JP2001005258A - Electrifying device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrifying device, by which body to be electrified can be electrified by electrostatically charging the body from a discharge member by impressing a specified voltage on the discharge member arranged adjacently to the body, to carry out uniform discharge even when the discharge member is soiled and to electrify the body stably and uniformly over a long period of time. SOLUTION: In this electrifying device D1, a photoreceptor 91 is electrified by electrostatically charging the photoreceptor 91 from a discharge member 11 by impressing voltage on the discharge member 11 from a voltage impressing device 61. Voltage where AC voltage where peak to peak value is VPP is superposed on DC voltage VDC is impressed on the discharge member 11. Current flowing through the discharge member 11 is measured at a current measuring device 41 and the degree of soiling of the discharge member 11 is detected. The voltage impressed on the discharge member 11 is controlled based on the degree of soiling. When the degree of soiling is large, VPP is made larger, thus the range of discharge is extended and the range being a non discharge range is newly made into the discharge range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for discharging a charged object to charge the charged object. Further, the present invention is an image forming apparatus for forming an image based on a document image on a recording sheet, wherein the charging device discharges toward a member to be charged such as a photoconductor and charges the member to be charged. The present invention relates to an image forming apparatus including:

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, for example, an electrostatic latent image corresponding to a document image is formed on a photosensitive member, and the electrostatic latent image is developed to form a toner image on the photosensitive member. By forming and transferring this toner image onto a recording sheet,
A toner image corresponding to the document image is formed on the recording sheet.

An electrostatic latent image is formed on a photoreceptor by uniformly charging the photoreceptor and exposing it based on a document image.
A corona charger is widely used as a charging device for charging a photoconductor. However, when a photoconductor is charged using a corona charger, ozone is generated relatively frequently. To reduce the amount of ozone generated,
The following charging device called a proximity charging device has been proposed.

[0004] The proximity charging device has a discharge member disposed close to a member to be charged (for example, a photoreceptor). When a predetermined voltage is applied to the discharge member, the member is directed from the discharge member to the member to be charged. By discharging, the charged object is charged. Since the discharge distance is short, generation of ozone is relatively small.

[0005]

However, in the proximity charging device, since the discharge member is disposed close to the member to be charged, foreign substances such as dust adhere to the discharge member and the discharge member is easily stained. In a case where a proximity charging device is used for charging a photoconductor in an image forming apparatus, if the number of times of image formation increases, foreign substances such as toner and paper powder adhere to the discharge member and become dirty. If the discharge member is contaminated, the discharge from the discharge member to the photoconductor tends to be non-uniform, and the photoconductor is non-uniformly charged. As a result, noise (for example, unevenness due to dot-like discharge and unevenness in the form of stripes) occurs in the toner image formed on the recording sheet.

Accordingly, the present invention is a charging device for applying a predetermined voltage to a discharge member disposed in proximity to a member to be charged, thereby discharging the member from the discharge member to the member to be charged and charging the member to be charged. It is another object of the present invention to provide a charging device capable of performing uniform discharge even if a discharge member is contaminated, and stably and uniformly charging an object to be charged over a long period of time.

Further, the present invention includes a charging device including a discharging member for charging a predetermined member such as a photosensitive member for a predetermined purpose in order to form an image based on a document image on a recording sheet. It is an object of the present invention to provide an image forming apparatus which can stably and uniformly charge a predetermined member for a long period of time even if it is soiled, and which can perform good image formation for a long period of time.

[0008]

(1) Charging device In order to solve the above-mentioned problems, the present invention is a charging device for discharging an electric charge toward an object to be charged and charging the object to be charged. A discharge member disposed at a predetermined distance from the discharge member and having a facing surface facing the member to be charged, in order to discharge toward the member to be charged from a predetermined discharge region on the surface facing the discharge member,
A voltage application device that applies a predetermined voltage to the discharge member, a detection device for detecting the degree of contamination of the discharge member-facing surface, and, according to the degree of contamination of the discharge member-facing surface detected by the detection device, A control device for controlling a voltage applied from the voltage application device to the discharge member.

The charging device of the present invention discharges electricity to an object to be charged (object to be discharged) and supplies a predetermined polarity charge to the object to be charged. By supplying a predetermined polarity charge to the member to be charged, the member to be charged can be charged. The charging operation performed by the charging device of the present invention is an operation of changing the charge amount (charge potential) of the member to be charged, and includes both an operation of increasing the charge amount of the member to be charged and an operation of decreasing the charge amount.
The charging device of the present invention can discharge, for example, an object to be charged to increase, for example, the absolute value of the charge amount of the object to be charged. Further, the charging device of the present invention can discharge toward the member to be charged and reduce the absolute value of the charge amount of the member to be charged to 0, in other words, can also perform charge elimination of the member to be charged. .

[0010] The charging device of the present invention has a discharging member, a detecting device, a voltage applying device, and a control device. The discharge member is separated from the member to be charged by a predetermined distance, and faces the member to be charged. The surface of the discharge member facing the member to be charged may be hereinafter referred to as the discharge member facing surface. The discharge member may be disposed close to the member to be charged, for example, to suppress the generation of ozone.

