JPH10198131A - Electrifier and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the shaving degree of the front layer of an electrified means and to prolong its endurance limit by detecting AC and DC currents flowing into the means to be electrified from an electrifying means when fixed vibrating voltage is applied to the electrifying means and controlling an AC voltage or the AC current applied to the electrifying means at the time of forming an image in accordance with the detected current value. SOLUTION: The AC and DC currents flowing in a photoreceptor drum 1 from an electrifying roller 3, when the fixed vibrating voltage is applied to the electrifying roller 3 is detected and the peak-to-peak voltage of the AC voltage applied to the electrifying roller 3 is controlled according to the detected value. Therefore, a CPU 12 controls the AC voltage or current applied to the electrifying roller 3, according to the results of the detection from a current detecting means 13 for detecting the AC and DC currents flowing in the drum 1 from the electrifying roller 3. Thus, the peak-to-peak voltage of the applied AC voltage can be adjusted to the absolute minimum level corresponding to ambient temp. and humidity and the film thickness of the front layer of the drum 1.

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 charging a surface of a member to be charged, and an electrophotographic apparatus (copying machine, printer, etc.) having the charging device for executing an image forming process including image exposure, and a static device. The present invention relates to an image forming apparatus such as an electronic recording device.

[0002]

2. Description of the Related Art Conventionally, in this type of image forming apparatus,
2. Description of the Related Art A corona charging method using corona discharge has been widely used as a charging device for charging a charged member such as a photoconductor or a dielectric as an image carrier. However, the corona charging method using the corona discharge generates a large amount of undesired ozone at the time of discharge, and also requires a high-pressure power source, and so requires a countermeasure or mechanism.
The equipment has increased in size and cost. For this reason, in recent years, low power consumption has been achieved, and a contact charging method that generates very little ozone has been put to practical use.

In this contact charging system, a charging means is disposed in direct contact with or close to a charged means, and a voltage is applied to the charging means to form a roller-shaped image carrier as a charged means. In this method, the surface of a photoconductor (hereinafter, referred to as a photoconductor drum) is subjected to a charging process (including a charge removing process).

FIG. 7 is a cross-sectional view showing a schematic structure of a conventional contact charging device. Reference numeral 1 denotes a photosensitive drum, which is an image bearing member as a member to be charged, and is rotatably supported in the direction of arrow R1. The photosensitive drum 1 has a conductive base layer lb of aluminum or the like and a photoconductive layer 1a formed on the outer periphery thereof.
Is an OPC photosensitive drum having a basic constitution layer.

Reference numeral 3 denotes a roller-type charging member (hereinafter, referred to as a charging roller) as a charging means. The charging roller 3 includes a central core 3c and a conductive layer 3b formed on the outer periphery thereof.
And a resistance layer 3a formed on the outer periphery thereof as a basic structure.

The charging roller 3 is configured such that both ends of a cored bar 3c are rotatably supported by bearing members (not shown),
Are pressed in contact with the photosensitive drum 1 by a pressing means (not shown) with a predetermined pressing force.
The rotation is driven by the rotation driving of. Alternatively, a gear or the like may be attached to the cored bar 3c, and the driving force may be transmitted from a motor to rotate the photosensitive drum 1 independently in the forward or reverse direction.

Reference numeral 4 denotes a power supply for applying a voltage to the charging roller 3. The power supply 4 is electrically connected to the metal core 3 c of the charging roller 3, and a predetermined voltage is applied from the power supply 4 to the charging roller 3. When the photosensitive drum 1 is driven to rotate, the photosensitive drum 1 is rotated.
The charging roller 3 is pressed against and applied with a voltage,
The outer peripheral surface of the photosensitive drum 1 is charged to a predetermined polarity potential.

