JPH07191534A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To prevent the adherence of toner onto a photoreceptor from an intermediate roller at the time of stopping the photoreceptor and to prevent the staining on the rear side of a recording paper from causing by composing a device so that a changeover switch is switched to a second power source side at the time of stopping the photoreceptor until the time of driving again. CONSTITUTION:In addition to an ordinary bias power source (first power source) 21 for the intermediate roller 17, a second power source 23 having the polarity opposite to its polarity is provided and either of them can be switched by the changeover switch 25. Moreover, the bias power source 24 is provided for the developing roller 14. In the above constitution, the power is switched to the second power source 23 before stopping the photoreceptor 1. Thus, although the photoreceptor 1 is held in contact with the intermediate roller 17, the toner does not stuck to the the photoreceptor 1, as the toner is statically attracted by the intermediate roller side, even when the photoreceptor 1 is subsequently driven. As a result, the staining on the rear side of the recording paper is prevented from causing by preventing the toner from sticking onto the photoreceptor 1 from the intermediate roller 17 at the time of stopping the photoreceptor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus such as a copying machine, a plain paper facsimile and a printer.

[0002]

2. Description of the Related Art An outline of an electrophotographic process is shown in FIG.
The photoconductor 1 rotates counterclockwise. The photoconductor 1 has a charging unit 2
Then, the surface is uniformly charged, the photosensitive body 1 moves as the photosensitive body 1 rotates, and the light is exposed in the optical writing section 3 to form a latent image. Further, the developing unit 4 is rotated and selectively developed with toner according to the latent image to form a toner image. This toner image is
At a certain timing, in synchronization with each other, the cut paper 10 fed from the paper feed roller 11 and the registration roller 12 comes into contact with the transfer unit 5 and is transferred onto the cut paper 10. The cut sheet 10 to which the toner is attached after being transferred is fixed by the fixing unit 6, is discharged from the paper discharging unit 7 to the outside of the apparatus, and is made into a hard copy. On the other hand, in the photoconductor 1, the cleaning unit 8 collects the toner and the like that have not been completely transferred after passing through the transfer unit 5, and the charge removing unit 9
Then, the surface potential of the photoconductor is set to approximately 0 V, and the charging unit 2 is returned to.
These series of operations are repeated to continuously form hard copies.

FIG. 6 is a detailed configuration diagram of the developing section. 14 is a developing roller, 15 is a developing blade, 16 is a replenishing roller, 17 is an intermediate roller, 21 is a bias power source for the intermediate roller, and 24 is a developing roller. It is a bias power supply. Reference numeral 22 is a photosensitive member driving means.

An electrophotographic process using an intermediate roller will be described. The process up to exposure is the same as in the electrophotographic process. Description will be given assuming N / P (negative / positive) as a process. An electrostatic latent image of about -100V is formed on the photosensitive member 1 at the recording portion and about -800V at the background portion. A bias power source 21 applies a bias of about -500 V to the intermediate roller 17 with respect to this latent image. The developing roller 14 is applied with a developing bias of about -1000V by a bias power source 24. The developing roller 14 is rotating in the opposite direction to the intermediate roller 17. Further, the charging polarity of the toner is negative. In this state, the toner electrostatically adheres from the developing roller 14 to the intermediate roller 17. Next, the intermediate roller 17 has a bias voltage of about −
Since it is 500 V, the surface of the photoconductor 1 is developed according to the electrostatic latent image on the photoconductor 1. Development is performed by repeating such operations. The same applies to the case where the photoconductor 1 is not a roller shape but a belt.

[0005]

As described above, in the electrophotographic apparatus using the contact transfer system such as roller transfer, when the recording paper is not located between the photoconductor and the transfer means (transfer roller), When the toner adheres, the transfer means is soiled with the toner, and as a result, the back surface of the recording paper is soiled.

Particularly when the photosensitive member is stopped, the contact portion on the photosensitive member (see FIG.
Toner adheres before and after the point A). When the photosensitive member is driven next in this state, there is a problem that the toner adheres to the transfer unit at point B in FIG. 6 and back stain occurs.

An object of the present invention is to provide an electrophotographic apparatus capable of preventing the occurrence of dirt on the back of recording paper by preventing toner from adhering onto the photosensitive member from the intermediate roller when the photosensitive member is stopped. It is in.

