JP2002108162A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the elongation of the FCOT and the deterioration of a photosensitive body due to the preliminary electrification performed for stabilizing image quality. SOLUTION: The time of the preliminary electrification is controlled in accordance with the suspension period of an image forming device, use history of the photosensitive body, an image gradation mode, an environmental condition and the like.

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 for forming an image on a recording material by an electrophotographic method, and more particularly to a technique for controlling pre-charging in such an image forming apparatus.

[0002]

2. Description of the Related Art In an image forming process for forming an image by an electrophotographic method, as is well known, a charging process for uniformly charging a photosensitive member, and an image exposure of the charged photosensitive member to form an electrostatic latent image. A toner image is formed on the photoconductor by an exposure process and a development process of developing the electrostatic latent image formed on the photoconductor.
It is known that in a photoconductor used in such an image forming process, a surface potential formed in the charging process varies due to various factors. In particular, it is known that in the case of a circulating photosensitive member, a difference occurs between the surface potential due to charging in the first cycle and the surface potential due to charging in the second cycle, which affects image quality.

It is also known that such a difference in potential is caused by a defect formed by impurities or the like in a photosensitive layer of a photoreceptor acting as a carrier trap. Therefore, in the second week from the first week and the third week from the second week of the photoconductor,
As a result of filling the traps, the number of traps decreases, and the surface potential formed by charging, that is, the charging potential becomes stable.

In consideration of such properties of the photoreceptor, it has been conventionally performed to perform pre-charging for charging the photoreceptor before image formation to stabilize the charging potential.

[0005]

The introduction of the pre-charging step makes it possible to form a high-quality image with stable charging potential and little fluctuation in image quality. The problem that the first copy time or the first print time, that is, the time from the image formation command to the output of the first image (hereinafter referred to as FCOT) becomes longer due to the addition of the step of charging by driving. Occurs. The length of the FCOT greatly affects the actual image forming efficiency because the ratio of producing a small number of sheets is large in the ordinary document production work.
Reducing the OT is an important means for improving the image forming efficiency.

It is known to use a separating means for precharging in order to avoid the extension of FCOT due to precharging. According to this means, the pre-charging is performed in about half the circumference of the photoreceptor due to the arrangement of the respective processing units with respect to the photoreceptor in the image forming apparatus, so that the pre-charging time is shortened. However, in this method, although the precharging time is shortened, the FCOT is extended by the precharging. Further, since the charging process is a factor that promotes the deterioration of the photoconductor, there is a problem that the deterioration of the photoconductor proceeds due to the preliminary charging, and the life of the photoconductor is shortened.

Furthermore, since a small-capacity power source was originally used for the separation means, a sufficient amount of charging could not be performed in preliminary charging, and the charging potential was insufficient to stabilize the charging potential. There is. Further, when the capacity of the power supply of the separating means is increased, there is a problem that the cost increases.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems in the conventional technology for countermeasures to the fluctuation of the charging potential due to the trapping of carriers in a photoreceptor, to shorten the FCOT and extend the life of the photoreceptor. I do.

[0009]

The above-mentioned object of the present invention is achieved by the following inventions.

[0010] 1. Photoreceptor, charging means for uniformly charging the photoreceptor, exposure means for imagewise exposing the charged photoreceptor,
In an image forming apparatus having a developing unit for developing an electrostatic latent image formed on the photoreceptor by charging and exposure, and a control unit, the control unit is configured to start the charging by the charging unit and to expose the image by the exposing unit. An image forming apparatus for setting a pre-charging time until the start of a next image forming step from the end of the previous image forming step.

2. Photoreceptor, charging means for uniformly charging the photoreceptor, exposure means for imagewise exposing the charged photoreceptor,
In an image forming apparatus having a developing unit for developing an electrostatic latent image formed on the photoreceptor by charging and exposure, and a control unit, the control unit is configured to start the charging by the charging unit and to expose the image by the exposing unit. An image forming apparatus, wherein a pre-charging time up to the time is set based on an operation time of the image forming unit.

3. Photoreceptor, charging means for uniformly charging the photoreceptor, exposure means for imagewise exposing the charged photoreceptor,
In an image forming apparatus having a developing unit for developing an electrostatic latent image formed on the photoreceptor by charging and exposure, and a control unit, the control unit is configured to start the charging by the charging unit and to expose the image by the exposing unit. An image forming apparatus, wherein a pre-charging time until the pre-charging time is set based on the number of formed images.

