JPH10111590A - Electrifier and image forming device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrifier which substantially improves the efficiency of the use of discharge current, gives sufficiently satisfactorily uniform electrification, and considerably reduces the generation of ozone and so on. SOLUTION: A discharge electrode 53 is stretched inside a conductive shield member 52. A member to be electrified is electrified by applying a high voltage to the discharge electrode 53, thereby subjecting the member moving from the opening 55 of the conductive shield member 53 to corona discharge. A grid electrode 54 is partially interposed between the opening 55 of the conductive shield member 52 and the member and downstream in the direction where the member is moved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device used for charging a photosensitive drum in an image forming apparatus such as an electrophotographic apparatus or a printer, and more particularly to a plurality of image forming apparatuses for forming images of different colors. A charging unit suitable for a so-called tandem-type color copying apparatus capable of forming a full-color image at high speed by sequentially transferring a plurality of images formed by each image forming unit onto a transfer material. It concerns the device.

[0002]

2. Description of the Related Art Conventionally, a tandem-type color copying apparatus has a plurality of image forming units for forming images of different colors from each other. There is a type in which a full-color image can be formed at high speed by sequentially transferring these plural images onto a transfer material while sequentially forming images of different colors in a forming unit.

Such a tandem type color copying apparatus has a plurality of image forming units. In each image forming unit, as is well known, the surface of the photoconductor drum is uniformly charged by a charging device such as a scorotron, and then the surface of the photoconductor drum is exposed to an image corresponding to a predetermined color and statically exposed. By forming an electrostatic latent image and developing the electrostatic latent image with a developing device provided for each image forming unit,
It is configured to form an image of a predetermined color.

As described above, the tandem type color copying apparatus has a charging device such as a scorotron for uniformly charging the surface of the photosensitive drum provided for each image forming unit. The amount of discharge products such as ozone and nitrogen oxides generated from the charging device is larger than that of a monochrome copying device having a single photosensitive drum. Therefore, in the tandem-type color copying machine, the charging device is used to prevent the deterioration of the photosensitive drum and members in the copying machine due to discharge products such as ozone generated from the charging device, or the influence on the human body. The following problems are associated with the treatment of ozone and the like.

(1) In the tandem type color copying apparatus, images of different colors formed by a plurality of image forming units are multiplex-transferred onto a transfer material to form a full-color image. In order to obtain a full-color image, it is necessary to accurately form an image having a predetermined density in each image forming unit. Therefore, in each image forming unit, it is necessary to make the potential of the primary charging of the photosensitive drum accurate and uniform, and the charging device for charging the photosensitive drum of each image forming unit is not a corotron but a scorotron. Commonly used. But,
Although the scorotron 100 satisfies charging uniformity as shown in FIG. 19, unlike the corotron, the scorotron 100 has the grid electrode 103 in the opening 102 of the shield 101, so that the discharge current from the discharge wire 104 Since it also flows to the electrodes, there is a problem in that the utilization efficiency of the discharge current is low and the amount of discharge products such as ozone is increased.

(2) In the tandem type color copying apparatus, as described above, it is necessary to use a scorotron, which generates a large amount of discharge products such as ozone, as a charging device. In order to forcibly exhaust the ozone and the like generated by the charging device, it is indispensable to arrange a large-capacity duct around the charging device, and there is also a problem that the copying device itself becomes large. I have.

(3) Further, in the tandem-type color copying apparatus, the exhaust device is forcibly evacuated from a large-capacity duct provided around the charging device, so that the size of the exhaust device is increased, and the size of the copying apparatus is increased. In addition, there is a problem that the cost is increased.

(4) Further, in the tandem-type color copying apparatus, since a large exhaust device needs to be used, exhaust noise increases, and the quietness required in offices and the like is reduced. It also has

As a technique that can solve these problems (1) to (4), the present inventor has studied and studied from a very long time to a recent one, and as a result, there are several methods listed below. It turns out that it has already been proposed.

(1) Japanese Patent Laid-Open Publication No. Sho 50-17646 The corona discharge device disclosed in Japanese Patent Laid-Open Publication No. Sho 50-17646 is for removing an AC corona, and surrounds the corona discharge electrode and the corona discharge electrode. In a corona discharge device having at least a shield having a discharge opening and a grid electrode provided near the discharge opening of the shield, the grid electrode is moved in the latter half of the relative movement with respect to the member to be neutralized. And the grid interval is narrow on the rear side.

(2) Japanese Unexamined Patent Publication No. 5-34999 The method of charging an electrophotographic apparatus according to Japanese Unexamined Patent Publication No. Hei 5-34999 discloses a method of charging an electrophotographic apparatus by providing a grid electrode at least downstream of a corona discharge device. With a configuration having corotron-type and scorotron-type functions, a step of directly applying a corona discharge to the surface of the photoconductor, and a step of applying a corona discharge to the surface of the photoconductor through a grid electrode,
This makes it possible to charge the photosensitive member to a uniform surface potential.

(3) JP-A-54-12847 In the corona charger according to JP-A-54-12847, the dielectric layer is fixed by corona ions on the front surface of a dielectric layer fixed on a ground electrode. In a corona charger provided with a corona wire whose side and back are surrounded by a shield electrode via a mesh grid charged to a specified voltage, an insulating layer or a high resistance layer is provided on an inner wall of the shield electrode. It is.

[0013]

However, the prior art described above has the following problems. (1) The corona discharge device disclosed in Japanese Patent Application Laid-Open No. 50-17646 is for removing an AC corona, and the technology cannot be immediately applied to a charging device. Further, even if this corona discharge device is used as a charging device, the technology disclosed in the publication discloses that the grid electrode is provided only in the latter half of the relative movement, so that the charging potential of the photosensitive drum and the like is not changed. However, there is a problem that the function of the grid electrode is not always expected, and it is difficult to make the charging potential uniform, because the method largely depends on charging in a portion of the first half where the grid electrode is not provided. doing.
Therefore, the first method is insufficient as a charging device for a tandem type color copying machine.

(2) In the charging method of the electrophotographic apparatus according to the second Japanese Patent Application Laid-Open No. 5-34999, most of the charging is performed by a corotron having a high discharge current utilization efficiency, and unevenness is corrected by a scorotron. Therefore, each corona discharge current can be reduced. However, in consideration of discharge unevenness and deterioration, the corona discharge current of one wire cannot be reduced without limit. Therefore, the total discharge current of a plurality of wires is rather larger than that of a normal scorotron alone. However, the overall use efficiency of the discharge current is rather deteriorated, and the effect of reducing ozone or the like cannot be expected.

