JP2002169358A - Contact electrifying device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a fine output image by obtaining uniform surface potential while removing electrification unevenness due to abnormal discharge with a conductive contact member. SOLUTION: Surface potential having a prescribed value or more is imparted to a photosensivive body by applying a DC voltage on the electrifying brush roller 3 positioned at the upstream side of a photosensive drum 1 and the photosensive body is destaticized to a prescribed voltage with a conductive contact member 5 and resistance 6 whose resistance value is variable which are positioned at the downstream side of the drum 1. As a result, parts having high voltages which are imparted to the photosensitive body by dirt of the electrifying brush roller 3 or the like are removed and then uniform electrification can be obtained in this contact electrifying device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a contact charging device in an electrophotographic image forming apparatus, and more particularly, may be a surface potential of the photosensitive member in the exposed area is for charging to be uniform at a predetermined potential The present invention relates to a contact charging device.

[0002]

2. Description of the Related Art In a conventional electrophotographic image forming apparatus or the like, a contact charging method is used in which a member to which a voltage is applied from the outside is brought into contact with a photosensitive member to perform charging. This contact charging method, compared to the widely used corona charging method,
(1) In the case of the contact charging method, the voltage is as low as about 1 KV, whereas the power supply is several KV in the case of the corona charging method.
(2) There are various advantages that ozone is not generated, and (3) the charging potential depends on the applied voltage, and does not depend on the process speed and the capacitance of the photoconductor.

As a contact charging method, a roller charging method and a brush charging method are known. In the roller charging method,
Rollers having a function-separated multilayer structure have been put to practical use. This is because there was no other way to obtain the desired elastic force, resistance value and surface smoothness except by using a multilayer structure, and therefore, it was undeniable that the cost was increased. However, in practice, even if the surface of the photoreceptor is charged by the roller charging method, the respective portions of the surface of the photoreceptor are not uniformly charged, and "spotted charging unevenness" occurs. This is because the electrically conductive member (charged body) to which the voltage is applied and the surface of the photoreceptor (charged body) contacted with it are microscopically difficult to ideally obtain a close contact surface due to unevenness on both surfaces. it is conceivable that. Then, even if an image forming process after exposure is applied to the photoreceptor surface in the spotted charging unevenness state, a spotted black spot image corresponding to the spotted charging unevenness occurs in the output image, and a high-quality image is obtained. Absent. On the other hand, the brush charging method does not need to be multilayered like the roller charging method, and the elasticity, the resistance value, and the like can be set to desired values with one type of brush. The present invention relates to such a brush-type contact charging device.

[0004] As a driving method of the contact charging method, there are a method of applying a constant voltage, a method of flowing a constant current, and a method of applying a voltage obtained by superimposing an AC voltage on the constant voltage. Since the constant voltage method is easily affected by the environment, the charging stability of the photoconductor is low,
There is a problem that the charging potential is reduced in a low-temperature and low-humidity environment. Specifically, in a solid image (solid image), many white stripes parallel to the longitudinal direction of the photoconductor appear. Constant current method,
Concentration of current may occur in the defective portion of the photoconductor drum, and the photoconductor drum and the contact charger may be burned. Further, in the case of applying a voltage obtained by superimposing an AC voltage on a constant voltage, there is no environmental fluctuation of the constant voltage, and there is no risk of burning of the photosensitive drum as in the constant current method. Therefore, a driving method that superimposes an AC voltage on a constant voltage is effective.

For example, as disclosed in Japanese Patent Application Laid-Open No. 63-149669, an oscillating electric field having a peak-to-peak voltage that is at least twice the charging start voltage when a DC voltage is applied to a charged body is applied to the charged body. By forming between the photoreceptor,
A method for achieving uniform charging of a member to be charged has been proposed. However, when charging is performed with an applied voltage in which an AC voltage is superimposed on a DC voltage, the surface potential fluctuation of the spatial frequency corresponding to the frequency of the output voltage of the AC power supply and the rotational peripheral speed of the photoconductor is caused on the surface of the photoconductor. As a result, the change of the surface potential is periodically repeated.

When a latent image is formed by exposing a photoreceptor having the above-mentioned surface potential fluctuation to form a latent image, it is a matter of course that there is a potential fluctuation in the potential of a portion where exposure is not performed (hereinafter referred to as dark potential). The potential of the exposed portion (hereinafter referred to as a bright potential) also has a slight potential variation, although not as large as the variation of the dark potential. Therefore, the difference between the light potential at the portion where the surface potential is high and the light potential at the portion where the surface potential is low affects the amount of toner adhered during development.