In this case, a method of applying only a DC voltage to the charging roller (DC charging method) and a method of applying an oscillating voltage having an amplitude that changes with time, such as an AC voltage or a voltage obtained by superimposing a DC voltage on an AC voltage. (AC charging system). In particular, the latter AC charging method is preferably used because it has better charging uniformity and provides a beautiful image than the DC charging method.

Note that the charging member does not necessarily need to be in contact with the charged member, as long as the dischargeable region determined by the gap voltage and the corrected Paschen curve between the charging member and the charged member is reliably guaranteed. And non-contact (proximity), which is also included in the category of contact charging.

[0010]

However, the AC charging system has the following problems.

That is, the AC charging method has a greater amount of scraping of the photosensitive drum than the DC charging method, which hinders a longer life. This scraping of the photoreceptor drum is particularly caused by the OPC
This is remarkable when a photoconductor drum is used, and the photoconductive layer 1a serving as a surface layer is mainly scraped. Here, the shaving of the photoconductor drum means that the surface of the photoconductor drum is shaved and the thickness of the photoconductive layer 1a becomes thin.

When the thickness of the photoconductive layer 1a is reduced, the photosensitivity is reduced accordingly, so that the surface potential does not drop sufficiently and the contrast between the dark portion potential portion and the bright portion potential portion narrows. As a result, in the normal development system, if an attempt is made to obtain a sufficient development contrast at the time of development, a sufficient reverse contrast cannot be obtained with respect to the bright portion potential portion. Phenomenon becomes remarkable. Further, in the reversal development system, since the development contrast cannot be sufficiently obtained, the image density becomes low.

For the reasons described above, when controlling the oscillating voltage applied to the charging roller so that the alternating current flowing from the charging roller to the photosensitive drum becomes a certain current,
Regardless of the environmental temperature, humidity, etc., and regardless of the initial stage or end stage of use of the photoconductor drum, control is performed so that a sufficient and sufficient AC current is always supplied so that a good charging process of the photoconductor drum can be performed. In many cases, an unnecessarily high AC voltage is applied to the charging roller, and there has been a problem in that the surface layer of the photosensitive drum is scraped. FIG. 8 shows the relationship between the peak-to-peak voltage of the vibration voltage applied to the charging roller and the degree of abrasion of the surface layer of the photosensitive drum (abrasion amount at 10,000 durability sheets).

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems.
By controlling the size to the minimum necessary according to the environmental temperature and humidity and the thickness of the surface layer of the photoconductor drum, the shaving of the surface layer of the photoconductor drum is reduced, and the life of the photoconductor drum is extended. It is an object to provide a charging device.

It is another object of the present invention to provide an image forming apparatus including the charging device and performing an image forming process including image exposure to obtain good image quality with a sufficient image density.

[0016]

According to a first aspect of the present invention, there is provided a charging device which is disposed in contact with or close to a charged means and has a relative movement relationship with the charged means;
A power supply means for supplying and applying an oscillating voltage to the charging means; a current detecting means for detecting an alternating current and a direct current flowing from the charging means to the charged means; and the charging means in accordance with a detection result of the current detecting means. And control means for controlling an AC voltage or an AC current applied to the power supply.

The charging device according to the second aspect of the present invention is
The oscillating voltage is a voltage obtained by superimposing a DC voltage on an AC voltage.

According to a third aspect of the present invention, there is provided a charging device,
The charging means includes a core to which an oscillating voltage is to be applied, a conductive layer formed on the surface of the core, and a resistance layer formed on the surface.

The charging device according to the invention of claim 4 is
The charging means is brought into pressure contact with the charged means with a constant pressing force.

According to a fifth aspect of the present invention, there is provided a charging device,
It is characterized in that one or both of the charging means and the charging means are relatively moved.

According to a sixth aspect of the present invention, there is provided an image forming apparatus for forming an image on the charging device according to any one of the first to fifth aspects and the surface of the means to be charged. Image forming process means.

