JPH05297687A - Corona discharge device - Google Patents

Abstract

PURPOSE:To realize the shift control of grid bias potential and to enhance electric discharging efficiency by connecting an interval between a grid and a charger case by a voltage dropping element. CONSTITUTION:A corona discharger is constituted of a charge wire 1, the charger case 2 which covers the circumference of three directions of the wire 1 and whose lower part is opened and the grid 3 arranged at the lower part of the wire 1. The surface of a photosensitive drum 6 being a material to be electrostatically charged is arranged by being faced to the grid 3. Besides, a high-voltage transformer 4 is connected to the corona discharger and the potential of a high voltage to the extent of -5.5 to -7kV is impressed on the wire 1. Simultaneously, bias potential to the extent of -60 to -900V is given to the grid 3. Then, the Zener voltage of a Zener diode 7 connected between the case 2 and the grid 3 is set at 300V. Therefore, the bias potential which is larger than the grid 3 by 300V is impressed on the case 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corona discharge device having a grid, which is used when the surface of a photosensitive drum of an electrophotographic copying machine is charged.

[0002]

2. Description of the Related Art Generally, in a corona discharger including a grid, a charger case is grounded to GND regardless of whether a bias voltage is applied to the grid.
Also, as shown in Japanese Utility Model Application Laid-Open No. 61-92958, a charger case is applied with a bias potential so that the case and the grid are electrically connected.

[0003]

However, in the case of the structure in which the charger case is grounded to GND, there is a limit to increase the discharge efficiency (drum effective current / total current).
Therefore, it has been attempted to reduce the effective area of the charger case or to improve the discharge efficiency by attaching an insulator to the effective area of the charger case. However, in this configuration, if the discharge efficiency is increased, the discharge current becomes unstable, and if the discharge is attempted to be stabilized, the discharge efficiency is reduced, and the like have a trade-off relationship. For example, it has been found that the discharge efficiency decreases to about 10 to 20% when the discharge current is stabilized. (The ideal value is 30% or more).

On the other hand, in the configuration in which the bias potential is applied to the charger case, the efficiency can be increased without reducing the effective area of the charger case, but since the output from the high voltage transformer is not directly applied to the grid, It is impossible to adjust the exposure value by controlling the bias potential of the grid.

An object of the present invention is to provide a corona discharge device which enables shift control of the grid bias potential and can improve discharge efficiency while maintaining discharge stability.

[0006]

According to the present invention, a predetermined bias voltage is applied to a grid by a high voltage transformer that applies a high voltage to a charge wire, and the grid and the charger case are connected by a voltage drop element. Is characterized by.

[0007]

Since a predetermined bias potential is applied to the grid by a high voltage transformer that applies a high voltage to the charge wire, shift control of the bias potential can be easily performed.

Since the grid and the charger case are electrically connected by a voltage drop element such as a varistor or a Zener diode, the bias of the charger case becomes deeper with respect to the grid. Therefore, the discharge efficiency is further improved as compared with the method of applying the same potential bias to the charger case and the grid.

[0009]

1 is a block diagram of a corona discharge device according to an embodiment of the present invention.

The corona discharger comprises a charge wire 1, a charger case 2 which covers the periphery of the charge wire 1 in three directions and is open at the bottom, and a grid 3 which is arranged below the charge wire 1. In this embodiment, the photosensitive drum 6 of the copying machine is shown as the member to be charged. The surface of the photosensitive drum 6 is arranged so as to face the grid 3.

A high voltage transformer 4 is connected to the above corona discharger, and is -5.5 to -7k with respect to the charge wire 1.
A high potential of about V is applied and the grid 3
Is applied with a bias potential of about -600 to -900V. The concentration setting switch 5 connected to the high-voltage transformer 4 is a switch for setting the concentration in seven steps, and the high-voltage transformer 4 receives the switch output to control the bias potential of the grid 3 to a potential of -600 to -900V. To do.

A Zener diode 7 is connected between the charger case 2 and the grid 3. The Zener voltage of this Zener diode 7 is set to 300V. Therefore, the bias potential applied to charger case 2 is 300 V higher than the bias potential applied to grid 3. FIG. 2 shows the relationship between the concentration set by the concentration setting switch 5, the grid bias potential applied to the grid 3, and the charger case bias potential applied to the charger case 2. The charging potential of the photosensitive drum 6 is charged to a voltage that is lower by about 100 V in absolute value than the grid bias potential. Therefore, the charging potential of the photosensitive drum 6 changes in the range of -500 to -800 V with respect to the density setting value of FIG.

In the above structure, the charger case 2
The bias potential applied to the grid 3 becomes larger than the bias potential applied to the grid 3 by 300 V, so that the corona discharge current from the charge wire 1 is more likely to flow to the photosensitive drum 4 side and the discharge efficiency is improved. ..

In this embodiment, the corona discharge device for charging the photosensitive drum 6 is shown, but the member to be charged may be any member.

[0015]

The bias potential applied to the grid can be easily controlled because of the structure in which the high-voltage transformer directly applies the bias potential to the grid, whereby the charging potential of the member to be charged can also be easily controlled. Also, by connecting the grid and the charger case with a voltage drop element and making the bias potential of the charger case larger than the grid, the corona discharge current from the charge wire becomes easier to flow to the grid side, that is, the charged member side. The discharge efficiency can be increased. By increasing the discharge efficiency, the size of the transformer can be reduced, ozone generation can be reduced, SiO ₂ generation can be suppressed, and the charge wires can be prevented from being contaminated.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a grid bias potential and a charger case bias potential.

[Explanation of symbols]

 1-Charge wire 2-Charger case 3-Grid 4-High voltage transformer 6-Zener diode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshikazu Harada 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (72) Inventor Taku Nakagawa 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside the company

Claims (1)

[Claims] 1. A corona discharge device characterized in that a predetermined bias voltage is applied to a grid by a high-voltage transformer that applies a high voltage to a charge wire, and the grid and the charger case are connected by a voltage drop element.