For example, when a straight line in the main scanning direction is repeatedly drawn every other line, the line width slightly changes depending on whether the edge portion of the latent image of the other line has a high light potential or a low light potential. For this reason, when the spatial frequency of the latent image of the photoreceptor and the spatial frequency of the surface potential fluctuation due to repeated drawing of a straight line are equal, or when there is a slight difference in the frequency in the case of an integral multiple, the line of the adjacent line is used. The position of the thick / narrow width is slightly shifted. As a result, non-uniformity occurs in a cycle lower than the frequency of the repeated line drawing. This interference unevenness is generally called moiré, and a high quality image may not be obtained due to a density difference due to the moiré.

[0008] As such a means for preventing moire, means for setting, as the spatial frequency of the fluctuations of the surface potential is higher than the spatial frequency of the repetitive drawing a straight line, and means for setting a region where no moire at a frequency lower than There is. However, in order to adopt such a means, it is necessary to increase the frequency of the charged AC power supply in accordance with the increase in resolution of the image forming apparatus. Therefore, the AC current increases, and the capacity of the AC power supply needs to be increased. . Further, the charged body may vibrate at the frequency, and the vibration may reach an audible frequency and become a noise source.

Therefore, conventionally, there has been proposed a configuration in which a charging device is provided with two charging members for charging the photosensitive member by contacting the photosensitive member, and the photosensitive member is charged twice. For example, Japanese Patent Application Laid-Open No. Hei 4-30186 discloses that at least an AC voltage is applied to a first charging unit disposed on the upstream side in the rotation direction of the photoconductor, and the first charging unit is located on the downstream side in the rotation direction of the photoconductor relative to the first charging unit. A DC voltage is applied to the second charging means disposed at
It is described that a float state is set. According to this, even if the frequency of the AC voltage applied to the first charging means is set low enough not to generate a charging noise, the second charging means uniformly charges the surface to be charged by the first charging means. The performance can be reduced, and uneven charging can be prevented.

[0010] Japanese Patent Application Laid-Open No. 6-95478 discloses that
A voltage in which a DC component is superimposed on an AC component is applied to the first charging means disposed on the upstream side in the photoconductor rotation direction,
A configuration is described in which a voltage having only a constant voltage component is applied to the second charging means disposed downstream of the photoconductor in the rotation direction of the photoconductor. According to this, at the time of charging by the first charging unit, minute discharge unevenness occurs on the photoreceptor, but this is resolved by contacting the second charging unit after that, and the minute unevenness is eliminated. The potential can be stabilized.

[0011] Also, although not using a superimposed voltage,
Japanese Patent Application Laid-Open No. 7-4 / 1994 uses a plurality of contact charging members.
Japanese Patent No. 3988 discloses that, in addition to a main charging device to which a DC voltage is applied, a pre-charging device is provided on the upstream side in the photoconductor rotation direction, and the same polarity as applied to the main charging device by the pre-charging device. And a configuration in which a voltage having a small absolute value is applied. According to this, since the charging voltage is increased stepwise, the charging voltage of the photoconductor can be stabilized.

[0012]

[SUMMARY OF THE INVENTION However, at least the AC voltage is applied to the first charging means disposed upstream of the conventional photosensitive member rotation direction, the rotation direction of the photosensitive member than the first charging means In the second charging means disposed on the downstream side,
In a method in which the surface potential of the photoreceptor is leveled by applying a DC voltage or by making it float, the effect of the first charging unit is lost due to contamination by toner or the like. Therefore, in the present invention, the charging means is charged in advance by a contact charging member at a higher potential than a predetermined surface potential, and is discharged to a predetermined surface potential by a conductive contact member provided downstream of the photoconductor in the rotation direction. It is an object of the present invention to provide a uniform potential in an exposure unit for forming an electrostatic latent image even when the device is contaminated and charging uniformity is considerably impaired.

[0013]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the first technical means is that a contact charging member is provided along a rotation direction of a photoreceptor. In a contact charging device that contacts the contact charging member to the photosensitive member before forming an electrostatic latent image and charges the surface thereof, a resistance is provided on the downstream side of the contact charging member in the rotation direction of the photosensitive member. A charge removing means comprising a conductive contact member grounded through the contact member, the contact charging member charges the surface potential of the photoconductor higher than a predetermined charging potential, and the charge removing means reduces the surface potential of the photoconductor to the predetermined potential. It is characterized in that charge is removed up to the charged potential of.

According to a second technical means, in the contact charging device according to the first technical means, the resistance has a variable resistance value.

