JP2002006592A - Electrification device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrification device capable of using a Zener diode, having large dispersion with simple constitution, using a constant-current power source which is made compact and selecting a proper adjusting range. SOLUTION: This electrification device is provided with a corona discharge electrode (2), arranged counterposed to an image carrier 1 and connected to the constant-current power source (3), a corona house (4) provided to surround the electrode (2), and a grid electrode (5) for controlling corona discharge which is discharged from the electrode (2). In the device, the corona house (4) and the electrode (5) are electrically connected, and this connection part, the Zener diode (7) and a 1st resistance (9) are electrically connected in series, and a 2nd resistance (10), branched from connection between the corona house (4) and the electrode (5), is connected to the Zener diode (7) and the 1st resistance (9) in parallel and grounded. By varying the power source (3), the surface potential of the image carrier (1) is set to a prescribed value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device provided in an image forming apparatus such as a copying machine and a printer.

[0002]

2. Description of the Related Art In order to uniformly charge the surface of an image carrier 1 such as a photosensitive drum or a photosensitive belt, a predetermined distance is provided in a direction perpendicular to the moving direction of the image carrier 1 as shown in FIG. Charging device having a corona discharge electrode 2 extending in a direction extending therefrom, a constant current power supply 3 for applying a constant current around the corona discharge electrode 2, and a grid electrode 5 for controlling corona discharge discharged from the corona discharge electrode 2. Is known. With such a configuration, a constant current flows on the surface of the image carrier 1.

Conventionally, the grid electrode 5 is grounded via a zener diode 7 to stabilize the charging, and the current flowing through the grid electrode 5 is regulated. In the case of an image forming apparatus having a high process speed, the image forming apparatus may be grounded via the resistor 8 in order to regulate the current flowing through the corona house 4. As a result, the current flowing through the grid electrode 5 and the image carrier 1 is regulated so as to increase, and the image carrier 1 is charged efficiently and uniformly with a minimum current.

[0004]

On the other hand, when providing an inexpensive charging device in mass production, it is desirable to use a commercially available zener diode as much as possible. However, commercially available Zener diodes have large variations, for example, 80
It has a variation of 0V ± 10%. When the charging device is manufactured under the same conditions, the variation of 10% appears as a difference of 80 V as the surface potential, and the adjustment range of the constant current power supply is shifted, so that the adjustment may not be performed. . Further, forcible adjustment requires an even larger constant current power supply, which inevitably increases the cost and size of the device. Furthermore, a Zener diode which is commercially available for charge control generally has a small current that can flow, and even if the current is within the standard, if the current is increased, a temperature drift occurs and the variation is further increased.

FIG. 4 shows the relationship between the surface potential of an image carrier and the current value of a constant current power supply in a conventional circuit. Line a,
b and c use the same standard Zener diode, but the surface potential of the image carrier shows different values due to the variation of the Zener diode. That is, in order to make the surface potential of the image carrier constant, the current value of the constant current power supply must be varied and adjusted. However, in the illustrated example, even if the current value is varied, the surface potential of the image bearing member changes only slightly, which may exceed the adjustment range of the constant current power supply (line c), and exceeds the adjustment range. Requires a larger constant current power supply.

Further, a Zener diode with reduced variation is expensive and unsuitable for mass production. If only a zener diode with little variation is selected and used by inspection or the like, the operation of selecting becomes complicated. Particularly in a high-speed image forming apparatus, the time required for the image carrier to pass through the charging device is shortened, and the current flowing per unit time must be increased. This is more effective when a small-sized constant current power supply is used. The area is narrowed, and the adjustment range of the current value is narrowed, so that the yield of usable zener diodes is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems. A zener diode having a large variation can be used with a simple configuration, a constant current power supply can be reduced in size, and an appropriate adjustment range can be obtained. It is an object to provide a charging device that can be selected.

[0008]

According to the present invention, there is provided a corona discharge electrode disposed opposite to an image carrier and connected to a constant current power supply, and a corona discharge electrode provided so as to surround the corona discharge electrode. In a charging device having a house and a grid electrode for controlling corona discharge discharged from the corona discharge electrode, the corona house and the grid electrode are electrically connected, and the connection portion, the zener diode, and the first A second resistor branched from the connection between the corona house and the grid electrode by electrically connecting a resistor in series.
Wherein the resistance is connected in parallel to the Zener diode and the first resistance and grounded, and the constant current power supply is varied to set the surface potential of the image carrier to a predetermined value. I do.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a block diagram of the charging device of the present invention. For the sake of simplicity, the same components as those of the conventional example will be described with the same reference numerals. As shown in FIG. 1, the charging device 6
Constant current power supply 3, corona discharge electrode 2, corona house 4
, A grid electrode 5, a Zener diode 7, a first resistor 9, and a second resistor 10.

