JP2010060829A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a single component developer image forming apparatus capable of suppressing fogging (in particular, reverse fogging) while giving consideration to the problems. <P>SOLUTION: The electrophotographic image forming apparatus using single-component developer as developer, includes a surface potential control means that controls the surface potential of a photoreceptor in accordance with a toner supply amount per unit time. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus using a one-component developer as a developer capable of suppressing the occurrence of fog.

  Development methods for image forming apparatuses such as copiers, printers, and facsimiles using an electrophotographic method include a one-component development method using a one-component developer consisting only of toner, and a two-component developer consisting of a toner and a carrier. Examples of the two-component development method to be used can be given.

  Further, in such an image forming apparatus, when new toner is rapidly replenished, uncharged toner and reversely charged toner are more likely to be generated than in a steady state due to contact with old deteriorated toner. As a result, there is a problem that a phenomenon (hereinafter referred to as fogging) in which the toner adheres to a non-image portion that should originally be whitened to increase the density occurs.

In view of such a problem, the following Patent Documents 1 to 3 disclose techniques for preventing fogging and making the image density constant by changing the developing bias condition.
Specifically, Patent Document 1 discloses a technique for preventing fogging in an image forming apparatus of a two-component development system by changing the development bias condition according to the toner replenishment time.
Japanese Patent Application Laid-Open No. 2004-228561 discloses a technique for changing a developing bias condition in conjunction with a toner density of a developer present in a developing unit in an image forming apparatus of a two-component developing system.
Further, Patent Document 3 discloses a technique for changing the developing bias condition in a magnetic one-component image forming apparatus using a magnetic one-component developer composed only of magnetic toner.

However, the techniques disclosed in Patent Documents 1 to 3 have positive fog (the potential difference between the surface potential and the developing bias is reduced due to a decrease in the surface potential or the like, and the normally charged toner is reduced to a portion where the potential difference is small. Although it is effective against fogging caused by adhering, reverse charging (uncharged toner (low chargeability) in a portion where the potential difference between the surface potential and the developing bias is large (a portion where normal charged toner does not adhere)) It is less effective against toner) and fog caused by reversely charged toner.
The reason is that even if the development bias condition is changed, uncharged toner and reversely charged toner that cause reverse fogging are not lost, and the occurrence of reverse fogging cannot be suppressed.
Reverse fog is likely to occur when toner is replenished rapidly, such as when the toner replenishing means is replaced. In particular, in the one-component development method, compared to the two-component development method in which the toner is charged with a carrier, there is a large difference in the chargeability between the toner in the developing device and the newly supplied toner. Charged toner and uncharged toner) are likely to occur, and reverse fogging tends to occur.

Japanese Patent Laid-Open No. 11-3022 JP-A-5-257369 JP-A-6-95496

  SUMMARY An advantage of some aspects of the invention is to provide an image forming apparatus capable of suppressing the occurrence of fog (particularly reverse fog) in an image forming apparatus of a one-component development system. To do.

  According to a first aspect of the present invention, there is provided an electrophotographic image forming apparatus using a one-component developer as a developer, wherein the surface potential controls the surface potential of the photoreceptor according to the amount of toner replenished per unit time. The present invention relates to an image forming apparatus having a control unit.

  According to a second aspect of the present invention, the surface potential control means sets the surface potential when the reference potential of the photosensitive member is positive if the toner replenishment amount per unit time is equal to or greater than a certain amount during toner replenishment. 2. The image forming apparatus according to claim 1, wherein when the reference potential is lower than the reference potential and the reference potential is negative, the surface potential is set higher than the reference potential.

  The invention according to claim 3 is characterized in that the surface potential control means changes the surface potential at the time of toner replenishment, and then returns the surface potential to the reference potential step by step at regular intervals. The present invention relates to the described image forming apparatus.

  4. The image forming apparatus according to claim 1, further comprising: a developing bias control unit for controlling a developing bias condition in accordance with a change in surface potential of the photosensitive member. About.

  The invention according to claim 5 relates to the image forming apparatus according to claim 4, wherein the developing bias condition is at least one of a voltage, a duty, a frequency, and an amplitude of the AC bias.

  According to the first aspect of the present invention, there is provided an electrophotographic image forming apparatus using a one-component developer as a developer, and the surface potential of the photosensitive member is controlled in accordance with a toner replenishment amount per unit time. By having the surface potential control means, occurrence of fog (particularly reverse fog) can be suppressed.

