JPH04355770A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device whose configuration can be simplified by reducing transformers. CONSTITUTION:In the image forming device electrifying a rotary photosensitive body 30 by the electrostatic chargers of a main electrostatic charger 1, etc., to form a toner image, and simultaneously, transferring the toner image on the photosensitive body 30 by a transfer roller 3, the power sources of a transformer 6 having a first tap 6a generating a high voltage for electrifying the transfer roller 3, and a second tap 6b generating a low voltage for electrifying the photosensitive body 30, etc., the switching means of a switching part 5, etc., changing over the high and low voltages and applying it to the electrostatic charger, and the switch control means of a control part 7 applying the high voltage to the electrostatic charger to electrify the transfer roller 3 via the photosensitive body 30 over a prescribed time, etc.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an image forming apparatus in which a rotating photoreceptor is charged by a charging device to enable the formation of a toner image, and a transfer roller transfers the toner image on the photoreceptor to a transfer paper. Regarding.

0002

2. Description of the Related Art Conventionally, a photoreceptor drum that is charged and exposed to light by a charger is brought into pressure contact with a transfer roller, and when transfer starts, a voltage is applied to the transfer roller to form a toner image on the photoreceptor drum. An image forming apparatus is known that transfers images onto transfer paper.

0003

However, the conventional image forming apparatus requires a transformer for applying voltage to the transfer roller and a transformer for applying voltage to the charger, resulting in high cost. At the same time, space for arranging transformers and the like is required.

On the other hand, Japanese Patent Laid-Open No. 58-10770, Japanese Patent Laid-Open No. 61-167968, or Japanese Patent Laid-Open No. 63-1
As shown in Japanese Patent No. 94283, there are known devices that charge the photoreceptor drum using a developing device, transfer roller, etc., and devices that perform the developing and cleaning mechanism in one device. There is nothing to charge the roller to the voltage for transfer.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an image forming apparatus that can simplify the configuration by reducing the number of transformers.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention charges a rotating photoreceptor with a charging device to enable the formation of a toner image, and also uses a transfer roller to charge the toner image on the photoreceptor. An image forming apparatus that transfers an image to a transfer paper, comprising a first tap that generates a high voltage for charging the transfer roller and a second tap that generates a low voltage for charging the photoreceptor. a power supply, a switching means for switching between the high voltage and the low voltage and applying the same to the charging device, and applying the high voltage to the charging device to charge the transfer roller via the photoreceptor for a predetermined period of time. and a switching control means for applying the voltage.

[0007]

[Operation] According to the image forming apparatus configured as described above, a high voltage for charging the transfer roller is applied to the charging device, the photoreceptor is charged at a high voltage, and the electric charge of the photoreceptor is supplied to the transfer roller for transfer. After the roller is charged and the transfer roller is charged for a predetermined period of time, a low voltage is applied to the charging device to charge the photoreceptor. After a toner image is formed on the photoreceptor, it is transferred to transfer paper.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 is a schematic diagram showing an example of an image forming apparatus equipped with a transfer device according to the present invention. The image forming apparatus has a document mounting table 21 and a document presser 22 on its upper surface, and is equipped with an optical system L and an image forming means P inside.

The optical system L includes a light source consisting of a halogen lamp 23 and a reflecting plate 24, reflecting mirrors 25, 26, 27,
It is composed of a lens section 28 and a fixed mirror 29. When the copying operation is started, the light from the light source is reflected by the original placed on the original placing table 21, and the reflected light is guided to the lens section 28 via the reflecting mirrors 25 to 27. Thereafter, the following photosensitive drum 30 is exposed through the fixed mirror 29.

The image forming means P includes a photosensitive drum 30, a main charging device 1 including a charging charger, a charging brush or a charging roller, a blank lamp 31, a developing device 32,
It includes a transfer device 2, a cleaning section 33, a static elimination lamp 34, and the like. After the transfer roller 3 is charged by the main charging device 1 via the photoreceptor drum 30, the surface of the photoreceptor drum 30 is charged by the main charging device 1, and is then exposed to the reflected light to absorb the electrostatic potential. An image is formed.