(3) Third Japanese Patent Application Laid-Open No. 54-12847
From the viewpoint of improving the utilization efficiency of the discharge current, the corona charger according to the publication discloses that an extra layer does not flow through the shield electrode by providing an insulating layer or a high resistance layer on the inner wall of the shield electrode, The effect can be expected,
It is necessary to determine parameters such as the distance between the insulator and the wire and the voltage applied to the wire in consideration of the margin for unevenness and deterioration of the discharge. Therefore, in order to reduce the influence of discharge unevenness and deterioration, it is necessary to set the distance between the corona wire and the shield electrode to be large, and the corona charger becomes large accordingly. . In addition, considering that most of the discharge current flowing in the photoconductor direction flows to the grid even if the current to the shield electrode is restricted, the efficiency of use of the discharge current is greatly improved, and ozone etc. is reduced. However, there is a problem that the great effect of making it impossible can be expected.

Therefore, the present invention has been made to solve the above-mentioned problems of the prior art. It is an object of the present invention to greatly improve the efficiency of use of discharge current and to achieve uniform charging. It is an object of the present invention to provide a charging device which can sufficiently satisfy the characteristics and can greatly reduce the generation of ozone and the like.

[0017]

That is, according to the first aspect of the present invention, a discharge electrode is stretched inside a conductive shield member, and a high voltage is applied to the discharge electrode to form a conductive shield. In a charging device that performs corona discharge toward a member to be charged moving from an opening of the member to charge the member to be charged, a charging device is provided between the opening of the conductive shield member and the member to be charged. The grid electrode is configured to partially intervene on the downstream side in the moving direction of the member.

According to a second aspect of the present invention, there is provided a conductive shield member, and a discharge electrode which is stretched inside the conductive shield member and generates a corona discharge by applying a high voltage. In a charging device having a grid electrode disposed between the discharge electrode and the member to be charged,
The grid electrode is located on the downstream side in the moving direction of the member to be charged, and the upstream side in the moving direction of the member to be charged is configured such that the member to be charged is exposed to the discharge electrode over a predetermined width. is there.

Further, according to a third aspect of the present invention, in the charging device according to the first or second aspect, before the member to be charged moves to a region of the charging device where the grid electrode is provided, The charging member is configured so that the charging potential charged by the region where the grid electrode is not provided is 90% or less of the charging potential of the member to be charged after passing through the charging device.

Further, the invention described in claim 4 is:
3. The charging device according to claim 1, wherein the member to be charged is charged by a region where the grid electrode is not provided before the member to be charged moves to a region where the grid electrode of the charging device is provided. A charging potential control means for controlling the charging potential to be 90% or less of the charging potential of the member to be charged after passing through the charging device is provided.

According to a fifth aspect of the present invention, in the charging device of the fourth aspect, the charging potential control means is disposed at a position which is not electrostatically shielded from the discharge electrode. It is configured to include a discharge distribution control electrode and an applied voltage control means for controlling a voltage applied to the discharge distribution control electrode.

According to a sixth aspect of the present invention, in the charging device according to the fourth aspect, the charging potential control means comprises a discharge current control means for controlling a discharge current flowing through the discharge electrode. It is what was constituted.

According to a seventh aspect of the present invention, in the charging device according to the fourth aspect, the member to be charged is a photosensitive member, and the charging potential control means includes a member to be charged of the charging device. And a light amount control means for controlling the light amount of the light to be irradiated on the upstream side in the moving direction.

[0024] Still further, the invention according to claim 8 is as follows.
5. The charging device according to claim 4, wherein a set value of the charging potential controlled by the charging potential control unit is set according to at least one of environmental conditions such as temperature and humidity and a cause of deterioration such as a change in film thickness of the member to be charged. It is configured to be changed.

Further, according to a ninth aspect of the present invention, in the charging device according to the eighth aspect, the set value of the charging potential controlled by the charging potential control means is changed in an image forming apparatus using the charging device. The selection is made from a predetermined setting table according to the deterioration index of the member to be charged, such as the number of formed images of the apparatus, the number of rotations of the member to be charged, and the operation time of the member to be charged.

According to a tenth aspect of the present invention, there is provided an image forming apparatus using the charging device according to the fourth aspect and having a potential measuring means for measuring the potential of the charged member after charging. After setting the applied voltage to 90% or less of the target charged potential of the member to be charged, the charging potential of the member to be charged before the member relatively moves to the area where the grid electrode is provided is controlled. The charging potential control means is charged by sequentially performing a plurality of settings, the potential of the member to be charged after passing through the charging device is measured by the potential measurement means,
The apparatus is configured to include a set value control unit that calculates a set value at which the potential of the member to be charged is substantially equal to the potential applied to the grid electrode and sets the charge potential control unit.

Further, the invention described in claim 11 is:
11. The image forming apparatus according to claim 10, wherein the charging potential control means for controlling the charging potential of the member to be charged before the member relatively moves to the area where the grid electrode is provided, comprises: It is configured to include a discharge distribution control electrode provided at a position that is not shielded, and an applied voltage control unit that controls a voltage applied to the discharge distribution control electrode.

According to a twelfth aspect of the present invention, in the image forming apparatus according to the tenth aspect, the charging potential of the charged member before the member relatively moves to the area where the grid electrode is provided. Is configured to be a discharge current control means for controlling a discharge current flowing through the discharge electrode.

According to a thirteenth aspect of the present invention, in the image forming apparatus according to the tenth aspect, the member to be charged is a photosensitive member, and the member to be charged is relatively moved to a region where the grid electrode is provided. The charging potential control means for controlling the charging potential of the member to be charged before the charging is a light amount control means for controlling the amount of light irradiated on the upstream side in the moving direction of the member to be charged of the charging device. It is.

As the member to be charged, for example,
Although a drum-shaped or belt-shaped photoconductor is used, the present invention is not limited to this, and a drum-shaped or belt-shaped photoconductor may be used.

[0031]

According to the present invention, basically, a grid electrode is partially interposed between an opening of a conductive shield member and a member to be charged and downstream in the moving direction of the member to be charged. In addition to efficiently charging the member to be charged in the region where the grid electrode does not intervene, uniformly charging the member to be charged in the region where the grid electrode intervenes, the discharge current utilization efficiency can be greatly improved, and The uniformity can be sufficiently satisfied, and the generation of ozone and the like can be greatly reduced.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on an embodiment shown in the drawings.

FIG. 2 is an overall configuration diagram showing one embodiment of a tandem type color copying apparatus to which the charging device according to the present invention can be applied.

In this tandem type color copying apparatus, as shown in FIG. 2, a document 2 placed on a platen glass 1 is scanned by a color CCD sensor 3 via a scanning optical system including a light source and a scanning mirror. Is read as an RGB analog image signal by an image scanner equipped with. The RGB analog image signals read by the color CCD sensor 3 are converted into KYMC image signals by the image processing unit 4 and temporarily stored in a memory provided inside the image processing unit 4.

