JP4273049B2 - Potential measuring apparatus and image forming apparatus - Google Patents

Description

The present invention relates to a non-contact type potential measuring device and an image forming apparatus applicable to a copying machine, a printer, and the like having the potential measuring device.

As a conventional image forming apparatus, for example, in an apparatus that has a photosensitive drum and performs image formation by electrophotography, the potential of the photosensitive drum is charged uniformly in any environment in order to always obtain a stable image quality. It is necessary to keep it. For this reason, the charging potential of the photosensitive drum is measured using a potential measuring device, and feedback control is performed using the result to keep the photosensitive drum potential uniform.

The operation of the conventional potential measuring device will be described below. As a first method of the non-contact potential measuring device, a method called a mechanical AC electric field induction type is often used. In this method, the potential of the surface of the measurement object is a function of the magnitude of the current i taken from the detection electrode built in the potential measuring device,
i = dQ / dt = d (C · V) / dt (1)
It is given by the formula. Here, Q is the amount of charge appearing on the detection electrode, C is the coupling capacitance between the detection electrode and the measurement object, and V is the voltage on the surface of the measurement object.

The capacity C is C = A · S / x (2)
It is given by the formula. Here, A is a proportionality constant, S is the area of the detection electrode, and x is the distance between the detection electrode and the measurement object.

The amount of charge Q appearing on the detection electrode is a very small value, and is easily affected by noise existing around it. For this reason, a synchronous detection method is often used to accurately measure a minute Q. That is, in such a potential measuring apparatus, a necessary signal is obtained by periodically modulating the size of the capacitance C between the detection electrode and the measurement object by using an appropriate means, and detecting the same frequency component from the measured signal. ing.

As a typical example of the first method, a fork-shaped shutter is inserted between the measurement object and the detection electrode, and this shutter is periodically moved in a direction parallel to the surface of the measurement object, thereby The modulation of the capacitance C between the measurement target and the detection electrode is realized by blocking the electric field lines from the measurement target reaching the position in a manner that periodically modulates and effectively changing the area S of the detection electrode. Or a metal shield material having an opening at a position facing the object to be measured, a detection electrode is provided at the tip of the fork-shaped vibration element, and the position of the detection electrode is directly below the opening. There are some which modulate the capacitance by modulating the number of lines of electric force from the measurement object that reach the detection electrode by changing in parallel.

On the other hand, in recent years, in order to reduce the size of an electrophotographic image forming apparatus, it is necessary to reduce the diameter of the photosensitive drum and increase the density around the drum, and the potential measuring apparatus is also required to be reduced in size and thickness. However, in the above-described current mechanical AC electric field induction type sensor, most of the internal volume of the sensor structure is occupied by assembly parts such as a fork-like shutter or a drive mechanism for vibrating the fork-like vibrating element. Yes. Therefore, miniaturization of these drive mechanisms is essential for miniaturization of the potential measuring device.

Therefore, attempts have been reported to form a fine mechanical structure on a semiconductor substrate using a semiconductor processing technology called Micro Electro Mechanical System (MEMS) technology, and mechanical AC electric field induction potential measurement using this technology is reported. Equipment reports have also been made. As a typical example, there is one that attempts to measure the potential of a measurement object by vibrating a shutter structure having a fine opening produced by a semiconductor processing technique directly above a detection electrode (see Patent Document 1).

When a potential measuring device is manufactured using the MEMS technology, an electrode for detecting a potential is a metal thin film formed on a semiconductor substrate via a thin insulating film. In this case, the detection electrode and the semiconductor substrate form a metal-insulator-semiconductor (MIS) junction, and the capacitance depends on the area of the detection electrode, the thickness of the insulator, and the density of carriers in the semiconductor. Comes with ingredients. In general, since the semiconductor substrate is electrically grounded, a parasitic capacitance component is generated between the detection electrode and the ground.

FIG. 8 shows a conceptual schematic diagram of a conventional mechanical AC electric field induction type potential measuring device. The electric lines of force 507 emitted from the measurement object 505 reach the detection electrode 501 after being modulated by the vibration of the chopper 502. Due to the lines of electric force, the amount of charge induced on the detection electrode 501 is modulated, and a minute alternating current is generated. This current is converted into a voltage by a high resistance 503 grounded to the ground, and a signal amplified by an amplifier 504 is used for measurement.

