JP2002207402A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the precision in detecting a service life of a photosensitive drum by eliminating any error in the estimated service life of the photosensitive drum due to the difference in the printing amount. SOLUTION: The service life of the photosensitive drum 11 is detected when the accumulated electrified time reaches a specified value by changing over AC voltage value applied to an electrifying roll 12 according to the accumulated pixel count twice and starting the counting of the accumulated electrified time from the second change over.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine or a printer.

[0002]

2. Description of the Related Art Conventionally, a corona charger has been used as a charging device used in an image forming apparatus such as an electrophotographic copying machine or a laser printer. In recent years, a contact charging device has been put to practical use instead. This is for the purpose of low ozone and low power, and a roller charging method using a conductive elastic roller as a charging member is particularly preferable in terms of charging stability.

The required current value during charging in the roller charging method will be described with reference to FIG. A conductive elastic roller (hereinafter referred to as a “charging roller”) is pressed against a member to be charged, that is, a photosensitive drum serving as an image carrier, and charging is started by applying a voltage higher than a certain threshold voltage. This threshold voltage is defined as charging start voltage Vth.

In order to obtain the photosensitive drum surface potential Vd required for electrophotography, (Vd + Vt) is applied to the charging roller.
h) DC voltage (DC voltage) is required. Such a method of applying only a DC voltage to the charging roller to perform charging is called a DC charging method.

However, in the DC charging system, the threshold value Vth changes when the resistance value of the charging roller changes due to environmental fluctuations or when the film thickness of the photosensitive layer changes due to abrasion of the photosensitive drum surface. Therefore, it was difficult to set the potential of the photosensitive drum to a desired value.

[0006] Therefore, in order to further uniform the charging, an AC voltage (AC voltage) having a peak-to-peak voltage of twice or more the charging start voltage Vth is superimposed on a DC voltage corresponding to a desired surface potential Vd. An AC charging method of applying the so-called superimposed voltage to a charging roller is used. This is AC
The purpose of this is to achieve a leveling effect of potential by voltage,
The potential of the photosensitive drum surface is Vd which is the center of the peak of the AC voltage. And the influence of disturbances such as the environment is small. In this AC charging method, an AC current (hereinafter, “Iac”) flowing therethrough is used to uniformly charge the surface of the photosensitive drum.
) Is controlled to be constant.

When an AC voltage is applied to the charging roller, three kinds of currents flow between the charging roller and the photosensitive drum. That is, there are a resistive load current flowing through the resistive load, a capacitive load current flowing through the capacitive load, and a discharge current.

Here, the characteristics of the discharge current are shown in FIGS.
This will be described with reference to FIG.

In general, as the total number of formed images increases, residual toner or paper powder that cannot be transferred or cleaned adheres to the charging roller and the resistance value of the charging roller increases. Accordingly, the discharge start current value decreases. FIG. 8 shows the relationship between the peak current amount and the discharge current amount. The discharge start current value decreases from the A value to the B value. Then, if the peak value of Iac is controlled to a predetermined value, the discharge current amount will eventually increase.

FIG. 9 shows the relationship between the discharge current (μA) and the integrated charging time (sec). In the curve A, the discharge current amount first increases for the above-described reason, and the contamination of the charging roller is saturated after a certain integrated charging time, so that the discharge current amount does not increase. When the amount of discharge current increases, the amount of scraping of the photosensitive drum increases accordingly, so that the life of the photosensitive drum is shortened. Accordingly, a control method has been devised in which the integrated charging time and the like are measured in order to keep the discharge current constant, and Iac is switched in multiple stages in accordance with the predetermined values. As a result, stable image forming can be performed over a long period of time.

FIG. 10 shows the relationship between Iac switched in multiple stages and the integrated charging time. The horizontal axis is the integrated charging time, and the vertical axis is Iac. As shown in FIG. 9, the integrated charging time is counted from the start of the integrated charging time, and Iac is switched at the integrated charging times a and b in FIG. When Iac is switched, the discharge current amount can be kept constant as shown by the curve B in FIG.

As a method of detecting the life of the photosensitive drum in the above-described image forming apparatus, the charging time and the like are counted and accumulated from the time when the photosensitive drum is new, and the life is determined by a predetermined integrated charging time.