According to a seventh aspect of the present invention, there is provided an image forming apparatus, comprising: a charging unit which is disposed in contact with or close to a charged unit and has a relative movement relationship with the charged unit; Power supply means for supplying and applying an electric current, image forming means for executing an image forming step including image exposure, current detecting means for detecting an alternating current and a direct current flowing from the charging means to the charged means, and current detecting means Control means for controlling the AC voltage or AC current applied to the charging means and the image exposure amount in accordance with the detection result.

An image forming apparatus according to the present invention is characterized in that current detection is performed for each image forming process start signal.

An image forming apparatus according to a ninth aspect of the present invention is characterized in that the current detection is performed at the time of relative movement between the charging unit and the charged unit after the completion of the image forming step.

An image forming apparatus according to a tenth aspect of the present invention is characterized in that current detection is performed every predetermined number of times of image formation.

According to an eleventh aspect of the present invention, in the image forming apparatus according to the present invention, the charged member is an image carrier for forming an image.

An image forming apparatus according to a twelfth aspect of the present invention is characterized in that the image carrier has a charge generating layer and a charge transporting layer formed on the surface of the charge generating layer as basic components. I do.

The image forming apparatus according to the present invention is characterized in that the charged means is a transfer means for transferring an image on the image carrier to the transferred means.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below.

Embodiment 1 FIG. 1 is a schematic diagram showing a configuration of an image forming apparatus according to Embodiment 1 of the present invention. In the figure, 1 is a photosensitive drum having a diameter of 30 mm as an image carrier. This photoconductor drum 1 is an OPC photoconductor drum having a basic structure layer of a conductive base layer 1b such as aluminum as a charge generation layer and a photoconductive layer 1a as a charge transport layer formed on an outer peripheral surface thereof. It is rotationally driven at a predetermined speed in the direction of arrow R1 by the illustrated drive source.

Around the photosensitive drum 1, a pre-exposure lamp 2 for removing the surface charge of the photosensitive drum 1 by pre-exposure in order along the rotation direction, and a surface of the photosensitive drum 1 having a predetermined potential. A charging roller 3 having a diameter of 12 mm as a charging member for uniformly contact charging, a power supply device 4 for applying an oscillating voltage to the charging roller 3, and forming an electrostatic latent image on the photosensitive drum 1 in accordance with image information Exposure device 5, a developing device 6 that attaches toner to the electrostatic latent image to visualize it as a toner image (in the first embodiment, a reversal development system using negative toner is used), and a photosensitive drum A transfer roller 7 having a diameter of 12 mm as a transfer member for transferring the toner image on the transfer paper 8 to a transfer paper 8 as a recording material; a static eliminator 9 for removing charges from the transfer paper 8 after the transfer of the toner image; Photoconductor drum 1 A cleaner 10 for removing the residual toner adhering to the surface collection is arranged.

The charging roller 3 and the power supply device 4 constitute a contact charging device, and the charging roller 3 is formed on a center metal core 3c, a conductive layer 3b formed on the outer periphery thereof, and further formed on the outer periphery thereof. The resistance layer 3a is used as a basic structure. Both ends of the cored bar 3c are rotatably supported by bearing members (not shown), and are disposed in parallel with the photosensitive drum 1,
The photosensitive drum 1 is pressed against the photosensitive drum 1 with a constant pressing force by a pressing member (not shown), and is rotated by the rotation of the photosensitive drum 1. Further, a driving force transmitting member such as a gear or a roller (not shown) is attached to an end of the cored bar 3c to receive the driving force and rotate the photosensitive drum 1 in the forward direction or the reverse direction. It is possible.

Then, by applying an oscillating voltage obtained by superimposing an AC voltage on a DC voltage from the power supply device 4 to the metal core 3 c of the charging roller 3, the surface of the photosensitive drum 1 that is driven to rotate is fixed to a predetermined position. Charges to polarity and potential. Here, the AC voltage means all the voltages such as a sine wave, a rectangular wave, and a triangular wave whose amplitude changes with time.