The discharge member may have any shape, for example, a sheet shape, a film shape, a blade shape, a roller shape, or a thin plate shape. By applying a voltage to the discharge member from the voltage applying device, the discharge member is discharged from the surface of the discharge member facing the member (the surface facing the discharge member). The region where the discharge occurs on the surface facing the discharge member is hereinafter referred to as a discharge region.

Discharge member (surface of discharge member facing charged member)
Alternatively, the member to be charged may be charged by discharging the member to be charged from the discharging member while relatively moving the member to be charged (the surface of the member facing the discharging member) in a predetermined direction. With this configuration, the entire surface of the member to be charged can be charged. For example, when the member to be charged is in the form of a rotating member such as a roller or an endless belt, the discharging member is arranged at a fixed position facing the peripheral surface of the member to be charged, and the discharging member discharges while rotating the member to be charged. By doing so, the entire surface of the peripheral surface of the member to be charged can be charged.

In order to discharge a member to be charged from a discharging member
The voltage application device is, for example, a DC voltage V _DCTo peak to
ー Peak value is V_PPIs superimposed with an AC voltage having a predetermined waveform
The applied voltage (superimposed voltage) may be applied to the discharge member. this
The superimposed voltage (oscillation voltage) is such that the center voltage of the AC component is the voltage V
_DCOnly offset from 0 [volt]
is there. The voltage waveform of the AC component of the superimposed voltage is
Any waveform can be used as long as the value changes.
And a sine wave shape. Release such superimposed voltage
Applying to the electrical member and discharging from the discharging member,
Than when applying a DC voltage to the material and discharging it.
Thus, the member to be charged can be charged uniformly.

In order to perform stable discharge from the discharge member,
The discharge member has a volume resistance of, for example, 10 ³ Ω · cm to 10 ⁹ Ω.
It may be formed of a resistive material of cm. The discharge member is
For example, polyurethane, polyamide, polyimide, ET
A conductive material such as carbon may be dispersed in a resin such as FE or PVdF. In order to stabilize the distance between the discharge member and the member to be charged and perform a stable discharge, the discharge member is supported between the discharge member and the member to be charged, and is supported by an insulating member that comes into contact with the member to be charged. You may. If the discharge member is supported by an insulating member that comes into contact with the member to be charged, the distance between the discharge member and the member to be charged can be stabilized. For example, the insulating member may support an end of the discharging member so that the entirety of the discharging member is not covered by the insulating member with respect to the member to be charged. When discharging from the discharge member while moving the member to be charged relatively in the predetermined movement direction with respect to the discharge member, if the discharge member is made to protrude upstream or downstream in the movement direction from the insulating member. Good.

The detecting device is for detecting the degree of contamination (the amount of adhered foreign matter such as toner and paper dust) on the surface of the discharge member facing the member to be charged (the surface facing the discharge member). The detecting device may directly detect the degree of contamination on the discharge member-facing surface, or may indirectly detect the degree of contamination. The detection device can detect the degree of contamination on the discharge member facing surface, for example, as follows.

For example, by detecting the density on the discharge member-facing surface with a density detection sensor, the amount of foreign matter adhering to the discharge member-facing surface, in other words, the degree of contamination can be detected. The concentration detection sensor is separated from, for example, a position facing the discharge member-facing surface (a position between the discharge member and the member to be charged) and the discharge member so as not to hinder the discharge from the discharge member to the member to be charged. What is necessary is just to be able to move between positions.
If there is not enough space between the discharge member and the member to be charged to dispose the concentration detection sensor, the discharge member is moved to detect the degree of contamination of the discharge member, and the surface facing the discharge member faces the concentration detection sensor. You may not.

In order to discharge from the discharge member, the degree of contamination on the discharge member-facing surface can be detected from the current flowing through the discharge member when a voltage is applied to the discharge member from a voltage application device. Even when a voltage of the same magnitude is applied to the discharge member, when the degree of contamination on the surface facing the discharge member is large, it is difficult to discharge, and sometimes the discharge does not occur. In any case, when the degree of contamination on the discharge member facing surface is large, the current flowing through the discharge member becomes small. Therefore, when the current flowing through the discharge member is small, it can be understood that the degree of contamination on the discharge member facing surface is large.

When a voltage is applied to the discharge member from the voltage application device to discharge the member to be charged from the discharge member,
When the degree of contamination of the surface facing the discharge member is large, the discharge is difficult, and the change in the charge amount or the change in the charge potential of the member to be charged is small. Therefore, the detection device can also detect the degree of contamination on the surface facing the discharge member from a change in the charge amount or a change in the charge potential of the member to be charged.

