JPH0782260B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a charger around a photoconductor drum, an exposure unit for forming an electrostatic image on the surface of the photoconductor drum charged by the charger, and a static charger. A developing device for developing an electric image with toner charged to the same polarity as the charging is provided, and a composite image of a plurality of toner images is formed on the surface of the photoconductor drum by repeating electrostatic image formation and development. The present invention relates to an image forming apparatus.

[Background of the Invention]

Most of the image forming apparatuses as described above are provided with a plurality of developing devices to form a color image, in which one charging device and an exposing part are provided and one of the photosensitive drums is provided. There are one that forms one color toner image for each rotation, and one that forms a plurality of color toner images by one rotation of the photosensitive drum by disposing a plurality of chargers and exposure units. In any of the image forming apparatuses, in the second and subsequent electrostatic image formation, the surface of the photosensitive drum on which the toner image has already been formed is charged and exposed. Then, when the surface of the photoconductor drum having the toner image is exposed, a part of the toner of the toner image is easily scattered, and the charging device and the developing device near the exposed portion are easily contaminated with the toner. To prevent this, an electrode facing the surface of the photoconductor drum is provided near the exposed area, and a voltage of the same polarity as the toner charging is applied to the electrode to suppress toner scattering, or toner charging is performed. It is effective to apply a voltage of the opposite polarity to attract the scattered toner. But,
Even if this is done, the charger is still liable to be contaminated, especially in the charger that charges the surface of the photosensitive drum having the toner image.

[Object of the Invention]

The present invention has been made in order to solve the above-mentioned problems, in which the toner contamination of the charging device is small, and the electrostatic image is developed by the toner charged to the same polarity as the charging of the photosensitive drum. An object of the present invention is to provide an image forming apparatus in which a toner image is combined on a drum.

[Structure of Invention]

The present invention relates to a charging device around a photoconductor drum, an exposure unit that forms an electrostatic image on the surface of the photoconductor drum charged by the charging unit, and a toner that charges the electrostatic image to the same polarity as the charging. In the image forming apparatus that forms a composite image of a plurality of toner images on the surface of the photoconductor drum by disposing a developing device that develops with, and repeating electrostatic image formation and development, in the vicinity of the charging device. The image forming apparatus is characterized in that an electrode facing the surface of the photosensitive drum is provided so that a voltage having the same polarity as that of the charging is applied to the electrode, and this configuration achieves the above object.

〔Example〕

 Hereinafter, the present invention will be described with reference to illustrated examples.

FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus of the present invention,
FIG. 2 is a block diagram of the image exposure optical system, FIG. 3 is a process diagram showing the potential change on the surface of the photosensitive drum, and FIGS. 4 to 7 and 9 are partial views showing the charger portion, respectively. 8 is the seventh
It is a perspective view of a figure.