As shown in FIGS. 2 and 3, the tandem type color copying apparatus has black (K), yellow (Y), magenta (M), and cyan (C) inside the copying apparatus main body. 4) Four image forming units 5 corresponding to each color
K, 5Y, 5M, and 5C, and these image forming units 5K, 5Y, 5M, and 5C are arranged in parallel at predetermined intervals along the horizontal direction. From the image processing unit 4, the image forming units 5K, 5Y, 5
Laser beam scanning devices 8K, 8 provided in M, 5C
Image data of each color is sequentially output to Y, 8M, and 8C at a predetermined timing. Then, from these laser beam scanning devices 8K, 8Y, 8M, 8C, a laser beam LB modulated according to image data is emitted, and this laser beam LB is applied to each of the image forming units 5K, 5K, and 5C.
Y, 5M, and 5C, the photosensitive drums 6K, 6Y,
The surfaces of 6M and 6C are scanned and exposed to form an electrostatic latent image. The electrostatic latent images formed on the photosensitive drums 6K, 6Y, 6M, and 6C are stored in the respective image forming units 5K, 5K, and 5C.
Developing devices 9K, 9Y, 9M provided in Y, 5M, 5C,
9C, the toner image is developed as a toner image of each color of black (K), yellow (Y), magenta (M), and cyan (C).

The photosensitive drums 6K, 6Y, 6M, 6
As shown in FIG. 3, the toner images of the respective colors formed on C are sequentially transferred onto transfer paper 14 conveyed below the respective photosensitive drums 6K, 6Y, 6M, 6C. The transfer paper 14 to which the toner image of each color is transferred is a transfer paper 14 of a predetermined size from any of the plurality of paper feed cassettes 15, 16, 17.
The sheet is conveyed via a sheet conveying path 22 provided with 20, 21 and the like. The transfer paper 14 fed from any of the paper feed cassettes 15, 16, 17 is sent out onto a transfer belt 24 by a registration roller 23 which is rotated at a predetermined timing.

The transfer belt 24 is driven by the drive roller 2
5, a stripping roller 26, a tension roller 27, and an idle roller 28, which are endlessly wound around with a constant tension, and are rotationally driven by a dedicated motor (not shown) having excellent constant speed. The drive roller 25 is driven to circulate at a predetermined speed in the direction of the arrow. As the transfer belt 24, for example, a film made of a synthetic resin having flexibility such as polyethylene terephthalate or polyvinylidene fluoride is formed in a belt shape, and both ends of the synthetic resin film formed in the belt shape are welded or the like. By being connected, an endless belt is used.

The leading end of the transfer paper 14 conveyed by the transfer belt 24 and the leading end of the image on the first photosensitive drum 6K formed by the first image forming unit 5K are located on the photosensitive drum 6K. The paper feeding timing and the image writing timing are determined so that they coincide at the lowest transfer point. The black visible image on the photosensitive drum 6K is transferred to the transfer sheet 14 having reached the transfer point by the transfer corotron 11K, and further moves to a transfer point immediately below the photosensitive drum 6Y. next,
The transfer paper 14 that has reached the transfer point immediately below the photosensitive drum 6Y transfers a yellow visible image on the photosensitive drum 6Y in the same manner as the transfer on the photosensitive drum 6K. Similarly, the transfer paper 14 that has completed all the transfer is further conveyed by the transfer belt 24 and, when reaching the vicinity of the stripping roller 26, as shown in FIG. The stripping roller 2 having a small radius of curvature.
6 and the peeling claw 30, the film is peeled from the transfer belt 24. Thereafter, the four color toner images transferred onto the transfer paper 14 are fixed on the transfer paper 14 by the heating roller 32a and the pressure roller 32b of the fixing device 31, and the discharge tray 33 shown in FIG. 34, and the color image copying process is completed.

When copying a full-color image on both sides of the transfer sheet 14, the transfer sheet 14 having a color image formed on one side is not discharged directly by the discharge roller pair 33 as shown in FIG. , Switching plate 35
The transfer direction of the transfer paper 14 is switched downward by
With the transfer paper 14 turned upside down via the paper transport path 40 including the paper transport roller pairs 36, 37, 38, 39, etc., the transfer paper 14 is again transferred onto the transfer belt 24 via the paper transport path 22. The transfer image is conveyed, and a color image is copied on the back surface of the transfer sheet 14 by the same process as described above.

The four image forming units 5K, 5Y, 5M, and 5 for the above black, yellow, magenta, and cyan colors
C are all formed similarly as shown in FIG. 3, and these four image forming units 5K, 5Y, 5M,
5C, black, yellow, magenta, and cyan toner images are sequentially formed. The image forming units 5K, 5Y, 5M for each of the above colors,
5C is a photosensitive drum 6K, 6Y as a member to be charged,
6M, 6C, and these photosensitive drums 6K,
The surfaces of 6Y, 6M and 6C are provided with scorotrons 7K, 7Y and 7 for primary charging as charging devices to which the present invention is applied.
After being uniformly charged by the laser beams M and 7C, laser beams LB for image formation emitted from the laser beam scanning devices 8K, 8Y, 8M and 8C in accordance with image data are scanned and exposed, and static electricity corresponding to each color is obtained. An electrostatic latent image is formed. The electrostatic latent images formed on the surfaces of the photosensitive drums 6K, 6Y, 6M, and 6C are stored in the respective image forming units 5K, 5Y, 5M, and 5C.
The developing devices 9K, 9Y, 9M, and 9C of C respectively develop black, yellow, magenta, and cyan toners into visible toner images, and these visible toner images are transferred to the pre-transfer charger 10K, 10Y, 10M, 1
After receiving the pre-transfer charging by the charging of 0C, the transfer charger 1
Due to the electrification of 1K, 11Y, 11M, and 11C, the image is sequentially transferred to the transfer sheet 14 held on the transfer belt 24. The transfer paper 14 onto which the toner images of the black, yellow, magenta, and cyan colors have been transferred is separated from the transfer belt 24, and then subjected to the fixing process by the fixing device 31 as described above, thereby forming a color image. The formation takes place.

Further, as described above, the transfer paper 14 is supplied from one of the plurality of paper feed cassettes 15, 16 and 17, and is conveyed onto the transfer belt 24 at a predetermined timing by the registration rollers 23. Then, the sheet is held and conveyed while being electrostatically attracted onto the transfer belt 24 by the charging device 41 and the charging roller 42 for adsorbing the sheet.

The photosensitive drums 6K, 6Y, 6
After the transfer process of the toner image is completed, M and 6C are neutralized by the pre-cleaning neutralizers 12K, 12Y, 12M and 12C, and the cleaning devices 13K and 13C.
The remaining toner and the like are removed by Y, 13M, and 13C to prepare for the next image forming process.

