JP2001272847A - Charging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To electrically remove toner being stuck on an charging brush. SOLUTION: This charging device charge an body 1 to be charged to a prescribed voltage by holding the charging brush 2 in contact with surface on the body 1 where an electrostatic latent image is formed thereon. A voltage generated by superimposing an AC voltage on DC voltage is applied on the charging brush 2 and the frequency of AC component of being superimposed voltage in an image forming and not forming is mutually differed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact type charging device used in an electrophotographic apparatus.

[0002]

2. Description of the Related Art In recent years, with the spread of computers, electrophotographic devices such as printers as peripheral devices have become widespread. Conventionally, a charging device called a scorotron has been used in an electrophotographic apparatus. However, since the scorotron charging device generates ozone harmful to the human body, a contact-type charging device that does not generate ozone has attracted attention.

Here, an electrophotographic apparatus equipped with a conventional charging device will be described.

FIG. 4 is a schematic diagram showing the configuration of an electrophotographic apparatus provided with a conventional charging device.

As shown in FIG. 4, a roll-shaped charging brush (contact charging means) 2 for uniformly charging the surface of a charged body 1 such as a photosensitive drum to a predetermined potential is provided in an electrophotographic apparatus. The body 1 is provided with a bite of about 1.0 mm. The charging brush 2 rotates at a peripheral speed ratio of 2 in an opposite mode in which the charging brush 2 rotates in a direction opposite to that of the member 1 to be charged. The charging brush 2 is supplied with an AC superimposed voltage from a power supply 9.

In addition to the charging brush 2, an exposure device 7 for forming an electrostatic latent image on the surface of the charged body 1 is developed around the body 1 to be charged, and the formed electrostatic latent image is developed. A developing device 4 for forming a toner image, a transfer device 5 for rolling the recording medium 8 by rotating in pressure contact with the member 1 to be charged, and transferring the toner image to the recording medium 8, and a transfer device 5 for transferring the toner image to the recording medium 8. The cleaning member 6 and the charge removing lamp 3 for removing the toner and the potential remaining on the charged body 1 respectively include the charged body 1
Are sequentially arranged along the rotation direction.

Further, a cleaner 10 such as a sponge for contacting the charging brush 2 and cleaning the charging brush 2 is provided.

Next, the operation of such an electrophotographic apparatus will be described.

First, the charged object 1 is charged to a predetermined potential by the charging brush 2. Next, an electrostatic latent image is formed on the surface of the charged member 1 charged by the exposure device 7, and this is converted into a toner image by the developing device 4. Then, the transfer device 5 transfers the toner image to the recording medium 8. The transferred toner image is fixed on a recording medium by a fixing device, whereby an image is obtained.

On the other hand, the toner remaining on the member 1 without being transferred to the recording medium 8 is removed from the member 1 by the cleaning member 6.

However, the toner remaining on the charged member 1 cannot be completely removed by the cleaning member 6, and a part of the toner passes through the cleaning member 6 and adheres to the charging brush 2. Therefore, with the printing, the charging brush 2
Is accumulated in the toner.

Here, the member to be charged 1 and the charging brush 2 will be described.

As described above, the charging brush 2 is a member to be charged 1
, And rotate in an agonist mode with a peripheral speed ratio of about 2. An AC superimposed voltage is applied to the charging brush 2 from a power supply 9.

In such a configuration, when toner accumulates on the charging brush 2, the resistance of the charging brush 2 increases, the current flowing into the member 1 to be charged decreases, and charging ability such that charging to a predetermined potential becomes impossible is prevented. descend. And as a result,
Image defects occur.

Therefore, in order to clean the charging brush 2, a cleaner 10 such as a sponge is brought into contact with the charging brush 2 to physically scrape the toner.

[0016]

However, with such physical means, when the toner is gradually absorbed by the cleaner, the cleaning performance deteriorates and the cleaner cannot scrape off the toner of the charging brush.

Accordingly, an object of the present invention is to provide a charging device capable of electrically removing toner attached to a contact charging means.

[0018]

In order to solve this problem, a charging device according to the present invention comprises a contact charging means in contact with the surface of a member on which an electrostatic latent image is to be formed, and the member to be charged is charged. A charging device for charging to a predetermined potential, wherein a voltage in which an AC voltage is superimposed on a DC voltage is applied to the contact charging means, and the frequency of the AC component of the superimposed voltage during image formation and during non-image formation is changed. It is different.

As a result, the toner attached to the contact charging means is returned to the member to be charged, so that the toner attached to the contact charging means can be electrically removed.

[0020]

DETAILED DESCRIPTION OF THE INVENTION According to the first aspect of the present invention, a contact charging means contacts a surface of a member on which an electrostatic latent image is formed to charge the member to a predetermined potential. A charging device in which a voltage obtained by superimposing an AC voltage on a DC voltage is applied to a contact charging means, and the frequency of the AC component of the superimposed voltage is different from that of an AC component during image formation and during non-image formation. Since the toner adhered to the contact charging means is returned to the member to be charged, the toner adhering to the contact charging means can be electrically removed.