[0013]

However, in the method of measuring the cumulative charging time from the start of the charging time of the photosensitive drum to detect the life of the photosensitive drum as described above, the printing rate and the difference in environment are factors. Since there is an error in estimating the life of the photosensitive drum, the accuracy of detecting the life of the photosensitive drum is poor. This is because the charging roller is stained differently depending on the printing rate and the environment, and the discharge current amount at the final stage of Iac switching is different, resulting in a variation in the calculation of the photosensitive drum life.

The variation in the calculation of the life of the photosensitive drum due to the difference in the printing rate will be described in detail with reference to FIGS. FIG. 11 is a diagram showing the relationship between the discharge current value and the pixel count after printing a certain number of sheets. As can be seen from FIG. 11, the increase in the discharge current value is almost proportional to the pixel count.
FIG. 12 is a diagram showing the relationship between the discharge current and the total number of printed sheets when the printing rate is 4% and 15%. FIG.
In FIG. 12A, a1 and b1 indicate variations in the discharge current of 4% and 15% of the printing rate, respectively, and a2 and b2 of FIG. 12B indicate Iac at a predetermined integrated charging time of 4% and 15% of the printing rate, respectively.
Shows the fluctuation of the discharge current when is changed to a predetermined value.

As is clear from comparison between a1 and b1,
A larger printing rate of 15% causes more toner contamination on the charging roller, and the discharge current increases faster by that much. However, when Iac is switched at a predetermined integrated charging time, a2, b
2 clearly shows that a difference d occurs in the discharge current at the final stage. In other words, printing rate 4%
Although the life of the photosensitive drum is different at the time of 15% and 15%, the conventional method determines that the life of 4% and 15% is the same.

Next, a description will be given, with reference to FIG. 13, of how the calculation of the photosensitive drum life varies depending on the environment.

FIG. 13 shows the amount of dirt on the charging roller at a temperature of 15 ° C., a humidity of 10% (referred to as LL environment), a temperature of 20 °, a humidity of 60% (referred to as NN environment), a temperature of 30 ° C., and a humidity of 80% (referred to as HH environment). Is a graph showing the dependency of the total number of printed sheets on curves LL, N, and III, respectively.
N, HH environment. As can be seen from FIG. 13, the degree of dirt on the charging roller differs depending on the environment. This is the same as described above in that the calculation of the photosensitive drum life varies due to the difference in the printing ratio.
A difference occurs in the amount of discharge current at the final stage of ac switching, which causes variation in the calculation of the photosensitive drum life.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of eliminating an error in estimating the life of an image carrier due to a difference in printing rate and improving the accuracy of detecting the life of the image carrier.

It is another object of the present invention to provide an image forming apparatus capable of eliminating errors in estimating the life of an image carrier due to differences in printing ratio and environment, and improving the accuracy of detecting the life of the image carrier. .

[0020]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
A process cartridge including an image carrier, a charging member that contacts and charges the image carrier, and a storage unit that can store an accumulated operation amount of the image carrier is removably mounted. In an image forming apparatus having voltage applying means for applying an AC voltage and a DC voltage to a member and performing switching control of an AC voltage value to be applied to the charging member a plurality of times, the image forming apparatus according to a developer usage state of the process cartridge The AC voltage value is switched, and from the last switching of the AC voltage value, the accumulated operation amount of the image carrier is stored in the storage means, and the life of the image carrier is determined when the accumulated operation amount reaches a predetermined value. An image forming apparatus characterized in that:

According to another aspect of the present invention, an image carrier on which an electrostatic latent image is formed, a charging member that contacts and charges the image carrier, and develops the electrostatic latent image with a developer Developing means, storage means capable of storing the cumulative operation amount of the image bearing member, and voltage applying means for applying an AC voltage and a DC voltage to the charging member, wherein an AC voltage value applied to the charging member is In the image forming apparatus that performs the switching control a plurality of times, the AC voltage value is switched according to the usage state of the developer, and the accumulated operation amount of the image carrier is stored in the storage unit from the last switching of the AC voltage value. The image forming apparatus is characterized in that when the cumulative operation amount reaches a predetermined value, the life of the image carrier is determined.

According to one embodiment of each of the above inventions,
The cumulative operation amount of the image carrier is an integrated charging time. Alternatively, the cumulative operation amount of the image carrier is an integrated rotation time.