4. Photoreceptor, charging means for uniformly charging the photoreceptor, exposure means for imagewise exposing the charged photoreceptor,
In an image forming apparatus having a developing unit that develops an electrostatic latent image formed on the photoreceptor by charging and exposure, and a control unit, the control unit is configured to start the charging by the charging unit and to perform the exposure by the exposure unit. An image forming apparatus for performing control to change the pre-charging time up to the pre-charging time in accordance with an image gradation mode.

5. Photoreceptor, charging means for uniformly charging the photoreceptor, exposure means for imagewise exposing the charged photoreceptor,
In an image forming apparatus having a developing unit for developing an electrostatic latent image formed on the photoreceptor by charging and exposure, and a control unit, the control unit is configured to start the charging by the charging unit and to expose the image by the exposing unit. An image forming apparatus, wherein control is performed to change the pre-charging time up to the time according to the environment.

6. 6. The image forming apparatus according to claim 5, further comprising an environment sensor for detecting temperature or humidity, wherein the control unit performs the control based on an output of the environment sensor.

[7] Photoreceptor, charging means for uniformly charging the photoreceptor, exposure means for imagewise exposing the charged photoreceptor,
In an image forming apparatus having a developing unit for developing an electrostatic latent image formed on the photoreceptor by charging and exposure, and a control unit, the control unit is configured to start the charging by the charging unit and to expose the image by the exposing unit. Pre-charging time is selected from the pause time from the end of the previous image forming process to the start of the next image forming process, the operation time of the image forming unit, the number of formed images, the image gradation mode, and the environment. An image forming apparatus that performs control for changing based on two or more parameters.

8. Photoreceptor, charging means for uniformly charging the photoreceptor, exposure means for imagewise exposing the charged photoreceptor,
Developing means for developing an electrostatic latent image formed on the photoconductor by charging and exposure; transfer means for transferring a toner image formed on the photoconductor to a recording material; and recording on which the toner image is formed. An image forming apparatus that includes a separation unit that separates the material from the photoconductor by static elimination and a control unit, and that performs the preliminary charging by the separation unit. An image forming apparatus, wherein the setting is based on a pause time from an end point to a start point of a next image forming step.

9. Photoreceptor, charging means for uniformly charging the photoreceptor, exposure means for imagewise exposing the charged photoreceptor,
Developing means for developing an electrostatic latent image formed on the photoconductor by charging and exposure; transfer means for transferring a toner image formed on the photoconductor to a recording material; and recording on which the toner image is formed. An image forming apparatus comprising: a separating unit configured to separate a material from the photoconductor by static elimination; and a control unit, wherein the control unit determines a time of the preliminary charging by an operation time of the image forming unit. An image forming apparatus, wherein the setting is performed based on the following.

10. A photoreceptor, charging means for uniformly charging the photoreceptor, exposure means for imagewise exposing the charged photoreceptor, developing means for developing an electrostatic latent image formed on the photoreceptor by charging and exposure Transfer means for transferring a toner image formed on the photoconductor to a recording material, separation means for separating the recording material on which the toner image is formed from the photoconductor by static elimination, and control means; In the image forming apparatus which performs pre-charging by means, the control unit sets the pre-charging time based on the number of formed images.

11. A photoreceptor, charging means for uniformly charging the photoreceptor, exposure means for imagewise exposing the charged photoreceptor, developing means for developing an electrostatic latent image formed on the photoreceptor by charging and exposure Transfer means for transferring a toner image formed on the photoconductor to a recording material, separation means for separating the recording material on which the toner image is formed from the photoconductor by static elimination, and control means; In the image forming apparatus which performs pre-charging by means, the control unit performs control for changing the pre-charging time according to an image gradation mode.

[12] A photoreceptor, charging means for uniformly charging the photoreceptor, exposure means for imagewise exposing the charged photoreceptor, developing means for developing an electrostatic latent image formed on the photoreceptor by charging and exposure Transfer means for transferring a toner image formed on the photoconductor to a recording material, separation means for separating the recording material on which the toner image is formed from the photoconductor by static elimination, and control means; In the image forming apparatus which performs pre-charging by means, the control unit performs control for changing a time of the pre-charging according to an environment.