The power supply 4 is connected to a CPU 12 as control means for controlling the voltage applied to the charging roller 3. The CPU 12 controls an AC voltage or an AC current applied to the charging roller 3 according to a detection result from a current detection unit 13 that detects an AC current and a DC current flowing from the charging roller 3 to the photosensitive drum 1.

Next, the operation at the time of image formation by the image forming apparatus configured as described above will be described. Photoconductor drum 1
Is driven to rotate at a predetermined speed in the direction of arrow R1. The charging roller 3 includes a power supply 4 controlled by the CPU 12.
From, for example, the AC voltage (peak-to-peak voltage Vpp = 2.0
An oscillating voltage obtained by superimposing a DC voltage (a constant voltage of 625 V) on a sine wave of KV and a frequency of 400 Hz is applied, and the surface of the photosensitive drum 1 is charged to a uniform potential of 1600 V.
Here, the magnitude of the AC voltage applied to the charging roller 3 is determined by control described later.

The charged photosensitive drum 1 is subjected to exposure of target image information (slit exposure of a document image, laser beam scanning exposure, etc .; in the illustrated example, slit exposure of the document image) by the exposure means 5 and becomes static. An electrostatic latent image is formed.
Next, this electrostatic latent image is visualized with toner in the developing means 6 to become a toner image.

The transfer means 7 transfers the visualized toner image on the photosensitive drum 1 to the recording material 8, and then the charge eliminator 9 removes the charge of the transferred recording material 8 and further fixes the image (not shown). To fix the toner image on the recording material 8.

On the other hand, after the toner remaining on the surface of the photosensitive drum 1 after the transfer is cleaned and removed by the cleaner 10, the remaining charge is removed by the pre-exposure by the pre-exposure lamp 2, and the next time. For image formation.

Next, the basic concept for determining the AC voltage will be described. The minimum AC voltage required for the charging roller 3 to properly charge the surface of the photosensitive drum 1 depends on the ambient temperature and humidity and the thickness of the surface layer of the photosensitive drum 1. The minimum required AC voltage is smaller as the temperature and the humidity are higher, and is larger as the temperature is lower and the humidity is lower. The larger the thickness of the surface layer of the photosensitive drum 1 is, the larger the thickness is.

Accordingly, if the ambient temperature and humidity and the film thickness of the surface layer of the photosensitive drum 1 can be detected, the minimum required vibration voltage required for the charging roller 3 to satisfactorily charge the surface of the photosensitive drum 1 is obtained. Can be requested.

Here, when a predetermined oscillating voltage is applied to the charging roller 3, the alternating current flowing from the charging roller 3 to the photosensitive drum 1 depends on the environmental temperature and humidity. The smaller it becomes.

When a predetermined oscillating voltage is applied to the charging roller 3, the DC current flowing from the charging roller 3 to the photosensitive drum 1 is smaller as the surface layer of the photosensitive drum 1 is thicker, and is larger as the surface layer is thinner.

Therefore, by utilizing the above relationship, when a predetermined oscillating voltage is applied to the charging roller 3 and an AC current and a DC current flowing from the charging roller 3 to the photosensitive drum 1 are detected, the environmental temperature / humidity and The film thickness of the surface layer of the photoconductor drum 1 can be detected, and the minimum necessary AC voltage for favorably charging the surface of the photoconductor drum 1 by the charging roller 3 can be obtained.

Table 1 shows the environmental temperature and humidity and the environmental temperature and humidity.
4 shows the relationship between the AC voltage and the minimum required peak-to-peak voltage in humidity. FIG. 2 shows the relationship between the film thickness of the surface layer of the photosensitive drum 1 and the minimum necessary peak-to-peak voltage of the AC voltage at the film thickness.

