JPS60189772A - Control method of corona electrifier of electrophotographic device - Google Patents

Abstract

PURPOSE:To eliminate the residue of ozone when image forming operation is stopped by grounding a conductive shield through a varistor with a larger value than the potential value of a dark part on a photosensitive body during the image forming operation, and grounding it directly or through a varistor with a smaller value than the potential value of a dark part during rotation after copying operation. CONSTITUTION:The conductive shield 12 is connected to the varistor A having the higher rated value than the potential of the dark part on the photosensitive drum 2 during the copying operation, so a corona a wind flows from an opening (a) in the back surface of the shield 12 to the photosensitive drum 2, and the surface of the drum 2 is therefore charged easily and held at an uniform potential. The conductive shield 12 is grounded B directly during the rotation after the copying operation and the shield potential is at ''0''V; and the corona wind flows to the shield side to flow in from the gap (b) between the shield 12 and drum 2 and flows out from the opening (a) of the shield back surface, removing ozone remaining in the charger.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling a corona charger in an electrophotographic apparatus, and in particular to a method for reducing the adverse effect of ozone, which is often generated by corona, on a photoreceptor and for always obtaining good images. This invention relates to a method of controlling a corona charger.

A photoreceptor (latent image carrier) used in an electrophotographic apparatus is repeatedly subjected to processes such as charging, exposure, development, and transfer cleaning. When a photoreceptor is subjected to corona charging many times during a charging process or a transfer charging process, it is exposed to ozone generated by the corona.

A photoreceptor exposed to ozone generated by this corona will experience the following phenomena.

(1) When used many times, the bright area potential of the photoreceptor gradually increases, causing fog.

(2) Similarly, the dark area potential decreases and the image density decreases.

(3) Especially when the humidity is high, letters and the like may become blurred, or the image may appear as if the solid parts are trailing in a sushi-like pattern.

These phenomena are due to a decrease in the sensitivity of the photoreceptor, and also because ozone and moisture reduce the surface resistance of the photoreceptor surface, causing surface charges to move. In particular, these phenomena are likely to occur during copying operations after the machine has been stopped and left unattended. This is because ozone remains in the charger even after the machine is stopped, and the residual ozone deteriorates the drum surface along with moisture and the like.

The above phenomenon will be explained using a conventional corona charger shown in a perspective view in FIG. 1 and in a sectional view in FIG. The corona charger 1 includes a corona discharge wire 11 at the center, conductive shields 12 surrounding the wire on three sides, insulating blocks 13 at both ends,
It consists of a connecting rod made of a conductor attached to it, and a wire tensioning set screw connected to this, and a high voltage power source 16 is connected between the wire 11 and the ground. The charger 1 is closely opposed to the photoreceptor drum 2. Ozone generated by the corona is exposed to the photoreceptor drum 2- by the corona wind (wind generated by the corona). That is, the flow of corona air flows in from the insulating block 13 at the end of the charger and flows out from the gap between the shield 12 and the photoreceptor drum 2 at the center of the charger, exposing the photoreceptor 2 to ozone. When the machine stops, a large amount of ozone remains in the charger.

As a means to change the flow of this corona wind and prevent ozone from exposing the drum, the conductive shield 12
An attempt was made to provide a corona wind discharge opening in a part of the conductive shield 12 so that it would flow easily (Japanese Patent Publication No. 51-10
Publication No. 785). This method is certainly effective, and since ozone is discharged through a part of the shield 12 without exposing the photoreceptor, there are problems such as a decrease in the dark area potential, an increase in the bright area potential, brushing, and flowing edges due to multiple copying. did not occur.

However, a new problem has arisen here. That is, although the above-mentioned means certainly removed the adverse effects of ozone, the copied images deteriorated if the copying operation was continued for a long period of time. ``Specifically, it appears that density unevenness in halftones called υ halftone, in which black slivers appear in the copied image, has occurred.