The constant current power supply 3 is provided so as to be able to change the current flowing through the corona discharge electrode 2, and can adjust the surface potential of the image carrier 1 to an appropriate value. In addition, by setting the corona house 4 and the grid electrode 5 at the same potential, the current flowing in the corona house 4 decreases, and the current flowing in the image carrier 1 increases, which makes it possible to cope with a high-speed image forming apparatus. Become. In the embodiment, a constant current power supply 3 of 1.5 mA or less is preferably used, and more preferably, a constant current power supply 3 of 1.0 mA is used. The corona discharge electrode 2 is made of a metal wire such as a tungsten wire, and is stretched around a corona house 4 described later at a predetermined distance in a direction orthogonal to the moving direction of the image carrier 1. The corona house 4 is made of a substantially U-shaped metal plate and has a corona discharge electrode 2.
The opening 11 of the corona house 4 faces the image carrier. The grid electrode 5 is provided with a plurality of metal wires or an etched metal plate so as to cover the opening 11 of the corona house 4, and regulates the amount of corona discharge to the surface of the image carrier 1.

In addition to the above configuration, furthermore, the corona house 4 and the grid electrode 5 are electrically connected, and the connection portion 12, the zener diode 7, and the first resistor 9 are electrically connected in series. A circuit is provided in which the second resistor 10 branched from the connection between the corona house 4 and the grid electrode 5 is connected in parallel to the zener diode 7 and the first resistor 9 to ground. In the embodiment, it is grounded to the rotation shaft 13 of the image carrier. In consideration of the required surface potential of the image carrier 1 and the variation of the Zener diode 7, the current flowing through the Zener diode to reduce the variable width of the constant current power supply 3 and the temperature drift of the first resistor 9 and the Zener diode. A second resistor 10 for reduction is set. In the embodiment, for example, in order to set the surface potential of the image carrier 1 to 800 V, the constant current power supply 3 is caused to flow at 1 mA. A 500 V Zener diode 7, a first resistor of 300 KΩ, and a second resistor 10 of 1 MΩ so that the surface potential can be varied by 30 V at 0.1 mA in consideration of the variation of the Zener diode 7. Are provided.

The relationship between the surface potential of the image carrier 1 and the current value of the constant current power supply 3 by the circuit of the charging device 6 according to the present invention shown in FIG. Lines A, B, and C use the same standard zener diode 7,
The surface potential of the image carrier 1 shows different values due to the variation of the Zener diode 7. Even when the zener diodes 7 that vary from one another are used, since the variable region is provided with a certain inclination as shown in FIG. 3, the desired image carrier can be obtained by varying the current value of the constant current power supply 3. 1 can be adjusted. Further, since the current flowing through the Zener diode 7 can be optimized, the change in the surface potential due to the temperature drift of the Zener diode 7 can be reduced.

Further, since the first resistor 9 has a resistance of 300 KΩ, the constant current power supply 3 is changed by
It can be adjusted in the range of V. Also, the first resistor 9
Where a 800V zener diode 7 is normally required to have
Even if there is a variation of 10%, the variation becomes ± 50 V, which is smaller than the conventional ± 80 V.

[0014]

The surface potential of the surface of the image carrier can be adjusted to a desired value by varying the current value of the constant current power supply even when a zener diode having a variation is used for the grid electrode. Further, by setting the corona house and the grid electrode to the same potential, it is possible to cope with a high-speed image forming apparatus. Further, since a constant current power supply of a necessary minimum can be used, the cost is excellent and the variation of the Zener diode is reduced.

Since the Zener diode having a small value can be used, the Zener diode is excellent in temperature dependency and the influence of heat generated by flowing current can be minimized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a charging device according to the present invention.

FIG. 2 is a diagram showing a relationship between a surface potential and an applied current in the charging device according to the present invention.

FIG. 3 is a block diagram showing a conventional charging device.

FIG. 4 is a diagram showing a relationship between a surface potential and an applied current in a conventional charging device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier 2 Corona discharge electrode 3 Constant current power supply 4 Corona house 5 Grid electrode 6 Charging device 7 Zener diode 8 Resistance 9 First resistance 10 Second resistance 11 Opening 12 Connecting part 13 Axis

Claims (1)

[Claims] 1. A corona discharge electrode disposed opposite to an image carrier and connected to a constant current power supply, a corona house provided to surround the corona discharge electrode, and a corona discharge discharged from the corona discharge electrode. A charging device having a grid electrode that electrically connects the corona house and the grid electrode, and electrically connects the connection part, the zener diode, and the first resistor in series, and A second branch branched from the connection with the grid electrode;
Wherein the resistance is connected in parallel to the Zener diode and the first resistance and grounded, and the constant current power supply is varied to set the surface potential of the image carrier to a predetermined value. Charging device.