JPH11223965A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device constituted so that a proper image can be maintained even when the surface of a photoreceptor is shaved because the number of image forming sheets is increased. SOLUTION: When a voltage is impressed on an electrifying roller 2 from an electrifying power source 3, a current flowing to a gap between the roller 2 and the photoreceptor 1 is detected by an amperemeter 15. Based on a current value detected by the amperemeter 15, the film thickness of the photoreceptor 1 is calculated by a controller 16. When the calculated film thickness of the photoreceptor 1 arrives at the prescribed film thickness, the power source 3 is controlled so that potential difference between the dark potential and the light potential of the surface of the photoreceptor by the exposure action of an exposure device 10 becomes larger than the prescribed potential difference required until the film thickness arrives at the prescribed film thickness. Thus, even when the surface of the photoreceptor is shaved because the number of image forming sheets is increased, the proper image can be maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, etc., which forms an image by an electrophotographic method. More specifically, the present invention relates to an electrophotographic photosensitive member which is a member to be charged. The present invention relates to an image forming apparatus provided with a contact charging member for charging a photographic photosensitive member.

[0002]

2. Description of the Related Art Conventionally, an electrophotographic apparatus (for example, a copying machine,
2. Description of the Related Art In an image forming apparatus such as a laser beam printer or an electrostatic recording apparatus, a corona charging device is widely used as a device for charging a charged surface such as a photosensitive member as an image carrier and a dielectric pair.

A corona charging device is a device that charges using a corona discharge, which is an air discharge, and is very effective as a means for uniformly charging a charged surface to a predetermined potential. Are required, and a lot of ozone is generated during corona discharge.

[0004] In contrast to such a corona charging device, the contact charging device has the advantages that the voltage of the power supply can be reduced and the amount of generated ozone is small. The contact charging device charges the charged surface by directly contacting the charging member with the charged surface. From the advantages described above, for example, in an image forming apparatus, it is changed to a corona discharge device for an image carrier or the like. It is attracting attention as a charging treatment means and is in practical use.

[0005] For example, Japanese Patent Application Laid-Open No. 62-51492,
In a contact charging device disclosed in Japanese Patent Application Laid-Open No. 62-230334, an oscillating electric field (alternating electric field) having a peak-to-peak voltage twice or more as high as a charging start voltage when a DC voltage is applied to a charging member, Forming an object to be charged such as a charging member and a photoreceptor (alternating electric field, an electric field (voltage) whose voltage value periodically changes with time) between the charging member and the object to be charged; By using a charging member provided with a layer, charging uniformity of the member to be charged and prevention of leakage due to pinholes, scratches, etc. on the surface of the member to be charged such as a photoreceptor can be achieved.

[0006] Further, as a charging member, a conductive member (conductive potential maintaining member) such as a conductive fiber bristle brush or a conductive elastic roller is brought into contact with the member to be charged, and a DC voltage is applied from the outside to charge the member. In some cases, charge is directly injected into the body surface to charge the surface of the body to be charged to a predetermined potential.

FIG. 8 is a schematic configuration diagram showing a conventional image forming apparatus having a conductive member as a contact charging member.

This image forming apparatus includes a drum-type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive member) 1, a charging roller 2, which is a conductive member, around the photosensitive member, an exposure device 10, and a developing device 1.
1, a transfer roller 12, a cleaning device 13, and a pre-exposure device 14. When the photoconductor 1 is driven to rotate, the charging roller 2 to which a predetermined bias is applied from the charging power source 3 applies a charge to the photoconductor 1. The surface (the surface to be charged) is charged to a predetermined polarity and potential.

The charged photoreceptor 1 is subjected to image exposure L in accordance with the image content, and a latent image is formed. The latent image is visualized by the toner of the developing device 11, and the developed toner image is transferred to the transfer material P by the transfer roller 12 to which a predetermined bias is applied from the transfer power supply 12a. The transfer material P to which the toner image has been transferred is discharged outside the apparatus after the toner image is fixed by a fixing device (not shown).

On the other hand, the transfer residual toner remaining on the photoreceptor 1 after the transfer is removed by the cleaning blade 13a of the cleaning device 13, and subsequently, the pre-exposure device 14 prepares the photoreceptor 1 for the next image formation. The surface is neutralized.