A third technical means is a contact charging device of the first or second technical means, wherein the conductive contact member is characterized by a rotating roller-shaped.

According to a fourth technical means, in the contact charging device according to the third technical means, a cleaning member is in contact with the conductive contact material in the form of the rotating roller.

[0017]

FIG. 1 is a block diagram showing an embodiment of the present invention.
A description will be given based on the embodiment shown in FIGS. FIG. 1 is a diagram illustrating an example of an image forming apparatus to which the present invention is applied. This image forming apparatus has a photosensitive drum 1 as an image carrier that rotates in the direction of an arrow, and a charging device 2, an exposure device 7, a developing device 9, a transfer device 11, and a cleaning device 13 are provided around the photosensitive drum 1. They are arranged in order.

As shown in FIG. 1, the charging device 2 includes a charging brush roller 3 disposed on the upstream side in the rotation direction of the photosensitive drum 1 and a downstream side in the rotation direction from the charging brush roller 3. And a conductive contact member 5, which is grounded via a resistor 6. A predetermined DC voltage is applied to the charging brush roller 3 from a constant voltage power supply 4. The charging brush roller 3 is configured by winding a cloth in which brush bristles made of nylon, rayon, or the like made conductive by incorporating carbon are wound around a conductive support shaft made of iron, copper, stainless steel, aluminum, or the like. It is.

In the above image forming apparatus, first, the surface of the photosensitive drum 1 rotating is charged so that the above predetermined charging potential is performed by the charging brush roller 3 of the charging device 2, and then the conductive contact member 5 Then, the surface of the photosensitive drum 1 is exposed by the optical unit 8 of the exposure device 7 according to the image information to form an electrostatic latent image.

Next, the photoreceptor of the photoreceptor drum 1 on which the electrostatic latent image is formed is developed by a developing device 9, and a toner image is formed on the surface by a developing roller 10, and the toner image is exposed to light. The image is transferred onto a sheet S conveyed so as to pass between the body drum 1 and the transfer roller 12 of the transfer device 11. On the other hand, the residual toner is removed from the photosensitive drum 1 after the transfer by the cleaning blade 14 of the cleaning device 13, and the photosensitive drum 1 waits for the next image forming process.

Next, the charging device 2 will be described in detail. A DC voltage is applied to the charging brush roller 3 located on the upstream side of the photoreceptor drum 1 to apply a surface potential higher than a predetermined charging potential to the photoreceptor, and thereafter, the contact conductive member 5 located on the downstream side To remove the charge to a predetermined charge potential.
Therefore, a portion of a high voltage applied by abnormal discharge due to contamination of the charging brush roller 3 is removed, and uniform charging can be obtained.

FIG. 2 is a diagram schematically showing the relationship between the photosensitive drum position and the photosensitive member surface potential when the conductive contact member 5 is provided downstream of the charging brush roller 3. With such a configuration, even if an abnormal discharge occurs in the charging brush roller 3 and the surface potential becomes non-uniformly charged as V0, the charge is removed by the conductive contact member 5 via the resistor 6. Therefore, at the time of image formation by the exposure device 7,
As with V1, a uniform surface potential can be obtained at a predetermined charging potential.

FIG. 3 is a diagram schematically showing the relationship between the resistance value and the surface potential when the resistance value of the resistor 6 is changed. Resistance 6
, The surface potential of the photoconductor can be changed. By providing such a variable resistor, it is possible to control the surface potential when a white spot or ground fog occurs due to dirt on the contact charging member 5 and to suppress the occurrence of these phenomena.

FIG. 4 is a view showing an embodiment in which the conductive contact member 5 is not a fixed type but a rotating roller type conductive contact member 5a. By rotating the conductive contact member 5a, the contact portion to the photoconductor drum 1 is constantly updated, so that the charging device 2 having excellent life characteristics can be obtained.

FIG. 5 is a conductive rotary roller type contact member 5
FIG. 6 is a diagram illustrating an example in which a cleaning member 15 is brought into contact with a. With this configuration, it is possible to eliminate uneven charge removal due to contamination of the conductive contact member 5a, and to obtain more uniform charging.

FIG. 6 is a view showing an example in which a portion 5b of the conductive contact charging member, which is on the downstream side in the rotation direction of the photosensitive drum and contacts the photosensitive member, has a rounded shape. With such a configuration, it is possible to uniformly contact the photoconductor of the photoconductor drum 1 and to obtain a uniform charge eliminating effect without damaging the photoconductor.

