JPH08334956A - Image forming device - Google Patents

Abstract

PURPOSE: To improve film-thickness detection accuracy, in an image forming device equipped with a film-thickness judge means which detects a current flowing in an image carrier when an electrifying member electrifies or discharges the image carrier, and which judges the film thickness of the image carrier based on the current signal. CONSTITUTION: The value of a voltage which is applied to the electrifying member 2 when the image carrier 1 is electrified, is different between at the time of image formation and at the time of film-thickness judgement. In the absolute value of the voltage which is applied to the electrifying member 2 at the time of electrifying the image carrier, a value at the film-thickness judgment is larger than a value at the image formation. The device is equipped with a temperature/humidity detection means 11 which detects the temperature or/and humidity in the main body of the device, and a means 9 which varies and controls the value of the voltage which is applied to the electrifying member 2 according to the output value of the means 11.

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 laser beam printer or an electrophotographic apparatus.

[0002]

2. Description of the Related Art For example, in an image forming apparatus such as an electrophotographic printer (ex. Carlson process) such as a printer or a copying machine, a rotary drum type electrophotographic photosensitive member is generally used as an image bearing member (charged member). A known image forming process of charging, exposing, and developing is applied to this to form and carry a toner image corresponding to target image information, and the toner image is transferred to a transfer material by a transfer means, and the transferred toner image is transferred. The fixing means fixes the transfer material as a permanently fixed image, and outputs the transfer material as an image-formed product (print / copy). After the transfer of the toner image to the transfer material, the photosensitive member is cleaned by removing the transfer residual toner and the like from the surface by a cleaning unit, and is repeatedly used for image formation.

In the image forming apparatus as described above,
Although the photoconductor serving as the image carrier is cleaned by removing the residual toner after transfer by the cleaning means, it is gradually contaminated by the components of the transfer material and the discharge products at the time of charging while being repeatedly used. To go.

As described above, when the photoconductor is contaminated, the resistance of the surface is lowered and the electrostatic latent image is disturbed, or the toner and its components are fused to the photoconductor surface, and the image is remarkably damaged. Will result. In recent years, image forming apparatuses such as laser printers are strongly demanded to have high image quality, and in terms of resolution, they are moving toward multi-valued image processing with image processing such as 600 dpi or 800 dpi and PWM (pulse width modulation). However, even a slight contamination of the photoconductor appears on the image.

Therefore, in the conventional image forming apparatus, the surface of the photosensitive drum is positively polished by the cleaning blade to refresh the surface to maintain a good image. As a result, the thickness of the photosensitive layer is durable. It gradually decreases with. The photoconductor acts as a capacitor in a dark portion (a portion not exposed to light), and when an electric charge is applied, it is retained and appears as a surface potential.

However, when the film thickness of the photoconductor is too thin, the amount of electric charge given by the charger is limited, so that the surface potential is lowered, and the film of the photoconductor has some defects. Therefore, the charge may locally escape, which may lead to poor charging.

Therefore, in order to maintain a good image,
There is a minimum required film thickness. For example, in an OPC photosensitive member, the minimum thickness of the uppermost charge transport layer (CT layer) is 10 μm.
Thus, the photoconductor reaches the end of its life when the thickness of the CT layer reaches 10 μm.

That is, since the photosensitive member as the image bearing member is a consumable item, it must be replaced due to its life.
Therefore, a function is provided to detect the film thickness of the photoconductor and inform the user of the photoconductor life when the film thickness is reduced to the limit.

The film thickness of the photoconductor is obtained by utilizing the above-mentioned characteristics of the photoconductor as a capacitor when the charge is removed from the charged state of the photoconductor or when the charge is removed from the charged state. It can be calculated from the current flowing through the photoconductor (Japanese Patent Laid-Open No. 5-53488).

Briefly, the surface potential of the photoconductor is set to 0 →
Vdpt. , Or Vdpt. → The DC current IDC flowing to the photoconductor when it is lowered by 0 is the film thickness of the photoconductor, the relative permittivity ε, the permittivity in vacuum ε0, the effective charging width of the primary roller charger L, the process When the speed is vp, it is expressed by the following relational expression.

| IDC | = ε · ε0 · L · vp · Vdpt / d, where ε, ε0, L, vp, Vdpt. Can be regarded as a constant, the DC current IDC is the film thickness d of the photoconductor.
Is inversely proportional to. Therefore, the film thickness of the photoconductor can be detected by measuring the DC current IDC (JP-A-5-223513).