As shown in FIG. 3, the transfer belt 24 is provided with a pair of charge removing corotrons 43 and 44 for the transfer belt in the orbit after the transfer paper 14 is peeled off.
And the surface of the transfer belt 24 is cleaned of toner, paper dust, and the like by a cleaning device 47 including a rotating brush 45 and a blade 46.

The charging device according to this embodiment is, for example, a tandem-type color copying device configured as described above, which is a charging device that uniformly charges the surface of the photosensitive drum of each image forming unit. What is used.

More specifically, in the charging device according to this embodiment, the discharge electrode is stretched inside the conductive shield member, and a high voltage is applied to the discharge electrode, whereby the opening of the conductive shield member is opened. In a charging device that performs corona discharge toward a member to be charged moving from the charging member to charge the member to be charged, the moving direction of the member to be charged is between the opening of the conductive shield member and the member to be charged. It is configured to partially interpose a grid electrode on the downstream side.

As shown in FIG. 1, a charging device 50 according to this embodiment includes a conductive shield 52 disposed opposite to a drum-shaped or belt-shaped photosensitive member 51 as a member to be charged. A discharge wire 53 is disposed inside the conductive shield 52 as a discharge electrode, and a grid electrode 54 controls a discharge current from the discharge wire 53 to the photoconductor 51. The conductive shield 52 is made of a metal plate such as stainless steel.
A horizontal plate portion 52a disposed in parallel with the surface of the photosensitive member 51, and both side plate portions 52b disposed at both ends of the horizontal plate portion 52a so as to be orthogonal to the photosensitive member 51 side.
The portion facing 1 is an opening 55 that is fully open. The discharge wire 53 is connected to the conductive shield 5.
In the center near the opening 55 of the second conductive shield 52,
The discharge wire 53 is stretched along the longitudinal direction (perpendicular to the drawing), and the stretched position of the discharge wire 53 is set as appropriate, such as at the center of the conductive shield 52 or near the opening 55. A predetermined high voltage (for example, −5 kV) is applied to the discharge wire 53 by a DC high-voltage power supply 56.

In the charging device 50, a grid electrode 54 is provided below the opening 55 of the conductive shield 52 and between the conductive shield 52 and the photoconductor 51 on the downstream side in the moving direction of the photoconductor 51. Are arranged only to intervene. The grid electrode 54 is connected to the discharge wire 53
Is located at a predetermined distance L1 below, and the tip 54a of the photosensitive member 51 on the upstream side in the moving direction is located at a position separated from the side plate portion 52b of the conductive shield 52 by a predetermined distance L2. Further, as the grid electrode 54, for example, an electrode made of a mesh-like thin metal plate is used. However, the present invention is not limited to this, and it is needless to say that various types of grid electrodes 54 can be used, such as those in which a plurality of thin metal wires are arranged at predetermined intervals.

The grid electrode 54 has a DC power supply 57
, A predetermined voltage (for example, -700 V) is applied. The voltage applied to the grid electrode 54 is set to, for example, a voltage substantially equal to the charged potential of the photoconductor 51. In the illustrated embodiment, the conductive shield 52
The same predetermined voltage as that of the grid electrode 54 (for example, -7
00V) is applied.

With the above configuration, the charging device according to this embodiment can greatly improve the efficiency of using the discharge current and sufficiently satisfy the uniformity of charging as follows. It is possible to greatly reduce the generation of ozone and the like.

That is, in the charging device 50 configured as described above, as shown in FIG. 1, a predetermined high voltage (for example, -5 k
V) and a predetermined high voltage (for example, −700 V) from the DC power supply 57 to the grid electrode 54, thereby generating a corona discharge from the discharge wire 53 and accompanying the corona discharge. The surface of the photoconductor 51 is charged by corona ions. that time,
In the charging device 50, the upstream side in the moving direction of the photoconductor 51,
That is, since the photoconductor 51 is exposed to the discharge current generated from the discharge wire 53 in the corotron region where the grid electrode 54 does not intervene, the corona ions directly reach the photoconductor 51, so that FIGS. As shown in (2), the surface of the photoconductor 51 can be efficiently charged.

On the other hand, the conventional Scorotron 100
Since the grid electrode 103 is interposed on the entire surface between the discharge wire 104 and the photoconductor 105 as shown in FIG. 19, a part of the corona ions toward the photoconductor 105 also flows to the grid electrode 103. The utilization efficiency of the discharge current is reduced accordingly.

Further, in the charging device 50, the photosensitive member 5
Since the grid electrode 54 is partially interposed on the downstream side in the moving direction of the photoconductor 1, the surface of the photoconductor 51 charged efficiently in the corotron region has a charging potential unevenness of about ± 5% as shown in FIG. Is present in the scorotron region where the grid electrode 54 exists,
Can be controlled by the voltage applied to the grid electrode 54. Therefore, the charging device 5
By using 0, the surface of the photoconductor 51 can be efficiently and uniformly charged to a predetermined potential.

However, in the charging device 50 according to the above-described embodiment, the surface of the photoconductor 51 is charged at a predetermined charging potential or higher (in the above numerical example, a potential lower than -700 V) in the corotron region where the grid electrode 54 is not interposed. ) In the scorotron region provided with the grid electrode 54 located on the downstream side in the moving direction of the photoconductor 51,
Cannot be controlled to a predetermined potential. Therefore, in the corotron region of the charging device 50, it is necessary to set the charging potential of the photoconductor 51 to a value lower than a predetermined charging potential (about -500 V).

More specifically, in the charging device 50 configured as described above, the grid electrode 54 is provided on the downstream side (scorotron region) in the moving direction of the photoconductor 51.
If the surface potential of the photoconductor 51 is lower than the potential of the grid electrode 54, corona ions flow through the gap between the grid electrodes 54 and flow to the photoconductor 51, but the surface potential of the photoconductor 51 is the same as the potential of the grid electrode 54. Or higher,
Corona ions flow into the grid electrode 54.

Incidentally, the charging in the corotron region of the charging device 50 is directly affected by the non-uniformity of the discharge in the vicinity of the discharge wire 53, so that the charging is usually inferior in uniformity. Therefore, when the surface of the photoconductor 51 is charged to a value whose absolute value is lower than a target charging potential (for example, −700 V) by the corotron region of the charging device 50, the scorotron region located on the downstream side. Can be corrected as described above, but the surface of the photoconductor 51 has a target charging potential (for example, −70).
When charged to a value having an absolute value higher than (0 V) (for example, -900 V), all the discharge current in the scorotron region flows to the grid electrode 54 side, and thus cannot be corrected. As a result, there is a possibility that charging unevenness due to the corotron region of the charging device 50 may remain as it is.

