JPH117210A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device constituted so that normally charged toner and reversely charged toner attached to a transfer roller can be recovered and eliminated at the prerotation processing time of a printing action and the back surface of a recording paper is prevented from being soiled at the time of the printing action. SOLUTION: At the prerotation processing time of the printing action, a negative bias voltage is applied on the transfer roller 16. Thereafter, a positive bias voltage is applied. Thus, when the negative bias voltage is applied on the roller 16, the normally charged toner attached to the roller 16 is recovered to a developing unit 15 from a photoreceptor 12 after it is recovered to the photoreceptor 12 from the roller 16. Besides, when the positive bias voltage is applied on the roller 16, the reversely charged toner attached to the roller 16 is recovered to the unit 15 from the photoreceptor 12 after it is recovered to the photoreceptor 12 from the roller 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus applied to a facsimile machine, a copying machine, a printer and the like.

[0002]

2. Description of the Related Art In a conventional electrophotographic image forming apparatus, a charging device, an exposing device, a developing device and a transfer roller are sequentially arranged around a photosensitive drum as a photosensitive member along a rotating direction of the photosensitive drum. Has been established. During the printing operation, the outer peripheral surface of the photosensitive drum is uniformly charged by the charger while the photosensitive drum is being rotated, and the outer peripheral surface of the photosensitive drum is irradiated with light by the exposing device to form an electrostatic latent image. Further, a toner is attached to the electrostatic latent image on the photosensitive drum by a developing device to form a toner image, and the toner image is transferred onto recording paper by a transfer roller.

In this type of image forming apparatus, when a power switch is turned on, the photosensitive drum is rotated at least once, and a pre-rotation process is performed prior to a printing operation. That is, during the pre-rotation process, the entire outer periphery of the photosensitive drum is uniformly charged by the charger, and the toner remaining on the outer periphery of the photosensitive drum is uniformly disturbed by the memory removing brush and uniformly spread on the photosensitive drum. After being dispersed, the residual toner is collected from the photosensitive drum to the developing device by electrostatic attraction.

[0004]

However, in this conventional image forming apparatus, for example, when a paper jam is removed, when there is untransferred toner on the drum, the toner is transferred to the outer peripheral surface of the transfer roller. If so, there is a problem that the toner adheres to the back surface of the recording paper to be printed and stains the back surface of the recording paper. Moreover, the toner adhered to the transfer roller includes a normal negatively charged regular charge toner and a reversely charged positively charged reverse charge toner, and both of them can be removed together. It was difficult.

[0005] The present invention has been made by paying attention to such problems existing in the prior art. The purpose is to collect and remove both the normal charge toner and the reverse charge toner adhering to the transfer roller during the pre-rotation process of the printing operation, thereby reducing the possibility that the back surface of the recording paper becomes dirty during the printing operation. It is an object of the present invention to provide an image forming apparatus capable of preventing the occurrence.

[0006]

In order to achieve the above object, according to the first aspect of the present invention, a transfer roller is provided so as to face a photosensitive member, and a recording paper is transferred by the transfer roller. And a predetermined bias voltage is applied to the transfer roller to transfer the toner image on the photoreceptor onto recording paper. After the application of the bias voltage, control means for controlling so as to apply a positive bias voltage is provided.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the control means controls the bias of the transfer roller when a negative bias voltage is applied to the charging device and the developing device. The control is performed so that the voltage is switched from minus to plus.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the control means applies a negative bias voltage to the charging device and applies a positive bias voltage to the developing device. In this state, the bias voltage of the transfer roller is controlled to be switched from minus to plus.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 1 and FIG.
A photosensitive drum 12 as a photosensitive member having a photoconductive film on the outer peripheral surface is disposed inside 1, and is grounded via an apparatus case 11. The photosensitive drum 12 is connected to a drive motor 4 (described later) provided outside the drum unit 18.
2, the rotation is performed in a direction indicated by an arrow A1 in FIG.