According to a second aspect of the present invention, there is provided a charging device for charging a charged body to a predetermined potential by contact charging means contacting the surface of the charged body on which an electrostatic latent image is formed. Assuming that the peak-to-peak voltage (V) of the AC voltage component is V _PP and the offset voltage (V) is V _DC , the contact charging means has a DC voltage that satisfies the relationship of V _PP ≦ 2 | V _DC | A charging device to which a voltage on which a voltage is superimposed is applied and the frequency of an AC component of the superimposed voltage during image formation and non-image formation is made different from each other. Since the toner is returned, the toner attached to the contact charging means can be electrically removed.

According to a third aspect of the present invention, there is provided a charging device for charging a charged body to a predetermined potential by contact charging means contacting the surface of the charged body on which an electrostatic latent image is formed. Assuming that the peak-to-peak voltage (V) of the AC voltage component is V _PP and the offset voltage (V) is V _DC , the contact charging means has a DC voltage that satisfies the relationship of V _PP ≦ 2 | V _DC | A voltage on which a voltage is superimposed is applied, and the frequency of the AC component of the superimposed voltage during image formation and non-image formation is made different from each other. This is a charging device that turns off the light, and has an effect that it is possible to electrically remove the toner attached to the contact charging unit because the toner attached to the contact charging unit is returned to the member to be charged.

According to a fourth aspect of the present invention, in the first, second or third aspect of the present invention, the peripheral speed (mm / sec) of the member to be charged is νp, and the nip between the contact charging means and the member to be charged is used. When the width (mm) is χ, the frequency (f (Hz)) at the time of image formation is f> νp / χ, and the frequency (f (Hz)) at the time of non-image formation is f ≦ νp / χ. This is a charging device, and has an effect that the toner adhered to the contact charging means can be electrically removed because the toner adhered to the contact charging means is returned to the member to be charged.

An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a schematic diagram showing the configuration of an electrophotographic apparatus provided with a charging device according to an embodiment of the present invention, and FIG. 2 is a diagram showing the surface potential of a member to be charged and a charging brush when a static elimination lamp is turned on. FIG. 3 is a graph showing the relationship between the surface potential of the member to be charged and the voltage applied to the charging brush when the discharge lamp is off.

As shown in FIG. 1, the electrophotographic apparatus includes, for example, a surface of a charged member 1 such as a photosensitive drum made of rayon fiber having a resistance of about 10 ⁸ Ω · cm and rotating at a peripheral speed of 100 mm / sec. A roll-shaped charging brush (contact charging means) 2 that is uniformly charged to a predetermined potential is provided in contact with the surface of the member 1 to be charged.

The charging brush 2 is rotated at a peripheral speed ratio of 2 in an opposite mode in which the charging brush 2 rotates in a direction opposite to that of the charged body 1, and has a nip width of 3 mm with the charged body 1. The charging brush 2 is supplied with an AC superimposed voltage (V
_PP (peak voltage of AC voltage component): 1.3 kV, o
(ffset voltage: -700 V, frequency: 1000 Hz)
Is supplied. As the contact charging means, a member other than the charging brush 2 can be used as long as it can contact the charged body 1 and charge it to a predetermined potential.

Around the member 1 to be charged, the charging brush 2
An exposure device 7 for forming a predetermined electrostatic latent image on the surface of the charged member 1; a developing device 4 for developing the electrostatic latent image formed by the exposure device 7 to form a toner image; A transfer device 5 for rolling the recording medium 8 by rolling in pressure contact with the member to be charged 1 and transferring the toner image to the recording medium 8, removing toner remaining on the member to be charged 1 after the toner image is transferred to the recording medium 8 A cleaning member 6 and a charge removing lamp (charge removing means) 3 for removing a potential remaining on the member 1 after the toner image is transferred to the recording medium 8 are sequentially arranged along the rotation direction of the member 1. I have.

Next, the operation of such an electrophotographic apparatus will be described.

First, the charged object 1 is charged to a predetermined potential by the charging brush 2. Next, an electrostatic latent image is formed on the surface of the charged member 1 charged by the exposure device 7, and this is converted into a toner image by the developing device 4. Then, the transfer device 5 transfers the toner image to the recording medium 8. The transferred toner image is fixed on a recording medium by a fixing device (not shown), whereby an image is obtained.

In the illustrated apparatus, the frequency (f) of the AC superimposed voltage during non-image formation is changed from 1000 Hz (the same frequency as during image formation) to 20 Hz (f ≦ νp /
Then, the number of printed sheets until an image failure occurs when the static elimination lamp 3 is constantly turned on and turned off during non-image formation was examined.

The results are shown in (Table 1).

[0033]

[Table 1]

As is clear from Table 1, by changing the frequency at the time of image formation and at the time of non-image formation, the number of printed sheets up to the occurrence of an image defect was improved. Further, when the frequency at the time of non-image formation satisfies the relationship of f ≦ νp / 印字, the number of printed sheets up to the occurrence of an image defect is dramatically improved, and by turning off the neutralizing lamp 3 at the time of non-image formation, the life of the cartridge is reduced. The occurrence of defects could be prevented.

