JPH0451032B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an image forming apparatus such as an electrophotographic copying apparatus, and more particularly to an image forming apparatus having a charger and a transfer device using corona discharge.

[Prior art]

MD is used in the image forming process of electrophotographic copying equipment.
Among them, the so-called Carlson method, in which a charger, developer, transfer device, etc. are placed near the photoreceptor drum, is the most commonly used image forming method. It is a method.

The charger and transfer device used in this type of image forming apparatus apply a high voltage to a discharge wire to generate a corona discharge, the charger applies a uniform charge to the photosensitive surface, and the transfer device applies a uniform charge to the transfer paper. The toner image is being transferred. For this reason, it is necessary to connect a high-voltage power source to the discharge wires provided in the charger and transfer device.

Conventional image forming apparatuses include devices that use two separate high-voltage power supplies, one for supplying this high voltage to the charger and the other for supplying the transfer device, and devices that use a single high-voltage power supply in common. do. For example, when using two high-voltage power supplies, a constant-voltage high-voltage power supply is used for the charger, which is desired to uniformly charge the surface of the photoreceptor, and a transfer device, which is desired to keep the transfer current constant, is used. A constant current high voltage power supply is used. Further, when a single high voltage power source is commonly used, for example, the charging current value is controlled and the output of the high voltage power source is supplied to the charger and the transfer device.

[Problems with conventional technology]

In the conventional image forming apparatus as described above, connecting two high voltage power supplies, one each to the charger and the transfer device, increases the cost of the image forming apparatus itself because the high voltage power supplies are expensive. Furthermore, in cases where a single voltage power supply is simply shared between the charger and the transfer device, high voltage is applied only to the charger to perform corona discharge, and even when the transfer device does not require corona discharge, Since the high-voltage power supply itself cannot be controlled to open or close, and corona discharge continues in the transfer device, various adverse effects occur. For example, the life of the photoreceptor is shortened because areas without the transfer paper are also subjected to corona discharge. Additionally, when image formation is required to the very edge of the transfer paper, toner may adhere to the photoconductor in areas other than those corresponding to the transfer paper, and such toner is not transferred to the transfer paper.
When the photoconductor passes through the transfer section, it is directly exposed to corona discharge because there is no transfer paper, and the toner on the photoconductor is charged by the corona discharge, and has the opposite polarity to the original toner polarity. I end up. Such toner cannot be removed by a cleaner that utilizes electrostatic attraction, for example, fur brush cleaning to which a bias voltage is applied, and the toner is accumulated on the photoreceptor as a cleaning failure.

[Purpose of the invention]

In view of the above conventional drawbacks, the present invention provides an inexpensive image forming apparatus using a single high-voltage power source, allows stable transfer operation even with a single high-voltage power source, and simultaneously performs charged corona discharge. It is an object of the present invention to provide an image forming apparatus that allows transfer corona discharge to be turned on and off.

[Key points of the invention]

In order to achieve the above object, the present invention provides a charger that has a charging corona discharge wire and a grid electrode surrounded by a charging shield case and charges a photoreceptor, and a charger that charges a photoreceptor according to image information. A means for forming an electrostatic latent image, a developing means for developing the electrostatic latent image into a visible image, and a transfer corona discharge wire surrounded by a transfer shield case, and the developed image is transferred to a transfer paper. a transfer device for transferring, a high voltage generation section that outputs high voltage for corona discharge from the same output terminal to each of the charging corona discharge wire and the transfer corona discharge wire, and an output current from the high voltage generation section. a single high-voltage power supply unit comprising current control means for controlling the charger and the transfer device;
In the image forming apparatus, the grid electrode and the charging shield case are grounded via the constant voltage element while the transfer paper is not passing between the photoreceptor and the transfer device. While the transfer paper is passing between the photoreceptor and the transfer device, the high voltage is generated between the grid electrode and the charging shield case via a constant voltage element. connection switching control means for switching the connection to the second connection path connected to the feedback terminal of the section; A first current flowing from the electric wire to the photoreceptor, a second current flowing to the ground via the first connection path, a third current flowing from the transfer corona discharge wire to the photoreceptor, and a third current flowing to the transfer shield case. 4 currents, and the second current by the connection switching control means.
a current detection circuit capable of detecting the total current of the first current, the third current, and the fourth current when the connection is switched to the connection path; The present invention is characterized by comprising a control section that controls the high voltage output from the high voltage generation section so as to keep the total current constant.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of a part of the image forming apparatus of the present invention, particularly showing each device, high-voltage power supply, etc. arranged near the photoreceptor drum. In the figure, a charger 2, a developing device 3, a transfer device 4, and a cleaner 5 are provided near the photosensitive surface 1a of the photosensitive drum 1, and the photosensitive drum 1 has a conductive base member 1b. It is configured with a photosensitive surface 1a made of a conductive material, and the inner surface is grounded. In addition, the charger 2 includes a corona discharge wire 2a, a shield plate 2b, and a grid 2c.
The discharge wire 2a is connected to the high voltage output terminal 6a of the high voltage power supply 6, and the shield member 2b and the grid 2c are connected to the common side of the switching circuit 8 via the constant voltage element 7. Further, the A terminal of the switching circuit 8 is connected to the terminal 6b of the high voltage power supply 6, and the B terminal is grounded.