Generally, the degree of contamination on the discharge member facing surface increases in proportion to the time during which a voltage is applied to the discharge member from the voltage application device. Therefore, the detection device can also detect the degree of contamination of the discharge member facing surface from the time when the voltage is applied to the discharge member by the voltage application device. When the predetermined amount is substantially proportional to the time during which the voltage is applied to the discharge member, the detection device may detect the degree of contamination on the discharge member facing surface based on the predetermined amount. For example, when the charging device of the present invention is mounted on an image forming apparatus for forming an image based on a document image on a recording sheet and a predetermined member (including a recording sheet) included in the image forming apparatus is charged for a predetermined purpose, Since the charging device charges a predetermined member when forming an image on a recording sheet, the time during which voltage is applied to the discharge member (integrated time) is as follows:
It is almost proportional to the number of recording sheets on which an image has been formed. Also,
When an electrostatic latent image is formed by exposing a charged photoreceptor in an electrophotographic image forming apparatus, the time during which a voltage is applied to the discharge member depends on the number of exposure dots (writing amount) based on image resolution on the photoreceptor. Is also approximately proportional. Therefore, when the charging device of the present invention is mounted on an image forming apparatus, the detecting device may detect the degree of contamination of the discharge member from the number of recording sheets on which an image is formed or the amount of writing. As the number of recording sheets on which an image is formed and the writing amount increase, the degree of contamination of the discharge member increases.

In the charging device of the present invention, when a voltage is applied to the discharge member from the voltage application device and the object to be charged is discharged from the discharge member, the control device detects the degree of dirt on the surface facing the discharge member detected by the detection device. The voltage applied from the voltage application device to the discharge member is controlled in accordance with. For example, when the degree of contamination of the discharge member facing surface detected by the detection device is large, the voltage applied from the voltage application device to the discharge member may be larger than when the degree of contamination is small, and the discharge region may be changed as follows. . On the surface facing the discharge member, a region that was a non-discharge region before increasing the voltage applied to the discharge member may be changed to a discharge region. The discharge region after the change may or may not include part or all of the discharge region before the change. In any case, the discharge region after the change includes a region (non-discharge region) that was not the discharge region before the change. For example, the discharge region may be changed so that the discharge region expands.

The charging device of the present invention has the following advantages by changing the discharge area in this way. On the discharge member-facing surface, the discharge region is usually contaminated, and most of the dirt (foreign matter) adheres to the discharge region. If the degree of contamination in the discharge region is large, it is difficult to perform stable and good discharge from the discharge region. When charging an object to be charged,
If the degree of dirt in the discharge area is large,
It is difficult to charge evenly. On the other hand, a region other than the discharge region on the discharge member facing surface (non-discharge region)
Is hardly stained compared to the discharge area, and the degree of stain is small. Therefore, when the degree of dirt in the discharge area increases, the discharge area is changed, and the area that was a non-discharge area is newly set as a discharge area. It can be performed. By setting a region that was a non-discharge region as a new discharge region, the member to be charged can be uniformly and uniformly charged. When the degree of contamination in the area newly set as the discharge area increases, the discharge area may be further changed. By changing the discharge area in this way, a good discharge can be stably performed over a long period of time without cleaning the discharge member. The object to be charged can be stably and uniformly charged for a long time.

The voltage applied to the discharge member is more specific.
May be controlled, for example, as follows. As aforementioned
DC voltage V from the voltage application device_DCPeak to P
Value is V _PPA voltage obtained by superimposing an AC voltage having a predetermined waveform
(Superimposed voltage) is applied to the discharge member, and the discharge member discharges.
The voltage applied to the discharge member is controlled as follows:
do it. For example, facing the discharge member detected by the detection device
When the degree of dirt on the surface is large, the degree of dirt is small
The peak-to-peak AC component voltage of the superimposed voltage
Peak value V_PPShould be increased.

In controlling the voltage applied to the discharge member according to the degree of contamination of the discharge member,
The voltage applied to the discharge member may be increased in proportion to the degree of contamination of the discharge member. The voltage applied to the discharge member may be increased stepwise according to the degree of contamination of the discharge member. When applying a predetermined voltage to the discharge member and discharging from the discharge member to the member to be charged, the distance to the member to be charged falls within a range determined by the magnitude of the voltage applied to the discharge member on the discharge member facing surface. The area in which it is located is the discharge area. Therefore, to increase the predetermined voltage applied to the discharge member to change the discharge region on the discharge member facing surface as described above, for example, the following method may be used. For example, the surface of the discharge member facing the discharge member (surface facing the discharge member) is moved relative to the surface facing the discharge member (surface facing the discharge member) in a predetermined moving direction. When discharging from the discharge member to the member to be charged, it is sufficient that the distance between the surface facing the discharge member and the surface facing the member changes in the moving direction. When the surface to be charged is flat,
For example, the surface facing the discharge member may be curved. When the surface to be charged is flat, the surface to face the discharge member may be flat, and the plane of the discharge member facing the member to be charged may be arranged obliquely with respect to the member to be charged. When the surface to be charged is a curved surface, the surface facing the discharge member may be flat or curved.

The charging device of the present invention can be mounted on, for example, an image forming apparatus for forming an image based on a document image on a recording sheet and used for charging a predetermined member of the image forming apparatus. Of course, it can also be used by mounting it on equipment other than the image forming apparatus. (2) Image Forming Apparatus The present invention also provides an image forming apparatus including the above-described charging device of the present invention.