Therefore, in order to uniformly and efficiently charge the surface of the photosensitive member 51 using the charging device 50 configured as described above, the potential of the maximum potential portion must be set in consideration of charging unevenness in the corotron region. It is necessary to limit the charge potential of the photoconductor 51 to be lower than the target charge potential. Normally, the non-uniformity of the discharge current due to the non-uniformity of the surface of the discharge wire 53 is expected to be about ± 5%. Therefore, even when the potential sensor that measures the surface potential of the photoconductor 51 measures a value of −5%. In order to prevent the maximum value from exceeding the target charging potential, the charging potential in the corotron region must be 90% or less of the final target charging potential. In addition, the surface of the discharge wire 53 is deteriorated by the discharge,
In the case where contamination is likely to occur due to the adhesion of foreign substances such as toner and discharge products, it is necessary to set the charging potential in the corotron region to a lower absolute value with a margin more than the target charging potential.

Shape factors that determine the charging potential in the corotron region of the charging device 50 are roughly determined by the arrangement of the discharge wires 53, the shape of the conductive shield 52, and the width L2 of the corotron region in the moving direction. The optimum value can be experimentally obtained using the position of the discharge wire 53 and the position L2 of the tip 54a of the grid electrode 54 on the corotron region side as adjustment parameters. In this case, it is important to control the arrangement of the discharge wires 53, the shape of the conductive shield 52, and the length of the corotron region in the process direction with high accuracy.

Therefore, in the charging device 50, the arrangement of the discharge wire 53, the shape of the conductive shield 52, the width L2 in the moving direction of the corotron region, and the like are appropriately set so that the charging potential in the corotron region finally reaches the target. It is necessary to set the charge potential to at least 90% or less.

Therefore, if necessary, the discharge wire 5
The charging device 50 is provided with a member capable of appropriately adjusting the arrangement of the discharge wire 53 and the grid electrode 5.
The arrangement of 4 may be configured so that a service engineer or the like can appropriately adjust the arrangement.

Second Embodiment FIG. 7 shows a second embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals and described. Before the member to be charged moves to the region where the grid electrode of the charging device is provided, the charging potential at which the member to be charged is charged by the region where the grid electrode is not provided is the charged member after passing through the charging device. The charging potential control means for controlling the charging potential to be 90% or less of the charging potential is provided. As the charging potential control means, for example, a discharge distribution control electrode disposed at a position that is not electrostatically shielded from the discharge electrode,
An apparatus comprising an applied voltage control means for controlling a voltage applied to the discharge distribution control electrode is used.

That is, in the charging device 50 according to the second embodiment, as shown in FIG.
Below the one side plate portion 52a of the conductive shield 52, the photosensitive member 5 in the opening 55 of the conductive shield 52.
It is arranged at the upstream end along one movement direction. As the discharge distribution control electrode 60, for example, a metal rod-shaped member having a rectangular cross section is used, but the present invention is not limited to this, and a metal wire or mesh-shaped member may be used. A predetermined voltage is applied to the discharge distribution control electrode 60 from a high voltage power supply 61 via a voltage control circuit 62.

The discharge distribution control electrode 60 is connected to the high voltage power source 6
1 through a voltage control circuit 62 to apply a predetermined voltage to one side plate 52 of the conductive shield 52.
b, an electric field is formed in the opening 55 through the discharge wire 5.
3 controls the distribution of the corona discharge current emitted to the photoconductor 51 through the opening 55 corresponding to the corotron region of the conductive shield 52.

That is, the grid electrode 54 is provided on the downstream side (scorotron region) of the photosensitive member 51 in the moving direction, and the surface potential of the photosensitive member 51 is lower than the potential of the grid electrode 54 as described above. For example, corona ions flow to the photoconductor 51. If the surface potential of the photoconductor 51 is equal to or higher than the potential of the grid electrode 54, all the corona ions flow into the grid electrode 54. By the way, the charging in the corotron region is
Since it is directly affected by the non-uniform discharge near the discharge wire 53, the uniformity is poor. Therefore, when the photosensitive member 51 is charged to a value whose absolute value is lower than the target charging potential, the correction is performed in the downstream scorotron region. However, when the absolute value is high, as shown in FIG.
It cannot be corrected. As a result, the non-uniformity of the charged potential on the surface of the photoconductor 51 remains as it is.

Therefore, in order to obtain a highly efficient charging device 50 having good charging uniformity, the potential of the maximum potential portion is limited to be lower than the target charging potential in consideration of charging unevenness in the corotron region. There is a need. The unevenness of the discharge current due to the unevenness of the surface of the discharge wire 53 is ± 5%
Therefore, even when the potential sensor measures a position of -5%, the maximum value needs to be 90% or less of the target charging potential so that the maximum value does not exceed the target charging potential. . When the surface of the discharge wire 53 is deteriorated by discharge or easily contaminated by toner adhesion or discharge products, the charging potential in the corotron region is set to a lower value with more margin than the target charging potential. Must be set to

For this reason, in the first embodiment, the arrangement of the discharge wire 53 and the shape of the conductive shield 52, which are the shape elements that determine the charging potential in the corotron region of the charging device 50, and the moving direction of the corotron region By adjusting the width L2 and the like as an initial state, the charging potential in the corotron region is set to a predetermined value whose absolute value is lower than the target charging potential.

However, when the photoreceptor 51 or the like as the charged body charged by the charging device 50 is worn due to repeated use for a long period of time and the thickness of the photoreceptor 51 as the charged body is reduced, the static electricity is reduced. Since the capacitance C of the photoconductor 51, which can be approximated as a capacitor having the capacitance C, increases,
It becomes necessary to increase the amount of charge Q (V = Q / C) for charging the surface of the photoconductor 51 to a predetermined potential V.
It is necessary to readjust the geometrical elements of the charging device 50 that are optimally designed with the initial film thickness of 1. Even in such a use environment, for example, an appropriate one is selected from a plurality of grid electrodes 54 having different widths prepared in advance and used,
By adjusting the relative positions of the charger and the grid electrode including the discharge wire 53, an insulating block (not shown) that supports the discharge wire 53, the conductive shield 52, and the like, an optimum state can be maintained even in repeated use. it can.

However, by adopting such a configuration, it is possible to cope with the aging of the photoconductor 51, but from the viewpoint of reliability and cost, a system that can automatically maintain the optimum state is desirable.

For this reason, in the charging device 50 according to the second embodiment, the charging potential in the corotron region can be automatically controlled, and as shown in FIG. A discharge distribution control electrode 60 is provided in the vicinity to control the discharge current in the corotron region.