FIG. 1 used in the description of the embodiments of the present invention to be described later is also a schematic view of a mechanical AC electric field induction type potential measuring device manufactured on a semiconductor substrate by using MEMS technology. In FIG. 1, a signal detection electrode 101 is formed on the surface of a flat semiconductor substrate 100. A measurement object 104 is installed above the signal detection electrode 101, and a chopper 102 that periodically vibrates between the detection electrode 101 and the measurement object 104 and a drive mechanism 103 for vibrating the chopper. Are installed on the substrate 100. Then, a signal from the detection electrode 101 is sent to the circuit 106 through the electric wiring 105.

FIG. 2 is a detailed cross-sectional view of the vicinity of the detection electrode 101 of the potential measuring device of FIG. 1 described above. An insulating film layer 201 is formed between the semiconductor substrate 100 and the detection electrode 101 (this may be an oxide film that is semi-naturally formed on the surface of a semiconductor such as Si). The detection electrode 101 is connected to the signal amplifier 204 through the electric wiring 202. The high resistance 203 connected to the ground is also connected to the electric wiring 202. Further, the output of the amplifier 204 is a signal detection circuit. 205 is connected. In general, in an element or apparatus using a semiconductor substrate, it is grounded via a container or the like for mounting the element, and the wiring 206 in FIG. 2 represents this function.

However, as described above, when the detection electrode 101 has a parasitic capacitance between the detection electrode 101 and the ground, an impedance Z expressed by the following equation is generated between the detection electrode 101 and the ground.

ここで、Ｒ’は検知電極１０１が形成されている半導体基板１００を介して発生する、検知電極１０１とアース間の抵抗、Ｃ’は寄生容量、ｆはチョッパーの機械的な振動周波数などである容量変調手段による容量変調周波数である。

Here, R ′ is a resistance between the detection electrode 101 and the ground generated through the semiconductor substrate 100 on which the detection electrode 101 is formed, C ′ is a parasitic capacitance, f is a mechanical vibration frequency of the chopper, and the like. It is a capacity modulation frequency by the capacity modulation means.

FIG. 3 shows the electrical equivalent circuit of FIG. Here, 207 and 208 represent the resistance R ′ between the detection electrode 101 and the ground and the parasitic capacitance C ′, which are generated through the semiconductor substrate 100, respectively, and are the same as those described in Expression (3). Is.

In a general mechanical AC electric field induction type potential measuring device, the modulation frequency of a chopper used is about several hundred hertz. On the other hand, in the potential measuring device using the MEMS technology, the chopper can be miniaturized in order to form the chopper using the microfabrication technology, and compared with a general mechanical AC electric field induction potential measuring device. A chopper having a high vibration frequency and a frequency of several khertz to several hundred khertz is often used.
US Pat. No. 6,177,800

As a result, in the expression (3), the value of the frequency f is several tens to several hundreds times that of a general conventional one, and as a result, the impedance Z between the detection electrode and the ground is lowered. Z <R. As shown in FIG. 3, the impedance Z is in parallel relation with the high resistance R for current-voltage conversion installed in front of the amplifier 204 and the ground. For this reason, the combined resistance is Z / (R + Z) times (<1) the value of the high resistance R, and the detection signal voltage originally input to the amplifier 204 is reduced. Accordingly, it is important to reduce the parasitic capacitance C ′ when manufacturing the potential measuring device using the semiconductor substrate serving as the detection electrode and the capacitance modulation means for modulating the coupling capacitance between the measurement object and the detection electrode.

In view of the above problems, the potential measuring device of the present invention is a sensing electrode formed on a substrate using a semiconductor having a dielectric constant ε ₁ that is installed at a position facing a measurement object, in an insulated state from the semiconductor substrate. When having a capacity modulation means for modulating the coupling capacitance between the measuring object and the electrode, to the semiconductor substrate, the average value epsilon ₂ of the dielectric constant has a value of less than epsilon _1, the semiconductor substrate A region made of an oxide or nitride of a semiconductor material to be formed, or an organic compound is provided, and the electrode is formed on a surface of the region facing the object to be measured. The semiconductor substrate may be provided with a region in which a material constituting the semiconductor substrate is formed in a porous state and has an average dielectric constant ε ₂ of less than ε ₁ . The capacity modulation means is configured to modulate the distance between the detection electrode provided on the swing plate and the measurement target by swinging the swing plate supported by the torsion spring so as to be swingable with respect to the measurement target. And a configuration in which the exposure area of the detection electrode with respect to the measurement target is modulated by moving a shutter having an opening between the measurement target and the detection electrode on the fixed substrate.