In the image forming apparatus of the present invention, the charging device of the present invention is provided to supply a predetermined polarity charge to the predetermined member in order to charge a predetermined member (a member to be charged) included in image formation for a predetermined purpose. The image forming apparatus may form an image based on a document image on a recording sheet by any method. The image forming apparatus is for forming a toner image on a recording sheet by an electrophotographic method, for example. The image forming apparatus forms a toner image directly on a recording sheet without forming an electrostatic latent image, for example.

In the image forming apparatus, for example, the charging device of the present invention may be used as follows. For example, in an electrophotographic image forming apparatus, an electrostatic latent image carrier (for example, a photoconductor) for forming an electrostatic latent image may be charged by a charging device. In order to electrostatically transfer the toner image formed on the image carrier to the transfer body facing the image carrier, a charging device may be used to supply electric charges to the back surface of the transfer body. The image carrier is, for example, an electrostatic latent image carrier (for example, a photoconductor), an intermediate transfer body, or the like. The transferred object is, for example,
An intermediate transfer member and a recording sheet. The charging device is, for example,
Electrostatic transfer of a toner image from an electrostatic latent image carrier to an intermediate transfer member, electrostatic transfer of a toner image from an intermediate transfer member to a recording sheet, electrostatic transfer of a toner image from an electrostatic latent image carrier to a recording sheet Can be used for transcription. The charging device may transfer the toner image from the image carrier to the recording sheet, and then supply the charge to the recording sheet adsorbed on the image carrier, and may be used to separate the recording sheet from the image carrier. . The charging device is, for example, an electrostatic latent image carrier (for example, a photoconductor) after transferring a toner image.
May be used to erase charges remaining on the electrostatic latent image carrier. The image forming apparatus may be provided with a plurality of charging devices of the present invention.

In the image forming apparatus of the present invention, since the predetermined member (charging member) is charged by the charging device of the present invention, the predetermined member is stably and uniformly charged over a long period of time as described above. Can be done. Therefore, according to the purpose for which the charging device is provided, the purpose can be stably and satisfactorily achieved for a long time. For example, good charging can be stably performed over a long period, good electrostatic transfer can be stably performed over a long period, and good static elimination can be performed stably over a long period. Since the charging device of the present invention can stably and satisfactorily achieve its object over a long period of time, the image forming apparatus of the present invention can stably form a good image on a recording sheet for a long period of time.

When the charging device of the present invention is mounted on an image forming apparatus, the detecting device of the charging device may detect the degree of contamination of the discharge member from the number of recording sheets on which an image has been formed as described above. Further, the detection device may detect the degree of contamination of the discharge member from the writing amount (dot count).

[0029]

Embodiments of the present invention will be described below with reference to the drawings. (1) FIG. 1 shows a schematic configuration diagram of an example of an image forming apparatus according to the present invention. The image forming apparatus A1 shown in FIG. 1 can form a toner image based on a document image on a recording sheet by electrophotography.

The image forming apparatus A1 includes a drum-shaped photosensitive member 9 for forming a toner image on a recording sheet by electrophotography.
1, an eraser lamp 92 arranged around a photoconductor 91, a charging device D1, a laser device 93 according to the present invention,
It has a developing device 94, a transfer device 95, and a cleaning device 96. The image forming apparatus A1 can form a toner image based on a document image on a recording sheet as follows. At the time of image formation, the photoconductor 91 is driven to rotate clockwise in FIG. 1 by a driving device (not shown). First, the photosensitive member 91 is neutralized by irradiating light from an eraser lamp 92. Next, the outer peripheral surface of the photoconductor 91 is uniformly charged by the charging device D1 of the present invention. In addition,
The structure and charging operation of the charging device D1 will be described later in detail. By irradiating the charged photoconductor 91 with light from the laser device 93 based on the original image, an electrostatic latent image based on the original image is formed on the photoconductor 91. This electrostatic latent image is developed using toner in the developing device 94, and a toner image based on a document image is formed on the photoconductor 91. The toner image on the photoconductor 11 is electrostatically transferred by the transfer device 95 to a recording sheet 98 supplied between the transfer device 95 and the photoconductor 91. The toner remaining on the photoconductor 91 without being transferred to the recording sheet is removed by the cleaning device 96. The recording sheet to which the toner image has been transferred is
After the toner image is fixed in the image forming apparatus, the toner image is discharged outside the image forming apparatus.

The image forming apparatus A1 includes the charging device D1 of the present invention for charging the photosensitive member 91 as described above. The charging target (charged body) to be charged by the charging device D1 is the photoconductor 91. Hereinafter, the charging device D1 of the present invention will be described in detail. The charging device D1 is a charging device (photoconductor 9).
By discharging toward 1), the photoconductor 91 can be charged. The charging device D1 includes a discharging member 1 facing the photoconductor 91.
1. a voltage application device 61 for applying a predetermined voltage to the discharge member 11; a current measurement device 41 for detecting the degree of contamination of the discharge member 11;
A control device 51 for controlling the application of voltage to the power supply.