As described above, the photosensitive member 1 is moved during image formation.
Charged to a predetermined polarity and potential by the charging roller 2,
A latent image is formed by image exposure of the exposure device 10. The surface potential of the photoconductor 1 when the latent image is formed is controlled to a constant value for both the dark potential (dark potential) and the light potential (bright potential).

[0012]

By the way, in the above-mentioned conventional image forming apparatus, as the number of formed images increases, the surface of the photosensitive member 1 (the surface to be charged) contacts the charging roller 2, the transfer roller 12, the cleaning blade and the cleaning blade. 13a, and is gradually scraped by the effect of waste toner stagnating near the cleaning blade 13a. The sensitivity of the photoreceptor 1 decreases along with the deterioration of the surface of the photoreceptor 1 according to the shaved amount. Therefore, as the surface of the photosensitive drum 1 deteriorates, it becomes difficult to maintain an appropriate image.

The cleaning blade 13a collects the transfer residual toner remaining on the surface of the photoreceptor 1 after the transfer by the transfer roller 12, and collects the transfer residual toner and also removes the paper dust of the transfer material P. They will be collected at the same time. The collected paper dust and the like are used as the cleaning blade 13
The stagnation at the leading end of “a” damages the surface of the photoconductor 1 (the surface to be charged), and as a result, it becomes difficult to maintain an appropriate image.

Due to the above-described problems, the life of the photoconductor is shortened, and further, these problems hinder the extension of the life of the photoconductor.

As a countermeasure, the dark potential (dark potential) and the light potential (bright potential) of the surface potential of the photosensitive member are controlled,
By gradually widening the potential difference between the dark potential and the light potential, it is considered effective for maintaining a proper image. However, if the potential difference between the dark potential and the light potential is gradually widened, the toner consumption increases, and the waste toner amount increases accordingly. However, these problems prevent the life of the photoconductor from being prolonged, and at the same time make it difficult to maintain a proper image.

Accordingly, an object of the present invention is to provide an image forming apparatus capable of maintaining an appropriate image and extending the life of an electrophotographic photosensitive member.

[0017]

According to the present invention, there is provided a movable electrophotographic photosensitive member having a surface to be charged, and a movable electrophotographic photosensitive member having a surface to be charged which is in contact with the surface of the member to be charged. An image forming apparatus comprising: a contact charging unit that charges a charged body surface; a power supply that applies a voltage to the contact charging unit; and an exposure unit that exposes the charged body surface to form an electrostatic latent image. When a voltage is applied to the contact charging unit from a power supply, a current detection unit that detects a current flowing between the contact charging unit and the electrophotographic photosensitive member, and current value information detected by the current detection unit. Input, calculate the film thickness of the surface to be charged based on the input current value information,
When the calculated thickness of the charged body surface reaches a predetermined thickness, the potential difference between the dark potential and the bright potential of the charged body surface charged by the exposure of the exposure unit is reduced until the calculated thickness is reached. And control means for controlling the power supply so as to be larger than a predetermined potential difference between a dark potential and a bright potential on the surface of the charged body.

Further, the contact charging member is a conductive charging member having a high resistance layer.

Also, a movable electrophotographic photosensitive member having a surface to be charged, contact charging means for contacting the surface of the charged object of the electrophotographic photosensitive member and charging the surface of the charged object; In an image forming apparatus including a power supply for applying a voltage, and an exposure unit for exposing the surface of the charged body to form an electrostatic latent image, when applying a voltage from the power supply to the contact charging unit, Current detecting means for detecting a current flowing between the contact charging means and the electrophotographic photosensitive member, environment detecting means for detecting an environment near the electrophotographic photosensitive member and the contact charging means, and detection by the current detecting means The current value information to be input is input, the film thickness of the surface to be charged is calculated based on the input current value information, and the calculated film thickness of the surface to be charged is environmental information input from the environment detecting means. Correction based on When the corrected thickness of the charged body surface reaches a predetermined thickness, the potential difference between the dark potential and the bright potential of the charged body surface charged by the exposure of the exposure unit is changed until the predetermined thickness is reached. And control means for controlling the power supply so as to be larger than a predetermined potential difference between a dark potential and a bright potential on the surface of the charged body.

