripheral speed ratio exceeds 0 as the minimum condition for realizing the refresh.

In this toner refresh process, the toner transferred to the photosensitive drum 11 is not transferred onto the recording paper.
On the other hand, the photosensitive drum 11 is rotated by the drum motor 2, and the toner transferred onto the photosensitive drum 11 is removed from the photosensitive drum 11 by the cleaning unit 14 and discharged.
With the above configuration, it is possible to provide an image forming apparatus in which the quality of the formed image does not deteriorate.
In this embodiment, the peripheral speed of the photosensitive drum 11 is constant, and the peripheral speed of the developing roller 21 is changed between image formation and toner refresh. However, the peripheral speed of the photosensitive drum 11 is changed. If the peripheral speed ratio of the developing roller 21 is 1.0 or less, the peripheral speed of the photosensitive drum 11 may be changed.

1 is a schematic cross-sectional view of an image forming unit G of an image forming apparatus X according to an embodiment of the present invention. 1 is a block diagram of a control system of an image forming apparatus X according to an embodiment of the present invention. FIG. 6 is a graph showing an image density formed when the peripheral speed of the developing roller 21 is changed in the image forming apparatus X according to the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Memory | storage part 2 ... Drum motor 3 ... Developing roller voltage application part 4 ... Charging roller voltage application part 5 ... Transfer roller voltage application part 6 ... Development roller motor 10 ... Control part 11 ... Photoconductor drum 12 ... Charging roller 13 ... Exposing section 14 ... cleaning section 15 ... neutralizing section 16 ... transfer belt 17 ... transfer roller 20 ... developing device 21 ... developing roller 22 ... supply roller 23 ... stirring roller 24 ... developing tank 25, 26 ... replenishing roller 27 ... toner replenishing tank 28 ... Layer thickness regulating member

Claims (2)

A developer carrying body carrying a developer, an image carrying body carrying a document image, and a driving means for driving the developer carrying body and the image carrying body,
The developer is transferred from the developer carrier to the image carrier by driving the developer carrier by the driving means without performing image forming processing on the recording material. An image forming apparatus having a function of executing developer refresh processing for removing developer on a body,
An image forming apparatus, wherein, during the developer refresh process, the driving means drives the developer carrying member so that a peripheral speed thereof is equal to or lower than a peripheral speed of the image carrier.   2. The image according to claim 1, wherein a peripheral speed ratio of the developer carrier to a peripheral speed of the image carrier during the developer refresh process driven by the driving unit is 1.0 or more, exceeding 0. 3. Forming equipment.

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