13. 13. The image forming apparatus according to claim 12, further comprising an environment sensor for detecting temperature or humidity, wherein the control unit performs the control based on an output of the environment sensor.

14. A photoreceptor, charging means for uniformly charging the photoreceptor, exposure means for imagewise exposing the charged photoreceptor, developing means for developing an electrostatic latent image formed on the photoreceptor by charging and exposure Transfer means for transferring a toner image formed on the photoconductor to a recording material, separation means for separating the recording material on which the toner image is formed from the photoconductor by static elimination, and control means; In the image forming apparatus which performs preliminary charging by means, the control unit controls the time of the preliminary charging to be a pause time from the end of the previous image forming step to the start of the next image forming step, and to operate the image forming unit. An image forming apparatus that performs control to change based on two or more parameters of time, number of formed images, image gradation mode, and environment.

[0024]

FIG. 1 shows an image forming apparatus according to an embodiment of the present invention.

Around the photoreceptor 1, a charging means 2, an exposing means 3, a developing means 4, a transferring means 5, a separating means 6, and a cleaning means 8 are arranged. At the bottom of the device is a recording paper P
The paper feed cassette 1 is disposed in the transport path of the recording paper P unloaded from the paper feed cassette 10.
1, a registration roller 12 and a fixing unit 7 are provided.
13 is a control means for controlling the whole of the respective parts,
For the preliminary charging described later, the charging unit 2 or the separating unit 6 is controlled. Reference numeral 14 denotes an environment sensor for detecting an environment in the image forming apparatus, that is, a sensor for detecting temperature and humidity in the image forming apparatus.

As the photosensitive member 1, a drum-shaped OPC photosensitive member having an intermediate layer and an OPC photosensitive layer formed on a metal drum substrate is used. As the charging means 2, a scorotron charger having a control electrode and a discharge electrode is used. As the exposure means 3, a scanning exposure device including a laser diode and a scanning optical system or a scanning exposure device including a light emitting diode array is used, and the photosensitive member 1 is scanned in the main scanning direction and the sub-scanning direction to perform image exposure. The developing device 4 performs a reversal development using a two-component developer and attaching a negatively charged toner to an exposed portion on the photoconductor 1 with a developing bias having the same polarity as that of the electrostatic latent image on the photoconductor 1. Is used. As the transfer means 5, a corotron charger having a discharge electrode and positively charging the recording paper P is used. As the separating means 6,
A corotron charger that has a discharge electrode and discharges the recording paper P is used.

At the time of image formation, the photosensitive member 1 rotates as indicated by an arrow, and in accordance with the rotation of the photosensitive member 1, charging by the charging means 2, image exposure by the exposure means 3, and development by the developing means 4 are performed. A toner image is formed thereon. The formed toner image is transferred to the recording paper P by the transfer unit 5 and then fixed by the fixing unit 7. The photoconductor 1 that has passed the transfer position where the image is transferred by the transfer unit 5 is cleaned by the cleaning unit 8 to remove the residual toner.

In the embodiment of the present invention described below, prior to the image forming step of forming a toner image on the photosensitive member 1 by the above-described charging, exposure and development, a pre-charging step of charging the photosensitive member 1 Is selectively implemented. The conditions for the selective execution of the pre-charging step vary depending on the type of the photoreceptor used and the like. The pre-charging time is the main pre-charging condition, and this requirement is set by experiments performed using various photoconductors.

The pre-charging, which will be described next, is performed on the photosensitive member 1 shown in FIG. Note that the correction of the charging potential by the preliminary charging described below is performed by adding the intermediate layer and the OP to the metal drum base as described above.
This was performed on an OPC photoreceptor on which a C photoreceptor was formed. The OPC photoreceptor was a negatively charged OPC photoreceptor containing titanyl phthalocyanine as a charge generating substance and styryltriphenylamine as a charge transporting substance. is there.

FIG. 2 shows the charging potential when uniform charging is performed while rotating the photosensitive member. V1 is the charging potential in the first cycle, V2 is the charging potential in the second cycle, and ΔV12 is the potential of V1 and V2. The difference (charge potential difference) is shown.