[0008]

To achieve the above object, the present invention is an electrophotographic apparatus using a two-stage developing device having an intermediate roller and a developing roller, and a contact transfer device, wherein a bias is applied to the intermediate roller. And a second power supply for applying a voltage having a polarity opposite to that of the bias, and a changeover switch for switching between the two. It is characterized in that it is configured to switch to the power supply side of.

Further, 2 having an intermediate roller and a developing roller
In an electrophotographic apparatus using a stage developing device and a contact transfer device, a first power source for applying a bias to the intermediate roller and a second power source for applying a bias having the same polarity as the bias and higher than the bias of the developing roller. It is characterized in that it is provided with a power source and a changeover switch for changing over the two, and the changeover switch is changed over to the side of the second power source before the photoconductor is stopped.

2 having an intermediate roller and a developing roller
In an electrophotographic apparatus using a stage developing device and a contact transfer device, a first power source for applying a bias to the developing roller and a second power source for applying a bias having the same polarity as the bias and lower than the bias of the intermediate roller. It is characterized in that it is provided with a power source and a changeover switch for changing over the two, and the changeover switch is changed over to the side of the second power source before the photoconductor is stopped.

2 having an intermediate roller and a developing roller
In an electrophotographic apparatus using a step developing device and a contact transfer device, a photoconductor contacting / separating means for contacting / separating the photoconductor with the intermediate roller is provided, and the photoconductor is set to the above-mentioned state between the stop and the re-driving of the photoconductor. It is characterized in that it is configured to be separated from the intermediate roller.

[0012]

According to the electrophotographic apparatus having the above-described structure, since the toner is electrostatically attracted to the intermediate roller side even if the photosensitive body and the intermediate roller are in contact with each other, the photosensitive body is driven next. Toner does not adhere to the photoconductor.

Further, by making the voltage applied to the intermediate roller higher than the voltage applied to the developing roller in absolute value, the toner on the intermediate roller is collected by the developing roller, and the photosensitive member is stopped after the collection is completed. Since there is no toner on the intermediate roller, the toner does not adhere to the photoconductor when the photoconductor is driven next time.

Further, by making the applied voltage of the developing roller lower than the applied voltage of the intermediate roller in absolute value, the toner on the intermediate roller is collected by the developing roller, and the photosensitive member is stopped after the collection is completed. Since there is no toner on the intermediate roller, the toner does not adhere to the photoconductor when the photoconductor is driven next time.

Further, since the photosensitive member is not in contact with the intermediate roller when the photosensitive member is stopped, toner does not adhere to the photosensitive member.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. Note that each of the embodiments is basically used in the electrophotographic process described with reference to FIGS.

FIG. 1 is an explanatory view showing a main part of the first embodiment of the present invention, showing a state in which a transfer roller 5 as a contact transfer device and an intermediate roller 17 are in contact with the peripheral portion of the photosensitive member 1. The normal bias power supply for the intermediate roller 17 (first power supply)
In addition to 21, a second power source 23 having the opposite polarity is provided, and both can be switched by a changeover switch 25. Reference numeral 24 is a bias power source for the developing roller 14.

Before the photosensitive member 1 is stopped, it is switched to the second power source 23 side. As a result, even if the photoconductor 1 and the intermediate roller 17 are in contact with each other, the toner is electrostatically attracted to the side of the intermediate roller 17, so that the photoconductor 1 is driven next time even if the photoconductor 1 is driven next. No toner adheres. The bias voltage of the intermediate roller 17 in this state is preferably about + 300V.

FIG. 2 shows a second embodiment of the present invention.
A second power supply 28 having a setting higher than the bias power supply 24 of the developing roller 14 is provided, and the normal bias power supply 21 and the second power supply are provided.
It is possible to switch between 28 by the changeover switch 25.

The second power source 28 is switched before the photosensitive member 1 is stopped. When the developing roller 14 and the intermediate roller 17 are driven in this state, the toner on the intermediate roller 17 is collected by the developing roller 14. After the collection is completed, the photoconductor 1 is stopped. Since there is no toner on the intermediate roller 17, the toner does not adhere to the photoconductor 1 when the photoconductor 1 is driven next time.

FIG. 3 shows a third embodiment of the present invention.
A second power supply 29 is provided on the developing roller 14 side, and a bias power supply 24
The changeover switch 26 can be used to switch between and.

Before the photosensitive member is stopped, the bias is switched to the second power source 29 side so that the bias is lower than the bias of the intermediate roller 17. When the developing roller 14 and the intermediate roller 17 are driven in this state, the toner on the intermediate roller 17 is collected by the developing roller 14. After the collection is completed, the photoconductor 1 is stopped. Since there is no toner on the intermediate roller 17, the toner does not adhere to the photoconductor 1 when the photoconductor 1 is driven next time.

