JPS61294467A - Corona electrifying device - Google Patents

Abstract

PURPOSE:To improve the service property by a simple constitution, by connecting in series a varistor and a Zener diode to a grid of a corona electrifying device and applying a bias voltage, and selecting and switching the number of Zener diodes to be used, in accordance with an electrifying function of a photosensitive body. CONSTITUTION:The potential of a photosensitive body is influenced by the grid potential of an electrifying device. When an electrifying function of a photosensitive body 1 is inspected in advance and a correct bias value of a grid 4 is displayed at every photosensitive body, a shadow potential can be set to a correct value by switching contacts A-E in accordance with its display value, when replacing the photosensitive body. When four pieces of Zener diodes 7 of 51V rating, and one piece of varistor 6 of 680V rating are used, the varistor 6 generates a voltage of 640V being lower than a rated value, since a current flowing to the grid 4 is 100-150muA, and on the other hand, the Zener diodes 7 generate 50V of about a rated value per piece, and the adjustment can be executed extending from 640V to 840V at intervals of 50V. Accordingly, a variance of an electrifying function of the photosensitive body can be corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a corona charging device that charges an electrophotographic photoreceptor.

(Background Art) The charging ability of photoreceptors used in electrophotographic devices and the like usually varies from production lot to production lot depending on the production environment, production equipment, and the like. If the charging ability of the photoreceptor varies, a predetermined latent image potential cannot be obtained under constant charging conditions, and the dark area potential becomes too high or too low.

Therefore, it is preferable to adjust the charging conditions depending on the photoreceptor, but in reality, this is not easy to do when the photoreceptor is replaced at the user's site.

(Objective of the Invention) The present invention has been made in order to deal with the above-mentioned variations in the charging ability of photoreceptors, and has an extremely simple configuration.
The present invention provides a corona charging device with excellent serviceability in the market.

(Summary of the Invention) The present invention applies a bias voltage to the grid of a corona charging device by connecting a varistor and a Zener diode in series, and also selects and switches the number of Zener diodes to be used depending on the charging ability of the photoreceptor. This is how it was done.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the basic configuration of the corona charging device of the present invention.
1 is a photoreceptor moving in the direction of the arrow; C is a corona charger; a high voltage power supply 5 applies positive high voltage to the charging wire 3 to perform corona discharge; 4 is a corona charger C;
The grid is provided in the opening of the grid and is grounded via a varistor 6 and a Zener diode 7 as constant voltage elements. Further, 8 can be switched to contacts A to H using a rotary switch.

By the way, it is generally known that the potential of the photoreceptor depends on the grid potential of the charger. For example, as shown in FIG. 5, if the horizontal axis is the grid voltage and the vertical axis is the surface potential of the photoreceptor, then The grid voltage and the surface potential are approximately proportional, and the extent to which the surface potential of the -force photoreceptor depends on the current value of the charging wire is small.

In the above, if the charging ability of the photoconductor 1 is checked in advance and the appropriate bias value of the grid 4 is displayed for each photoconductor, then when replacing the photoconductor, the contacts A to E of the rotary switch can be switched according to the displayed value. , it is possible to set the dark potential to an appropriate value.

In the configuration shown in FIG. 1, by increasing the number of contacts between the Zener diode 7 and the rotary switch, it is possible to finely adjust the dark potential. In Figure 1, four Zener diodes 7 have a rating of 51V, and the varistor 6 has a rating of 680V, considering the trouble of managing the chargeability of the photoreceptor and the size of the device itself.
One v item was used. At this time, the current flowing through the grid 4 was 100-150pA, so the varistor 6
generated a voltage of 640V, which is approximately 5% lower than the rated value, whereas each Zener diode 7 generated 50V, which is approximately as rated. As a result, the rotary switch 8 can be adjusted from 640V to 840V in 50V increments.

In addition, as a bias voltage application means, a method of inserting a variable resistor in series with a constant voltage element instead of the Zener diode 7 and rotary switch 8 may be considered, but the bias value may become unstable when the grid current changes, or the resistance value itself may become unstable. Since this may vary depending on the environment, variations from machine to machine and factors such as environmental changes intervene, making it unsuitable for independently correcting the charging ability of the photoreceptor.

FIG. 2 shows another embodiment of the present invention, which has basically the same configuration as FIG. NS1, but uses a short bin connector 9 instead of the rotary switch 8 in FIG. The voltage applied to the grid 4 is adjusted by replacing the . Further, by connecting the bias voltage applying means to the charger by connecting the bias voltage applying means to the ground through the shield 2. With such a configuration, a compact and inexpensive mechanism can be realized. Of course, Barista 6,
The Zener diode 7 and the short bin connector IO may be provided in whole or in part in the main body.

Furthermore, when connecting the varistor 6 and the Zener diode 7 in series, it is preferable to connect the Zener diode 7 to the low voltage side in consideration of withstand voltage, and the switching state of the Zener diode 7 can be controlled from the outside of the corona charging device. It is preferable to provide it in an easily visible part.

In Figures 3A and 3B, a second
In the figure, 13 is an insulating end block of a charger, in which a varistor 6, a Zener diode 7, a short bin 1
0 and connector 9 are incorporated, and the position of the short bin 10 is visible through the window 12. 11 is a printed circuit board. Also, the grid 4 has screws 16. It is connected to one leg of the varistor 6 by a washer 18, and the ground side of the Zener diode 7 in FIG. 2 is connected to the charger shield 2. The pins 14 and 15 are pins for positioning the corona charger when the corona charger is inserted into the main body of the electrophotographic apparatus. Like this,
The bias voltage application means of the present invention can be easily incorporated even in a small space such as an end block.

Figures 4A and 4B show a configuration in which a bias voltage is applied to the shield 2 without grounding the shield 2.
In general, several tenths of the reactive current of the total current flows into the shield of the charger, so if a bias voltage with the same polarity as the charging polarity is applied to this part, the current flowing into the shield 5 will decrease, and the total current will also decrease. This also contributes to reducing the capacity of high-voltage transformers.

FIG. 4A shows a case where a voltage of the same potential as that of the grid 4 is applied to the shield 2, and FIG. 4B shows a case where the varistor 20 is provided independently. In either case, grid 4 and shield depending on the position of short bin 10? Since the potentials of both sides change, it is possible to obtain an even greater writing effect than in the case of only the grid. Note that the value of the varistor 20 in FIG. 4B is related to the capacity of the transformer 5, etc. as described above, so the optimum value naturally differs depending on the machine, so the optimum value can be found at the time of design.

(Effects of the Invention) As explained above, by using the present invention, variations in the charging ability of the photoreceptor can be corrected with a simple configuration consisting of a combination of a varistor, a plurality of Zener diodes, and a changeover switch. Also, it is very easy to adjust the dark potential (with the arrival of IB, key WII! 11)
Since it is possible to obtain a high range of values, it is also possible to widen the tolerance range for manufacturing variations in photoreceptors.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the present invention, and FIG. 5 is a graph showing the relationship between the photoreceptor surface potential and the grid voltage. 1-111 photoreceptor 2-111 shield member 3---
Charging wire 4-111 Grid 5---High voltage transformer 6.20---Varistor 7---Zener diode 8-111 Rotary switch

Claims (1)

[Claims] In a corona charger that is provided facing a moving photoreceptor and has a grid in a discharge opening of a shield member,
It has a bias voltage applying means for applying a bias voltage to the grid, and as the bias voltage applying means, a varistor and a plurality of Zener diodes are connected in series, and the Zener is A corona charging device characterized in that the number of diodes used can be selected and switched.