FIG. 3 shows an example of the downtime of the image forming apparatus, that is, the time from the end of the previous image formation to the start of the next image formation and the change in the charging potential difference ΔV12. As shown, the charging potential difference ΔV12 shows a change that increases with an increase in the pause time. Therefore, by performing the pre-charging corresponding to the pause time to form an image, a good image having a desired density can be formed with the minimum necessary pre-charging. Although the increasing tendency of the charging potential difference shown in FIG. 3 is common to various photoconductors, the value of the charging potential difference varies depending on the photoconductor. Therefore, the preliminary charging time for correcting the charging potential to be performed for each photoconductor is set by an experiment.

Table 1 shows an example of correction of the charging potential by the preliminary charging with respect to the downtime of the image forming apparatus. By the pre-charging shown in Table 1, an image of good image quality without density fluctuation was formed.

[0033]

[Table 1]

FIG. 4 shows an example of a change in the charging potential with respect to the usage history of the photosensitive member. In the figure, V0 indicates the lower limit of the usable charging potential, Va indicates the potential of a new photoconductor, that is, the potential of an unused photoconductor, and Vb indicates the potential of the used photoconductor.

As is apparent from the figure, the charging potential Va of the new photosensitive member has exceeded the lower limit value V0 from the first round. Therefore, a new photoreceptor does not require pre-charging, and an image having a desired density can be formed even if an image is formed from the first week.

On the other hand, the charged potential Vb of the used photoconductor exceeds the lower limit value V0 for the first time in the third cycle. Therefore, it is necessary to precharge the used photoconductor by rotating the photoconductor twice.

The tendency of the charging potential with respect to the usage history as shown in FIG. 4 commonly appears in various photoconductors, but the change value varies depending on the type of photoconductor. Therefore, the correction of the charging potential by the pre-charging for the usage history also differs depending on the type of the photoconductor, and the pre-charging time for the usage history is set by an experiment.

Table 2 shows an example of correction of the charging potential by the preliminary charging. By the preliminary charging shown in Table 2, it was possible to form a good image without fluctuation in density without performing unnecessary preliminary charging.

[0039]

[Table 2]

In Table 2, the preliminary charging time is changed in accordance with the number of image formations (the number of copies), but the operation time of the image forming apparatus is used in place of the number of image formations, and the preliminary charging time is changed in accordance with the operation time. A similar effect can be obtained by performing control to change the pre-charging time.

The change in image quality due to the charging potential greatly affects the image quality in forming a continuous tone image such as a photographic image or a pattern image, but has a large effect in forming a binary image such as a character image. Has no effect. Further, even in the case where there is an influence, it is possible to perform correction based on developing conditions such as a developing bias. Therefore, in the embodiment of the present invention, the image process is performed without performing the pre-charging in the binary image forming, and the correction by the pre-charging is performed in the image forming process for forming the continuous tone image such as the multi-valued image forming. Was done. That is, in the embodiment of the present invention, the preliminary charging is selectively executed in accordance with the image gradation mode.

Table 3 shows an example of preliminary charging for a binary image and a multi-valued image (the number of density values is 256). By the preliminary charging shown in Table 3, high-quality images were stably formed in both the binary image and the multi-valued image.

[0043]

[Table 3]

The pre-charging time in the selection of the pre-charging for the image gradation mode also changes according to the type of the photosensitive member. Therefore, the pre-charging times for various photoconductors are set by experiments.

The charge potential of the photosensitive member varies depending on the environment, that is, at least one of humidity and temperature. In particular, the charging potential of the photoconductor is affected by changes in humidity.
Therefore, by controlling the pre-charging time in accordance with the change in humidity, it is possible to form a stable image that is not affected by changes in the environment.

Table 4 shows examples of the pre-charging time with respect to the relative humidity. By performing the pre-charging shown in Table 4, a high-quality image was formed stably without being affected by changes in the environment.

[0047]

[Table 4]

The fluctuation of the charging potential due to the environment also varies depending on the type of the photoreceptor, and the optimal conditions for the pre-charging are set by experiments according to the type of the photoreceptor. Table 4
In the above, the pre-charging time is changed in response to a change in humidity. However, depending on the type of the photoconductor, the pre-charging time can be made to correspond to a change in humidity and temperature or a change in temperature, whereby image quality can be stabilized. In some cases. The control of the pre-charging time corresponding to the environment is performed using the detection output of the temperature and the humidity by the sensor 14 in FIG.