The discharge member 11 has a thickness of about 100 μm in this embodiment.
And extends in the rotation axis direction of the photoconductor 11. The discharge member 11 is supported by support means (not shown), and is disposed at a predetermined distance from the photoconductor 11. The discharge member 11 is close to the photoconductor 11. The discharge member 11 is made of a material obtained by dispersing carbon in polyurethane, and has a volume resistance of 10 ³ to 10 ⁹ Ω ·
cm.

The voltage applying device 61 has a DC power supply 611 and a sine-wave AC power supply 612 connected in series. The voltage applying device 61 discharges a voltage (see FIG. 2) obtained by superimposing a sine-wave AC voltage (sine-wave oscillating voltage) having a peak-to-peak value of V _PP on a DC voltage having a magnitude of V _DC . 11 can be applied. More specifically, the voltage application device 61 applies to the discharge member 11 a sine-wave AC voltage having a peak-to-peak value of V _PP and a center voltage offset from 0 [volt] by the voltage _VDC. Can be. The voltage obtained by superimposing the sine-wave AC voltage on the DC voltage in this manner may be referred to as an offset sine-wave AC voltage in the following description. The magnitude of the DC component voltage of the offset sine wave AC voltage applied to the discharge member 11 is _VDC , and the peak-to-peak value of the AC component voltage is V _PP .

An electrode 31 is in contact with the surface of the discharge member 11 opposite to the photoreceptor 91, and the discharge member 11
A voltage is applied via 1. By applying a voltage to the discharge member 11 from the voltage application device 61, the discharge member 11 can be discharged from the surface 111 facing the photoconductor 91 (discharge member facing surface) to the photoconductor 91. By this discharge, in this example, a negative charge is supplied to the photoconductor 91, and the photoconductor 91 can be charged to a predetermined negative polarity charge.

In the image forming apparatus A1, the charging device D
When the image forming operation including the charging operation of the photoreceptor 91 is repeatedly performed, the surface of the discharge member 11 facing the photoreceptor 91 (discharge member-facing surface) 111 contains foreign matter such as toner and paper dust. In addition, the discharge member facing surface 111 becomes dirty. In order to suppress uneven discharge that occurs when the degree of contamination of the discharge member facing surface 111 increases, in the charging device D1 of the present invention, the discharge member 1
The voltage applied to 1 is controlled by the control device 51 as described below. The control device 51 includes the current measuring device 41
The voltage applied to the discharge member 11 is controlled based on the degree of contamination of the surface 111 of the discharge member 11 facing the photoreceptor 91 detected in step (1).

The current measuring device 41 measures the current flowing through the discharge member 11. When a voltage is applied to the discharge member 11 from the voltage applying device 61, the surface of the discharge member 11 facing the photoreceptor 91 (discharge member facing surface) 111 becomes more difficult to discharge as the degree of contamination increases, and the discharge member 11 becomes harder to discharge. The current flowing through becomes smaller. More specifically, as the degree of contamination in the discharge region of the discharge member facing surface 111 increases, the discharge becomes difficult, and the current flowing through the discharge member 11 decreases. Therefore, when a voltage is applied to the discharge member 11 from the voltage application device 61, the degree of contamination of the discharge member 11 can be detected by measuring the current flowing through the discharge member 11 with the current measurement device 41. Discharge member 1
When the degree of contamination of 1 is large, the current flowing through the discharge member 11 becomes small even when the same voltage is applied to the discharge member 11.

The control device 51 controls the voltage applied from the voltage application device 61 to the discharge member 11 based on the degree of contamination of the discharge member 11 detected by the current measurement device 41 as follows. This will be described with reference to the flowchart shown in FIG.
When it is detected that the degree of contamination of the discharge member 11 has increased by measuring the current flowing through the discharge member 11 with the current measuring device 41 (step S in FIG. 3).
2: YES), the peak-to-peak value V _PP of the AC voltage component of the offset sine wave AC voltage applied to the discharge member 11 is increased by a predetermined voltage ΔV ₁ (S3).
That is, when the degree of contamination of the discharge member 11 is large, the peak-to-peak value V _PP of the AC component of the offset sine-wave AC voltage applied to the discharge member 11 is made larger than when the degree of contamination is small. By increasing the peak-to-peak value V _PP , the surface (discharge member facing surface) 11 of the discharge member 11 facing the photoconductor 91 is increased.
The discharge area in 1 is changed as follows. Discharge member 11
The manner in which the discharge area is changed in accordance with the degree of contamination of the discharge member facing surface 111 from the beginning of the use will be described with reference to FIG.

The surface 111 of the discharge member 11 facing the photoreceptor 91 (surface facing the discharge member) 111 is not dirty at the beginning of use of the discharge member 11 (see FIG. 4A). By applying the offset sine wave AC voltage to the discharge member 11, a discharge is generated from the discharge region of the discharge member facing surface 111. In addition,
At the beginning of use of the discharge member 11, in this example, V
_DC = −800 V and V _PP = 2 kV. In the discharge member facing surface 111, a region where the distance to the outer peripheral surface 911 of the photoconductor is within a range according to the magnitude of the voltage applied to the discharge member 11 is the discharge region. When the discharge from the discharge member 11 to the photosensitive member 91 is repeatedly performed for image formation, FIG.
As shown in (B), foreign substances such as toner and paper dust adhere to the discharge area, and the discharge area becomes dirty. The non-discharge area on the discharge member facing surface 111 is less contaminated than the discharge area.

