JP3207262B2 - Contact charging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact charging device used for charging an electrostatic recording medium.

A recording medium such as a photoreceptor or a dielectric used in an electrophotographic apparatus or the like is used for performing electrostatic recording.
It must be charged to a predetermined potential in advance.

[0003]

2. Description of the Related Art The so-called corona charging method for charging an electrostatic recording medium by corona discharge has problems such as high power supply voltage and generation of ozone.

Therefore, a so-called contact charging method in which a medium contact member to which a voltage is applied from the outside is brought into contact with an electrostatic recording medium to perform charging is used in an electrophotographic image forming apparatus and the like.

[0005] As a driving method of the contact charging method, there are a method of applying a constant voltage, a method of applying a constant current, and a method of superimposing an AC voltage on the constant voltage. However, the constant voltage method is easily affected by the environment, and has a problem that the charging potential is reduced in a low temperature and low humidity environment.

Further, the constant current method has a problem in that the charging potential fluctuates due to a difference in capacitance of the electrostatic recording medium, and is thus affected by deterioration of the electrostatic recording medium. On the other hand, in the case of a system in which an AC voltage is superimposed on a constant voltage, environmental fluctuations are slight and there is no dependence on the capacity of the electrostatic recording medium. Therefore, a method of applying a voltage obtained by superimposing an alternating current on a constant DC voltage to an electrostatic recording medium is generally used.

[0007]

However, even in a system in which an AC voltage is superimposed on a DC constant voltage and applied to an electrostatic recording medium, the system is affected by the environment. In a low humidity environment, the charging voltage decreases. Occurs.

According to the results of the experiment, the relative humidity was 6
If it is lower than 0%, the charging potential decreases in accordance with the humidity, and the quality of electrostatic recording deteriorates. Note that the “charge voltage” in the case of “decrease in charge voltage” is an absolute value (the same applies hereinafter).

SUMMARY OF THE INVENTION It is an object of the present invention to provide a contact charging device in which the charging potential of an electrostatic recording medium does not decrease even if the humidity of the environment decreases, and a stable charging potential can always be obtained.

[0010]

In order to achieve the above object, a contact charging device of the present invention is used to charge an electrostatic recording medium 1 as shown in FIG. A medium contact member 2 arranged to be in contact with the electrostatic recording medium 1, a power supply 23 for applying an AC voltage to the medium contact member 2 by superimposing a DC constant voltage thereon, Humidity sensor 24 for detecting nearby humidity
And a power supply control means 8 for distorting the waveform of the AC component of the voltage applied to the medium contact member 2 from the power supply 23 in response to the detection output from the humidity sensor 24.

The power supply control means 8 preferably distorts the waveform of the AC component when the humidity detected by the humidity sensor 24 becomes low.

[0012]

[0013]

When the humidity of the environment decreases, the waveform of the AC component of the voltage applied to the medium contact member 2 is distorted by the power supply control means 8 in response to the detection output from the humidity sensor 24. It is possible to prevent a decrease in the charged potential of the electrostatic recording medium 1.

[0014]

[0015]

An embodiment will be described with reference to the drawings. FIG.
1 shows an electrophotographic printer device to which the present invention is applied.

In FIG. 1, reference numeral 1 denotes a photosensitive drum which is an electrostatic recording medium, and an organic photosensitive layer 12 is formed on an outer peripheral surface of a base 11 made of an aluminum alloy. The photosensitive drum 1 has a cylindrical shape with an outer diameter of, for example, 40 mm, and is driven to rotate at a surface speed of, for example, 70 mm / sec in the direction of the arrow.

Reference numeral 2 denotes a charging brush which is a medium contact member arranged to contact the surface of the photosensitive drum 1 to charge the photosensitive drum 1. In the charging brush 2, for example, a conductive brush fiber 22 is planted in a roll shape on a conductor 21 made of stainless steel, and the length of the brush fiber 22 is, for example, 5 mm.

The brush fibers 22 are provided with conductivity by uniformly dispersing carbon particles in rayon fibers.
The resistance value per line is, for example, 10 ⁹ Ω. The fiber thickness is, for example, 6 denier / fiber, and the fineness is 600 /
100 denier / fiber.

After the surface of the photosensitive drum 1 is charged by the charging brush 2, an electrostatic latent image is formed by the exposing device 3 and is developed as a toner image by the developing device 4. Next, the toner image on the surface of the photosensitive drum 1 is transferred to the recording paper 100 by the transfer device 5, and the toner image transferred onto the recording paper 100 is fixed by the fixing device 6. Photosensitive drum 1
Part of the toner remaining on the surface is cleaned by the cleaner 7.