The electrostatic latent image is developed with toner by the developing device 32, transferred to a transfer paper by the charged transfer device 2, and then separated from the photosensitive drum 30. on the other hand,
In order from upstream in the feeding direction, the paper feed port 35, the paper feed cassette 3
6, 37, paper feed rollers 38, 39, conveyance roller pair 40,
A pair of transport rollers 41 and a pair of registration rollers 42 are provided, and the transfer paper is fed to the photosensitive drum 30 by these. Further, after the electric charge remaining on the photoreceptor drum 30 is discharged by the discharge lamp 34, the cleaning section 33 cleans the toner remaining on the surface of the photoreceptor drum 30 after the transfer.

A conveyor belt 43, a fixing device 44, a discharge roller 45, etc. are arranged downstream in the conveyance direction of the transfer paper after transfer. After the transfer paper is transferred, it is fixed by a fixing device 44, and then transferred to a discharge tray 4 by a discharge roller 45.
It is discharged at 6.

Next, the detailed structure of the transfer device 2 will be explained using FIG. 1. That is, the transfer device 2
The transfer roller 3 includes a transfer roller 3, a switch 4, etc., and the transfer roller 3 has a circumferential surface made of sponge, urethane rubber, etc., and is arranged so as to be in pressure contact with the photoreceptor drum 30. The transfer roller 3 is charged by the main charging device 1 to a voltage for transfer, so that the toner image on the photosensitive drum 30 is transferred onto the transfer paper.

The switch 4 is connected between the transfer roller 3 and the ground, and discharges the charge on the transfer roller 3 when turned on by an on signal from a control section 7, which will be described later. Note that the charge on the transfer roller 3 is maintained during the off period of the switch 4.

Next, a block configuration showing an example of the control system of the image forming apparatus will be described with reference to FIG. 1. The switching unit 5 switches to either the high voltage from the first tap 6a of the power transformer 6 or the low voltage from the second tap 6b in response to a switching signal from the control unit 7, and converts it into a DC voltage. The voltage is applied to the main charging device 1. That is, the tap 6a outputs, for example, 6KV alternating current, and the tap 6b outputs, for example, 4KV alternating current. Then, when the above-mentioned high voltage is applied to the main charging device 1,
The transfer roller 3 is charged with a voltage for transfer via the photosensitive drum 30. On the other hand, the main charging device 1
When the low voltage is applied to the photoreceptor drum 30 and the photoreceptor drum 30 is further exposed, an electrostatic latent image is formed.

The control section 7 has a built-in timer, for example, and outputs a switching signal to the switching section 5 to apply the high voltage to the main charging device 1 in order to charge the transfer roller 3 when copying is started. After applying the high voltage, a switching signal is output to the switching section 5 to apply the low voltage to the main charging device 1. Further, the control unit 7 controls the drive of the pair of registration rollers 42 to place the transfer paper after the transfer roller 3 is charged, thereby controlling the conveyance timing of the transfer paper. Further, the control section 7 outputs an on signal to the switch 4 when the transfer paper passes the transfer roller 3 after a predetermined period of time has elapsed from the high voltage application period.

Further, the control unit 7 controls the toner in the developing device 32 to be transferred to the photoreceptor drum 30 by high voltage charging of the photoreceptor drum 30.
Switching control is performed so that the voltage applied to the developing device 32 is set to a predetermined high voltage only while the high-voltage charged portion of the photosensitive drum 30 passes through the developing device 32.

Next, the operation of the above configuration will be explained using FIG. 3. When a print key (not shown) is turned on at time t0 to start copying, the transfer paper fed from the paper feed cassette 36 or the like is conveyed by the paper feed rollers 38, 39, etc. to the pair of registration rollers 42, and then stopped.