A charger 1 is provided around the photosensitive drum 12.
3, exposure unit 14, developing unit 15, transfer roller 16
And a memory removing brush 17 are arranged in order along the rotation direction A1 of the photosensitive drum 12. Charger 13
Is a brush roller type in which a large number of conductive brush bodies are implanted on the outer periphery of a shaft. The charger 13 is rotated in a printing operation while a predetermined bias voltage is applied to uniformly charge the outer peripheral surface of the photosensitive drum 12 to about -750V.

The exposing device 14 is provided with a number of LEDs, and irradiates the outer peripheral surface of the photosensitive drum 12 with light based on the input image data. With this light irradiation, the potential of the light-irradiated portion (the portion corresponding to the black of the image data) on the outer peripheral surface of the photosensitive drum 12 becomes about −50 V, and the light-irradiated portion and the non-irradiated portion A potential difference occurs between the portion (the portion corresponding to white in the image data). As a result, an electrostatic latent image corresponding to the image data is formed on the outer peripheral surface of the photosensitive drum 12.

The developing unit 15 includes a toner case 20 for storing the toner 19, a supply roller 21 disposed at a lower portion of the toner case 20, and a gap between the supply roller 21 and the photosensitive drum 12. Developing roller 2 disposed at the lower end opening of toner case 20 so as to be positioned
2 is provided. Then, the developing roller 22 is brought into contact with the outer peripheral surfaces of the supply roller 21 and the photosensitive drum 12. In this state, the supply roller 21 and the developing roller 22 are moved by a drive motor (not shown) provided outside the developing unit 15 as shown in FIG. Each is rotated in the directions indicated by arrows A2 and A3.

The supply roller 21 includes a shaft 21a made of metal such as stainless steel, and a foam layer 21b such as urethane foam having conductivity attached around the shaft 21a. A predetermined bias voltage (−400 to −600) is applied to the supply roller 21 during the printing operation.
V, preferably about -500 V).

The developing roller 22 comprises a shaft 22a made of metal such as stainless steel, and a conductive rubber layer 22b mounted around the shaft 22a. For forming the conductive rubber layer 22b, butadiene acrylonitrile rubber (NBR), silicon rubber or urethane rubber can be preferably used. A predetermined bias voltage (−200 to −400 V, preferably −300 V) is applied to the developing roller 22 during a printing operation.
Is applied.

A stirring member 23 is rotatably disposed in the toner case 20. The agitator 23 is rotated by a drive motor (not shown) to agitate the toner 19 in the toner case 20.

At the lower end opening of the toner case 20,
The regulating blade 24 is attached to the outer peripheral surface of the developing roller 22 so as to be able to make elastic contact with the outer peripheral surface of the developing roller 22 so that the layer thickness of the toner 19 attached to the outer peripheral surface of the developing roller 22 is made uniform. The regulating blade 24 is made of a conductive rubber or metal elastic material, preferably a urethane rubber sheet or a stainless steel plate. further,
During the printing operation, the regulating blade 24 has a predetermined bias voltage (-200 to -700 V, preferably about -400 V).
V) is applied.

In a printing operation, the supply roller 21 and the developing roller 22 in the developing unit 15 are rotated while making frictional contact, and a bias voltage is applied to the rollers 21 and 22. As a result, the toner 1 existing near the rollers 21 and 22
9 is charged.

Further, with the rotation of the supply roller 21, the toner 19 filled in the pores of the foam layer 21b of the roller 21 is transferred to the developing roller 22 side. That is, at the pressure contact portion between the supply roller 21 and the developing roller 22,
Based on the potential difference between the two rollers 21 and 22, the toner 19 moves from the supply roller 21 to the developing roller 22, and adheres to the outer peripheral surface of the developing roller 22.

The toner 19 attached to the outer peripheral surface of the developing roller 22 is transferred to the photosensitive drum 12 via the regulating blade 24 as the developing roller 22 rotates. When the toner 19 on the developing roller 22 passes through the regulating blade 24, the thickness of the layer is made uniform by the blade 24.