According to another embodiment of the present invention,
The usage of the developer is a cumulative pixel count.

According to another embodiment, the apparatus further comprises an environment detecting means, and the switching timing of the AC voltage value is changed based on a toner use state according to environment information by the environment detecting means.

According to another embodiment, the apparatus further comprises environment detecting means, and the AC voltage value is changed based on environment information from the environment detecting means.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Embodiment 1 A first embodiment of the present invention will be described with reference to FIGS.

The process cartridge of this embodiment and an electrophotographic image forming apparatus (hereinafter, referred to as a "laser printer") to which the process cartridge can be mounted will be specifically described with reference to FIG.

In the laser printer 1 of the present embodiment, the oscillating voltage obtained by superimposing the AC voltage and the DC voltage in which the peak value of the output current is controlled to a constant current from the high voltage power supply 51 as the voltage applying means is applied to the charging roller 12 as the charging member. To charge the photosensitive drum 11 uniformly. Then, the photosensitive drum 11 is irradiated with a laser beam 31 modulated by image information sent from an information processing device, that is, a PC from the optical system 30 to form an electrostatic latent image on the photosensitive drum 11. The image is developed by a developing device (developing means) 16 having a developing roller 13 and a regulating blade 3 with a developer (hereinafter referred to as “toner”).
To form a toner image.

On the other hand, in synchronization with the formation of the toner image, the recording medium 100 is separated and fed one by one from a cassette 21 containing the recording medium 100 by a pickup roller 22, and a conveying roller (not shown)
3. The toner image formed on the photosensitive drum 11 is conveyed to a transfer unit by a conveyance unit including a conveyance guide 24, and is transferred to the recording medium 100 by applying a voltage to a transfer roller 14 as a transfer unit. Then, the recording medium 100 is conveyed to a fixing device 40 as a fixing unit via a conveyance guide 25. The fixing device 40 applies heat and pressure to the passing recording medium 100 to fix the transferred toner image. Then, the recording medium 100 is conveyed by a discharge roller 26 and discharged to a discharge section 27 through a reverse conveyance path. After the transfer, the photosensitive drum 11 is cleaned by the cleaning device 15 and used for the next image formation.

In the present embodiment, the photosensitive drum 11, the charging roller 12, the developing device 13, and the cleaning device 15 are integrally formed as a process cartridge 10 and, for example, are mounted via a mounting means 60 for replacement due to a life. To be detachable from the printer body. The charging roller 12 is pressed against the photosensitive drum 11 that is driven to rotate in the direction of the arrow at a predetermined pressure, and is driven to rotate with the rotation of the photosensitive drum 11.

Such a process cartridge 10 includes:
As described above, the high voltage power supply 51 supplies the charging roller 12 with the AC voltage and the DC voltage whose peak value of the output current is controlled to a constant current.
The photosensitive drum 11 is uniformly charged by applying a vibration voltage on which a voltage is superimposed. Then, the photosensitive drum 11 is selectively exposed to form an electrostatic latent image, and the electrostatic latent image is visualized as a toner image with the toner T, and the toner image is transferred to the recording medium 100. Perform image recording.

The process cartridge 10 is provided with a non-volatile memory 50 as a storage means capable of reading and writing the accumulated charging time and the accumulated rotation time of the photosensitive drum 11 in a non-contact manner. A CPU 52 is provided in the printer main body, and detects a toner consumption state, that is, a usage state, by counting individual image signals forming image dots (hereinafter, referred to as “pixel count”).

Here, a method for detecting the life of the photosensitive drum according to the present embodiment will be described with reference to FIG.

FIG. 2 shows the AC current Iac in this embodiment.
The relationship between the discharge current and the integrated charging time when switching is performed is shown. Note that α and β in FIG.
It shows a change in discharge current of 5%.

First, the pixel count is detected, and if the cumulative pixel count X is exceeded, the first Iac switching is performed. Specifically, the laser beam printer of this embodiment is 600 dpi (dot per inch),
Letter size paper (216 mm × 279 mm) was used. In this case, the image formable area is 204 mm × 269
mm, the pixel count per sheet is 4878 ×
6240 (= 30,438,720). Therefore,
Pixel counts per sheet with a printing ratio of 4% and 15% are 1,217,549, 4,565,808, respectively.
It is. Then, the cumulative pixel count X = 3.7
× 10 ⁹ . As a result, the first Iac switching timing is 3000 sheets at a printing rate of 4%, and
800 sheets.