The environment detecting means includes at least one of a temperature detection sensor and a humidity detection sensor, and the environment information includes temperature information detected by the temperature detection sensor and temperature information detected by the humidity detection sensor, respectively. It is characterized by humidity information.

(Effect) According to the structure of the present invention, even when the film thickness of the electrophotographic photosensitive member is reduced and the surface of the electrophotographic photosensitive member is deteriorated with the increase in the number of formed images, the film thickness is reduced in accordance with the reduced film thickness. By making the potential difference between the dark potential and the bright potential due to exposure of the charged electrophotographic photosensitive member surface larger than the initial potential, an appropriate image can be obtained for a long period of time.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to the present embodiment. Note that the same members as those of the conventional image forming apparatus shown in FIG.

This image forming apparatus includes an electrophotographic photosensitive member (photosensitive member) 1, a charging roller 2 serving as a contact charging unit, an exposing device 10, a developing device 11, a transfer device 12, a cleaning device 13, and a pre-exposing device 14. ing.

In the present embodiment, the photosensitive member 1 is a negatively charged organic photosensitive member and has a photoconductive layer 1a on a drum base 1b made of aluminum. It is driven to rotate at a peripheral speed (process speed).

The charging roller 2 includes a cored bar 2c, a rubber layer 2b formed sequentially on the outer periphery of the cored bar 2c, and two resistance layers 2a2 and 2a.
1 and a conductive member having both ends of the cored bar 2c rotatably supported by a bearing member (not shown), and having a predetermined pressing force against the photoreceptor 1 by pressing means (not shown). And is driven to rotate in the direction of arrow R <b> 2 with the rotation of the photoconductor 1. Further, the sliding contact 3
A predetermined direct current (DC) bias is applied to the metal core 2c via the line a, whereby the photoconductor 1 is charged to a predetermined polarity and potential. The charging power source 3 includes an ammeter 15 and a control device (CP
U) 16 is connected and the control device (CPU) 16
Can detect the thickness of the photoconductive layer 1a of the photoconductor 1 based on the current value input from the ammeter 15 (the details will be described later).

In the present embodiment, the exposure apparatus 10 is a known document table fixed-optical system moving type document imaging slit exposure unit. In the exposure apparatus 10, reference numeral 20 denotes a fixed platen glass on which a document D is placed facing downward, reference numeral 21 denotes a document pressing plate, reference numeral 22 denotes a document illumination lamp (exposure lamp), reference numeral 23 denotes a slit plate, and reference numerals 24, 25 and 26 The moving first, second and third mirrors, 27 are imaging lamps, and 28 is a fixed mirror.

The ramp 22, the slit plate 23, and the movable first mirror 24 move the lower surface of the platen glass 20 from one end to the other end at a predetermined speed V, and the second and third mirrors 25,
6 is driven to move at a speed of V / 2,
The upper downward document surface is scanned from one end side to the other end side, image exposure is performed on the surface of the photoconductor 1 by image forming slit exposure L, and an electrostatic latent image corresponding to image information of the original D is formed.

The developing device 11 includes a developing sleeve 11a that rotates in the direction of arrow R11.
The toner is adhered to the electrostatic latent image by a, and is visualized as a toner image.

The transfer roller 12 is disposed in contact with the photoreceptor 1 and rotates in the direction of arrow R12, and a transfer bias having a polarity opposite to that of the toner is applied from a transfer power supply 12a. By transferring a transfer material P such as paper conveyed to a transfer nip between the photoconductor 1 and the transfer roller 12 by the transfer roller 12 to which the transfer bias is applied, the toner image formed on the photoconductor 1 is formed. Transfer to the transfer material P. The transfer roller 12
An elastic body is provided on the surface of the metal core.

Next, an image forming operation of the above-described image forming apparatus will be described.

At the time of image formation, the photosensitive member 1 is driven to rotate at a predetermined process speed by a driving means (not shown).
The charging is performed to a predetermined polarity and potential by the charging roller 2 to which a predetermined charging bias is applied from the charging power source 3.

Then, the above-mentioned image forming slit exposure L is given by the exposure device 10 on the charged photoreceptor 1,
An electrostatic latent image corresponding to the image information of the document D is formed. Next, the electrostatic latent image is transferred to the developing sleeve 11 of the developing device 11.
The toner is adhered to the electrostatic latent image by a, and is visualized as a toner image.