Further, the toner 19 on the developing roller 22
Is charged to about −650 V by the regulating blade 24. Therefore, when the toner 19 on the developing roller 22 contacts the photosensitive drum 12, the toner 19 is attracted to the electrostatic latent image based on the potential difference between the toner 19 and the electrostatic latent image on the photosensitive drum 12, and A toner image is formed on the photosensitive drum 12.

As shown in FIG. 1, a paper feed cassette 25 is detachably mounted at a lower portion of the apparatus case 11. In the paper feed cassette 25, a large number of recording papers 26 as paper are stored in a stacked state. With the rotation of the pickup roller 27, the recording paper 26 is fed out one by one from the paper feed cassette 25, and is transferred to the photosensitive drum 12 and the transfer roller via a paper guide 28 and a pair of transport rollers 29 and 30. 16.

As shown in FIGS. 1 and 2, the transfer roller 16 is disposed so as to be in contact with the outer peripheral surface of the photosensitive drum 12 across the recording paper transport path, and is rotated by a drive motor (not shown). Has become. The transfer roller 16 includes a shaft 16a made of metal such as stainless steel and a foam layer 16b made of conductive urethane or the like attached around the shaft 16a. Further, a predetermined positive bias voltage (500 V to 4 kV) is applied to the transfer roller 16 during a printing operation.

The recording paper 26 sent between the photosensitive drum 12 and the transfer roller 16 is
6, the photosensitive drum 12 is brought into close contact with the outer peripheral surface. As a result, the back side of the recording paper 26 comes into contact with the transfer roller 16 to which the voltage is applied. Then, based on the potential difference between the photosensitive drum 12 and the transfer roller 16, the toner image on the photosensitive drum 12 is drawn toward the recording paper 26 and is transferred onto the recording paper 26. The recording paper 26 after the transfer of the toner image is sent out toward the fixing unit 31 by the rotation of the photosensitive drum 12 and the transfer roller 16.

The fixing unit 31 includes the photosensitive drum 12
The heating roller 31a and the heating roller 31a are disposed in the apparatus case 11 so that the heating roller 31a
a pressure roller 31 pressed against the recording paper transport path
b. Then, the recording paper 26 is
The resin component in the toner is melted by being fed between the heating roller 31 a and the pressure roller 31 b through the second step, and is fused on the recording paper 26. As a result, the recording paper 26
The toner image is fixed thereon as a permanent image. Thereafter, the recording paper 26 is discharged out of the apparatus case 11 by the pair of discharge rollers 33.

The memory removing brush 17 is formed of a conductive brush. The memory removal brush 17
Is applied with a predetermined positive bias voltage during a printing operation. Then, the outer peripheral surface of the photosensitive drum 12 after the transfer of the toner image is moved to a position facing the memory removing brush 17 as the photosensitive drum 12 rotates. At this time, a small amount of untransferred toner remaining on the outer peripheral surface of the photosensitive drum 12 is disturbed by the memory removing brush 17 and is uniformly dispersed on the outer peripheral surface of the photosensitive drum 12.

Further, the dispersed residual toner is conveyed to a position facing the charger 13 as the photosensitive drum 12 rotates, and is charged to about -750 V by the charger 13. Thereafter, the residual toner is conveyed to a position facing the developing roller 22 of the developing unit 15 with the rotation of the photosensitive drum 12, and is attracted to the developing roller 22 based on a potential difference from the developing roller 22 so that the toner case 20
Will be returned within. In other words, the developing device unit 15
In parallel with the developing operation, a cleaning operation for collecting the residual toner dispersed by the memory removing brush 17 is also performed.

Next, the circuit configuration of the main components of the image forming apparatus will be described. As shown in FIG.
A (central processing unit) 36 has a ROM (read only memory) 3 storing a program for controlling the operation of the entire apparatus.
7 and a RAM (random access memory) 38 for temporarily storing various data are connected. The CPU 36, the ROM 37, and the RAM 38 constitute control means.

An input / output interface circuit 39 is connected to the CPU 36. An operation panel 40 is connected to the input / output interface circuit 39, and the operation panel 4
0 has a power switch and various operation keys. When a power switch or an operation key on the operation panel 40 is operated, an operation signal is input to the CPU 36 via the input / output interface circuit 39.