Next, when the accumulated pixel count Y is exceeded, the second Iac switching is performed. Y = 11 × 10
^{It was set to 9} . As a result, the second Iac switching timing is 9000 sheets at a printing rate of 4% and 240 at a printing rate of 15%.
It is zero.

As shown in FIG. 2, by performing the Iac switching twice, the discharge current amount at the final stage becomes almost equal in both the printing rates of 4% and 15%.

Next, at the same time when the second Iac switching is completed, the nonvolatile memory 50 counts the accumulated charging time. When the printing rate is 4%, the integrated charging time is counted from (1) in FIG. 2 and when the printing rate is 15%, the integrated charging time is counted from (2) in FIG. Judge as life. In this embodiment, F = 80,00
0 sec. As a result, the life of the photosensitive drum when the printing rate is 4% and 15% is Fin1 and Fin2, respectively.

As described above, the switching of Iac is performed in accordance with the accumulated pixel count, and the discharge current during the period until the discharge current is stabilized is controlled within a predetermined range. As a result, the drum life can be accurately detected.

In this embodiment, the switching of Iac is performed twice, but is not particularly limited.

In this embodiment, the life of the photosensitive drum is determined by counting the integrated charging time, but may be determined by counting the integrated rotating time of the photosensitive drum.

Embodiment 2 Next, a second embodiment of the present invention will be described with reference to FIGS.

The laser printer of the present embodiment is provided with environment detecting means for observing the temperature and humidity during use. The rest of the configuration and the operation of the laser printer are the same as in the first embodiment, and will not be described. The environment detecting means is mounted near the charging roller 12 shown in FIG. In this embodiment, an absolute humidity sensor unit HS-6 manufactured by Shibaura Electronics Works was used as the environment detecting means.

In this embodiment, the switching timing of the AC current Iac is changed according to the environment, and the final stage Ia is changed.
The life of the photosensitive drum is detected from c. This will be described in detail below.

First, an environment sensor 53 serving as environment detection means
Reads the environment in the vicinity of the charging roller 12, that is, temperature and humidity, and outputs NN, H as shown in FIG.
An environment area divided into three areas of H and LL is selected. Here, the environment below the temperature of 15 ° C. and the humidity of less than 12% is LL, and the temperature of 15 ° C. or more and less than 25 ° C. and the humidity of 12%
NN in an environment of at least 65% but less than 65% and humidity of 6
The environment of 5% or more is defined as HH.

Next, the environment N detected by the environment sensor 53
The cumulative pixel count value at the time of Iac switching is changed according to N, HH, and LL. The symbol A described below,
B and C are cumulative pixel count values at the time of the first Iac switching in the NN, HH, and LL environments, respectively.
Symbols A'B 'and C' are cumulative pixel count values at the time of the second Iac switching in the NN, HH, and LL environments, respectively.

With the NN environment in FIG. 3 as a reference environment, the accumulated pixel count value at the time of the first Iac switching is A. Since the HH environment has a high temperature and a high humidity, the discharge current amount increases more quickly than the NN environment, and the shaving amount of the photosensitive drum becomes faster. Therefore, the cumulative pixel count value B at the time of switching Iac is set to 0.8A. Further, in the LL environment, since the temperature is low and the humidity is low, the discharge current amount increases more slowly and the shaving amount of the photosensitive drum becomes slower than in the NN environment. Let C = 1.2A. Specifically, when letter size paper was used with a laser printer of 600 dpi and the printing rate was 4%, A = 3.7 × 10 ⁹ .

Next, at the second Iac switching timing, the amount of increase in the discharge current is larger in the LL environment than in the HH environment. Therefore, the cumulative pixel count value at the time of Iac switching is B ′ = 1. 2A ', LL
In the environment, C '= 0.8A'. At this time, A '= 11
× 10 ⁹ .

After the second Iac switching, the accumulated charging time is counted, as in the first embodiment.
The drum life is defined as the point where the integrated charging time F is reached. In this embodiment, F = 80,000 sec.

