JPH04298768A - Electrostatic charging device - Google Patents

Abstract

PURPOSE:To offer the electrostatic charging device used for a copying machine which takes a copy of high picture quality. CONSTITUTION:A tungsten wire electrode 2 is connected to the plus electrode of a variable constant-current power source 6 and a photosensitive drum 4 which is charged electrostatically to the positive polarity (cerium, etc.) is grounded; and three Zener diodes ZD1, ZD2, and ZD3 are connected to a corona discharger 1 in scorotron structure with a grid electrode 5 in series between the grid electrode 5 and ground and switches S1 and S2 are connected to the Zener diodes ZD2 and ZD3 in parallel. Then the potential of the grid electrode 5 is held constant through the Zener diodes ZD1, ZD2, and ZD3 and the switches S1 and S2 are opened and closed to vary the potential of the grid electrode 5.

Description

[Detailed description of the invention]

[Object of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device having a scorotron structure used, for example, in copying machines.

0003

2. Description of the Related Art Conventionally, in a copying machine using a charging device, for example, a cerium (Ce) based photosensitive drum is used as a load of a scorotron structure, and in this case, the charging potential of the photosensitive drum is positive.

When controlling the surface potential of the photosensitive drum, it is difficult to directly control the current of the grid electrode, so the output voltage or output current of the power source is controlled.

[0005]

[Problems to be Solved by the Invention] However, if the output voltage or output current of the power supply is controlled without feedback of the status of the surface potential of the photosensitive drum, deviations will occur in the surface potential of the photosensitive drum, making it impossible to obtain uniform image quality. It is difficult to do so.

[0006] Therefore, in order to control the surface potential of the photosensitive drum, it is conceivable to use a surface electrometer to provide feedback to the power supply and control the surface potential of the photosensitive drum using the power supply, but this method is expensive and large. I have a problem.

[0007] Furthermore, a grid electrode is provided on the photosensitive drum,
It is possible to change the surface potential of the photosensitive drum by controlling the grid current, but if the charged potential of the photosensitive drum is positive, the current of the grid electrode can be controlled by making the ground of the power supply and the ground of the photosensitive drum common. The problem is that it is difficult to do.

The present invention was made in view of the above problems, and an object of the present invention is to provide a charging device that can perform uniform charging.

[Configuration of the invention]

0010

A charging device according to claim 1 has a scorotron structure in which a voltage is applied to a grid electrode and the grid electrode is charged with a positive potential that controls charging. The device includes a constant voltage means connected between grounds and a switching means connected in parallel to the constant voltage means.

A charging device according to a second aspect of the present invention is a charging device having a scorotron structure in which a voltage is applied to a grid electrode and charging is controlled by this voltage, and includes a constant current means for supplying a constant current to the grid electrode, and a corona discharger. The device is equipped with constant voltage means for performing this at a constant voltage.

The charging device according to a third aspect of the present invention is the charging device according to the second aspect, wherein the constant voltage means varies the constant voltage output in accordance with the current flowing through the grid electrode.

[0013]

[Function] The charging device according to claim 1 maintains the potential of the grid electrode with respect to the ground by providing a constant voltage means between the grid electrode and the ground, and also performs switching in parallel to the constant voltage means. By providing the means, the potential of the grid electrode can be varied, uniform charging can be performed, and the amount of charging can be varied.

[0014] In the charging device according to the second aspect, the voltage applied to the grid electrode is controlled by making the current to the grid electrode constant by the constant current means and by causing the corona discharge to be performed at a constant voltage by the constant voltage means. Even if it is changed, corona discharge can be performed stably and reliably.

In the charging device according to claim 3, in the charging device according to claim 2, the constant voltage means outputs a variable voltage following the current of the grid electrode, so that uniform charging can be achieved. .

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the charging device of the present invention will be described below with reference to the drawings.

FIG. 1 shows a part of the circuit diagram of a copying machine.
, 1 is a corona discharger serving as a charging device, and this corona discharger 1 includes a tungsten wire electrode 2 serving as a corona discharge wire, a case 3 of this tungsten wire electrode 2, and a case 3 of the tungsten wire electrode 2. It has a scorotron structure including a photosensitive drum 4 and a grid electrode 5.

The positive electrode of a variable constant current power source 6 is connected to the tungsten wire electrode 2, and the negative electrode of the variable constant current power source 6 is grounded. Further, the photosensitive drum 4 is also grounded. Further, the grid electrode 5 is grounded through three series-connected Zener diodes ZD1, ZD2, and ZD3 as constant voltage means, and switches S1 and S2 as switching means are connected in parallel to the Zener diodes ZD2 and ZD3, respectively. It is connected to the.