The pre-charging shown in Tables 1 to 4 was performed using the charging means 2 in FIG. 1, but in the present invention, the pre-charging was performed using the separating means 6 instead of the charging means 2. You can do it too. When the preliminary charging is performed using the separation unit 6, the power supply is switched from an AC power supply to a DC power supply that negatively charges the photoconductor 1.

The pre-charging control shown in Tables 1 to 4
By implementing the above in combination, furthermore, FCOT
And stable image formation can be performed.

[0051]

According to the first or eighth aspect of the present invention, depending on the idle time of the image forming apparatus, pre-charging is not performed or a high-quality image is formed in a short pre-charging time. Image formation and FC
An image forming apparatus with a short OT and little deterioration of the photoconductor is realized.

According to the second, third, ninth or tenth aspect of the present invention,
As long as the usage history of the photoconductor is small, high-quality images are formed without precharging or with a short precharging time, so that an image forming apparatus with a short FCOT and little deterioration of the photoconductor is realized. You.

According to the fourth or eleventh aspect of the present invention, an image is formed without performing preliminary charging depending on the image gradation mode, so that stable image formation with a small change in density can be performed, the FCOT is short, and An image forming apparatus with less deterioration of the photoconductor is realized.

According to the fifth, sixth, twelfth, and thirteenth aspects of the present invention, a high-quality image is formed without precharging or with a short precharging time depending on the environment, that is, humidity or temperature. An image forming apparatus that performs stable image formation with little change in density, has a short FCOT, and has little deterioration of the photoconductor is realized.

According to the seventh or fourteenth aspect of the present invention, since the conditions of the pre-charging are set based on a plurality of factors, the pre-charging can be stopped to a necessary minimum and stable image formation with little change in density can be performed. At the same time, shortening of FCOT and prevention of deterioration of the photoconductor are most effectively performed.

According to any one of claims 8 to 14,
Since the movement time of the photoconductor from the separation unit to the charging unit is the time required for the preliminary charging, the time for the preliminary charging time is shortened, and an image forming apparatus with a short FCOT is realized.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a charging potential when charging is performed while rotating a photosensitive member.

FIG. 3 is a diagram showing an example of a change in a charging potential difference ΔV12.

FIG. 4 is a diagram illustrating an example of a change in charging potential with respect to a use history of a photoconductor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging means 3 Exposure means 4 Developing means 5 Transfer means 6 Separation means ΔV12 Charge potential difference

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Watanabe Wataru 2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica Corporation F-term (reference) 2H003 BB11 CC01 DD00 2H027 DA13 DA14 DA39 DA40 DA44 DA45 ED03

Claims (14)