When the discharge region becomes dirty and the degree of the contamination becomes large, the peak-to-peak value V _PP of the offset AC voltage applied to the discharge member 11 is increased as described above. Thereby, the discharge region on the discharge member facing surface 111 is expanded as shown in FIG. peak·
By increasing the to-peak value V _PP, in the discharge member facing surface 111, a peak-to-peak value V _PP
Is greater than the distance between the discharge area and the photoconductor 91 before
A region having a long distance is also a discharge region. Region before were non-discharge regions to increase the peak-to-peak value V _PP becomes a possible by new discharge region to increase the peak-to-peak value V _PP, discharge area expands. The discharge area is expanded before the discharge area becomes so dirty that only a non-uniform discharge can be performed from the discharge area. Since the area which has newly become the discharge area has little foreign matter attached and is not contaminated, good discharge can be performed from this new discharge area. When foreign matter adheres to the new discharge region as shown in FIG. 4D and the degree of contamination of the discharge member facing surface 111 is further increased, the peak-to-peak value V _PP is further increased. , FIG.
As shown in (E), the discharge region is further expanded.

As described above, in the charging device D1 of the present invention, before the unevenness of the discharge member facing surface 111 becomes severe and an uneven discharge occurs, the discharge region is expanded and a region that is hardly stained is newly formed. Since the discharge region is used as a discharge region, a uniform discharge can be stably performed over a long period of time. Even if the discharge member 11 is not cleaned, a stable and uniform discharge can be performed from the discharge member 11 for a long time. Therefore, the charging device D1 can uniformly charge the photoconductor 91 over a long period of time. As a result, the image forming apparatus A1
In the above, image noise generated due to uneven charging of the photoconductor 91 can be suppressed. Therefore, in the image forming apparatus A1, good image formation can be performed over a long period while suppressing image noise. (2) In the image forming apparatus A1, image formation was repeatedly performed on the recording sheet while controlling the applied voltage (peak-to-peak value V _PP ) to the discharge member 11 as described above. As shown, the peak-to-peak value V _PP increased substantially in proportion to the number of recording sheets on which images were formed.

As described above, the peak-to-peak value V
_{Since the PP} increases in accordance with the degree of contamination of the surface 111 of the discharge member 11 facing the photoreceptor 91 (surface facing the discharge member),
It can be seen from FIG. 5 that the degree of contamination increases almost in proportion to the number of recording sheets on which images have been formed. Additionally,
Since the number of recording sheets on which an image is formed is proportional to the time during which a voltage is applied to the discharge member 11, it can be seen that the time during which a voltage is applied to the discharge member 11 and the degree of contamination of the discharge member 11 are substantially proportional.

Since the number of recording sheets on which an image is formed and the degree of contamination of the discharge member facing surface 111 are substantially proportional, the degree of contamination may be detected based on the number of recording sheets on which an image has been formed. Instead of detecting the degree of contamination of the discharge member facing surface 111 by measuring the current flowing through the discharge member 11 with the current measuring device 41, the degree of contamination can be detected based on the number of recording sheets on which images are formed. Good. The degree of contamination of the discharge member 11 may be detected based on the time during which the voltage is applied to the discharge member 11.

The voltage applied to the discharge member 11 may be controlled as described above based on the degree of contamination detected from the number of recording sheets on which an image has been formed. The voltage applied to the discharge member 11 may be controlled in the same manner as described above based on the number of recording sheets on which an image has been formed. Based on the degree of contamination detected from the time when voltage was applied to the discharge member 11, the discharge member 1
The voltage applied to 1 may be controlled. The voltage applied to the discharge member 11 may be controlled in the same manner as described above based on the time during which the voltage is applied to the discharge member 11. In any case, the voltage application can be controlled according to the degree of contamination of the discharge member 11, and the discharge area can be changed according to the degree of contamination.

For example, as shown in FIG. 6, the peak-to-peak value V _PP may be increased in proportion to the number of recording sheets on which an image has been formed. By controlling the peak-to-peak value V _PP in this manner, the discharge member facing surface 111
The peak-to-peak value V _PP increases substantially in proportion to the degree of contamination of the discharge member 11, and the discharge region can be expanded in accordance with the degree of contamination of the discharge member 11 as described above.

As shown in FIG. 7, the peak-to-peak value V _PP may be increased stepwise according to the number of recording sheets on which an image has been formed. Also thus controls the peak-to-peak value V _PP, approximately in proportion to the degree of dirt discharge member facing surface 111, a peak-to-peak value V _PP
Becomes larger, and the discharge area can be expanded in accordance with the degree of contamination as described above.

Therefore, in the image forming apparatus A1, even if the voltage applied to the discharge member 11 is controlled based on the number of recording sheets on which an image has been formed in this way, stable and uniform discharge can be performed for a long period of time. it can. (3) When a voltage (oscillating voltage) obtained by superimposing an AC voltage on a DC voltage is applied to the discharge member, the waveform of the AC voltage component need not be the sine wave shown in FIG. It may be.