Table 2 shows the environmental temperature and humidity and the charging roller 3
AC voltage (sine wave of peak-to-peak voltage Vpp = 2.0 KV, frequency f = 400 Hz) to DC voltage (constant voltage -625
V) when a vibration voltage superimposed on the charging roller 3 is applied.
1 shows the relationship with the AC current flowing from the photosensitive drum 1 to the photosensitive drum 1.

[0046]

[Table 1]

[0047]

[Table 2] FIG. 3 shows the thickness of the surface layer of the photosensitive drum 1 and the AC voltage (beak-to-beak voltage Vpp = 2.0 KV, frequency f) applied to the charging roller 3.
= 400 Hz sine wave) and DC voltage (constant voltage -625)
V) is applied to the charging roller 3
1 shows the relationship with the DC current flowing to the photosensitive drum 1 from FIG.

FIG. 4 is an operation sequence diagram for explaining a control operation in the image forming apparatus shown in FIG. 1, and this operation sequence diagram shows a case of continuous printing of two sheets. In the first embodiment, current detection for determining the peak-to-peak voltage of the AC voltage applied to the charging roller 3 is performed for each print (copy) start signal.

First, based on the print (copy) start signal, the rotation drive of the photosensitive drum 1 of the apparatus in the standby state is started.

Next, the pre-exposure lamp 2 is turned on, and the pre-exposure 11
As a result, the surface charge of the photosensitive drum 1 is eliminated, and the surface potential of the photosensitive drum 1 becomes almost 0V. Thereafter, when an oscillating voltage obtained by superimposing a DC voltage (constant voltage −625 V) on an AC voltage (a sine wave having a peak-to-peak voltage of 2.0 KV and a frequency of 400 Hz) is applied to the charging roller 3 from the power supply device 4 immediately, The AC and DC currents flowing from the charging roller 3 to the photosensitive drum 1 are detected by the current detecting means 13.

When the CPU 12 receives the AC current and the DC current detected from the current detecting means 13, the CPU 12 sets the "AC current value and DC current value vs. the minimum required AC voltage peak" as shown in Table 3 previously set. Voltage table
The minimum necessary peak-to-peak voltage of the AC voltage according to the detected AC current value and DC current value is determined.

[0052]

[Table 3] Now, assuming that the detected AC current value is 450 μA and the DC current value is 16 μA, the minimum necessary peak-to-peak voltage of the AC voltage is determined to be 1470 V, and the determined minimum necessary peak-to-peak voltage is 1470 V. AC voltage (sine wave of frequency 400 Hz) to DC voltage (constant voltage 625
The vibration voltage superimposed with V) is applied to the charging roller 3 from the power supply device 4. Then, the first image is formed by the exposure unit 5.

Next, as described above, an AC current and a DC current flowing from the charging roller 3 to the photosensitive drum 1 when a predetermined oscillating voltage is applied to the charging roller 3 are detected, and according to the detected current value, By controlling the peak-to-peak voltage of the AC voltage applied to the charging roller 3 during image formation, the peak-to-peak voltage of the AC voltage applied to the charging roller 3 can be adjusted to the ambient temperature / humidity and the surface layer of the photosensitive drum 1. It can be controlled to the minimum necessary size according to the thickness, the surface layer of the photosensitive drum 1 can be reduced due to the use of the apparatus, and the durability life of the photosensitive drum 1 can be extended.

In the first embodiment, the peak-to-peak voltage of the AC voltage applied to the charging roller 3 during image formation is controlled as described above. May be controlled.

In the first embodiment, the charging roller 3
When a predetermined oscillating voltage is applied to the photosensitive drum 1, the current flowing from the charging roller 3 to the photosensitive drum 1 is detected. However, the current flowing from the charging roller 3 to the photosensitive drum 1 is controlled at a constant current. By detecting the applied voltage to the roller 3,
The AC voltage or AC current applied to the charging roller 3 during image formation may be controlled in accordance with the detected voltage.