The photoconductor current IDC is calculated from the voltage generated across the current detection resistor connected to the ground of the photoconductor.

The above-described method for detecting the life of the photoconductor by directly measuring the film thickness of the photoconductor has the following merits. That is, the amount of photoconductor scraping per number of prints varies greatly depending on the operating environment (temperature, humidity, etc.) of the device, but if the film thickness of the photoconductor is directly measured, the photoconductor will reach the limit under all use conditions. It can be used up. Therefore, the life of the photoconductor can be extended and the running cost can be minimized as compared with the method of determining the life of the photoconductor by the number of prints.

The above-mentioned film thickness detecting means is used not only for detecting the life of the photosensitive member but also for determining whether or not the photosensitive member is mounted, determining whether or not the photosensitive member has been replaced.

In particular, it is an effective means for judging the life of the process cartridge including the photoconductor, the presence / absence of attachment, and the presence / absence of replacement.

[0016]

However, as a result of repeated studies by the present inventors, the image forming apparatus using the above-described method for detecting the film thickness of the photoconductor has the following problems.

(A) In the conventional image forming apparatus, the voltage (Vdpt.) For charging the photoconductor when the film thickness of the photoconductor is detected is
Since it is set to be equal to the charging voltage (hereinafter, Vd) at the time of image formation, when Vd is changed by, for example, the density adjusting volume or environmental control, Vdpt. Since it also changes in conjunction with the above, the detection current IDC in the above equation changes, and as a result, the film thickness cannot be accurately detected.

(B) When the film thickness is detected, the current flowing through the photoconductor is very small, so the voltage obtained by the current detection resistor is also small, and therefore it is difficult to improve the detection accuracy. Further, if the detection resistance value is increased in order to increase the detection voltage, the voltage applied to the detection resistance during charging is largely divided, which is not preferable.

(C) The environment in which the image forming apparatus is used varies from high temperature and high humidity to low temperature and low humidity, but after the detection voltage obtained by the current detection resistor is amplified by the amplification circuit in the film thickness detection circuit, the film thickness is measured. If the temperature characteristic of the amplifier circuit is large, the detected film thickness will change due to changes in the environment.

The present invention has a film thickness judging means for detecting the current flowing through the image carrier when the image carrier is charged or discharged by the charging member and judging the film thickness of the image carrier from the current signal. An object of the image forming apparatus is to solve the above-mentioned problems, that is, to accurately detect the film thickness of the image carrier and to improve the accuracy of film thickness detection.

[0021]

The present invention is an image forming apparatus having the following configuration.

(1) A means for applying a voltage to a charging member to charge or discharge an image carrier as a member to be charged to a predetermined potential, and a means for flowing through the image carrier when charging or discharging the image carrier. In an image forming apparatus having a current detection unit that detects a current signal and a film thickness determination unit that determines the film thickness of the image carrier from the current signal, the voltage value applied to the charging member when the image carrier is charged. The image forming apparatus is characterized in that it is different when the image is formed and when the film thickness is judged.

(2) A means for applying a voltage to the charging member to charge or discharge the image carrier as a member to be charged to a predetermined potential, and a means for flowing the image carrier when charging or discharging the image carrier. In an image forming apparatus having a current detection unit that detects a current signal and a film thickness determination unit that determines the film thickness of the image carrier based on the current signal, the voltage applied to the charging member when the image carrier is charged. The image forming apparatus is characterized in that the absolute value is larger in the film thickness determination than in the image forming.

(3) The image forming apparatus according to (1) or (2), wherein the voltage value applied to the charging member when the image carrier is charged during image formation is variably controlled. .

(4) The image formation according to (1) or (2), wherein the voltage value applied to the charging member when the image carrier is charged when the film thickness is judged is variably controlled. apparatus.

(5) A voltage value applied to the charging member when the image carrier is charged during image formation, and a voltage value applied to the charging member when the image carrier is charged during the film thickness determination. Is independently and variably controlled (1)
Alternatively, the image forming apparatus according to (2).

(6) Temperature / humidity detecting means for detecting either or both of the temperature and humidity inside the apparatus main body, and the voltage value applied to the charging member is variably controlled according to the output value of the temperature / humidity detecting means. The image forming apparatus according to any one of (3) to (5), further comprising:

(7) The image forming apparatus according to any one of (1) to (6), wherein the charging member is in contact with the image carrier.

(8) The image forming apparatus described in any one of (1) to (7), wherein the image bearing member is an electrophotographic photosensitive member or an electrostatic recording dielectric member.