In the image forming apparatus of FIG. 1, the lamp of the document reading unit 2 irradiates the document on the document table 1 with the document table 1 or the document reading unit 2.
Is moved to the left or right in the figure, the original is scanned and exposed, and the reflected light from the original enters the one-dimensional color CCD image pickup device 6 via the mirror 4 and the lens 5, and the image pickup device 6 receives a signal. Timing for outputting color-separated image signals to the processing unit 7, the signal processing unit 7 converting the image signals into image signals corresponding to the respective color toner images and temporarily storing them, and then forming an electrostatic image of the respective color toner images The details are output to the laser optical systems 8A to 8D as shown in FIG. 2, whereby the laser optical systems 8A to 8D perform image exposure on the photosensitive drum 9 to form an electrostatic image. is there. To further explain this point, the photosensitive drum 9 rotates in the direction of the arrow, and the charging device 10A uniformly charges the surface potential E of the laser optical system 8A as shown in FIG. Is an image signal from the signal processing unit 7 and is a semiconductor laser oscillator 81 shown in FIG.
By receiving the modulated laser light output from the semiconductor laser oscillator 81 through the rotary polygon mirror 82 and the f-θ lens 83, the distribution of the portion where the potential is lowered is shown in FIG. A developing device 11 using, for example, a yellow toner as a developer, which forms an electrostatic image of one color of the color separation formed, and the electrostatic image is triboelectrically charged to the same polarity as the charging of the photosensitive drum 9.
The toner T A is reversely developed by _A and adhered to the low potential portion as shown in FIG. 3, so that the surface on which the yellow toner image is formed is charged again by the charger 10B as shown in FIG. The laser beam is charged uniformly at the electric potential E, and the laser optical system 8B makes laser light incident on the charged surface in the same manner as 8A to form an electrostatic image of one color with different color separation as shown in FIG. The electrostatic image is reverse-developed into a magenta toner image as shown in FIG. 3 by the developing device 11B using magenta toner as a developer, and the surface on which the yellow toner image and the magenta toner image are formed is charged as described above. The potential is uniformly charged again by the container 10C, and the laser optical system 8C makes laser light incident on the charged surface in the same manner as before to form an electrostatic image of another color separation, and the electrostatic image is formed. For example, when cyan toner is used as a developer, The image device 11C reverse-develops the image as before, and the surface on which the yellow, magenta, and cyan toner images have been formed is again uniformly charged by the charging device 10D, and the laser optical system 8D is applied to the charged surface.
In the same way as before, a laser beam is incident to form an electrostatic image of black, for example, and the electrostatic image is reversely developed by the developing device 11D using black toner as a developer. The image is formed and developed.

As described above, a color image formed by synthesizing toner images is formed on the photoconductor drum 9, and the color image is easily transferred by exposing the photoconductor drum 9 by the exposure lamp 12, and by the paper feeding device 13. It is transferred by the transfer device 14 to the recording paper P fed in. The recording paper on which the color image has been transferred is separated by the separator 15 into the photosensitive drum 9
The color image is fixed by the fixing device 16 and is discharged out of the apparatus.

On the other hand, the surface of the photoconductor drum 9 onto which the color image is transferred is
The residual toner is removed by the cleaning device 17 having a cleaning means such as a cleaning blade and a fur brush, and a means such as a collecting roller, and the state returns to the state where the next image forming step is started.

As described above, the image forming apparatus shown in FIG. 1 synthesizes toner images of up to four colors by one rotation of the photosensitive drum 9, and the toner image of any one of the charger, the laser optical system, and the developing device is formed. It is possible to record a single-color image or a two-color or three-color toner image by disabling the set. This image forming device has a charger
Since the surfaces 10B to 10D and the laser optical systems 8B to 8D perform charging and image exposure on the surface on which the toner image is formed, the chargers 10B to 10D are particularly likely to be contaminated by the toner scattered from the toner image. In order to prevent this, the charging device 10B to 10D is provided with an electrode 18 which faces the surface of the photosensitive drum 9 in close proximity to them and which is applied with a voltage having the same polarity as the charging of the photosensitive drum 9 in detail with reference to FIGS. It is provided as shown in FIG. In the illustrated example, the photosensitive drum 9 is positively charged.

The electrodes 18 shown in FIGS. 4, 5 and 7 to 9 are all attached to the side wall of the case 19 of the scorotron charger 10 via an insulator 20, and the electrode 18 shown in FIG. It is connected to a DC power supply similar to the DC power supply that applies the bias voltage V ₁ to the 10 grid, and a voltage V ₂ having the same polarity as the grid and the discharge wire is applied. It is preferable that the power source voltages V ₁ and V ₂ are approximately equal to the photoconductor potential and 500 to 1000 V, and | V ₂ | ≧ | V ₁ |. Since the electrode 18 of FIGS. 5 and 7 and 8 is grounded in parallel with the grid of the charger 10 through the Zener diode 21, the corona discharge of the charger 10 causes the charging of the photosensitive drum 9 together with the grid. Voltages of the same polarity are applied. Further, the electrode 18 on the downstream side in FIGS. 7 and 8 is provided with a slit 18a through which the laser light from the laser optical system passes, and the insulator 2 is formed on the slit 18a so as not to close the slit 18a.
The cover electrode 22 is provided via 0. The cover electrode 22 attracts the scattered toner to the outer surface by applying a bias voltage having a polarity opposite to that of the ground or toner charging, and prevents the toner from scattering along with the electrode 18 that suppresses the scattering of the toner. It prevents the downstream developing device from being contaminated. The electrode 18 in FIG. 9 is a Zener diode 21.
High withstand voltage in parallel with the wire stretched closer to the discharge wire than the grid grounded through (500 to 2000
Since it is grounded via the V) Zener diode 21 ', a voltage whose absolute value is higher than that of the grid is applied. Unlike the electrode 18 attached to the charger 10 described above,
The electrode 18 shown in FIG. 6 is composed of a portion where the grid of the charger 10 projects outside the side wall of the case. Therefore, the charging of the electrode 18 is the same as the potential of the grid, and since the grid is grounded via the Zener diode 19, a voltage is applied similarly to the grid in FIGS. 5 and 7, 8.

