JP2000122450A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of precisely performing cleaning of a transfer roller and the cleaning roller. SOLUTION: This image forming device is allowed, to arrange on the periphery of a photoreceptor drum 1 as the toner image carrier, in an order of electrophotographic process, an electrifying roller 2, an optical writing system 3, a developing unit 4, the transfer roller 5 and the cleaning unit 6. Moreover, the device is provided with a bias power source 7 for applying transfer bias on the transfer roller 5. At the time of cleaning the transfer roller 5, a voltage superposing the DC voltage and the AC voltage is applied on the transfer roller 5 by the bias power source 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, etc., which uses an electrophotographic system, and more particularly to a technique for controlling bias application to a transfer roller and a transfer belt cleaning roller.

[0002]

2. Description of the Related Art In an image forming apparatus having an electrophotographic process, processes such as charging, exposure (light writing), development, transfer and separation, cleaning, and static elimination are sequentially performed on a photoreceptor. Form a toner image. As a transfer unit, there is a transfer charger that is not in contact with the photoconductor. In addition, there are a transfer roller and a transfer belt of a type that is in contact with a photoconductor. When a transfer roller or a transfer belt is used, a DC voltage having a polarity that attracts toner is applied to the transfer roller and the transfer belt in a process of nipping and transferring the transfer paper between the nip portion of the photoconductor and the transfer roller or the transfer belt. Transcribed.

Here, the time for applying the bias voltage to the transfer roller includes only a time for performing the transfer and a short time before and after the time. The reason is to prevent the floating toner from adhering to the transfer roller and preventing the photoconductor from deteriorating.

However, when the transfer paper is not conveyed well, or when the transfer roller is contaminated by a small amount of toner adhering to the photosensitive member, the transfer roller is contaminated. Then, due to the contamination of the transfer roller, the resistance value of the transfer roller partially changes, the electric field intensity distribution in the axial or rotational direction becomes non-uniform, and due to this effect, the toner adhesion to the transfer paper also becomes non-uniform. . As a result, image quality has deteriorated.

To solve this problem, Japanese Patent Laid-Open Publication No.
Japanese Patent Application Laid-Open No. 332301 discloses a technique of applying a voltage having a polarity opposite to that at the time of transfer to a transfer roller in order to remove toner attached to the transfer roller.

On the other hand, when a transfer belt is used, Japanese Patent Laid-Open No.
As described in JP-179640, the transfer belt is cleaned using a cleaning roller to which a DC voltage having a polarity to attract the toner is applied, and the toner attached to the cleaning roller is removed by a bias roller blade to which the voltage is applied. Techniques for scraping and collecting are known.

[0007]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-Open No. Hei 6-3
According to the technique disclosed in Japanese Patent No. 32301, it is usually possible to clean the transfer roller without much problem. However, when a large amount of toner adheres to the transfer roller in a short time, or when a large amount of toner is In the case of toner, the remaining toner cannot be applied to the transfer roller in consideration of the withstand voltage of the photoreceptor even if a DC voltage of the opposite polarity is applied. Cleaning could not be carried out more than enough, and the above-mentioned problems could not be completely removed.

Further, even when only a DC voltage is applied to the bias roller blade as in the technique disclosed in Japanese Patent Application Laid-Open No. 8-179640, the residual toner cannot be sufficiently cleaned from the cleaning roller. .

Since only a voltage of a polarity that attracts toner is applied to the cleaning roller, toner that cannot be completely cleaned by the bias roller blade accumulates on the cleaning roller, thereby deteriorating the cleaning efficiency of the transfer belt. In addition, the image quality on the transfer paper is degraded due to the effect of the toner remaining on the transfer belt.

The present invention has been made in view of such a background, and an object of the present invention is to provide an image forming apparatus capable of accurately cleaning a transfer roller and a cleaning roller.

[0011]

According to one aspect of the present invention, there is provided a toner image bearing member for carrying a toner image, a transfer roller for transferring the toner image to a recording medium, and In an image forming apparatus having a power supply for applying a bias to a transfer roller, the transfer roller is cleaned by applying a voltage obtained by superimposing a DC voltage and an AC voltage having the same polarity as the charging polarity of the toner to the transfer roller. It is characterized by the following.

According to another aspect of the present invention, the above object is achieved.
The described invention includes a transfer belt for transferring a toner image from a toner image carrier to a recording medium, a cleaning roller for cleaning the transfer belt, a power supply for applying a bias to the cleaning roller, and a cleaning roller. In an image forming apparatus having a contact / separation mechanism for contacting / separating the transfer belt, the cleaning roller is cleaned by applying a voltage obtained by superimposing a DC voltage and an AC voltage having the same polarity as the charging polarity of the toner to the cleaning roller. It is characterized by the following.