The CPU 36 controls the photosensitive drum 12 via an input / output interface circuit 39 and a driver 41.
A drive signal is output to the drive motor 42 for rotating the. Further, the CPU 36 controls the L of the exposure unit 14 via the input / output interface circuit 39 based on the input image data.
An emission signal is output to the ED. Further, the CPU 36 includes an input / output interface circuit 39 and a high-voltage generation circuit (HV).
PS) 43, 44, 45, and 46, a predetermined bias voltage is applied to the transfer roller 16, the memory removing brush 17, the charger 13, and the developing unit 15 at a predetermined timing. Moreover, the CPU 36 outputs an on / off signal to the fixing unit 31 via the input / output interface circuit 39 and the driver 47.

The CPU 36 operates the operation panel 4.
0 is turned on, the drive motor 42
To rotate the photosensitive drum 12 at least once,
A pre-rotation process is performed prior to the printing operation. Also, CP
In the pre-rotation process, U36 applies a negative bias voltage to the transfer roller 16 and then applies a positive bias voltage to the transfer roller 16 as shown in FIG.

Further, the CPU 36 applies a negative bias voltage to the charger 13 from the beginning during the pre-processing rotation. In addition, the CPU 36 controls the developing unit 1
The bias voltage applied to the supply roller 21, the developing roller 22, and the regulating blade 24 is set to be positive at the beginning of the pre-rotation process, and is switched from plus to minus during the pre-rotation process.

After the switching of the bias voltage of the developing unit 15, the CPU 36
The bias voltage to the transfer roller 16 is switched from negative to positive while a negative bias voltage is applied to the developing unit 15.

Next, the operation of the image forming apparatus configured as described above will be described. In the image forming apparatus of this embodiment, when the power switch on the operation panel 40 is turned on, the drive motor 42 drives the photosensitive drum 12
Is rotated at least once, and a pre-rotation process is performed prior to the printing operation. In this pre-rotation process, as shown in FIG. 4, a negative bias voltage is applied to the transfer roller 16 from the high voltage generation circuit 43, and a higher potential is applied to the charger 13 from the high voltage generation circuit 45 to the transfer roller 16. A negative bias voltage is applied. Therefore, the negative regular charge toner on the transfer roller 16 is
2 and adhere to it. At this time, since the charger 13 has a negative potential from the beginning of the pre-rotation process, the regular charge toner attached to the photosensitive drum 12 does not adhere to the charger 13 and the charger 13 is not stained.

Further, a positive bias voltage is applied from the high voltage generating circuit 46 to the developing unit 15. Therefore, the regular charge toner attached to the photosensitive drum 12 is collected by the developing unit 15 as the photosensitive drum 12 rotates.

After the removal of the regular charge toner on the photosensitive drum 12 is completed, the bias voltage of the developing unit 15 is switched to a negative voltage higher than the negative potential of the photosensitive drum 12 during the pre-rotation process. Then, the bias voltage of the transfer roller 16 is switched to plus. At this time, since the photosensitive drum 12 is negatively charged, the positive reverse charge toner on the transfer roller 16 is transferred to and adheres to the photosensitive drum 12. Then, with the rotation of the photosensitive drum 12, the toner on the photosensitive drum 12 becomes a developing unit 15 having a higher potential than the photosensitive drum 12.
Will be collected. Further, since the charger 13 maintains the negative potential, the reversely charged toner on the photosensitive drum 12 does not adhere to the charger 13.

As described above, when the toner adheres to the outer peripheral surface of the transfer roller 16, the regular charge toner and the reverse charge toner on the transfer roller 16 are collected by the developing unit 15. Thereafter, the apparatus shifts to the standby mode.

In the pre-rotation processing, the memory removing brush 17 maintains zero potential. The effects that can be expected from the above embodiment will be described below.