FIG. 4 shows a fourth embodiment of the present invention.
A photosensitive member contacting / separating means 27 including a solenoid for vertically moving the photosensitive member 1 is provided.

Before the photosensitive member 1 stops, the solenoid 27 is turned on to separate the photosensitive member 1 from the transfer roller 5 and the intermediate roller 17 (separate from the points A and B described above). In this state, the photoconductor 1
To stop. Since the photoconductor 1 is not in contact with the intermediate roller 17, it is possible to prevent toner from adhering to the photoconductor 1.

[0025]

As described above, in the electrophotographic apparatus of the present invention, according to the first aspect of the invention, the toner is electrostatically attracted to the side of the intermediate roller even when the photoconductor and the intermediate roller are in contact with each other. The toner does not adhere to the photoconductor even when the photoconductor is driven next time because it is pulled to the back side, so that the transfer device is not contaminated with the toner and the back stain can be prevented.

According to the second aspect of the present invention, by making the applied voltage of the intermediate roller higher in absolute value than the applied voltage of the developing roller, the toner on the intermediate roller is collected by the developing roller, and the collection is completed. Since the photoconductor is stopped later, there is no toner on the intermediate roller, so that the toner does not adhere to the photoconductor when the photoconductor is driven next time, and the same effect as described above is obtained.

According to the third aspect of the present invention, the applied voltage of the developing roller is made lower than the applied voltage of the intermediate roller in absolute value, whereby the toner on the intermediate roller is collected by the developing roller, and the collection is completed. Since the photoconductor is stopped later, there is no toner on the intermediate roller, so that the toner does not adhere to the photoconductor when the photoconductor is driven next time, and the same effect as described above is obtained.

According to the fourth aspect of the invention, since the photosensitive member is not in contact with the intermediate roller when the photosensitive member is stopped, the toner does not adhere to the photosensitive member, so that the same effect as described above can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a main part of a first embodiment of an electrophotographic apparatus of the present invention.

FIG. 2 is an explanatory diagram showing a main part of a second embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a main part of a third embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a main part of a fourth embodiment of the present invention.

FIG. 5 is a schematic diagram of a general electrophotographic apparatus.

FIG. 6 is a detailed view of a developing unit in FIG.

[Explanation of symbols]

1 ... Photoconductor, 5 ... Transfer roller, 14 ... Developing roller,
17 ... Intermediate roller, 21 ... Bias power source (first power source) for intermediate roller, 23, 28 ... Second power source for intermediate roller, 24 ...
Bias power source for developing roller (first power source), 25, 26 ... Changeover switch, 27 ... Solenoid (photosensitive member contacting / separating means), 29
... Second power source for developing roller.

Claims (4)

[Claims] 1. A two-stage developing device having an intermediate roller and a developing roller, and an electrophotographic apparatus using a contact transfer device, a first power source for applying a bias to the intermediate roller, and a voltage having a polarity opposite to the bias. An electronic device comprising a second power supply for supplying the power and a changeover switch for switching the two power supplies, and is configured to switch the changeover switch to the second power supply side from the stop of the photoconductor to the re-driving. Photographic equipment. 2. A two-stage developing device having an intermediate roller and a developing roller, and an electrophotographic apparatus using a contact transfer device, a first power source for applying a bias to the intermediate roller, the same polarity as the bias, and A second power supply for applying a bias higher than the bias of the developing roller and a changeover switch for changing over the two are provided, and the changeover switch is changed over to the second power supply side before the photoconductor is stopped. Characteristic electrophotographic device. 3. A two-stage developing device having an intermediate roller and a developing roller, and an electrophotographic apparatus using a contact transfer device, a first power source for applying a bias to the developing roller, the same polarity as the bias, and A second power source for applying a bias lower than the bias of the intermediate roller and a changeover switch for changing over the two are provided, and the changeover switch is changed over to the side of the second power source before the photoconductor is stopped. Characteristic electrophotographic device. 4. An electrophotographic apparatus using a two-stage developing device having an intermediate roller and a developing roller, and a contact transfer device, comprising a photosensitive member contacting / separating means for contacting / separating the photosensitive member with the intermediate roller. An electrophotographic apparatus, characterized in that the photoconductor is separated from the intermediate roller during a period from stop to re-driving.