JPH11102103A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a photoreceptor drum from being electrified to a polarity opposite to that at the time of forming an image, while preventing the soiling of an electrifying roller coming into contact with the photoreceptor drum. SOLUTION: In a nonimage forming part or at the time of forming a nonimage, after the formation of the image is completed, a voltage of <=50 V in an absolute value, which has the 'positive' polarity (the same polarity as that of toner 28) opposite to that in an image footing part or at the time of forming the image is applied to the electrifying roller 3. Thus, the toner 28 stuck to the surface of the electrifying roller 3 is attracted to the side of the drum 1, to clean the surface of the roller 3. Therefore, electrification unevenness is eliminated to prevent the staining of the image. Since the voltage applied to the roller 3 is <=500 V in the absolute value, a photoreceptor is never reversely electrified to the 'positive' polarity by the applied voltage. Thus, the drum 1 is never damaged.

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 provided with a charging means for uniformly charging the surface of an image forming body in contact with the image forming body.

[0002]

2. Description of the Related Art For example, an image forming apparatus such as an electrostatic copying machine or a printer is provided with a charging device for charging a photosensitive member as an image forming member. Attention has been paid to a contact roller charging type charging device that charges the battery by contact with the charging roller. In such a contact roller charging type charging device, when a toner image formed on a photoconductor and developed with toner is transferred to transfer paper, the surface of the photoconductor is cleaned by a cleaning device. Usually, some toner remains on the surface of the photoconductor. Therefore, the toner is likely to be transferred to the surface of the rotating charging roller while being in contact with the surface of the photoconductor.

If such a state is continued, the surface of the charging roller is gradually stained with toner, thereby causing uneven charging and causing the image to be stained. Therefore, for example, in a conventional image forming apparatus, when a non-image is formed, a voltage having a polarity opposite to that at the time of image formation is applied to the conductive cylinder of the charging unit, so that the toner on the charging unit is attached to the photoconductor. (See, for example, JP-A-6-19274).

[0004]

However, in the case where a voltage having a polarity opposite to that of the image forming operation is applied to the conductive cylinder of the charging means at the time of non-image formation, the applied voltage at that time is, for example, When the voltage is set to about 1000 V, the toner adhering to the conductive cylinder on the charging means side can be adhered to the photoreceptor side, but at that time, the photoreceptor is charged to a polarity opposite to that of image formation. was there. In such a case, the photoconductor is damaged, so that charging stability, photosensitivity characteristics, photoconductor life, and the like are deteriorated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and it is possible to prevent charging unevenness by preventing a charging unit that comes into contact with an image forming body such as a photoreceptor from being stained. An object of the present invention is to prevent the image forming body from being charged to the polarity opposite to that at the time of image formation so that the image forming body is not damaged.

[0006]

In order to achieve the above object, the present invention comprises a charging means for uniformly charging the surface of an image forming body in contact with the image forming body, and comprises an image forming section or an image forming apparatus. At the time of forming, a voltage is applied to the charging means to uniformly charge the surface of the image forming body, and at the time of non-image forming portion or non-image forming, the polarity is opposite to the voltage applied to the image forming portion or the charging means at the time of image forming. In the image forming apparatus for applying a voltage to the charging means, the voltage of the opposite polarity applied to the charging means at the time of the non-image forming portion or the non-image formation is set to 500 V or less in absolute value.

With this configuration, in the non-image forming section or the non-image forming operation, the polarity is opposite to the voltage applied to the charging means during the image forming section or the image forming operation, and the absolute value is 500 V.
Since the following voltage is applied to the charging unit, it is possible to prevent the image forming body from being reversely charged to the opposite polarity to that during image formation. Therefore, the image forming body can be prevented from being damaged.