[0013] To achieve the above object, a third aspect of the present invention is provided.
According to the invention described in claim 1 and claim 2, the frequency of the AC voltage of the applied bias is 10 to 10000.
It is characterized by being set to 0 Hz.

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a configuration diagram around a photoconductor of an image forming apparatus using a transfer roller. Around the photosensitive drum 1 as a toner image carrier, a charging roller 2, an optical writing system 3, a developing unit 4,
A transfer roller 5 and a cleaning unit 6 are provided. Further, a bias power supply 7 for applying a transfer bias to the transfer roller 5 is provided.

In such a configuration, first, the photosensitive drum 1 rotating clockwise is uniformly charged by the charging roller 2. Next, optical writing is performed by the optical writing system 3 to form an electrostatic latent image on the surface of the photosensitive drum 1. Then, the developing unit 4 attaches toner to the electrostatic latent image and develops the electrostatic latent image to obtain a toner image (visible image).

This toner image is transferred to a transfer paper P which is conveyed while being held between the photosensitive drum 1 and the transfer roller 5 at the transfer nip portion.
Is transferred under the action of a bias voltage. The transfer paper P on which the toner image has been transferred is then conveyed to a fixing unit (not shown), while the surface of the photosensitive drum is cleaned by the cleaning unit 6 and further discharged by a discharge lamp.

As described above, when a toner image is transferred onto the transfer paper P, a DC bias voltage is applied to the back surface of the transfer paper P via the transfer roller 5 by the bias power supply 7. The bias voltage is often controlled by feedback control based on the resistance value of the transfer paper P, or by current control that keeps the current flowing through the transfer roller 5 constant. In addition, the application time of the bias voltage is limited to the transfer time and a short time before and after the transfer in order to prevent the floating toner from adhering to the transfer roller 5 and the deterioration of the photosensitive drum 1.

However, as described above, toner contamination of the transfer roller 5 occurs even in this case. Conventionally, by applying a DC voltage having a polarity opposite to that at the time of transfer to the transfer roller 5, As described above, the transfer roller 5 is cleaned.

In the present invention, when the transfer roller 5 is cleaned, a bias in which a DC voltage and an AC voltage are superimposed is applied to the transfer roller 5 by the bias power supply 7.

FIG. 4 is a diagram showing an example of an applied bias according to the present invention. A voltage is a voltage waveform at the time of transfer. A
B shown below is a waveform at the time of cleaning. The voltage value (absolute value) when integrating the voltage value of A and the waveform of B is
Although they are shown as the same on the figure, it is needless to say that they do not need to be the same value. Although the waveform duty is shown as 20% in the figure, it is not necessary to make the same value. In particular, the frequency of the AC voltage, which is closely related to the movement (vibration) of the toner, slightly varies depending on the average particle diameter and mass of the toner, but is preferably about 1 to 10 KHz. In addition, a frequency of 10 Hz or less and 100
At a frequency equal to or higher than KHz, the toner hardly vibrates, and the effect does not appear. That is, the toner remains on the transfer roller 5 and the backing of the transfer paper P and the deterioration of the image quality cannot be suppressed.

When the transfer roller 5 is a foam roller, the frequency of the AC voltage applied to the transfer roller 5 does not always directly contribute to the toner. As described above, various patterns can be considered for the waveform and the frequency. In short, it is important that the toner is easily separated from the transfer roller 5 by vibrating the toner. In many cases, the transfer roller 5 is made up of a conductive shaft (usually stainless steel) and a middle to high-resistance foamed rubber layer. However, the transfer roller 5 is not limited to this.

FIG. 2 is a configuration diagram around a photosensitive member of an image forming apparatus using a transfer belt. A transfer belt 11 is arranged below the photosensitive drum 1 instead of the transfer roller 5. The transfer belt 11 is stretched between the driving roller 12 and the driven roller 13, and pinches and conveys the transfer paper conveyed from the paper supply unit to the photosensitive drum 1. On the back surface of the transfer belt 11, there is a transfer bias roller 14 near the transfer portion, and the transfer bias of the transfer bias roller 14 transfers a toner image to transfer paper. The transfer paper on which the toner image has been transferred is conveyed by the transfer belt 11 to the vicinity of the fixing unit.

A cleaning roller 15 for cleaning the back surface of the transfer belt 11 is provided. The cleaning roller 15 is applied with a DC voltage of a polarity for adsorbing toner by a bias power supply 16, and the transfer belt 1 is
The toner remaining on the surface 1 is adsorbed.