In view of the above problems, an image forming apparatus according to the present invention includes the above-described potential measuring device and an image forming unit, and a surface of the detection electrode of the potential measuring device faces a surface of the image forming unit that is a potential measurement target. The image forming means controls image formation using the signal detection result of the potential measuring device. The image forming unit may have a copying function, a printing function, a facsimile function, or the like. For example, the image forming unit may be configured to have a photosensitive drum that rotates about a predetermined axis, and to measure a charged potential on the surface of the photosensitive drum using a potential measuring device. This image forming apparatus also makes use of the characteristics of the potential measuring apparatus.

According to the present invention, there is provided a potential measuring apparatus including a sensing electrode formed in an insulating state on a substrate using a semiconductor, and capacitance modulation means for modulating a coupling capacitance between the measurement object and the electrode. It becomes possible to reduce the parasitic capacitance.

Before describing the embodiment of the present invention, the principle of the present invention will be described. In general, a parasitic capacitance C ′ included in a detection electrode insulated and provided on a semiconductor substrate is given by the following equation.

ここで、Ｓは検知電極の面積、ｄ_ｉ、ε_ｉ、ε_ｓ、Ｌ _Ｄ は、それぞれ検知電極と半導体基板との間に形成される薄い絶縁膜層の厚さ、薄い絶縁膜層の誘電率、検知電極直下の半導体部の誘電率、デバイ長を、それぞれ表す。デバイ長Ｌ_Ｄは、半導体の分野では良く知られた数値であり、次式で与えられる。

Here, S is the area of the detection electrode, d _i , ε _i , ε _s , and L _D are the thickness of the thin insulating film layer formed between the detection electrode and the semiconductor substrate, and the dielectric of the thin insulating film layer, respectively. , And the dielectric constant and Debye length of the semiconductor portion immediately below the detection electrode, respectively. Debye length L _D is a numerical value well known in the field of semiconductor, given by the following equation.

ここで、ｋ、Ｔ，Ｂはそれぞれ、ボルツマン定数、絶対温度、比例定数である。従って、寄生容量Ｃ’は、次式のように表すことができる。

Here, k, T, and B are Boltzmann constant, absolute temperature, and proportionality constant, respectively. Therefore, the parasitic capacitance C ′ can be expressed as follows:

In the present invention, the parasitic capacitance C ′ is reduced, but there are the following two methods for reducing the average value of the dielectric constant immediately below the detection electrode as a method for that purpose.
(a) Decrease the dielectric constant of the semiconductor portion.
(b) A part of the semiconductor portion is replaced with an insulator having a dielectric constant smaller than that of the semiconductor.

In the case of (a), from equation (6), the value of the dielectric constant ε _S of the semiconductor portion immediately below the sensing electrode is changed from ε ₁ (original dielectric constant of the semiconductor substrate) to ε ₂ (where ε ₂ <ε ₁ ), The value of the parasitic capacitance C ′ is reduced. As a concrete method, the dielectric constant can be effectively obtained by replacing the semiconductor constituting the substrate with a different semiconductor material having a dielectric constant ε ₂ or by making the original semiconductor porous structure as described later. There is a way to lower.

ここで、ｄ_ｉ’＝ｄ_ｉ＋ｄ_２・ε₁／ε_２であるため、ｄ_ｉ’はｄ_ｉよりも大きな値をとり、この場合でも、寄生容量Ｃ’を小さくすることが可能である。 On the other hand, in the case of the method (b), the region of the thickness d ₂ immediately below the detection electrode is replaced with an insulator material having a dielectric constant ε ₂ , and the equation (6) is transformed into the following equation: Can be explained.

Here, since d _i ′ = d _i + d ₂ · ε ₁ / ε ₂ , d _i ′ takes a larger value than d _i , and even in this case, the parasitic capacitance C ′ can be reduced. .