The charging device 5 according to the second embodiment
The tandem-type color copying apparatus to which 0 is applied has potential measuring means for measuring the potential of the charged member after charging, and the voltage applied to the grid electrode is 90% or less of the target charged potential of the charged member. After setting the voltage, the charging potential control means for controlling the charging potential of the member to be charged before the member relatively moves to the area where the grid electrode is provided is charged by sequentially performing a plurality of settings and charging. A set value for measuring the potential of the member to be charged after passing through the device by a potential measuring unit, calculating a set value at which the potential of the member to be charged is substantially equal to the applied potential of the grid electrode, and setting the charging potential control unit. It is configured to include control means.

That is, in a tandem-type color copying apparatus to which the charging device 50 according to the second embodiment is applied, as shown in FIG.
A potential sensor 63 that measures the charged potential of the photoconductor drums 6K, 6Y, 6M, and 6C of M and 5C is disposed downstream of the image exposure positions of the photoconductor drums 6K, 6Y, 6M, and 6C. The potential distribution sensor 63 is controlled by a voltage control circuit 62 via a control circuit 64 including a CPU or the like that performs a control operation for controlling the charging potential of the photosensitive drums 6K, 6Y, 6M, and 6C. Is controlled.

Hereinafter, a specific control method of the charging device according to the second embodiment will be described.

In the charging device 50 configured as described above, the corona current (Iw) flowing out of the discharge wire 53
10, a shield current (Is) flowing from the discharge wire 53 to the conductive shield 52, a grid region current (Isc) flowing from the discharge wire 53 to the grid electrode 54, and a The current is divided into an inflow current (Icp) flowing to the portion of the photoconductor 51 (in the corotron region) exposed to the 53 and an inflow current (Ic) flowing from the discharge wire 53 to the discharge distribution control electrode 60. The current (Isc) flowing through the grid region and the current (Igp) flowing into the photoconductor 51 through the grid electrode 54 and the current (Igp) flowing into the grid electrode 54 in accordance with the potential difference between the grid electrode 54 and the photoconductor 51. Current (Ig). When these relationships are represented by mathematical expressions, they can be written as follows. Iw = Is + Isc + Icp + Ic (1) Isc = Ig + Igp (2)

When the charged potential of the photoconductor 51 is higher than the voltage of the grid electrode 54, most of the current flows into the grid electrode 54, and almost no current flows through the photoconductor 51. Therefore, when | Vc |> | Vg | is satisfied, Isc ≒ Ig (3) when the charged potential Vc of the photoconductor 51 and the voltage Vg of the grid electrode 54 at the time of entering the area of the grid electrode 54 are satisfied.

Further, the ratio of the current flowing from the discharge wire 53 to each part depends on the geometrical arrangement of each member, the voltage applied to each part, and the photosensitive member 51.
-Determined by the surface potential of Therefore, in the charging device 50, the discharge wire 53 is connected to the discharge distribution control electrode 60.
By applying a voltage that repels a corona current flowing from the substrate to the corotron region, or by applying a voltage that attracts the corona current, the current (Ic) flowing into the photoconductor 51 in the corotron region can be controlled. As a result, the charging potential in the corotron region of the photoconductor 51 to be charged is always set to a predetermined value whose absolute value is lower than the target charging potential by the inflow current (Ic) into the portion of the photoconductor 51 in the corotron region. It is possible to control so that

The thickness of the photosensitive member 51 is initially 2
The case where the charged potential is set to −650 V when the thickness is 5 μm will be described step by step.

The charging device 50 shown in FIG. 7 was used. Since the current Ic flowing into the photoconductor 51 in the corotron region is directly affected by the discharge unevenness of the discharge wire 53, the charging potential before entering the region of the grid electrode 54 (hereinafter, referred to as “rush potential”). To -65
It is necessary to control the voltage to 0 × 0.9 = −585 V or less. In addition, if the margin for the discharge unevenness of the discharge wire 53 is further increased, the system is more resistant to the contamination of the discharge wire 53. Therefore, in the second embodiment, the inrush potential is set to -500V.

In this case, the voltage of the grid electrode 54 is
When set to 00V, if the inrush potential is -400V or more,
As described above, most of the current (Isc) flowing in the region of the grid electrode 54 flows into the grid electrode 54. Therefore, the voltage of the grid electrode 54 is
By setting the absolute value to a value smaller than the inrush potential which is the charging potential of the photoconductor 51 charged in the corotron region of 0, the surface potential of the photoconductor 51 after passing through the charging device 50 is measured. , It is possible to substantially know the inrush potential. Further, as shown in FIG. 11, the applied voltage to the discharge distribution control electrode 60 is changed from, for example, −400 V in steps of 100 V by the voltage control circuit 62, and the applied voltage at which the inrush potential becomes −500 V is obtained by interpolation. Can be. At this time, the voltage applied to the discharge distribution control electrode 60 was -900V.

After setting the voltage applied to the discharge distribution control electrode 60 in this way, the charging voltage of the photoconductor 51 in the corotron region is automatically set to a desired potential by adjusting the voltage applied to the grid electrode 54. can do.

Next, if the photoconductor layer of the photoconductor 51 is gradually worn and its film thickness is reduced by using the photoconductor 51 for a long time, it is necessary to maintain a desired charging potential of the photoconductor 51. In addition, it is necessary to increase the amount of charge on the photosensitive member 51, and it is necessary to adjust the voltage applied to the discharge distribution control electrode 60 again in order to obtain the same rush potential as in the initial stage.

Here, the control of the charging device 50 when the thickness of the photosensitive member 51 becomes 13 μm, which is almost half of the initial state, will be described. The method of adjusting the voltage applied to the discharge distribution control electrode 60 is the same as the adjustment method in the initial state. In this case, when the voltage applied to the discharge distribution control electrode 60 is -750 V, The inrush potential became -500 V which was equal to the predetermined value.

As described above, according to the charging device 50 of the second embodiment, regardless of the deterioration of the photosensitive member 51,
The charging conditions can be maintained optimally. Also, a change in the charging condition due to a mechanical dimensional tolerance in manufacturing can be similarly automatically corrected without adjusting a relative position of the grid electrode 54 and the like.

Further, the use efficiency of the discharge current of the conventional type scorotron and the charging device according to the embodiment of the present invention will be described.

Here, the process speed is 160 mm /
An example of a case where the photosensitive member 51 moving in sec is charged to −650 V will be described. The current required only for purely charging the photoconductor 51 to a predetermined potential of −650 V is estimated to be −35 μA from the capacitance of the photoconductor 51.

A conventional opening width of 24 m as shown in FIG.
In the case of a m scorotron, it was necessary to operate at a total current of -600 μA in order to uniformly charge the photosensitive member.
In this case, the voltage of the grid electrode is set to -670V. In this case, the current use efficiency is 5.8%
(-35 / -600 * 100). The current flowing through the shield was about 30%. The current flowing through the grid electrode and the photoconductor through the grid electrode is the remaining 70
% Of which, the current flowing through the grid electrode is 92%,
The current flowing through the photoconductor is considered to be the remaining 8%.