A bias roller bread 17 is in contact with the surface of the cleaning roller 15 so as to clean toner on the surface of the cleaning roller 15. Further, the cleaned toner is collected by a toner collecting coil 18.

FIG. 3 is a diagram showing a mechanism for moving the cleaning roller toward and away from the transfer belt. Cleaning roller 15
Is supported by the other end of an arm 20 having one end fixed to the support shaft 19. The support shaft 19 is connected to a motor (not shown). When the cleaning roller 15 is cleaned, the motor rotates the support shaft 19 clockwise in the drawing, and at the same time, the arm 20 overcomes the upward biasing force of the spring 21. Since the cleaning roller 15 rotates clockwise, the cleaning roller 15 separates from the surface of the transfer belt 11.

When the cleaning roller 15 is not being cleaned, the cleaning roller 15 is
Is pressed by the transfer belt 11 to clean the surface of the transfer belt 11. The mechanism for contacting and separating the cleaning roller 15 does not need to be limited to this, and can be implemented using an electromagnetic clutch or a cam.

Here, the bias roller blade 17 that contacts the surface of the cleaning roller 15 also needs to swing together with the cleaning roller 15. Therefore, both are configured as a unit.

Next, the cleaning operation of the cleaning roller 15 will be described. As described above, when cleaning the cleaning roller 15, the cleaning roller 15 is separated from the transfer belt 11. In this state, a voltage obtained by superimposing a DC voltage and an AC voltage (for example, a voltage shown in FIG. 4B) is applied to the cleaning roller 15 by the bias power supply 16. Then, the surface of the cleaning roller 15 is cleaned by vibrating the toner. At this time, the cleaning effect is further enhanced because the bias roller blade 17 is in sliding contact with the cleaning roller 15, but the cleaning of the cleaning roller 15 can be performed without the bias roller blade 17. The cleaning roller 15 is often a foaming roller, but may be of any other material.

[0029]

According to the first aspect of the present invention, by applying a voltage obtained by superimposing a DC voltage and an AC voltage to the transfer roller, the transfer roller can be accurately cleaned and the transfer roller can be cleaned. , It is possible to prevent image quality from deteriorating.

According to the second aspect of the present invention, by applying a voltage in which a DC voltage and an AC voltage are superimposed on the cleaning roller that can be brought into contact with and separated from the transfer belt, the cleaning roller can be accurately cleaned. At the same time, since the cleaning roller can be kept in a clean state, deterioration of image quality can be prevented.

According to the third aspect of the present invention, the frequency of the AC voltage of the bias applied to the transfer roller and the cleaning roller is limited to a frequency at which the toner can easily move, thereby facilitating the discharge of the toner from the roller. And the deterioration of the roller can be prevented.

[Brief description of the drawings]

FIG. 1 is a configuration diagram around a photoconductor of an image forming apparatus using a transfer roller.

FIG. 2 is a configuration diagram around a photoconductor of an image forming apparatus using a transfer belt.

FIG. 3 is a diagram illustrating a mechanism of contacting and separating a cleaning roller from a transfer belt.

FIG. 4 is a diagram showing an example of an applied bias according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum 2 charging roller 3 optical writing system 4 developing unit 5 transfer roller 6 cleaning unit 7 bias power supply 11 transfer belt 12 drive roller 13 driven roller 14 transfer bias roller 15 cleaning roller 16 bias power supply 17 bias roller blade 18 recovery coil 19 Support shaft 20 Arm 21 Spring

Claims (3)

[Claims] 1. A toner image carrier for carrying a toner image,
In an image forming apparatus having a transfer roller for transferring a toner image onto a recording medium and a power supply for applying a bias to the transfer roller, a DC voltage and an AC voltage having the same polarity as the charged polarity of the toner are superimposed on the transfer roller. An image forming apparatus, wherein the transfer roller is cleaned by applying the applied voltage. 2. A transfer belt for transferring a toner image from a toner image carrier to a recording medium, a cleaning roller for cleaning the transfer belt, a power supply for applying a bias to the cleaning roller, and a cleaning roller. In an image forming apparatus having a contact / separation mechanism for contacting / separating the transfer belt, the cleaning roller is cleaned by applying a voltage obtained by superimposing a DC voltage and an AC voltage having the same polarity as the charged polarity of the toner to the cleaning roller. An image forming apparatus comprising: 3. The method according to claim 1, wherein the frequency of the applied AC voltage is 10 to 1000.
An image forming apparatus characterized by setting to 00 Hz.