In the above image forming apparatus, the voltage applied to the image forming section or the charging means during image formation is an AC bias voltage in which an AC component is superimposed on a DC component.
When the voltage applied to the charging means at the time of non-image formation or non-image formation is a DC component bias voltage having a polarity opposite to the voltage applied to the charging means at the time of image formation or image formation and having an absolute value of 500 V or less. Good.

In this case, even when the voltage applied to the image forming section or the charging means at the time of image formation is an AC bias voltage in which an AC component is superposed on a DC component, the voltage is applied to the charging means at the time of a non-image forming section or non-image formation. The applied voltage is a DC component bias voltage, and has a polarity opposite to that of the image forming section or the voltage applied during image formation and has an absolute value of 500 V or less. it can.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a charging roller as a charging unit of an image forming apparatus according to the present invention and a photosensitive drum as an image forming body charged by the charging roller. FIG. 2 also shows the vicinity of an image forming unit of the image forming apparatus. It is a block diagram.

As shown in FIG. 2, a photosensitive drum 1, which is an image forming body, is rotatably provided in an image forming section of the image forming apparatus in the direction of arrow A. A charging roller 3 is provided as charging means for uniformly charging the surface of the charging roller 3 in contact with the charging roller 1. Then, a voltage is applied to the charging roller 3 from a charging power source 27 as shown in FIG. 1, whereby the surface of the photosensitive drum 1 is charged.

As shown in FIG. 2, a discharge lamp 2, a developing device 4, a transfer roller 11, a separation electrode 12, and a cleaning device 13 are arranged around the photosensitive drum 1. I have. The developing device 4 includes a developing roller 8, a left screw 9, and a right screw 10 in a lower case 7.
Are rotatably accommodated in the directions indicated by arrows, and the lower case 7 is covered with the upper lid 6 except for a part. The doctor 5 is attached to the end of the upper lid 6 on the side of the developing roller 8.

In the cleaning device 13, a toner discharge screw 16 is rotatably housed in a cleaning case 18, and an upper portion of the cleaning case 18 is covered with an upper cleaning case 17. An inlet seal 15 is fixed to a lower portion of the cleaning case 18 on the left side in FIG. 2 via an inlet seal holder 14, and a cleaning blade is fixed to a lower portion of the right side case via a blade holder 19. 20 is fixed.

In FIG. 2, reference numeral 21 denotes a pair of registration rollers. The transfer roller P conveyed by the pair of registration rollers 21 in the direction indicated by the arrow B accurately coincides with the image formed on the photosensitive drum 1. And guides it to a transfer position where the photosensitive drum 1 and the transfer roller 11 are in contact with each other by a pair of guide plates 23 and 24.

The image forming process of the image forming apparatus is started by pressing a print button provided on an operation unit (not shown). That is, when the print button is pressed, a predetermined voltage is sequentially applied to the charge removing lamp 2, the charging roller 3, the developing roller 8, the transfer roller 11, and the separation electrode 12 at a predetermined timing, or A predetermined current flows. At substantially the same time, the photosensitive drum 1, the developing roller 8, the left screw 9, the right screw 10, the transfer roller 11, and the toner discharge screw 16 start rotating in predetermined rotation directions.

The surface of the photosensitive drum 1 is neutralized by a neutralizing lamp 2 and is uniformly negatively charged to, for example, -850 V by a charging roller 3 whose surface is in contact. Then, when the charged portion rotates to the irradiation position of the laser light L, the laser light L is irradiated thereon, and an electrostatic latent image having a potential of -150 V where a solid black portion is formed is formed. . The electrostatic latent image is developed by the developing roller 8 functioning as a magnetic brush (applied voltage −650).
V) to form a toner image.

On the other hand, a transfer paper P is fed from a paper feeding unit (not shown), and the transfer paper P is exposed to light by a pair of registration rollers 21 which convey the transfer paper P at an accurate timing coincident with an image formed on the photosensitive drum 1. The toner image on the photosensitive drum 1 is transferred by the transfer roller 11 to the transfer position where the body drum 1 and the transfer roller 11 are in contact with each other (+10 μA).
Is done. The transfer paper P is separated from the photosensitive drum 1 by the separation electrode 12, and is discharged to a discharge tray or the like outside the apparatus via a fixing device (not shown).