  According to the second aspect of the present invention, the surface potential control means is configured to supply the surface potential when the reference potential of the photosensitive member is positive if the toner replenishment amount per unit time is equal to or greater than a certain amount during toner replenishment. When the potential is set lower than the reference potential and the reference potential is negative, the surface potential is set higher than the reference potential, thereby effecting the reverse fog that is likely to occur when the toner is replenished over a certain amount per unit time. Can be suppressed.

  According to the invention of claim 3, the surface potential control means changes the surface potential at the time of toner replenishment, and then returns the surface potential to the reference potential step by step at regular intervals, thereby generating fog. Can be effectively suppressed. In other words, as time passes from the time of toner replenishment, uncharged toner decreases due to toner agitation, but by gradually returning the surface potential to the reference potential, a surface potential suitable for the amount of uncharged toner can be obtained. it can.

  According to the fourth aspect of the invention, the development bias control means for controlling the development bias condition in accordance with the change in the surface potential of the photoconductor can suppress not only reverse fog but also normal fog. it can.

  According to the fifth aspect of the present invention, since the developing bias condition is at least one of the voltage, duty, frequency, and amplitude of the AC bias, it is possible to reliably suppress the positive fog.

Hereinafter, an image forming apparatus according to the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an image forming apparatus (100) according to an embodiment of the present invention.
The image forming apparatus (100) is an electrophotographic apparatus that employs a magnetic one-component developing method using a magnetic one-component developer composed only of toner, and includes a paper feeding unit (1), a paper conveying unit (2), and an image. A forming unit (3), a fixing unit (4), an image reading unit (5), and the like are provided.

The paper feed unit (1) includes a plurality of paper feed cassettes (11) (four in FIG. 1) that contain paper (P). Then, the paper (P) is sent out from any one of the paper feed cassettes (11) to the paper transport unit (2) by the paper feed roller (12).
The paper (P) sent out from the paper supply unit (1) is conveyed to the image forming unit (3) by the paper conveyance unit (2). Then, the image forming unit (3) transfers a predetermined toner image onto the paper (P) based on the image of the original read by the image reading unit (5) by an electrophotographic process.
The paper (P) on which the toner image is transferred is heated and pressed by the heating roller (41) and the pressure roller (42) provided in the fixing unit (4), so that the toner is transferred onto the paper (P). The image is fixed and discharged onto the discharge tray (7) by the discharge roller pair (6).

Hereinafter, the image forming unit (3) in the image forming apparatus (100) will be described.
The image forming unit (3) includes a photoconductor (31), a charging unit (32) provided around the photoconductor (31), an exposure unit (33), a developing unit (34), a transfer unit (35), It has a cleaning means (36) and a charge eliminating means (37).

The photoconductor (31) plays a role as a drum-shaped image carrier and rotates in the direction of the arrow (X).
The photosensitive member (31) is irradiated with laser light from the exposure means (33) to form an electrostatic latent image based on the original image read by the image reading unit (5). More specifically, the photosensitive member (31) charged to a predetermined potential by the charging means (32) having a charging wire to which a high voltage is applied is irradiated with the laser light generated from the exposure means (33). As a result, the resistance of the portion irradiated with the laser light decreases. And the part where this resistance fell becomes an electrostatic latent image.

After forming the electrostatic latent image, the toner stored in the developing means (34) is supplied to the surface of the photoreceptor (31).
The developing means (34) is provided with a developing roller (341). The developing roller (341) is connected to a developing bias power source, and a developing bias configured by superimposing an alternating current (AC) bias on a direct current (DC) bias is applied at a predetermined timing by the developing bias power source.
The toner in the developing means (34) adheres to the surface of the developing roller (341) by a magnetic pole (not shown) in the developing roller (341). Then, the toner flies from the surface of the developing roller (341) to the surface of the photosensitive member (31) due to the potential difference between the developing roller (341) and the surface of the photosensitive member (31). Since toner adheres electrostatically to the electrostatic latent image formed on the surface of the photoreceptor (31), a toner image corresponding to the electrostatic latent image is developed.
Then, the toner image on the surface of the photoconductor (31) is transferred to the paper (P) supplied between the photoconductor (31) and the transfer unit (35) by the transfer unit (35).
After the toner image is transferred, residual toner on the surface of the photoreceptor (31) is removed by the cleaning means (8), and residual charge on the surface of the photoreceptor (31) is removed by the charge eliminating means (36).
The toner in the developing means (34) decreases with the image formation, but the reduced amount of toner is supplied by a toner supply means (toner cartridge) (not shown).

  In the image forming apparatus (100), a surface potential control means (not shown) is connected to the charging means (32), and a bias condition control means (not shown) is connected to the developing means (34).