FIG. 5 shows the relationship between the discharge current in the HH and LL environments and the accumulated charging time when the Iac switching timing of this embodiment is changed. As shown in FIG. 5, the discharge current amount at the final stage has substantially the same value.

As described above, in this embodiment, the Iac switching timing is changed according to the environmental conditions, and the photosensitive drum life is detected from the last stage of the switching, so that the life of the photosensitive drum can be detected according to the user's usage. Not only can be performed, but also it is possible to eliminate an error in detecting the life of the photosensitive drum due to the environment.

In this embodiment, the environment area is divided into three areas. However, the present invention is not limited to this.

Embodiment 3 Next, a third embodiment of the present invention will be described.

In this embodiment, the switching amount of Iac is changed according to the environment. This will be described below with reference to FIG. 4 and Table 1. Note that the laser printer of this embodiment has the same configuration as that of the second embodiment shown in FIG.

First, the environment sensor 53 reads the temperature and the humidity, and the CPU 52 reads the NN, HH, L shown in FIG.
An environment area divided into three areas of L is selected. NN,
The temperature and humidity corresponding to HH and LL are the same as in the second embodiment.

Next, when the pixel count is detected and the cumulative pixel count X 'is exceeded, Iac switching is performed. At this time, Ia switching corresponding to the environment NN, HH, LL is performed.
Switch to c. Table 1 shows the environment NN, HH, LL and the value of Iac at the switching timing. The cumulative pixel count X ′ at the time of switching is 37 × 10 ^{9 for} the first time and 11 × 10 ⁹ for the second time. The symbols θ1, θ2, θ3
Are the initial Iac value and the Iac value after switching once, respectively.
Values and Iac values at the final stage. The higher the temperature and humidity, the faster the amount of discharge current increases, and the faster the amount of abrasion of the photosensitive drum. Therefore, the Hac is higher than the Iac value θ in the NN environment.
50 μA, and -50 μA in the LL environment.

After the second Iac switching, the accumulated charging time is counted, as in the first embodiment.
The drum life is defined as the point where the integrated charging time F is reached. Also in this embodiment, F = 80,000 sec.

FIG. 6 shows the relationship between the discharge current and the accumulated charging time in the HH and LL environments when the Iac value to be switched in this embodiment is changed according to the environment. As shown in FIG. 6, the discharge current amount at the final stage has substantially the same value.

As described above, in this embodiment, the Iac value is changed in accordance with the environmental conditions, and the life of the photosensitive drum is detected from the final stage of the Iac switching, thereby eliminating the error in detecting the life of the photosensitive drum due to the environment. it can.

[0061]

[Table 1]

The process cartridge in the above embodiment may be any one provided with a photosensitive drum and a charging means as at least one process means.

[0063]

As described above, the present invention comprises an image carrier, a charging member that contacts and charges the image carrier, and a storage unit that can store the cumulative operation amount of the image carrier. Equipped with a removable process cartridge,
In an image forming apparatus having voltage applying means for applying an AC voltage and a DC voltage to the charging member and performing switching control of an AC voltage value to be applied to the charging member a plurality of times, according to a developer usage state of the process cartridge. The AC voltage value is switched, and the accumulated operation amount of the image carrier is stored in the storage means from the last switching of the AC voltage value, and when the accumulated operation amount reaches a predetermined value, the image carrier is By setting the life as described above, it is possible to eliminate an error in estimating the life of the image carrier due to a difference in printing rate, and to improve the accuracy of detecting the life of the image carrier.

An image carrier on which an electrostatic latent image is formed;
A charging member that contacts and charges the image carrier, a developing unit that develops the electrostatic latent image with a developer, a storage unit that can store a cumulative operation amount of the image carrier, Voltage applying means for applying a voltage and a DC voltage,
In an image forming apparatus that performs switching control of an AC voltage value to be applied to the charging member a plurality of times, the AC voltage value is switched according to a usage state of a developer, and the image carrier is switched from the last switching of the AC voltage value Is stored in the storage means, and when the cumulative amount of operation reaches a predetermined value is regarded as the life of the image carrier, the same effect as described above can be obtained.