When the toner image on the surface of the photoreceptor 1 reaches the transfer nip between the transfer roller 12 and the photoreceptor 1, the transfer material P is conveyed to the transfer nip at this timing. The transfer roller 12 to which the transfer bias is applied transfers the toner image.
The transfer material P to which the toner image has been transferred is fixed by a fixing device (not shown).
The transfer toner image is fixed as a permanently fixed image on the transfer material P by heating and pressing by a fixing device, and is output.

On the other hand, the transfer residual toner remaining on the surface of the photoreceptor 1 after the transfer of the toner image is removed by the cleaning blade 13a of the cleaning device 13 and collected.
Further, the surface of the photoreceptor 1 is neutralized by the pre-exposure device 14 and repeatedly used for image formation.

In the above-described image forming apparatus, when a predetermined DC voltage (for example, -1300 V) is applied from the charging power source 3 between the charging roller 2 and the photosensitive member 1, the charging is performed by the ammeter 15. The value of the current flowing between the roller 2 and the photoconductor 1 can be detected. And the photoconductor 1
The film thickness of the photoconductive layer 1a on the surface (drum film thickness) and the value of the current flowing through the charging roller 2 and the photoconductor 1 are in inverse proportion as shown in FIG.

Accordingly, the control device 16 determines the thickness of the photoconductive layer 1a on the surface of the photosensitive member 1 (drum thickness) based on the inversely proportional relationship between the current flowing between the charging roller 2 and the photosensitive member 1. From the value of the current flowing between the charging roller 2 and the photoconductor 1 input from the ammeter 15, the photoconductive layer 1 on the surface of the photoconductor 1 is obtained.
a can be calculated.

Next, the control device 16 in the present embodiment will be described.
With respect to the thickness of the photoconductive layer 1a on the surface of the photoconductor 1
Control of a potential difference between a dark potential (dark potential) and a light potential (bright potential) on the surface of the photoconductor 1 will be described.

With respect to the surface potential of the photosensitive member 1 of this embodiment, the dark potential is initially -600 V, and the light potential is-.
The voltage is set to 200 V, and the potential of the photoconductive layer 1a on the surface of the photoreceptor 1 is maintained until a predetermined thickness. At this time, even if the number of formed images is increased so that the appropriate image density does not change, the initial dark potential (−600 V) and the write potential (−200 V)
The control unit 16 controls the charging power supply 3 and the exposure apparatus 1 to maintain
Control 0. In the present embodiment, the initial thickness of the photoconductive layer 1a of the photoconductor 1 is 30 μm. Thereafter, as the number of formed images increases, the photoconductive layer 1
The film thickness of “a” tends to gradually decrease. Accordingly, the surface of the photoconductive layer 1a of the photoconductor 1 deteriorates, and it becomes difficult to maintain an appropriate image due to a problem such as deterioration of the sensitivity of the photoconductor 1.

Therefore, in the present embodiment, when the photoconductive layer 1a of the photoconductor 1 has a predetermined thickness, for example, when the initial thickness of 30 μm becomes 24 μm, the potential difference between the dark potential and the light potential is reduced. Make it wider than the value from the beginning.
For example, the dark potential is initially -600 V as described above.
Since the light potential is -200 V, the potential difference between the dark potential and the light potential is -400 V. In this embodiment, the dark potential is -700 V, and the write potential is -200 V. As a result, the potential difference between the dark potential and the light potential on the surface of the photoconductor 1 becomes -500.
V was controlled.

As described above, the photoconductive layer 1 on the surface of the photoreceptor 1
Since the film thickness a (drum film thickness) and the value of the current flowing through the charging roller 2 and the photoconductor 1 are in inverse proportion as shown in FIG. 2, for example, the film thickness of the photoconductive layer 1a of the photoconductor 1 Is 30μ
m, the detection current of the ammeter 15 is 60 μA,
When the thickness of the photoconductive layer 1a is 24 μm, the detection current is 75 μA.