The surface potential control means is for controlling the surface potential (Vo) of the photoreceptor (31) by controlling the charging means (32).
Specifically, the charging means (32) is controlled so that the surface potential (Vo) of the photoconductor (31) becomes the reference potential during normal times (except when toner is replenished).
At the time of toner replenishment, if the amount of toner replenished per unit time is greater than or equal to a certain amount, the surface potential (Vo) of the photoconductor (31) is temporarily set to a value different from the reference potential according to the amount of replenishment. Thus, the charging means (32) is controlled. The amount of toner replenished per unit time may be calculated based on the number of rotations of the toner motor of the toner replenishing means.
In general, an external additive is added to the toner for the purpose of controlling the chargeability, but the toner staying inside the developing means (34) may be detached or buried in the toner. Therefore, it has a surface state different from the surface state of the newly supplied replenishment toner. Therefore, the chargeability differs between the staying toner and the replenishment toner. When new toner is replenished and the two toners come into contact with each other, reversely charged toner or uncharged toner is generated, and fogging (reverse fogging) due to these toners occurs.
When the toner is replenished as described above, reverse fog is more likely to occur than in the normal state. Therefore, the difference between the surface potential (Vo) of the photoconductor (31) and the DC bias potential of the developing bias is not detected. The surface potential (Vo) is controlled so as to reduce the absolute value. That is, when the reference potential is positive, the surface potential is controlled to be lower than the reference potential, and when the reference potential is negative, the surface potential (Vo) is controlled to be higher than the reference potential. By controlling in this way, reversely charged toner or uncharged toner does not fly from the developing means (34) to the photosensitive member (31), so that reverse fog can be suppressed.

Further, the changed surface potential (Vo) is controlled to return to the reference potential step by step at regular time intervals. As the toner replenishes with time, the amount of uncharged toner decreases due to the stirring of the toner. Therefore, the surface potential (Vo) suitable for the amount of uncharged toner can be obtained by gradually returning the surface potential (Vo) to the reference potential. This is because the generation of fog can be effectively suppressed.
Specifically, a plurality of control levels may be provided in accordance with the toner replenishment amount, and the control level may be lowered step by step from the control level at the time of toner replenishment every predetermined time.

  Further, the change range of the surface potential (Vo) may be changed according to the surrounding environmental conditions (temperature, humidity, etc.). For example, uncharged toner is unlikely to be generated in a low-temperature and low-humidity environment, so the change width is reduced, and uncharged toner is likely to be generated in a high-temperature, high-humidity environment, so the change width may be increased.

  When the toner replenishment amount per unit time is less than a certain amount, that is, when the replenishment amount is such that fog does not occur, the surface potential of the photoconductor (31) is controlled to be the reference potential as usual. That's fine.

The bias condition control means is for changing the developing bias condition when the toner is replenished over a certain amount. Specifically, the developing bias condition is changed so as to suppress the occurrence of fogging (positive fogging) due to the normally charged toner.
In the image forming apparatus (100), the reverse fog can be suppressed by the surface potential control means, but the forward fog can also be suppressed by the bias condition control means, so that the occurrence of fog can be surely suppressed.
Examples of the development bias condition include various parameters (voltage (Vpp), duty (time ratio in the development direction during the vibration period), frequency (Vf), amplitude, etc.) of the AC bias in the development bias.

The degree to which the bias condition is changed may be appropriately changed according to the amount of toner replenishment, the surrounding environmental conditions, the degree of control of the surface potential control means, and the like.
Also, the bias condition control means preferably returns to the reference value in a stepwise manner after the change, like the surface potential control means.

Next, control of the surface potential of the photoreceptor (31) by the charging unit (32) (surface potential control unit) and control of the developing bias condition by the bias condition control unit will be described.
FIG. 2 is a flowchart showing the operation of the image forming apparatus (100) during toner supply.
In the image forming apparatus (100), when the toner in the developing means (34) decreases, toner is supplied from the toner supply means (step 1).
When the toner is replenished, it is determined whether or not the toner replenishment amount per unit time is a certain amount or more (step 2). If the amount is more than a certain amount, the control level of the surface potential (Vo) of the photoconductor (31) (width of change of the surface potential) and the control level of bias conditions (width of change of the bias conditions) according to the toner replenishment amount. ) Is determined (step 3). Then, the surface potential (Vo) and the bias condition are changed according to the control level (step 4).
If the amount of toner replenished per unit time is less than a certain amount, toner is replenished without changing the surface potential (Vo) and bias conditions (step 2).