When a voltage is applied between the tungsten wire electrode 2 and the photosensitive drum 4 from the variable constant current power source 6, corona discharge is generated between the tungsten wire electrode 2 and the photosensitive drum 4, and the photosensitive drum 4 is charged. .

Further, the grid electrode 5 is maintained at a predetermined potential by the Zener diodes ZD1, ZD2, and ZD3, and the surface potential relative to the ground can be stabilized, so that high image quality can be achieved.

Furthermore, switch S1 and switch S2
By opening and closing Zener diode ZD2 and Zener diode ZD3, the surface potential can be varied to a desired potential by short-circuiting Zener diode ZD2 and Zener diode ZD3, the amount of charge can be varied, and high-quality copying can be performed.

[0022] The switching means is not limited to a switch, but a semiconductor switching element such as a transistor may also be used.

FIG. 2 shows another embodiment. In the embodiment shown in FIG. 1, a Zener diode ZD4 as a constant voltage means, a resistor R1, and a constant current power source as a constant current means are connected between the grid electrode 5 and the ground. 7 are connected in series.

When the load voltage on the grid electrode 5 changes due to environmental conditions, etc., by supplying a constant current from the constant current power source 7, the potential on the grid electrode 5 changes as shown in FIG. This change in the potential of the grid electrode 5 changes the surface potential. That is, by changing the surface potential, the amount of charge becomes constant, and the quality of the copied image is stabilized.

Furthermore, even if the voltage between the tungsten wire electrode 2 and the photosensitive drum 4 changes due to environmental conditions,
As shown in FIG. 4, by the Zener diode ZD4,
The surface potential can be kept constant, and the image quality of copies can be stabilized.

FIG. 5 shows another embodiment in which a series circuit of a resistor R2 and a Zener diode ZD5 as a constant voltage means is connected between the grid electrode 5 and the variable constant current power source 6 in the embodiment shown in FIG. , the variable constant current power supply 6 supplies a constant current to the grid electrode 5.

Even if the current to the photosensitive drum 4 changes, the current to the grid electrode 5 is a constant current, so the surface potential remains constant. Note that the current flowing to case 3 has a substantially constant value regardless of the load state and environmental conditions.

Therefore, high image quality can be achieved using a single variable constant current power supply 6 that also has a constant voltage function.

[
0029

According to the charging device according to claim 1, by providing a constant voltage means between the grid electrode and the ground, the potential of the grid electrode with respect to the ground can be kept constant, so that the amount of charge can be reduced. can be kept constant. Furthermore, by providing a switching means in parallel to the constant voltage means, the potential of the grid electrode can be varied, and therefore the amount of charge can be varied.

According to the charging device according to the second aspect, by keeping the power supply to the grid electrode constant using the constant current means,
Since the surface potential is constant, the amount of charge can be kept constant. In addition, since corona discharge is performed at a constant voltage using a constant voltage means, even if the voltage of the grid electrode is changed, corona discharge can be performed reliably and stably, so that the amount of charge can be kept constant. can.

According to the charging device according to claim 3, in addition to the charging device according to claim 2, the constant voltage means performs uniform charging by outputting a variable voltage following the current of the grid electrode. be able to.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a charging device of the present invention.

FIG. 2 is a circuit diagram showing the embodiment same as above.

FIG. 3 is a graph showing the relationship between the surface potential and the grid potential.

FIG. 4 is a graph showing the relationship between the surface potential of the same as above and the potential between the tungsten wire and the photosensitive drum.

FIG. 5 is a circuit diagram showing another embodiment.

[Explanation of symbols]

1 Corona discharger 5 as a charging device Grid electrode 7 Constant current power supplies S1 and S2 as constant current means
Switches ZD1 and Z as switching means
D2, ZD3, ZD4, ZD5 Zener diode as constant voltage means

Claims (3)

[Claims] 1. A charging device having a scorotron structure in which a voltage is applied to a grid electrode and the grid electrode is charged with a positive potential for controlling charging, comprising: a constant voltage means connected between the grid electrode and ground; A charging device comprising: a switching means connected in parallel to the voltage means. 2. A charging device having a scorotron structure in which a voltage is applied to a grid electrode and charging is controlled by the voltage, comprising: constant current means for supplying a constant current to the grid electrode; and a constant current means for causing corona discharge to be performed at a constant voltage. A charging device characterized by comprising a constant voltage means. 3. The charging device according to claim 2, wherein the constant voltage means varies the constant voltage output in accordance with the current flowing through the grid electrode.