In the image forming apparatus of this embodiment, a positive bias voltage is applied to the transfer roller 16 during the pre-rotation processing of the printing operation, after a negative bias voltage is applied to the transfer roller 16. . For this reason, when toner adheres to the outer peripheral surface of the transfer roller 16, when a negative bias voltage is applied to the transfer roller 16, the regular charge toner on the transfer roller 16 becomes
After being collected on the photosensitive drum 12 as a photosensitive member from the transfer roller 16, it is collected by the developing unit 15 from the photosensitive drum 12.

When a positive bias voltage is applied to the transfer roller 16, the reversely charged toner on the transfer roller 16 is collected on the photosensitive drum 12 from the transfer roller 16 and then developed from the photosensitive drum 12. Unit 15
Will be collected. Accordingly, it is possible to prevent the toner attached to the transfer roller 16 from soiling the back surface of the recording paper 26 during the subsequent printing operation.

In the image forming apparatus of this embodiment, a negative bias voltage is applied to the charger 13 from the beginning of the pre-rotation process. Further, the bias voltage for the developing unit 15 is set to be positive at the beginning of the pre-rotation process, and is switched from plus to minus during the pre-rotation process. After the bias voltage of the developing unit 15 is switched, the charging unit 13 and the developing unit 1 are switched.
In a state where a negative bias voltage is applied to the transfer roller 5, the bias voltage to the transfer roller 16 is switched from negative to positive.

Therefore, it is possible to prevent the normal charge toner collected on the photosensitive drum 12 from the transfer roller 16 from moving from the photosensitive drum 12 to the charger 13 and from adhering to the charger 13. it can.

(Second Embodiment) Next, a second embodiment of the present invention will be described.
Will be described with reference to FIG. In the present embodiment, the bias voltage of the charger 13 is set to 0 during the pre-rotation process, and then changed to a negative value. In addition, the bias voltage of the developing unit 15 is initially set to be positive during the pre-rotation process, and is switched from positive to negative when a predetermined time T1 has elapsed after the bias voltage of the charger 13 is changed. I have.

The elapsed switching time T1 of the bias voltage of the developing unit 15 is the time until the charged portion on the photosensitive drum 12 negatively charged by the charger 13 is rotationally moved to a position corresponding to the developing unit 15. The time is set by a timer 48 shown by a chain line in FIG. When the bias voltage of the charger 13 is changed from zero to minus during the pre-rotation process, the timer 48 is started, and the charged portion on the photosensitive drum 12 charged by the charger 13 is developed. The time is up when the rotation is shifted to the position corresponding to the device unit 15. In this embodiment, the set time T1 of the timer 48 is about 1.5 seconds.

In the second embodiment,
As in the first embodiment, after the bias voltage of the developing unit 15 is switched, the bias voltage to the transfer roller 16 is changed while the negative bias voltage is applied to the charger 13 and the developing unit 15. It switches from minus to plus.

Therefore, also in the second embodiment,
As in the first embodiment described above, during the pre-rotation processing of the printing operation, both the normal charge toner and the reverse charge toner adhered to the transfer roller 16 can be collected and removed. The possibility that the back surface of the recording paper 26 becomes dirty can be prevented.

Further, in the second embodiment, since the bias voltage of the charger 13 is zero during the pre-rotation process, the potential difference between the photosensitive drum 12 and the transfer roller 16 is increased. Transfer roller 1
6, the recovery rate of the regular charge toner from the photosensitive drum 12 onto the photosensitive drum 12 can be increased.

Further, in the second embodiment,
After the bias voltage of the charger 13 is changed from zero to minus during the pre-rotation process, the timer 48 sets the time T1 until the bias voltage of the developing unit 15 is switched from plus to minus. It has become. Therefore, the switching timing of the bias voltage of the developing unit 15 can be easily changed according to the rotation speed of the photosensitive drum 12 and the like.

(Third Embodiment) Next, a third embodiment of the present invention will be described.
Will be described with reference to FIG. In this embodiment, a negative bias voltage is applied to the charger 13 from the beginning of the pre-rotation process. Further, a positive bias voltage is applied to the developing unit 15 throughout the pre-rotation processing. Then, during the pre-rotation processing, while the negative bias voltage is applied to the charger 13 and the positive bias voltage is applied to the developing unit 15, the bias voltage to the transfer roller 16 becomes negative. Can be switched to plus.