In the first embodiment, the current detection is performed for each print (copy) start signal. However, the present invention is not limited to this. First print (copy) is performed.
In order not to delay the time, it is performed at the time of post-rotation of the photosensitive drum 1 after the image forming process is completed, or in order to minimize the voltage application time to the photosensitive drum 1 (generally, voltage application to the photosensitive drum 1 is performed). The greater the number, the more the thickness of the photosensitive drum 1 is scraped, so that the durability of the photosensitive drum 1 is prolonged.

Embodiment 2 As described above, when the film thickness of the surface layer of the photosensitive drum 1 decreases with the use of the apparatus, the photosensitive sensitivity of the photosensitive drum 1 decreases accordingly, and as a result, A "fogging" image occurs. Therefore, in the second embodiment, the image exposure amount of the exposure unit 5 is controlled in accordance with the film thickness of the surface layer of the photosensitive drum 1 in order to correct the above-described decrease in the sensitivity.

FIG. 5 shows the film thickness of the surface layer of the photosensitive drum 1 and
The relationship with the image exposure amount required to maintain the potential contrast of the photosensitive drum 1 will be described. As described in the first embodiment, the thickness of the surface layer of the photosensitive drum 1 is
FIG. 3 shows the relationship between the direct current flowing from the charging roller 3 to the photosensitive drum 1 when a predetermined vibration voltage is applied to the photosensitive drum 1.

Therefore, in the second embodiment, when a predetermined oscillating voltage is applied to the charging roller 3, the current flowing from the charging roller 3 to the photosensitive drum 1 is detected, and the charging roller 3 And the image exposure of the exposure means 5 is controlled based on a table of "DC current versus image exposure" as shown in Table 4 set in advance.

[0060]

[Table 4] That is, the peak-to-peak voltage of the AC voltage applied to the charging roller 3 can be controlled to the minimum necessary value according to the ambient temperature and humidity and the film thickness of the surface layer of the photoconductor drum l. Abrasion of the surface layer of the photosensitive drum 1 can be reduced, and the image exposure amount of the exposure unit 5 is controlled to a size corresponding to the film thickness of the surface layer of the photosensitive drum 1 so that the potential contrast of the photosensitive drum 1 can be reduced. Therefore, the life of the photosensitive drum 1 can be further extended.

In the first and second embodiments,
Although the charging roller 3 has been described as an example of the charging member, the charging member may be a semiconductive blade 31 shown in FIG.
Appropriate shapes such as a semiconductive brush 32 shown in FIG. 6B and a semiconductive magnetic brush 33 shown in FIG. In these cases, the same effects as those of the roller type charging member can be obtained.

The charging roller 3 as a charging member is driven to rotate with the photosensitive drum 1 as a rotating image carrier, or independently rotated in the same or opposite direction as the photosensitive drum. Even if the charging member is fixed and the charging member is relatively moved with respect to the image carrier, the same effects as those of the above embodiments can be obtained.

[0063]

As described above, according to the present invention,
When a predetermined oscillating voltage is applied to the charging unit, an AC current and a DC current flowing from the charging unit to the charged unit are detected, and an AC voltage applied to the charging unit during image formation according to the detected current value. Alternatively, since the configuration is such that the AC current is controlled, the AC voltage applied to the charging means is controlled to a necessary minimum value according to the use environment temperature and humidity of the device and the film thickness of the charged means. Thus, there is an effect that a charging device capable of reducing the degree of shaving of the surface layer of the charged member due to use of the device and extending the durable life of the charged member can be obtained.

Further, since this charging device is configured to execute image formation including image exposure, there is an effect that a high quality image forming device with sufficient image density can be obtained.