Next, the above results will be described.

First, the frequency change during non-image formation will be described.

When the frequency is in the range of f ≦ νp / χ, the voltage becomes maximum within a time corresponding to the nip width between the charged object 1 and the charging brush 2. At this time, the toner adhering to the charging brush 2 moves to the member 1 to be charged.

FIG. 2 shows the relationship between the surface potential of the member 1 to be charged and the voltage applied to the charging brush 2 when the discharge lamp 3 is turned on. FIG. 3 shows the relationship between the surface potential of the member 1 to be charged and the voltage applied to the charging brush 2.

As shown in FIG. 2, in the vicinity of the maximum value of the voltage applied to the charging brush 2, the potential relationship is such that the surface potential of the charged body 1 <the voltage applied to the charging brush 2. On the other hand, charging brush 2
The polarity of most of the toner adhering to the toner has the opposite polarity (positive charge) to the original charge polarity (negative charge) due to the influence of the transfer device 5 and the like. Therefore, the toner of the opposite polarity moves to the charged body 1 having a lower potential.

Further, as shown in FIG. 3, when the static elimination lamp 3 is turned off during non-image formation, the surface potential of the member 1 to be charged≪applied voltage of the charging brush 2 near the maximum value of the voltage applied to the charging brush 2. Therefore, the transfer to the member to be charged 1 is further facilitated, and the cleaning effect is greatly improved.

The voltage applied to the charging brush 2 must satisfy the relationship of V _PP ≦ 2 | V _DC |, where the offset voltage is V _DC .

This is because, in the range of V _PP > 2 | V _DC |, a voltage opposite to the original charging polarity is applied to the charged body 1, and the charged body 1 is charged to the opposite polarity. Because it becomes. Then, the original function of the charged body 1 once charged to the opposite polarity is reduced, as the surface potential changes upon receiving light from the exposure device 7.

Therefore, it is desirable that the voltage applied to the charging brush 2 is in the range of V _PP ≦ 2 | V _DC |.

As described above, A is applied to the charging brush 2.
The C superimposed application voltage is applied at a frequency different from that at the time of image formation at the time of non-image formation, and the discharge lamp 3
By turning off the light, the toner that has once adhered to the charging brush 2 is returned to the member 1 to be charged, so that the toner that has adhered to the charging brush 2 can be electrically removed.

As a result, a reduction in the charging ability of the member to be charged 1 is prevented, and a high-quality image can be obtained.

[0046]

As described above, according to the present invention, the toner adhering to the contact charging means is returned to the member to be charged, so that the toner adhering to the contact charging means can be electrically removed. That is, an effective effect is obtained.

As a result, a reduction in the charging ability of the member to be charged is prevented, and an effective effect that a high quality image can be obtained is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an electrophotographic apparatus including a charging device according to an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the surface potential of a member to be charged and the voltage applied to a charging brush when the charge removing lamp is turned on.

FIG. 3 is a graph showing the relationship between the surface potential of a member to be charged and the voltage applied to a charging brush when the charge removing lamp is off.

FIG. 4 is a schematic diagram showing a configuration of an electrophotographic apparatus provided with a conventional charging device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Charged body 2 Charging brush (contact charging means) 3 Static elimination lamp (static elimination means)

Claims (4)

[Claims] 1. A charging device which contacts a surface of an object to be charged on which an electrostatic latent image is formed with a contact charging means to charge the object to be charged to a predetermined potential. A charging device, wherein a voltage obtained by superimposing an AC voltage on a voltage is applied, and the frequency of the AC component of the superimposed voltage during image formation and non-image formation is made different from each other. 2. A charging device for charging a charged body to a predetermined potential by contact charging means contacting a surface of the charged body on which an electrostatic latent image is formed, wherein a peak-to-peak voltage of an AC voltage component is provided. When (V) is V _PP and the offset voltage (V) is V _DC , a voltage in which an AC voltage is superimposed on a DC voltage satisfying the relationship of V _PP ≦ 2 | V _DC | is applied to the contact charging means. A charging device, wherein the frequency of the AC component of the superimposed voltage during image formation and non-image formation is different from each other. 3. A charging device for charging a charged body to a predetermined potential by contact charging means contacting the surface of the charged body on which an electrostatic latent image is formed, wherein a peak-to-peak voltage of an AC voltage component is provided. When (V) is V _PP and the offset voltage (V) is V _DC , a voltage in which an AC voltage is superimposed on a DC voltage satisfying the relationship of V _PP ≦ 2 | V _DC | is applied to the contact charging means. The charging device is characterized in that the frequency of the AC component of the superimposed voltage during image formation and during non-image formation is made different from each other, and at the time of non-image formation, the charge removing means for removing the residual potential of the charged body is turned off. apparatus. 4. The method according to claim 1, wherein the peripheral speed (mm / sec) of the member to be charged is ν.
p, the nip width between the contact charging means and the charged object (m
m) is χ, and the frequency (f (H (H
4. The charging device according to claim 1, wherein z)) is f> νp / χ, and the frequency (f (Hz)) during non-image formation is f ≦ νp / ν.