As shown in FIG. 3, the relationship between the charging bias voltage (primary applied voltage) applied to the charging roller 2 and the corresponding dark potential on the surface of the photosensitive member 1 is a linear relationship having a slope of 1. . Therefore, in the present embodiment, the photosensitive member 1
Assuming that the charging bias voltage (primary applied voltage) required for setting the dark potential to −600 V when the thickness of the photoconductive layer 1 a becomes 24 μm is −1300 V, the dark potential is set to −700 V. It can be seen from the above relationship that the charging bias voltage (primary applied voltage) should be set to -1400V.

Since the write potential increases with the increase in the dark potential, it is necessary to correct the write potential. The relationship between the image exposure amount by the exposure device 10 and the write potential is almost inversely proportional as shown in FIG. 4, and when the image exposure amount is increased, the write potential can be reduced. When it is lowered, the write potential can be raised. From this, it can be seen that the write potential increases with the increase in the dark potential, and that the increased light potential can be corrected by increasing the image exposure to an appropriate value.

Therefore, in the present embodiment, the image exposure amount is set to 0. 0 from the relationship between the image exposure amount and the write potential shown in FIG.
Since the write potential decreases by about 20 V when it increases by 1 (lux.sec), the write exposure can be corrected to -100 V by increasing the image exposure amount by 0.5 (lux.sec).

As described above, by correcting the surface potential (dark potential) of the photosensitive member 1, in the present embodiment, FIG.
And the thickness of the photoconductive layer 1a of the photoreceptor 1 as shown in FIG.
The surface potential (dark potential, light potential) can be obtained, the light potential can be kept constant, and the potential difference between the dark potential and the light potential can be made wider than the initial potential.

By adopting such a configuration,
Even when compared with the conventional method of gradually increasing the potential difference between the dark potential and the light potential, the toner consumption does not increase extremely. As a result, the life of the photosensitive member 1 can be extended, and an appropriate image can be maintained for a long period of time.

<Embodiment 2> FIG. 6 is a schematic configuration diagram showing an image forming apparatus according to the present embodiment. Note that the same members as those of the image forming apparatus described in the first embodiment are denoted by the same reference numerals, and redundant description will be omitted.

In this embodiment, a temperature / humidity detecting sensor 17 for detecting the temperature and humidity near the photosensitive member 1 and the charging roller 2 is provided on the developing device 11 near the photosensitive member 1.
Other configurations are the same as in the first embodiment.

Also in this embodiment, when a predetermined direct current (DC) voltage of, for example, -1300 V is applied between the charging roller 2 and the photosensitive member 1 from the charging power source 3 by the ammeter 15, the charging roller 1 The current value flowing between the photoconductor 2 and the photoconductor 2 can be detected. Since the film thickness of the photoconductor 1 and the value of the current flowing through the charging roller 2 and the photoconductor 1 are in inverse proportion as shown in FIG. The thickness of the photoconductor 1 can be detected.

The current value (detected current) detected by the ammeter 15 may vary depending on the temperature and humidity characteristics of the photoreceptor 1 and the charging roller 2 depending on the environmental conditions in the apparatus. For example, in an environment of normal temperature and normal humidity, when the thickness of the photoconductor 1 is 30 μm, the current value (detected current) detected by the ammeter 15 is 60 μA, and the thickness of the photoconductor 1 is 2 μm.
At 4 μm, the detection current is 75 μA.
In a high humidity environment, when the thickness of the photoconductor 1 is 30 μm,
The detection current is 55 μA, and the thickness of the photoconductor 1 is 2 μA.
At 4 μm, the detection current is 70 μA. In a low-temperature, low-humidity environment, when the thickness of the photoconductor 1 is 30 μm, the detection current is 65 μA, and when the thickness of the photoconductor 1 is 24 μm, the detection current is 80 μA.

Therefore, in the present embodiment, as shown in FIG. 7, the point at which the potential difference between the dark potential and the light potential of the surface potential of the photosensitive member 1 is increased in accordance with the environment (temperature and humidity) is, for example, normal temperature, normal temperature. When the detection current is 75 μA due to humidity,
The control device 1 changes the current according to the environment (temperature and humidity) so that the detection current is 80 μA in the case of high temperature and high humidity, and 70 μA in the case of low temperature and low humidity.
Correct at 6.