The transfer device 4 includes a corona discharge wire 4a and a shield plate 4b.
The corona discharge wire 4a is connected to the charger 2 described above.
It is connected to the high voltage output terminal 6a of the same high voltage power supply 6 as the corona discharge wire 2a, and the shield plate 4b is grounded. Further, the corona discharge wire 4a has a wire diameter larger than that of the corona discharge wire 2a.

Further, the high voltage power supply 6 is configured by connecting a high voltage generation section 9 and a constant current control section 10.
is grounded via the control feedback terminal 6c.

The constant current control section 10 controls the high voltage output from the high voltage output terminal 6a of the high voltage generating section 9 so that the current flowing through the control feedback terminal 6c is always constant.

To briefly explain the operation of the image forming apparatus configured by connecting the high-voltage power supply 6 and the like as described above, first, the corona of the charger 2 is applied to the photosensitive surface 1a of the photosensitive drum 1 rotating in the direction of the arrow 11. Discharge line 2a
This gives a more uniform charge. When the uniformly charged photosensitive surface 1a reaches the exposure area, reflected light from the light irradiated onto the document (not shown) or an optical signal modulated according to the signal to be recorded is transmitted through a lens (not shown), etc. The photosensitive surface 1a is exposed to light as shown by arrow 12, forming an electrostatic latent image of the original on the photosensitive surface 1a.

Furthermore, when the electrostatic latent image formed on the photosensitive surface 1a reaches the developing section, it is visualized by the developing device 3 with toner in the developing device 3, thereby forming a toner image. This toner image is transferred to a transfer paper conveyed to the transfer section by a mechanism (not shown) by corona discharge of the corona discharge wire 4a to which a high voltage is applied in the transfer device 4, and the transfer paper is transferred by a fixing device (not shown) to the transfer paper. After the toner image is thermally fixed, it is carried out of the machine. On the other hand, the toner that has not been completely transferred by the transfer device 4 remains as residual toner on the photosensitive surface 1a. A uniform charge is applied.

The cleaner 5 uses a fur brush to which a bias voltage is applied to rub the photosensitive surface, and removes toner using the physical rubbing force of the fur brush and the electrostatic adsorption force of the bias voltage.

In the image forming apparatus of the present invention having the above configuration and image forming process, the relationships among the charger 2, transfer device 4, corona discharge, switching circuit 8, and high voltage power supply 6, which are the main parts of the present invention, are as follows. I will explain.