On the other hand, at the time t0, the switch 4 is turned off, the transfer roller 3 and the photosensitive drum 30 are driven, and a high voltage for charging the transfer roller 3 is applied to the main charging device 1. In order to prevent the necessary toner supply, the voltage applied to the developing device 32 is switched to a high voltage after the T0 period has elapsed. Then, the transfer roller 3 is charged via the photosensitive drum 30, and the charged state is maintained.

Thereafter, when the charging of the transfer roller 3 is completed at time t1, the voltage application to the main charging device 1 is turned off. On the other hand, after the halogen lamp 23 is turned on to start exposure at the time t1, when the optical system L is driven to a predetermined position (at the time t2), the lower A voltage is applied to the main charging device 1, and after a period T0 has elapsed from time t1, the voltage applied to the developing device 32 is switched to a low voltage for toner images.

Next, the transfer paper is placed on the high-voltage charged portion of the transfer roller 3, and in order to match the timing of the toner image on the photoreceptor drum 30 and the transfer paper, that is, the leading edge of the transfer paper and the toner The pair of registration rollers 42 is driven so that the leading edge of the image coincides with the leading edge of the image (at time t3), and the transfer paper is conveyed to the transfer roller 3, and due to the potential difference between the transfer roller 3 and the photosensitive drum 30, the photosensitive drum 3
The toner image on 0 is transferred to the transfer paper. The transfer paper after the transfer is conveyed to a fixing device 44 by a conveyance belt 43.

On the other hand, when the trailing edge of the transfer paper passes the transfer roller 3 at time t4, the switch 4 is turned on and the transfer roller 3
The electric charge is discharged, and toner is prevented from adhering to the transfer roller 3.

In this way, the main charging device 1 charges the photosensitive drum 30 with a high voltage, and the transfer roller 3 is charged for a predetermined period of time via the photosensitive drum 30, so that the transfer roller 3 is directly charged. There is no need for a transformer etc. Furthermore, since the transfer roller 3 is connected to the ground via the switch 4 after the transfer is completed, it is possible to prevent toner from adhering to the transfer roller 3.

The transfer roller 3 may be charged at least as much as the size of the transfer paper. On the other hand, the entire circumference of the transfer roller 3 may be always charged regardless of the size of the transfer paper. In this case, since the entire circumference of the transfer roller 3 is charged, the pair of registration rollers 42 is driven so as to match only the timing of the toner image on the photosensitive drum 30 and the transfer paper.

Furthermore, instead of switching the voltage applied to the developing device 32 to a high voltage only while the photosensitive drum 30 is charged with a high voltage, the developing device 32 is separated from the photosensitive drum 30 only during that period. You can.

[0026]

[Effects of the Invention] In the present invention, a high voltage is applied to a charging device to charge a photoreceptor, and a transfer roller is charged via the photoreceptor, so a transformer for directly applying a voltage to the transfer roller is omitted. can do. Therefore, the configuration of the image forming apparatus can be simplified and space can be saved.

[Brief explanation of drawings]

FIG. 1 is a block configuration diagram showing an example of a control system of an image forming apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram showing an example of an image forming apparatus according to the present invention.

FIG. 3 is a timing chart showing an example of the operation of the image forming apparatus according to the present invention.

[Explanation of symbols]

1 Main charging device 2 Transfer device 3 Transfer roller 5 Switching section 6 Power transformer 6a First tap 6b Second tap 7 Control section 30 Photosensitive drum

Claims (1)

[Claims] 1. An image forming apparatus in which a rotating photoreceptor is charged by a charging device to enable the formation of a toner image, and a transfer roller transfers the toner image on the photoreceptor to a transfer paper. a power supply having a first tap that generates a high voltage for charging and a second tap that generates a low voltage for charging the photoreceptor; and a power source that switches between the high voltage and the low voltage to charge the photoreceptor. An image forming apparatus comprising: a switching means for applying voltage to the device; and a switching control means for applying the high voltage to the charging device to charge the transfer roller via the photoreceptor for a predetermined period of time. Device.