When the cause of these problems was investigated, it was found that the cause was that the surface potential on the photoreceptor drum 2 was non-uniform. This potential unevenness is due to unevenness in the corona current.

In other words, in order to avoid ozone exposure, the corona wind is discharged from the shield without hitting the drum, so that the electric charge that should be charged on the surface of the photoreceptor drum is also dragged by the corona wind, and the strength of the corona wind, flow direction, etc. As a result, the state of charge on the surface of the photoreceptor drum changes, and the surface potential tends to become non-uniform. This phenomenon is not a problem in the initial stage or when the number of copies is not very large, but it is sensitive to wire dirt, and if the wire becomes dirty, unevenness in surface potential is likely to occur.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for controlling a corona charger of an electrophotographic apparatus, which eliminates the above-mentioned drawbacks, allows good uniform charging at all times during image forming operation, and eliminates ozone remaining when the operation is stopped. be.

In the present invention, a corona discharge wire is covered on three sides with conductive shields, and a corona charger comprising an opening for discharging corona wind on the back side of the conductive shield is hidden on the side not covered with the conductive shields. In an electrophotographic apparatus that is placed close to the image carrier, the entire or part of the conductive shield is connected through a varistor having a varistor value larger than the dark potential value formed on the latent image carrier during image forming operation. A corona charger for an electrophotographic apparatus t, characterized in that the whole or a part of the conductive shield is grounded directly or through a varistor having a varistor value smaller than a dark potential value when the conductive shield is not in an image forming operation. The gist is the control method.

Embodiments of the present invention will be described in detail using FIGS. 3 and 4. Similar to that shown in FIG. 1, the corona charger has an opening a on the back side of a conductive shield 12 that covers the discharge wire (discharge electrode) 11 on three sides.

During the copying operation, the conductive shield 12 is closed as shown in Fig. 3(a).
is connected to a varistor A having a rated value higher than the dark potential value on the photoreceptor drum 2. Therefore, the cycorona wind having a high shield potential flows toward the photosensitive drum 2 side. Therefore, the corona wind flows in through the opening a on the back of the shield and flows out through the gap between the shield 12 and the drum 2. Since the corona wind flows toward the photosensitive drum 12, the charge on the drum is easily disposed of, and the drum surface has a uniform potential and is resistant to wire stains. If this corona discharger is used in the charging process of the photoreceptor drum for forming 6, a good uniform image can be obtained by forming a latent image in the next exposure process, and if it is used in the transfer process, a good uniform image can be obtained. Various types of transferred images can be obtained.

During the post-rotation after copying is completed, the conductive shield 12 is grounded B as shown in FIG. 3(b). Therefore, the shield potential becomes zero potential, and the corona wind flows toward the shield side. Therefore, the corona wind blows through the gap between the shield 12 and the drum 2 or at both longitudinal ends of the charger (block 1 in Figure 1).
3 etc.) and flows out from the opening a on the back of the shield. During the subsequent rotation, the corona wind completely removes ozone that had accumulated in the charger in the high humidity environment where it was left for a long time during normal copying operations. Therefore, since ozone does not remain in the charger when left in a high-humidity environment for a long time, the surface of the photoreceptor drum does not become low in resistance and a washed-out image does not occur.

FIG. 4 is a sea fence diagram of the above operation. Forward rotation is to uniformly expose the surface of the drum to light in order to eliminate the influence of the previous use (on the photosensitive drum), and to equalize the potential on the drum. Reverse rotation of the optical system is to uniformize the potential on the drum during copying. This is the backward movement of the optical system that scans the image forward, and the backward rotation is to erase the effects during copying, eliminate potential differences in paper marks, and even out the potential on the photoreceptor drum.At this time, ozone is also Remove the inside of the charger as described above.

Next, specific examples of the present invention will be described.