In one embodiment of the present invention in which the parasitic capacitance of the detection electrode is reduced by the above principle, an electrode formed on a substrate using a semiconductor placed at a position facing the measurement object, the measurement object, and the measurement object In an electric potential measurement apparatus including a modulation unit that modulates a coupling capacitance between electrodes, for example, a region having a value of an average value ε ₂ of a dielectric constant per unit volume is formed by an oxide or nitridation of a semiconductor material constituting the semiconductor substrate. Or an organic compound. Furthermore, in the semiconductor substrate, it is possible to form a region having a value of the average value ε ₂ of the dielectric constant per unit volume by forming a porous structure.

The dielectric constant under the sensing electrode can be lowered and the parasitic capacitance of the sensing electrode can be reduced by a method using an oxide or nitride, a method using an organic compound, or a method of introducing a porous structure. It becomes. The signal from the detection electrode is synchronously detected by the detection circuit at the modulation frequency of the capacitance modulation means. Therefore, for example, even if the potential measuring device is downsized to increase the vibration frequency of a mechanical chopper, rocking body, etc., it is possible to suppress a decrease in impedance between the sensing electrode and the ground, and the size is small and the performance is good. An electric potential measuring device and an image forming apparatus can be realized.

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings.
(Example 1)
A first embodiment of the present invention will be described with reference to FIGS. The external configuration of the potential measuring apparatus according to this embodiment is the same as that shown in FIG. In FIG. 4, the same reference numerals as those in FIGS. 1 to 3 denote the same parts or elements.

FIG. 4 shows a detailed structure of the substrate 100 of the potential measuring apparatus according to the first embodiment. An insulating film layer 201 is formed between the substrate 100 and the detection electrode 101 (this may be an oxide film that is semi-naturally formed on the surface of a semiconductor such as Si as described above). Further, a region 301 filled with an organic compound to a certain depth is formed immediately below the insulating film layer 201. The connection from the detection electrode 101 is as described above, and the output of the amplifier 204 is synchronously detected by the signal detection circuit 205 using the driving frequency of the chopper 102. The signal detection circuit 205 can be formed on the substrate 100 when a semiconductor substrate capable of forming an integrated circuit is used as the main material of the substrate.

Since the dielectric constant ε ₂ of the organic compound in the region 301 (strictly speaking, the average value of the dielectric constant per unit volume) has a value smaller than the dielectric constant ε ₁ of the semiconductor substrate 100, the parasitic capacitance of the detection electrode 101 C ′ can be made smaller than when the region 301 remains a semiconductor substrate. As a result, it is possible to suppress a decrease in impedance between the ground and the detection electrode 101.

A material and a manufacturing method suitable for constituting the first embodiment will be described. As a semiconductor substrate, silicon is generally used. In this substrate, a region corresponding to the region immediately below the detection electrode 101, that is, a region 301 is formed by a method called wet etching or dry etching, polyimide is filled as an organic material in that portion, and cured, A desired configuration can be obtained by forming the insulating film 201 and the detection electrode 101 on the surface.

Silicon has a dielectric constant of about 11.9, while polyimide has a dielectric constant of about 3.2. As a result, the parasitic capacitance generated in the detection electrode 101 can be reduced. It is also possible to form SiO ₂ in the region 201 by using a method of partially oxidizing the silicon substrate. The operation is essentially the same as the operation described with reference to FIGS.

(Example 2)
A second embodiment of the present invention will be described with reference to FIG. The second embodiment is characterized in that a part 401 immediately below the detection electrode 101 and the insulating film 201 in the semiconductor substrate 100 has a porous structure. In this case, the volume average value ε ₂ ′ of the dielectric constant of the region 401 can be expressed by the following equation.
ε ₂ ′ = ε ₁ · P (Formula 5)
Here, ε ₁ is the dielectric constant of the semiconductor substrate, and P is the filling factor of the region 401. However, the filling rate P indicates the ratio of the volume of the portion where the material is present excluding the void portion in the porous structure to the entire volume of the region 401.

In this case, since P has a value smaller than ₁ , the value of ε ₂ ′ is smaller than ε ₁ , which is effective in reducing the parasitic capacitance value of the detection electrode 101.

As a material constituting the second embodiment, a silicon substrate using an anodic oxidation method is suitable. In this case, a desired portion of the silicon substrate may be processed into a porous structure using an anodic oxidation method, and the insulating layer thin film 201 and the detection electrode 101 may be formed on the upper portion of the region.