A voltage obtained by superimposing an AC voltage on a DC constant voltage is applied to the charging brush 2 from a power supply 23. 8
A power supply control circuit for controlling the operation of the power supply 23 receives a humidity detection signal from a humidity sensor 24 disposed around the photosensitive drum and outputs a control signal to a drive circuit of the power supply 23. .

In this embodiment, as a basic setting, the DC voltage (offset voltage) of the power supply 8 is -650 volts,
AC voltage is 1200 volts peak-to-peak, frequency is 8
00 Hz.

FIG. 2 shows a state in which the waveform of the AC voltage is distorted, and the distortion rate is expressed as t1 / (t1 + t2). Therefore, a distortion-free sine wave or the like can produce a distortion rate of 50.
%, And the distortion rate decreases when the waveform is distorted to the left (rearward).

FIG. 3 shows the change in the charging potential of the photosensitive drum 1 when the waveform distortion rate is changed under the condition of constant humidity (for example, 70%). As the distortion rate decreases, the charging potential increases. Get higher.

Therefore, when the humidity becomes lower than 60%, the power supply control circuit 8 distorts the waveform of the AC component so that the distortion rate of the AC voltage becomes smaller in accordance with the humidity.
As a result, as shown in FIG. 4, in a low-humidity environment where the humidity does not reach 60%, the conventional (dashed line)
In this embodiment (Example), the charging potential can be maintained almost constant.

FIG. 5 shows an example of a circuit used in the above-described embodiment for distorting an AC voltage by an arbitrary amount. Here, the negative input terminal of the first operational amplifier A1 and the positive input terminal of the second operational amplifier A2 are grounded, and the output terminal of the first operational amplifier A1 is connected to the first resistor R1 and the first variable resistor. It is connected to the negative input terminal of the second operational amplifier A2 via the switch VR1.

The positive-side input terminal of the first operational amplifier A1 is connected between the first resistor R1 and the first variable resistor VR1 via the second resistor R2 and the second variable resistor VR2. To the output terminal of the second operational amplifier A2 via the third resistor R3. A capacitor C1 is connected between the negative input terminal and the output terminal of the second operational amplifier A2.

Further, in parallel with the first variable resistor VR1,
A fourth resistor R4 and a diode D1 are connected in series;
Between the first resistor R1 and the first variable resistor VR1,
It is connected to ground via first and second Zener diodes Z1 and Z2 connected in series in opposite directions.

In the thus configured waveform distortion circuit, the AC waveform input from the input terminal IN connected between the first resistor R1 and the first variable resistor VR1 is deformed. , From the output terminal OUT connected to the output terminal of the second operational amplifier A2.

The distortion rate t1 / (t1 + t2) is equal to the first
The resistance value of the variable resistor VR1 is r _V , and the fourth resistor R4
The resistance value is When r _4. Accordingly, in response to the humidity detection signal input from the humidity sensor 24, the power control circuit 8 changes the resistance value of the first variable resistor VR1 in response to the relative humidity falling below 60%. Accordingly, the waveform of the AC component can be distorted so as to keep the charged potential of the photosensitive drum 1 constant.

[0030]

[0031]

[0032]

The present invention is not limited to the above-described embodiment. For example, the medium contact member is not limited to a charging brush, but may be a charging roller or the like. Can be applied to various contact charging devices.

[0034]

According to the contact charging device of the present invention, even when the environmental humidity decreases, the fluctuation of the charging potential of the electrostatic recording medium is suppressed to maintain a good charging state, and high quality electrostatic recording is achieved. Has an excellent effect.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment.

FIG. 2 is an operation explanatory diagram of the first embodiment.

FIG. 3 is an operation explanatory diagram of the first embodiment.

FIG. 4 is an operation explanatory diagram of the first embodiment.

FIG. 5 is a partial circuit diagram of the first embodiment.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum (electrostatic recording medium) 2 charging brush (medium contact member) 8 power supply control circuit 23 power supply 24 humidity sensor

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Masahiro Wano 1015 Uedanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Tsuneo Mizuno 1015 Kamikodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited (56) reference Patent flat 4-186381 (JP, a) JP flat 2-223972 (JP, a) JP flat 3-48869 (JP, a) (58 ) investigated the field (Int.Cl. ⁷ , DB name) G03G 15/02

Claims (2)

(57) [Claims] 1. A medium contact member arranged to be in contact with the electrostatic recording medium to charge the electrostatic recording medium, and an AC voltage superimposed on a DC constant voltage applied to the medium contact member. A power supply, a humidity sensor for detecting humidity near the electrostatic recording medium, and a waveform of an AC component of a voltage applied from the power supply to the medium contact member in response to a detection output from the humidity sensor. And a power supply control means for distorting the voltage without changing the peak voltage . 2. The contact charging device according to claim 1, wherein said power supply control means distorts the waveform of said AC component when the humidity detected by said humidity sensor decreases.