On the other hand, a second embodiment of the present invention shown in FIG.
In the charging device 50 according to the above, the total current was −270 μA, and when −950 V was applied to the discharge distribution control electrode 60, the surface potential of the photoconductor 51 when entering the grid electrode 54 became −500 V. The current flowing through the grid electrode and the photoconductor 51 through the grid electrode is -110.
μA, the current flowing through the grid electrode is 93%,
The current flowing through the photoconductor 51 is estimated to be 7%.

The current use efficiency in this case is 13.0%
(-35 / -270 * 100), and the discharge current utilization efficiency was able to be greatly increased about twice or more as compared with the conventional type. The photoconductor 5 in the area of the grid electrode 54
Since the ratio of the current to 1 is also at the same level as that of the related art, it can be seen that the device has a sufficient capability with respect to charging uniformity.

The other configuration and operation are the same as those of the first embodiment, and the description is omitted.

Third Embodiment FIG. 12 shows a third embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals and described. The arrangement of the discharge distribution control electrodes is different from that of the second embodiment.

That is, in the charging device 50 according to the third embodiment, as shown in FIG.
Reference numeral 0 is disposed below one side plate 52 a of the conductive shield 52 at the downstream end of the opening 55 of the conductive shield 52 along the moving direction of the photoconductor 51.

Since the discharge distribution control electrode 60 is provided on the grid electrode 54 side, for controlling the discharge current flowing from the discharge wire 53 to the corotron region where the grid electrode 54 is not provided, for example, A positive voltage is applied to the discharge distribution control electrode 60 so as to attract the discharge current from the discharge wire 53, and the positive voltage is controlled. However, when a positive voltage is applied to the discharge distribution control electrode 60, the discharge current increases by the amount of the discharge current flowing from the discharge wire 53 to the discharge distribution control electrode 60. Therefore, by appropriately setting the position of the tip end portion 54 a of the grid electrode 54 and adjusting the opening width of the corotron region of the charging device 50, the discharge distribution control electrode 60 has the same polarity as the voltage applied to the grid electrode 54. A negative voltage may be applied to repel and control the discharge current flowing to the grid electrode 54, and of course, the discharge current flowing to the corotron region may be controlled.

The other configuration and operation are the same as those of the first embodiment, and the description thereof will be omitted.

Fourth Embodiment FIG. 13 shows a fourth embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals and described. The charging potential control means is configured to include a discharge current control means for controlling a discharge current flowing to the discharge electrode, and the discharge current is controlled by the discharge current control means, so that charging in the corotron region is performed. The potential is adjusted so as to be 90% or less of the target charging potential of the photoconductor.

That is, in the charging device 50 according to the fourth embodiment, as shown in FIG.
0 is not provided, and instead,
A discharge current control circuit 70 for controlling a discharge current flowing through the circuit is provided. In the charging device 50, FIG.
As shown in (5), the discharge current flowing through the discharge wire 53 is changed by the discharge current control circuit 70 at predetermined intervals, and the discharge current at which the inrush potential becomes -500 V can be obtained by interpolation.

The other structure and operation are the same as those of the second embodiment, and the description is omitted.

Fifth Embodiment FIG. 15 shows a fifth embodiment of the present invention. The same parts as those of the first embodiment are denoted by the same reference numerals and described. The charging potential control means comprises light quantity control means for controlling the quantity of light irradiated to the upstream side in the moving direction of the member to be charged of the charging device, and by controlling the quantity of light applied to the corotron area, Of the target charging potential of the photosensitive member to 9
It is configured to adjust to be 0% or less.

That is, in a tandem-type color copying apparatus to which the charging device 50 according to the fifth embodiment is applied, as shown in FIG.
M, 5C, the photoconductor drums 6K, 6Y, 6M, 6C, the photoconductor drums 6K, 6
An eraser light source 80 for erasing residual charges of Y, 6M, and 6C and preparing for the next image forming step is provided.
A part of the light emitted from the charging device 50 is also arranged to irradiate the corotron region of the charging device 50 where the grid electrode 54 is not provided. Further, in the fifth embodiment, a light amount control circuit 81 for controlling the light amount of light emitted from the eraser light source 90 is provided. In the tandem type color copying machine, the photosensitive drum 6K,
The photosensitive drums 6K, 6Y, 6Y, 6M, 6C
By detecting the surface potentials of the photoconductor drums 6K, 6Y, 6C by detecting the surface potentials of the photoconductor drums 6K, 6Y,
The inrush potentials of M and 6C are controlled to be equal to a predetermined potential.

The other configuration and operation are the same as those of the second embodiment, and the description is omitted.

Sixth Embodiment FIG. 16 shows a sixth embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals and described. The setting of the charging potential controlled by the charging potential control means is changed in accordance with at least one of environmental conditions such as temperature and humidity and a cause of deterioration such as a change in thickness of the member to be charged.

That is, in the tandem type color copying machine to which the charging device 50 is applied, the photosensitive drums 6K, 6K
The charging potentials of Y, 6M, and 6C may change according to environmental changes such as temperature and humidity. Therefore, the tandem-type color copying apparatus to which the charging device 50 according to the sixth embodiment is applied includes a temperature sensor 90 and a humidity sensor 91 for detecting the temperature and humidity inside the copying apparatus as shown in FIG. According to the detection values of the temperature sensor 90 and the humidity sensor 91, the photosensitive drums 6K, 6Y, 6M, and 6C are gridded by the applied voltage control circuit 92 with reference to a table as shown in FIG. It is configured to control a charging potential charged by a region where the electrode 54 is not provided.

Thus, the photosensitive drum 6
The surface potentials of K, 6Y, 6M, and 6C can be accurately controlled to predetermined potentials.

The other configuration and operation are the same as those of the second embodiment, and the description is omitted.

Seventh Embodiment FIG. 18 shows a seventh embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals and described. The set value of the charging potential controlled by the charging potential control means, the number of image formation of the image forming apparatus using the charging device, the number of rotations of the member to be charged,
It is configured to select from a preset setting table according to the deterioration index of the member to be charged such as the operation time of the member to be charged.

That is, in the charging device 50 according to the seventh embodiment, even if the above-described adjustment is performed initially, if the film thickness of the photosensitive member decreases with time, a desired charging potential is obtained. Since the required amount of charge increases, it is important to make appropriate adjustments in order to maintain an optimal state.