By providing the above-described electrodes 18 on the chargers 10B to 10D, the toner of the toner image formed on the photoconductor drum 9 is repelled by the electrodes 18 and pressed against the photoconductor drum 9 side, and thus scattered. Contamination of the charging devices 10B to 10D or the developing device on the downstream side is prevented. In order to enhance this prevention effect, it is preferable that the voltage of the electrode 18 be higher than the surface potential of the photosensitive drum 9. Although it can be easily satisfied by increasing the voltage of the DC power supply V _{2 in} the example of FIG. 4, it is almost satisfied in the examples of FIGS. 5 to 8.
If these are applied to the voltage application system as shown in FIG. 9, it will be further satisfied. The case 19 of the charger 10 is grounded.

The image forming apparatus of the present invention is not limited to the example shown in FIG. 1, but a charger and an image exposure unit are provided for each of a plurality of developing devices.
It is also possible to form a composite image of a plurality of toner images by a plurality of rotations of the photoconductor drum, or an electrode for preventing toner contamination is provided for a charger that charges the surface of the photoconductor drum on which the toner image is not formed. It may be provided.

〔The invention's effect〕

According to the present invention, image formation is performed in which a plurality of toner images are combined on the photoconductor drum by repeating formation of an electrostatic image on the photoconductor drum and development with toner charged to the same polarity as that of the photoconductor drum. It is possible to obtain an excellent effect that it is possible to remarkably reduce the contamination of the charging device of the device and the toner of the developing device.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus of the present invention,
FIG. 2 is a block diagram of the image exposure optical system, FIG. 3 is a process diagram showing the potential change on the surface of the photosensitive drum, and FIGS. 4 to 7 and 9 are partial views showing the charger portion, respectively. 8 is the seventh
It is a perspective view of a figure. 1 ... original table, 2 ... original reading section, 3 ... lamp, 4 ... mirror, 5 ... lens, 6 ... imaging device, 7 ... signal processing section, 8A-8D ... laser optical system, 81 …… Semiconductor laser oscillator, 82 …… Rotating polygon mirror, 83 …… f-θ lens, 9 …… Photosensitive drum, 10,10A-10D …… Charger, 11A-11D …… Developer, 18 ・ ・ ・… Electrodes, 18a …… Slits, V ₁ , V ₂ …… Bias voltage, 21,21 ′ …… Zener diode.

Claims (3)

[Claims] 1. A charger around the photoconductor drum, an exposure unit for forming an electrostatic image on the surface of the photoconductor drum charged by the charger, and the electrostatic image charged to the same polarity as the charge. A developing device that develops with toner is provided, and in an image forming apparatus that forms a composite image of a plurality of toner images on the surface of the photosensitive drum by repeating electrostatic image formation and development, the device is close to the charging device. An image forming apparatus is characterized in that an electrode facing the surface of the photosensitive drum is provided so that a voltage having the same polarity as the charging is applied to the electrode. 2. The image forming apparatus according to claim 1, wherein the charging device provided close to the electrodes is a charging device that charges a surface on which a toner image is formed. 3. The image forming apparatus according to claim 1, wherein the electrode and the grid of the charger adjacent to the electrode are short-circuited.