(9) The image forming apparatus according to any one of (1) to (8), wherein the image carrier is included in a process cartridge that is attached to and detached from the main body of the image forming apparatus. .

[0031]

When the film thickness of the image carrier is detected (when the film thickness is judged), the voltage Vdpt. Is determined to be a fixed value independent of the charging voltage Vd during image formation, the film thickness of the image carrier can be accurately detected.

Further, when the film thickness of the image carrier is detected, the voltage Vdpt. Is the charging voltage Vd during image formation
By setting a larger value, it is possible to improve the accuracy of detecting the image carrier thickness.

Furthermore, when the film thickness of the image carrier is detected, the voltage Vdpt. By controlling according to the temperature and humidity inside the main body of the image forming apparatus, the accuracy of film thickness detection can be improved.

[0034]

【Example】

<Embodiment 1> (FIGS. 1 and 2) (1) Example of image forming apparatus FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus according to the present invention. The image forming apparatus of this example is a laser beam printer using a transfer type electrophotographic process and having a process cartridge detachable type.

Reference numeral 1 denotes a rotary drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image bearing member, which is rotationally driven in a clockwise direction indicated by an arrow at a predetermined peripheral speed by a driving means (not shown). . The photosensitive drum 1 in this embodiment is
O formed by coating a photoconductor made of an organic photoconductor (OPC) on the outer peripheral surface of an aluminum cylinder as a drum substrate.
It is a PC photoconductor.

The rotating photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by the charging device 2. In the charging device of this embodiment, a charging roller 2 as a charging member is brought into contact with the photosensitive drum 1, and a predetermined charging voltage is applied to the charging roller from a power source 8 via a cored bar 2a, so that the surface of the photosensitive drum is exposed. It is a contact type roller charging device for charging.

Next, scanning exposure L by a laser beam, which is output from a laser scanner (not shown) and is modulated corresponding to the time-series electric digital pixel signals of the target image information, is applied to the surface of the rotary photosensitive drum 1 which is uniformly charged. As a result, the electrostatic latent image corresponding to the target image information is formed on the surface of the rotary photosensitive drum 1.

Then, the electrostatic latent image on the surface of the rotating photosensitive drum 1 is developed as a toner image by the developing device 3.

The developed toner image is conveyed to a transfer portion, which is a pressure nip portion between the photosensitive drum 1 and a transfer roller 5 as a transfer device, at a predetermined timing from a paper feed mechanism portion (not shown). The image is transferred onto the surface of the transfer paper 7 as a recording material.

The transfer paper 7 having undergone the toner image transfer at the transfer portion exits the transfer portion, is separated from the surface of the photosensitive drum 1 and is introduced into the fixing device 6, and undergoes a fixing process by heating and pressurizing the transferred toner image. Will be printed out.

Further, the surface of the photosensitive drum 1 after the toner image is transferred onto the transfer paper 7 is cleaned by removing adhered residual contaminants such as transfer residual toner by a known blade type cleaning device 4, and repeatedly used for image formation. To be done.

Further, the surface of the photosensitive drum 1 is positively and gradually polished by a cleaning blade to refresh and maintain a good image.

The image forming apparatus of the present embodiment is a process cartridge P in which four process devices including the photosensitive drum 1, the charging roller 2, the developing device 3, and the cleaning device 4 are collectively attached to and detachable from the image forming apparatus main body. is there.

(2) Control of Applied Voltage to Charging Roller 2 A) At the time of image formation At the time of image formation, the charging roller 2 as the photosensitive drum charging member is supplied from the high voltage power source (HVT) 8 through the roller core metal 2a. By applying an oscillating voltage (charging bias during image formation), which is a superimposed voltage of a DC voltage and an AC voltage,
The surface of the photosensitive layer of the photosensitive drum 1 is charged with a predetermined polarity and potential.

The charging bias during image formation in this embodiment has a frequency of 1000 Hz and Vpp (peak-to-peak).
This is an oscillating voltage obtained by superimposing a DC component of -600V to -750V (variable) on an AC voltage of 1800V.

Reference numeral 11 denotes a temperature / humidity sensor provided in the main body of the image forming apparatus, and temperature / humidity detection information of the sensor 11 is input to the control circuit (CPU) 9.

The control circuit 9 sets the center value of the DC voltage of the charging bias voltage at the time of image formation to be applied from the power source 8 to the charging roller 2 to -650 V (in a low temperature and low humidity environment) in accordance with the input temperature / humidity detection information from the sensor 11. ) To -700V
Environmental control up to (under high temperature and high humidity environment). Further, the density adjustment volume that can be adjusted by the user is used to adjust ± 50V.