(Example 3)
In the above embodiment, the number of lines of electric force reaching the detection electrode is modulated using a chopper (corresponding to changing S in the above equation (2)), but the distance x between the measurement object and the detection electrode is set as follows. Even if it is modulated, the coupling capacitance can be changed as can be seen from the above equation (2). The third embodiment of the present invention is an embodiment that adopts such a system. FIG. 6 shows a configuration of the potential measuring apparatus according to the present embodiment.

FIG. 6 shows a state in which the potential sensor is arranged with respect to the measurement target surface 1201. In FIG. 6, reference numeral 1202 denotes a case for accommodating the potential measuring device, which covers the upper portion of the oscillator 1104 except for the detection electrode portion. It is made of a conductive material and is grounded to ground. The support substrate 1100 that supports the oscillator 1104 is fixed to the case 1202 by appropriate mounting jigs 1203 and 1204. Due to the presence of the installed case 1202, the lines of electric force reach the detection electrodes 1111 and 1112 only from the portion of the measurement target surface 1201 that faces the oscillating body 1104 almost directly in front, and the noise component can be suppressed with high accuracy. Potential measurement is possible. In addition, an opening is formed in the central portion of the support substrate 1100, and the central hollow portion of the opening is rocked by two torsion springs on the front side and the other side of the flat plate-like rocking body 1104 in the direction perpendicular to the paper surface. A moving body 1104 is supported so as to be swingable about a central axis C. The oscillator 1104 and the support substrate 1100 are made of semiconductor.

Furthermore, two flat detection electrodes 1111 and 1112 having the same shape are arranged symmetrically with respect to the central axis C via an insulating film (not shown) on the upper surface of the oscillator 1104. Electrode wirings (not shown) are respectively provided on the front side and the other side of the detection electrode in the direction perpendicular to the paper surface. Regions 1211 and 1212 having a reduced dielectric constant are formed under such detection electrodes, and the configuration of these portions is as described in the above embodiment. When the oscillating body 1104 oscillates about the central axis C, the upper detection electrodes 1111 and 1112 periodically approach or move away from the surface 1201 to be measured in reverse phase. The differential amplification of the modulation current becomes possible. Each detection electrode is connected to an extraction electrode formed on the support substrate 1100 by an electrode wiring formed on the torsion spring, for example, inversion of a differential amplifier installed outside the support substrate 1100 Connected to input contact and non-inverting input contact. As a result, the modulation current from the detection electrode is differentially amplified and synchronously detected by the detection circuit in the same manner as in the above embodiment. Of course, only one detection electrode is provided on the upper surface of the oscillating body 1104 (that is, one of the detection electrodes is removed in FIG. 6), and the modulation current from the detection electrode is detected in the same manner as in the above embodiment without differential amplification. It may be configured.

By adding an appropriate oscillating body drive mechanism to this potential measuring device and appropriately selecting the shape and material of the oscillating body 1104 and the torsion spring, the oscillating body 1104 is periodically rotated about the central axis C of the torsion spring. The distance between the detection electrode on the oscillating body 1104 and the measurement target surface 1201 is periodically changed. Thus, by modulating the current from the detection electrode and synchronously detecting this current at the oscillation frequency of the oscillator 1104 by the detection circuit, the potential of the measurement object 1201 is detected as in the above embodiment. be able to. The oscillating body drive mechanism that oscillates the oscillating body 1104 is, for example, a magnet provided on the back surface of the oscillating body and an external coil that generates a magnetic field by flowing an alternating current.

(Example 4)
FIG. 7 illustrates an image forming apparatus according to the fourth exemplary embodiment. FIG. 7 is a schematic view around the photosensitive drum of the electrophotographic developing apparatus using the potential measuring apparatus according to the present invention. A charger 2102, a potential sensor 2101, an exposure device 2105, and a toner supply device 2106 are installed around the photosensitive drum 2108. A latent image is obtained by charging the surface of the drum 2108 with the charger 2102 and exposing the surface of the photosensitive drum 2108 with the exposure device 2105. Toner is attached to the latent image by a toner supplier 2106 to obtain a toner image. The toner image is transferred to a transfer material 2109 sandwiched between the transfer material feed roller 2107 and the photosensitive drum 2108, and the toner on the transfer material is fixed. Image formation is achieved through these steps.