FIG. 7 is a view showing an example in which the conductive contact member 5 on the downstream side in the rotation direction of the photosensitive drum is formed by a plate-shaped elastic body 5c. With such a configuration, there is no risk of damaging the photoconductor of the photoconductor drum 1.

FIG. 8 is a diagram showing an example in which a voltage obtained by superimposing an AC component on a DC component is applied to the contact charging member 3. Table 1 shows experimental results showing a situation in which a white spot occurs in an output image when a voltage in which an AC component is superimposed on a DC component is applied to the contact charging member 3. In Table 1, .largecircle. Means that no white spots were found, and .DELTA. Means that white spots were found. By applying a voltage obtained by superimposing an AC component from the AC power supply 4a to a DC component from the constant voltage power supply 4 to the contact charging member, even if the charging device is contaminated with toner or the like due to long-term use or the like, a white spot is formed. It is understood that there is an effect of suppressing the occurrence. Also, by sufficiently increasing the peak-to-peak voltage of the superposed AC component,
Since abnormal discharge due to the contact charging member can be reduced in advance, good image quality can be obtained without generating a white point for a longer time.

[0029]

[Table 1]

[0030]

As apparent from the above description, according to the present invention, according to the present invention, the following effects. According to the first aspect of the present invention, even if the contact charging device is contaminated with toner or the like and abnormal discharge occurs, resulting in a non-uniform charging potential, a uniform surface potential can be obtained by removing charges with the conductive contact member. And a dense image can be obtained.

According to the invention of claim 2, conductive contact member and the resistance value of the resistance between the ground by a variable, to control the surface potential at the time of exposure, it is possible to obtain a stable image.

According to the third aspect of the present invention, the contact portion with the photosensitive member is constantly updated by the rotation of the conductive contact member, so that the life characteristics can be improved.
In addition, by rotating, a good image quality without a stroke is obtained.

According to the fourth aspect of the present invention, since the cleaning member is in contact with the conductive contact material, the life characteristics can be further improved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of an image forming apparatus to which the present invention is applied.

FIG. 2 is a diagram illustrating a relationship between a location of a photoconductor drum and a surface potential of the photoconductor.

FIG. 3 is a diagram illustrating a relationship between a resistance value and a surface potential when a resistance value between a conductive contact member and a ground is changed.

FIG. 4 is a view showing an embodiment in which the conductive contact member is a rotating roller type.

FIG. 5 is a diagram showing an embodiment in which a cleaning member is brought into contact with a rotating roller type conductive contact member.

FIG. 6 is a view showing an embodiment in which a portion of the conductive contact charging member that contacts the photoconductor has a rounded shape.

FIG. 7 is a view showing an embodiment in which the conductive contact member is a plate-shaped elastic body.

FIG. 8 is a diagram showing an embodiment in which a voltage obtained by superimposing an AC component on a DC component is applied to a contact charging member.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photoreceptor drum, 2 ... Charging device, 3 ... Charging brush roller, 4 ... Constant voltage power supply, 4a ... AC power supply, 5, 5a, 5
b, 5c: conductive contact member, 6: resistance, 7: exposure apparatus,
8 optical unit, 9 developing device, 10 developing roller,
11: transfer device, 12: transfer roller, 13: cleaning device, 14: cleaning blade.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Sakita 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Hiroo Naoi 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka (72) Inventor Shoji Nakamura 22-22 Nagaikecho, Abeno-ku, Osaka City, Osaka Sharp Corporation (72) Inventor Mitsuru Tokuyama 22-22 Nagaikecho, Abeno-ku, Osaka City, Osaka Sharp Corporation F-term (reference) 2H003 AA01 AA12 BB11 BB14 CC06 DD08 EE11 EE20

Claims (4)

[Claims] 1. A contact charging member is provided along a rotation direction of a photoconductor, and the contact charging member is brought into contact with the photoconductor before forming an electrostatic latent image to charge the surface of the photoconductor. In the charging device, a static eliminator comprising a conductive contact member grounded via a resistor is provided downstream of the contact charging member in the rotation direction of the photoconductor, and the contact charging member reduces a surface potential of the photoconductor to a predetermined value. A contact charging device, wherein the charge is made higher than the charge potential, and the surface potential of the photoreceptor is removed by the charge removing means to the predetermined charge potential. 2. The contact charging device according to claim 1, wherein the resistance has a variable resistance value. 3. The contact charging device according to claim 1, wherein the conductive contact member has a shape of a rotating roller. 4. The contact charging device according to claim 3, wherein a cleaning member is in contact with the conductive contact material in the shape of the rotating roller.