Further, since the AC voltage or the AC current applied to the charging means and the image exposure amount at the time of image formation are controlled, the AC voltage applied to the charging means is controlled by the operating environment temperature of the apparatus. The image exposure amount can be controlled to a minimum necessary size according to the humidity and the film thickness of the charged member, and the image exposure amount is controlled to a size corresponding to the film thickness of the surface layer of the photosensitive drum 1. Can be. As a result, it is possible to reduce the degree of shaving of the surface layer of the member to be charged due to the use of the device, and to maintain the potential contrast of the member to be charged, thereby obtaining an image forming apparatus of good image quality with sufficient image density. There is.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a film thickness of a surface layer of a photoconductor drum and a peak-to-peak voltage of an AC voltage applied to a charging member with a minimum required with respect to the film thickness.

FIG. 3 is a characteristic diagram showing a relationship between a film thickness of a surface layer of the photosensitive drum and a DC current flowing from the charging member to the photosensitive drum with respect to the film thickness.

FIG. 4 is an operation sequence diagram of the image forming apparatus according to the first embodiment;

FIG. 5 is a characteristic diagram showing a relationship between a film thickness of a surface layer of a photosensitive drum and an appropriate image exposure amount with respect to the film thickness.

6 (a) is a side view showing a semiconductive blade, FIG. 6 (b) is a side view showing a semiconductive brush, and FIG. 6 (c) is a semiconductive magnet. Side view showing brush

FIG. 7 is a schematic diagram showing a configuration of a conventional contact charging device.

FIG. 8 is a characteristic diagram illustrating a relationship between a peak-to-peak voltage of an AC voltage applied to a charging member and a degree of abrasion of a surface layer of a photoconductor.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor drum (charged means) 3 charging roller (charging member) 4 power supply, 7 transfer means 12 CPU (control device) 13 current detection means

Claims (13)

[Claims] A charging means disposed in contact with or in proximity to the charged means and having a relative movement relationship with the charged means; a power supply means for supplying and applying an oscillating voltage to the charging means; Current detecting means for detecting an alternating current and a direct current flowing through the charged means, and control means for controlling an alternating voltage or an alternating current applied to the charging means in accordance with a detection result of the current detecting means. A charging device characterized by the above-mentioned. 2. The charging device according to claim 1, wherein the oscillating voltage is a voltage obtained by superimposing a DC voltage on an AC voltage. 3. The charging device according to claim 1, wherein the charging means comprises a core to which an oscillating voltage is to be applied, a conductive layer formed on the surface of the core, and a resistance layer formed on the surface. Item 3. The charging device according to any one of Items 2. 4. The charging device according to claim 1, wherein the charging unit is pressed against the charging unit with a constant pressing force. 5. The charging device according to claim 1, wherein one or both of the charging unit and the charging unit are relatively moved. 6. A charging device according to claim 1, further comprising: an image forming process unit configured to execute image formation on a surface of the charging unit. Image forming apparatus. 7. A charging means disposed in contact with or close to a charged means and having a relative movement relationship with the charged means, and an oscillating voltage is supplied to the charging means so as to charge the surface of the charged means. Power supply means for applying, image forming means for performing an image forming step including image exposure, current detecting means for detecting an alternating current and a direct current flowing from the charging means to the charged means, and detection of the current detecting means AC voltage or AC current applied to the charging means depending on the result,
An image forming apparatus comprising: a control unit configured to control an image exposure amount. 8. The image forming apparatus according to claim 7, wherein the current detection is performed for each image forming process start signal. 9. The image forming apparatus according to claim 7, wherein the current detection is performed when the charging unit and the charged unit move relative to each other after the image forming process is completed. 10. The image forming apparatus according to claim 7, wherein the current detection is performed every predetermined number of times of image formation. 11. The image forming apparatus according to claim 7, wherein the charging unit is an image carrier for forming an image. 12. The image forming apparatus according to claim 11, wherein the image carrier has a basic structure including a charge generation layer and a charge transport layer formed on a surface of the charge generation layer. 13. The image forming apparatus according to claim 7, wherein the charging unit is a transfer unit that transfers an image on the image carrier to the transfer unit.