B) When Photoreceptor Film Thickness is Detected As described above, in order to maintain a good image, the surface of the photosensitive drum is positively abraded by the cleaning blade little by little and refreshed, so that the photosensitive layer thickness is durable. Since the number of sheets gradually decreases with the passage of paper, the control circuit 9 executes the photosensitive member film thickness detection, that is, the photosensitive member life detection sequence at a predetermined time such as during the front rotation stroke and the rear rotation stroke of the image forming apparatus.

The photoconductor film thickness is detected by detecting the current flowing through the photoconductor when the charging roller 2 charges or removes the photoconductor drum 1, and the photoconductor film thickness is detected from the current signal.

Thus, in this embodiment, when the photosensitive member film thickness is detected, an AC voltage (static elimination bias) having a frequency of 1000 Hz and Vpp = 1800V is first applied for one rotation of the photosensitive drum or more to make the surface potential of the photosensitive drum 1 0V. To neutralize.

Next, frequency 1000 Hz, Vpp = 18
The photosensitive drum 1 is rotated three times or more while applying a voltage (charging bias at the time of detecting the photoconductor film thickness) in which a DC voltage of -700V is superimposed on an AC voltage of 00V, and the surface of the photosensitive drum is V
It is uniformly charged to dpt = -700V (corresponding to the DC component voltage of the voltage applied to the charging roller 2).

Further, the frequency is 1000 Hz, Vpp = 18
The photosensitive drum 1 is rotated in the state where the AC voltage of 00V is applied, and the surface of the photosensitive drum is removed again.

At this time, the direct current I flowing through the photosensitive drum 1
DC becomes the film thickness detection current. Specifically, the photoconductor current I
DC is a current detection resistor R connected to the ground of the photoconductor
The voltage information generated at the both ends of is input to the control circuit 9 via the amplifier 10 · A / D (analog-digital) conversion circuit 12 and calculated.

The control circuit 9 detects the current film thickness of the photoconductor based on the calculated photoconductor current IDC and determines the life of the photoconductor.

When the detected film thickness is below the permissible lower limit, it is considered that the photosensitive drum 1 has reached the end of its life, and the control circuit 9 executes a coping operation flow such as operation of the warning display means.

The above-mentioned film thickness detecting means can be used not only for detecting the life of the photoconductor, but also for determining whether or not the photoconductor is mounted, for determining whether or not the photoconductor has been replaced. In the image forming apparatus using the process cartridge P including the photoconductor, it is also possible to use it for the life judgment of the process cartridge, the presence / absence judgment / replacement judgment means of the cartridge with respect to the image forming apparatus body.

C) Comparison with Conventional Example A comparison between this embodiment and the conventional example will be described with reference to FIG.

In FIG. 2, the vertical axis indicates the film thickness detection current ID.
C, the horizontal axis represents the photoconductor film thickness d. Curves A, B, and C show that the charging potential Vdpt at the time of film thickness detection is -600V, -700V,
Each of those at -750V is shown.

In the conventional example, the charging potential Vdp during film thickness detection
Since t is interlocked with the charging potential Vd at the time of image formation, the relationship between the detected current and the film thickness changes from the curves A to C. That is, for example, when the film thickness of the photoconductor is 20 μm, the detection current has a detection error of 15.5 μA to 19.3 μA.

On the other hand, in this embodiment, since the charging potential Vdpt at the time of detecting the film thickness is a fixed value (-700 V), for example, the detected current value when the film thickness of the photoconductor is 20 μm is 18.1 μ.
Accurate detection with A is possible.

That is, the film thickness d of the photoconductor and the detected current IDC
As shown by the curve B, there is a one-to-one correspondence, and detection can be performed accurately.

As described above, the voltage Vdpt. It becomes possible to accurately detect the film thickness of the photoconductor by setting a fixed value that is independent of the charging voltage Vd during image formation.

<Embodiment 2> (FIG. 3) In this embodiment, the voltage applied to the charging roller 2 at the time of detecting the photosensitive member film thickness is controlled as follows in Embodiment 1 described above. Others are the same as in the first embodiment.

A) At the time of detecting the photoconductor film thickness First, an AC voltage (static elimination bias) having a frequency of 1000 Hz and Vpp = 1800 V is applied for one rotation of the photosensitive drum or more,
The surface potential of the photosensitive drum is eliminated to 0V.