[Claims] A photoconductor, a charging unit for uniformly charging the photoconductor, an exposure unit for exposing the charged photoconductor to an image, an electrostatic latent image formed on the photoconductor by charging and exposure A developing unit for developing the image forming apparatus, and the control unit sets a preliminary charging time from the start of charging by the charging unit to the exposure by the exposing unit to the next charging time from the end of the previous image forming process. An image forming apparatus which sets the image forming apparatus based on a pause time until the start of the image forming step. 2. A photoconductor, a charging unit for uniformly charging the photoconductor, an exposure unit for exposing the charged photoconductor to an image, and an electrostatic latent image formed on the photoconductor by charging and exposure A developing unit for developing the image forming unit, and the control unit sets a preliminary charging time from the start of charging by the charging unit to the exposure by the exposing unit based on an operation time of the image forming unit. An image forming apparatus. A photoconductor, a charging unit for uniformly charging the photoconductor, an exposure unit for exposing the charged photoconductor to an image, an electrostatic latent image formed on the photoconductor by charging and exposure A developing unit that develops the image, and a control unit, wherein the control unit sets a preliminary charging time from the start of charging by the charging unit to exposure by the exposure unit based on the number of formed images. An image forming apparatus comprising: 4. A photoconductor, a charging unit for uniformly charging the photoconductor, an exposure unit for imagewise exposing the charged photoconductor, an electrostatic latent image formed on the photoconductor by charging and exposure A developing unit that develops the image, and a control unit that changes a preliminary charging time from the start of charging by the charging unit to the exposure by the exposure unit in accordance with an image gradation mode. And an image forming apparatus. 5. A photoreceptor, a charging unit for uniformly charging the photoreceptor, an exposure unit for exposing the charged photoreceptor to an image, an electrostatic latent image formed on the photoreceptor by charging and exposure And an image forming apparatus comprising: a developing unit configured to develop the image forming apparatus; and a control unit that performs control to change a preliminary charging time from the start of charging by the charging unit to the exposure by the exposure unit in accordance with an environment. An image forming apparatus comprising: 6. An environment sensor for detecting a temperature or a humidity, wherein the control unit is configured to perform a control based on an output of the environment sensor.
The image forming apparatus according to claim 5, wherein the control is performed. 7. A photoreceptor, a charging unit for uniformly charging the photoreceptor, an exposure unit for exposing the charged photoreceptor to an image, an electrostatic latent image formed on the photoreceptor by charging and exposure A developing unit for developing the image forming apparatus, and the control unit sets a preliminary charging time from the start of charging by the charging unit to the exposure by the exposing unit to the next charging time from the end of the previous image forming process. Controlling the change based on two or more parameters selected from the pause time until the start of the image forming process, the operation time of the image forming unit, the number of formed images, the image gradation mode, and the environment. Image forming apparatus. 8. A photoreceptor, a charging unit for uniformly charging the photoreceptor, an exposure unit for exposing the charged photoreceptor to an image, an electrostatic latent image formed on the photoreceptor by charging and exposure Developing means for developing a toner image formed on the photosensitive member onto a recording material; separating means for separating the recording material having the toner image formed thereon from the photosensitive member by static elimination; and control means. In the image forming apparatus, wherein the preliminary charging is performed by the separation unit, the control unit determines the time of the preliminary charging based on a pause time from the end of the previous image forming process to the start of the next image forming process. An image forming apparatus, wherein: 9. A photoreceptor, charging means for uniformly charging the photoreceptor, exposure means for imagewise exposing the charged photoreceptor, an electrostatic latent image formed on the photoreceptor by charging and exposure Developing means for developing a toner image formed on the photosensitive member onto a recording material; separating means for separating the recording material having the toner image formed thereon from the photosensitive member by static elimination; and control means. The image forming apparatus according to claim 1, wherein the control unit sets the time of the preliminary charging based on an operation time of the image forming unit. 10. A photoreceptor, a charging unit for uniformly charging the photoreceptor, an exposure unit for exposing the charged photoreceptor to an image, an electrostatic latent image formed on the photoreceptor by charging and exposure Developing means for developing a toner image formed on the photosensitive member onto a recording material; separating means for separating the recording material having the toner image formed thereon from the photosensitive member by static elimination; and control means. The image forming apparatus, wherein the control unit sets the time of the preliminary charging based on the number of formed images. 11. A photoreceptor, a charging unit for uniformly charging the photoreceptor, an exposure unit for exposing the charged photoreceptor to an image, an electrostatic latent image formed on the photoreceptor by charging and exposure Developing means for developing a toner image formed on the photosensitive member onto a recording material; separating means for separating the recording material having the toner image formed thereon from the photosensitive member by static elimination; and control means. The image forming apparatus according to claim 1, wherein the control unit performs control for changing a time of the preliminary charging according to an image gradation mode. 12. A photoreceptor, a charging unit for uniformly charging the photoreceptor, an exposure unit for exposing the charged photoreceptor to an image, an electrostatic latent image formed on the photoreceptor by charging and exposure Developing means for developing a toner image formed on the photosensitive member onto a recording material; separating means for separating the recording material having the toner image formed thereon from the photosensitive member by static elimination; and control means. The image forming apparatus according to claim 1, wherein the control unit performs control for changing a time of the preliminary charging according to an environment. 13. The image forming apparatus according to claim 12, further comprising an environment sensor for detecting a temperature or a humidity, wherein the control unit performs the control based on an output of the environment sensor. 14. A photoreceptor, a charging unit for uniformly charging the photoreceptor, an exposure unit for exposing the charged photoreceptor to an image, an electrostatic latent image formed on the photoreceptor by charging and exposure Developing means for developing a toner image formed on the photosensitive member onto a recording material; separating means for separating the recording material having the toner image formed thereon from the photosensitive member by static elimination; and control means. In the image forming apparatus having pre-charging by the separation unit, the control unit sets the time of the pre-charging, a pause time from the end of the previous image forming process to the start of the next image forming process, An image forming apparatus that performs control to change based on two or more parameters of an operation time of an image forming unit, the number of formed images, an image gradation mode, and an environment.