In this configuration, the charged state of the drum 2108 is measured by the small and high-performance potential sensor 2101 of the present invention, the signal is processed by the signal processing device 2103, and the high voltage generator 2104 is fed back to the charger 2102. By controlling the above, stable drum charging is realized, and stable image formation is realized. At this time, by monitoring the output of the potential sensor 2101 in synchronization with the rotation of the photosensitive drum 2108, the potential distribution on the photosensitive drum can be measured. Based on the measured potential distribution, the light to be exposed on the photosensitive drum 2108 can be measured. By controlling the amount or controlling the charger 2102, image unevenness can be reduced.

It is a perspective view which shows the positional relationship of the electric potential measuring apparatus and measurement object in 1st Example of this invention. It is the figure which showed the detail of the detection electrode on the semiconductor substrate which comprises an electric potential measurement apparatus when not applying this invention. FIG. 3 is an equivalent circuit diagram around a detection electrode on a semiconductor substrate constituting the potential measurement device when the present invention is not applied. It is the figure which showed the detail of the detection electrode on the semiconductor substrate which comprises an electric potential measurement apparatus in the 1st Example of this invention. It is the figure which showed the detail of the detection electrode on the semiconductor substrate which comprises an electric potential measurement apparatus in the 2nd Example of this invention. It is sectional drawing which shows the positional relationship of the electric potential measuring apparatus and measurement object in 3rd Example of this invention. It is a figure explaining the image forming apparatus of the 4th Example of this invention. It is a conceptual schematic diagram of a mechanical AC electric field induction type potential measuring device used conventionally.

Explanation of symbols

100, 1104... Semiconductor substrate 101, 1111, 1112, ... Detection electrodes 102, 103 ... Capacitance modulation means (chopper, chopper Drive mechanism)
104, 1201 ... Measurement object 201 ... Insulating films 301, 401, 1211, 1212 ... Lower dielectric constant Area

Claims (6)

A detection electrode formed in an insulating state on a substrate using a semiconductor having a dielectric constant ε ₁ placed at a position facing the measurement object, and a capacitance modulation means for modulating the coupling capacitance between the measurement object and the electrode The semiconductor substrate has a region made of an oxide or nitride of a semiconductor material constituting the semiconductor substrate, or an organic compound, having an average value of dielectric constant ε ₂ of less than ε _1. An electric potential measuring device provided, wherein the electrode is formed on a surface of the region facing the measurement object. In the above semiconductor substrate, the potential measuring apparatus according to claim 1, wherein the average value epsilon ₂ regions of dielectric constant and wherein Rukoto to have a insulating. A detection electrode formed in an insulating state on a substrate using a semiconductor having a dielectric constant ε ₁ placed at a position facing the measurement object, and a capacitance modulation means for modulating the coupling capacitance between the measurement object and the electrode The semiconductor substrate is provided with a region in which the material constituting the semiconductor substrate is formed in a porous state, and the average value ε ₂ of the dielectric constant is less than ε ₁ . The potential measuring device , wherein the electrode is formed on a surface of the region facing the object to be measured. Dielectric constant ε installed at the position facing the measurement object ₁ A sensing electrode formed in an insulating state on a rocking body using a semiconductor, and a capacitance modulation means for modulating the coupling capacity between the measurement object and the electrode by rocking the rocking body. The oscillator has an average dielectric constant ε ₂ Is ε ₁ A region made of an oxide or nitride of a semiconductor material constituting the oscillator and an organic compound having a value of less than is provided, and the electrode is formed on a surface of the region facing the object to be measured. An electric potential measuring device. Dielectric constant ε installed at the position facing the measurement object ₁ A sensing electrode formed in an insulating state on a rocking body using a semiconductor, and a capacitance modulation means for modulating the coupling capacity between the measurement object and the electrode by rocking the rocking body. The oscillator has an average dielectric constant ε ₂ Is ε ₁ A region having a value less than that is formed in a porous state of the material constituting the oscillator, and the electrode is formed on a surface of the region facing the object to be measured. A potential measuring device. Comprising a potential measuring device and image forming means according to any one of claims 1 to 5, by detecting electrode formed surface of the potential measuring apparatus is opposed to subject to surface potential measurements of said image forming means An image forming apparatus, wherein the image forming unit controls image formation using a signal detection result of a potential measuring device.

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