When a voltage as shown in FIG. 8 is applied to the discharge member, the peak-to-peak value V _PP of the AC component voltage is controlled in accordance with the degree of contamination of the discharge member, as described above. Uniform discharge can be stably performed from the discharge member for a long time. (4) FIG. 9 shows a schematic configuration diagram of still another example of the charging device according to the present invention. The charging device D2 shown in FIG. 9 is substantially the same as the charging device D1 shown in FIG. 1 except for the following. Note that the charging target (charging target) of the charging device D3 is also the photoconductor 91 in this example.

In the charging device D2, an insulating member 21 is disposed between the discharge member 11 and the photosensitive member 91 (charged member). The insulating member 21 is in contact with the photoconductor 91. The discharge member 11 is supported by the insulating member 21. The insulating member 21 supports an upstream end of the discharge member 11 in the moving direction of the outer peripheral surface of the photoconductor. The discharge member 11 is made of the insulator 2
It projects to the downstream side from 1 and faces the photoconductor 11.

By disposing the insulating member 21 between the discharge member 11 and the photosensitive member 91 (charged member), the discharge member 11 can be easily arranged close to the photosensitive member 91. Further, by supporting the discharge member 11 with the insulating member 21 disposed between the discharge member 11 and the photosensitive member 91 (charged member), the distance between the discharge member 11 and the photosensitive member 91 can be stabilized. Even if the outer peripheral surface of the photoconductor 91 undulates, the distance between the discharge member 11 and the photoconductor 91 is stable. Since the discharge distance is stabilized, a better discharge can be performed, and the photosensitive member 91 can be uniformly charged.

In the charging device D2, similarly to the charging device D1, the peak-to-peak value V _PP of the AC component voltage may be controlled according to the degree of contamination of the discharge member 11. The same effect can be obtained. For example, FIG.
When the discharge area on the discharge member facing surface 111 is contaminated as shown in FIG. 3 and the degree of the contamination becomes large, the peak-to-peak value V _PP of the AC component voltage of the offset AC voltage applied to the discharge member 11 is _calculated . What is necessary is just to increase by a predetermined voltage. Thereby, as shown in FIG. 10B, the discharge region on the discharge member facing surface 111 is expanded.
The discharge area may be expanded before the degree of contamination of the discharge area becomes so large that only a non-uniform discharge can be performed from the discharge area. FIG. 10 shows the newly formed discharge region.
As shown in (C), foreign matter adheres to the discharge member facing surface 1.
When the contamination degree of No. 11 is further increased, the peak-to-peak value V _PP is further increased, and FIG.
The discharge region may be further expanded as shown in FIG. By performing such control, even in the charging device D2, uniform discharge can be stably performed over a long period of time. (5) The shape of the discharge member is the discharge member 1 of the charging device D1.
However, it is not limited to the sheet shape as in FIG. The shape of the discharge member is, for example, a blade shape, a film shape,
It may be a roller shape.

FIG. 11 is a schematic configuration diagram of still another example of the charging device according to the present invention. Charging device D3 shown in FIG.
Is the charging device D1 shown in FIG. 1 except for the following.
And are substantially the same. Note that the charging target (charging target) of the charging device D3 is also the photoconductor 91 in this example. The charging device D4 has a roller-shaped discharge member 12. An insulating member 22 is arranged between the discharge member 12 and the photoconductor 91. The insulating member 22 is in contact with the photosensitive member 91. The discharge member 12 is supported by the insulating member 22. The discharge member 12 protrudes downstream from the insulating member 22. By disposing the insulating member between the discharge member 12 and the photoconductor 91, the discharge member 12 can be easily arranged close to the photoconductor 91. Further, the distance between the discharge member 12 and the photoconductor 91 can be stabilized, and accordingly, a good discharge can be performed.

Also in the charging device D4, the photosensitive member 91 can be discharged from the discharge member 12 by applying an offset sinusoidal AC voltage to the discharge member 12.
Note that the roller-shaped discharge member 12 is not rotated during discharge. Also in the charging device D4, the discharging member 12
By controlling the voltage applied to the discharge member 22 in the same manner as the charging device D1 in accordance with the degree of contamination, uniform discharge can be stably performed over a long period of time. (6) The charging devices D1 to D3 described above can be used for any purpose other than charging the photoconductor 91 in the image forming apparatus A1.

For example, the charging device of the present invention can be used as a transfer device instead of the transfer device 95 in the image forming apparatus A1 of FIG. By discharging from the discharge member of the charging device of the present invention to the back surface of the recording sheet, charges can be supplied to the recording sheet, whereby the toner image on the photoconductor 91 can be electrostatically transferred onto the recording sheet.
By supplying charges to the recording sheet using the charging device of the present invention, uniform charge supply can be stably performed over a long period of time. Therefore, good transfer can be stably performed over a long period of time.

Of course, the charging device of the present invention can also be used by mounting it on equipment other than the image forming apparatus.