In addition, the time (stirring time) from the time of toner replenishment is detected (step 5), and the surface potential (Vo) and the control level of the bias condition are lowered step by step (step 6).
Then, the control level of the surface potential (Vo) and the bias condition is detected (Step 7), and the surface potential (Vo) and the bias condition are gradually returned to the reference level. Then, after returning to the reference level, the toner is supplied again.

  The present invention is not limited to the above embodiment. For example, in the above-described embodiment, the magnetic one-component development type image forming apparatus in which the toner has magnetism has been described. However, the toner does not have to be magnetic as long as it is a one-component development type image forming apparatus.

Hereinafter, the effect of the present invention will be made clearer by showing examples of the present invention.
In this example, an image was formed using the image forming apparatus (100) shown in FIG.
The developing bias was configured by superimposing an AC bias on a DC bias. The DC bias condition is a voltage (Vdc) of 180 V, and the AC bias condition is a voltage (Vpp) of 1.7 kV, a frequency (Vf) of 2.7 kHz, and a duty of 50%.
FIG. 3 is a graph in which the abscissa indicates the potential (V) of the surface of the photoreceptor, and the ordinate indicates the fog density (FD: Fog Density). Curve (A) shows a state before toner replenishment, curve (B) shows a state where 5 g of toner has been replenished to one place of developing means (34), and curve (C) shows a state after toner replenishment (curve). (B) shows a state where the duty is 60%.
The reference potential of the surface potential of the photoreceptor is 270 V, which is a value corresponding to the lowest value of FD in the curve (A).

  As shown by the curve (B), when 5 g of toner is replenished to one place of the developing means (34), the ratio of uncharged toner or reversely charged toner increases at the place where the toner is replenished, and the fog density (reverse fog) Are often caused by

Here, it can be seen that the fog density can be further suppressed by lowering the surface potential (Vo) by 20V. The fog that is suppressed by lowering the surface potential (Vo) is mainly reverse fog.
Further, as shown by the curve (C), it is understood that the fog density can be further suppressed by increasing the Duty by 10% to 60%. The fog that is suppressed by increasing the duty is mainly a positive fog.

Next, the relationship between the amount of toner replenishment and the decrease in surface potential when the average toner replenishment when the toner motor is turned on once is 0.25 g is shown.
Table 1 and FIG. 4 show the amount of toner replenishment and the width of decrease in the normal environment condition (NN), low temperature and low humidity environment condition (LL), and high temperature and high humidity condition (HH) in the image forming apparatus (100). An example of the relationship is shown.
The toner replenishment amount per unit time was calculated from the number of times the toner motor was turned on for 20 seconds.
In FIG. 4, the horizontal axis indicates the toner replenishment amount (g / 20 seconds), and the vertical axis indicates the Vo decrease width (V).

  If the control is performed as shown in Table 1 and FIG. 4, for example, when the surface potential (Vo) of the photoconductor (31) is controlled with the Vo decrease width of level 5 in Table 1 during toner replenishment, the control level is set every minute. Are returned to the reference potential over a period of 5 minutes (level 5, level 4, level 3, level 2, level 1, reference potential, etc.). As a result, it was confirmed that an image with less fog was obtained.

  The image forming apparatus according to the present invention can be suitably used for a copying machine, a printer, a facsimile, and the like.

1 is a schematic configuration diagram of an image forming apparatus of the present invention. FIG. 6 is a diagram illustrating an operation flow when a toner supply unit is replaced. FIG. 6 is a diagram illustrating a relationship between a potential on the surface of a photoreceptor and a fog density. FIG. 5 is a diagram illustrating an example of a relationship between a toner replenishment amount and a reduction width.

Explanation of symbols

31 photoconductor 100 image forming apparatus

Claims (5)

An electrophotographic image forming apparatus using a one-component developer as a developer,
An image forming apparatus comprising surface potential control means for controlling the surface potential of a photoconductor according to a toner replenishment amount per unit time. The surface potential control means includes
At the time of toner replenishment, if the toner replenishment amount per unit time is a certain amount or more, if the reference potential of the photoreceptor is positive, the surface potential is lower than the reference potential, and if the reference potential is negative, The image forming apparatus according to claim 1, wherein the surface potential is higher than the reference potential.   3. The image forming apparatus according to claim 2, wherein the surface potential control unit changes the surface potential at the time of toner replenishment and then returns the surface potential to the reference potential step by step at regular intervals.   4. An image forming apparatus according to claim 1, further comprising a developing bias control means for controlling a developing bias condition in accordance with a change in surface potential of the photosensitive member.   The image forming apparatus according to claim 4, wherein the developing bias condition is at least one of a voltage, a duty, a frequency, and an amplitude of the AC bias.

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