After the transfer of the image, the photosensitive drum 1
The residual toner remaining on the photosensitive drum 1 is further conveyed to the cleaning device 13 by the photosensitive drum 1 rotating in the direction of arrow A, and the photosensitive drum 1 is rotated by the cleaning blade 20.
Removed from the surface. Then, the surface of the photosensitive drum 1 is discharged by the discharge lamp 2 to prepare for the next image formation.

In this image forming apparatus, the voltage application from the charging power supply 27 to the charging roller 3 shown in FIG.
The surface of the photosensitive drum 1 is uniformly charged as a negative polarity at the time of image formation or image formation, and has a positive polarity opposite to that at the time of image formation or image formation at the time of non-image formation or non-image formation.

Control of the voltage applied from the charging power supply 27 to the charging roller 3 is entirely performed by the control device 50. Then, the control device 50 sets the voltage of the opposite polarity applied to the charging roller 3 to 500 V or less in absolute value at the time of the non-image forming section or the non-image forming. The control device 50 includes a central processing unit (CPU) having various judgment and processing functions, a ROM storing each processing program and fixed data, a RAM serving as a data memory for storing processing data, an input / output circuit (I / O).

In order to charge the surface of the photosensitive drum to a predetermined negative potential, a negative DC bias (having the same polarity as the predetermined potential and opposite to the toner) is applied to the charging roller, or a negative DC bias is applied. It is necessary to apply an AC bias by superimposing an AC bias on the bias. Therefore, in the image forming apparatus according to the present embodiment, the photosensitive drum 1 is charged to a negative polarity of −850 V by applying only a negative DC bias to the charging roller 3.

FIG. 3 is a diagram showing the relationship between the bias applied to the charging roller and the charging potential of the photosensitive drum surface charged by the bias. As is apparent from this figure, when a DC bias is applied, charging starts from an absolute value of about 500 V. In the case of a bias in which an AC component is superimposed on a DC component, the charging potential becomes substantially equal to the value of the AC component.

When the surface of the photosensitive drum 1 is cleaned by the cleaning device 13 having the cleaning blade 20 as shown in FIG. 2, the toner remaining on the photosensitive drum 1 is reduced to 100% by the cleaning blade 20 alone. Normally, for example, about 2 to 10 toners remain on the photosensitive drum 1 because the toner cannot be scraped off. As for the polarity of the toner remaining on the photosensitive drum 1, the polarity charged to "+" and the polarity charged to "-" are mixed.

Therefore, as shown in FIG. 4, the toner 28 charged to "+" remaining on the photosensitive drum 1 is moved by the rotation of the photosensitive drum 1 in the direction of arrow A, and the charged roller 3, the toner is attracted to the charging roller 3 to which a voltage having a polarity of "-" is applied, and adheres to the surface thereof as shown in the figure. If such a state continues for a long time, the amount of toner 28 adhering to the surface of the charging roller 3 gradually increases. Dirty soil can be formed.

However, in the image forming apparatus according to this embodiment, as described above, at the time of non-image formation or at the time of non-image formation after completion of image formation, the polarity of "+" opposite to that at the time of image formation or image formation ( (Same polarity as toner 28)
However, since a voltage of 500 V or less in absolute value is applied to the charging roller 3, the above-described problem does not occur.

That is, at the time of non-image forming portion or non-image forming, only a DC bias of not more than 500 V in absolute value, for example, +100 V to 500 V is applied to the charging roller 3,
In this state, the photosensitive drum 1 is kept rotating, so that the toner attached to the surface of the charging roller 3 is attracted to the photosensitive drum 1 as shown in FIG. Alternatively, the toner remains on the surface of the photosensitive drum 1 without adhering to the surface of the charging roller 3.