Therefore, in the charging device 50 according to the seventh embodiment, it is known that there is a good correlation between the rotation speed of the photoconductor, the number of copies used, and the reduction amount of the photoconductor thickness. The number of copies is detected by the number-of-copies detecting means 95, and a set value determined in advance according to those values is used as a set value of the charging potential controlled by the charging potential control circuit 96. .

The other configuration and operation are the same as those of the second embodiment, and the description is omitted.

[0106]

According to the present invention, which has the above-described structure and operation, it is possible to greatly improve the efficiency of using a discharge current without sacrificing image quality and maintainability, and to discharge ozone and the like. Since the amount of generated products can be reduced, an exhaust system with a small air volume can be used. The deterioration of the photoreceptor and the like can be prevented.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of a charging device according to the present invention.

FIG. 2 is a configuration diagram showing a tandem-type color copying apparatus to which the charging device according to the present invention can be applied.

FIG. 3 is a configuration diagram showing a main part of a tandem-type color copying apparatus to which the charging device according to the present invention can be applied.

FIG. 4 is a graph showing charging characteristics of the charging device shown in FIG.

FIG. 5 is a graph showing charging characteristics of the charging device shown in FIG.

FIG. 6 is an explanatory diagram showing unevenness of a charging potential of a member to be charged by a discharge wire.

FIG. 7 is a configuration diagram showing a second embodiment of the charging device according to the present invention.

FIG. 8 is an explanatory diagram showing charging characteristics of the charging device shown in FIG.

FIG. 9 is a configuration diagram showing a second embodiment of the charging device according to the present invention.

FIG. 10 is an explanatory diagram illustrating a charging operation of the charging device according to the second embodiment.

FIG. 11 is a graph showing a control state of a charging potential of the charging device according to the second embodiment.

FIG. 12 is a configuration diagram showing a third embodiment of the charging device according to the present invention.

FIG. 13 is a configuration diagram showing a fourth embodiment of the charging device according to the present invention.

FIG. 14 is a graph showing a control state of a charging potential of the charging device according to the fourth embodiment.

FIG. 15 is a configuration diagram showing a fifth embodiment of the charging device according to the present invention.

FIG. 16 is a configuration diagram showing Embodiment 6 of the charging device according to the present invention.

FIG. 17 is an explanatory diagram showing a setting table of the charging device according to the sixth embodiment.

FIG. 18 is a configuration diagram showing a charging device according to a seventh embodiment of the present invention.

FIG. 19A is a configuration diagram showing a conventional charging device, and FIGS. 19B and 19C are graphs showing charging characteristics of the conventional charging device, respectively.

[Explanation of symbols]

Reference Signs List 50 charging device, 51 photoconductor, 52 conductive shield, 53 discharge wire, 54 grid electrode, 55
Opening, 56 DC high voltage power supply.

Claims (13)

[Claims] Claims: 1. A discharge electrode is stretched inside a conductive shield member, and a high voltage is applied to the discharge electrode.
In a charging device for charging a member to be charged by performing corona discharge toward the member to be charged moving from the opening of the conductive shield member, the charging device may be located between the opening of the conductive shield member and the member to be charged. A charging electrode in which a grid electrode is partially interposed downstream in the moving direction of the member to be charged. 2. A conductive shield member, a discharge electrode stretched inside the conductive shield member, and generating a corona discharge by applying a high voltage, between the discharge electrode and the member to be charged. The grid electrode is located downstream of the moving direction of the member to be charged, and the charging member discharges over a predetermined width on the upstream side of the moving direction of the member to be charged. A charging device, which is exposed to an electrode. 3. The charging device according to claim 1, wherein the charged member is not provided with the grid electrode before the charged member moves to a region of the charging device where the grid electrode is provided. The charging potential charged by the region is 90% of the charging potential of the member to be charged after passing through the charging device.
% Or less. 4. The charging device according to claim 1, wherein the charged member is not provided with the grid electrode before the charged member moves to a region of the charging device where the grid electrode is provided. The charging potential charged by the region is 90% of the charging potential of the member to be charged after passing through the charging device.
%, Provided with a charging potential control means for controlling the charging potential to be equal to or less than 10%. 5. The charging device according to claim 4, wherein the charging potential control means is disposed at a position not electrostatically shielded from the discharge electrode, and a discharge distribution control electrode;
A charging device, comprising: applied voltage control means for controlling a voltage applied to the discharge distribution control electrode. 6. The charging device according to claim 4, wherein said charging potential control means comprises discharge current control means for controlling a discharge current flowing through said discharge electrode. 7. The charging device according to claim 4, wherein the member to be charged is a photoreceptor, and the charging potential control means controls the light emitted to an upstream side of the member to be charged in the moving direction of the charging device. A charging device comprising light amount control means for controlling a light amount. 8. The charging device according to claim 4, wherein the set value of the charging potential controlled by the charging potential control means is set to environmental conditions such as temperature and humidity and deterioration factors such as a change in film thickness of the member to be charged. The charging device is changed according to at least one of the following. 9. The charging device according to claim 8, wherein the set value of the charging potential controlled by the charging potential control means is set to the number of images to be formed by an image forming apparatus in which the charging device is used. A charging device, wherein the charging device is selected from a preset setting table according to a deterioration index of the member to be charged, such as a rotation speed and an operation time of the member to be charged. 10. An image forming apparatus having a potential measuring means for measuring the potential of a charged member after charging using the charging device according to claim 4. After setting the voltage to 90% or less of the charging potential of the charging member, the charging potential control means for controlling the charging potential of the charging member before the charging member relatively moves to the region where the grid electrode is provided, and a plurality of settings are sequentially performed. The potential of the member to be charged after passing through the charging device is measured by a potential measuring unit, and a set value at which the potential of the member to be charged becomes substantially equal to the potential applied to the grid electrode is calculated. An image forming apparatus comprising a set value control unit for setting a control unit. 11. The image forming apparatus according to claim 10, wherein the charging potential control means for controlling the charging potential of the member to be charged before the member relatively moves to a region where the grid electrode is provided, comprises: An image forming apparatus comprising: a discharge distribution control electrode provided at a position that is not electrostatically shielded from an electrode; and an applied voltage control unit that controls a voltage applied to the discharge distribution control electrode. 12. The image forming apparatus according to claim 10, wherein the charging potential control means for controlling the charging potential of the member to be charged before the member relatively moves to a region where the grid electrode is provided, comprises: An image forming apparatus, which is a discharge current control unit that controls a discharge current flowing through an electrode. 13. The image forming apparatus according to claim 10, wherein the member to be charged is a photosensitive member, and the charged potential of the member to be charged before the member relatively moves to a region where the grid electrode is provided. An image forming apparatus, wherein the charging potential control means to be controlled is a light quantity control means for controlling a light quantity of light emitted to an upstream side in a moving direction of a member to be charged of the charging device.