Further, in each of the above image forming apparatuses, an environment detecting means is provided, and the switching timing of the AC voltage value is changed based on the use condition of the developer according to the environment information by the environment detecting means, so that the printing rate can be improved. In addition, it is possible to eliminate an error in estimating the life of the image carrier due to a difference in environment, and to improve the accuracy of detecting the life of the image carrier.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a relationship between a discharge current and an integrated charging time when Iac is switched in the image forming apparatus of FIG. 1;

FIG. 3 is a configuration diagram showing another embodiment of the image forming apparatus according to the present invention.

FIG. 4 is a diagram illustrating an environment area.

FIG. 5 is a diagram illustrating a relationship between a discharge current and an accumulated charging time in an HH environment and an LL environment in the image forming apparatus of FIG. 3;

FIG. 6 is a diagram illustrating another relationship between the discharge current and the accumulated charging time in the HH environment and the LL environment in the image forming apparatus of FIG. 3;

FIG. 7 is a diagram for explaining a relationship between a surface potential of a photosensitive drum and an applied voltage.

FIG. 8 is a diagram for explaining a relationship between a peak current amount and a discharge current at the beginning of use of the photosensitive drum and after use for a certain period of time.

FIG. 9 is a diagram for explaining a relationship between a discharge current and an integrated charging time.

FIG. 10 is a diagram for explaining a relationship between an alternating current applied to a charging roller and an integrated charging time.

FIG. 11 is a diagram illustrating a relationship between a discharge current value and a pixel count number after printing an arbitrary number of sheets.

FIG. 12 is a diagram showing the relationship between discharge current and the total number of printed sheets when the printing ratio is 4% and 15%.

FIG. 13 is a diagram illustrating the dependence of the amount of dirt on the charging roller in the total number of printed sheets in each environment.

DESCRIPTION OF SYMBOLS 10 Process cartridge 11 Photosensitive drum (image carrier) 12 Charging roller (charging member) 16 Developing device (developing unit) 50 Nonvolatile memory (storage unit) 51 High voltage power supply (voltage applying unit)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Seishi Saito 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Dai Shimura 3-30-2 Shimomaruko 3-chome, Ota-ku, Tokyo Non-corporation F term (reference) 2H027 DA14 DA39 DA41 DA45 DB01 EC10 ED02 ED03 EE02 EE08 HB02 HB05 HB14 HB15 HB17

Claims (7)

[Claims] 1. A process cartridge having an image carrier, a charging member that contacts and charges the image carrier, and a storage unit that can store a cumulative operation amount of the image carrier is detachably mounted. An image forming apparatus further comprising voltage applying means for applying an AC voltage and a DC voltage to the charging member, and performing switching control of an AC voltage value to be applied to the charging member a plurality of times; The AC voltage value is switched according to the situation, and from the last switching of the AC voltage value, the accumulated operation amount of the image carrier is stored in the storage unit, and when the accumulated operation amount reaches a predetermined value, An image forming apparatus wherein the life of an image carrier is set. 2. An image bearing member on which an electrostatic latent image is formed, a charging member that contacts and charges the image bearing member, a developing unit that develops the electrostatic latent image with a developer, and the image bearing member. An image having storage means capable of storing the accumulated amount of movement of the body, and voltage applying means for applying an AC voltage and a DC voltage to the charging member, and performing switching control of the AC voltage value applied to the charging member a plurality of times. In the forming apparatus, the AC voltage value is switched according to the usage state of the developer,
From the last switching of the AC voltage value, the cumulative operation amount of the image carrier is stored in the storage unit, and the time when the cumulative operation amount reaches a predetermined value is defined as the life of the image carrier. Image forming apparatus. 3. The image forming apparatus according to claim 1, wherein the cumulative operation amount of the image carrier is an integrated charging time. 4. The image forming apparatus according to claim 1, wherein the cumulative operation amount of the image carrier is an integrated rotation time. 5. The image forming apparatus according to claim 1, wherein the use status of the developer is a cumulative pixel count. 6. The apparatus according to claim 1, further comprising an environment detecting unit, wherein the switching timing of the AC voltage value is changed based on a use state of the developer according to the environment information by the environment detecting unit. 2 image forming apparatus. 7. The image forming apparatus according to claim 1, further comprising an environment detection unit, wherein the AC voltage value is changed based on environment information from the environment detection unit.