The shield plate 2b and grid 2c constituting the charger 2 are connected to ground or the terminal 6b via a constant voltage element 7, and the shield plate 2b and grid 2c are connected to a predetermined potential determined by the constant voltage element 7. Retained. Charger 2 with such a configuration
When charging is performed, the relationship between the discharge current due to corona discharge from the charger 2 to the photosensitive surface 1a and the uniform potential formed on the photosensitive surface 1a by this corona discharge is as shown in FIG. Becomes a characteristic. That is,
Even if a discharge current exceeding a certain value is applied to the corona discharge wire 2a, the extra discharge current flows through the grid 2c and the shield plate 2b, and the potential of the photosensitive surface 1a is maintained at a constant value. Also, at this time, the switching circuit 8
is connected to the A terminal side, the shield plate 2b and the grid 2 will be damaged due to corona discharge from the discharge wire 2a.
The current flowing through C is input to the high voltage generator 9 via the constant voltage element 7 and the terminal 6b, and if the switching circuit 8 is connected to the B terminal side, the current flowing through the shield plate 2b and the grid 2c flows from the constant voltage element to the ground, and is connected to the control feedback terminal 6c via the ground.
flows to In either case, the shield plate 2b and the grid 2c are controlled to have a constant potential on the charger 2 by the constant voltage element 7. Therefore, a substantially constant discharge current is applied to the photosensitive surface 1a, and the charged potential on the photosensitive surface 1a is kept constant.

On the other hand, the discharge wire 2a of the charger 2 and the discharge wire 4a of the transfer device 4 have different thicknesses as described above.
The corona discharge line 2 is thicker, as shown in Figure 3.
Even if a voltage is applied to a and 4a, corona discharge will not occur below that voltage.The so-called discharge starting voltage is voltage V ₁ for corona discharge wire 2a, and corona discharge wire 4
a is the voltage _V2 . That is, the discharge starting voltage V ₁ of the discharge wire 2a is lower, and for example, when sequentially increased voltages are applied to the corona discharge wires 2a and 4a, the corona discharge wire 2a starts corona discharge first.
Therefore, by controlling the discharge voltage output from the high voltage generating section 9 to an appropriate value, the driving state of the charger 2 and the transfer device 4 can be controlled. For example, the output voltage of the high voltage generating section 9 can be controlled. If is set to a voltage value between voltage V ₁ and voltage V ₂ , it is possible to cause the charger 2 to perform corona discharge and leave the transfer device 4 not driven.
If the output voltage of the high voltage generator 9 is set to a voltage value equal to or higher than the voltage _V2 , corona discharge can be caused in the transfer device 4 as well as the charger 2.

Here, the operation of each part when the switching circuit 8 is switched will be explained. First, when the switching circuit 8 is connected to the terminal A, the current flowing from the corona discharge wire 2a to the photosensitive surface 1a due to corona discharge is _i1 , as shown in FIG. 1, and the current also flows into the shield plate 2b. Let the current value be _i2 , the current value flowing from the corona discharge wire 4a to the photosensitive surface 1a by corona discharge be _i3 , and the current value similarly flowing into the shield plate 4b be _i4 . The current value flowing from the high voltage power supply 6 to the transfer device 4 is i ₁ + i ₂ , and the current value flowing from the high voltage power supply 6 to the transfer device 4 is i ₃ + i ₄ .
The current value input to the constant current control section 9 via the control feedback terminal 6c is i ₁ +i ₃ +i ₄ .

Next, when the switching circuit 8 is connected to the terminal B, the current flowing from the high voltage power supply 6 to the charger 2 and the transfer device 4 is the same, but the current flows to the constant current control unit 10 via the control feedback terminal 6c. The current value to be input is i ₁ + i ₂ + i ₃ + i ₄ . Therefore, since the constant current control section 10 controls this input current to be constant, unlike when the switching circuit 8 described above is connected to the terminal A, the output voltage of the high voltage generation section 9 decreases, and the output voltage of the high voltage generation section 9 decreases. The discharge starting voltage _V2 of the corona discharge wire 4a is lower than that of the corona discharge wire 4a. For this reason, the corona discharge wire 4a
No corona discharge occurs, and the currents i ₃ and i ₄ become zero.