Next, frequency 1000 Hz, Vpp = 18
The photosensitive drum 1 is rotated three or more times while applying a voltage (charging bias at the time of detecting the photoconductor film thickness) in which a DC voltage of -1500V is superimposed on an AC voltage of 00V, and the surface of the photosensitive drum is uniformly Vdpt = -1500V. Get charged.

Further, the frequency is 1000 Hz, Vpp = 18
The photosensitive drum 1 is rotated while the AC voltage of 00V is applied, and the surface of the photosensitive drum is again neutralized.

At this time, the direct current I flowing through the photosensitive drum 1
DC becomes the film thickness detection current.

B) Comparison with Conventional Example A comparison between this embodiment and the conventional example will be described with reference to FIG.

In FIG. 3, the vertical axis represents the film thickness detection current ID.
C, the horizontal axis represents the photoconductor film thickness d. Curves D and E respectively represent those when the charging potential Vdpt during film thickness detection is -700V and -1500V.

Here, the film thickness of the photoconductor is 15 μm to 25 μm.
The difference in the detected current value when changing to m is: 22.9 μA-15.0 μA = 7.9 μA in the case of the curve D (Vdpt = −700 V), and 49.C in the case of the curve E (Vdpt = −1500 V). 1 μA-32.2 μA = 16.9 μA.

If the current detection resistance value is 10 kΩ, the difference between the voltages detected by the resistors is 790 mV (when Vdpt = −700 V) and 1690 mV (when Vdpt = −1500 V).

For example, when the detected voltage is converted by the A / D conversion circuit 12 having a sampling interval of 50 mV, the film thickness is 10
The number of steps per μm is: Vdpt = −700V, 790mV ÷ 50mV = 15.8 steps Vdpt = −1500V, 1690mV ÷ 50mV = 33.8 steps

That is, the charging voltage when detecting the film thickness is set to -150.
By setting a large value of 0 V, it is possible to improve the accuracy of film thickness detection.

As described above, the voltage Vdpt. It has become possible to improve the accuracy of film thickness detection by setting a value larger than the charging voltage Vd during image formation.

<Embodiment 3> (FIGS. 4 and 5) In this embodiment, the applied voltage control to the charging roller 2 at the time of detecting the photoconductor film thickness in the above-described Embodiment 1 is performed as follows. Others are the same as in the first embodiment.

A) At the time of detecting the photoconductor film thickness: First, an alternating voltage (static elimination bias) having a frequency of 1000 Hz and Vpp = 1800 V is applied for one rotation of the photosensitive drum or more,
The surface potential of the photosensitive drum is eliminated to 0V.

Next, frequency 1000 Hz, Vpp = 18
The photosensitive drum 1 is applied with a voltage (charging bias when the photoconductor film thickness is detected) in which a DC voltage is superimposed on an AC voltage of 00V.
Is rotated three times or more to uniformly charge the surface of the photosensitive drum.

Here, the DC voltage value superimposed on the alternating voltage is determined according to the temperature inside the image forming apparatus main body, and the relationship is as shown in FIG. The horizontal axis represents the temperature inside the main body, and the vertical axis represents the charging voltage Vdpt (= DC voltage value to be applied). The temperature inside the image forming apparatus main body is measured by the temperature sensor 11.

Thereafter, frequency 1000 Hz, Vpp = 1
The photosensitive drum 1 is rotated while the AC voltage of 800 V is applied, and the surface of the photosensitive drum is discharged again.

At this time, the direct current I flowing through the photosensitive drum 1
DC becomes the film thickness detection current.

After the detection current is converted into a voltage by the detection resistance of 10 kΩ, the voltage value is amplified by the 10 times amplification circuit 10, and the obtained voltage value is sampled by the AD conversion circuit to judge the film thickness.

B) Comparison with Conventional Example A comparison between this embodiment and the conventional example will be described with reference to FIG.

In FIG. 5, the vertical axis represents the detected voltage after being amplified by the amplifier circuit 10, and the horizontal axis represents the photoconductor film thickness.

When the charging potential Vdpt is fixed at -700 V and the temperature inside the image forming apparatus main body is changed from 10 ° C. to 30 ° C., the relationship between the film thickness and the current changes from curve L to curve H. The main reason is that the temperature characteristic of the voltage amplifier circuit 10 is large.

In order to cancel this temperature characteristic, the charging voltage is controlled with respect to the internal temperature of the image forming apparatus main body as described above.