As described above, in the present embodiment, in a high-temperature and high-humidity environment, the detection current value (75 μm) in a normal temperature and normal humidity environment is used.
The dark potential is raised at 80 μA, which is 5 μA larger than A), and in a low-temperature and low-humidity environment, the dark potential is raised at 70 μA, which is 5 μA smaller than the detected current value (75 μA) in a normal temperature and normal humidity environment. Accordingly, it is possible to maintain a proper image according to any environment, and to achieve a long life of the photoconductor and maintain a proper image for a long period of time.

[0052]

As described above, according to the present invention, it is possible to prevent the deterioration of the proper image due to the deterioration of the surface of the photoconductor caused by the shaving of the photoconductor, and to extend the life of the photoconductor. Can be planned.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a relationship between a film thickness of a photosensitive member (drum film thickness) and a detection current.

FIG. 3 is a diagram showing a relationship between a primary applied voltage and a dark potential.

FIG. 4 is a diagram illustrating a relationship between an image exposure amount and a write potential.

FIG. 5 is a diagram showing the relationship between the thickness of the photoconductor and the surface potential of the photoconductor in Embodiment 1 of the present invention.

FIG. 6 is a schematic configuration diagram illustrating an image forming apparatus according to a second embodiment of the present invention.

FIG. 7 is a diagram illustrating a relationship between a detection current and a photoconductor surface potential according to the second embodiment of the present invention.

FIG. 8 is a schematic configuration diagram showing a conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrophotographic photoreceptor 1a Photoconductive layer 1b Drum substrate 2 Charging roller (contact charging means) 2a1, 2a2 Resistance layer 2b Rubber layer 2c Core metal 3 Charging power supply 10 Exposure device (exposure device) 11 Developing device 11a Developing sleeve 12 Transfer roller 12a Transfer power supply 13 Cleaning device 13a Cleaning blade 14 Pre-exposure light source 15 Ammeter (current detection means) 16 Control device (control means) 17 Temperature / humidity detection sensor (environment detection means)

Claims (5)

[Claims] A movable electrophotographic photoreceptor having a surface to be charged, a contact charging means for contacting the surface of the electrophotographic photosensitive member and charging the surface of the charged object; An image forming apparatus comprising: a power supply for applying a voltage; and an exposing unit configured to expose the surface of the member to be charged to form an electrostatic latent image, wherein a voltage is applied from the power supply to the contact charging unit.
Current detection means for detecting a current flowing between the contact charging means and the electrophotographic photoreceptor; and inputting current value information detected by the current detection means,
The film thickness of the surface to be charged is calculated based on the input current value information, and when the calculated film thickness of the surface to be charged reaches a predetermined film thickness, the film charged by the exposure means is exposed. Control means for controlling the power supply so that the potential difference between the dark potential and the bright potential of the charged body surface is larger than the predetermined potential difference between the dark potential and the bright potential until the predetermined thickness is reached, An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein said contact charging member is a conductive charging member having a high resistance layer. 3. A movable electrophotographic photoreceptor having a surface to be charged, contact charging means for contacting the surface of the electrophotographic photosensitive member and charging the surface of the object, and contact charging means. An image forming apparatus comprising: a power supply for applying a voltage; and an exposing unit configured to expose the surface of the member to be charged to form an electrostatic latent image, wherein a voltage is applied from the power supply to the contact charging unit.
A current detecting unit that detects a current flowing between the contact charging unit and the electrophotographic photosensitive member; an environment detecting unit that detects an environment near the electrophotographic photosensitive member and the contact charging unit; and the current detecting unit. Information on the current value to be detected is input, the film thickness of the surface to be charged is calculated based on the input current value information, and the calculated film thickness of the surface to be charged is input to the environment from the environment detecting means. Corrected based on the information, when the corrected thickness of the charged body surface reaches a predetermined film thickness, the potential difference between the dark potential and the bright potential of the charged body surface charged by exposure of the exposure means, An image forming apparatus, comprising: a control unit that controls the power supply so as to make the potential greater than a predetermined potential difference between a dark potential and a bright potential on the surface of the member to be charged until a predetermined thickness is reached. 4. The image forming apparatus according to claim 3, wherein said contact charging member is a conductive charging member having a high resistance layer. 5. The environment detection means includes at least one of a temperature detection sensor and a humidity detection sensor, and the environment information includes temperature information detected by the temperature detection sensor and temperature information detected by the humidity detection sensor, respectively. The image forming apparatus according to claim 3, wherein the information is humidity information.