Accordingly, the surface of the charging roller 3 becomes the same as that after the cleaning, so that the charging unevenness is prevented and the image is not stained. And the charging roller 3
The absolute value of the voltage applied to the photoconductor is set to 500 V or less, so that the photoconductor is not reversely charged to the “+” polarity. Accordingly, the photosensitive drum 1 is not damaged while the charging roller 3 can be cleaned, so that good charging stability and light sensitivity characteristics can be maintained, and the life of the photosensitive member can be shortened. Absent.

In this embodiment, an example in which the charging roller 3 is used as the charging means has been described. However, the charging means uniformly charges the surface of the photosensitive drum 1 in a state of being in contact with the photosensitive drum 1. If so, the present invention can be similarly applied to charging systems such as blade charging, brush charging, and sheet charging.

The voltage applied to the charging roller 3 is an AC bias voltage in which an AC component is superimposed on a DC component by applying a voltage to the charging roller 3 at the time of image formation or an image forming unit. The voltage applied to the charging roller 3 at the time is opposite in polarity to the voltage applied to the charging roller 3 at the time of image formation or the image formation, and the absolute value is 5
Even if the DC component bias voltage is set to be equal to or less than 00 V, the surface of the charging roller 3 can be kept clean to prevent uneven charging. In addition, it is possible to prevent the photosensitive drum 1 from being damaged.

[0030]

As described above, according to the image forming apparatus of the present invention, in the non-image forming section or in the non-image forming, the absolute value is 500 V with the polarity opposite to the voltage applied in the image forming section or the image forming. Since the following voltage is applied to the charging means, it is possible to prevent the image forming body from being charged to the opposite polarity to that during image formation, and to prevent the charging means from being stained. Therefore, there is no possibility of damaging the image forming body, and it is possible to maintain good charging stability, photosensitivity characteristics, and photoreceptor life.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a charging roller as a charging unit of an image forming apparatus according to the present invention and a photosensitive drum as an image forming body charged by the charging roller.

FIG. 2 is a configuration diagram showing the vicinity of an image forming unit of the image forming apparatus.

FIG. 3 is a diagram illustrating a relationship between a bias applied to a charging roller and a charging potential on the surface of a photosensitive drum charged by the bias.

FIG. 4 is a schematic diagram illustrating a state in which toner remaining on a photosensitive drum is attracted to and adhered to the charging roller when passing through the charging roller.

FIG. 5 is a schematic view showing how toner adhered to the charging roller is drawn to the photosensitive drum side.

[Explanation of symbols]

 1: photosensitive drum (image forming body) 3: charging roller (charging means) 27: charging power supply 50: control device

Continued on the front page (72) Inventor Kei Yasutomi Ricoh Co., Ltd. 1-3-6 Nakamagome, Ota-ku, Tokyo

Claims (2)

[Claims] And a charging unit for uniformly charging the surface of the image forming body in contact with the image forming body, and applying a voltage to the charging unit at the time of forming an image or an image. In the image forming apparatus, the surface of the image forming apparatus is charged uniformly, and a voltage having a polarity opposite to a voltage applied to the charging unit at the time of image formation or image formation is applied to the charging unit at the time of non-image formation or non-image formation. An image forming apparatus, wherein the voltage of the opposite polarity applied to the charging means at the time of the non-image forming portion or the non-image forming is set to 500 V or less in absolute value. 2. The image forming apparatus according to claim 1, wherein
The voltage applied to the charging unit at the time of image formation or image formation is an AC bias voltage in which an AC component is superimposed on a DC component, and the voltage applied to the charging unit at the time of non-image formation or non-image formation is the image bias. An image forming apparatus comprising: a DC component bias voltage having a polarity opposite to that of a voltage applied to the charging unit at the time of forming or forming an image and having an absolute value of 500 V or less.