The relationship between the film thickness after the above control and the detection voltage converges to the curve M in the figure under all temperatures, and as a result, the film thickness detection accuracy is improved.

As described above, the voltage Vdpt. It is possible to improve the accuracy of detecting the photoconductor film thickness by controlling the temperature of the photoconductor according to the temperature inside the main body of the image forming apparatus.

In this embodiment, the case where the detected voltage value changes depending on the temperature has been described.
When the charging voltage value changes depending on both humidity, the charging voltage value is controlled according to humidity or temperature / humidity.

In each of the above embodiments, the charging device 2 (charging member) for the image bearing member is a contact charging roller, but other types of contact charging such as blade type, brush type, rod type other than roller type are used. It may be a member or a non-contact type charging means such as a corona charging device.

The image forming apparatus is not limited to the electrophotographic process type, but the present invention can be applied to an electrostatic recording process using an electrostatic recording dielectric as an image carrier.

The process cartridge P contains at least an image bearing member, and the type and combination of other process devices to be included are arbitrary.

It goes without saying that the image forming apparatus does not have to be the process cartridge detachable type.

[0093]

As described above, according to the present invention, the current flowing through the image carrier is detected when the image carrier is charged or discharged by the charging member, and the film thickness of the image carrier is determined from the current signal. With respect to an image forming apparatus having a film thickness determination means for determining, it is possible to solve the above-mentioned problems of the conventional device, to accurately detect the film thickness of the image carrier, and to improve the accuracy of film thickness detection. Yes, the intended purpose is often achieved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus.

FIG. 2 is a diagram showing a relationship between a film thickness detection current and a photoconductor film thickness in the apparatus of Example 1.

FIG. 3 is a diagram showing the relationship between the film thickness detection current and the photoconductor film thickness in the apparatus of Example 2.

FIG. 4 is a diagram showing the relationship between the temperature inside the apparatus body and the charging voltage in the apparatus of Example 3;

FIG. 5 is a diagram showing the relationship between the film thickness detection voltage and the photoconductor film thickness in the apparatus according to the third embodiment.

[Explanation of symbols]

 1 Photosensitive Drum (Image Carrier) 2 Roller Charging Device 3 Developing Device 4 Cleaning Device 5 Transfer Device 6 Fixing Device P Process Cartridge R Current Detection Resistor 8 High Voltage Power Supply 9 Control Circuit (CPU) 10 Amplifying Circuit 11 Temperature / Humidity Sensor 12 A / D conversion circuit

Claims (9)

[Claims] 1. A means for applying a voltage to a charging member to charge or neutralize an image carrier as a member to be charged to a predetermined potential, and a current flowing through the image carrier when the image carrier is charged or neutralized. In an image forming apparatus having a current detection unit that detects a signal and a film thickness determination unit that determines the film thickness of the image carrier based on the current signal, the voltage value applied to the charging member when charging the image carrier is An image forming apparatus, which is different between when forming an image and when determining a film thickness. 2. A means for applying a voltage to a charging member to charge or neutralize an image carrier as a member to be charged to a predetermined potential, and a current flowing through the image carrier when the image carrier is charged or neutralized. In an image forming apparatus having a current detection unit that detects a signal and a film thickness determination unit that determines the film thickness of the image carrier from the current signal, the absolute voltage applied to the charging member when the image carrier is charged. The image forming apparatus is characterized in that the value at the time of film thickness determination is larger than the value at the time of image formation. 3. The image forming apparatus according to claim 1, wherein the voltage value applied to the charging member when the image carrier is charged during image formation is variably controlled. 4. The image forming apparatus according to claim 1, wherein the voltage value applied to the charging member when the image carrier is charged at the time of determining the film thickness is variably controlled. . 5. A voltage value applied to the charging member when charging the image carrier during image formation and a voltage value applied to the charging member when charging the image carrier during film thickness determination. The image forming apparatus according to claim 1, wherein the image forming apparatus is independently and variably controlled. 6. A temperature / humidity detecting means for detecting one or both of temperature and humidity inside the apparatus main body, and variably controlling a voltage value applied to the charging member according to an output value of the temperature / humidity detecting means. And means.
The image forming apparatus according to claim 5. 7. The image forming apparatus according to claim 1, wherein the charging member is in contact with the image carrier. 8. The image forming apparatus according to claim 1, wherein the image bearing member is an electrophotographic photosensitive member or an electrostatic recording dielectric member. 9. The image forming apparatus according to claim 1, wherein the image carrier is included in a process cartridge that is attached to and detached from a main body of the image forming apparatus.