Further, the discharge current of the corona discharge wire 2a changes greatly when the switching circuit 8 is switched to the terminal B, but as mentioned above, the increase in current is
c. Due to the action of the constant voltage element 7 that flows through the shield plate 2b, the charged potential on the photosensitive surface 1a does not change. Therefore, as shown in this embodiment, the discharge voltage on the charger 2 side is held constant, and the switching circuit 8
The corona discharge of the transfer device 4 can be turned on and off by operating the transfer device 4. Therefore, by switching the switching circuit 8 in accordance with the timing at which the transfer paper passes through the transfer device 4,
Transfer discharge can be generated only when the transfer paper is in the transfer section. Further, even if the corona discharge of the transfer device 4 is controlled on and off in this manner, the potential charged to the photosensitive surface 1a by the charger 2 is not affected in any way.

Note that the embodiments of the present invention are not limited to the above, and the discharge starting voltage of the charger 2 and the transfer device 4 is configured by making the wire diameters of the corona discharge wires 2a and 4a different, and by using the shield plates 2b and 4b. They may be configured with different shapes or sizes. Furthermore, when the switching circuit 8 is connected to the terminal B, even if the output voltage of the high-voltage power supply 6 is not lower than the discharge starting voltage V ₂ of the discharge line 4a, the current i ₃ exhibits a transfer effect on the transfer paper. As long as the currents i ₃ and i ₄ are slightly flowing through the corona discharge wire 4a, it is acceptable.

〔Effect of the invention〕

As described in detail above, according to the present invention, by supplying power to the charging device and the transfer device using a single high-voltage power source, the cost of the image forming apparatus can be reduced, and a constant voltage is applied to the charging device. It is possible to turn on and off the corona discharge of the transfer device while supplying the toner, thereby preventing fatigue of the photoreceptor drum and improving the cleaning performance of the photoreceptor surface in an image forming apparatus equipped with fur brush cleaning.

Further, since the image forming apparatus of the present invention uses a single high-voltage power supply, the design can be simplified in terms of space within the apparatus.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a part of the image forming apparatus of the present invention, FIG. 2 is a characteristic diagram of photosensitive surface potential with respect to discharge current, and FIG. 3 is a characteristic diagram of discharge current with respect to discharge line voltage. 1... Photosensitive drum, 1a... Photosensitive surface, 2...
Charger, 2a, 4a...corona discharge wire, 2b, 4
b...Shield plate, 2c...Grid, 3...Developer, 4...Transfer device, 5...Cleaner, 6...High voltage power supply, 6a...High voltage output terminal, 6b...Terminal,
6c... Control feedback terminal, 7... Constant voltage element, 8
... Switching circuit, 9 ... High voltage generation section, 10
...constant current control section, 11...arrow, 12...arrow.

Claims (1)

[Scope of Claims] 1. A charger that has a charging corona discharge wire and a grid electrode surrounded by a charging shield case and charges a photoreceptor, and an electrostatic latent image on the photoreceptor according to image information. a developing means for developing the electrostatic latent image into a visible image; and a developing means for transferring the developed image onto a transfer paper, the developing means having a transfer corona discharge wire surrounded by a transfer shield case. a transfer device; a high voltage generation unit that outputs high voltage for corona discharge from the same output terminal to each of the charging corona discharge wire and the transfer corona discharge line; and a current that controls an output current from the high voltage generation unit. comprising control means;
A single high-voltage power supply unit that supplies power to the charger and the transfer device, the image forming apparatus comprising: a single high-voltage power supply unit that supplies power to the charger and the transfer device; The grid electrode and the charging shield case are connected to a first connection path connecting to ground via the constant voltage element, and while the transfer paper is passing between the photoreceptor and the transfer device, Connection switching control means is provided for switching the connection between the grid electrode and the charging shield case via a constant voltage element to a second connection path that connects to the feedback terminal of the high voltage generation section, and the current control means is configured to switch the connection between the grid electrode and the charging shield case. A first current flowing from the charging corona discharge wire to the photoreceptor when the connection is switched to the first connection path by a control means, a second current flowing to the ground via the first connection path, and the transfer corona. The total current of the third current flowing from the discharge wire to the photoreceptor and the fourth current flowing to the transfer shield case, and when the connection is switched to the second connection path by the connection switching control means, the first a current detection circuit capable of detecting the total current of the third current and the fourth current; and a current detection circuit capable of detecting the total current of the third current and the fourth current; An image forming apparatus comprising: a control section that controls high voltage output.