Example-1 An organic photoconductor (OPC) was used as the photoreceptor, and the charger was the third one.
The sea fence will be as shown in the figure, and the operating sea fence will be as shown in Figure 4. The high voltage power supply applied to the charger was a constant current transformer with a current of -400 μA, and the material of the conductive shield 12 was 5US430 stainless steel. The copying speed was 8 copies per minute, and a large number of copies were made intermittently in a high humidity environment.

During the copying operation, the shield 12 was grounded via the varistor A as shown in FIG. 3(a). The varistor value at this time is -6
80V, and the dark potential on the photoreceptor drum at this time was -550V. As a result, a good image with no unevenness was obtained. During the post-rotation, the shield 12 is rotated as shown in FIG.
) and grounded.

This operation was repeated for about 3000 sheets. Even at the end of copying 3,000 sheets, no blurred images or blurred images occurred.

Next, after leaving it for a day and night, a copying operation was performed, but no blurred or washed out images were produced, and a uniform and good image was obtained.

Example 2 As shown in Fig. 5, one conductive shield 12 is divided into a side shield 122 and a back shield 121, and a checkpoint a for discharging corona wind is provided on the back side, and a part of the shield 12 is controlled to discharge the corona wind. was controlled. That is, in accordance with the sea fence shown in FIG. 4, the rear shield 121 is grounded via the varistor A during the copying operation, and is placed in the grounded state B during the post-rotation after the copying operation. The side shield 122 was always grounded. The opening a on the back side of the shield does not need to be located in the center of the back side shield 121, and may be located on one side as shown in FIG.

Example 3 As shown in Fig. 6, the shield 12 is divided into two halves 123 and 124 with the aperture a as the center, and the shield 123 has a potential higher than the dark area during copying according to the sea fence shown in Fig. 4. It is grounded through a varistor A having a value of 1, and during post-rotation after copying, it is grounded through a varistor B having a value smaller than the dark potential. Shield 124 is always grounded.

In addition, in the present invention, the opening a for discharging corona wind provided on the back side of the conductive shield is not only a longitudinal slot as shown in FIG. 7, but also an opening shaped as shown in FIGS. 8 and 9. You can.

As explained above, according to the present invention, ozone is eliminated during image forming operation, and uniform and good charging is performed, and no ozone remains after the operation is stopped, and even and good charging is performed in subsequent image formation. We are able to consistently produce high quality images.

[Brief explanation of the drawing]

Figures 1 and 2 are a perspective view and a sectional view of a conventional corona charger, and gg3 Figures (11) and (b) are the state of the corona charger according to the embodiment of the present invention during copying operation and during post-rotation. 4 is an operational sea fence diagram of the embodiment of the present invention, and FIGS. 5 and 6 are sectional views of corona chargers according to other different embodiments of the present invention. 7 to 9 are diagrams showing examples of the shape of the opening for discharging the corona wind of the corona charger according to the present invention. 1: Corona charger, 2: Photosensitive drum, ll: Corona discharge wire, 12: Conductive shield, 13: Insulating block, 14: Connecting conductor bar, 15: Wire tensioning screw, 16: High voltage power supply, a: Opening. Figure 1 Figure 2 Figure 3 <a) 11-壓. Tram ON r-□□□□□"□□-;--FF I:1 Charge ON knee-7""""""lo"・1; ::1 N-) b Do R'J7s- + , , I'-, I-
---77, 1, Figure 5 Figure 6

Claims (1)

[Claims] A corona charger comprising a corona discharge wire covered with conductive shields on three sides and an opening for discharging corona air on the back of the conductive shield is attached to the latent image carrier on the side not covered by the conductive shield. In an electrophotographic apparatus which is placed in close proximity to the electrophotographic apparatus, during image forming operation, the entire or part of the conductive shield is grounded via a varistor having a varistor value larger than the dark area potential value formed on the latent image carrier, A method for controlling a corona charger of an electrophotographic apparatus, characterized in that, at times other than forming operations, the entire or part of the conductive shield is grounded directly or via a varistor having a varistor value smaller than a dark potential value.