[0055]

According to the present invention, there is provided a charging device for applying a predetermined voltage to a discharge member disposed close to a member to be charged, thereby discharging the member from the discharge member to the member to be charged and charging the member to be charged. Thus, even if the discharge member is contaminated, a uniform discharge can be performed, and a charging device capable of stably and uniformly charging the member to be charged over a long period of time can be provided.

Further, the present invention includes a charging device including a discharging member for charging a predetermined member such as a photoreceptor for a predetermined purpose in order to form an image based on a document image on a recording sheet. It is possible to provide an image forming apparatus that can stably and uniformly charge a predetermined member for a long period of time even if it is soiled, and that can perform good image formation for a long period of time.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an example of a charging device of the present invention and an example of an image forming apparatus according to the present invention including the charging device.

FIG. 2 is a diagram illustrating an example of a voltage applied to a discharge member of a charging device.

FIG. 3 is a flowchart of a discharge member applied voltage control process.

FIG. 4 is a diagram illustrating an example of a state in which a discharge member is soiled and a state in which a discharge region in the discharge member is changed in the charging device of FIG. 1;

FIG. 5 shows the relationship between the number of image-formed recording sheets and the peak-to-peak value when the peak-to-peak value of the AC component voltage applied to the discharge member is controlled according to the degree of contamination of the discharge member. It is a figure showing an example.

FIG. 6 shows the relationship between the number of recording sheets and the peak value when controlling the peak-to-peak value of the AC component voltage applied to the discharge member in accordance with the number of recording sheets on which an image has been formed.
It is a figure showing an example of the relation of a two peak value.

FIG. 7 shows the relationship between the number of recording sheets and the peak value when controlling the peak-to-peak value of the AC component voltage applied to the discharge member in accordance with the number of recording sheets on which an image has been formed.
It is a figure showing an example of the relation of a two peak value.

FIG. 8 is a diagram illustrating another example of the voltage applied to the discharge member of the charging device.

FIG. 9 is a schematic configuration diagram of still another example of the charging device according to the present invention.

FIG. 10 is a view showing a state in which the discharge member is soiled and a state in which the discharge region in the discharge member is changed in the charging device of FIG. 9;

FIG. 11 is a schematic configuration diagram of still another example of the charging device according to the present invention.

[Explanation of symbols]

A1 Image forming apparatus D1 to D3 Charging device 11, 12 Discharge member 111 Surface of discharge member facing charged object (discharge member facing surface) 21, 22 Insulating member 31 Electrode 41 Current measuring device (dirt degree detecting device) 51 Control device 61, 62 Voltage application device 611, 621 DC power supply 612 Sine wave AC power supply 91 Photoconductor (charged body) 911 Photoconductor outer peripheral surface 92 Eraser lamp 93 Laser device 94 Developing device 95 Transfer device 97 Fixing device 98 Recording sheet

Claims (8)

[Claims] 1. A charging device for discharging an object to be charged to charge the object to be charged, comprising: a discharge member disposed at a predetermined distance from the object to be charged and having a facing surface facing the object to be charged. And a voltage application device for applying a predetermined voltage to the discharge member in order to discharge toward a member to be charged from a predetermined discharge region on the discharge member facing surface; and a detection device for detecting a degree of contamination of the discharge member facing surface. A charging device, comprising: a control device that controls a voltage applied to the discharge member from the voltage application device according to a degree of contamination of the discharge member facing surface detected by the detection device. . 2. The discharge device according to claim 1, wherein the detection device detects a degree of contamination of the discharge member facing surface from a current flowing through the discharge member when a predetermined voltage is applied to the discharge member from the voltage application device. The charging device as described in the above. 3. The charging device according to claim 1, wherein the detection device detects a degree of contamination of the discharge member facing surface from a time when a voltage is applied to the discharge member by the voltage application device. 4. The control device increases the voltage applied from the voltage applying device to the discharge member when the degree of dirt on the discharge member facing surface detected by the detection device is higher than when the degree of dirt is low. 4. The charging device according to claim 1, wherein a region that was a non-discharge region before increasing a voltage applied to the discharge member on the discharge member-facing surface is increased to a discharge region. 5. 5. The voltage applying device applies a voltage obtained by superimposing an AC voltage having a predetermined waveform having a peak-to-peak value of V _PP on a DC voltage _VDC to the discharge member, and receives a voltage from the discharge member. When the degree of dirt on the discharge member-facing surface detected by the detection device is large, the control device is configured to control the alternating current of the voltage applied to the discharge member from the voltage application device more than when the degree of dirt is small. Peak-to-peak value of component voltage V _PP
The charging device according to any one of claims 1 to 4, wherein 6. An apparatus according to claim 1, wherein said discharge member is disposed between said discharge member and a member to be charged.
The charging device according to claim 1, further comprising an insulating member that is in contact with the member to be charged and supports the discharging member. 7. Discharging the member to be charged from the discharging member,
When charging the charged body, the charged body is moved in a predetermined movement direction relatively to the discharge member, and the discharge member is located upstream or downstream in the predetermined movement direction from the insulating member. The charging device according to claim 6, which protrudes to the side. 8. An image forming apparatus for forming an image based on a document image on a recording sheet, the image forming apparatus having the charging device according to claim 1.