Therefore, also in the third embodiment,
As in the first embodiment described above, during the pre-rotation processing of the printing operation, both the normal charge toner and the reverse charge toner adhered to the transfer roller 16 can be collected and removed. The possibility that the back surface of the recording paper 26 becomes dirty can be prevented. In addition, the charger 13
Is negative from the beginning of the pre-rotation process, the normal charge toner collected on the photosensitive drum 12 from the transfer roller 16 moves from the photosensitive drum 12 to the charger 13 side, and the charged toner is charged. It can be prevented from adhering to the container 13.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described.
Will be described with reference to FIG. In the fourth embodiment, as in the second embodiment, the bias voltage of the charger 13 is set to zero until the middle of the pre-rotation process, and thereafter, is changed to a negative value. It has become. In addition, the bias voltage of the developing unit 15 is initially set to be positive during the pre-rotation process, and is switched from positive to negative when a predetermined time T1 has elapsed after the bias voltage of the charger 13 is changed. I have. Then, during the pre-rotation processing, the transfer roller 16 is charged with the bias voltage of the charger 13 being zero and the bias voltage of the developing unit 15 being plus.
Is switched from minus to plus.

Therefore, also in the fourth embodiment,
Almost the same effects as in the above-described second embodiment can be exerted. The present invention can be embodied with the following modifications.

As shown by the dashed line in FIG. 3, a sensor 49 for detecting the temperature and the humidity in the apparatus case 11 is provided.
6. A configuration in which a bias voltage to the charger 13 and the developing unit 15 and an application timing thereof can be adjusted.

During the pre-rotation process, the transfer roller 1
6. When a negative bias voltage and a positive bias voltage are applied to 6, the time from the start to the end of the application can be adjusted.

At the start of the printing operation and at the time of post-rotation processing after the end of the printing operation, as in the case of the pre-rotation processing,
The transfer roller 16, the charger 13, and the developing unit 15 are configured to be applied with a bias voltage as described in each of the above-described embodiments.

[0056]

The present invention is configured as described above, and has the following effects. Claims 1 to 3
According to the invention described in (1), during the pre-rotation processing of the printing operation, both the normal charge toner and the reverse charge toner attached to the transfer roller can be collected and removed, and the back surface of the recording paper is The possibility of contamination can be prevented.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is an enlarged partial cross-sectional view illustrating a main part of the image forming apparatus.

FIG. 3 is a block diagram illustrating a circuit configuration of the image forming apparatus.

FIG. 4 is a time chart for explaining an operation during a pre-rotation process.

FIG. 5 is a time chart illustrating an operation during a pre-rotation process according to the second embodiment.

FIG. 6 is a time chart illustrating an operation during a pre-rotation process according to the third embodiment.

FIG. 7 is a time chart showing an operation during a pre-rotation process according to a fourth embodiment.

[Explanation of symbols]

12: a photosensitive drum as a photosensitive member; 13: a charger;
... Exposure unit, 15 ... Developer unit, 16 ... Transfer roller,
19: toner, 26: recording paper, 36: CPU constituting control means, 37: ROM constituting control means, 38: RAM constituting control means.

Claims (3)

[Claims] In an image forming apparatus, a transfer roller is disposed so as to face a photosensitive member, and a predetermined bias voltage is applied to the transfer roller to transfer a toner image on the photosensitive member onto recording paper. An image forming apparatus provided with control means for applying a negative bias voltage to the transfer roller and then applying a positive bias voltage during a pre-rotation process of a printing operation. 2. The image according to claim 1, wherein the controller controls the transfer roller to switch the bias voltage from negative to positive while a negative bias voltage is applied to the charger and the developing device. Forming equipment. 3. The control means switches the bias voltage of the transfer roller from negative to positive while a negative bias voltage is applied to the charger and a positive bias voltage is applied to the developing device. 2. The image forming apparatus according to claim 1, wherein the image forming apparatus controls the image forming apparatus.