JP2003029504A - Surface potential controller and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface potential controller which can hold the potential of a measured body at a specific value. SOLUTION: A surface potential sensor 1 includes a potential detection electrode 11 and a distance detection electrode 12. The potential detection electrode 11 outputs a potential distance signal s1 including a distance component corresponding to the distance to the measured body 40 and a potential component corresponding to the potential of the measured body 40. The distance detection electrode 12 outputs a distance signal s2 corresponding to the distance to the measured body 40. A signal processing part 20 removes the distance component from the potential distance signal s1 by using the distance signal s2, generates a potential signal corresponding to the potential Vs of the measured body 40, and inputs a control signal c1 corresponding to the potential signal to an electric charging device 81.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface potential control device and an image forming apparatus.

[0002]

2. Description of the Related Art Image forming apparatuses such as copying machines, laser beam printers and facsimiles include a surface potential control device.
The surface potential control device is used as a means for controlling the surface potential of the photosensitive drum which is the object to be measured.

The surface potential control device generates an AC signal corresponding to the surface potential of the photosensitive drum by mechanically interrupting the electric field between the detection electrode and the photosensitive drum by, for example, a tuning fork, and this AC signal. Is processed to detect the surface potential of the photosensitive drum. Then, the surface potential of the photosensitive drum is controlled based on the detected result.

In such a surface potential control device, when the distance between the detection electrode and the photosensitive drum changes, an error occurs in the detected value of the surface potential. For this reason, it is necessary to attach the detection electrode to the reference position with high accuracy so that the distance between the detection electrode and the photosensitive drum becomes a predetermined value, which causes difficulty in assembly.
Moreover, considering that it is practically impossible to keep the displacement of the sensing electrode from the reference position at zero for a long period of time, it is practically impossible to avoid the detection error. Then, when an error occurs in the detected value of the surface potential, there is a problem that the surface potential control device capable of performing appropriate feedback control cannot be configured.

As a means for avoiding a detection error caused by a distance variation between the detection electrode and the photosensitive drum, Japanese Patent Publication No. 3-646.
No. 7 discloses a surface potential control device that feeds back a high voltage to the detection electrode so that an error does not occur in the detected value of the surface potential even when the distance between the detection electrode and the photosensitive drum changes. ing.

However, since this surface potential control device needs to feed back a high voltage, it has a problem that the circuit structure becomes complicated and a large and expensive high withstand voltage component is required.

Further, US Pat. No. 4,977,620 discloses that by reducing the amplitude of mechanical vibration of a tuning fork,
Disclosed is a surface potential control device that prevents an error in the detected value of the surface potential even when the distance between the detection electrode and the photosensitive drum changes.

However, in this surface potential control device, since the amplitude of the mechanical vibration of the tuning fork is made small, there is a problem that the detection sensitivity becomes low and the S / N ratio cannot be made large.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a surface potential control device capable of accurately detecting the potential of the measured object even when the distance to the measured object changes. That is.

Another object of the present invention is to provide a surface potential control device capable of detecting the potential of an object to be measured with high sensitivity.

Still another object of the present invention is to provide a surface potential control device capable of maintaining the potential of the object to be measured at a predetermined value by applying appropriate feedback control.

Still another object of the present invention is to provide a surface potential control device having a simple circuit structure.

Yet another object of the present invention is to provide a small size,
An object of the present invention is to provide a lightweight surface potential control device.

Still another object of the present invention is to provide an inexpensive surface potential control device which does not use high breakdown voltage parts.

[0015]

In order to solve the above-mentioned problems, a surface potential control device according to the present invention comprises a charging device,
It includes a surface potential detection sensor and a signal processing unit. The charging device is a device that gives an object to be measured an amount of electricity corresponding to an input control signal.

The surface potential detecting sensor includes a potential detecting electrode and a distance detecting electrode. The potential detection electrode is an electrode capacitively coupled to the measured object, and a potential distance signal including a distance component corresponding to the distance to the measured object and a potential component corresponding to the potential of the measured object. Output.

The distance detection electrode is an electrode capacitively coupled to the object to be measured, and outputs a distance signal corresponding to the distance to the object to be measured.

The signal processing unit receives the potential distance signal and the distance signal, removes the distance component from the potential distance signal using the distance signal, and corresponds to the potential of the object to be measured. A potential signal is generated, and a control signal corresponding to the potential signal is input to the charging device.

The surface potential control device according to the present invention includes a potential detection electrode and a distance detection electrode. From the potential sensing electrode,
A potential distance signal including a distance component corresponding to the distance to the measured object and a potential component corresponding to the potential of the measured object is output. A distance signal corresponding to the distance to the object to be measured is output from the distance detection electrode. Therefore, even when the distance between the surface potential control device and the object to be measured changes, the distance signal is used to remove the distance component from the potential distance signal, and a signal corresponding to the potential of the object to be measured is obtained. Since it can be generated, the electric potential of the measured object can be accurately detected without having distance dependency.

Further, the surface potential control device according to the present invention is
Since the control signal corresponding to the potential signal is input to the charging device, the charging device can be controlled based on the potential of the measured object. Therefore, even when the environment around the object to be measured changes and the potential of the object to be measured fluctuates, appropriate feedback control can be added to maintain the potential of the object to be measured at a predetermined value.

Further, the surface potential control device according to the present invention is
Since the potential of the object to be measured can be accurately detected, appropriate feedback control can be added to maintain the potential of the object to be measured at a predetermined value.

Moreover, according to the above construction, since it is not necessary to feed back a high voltage, the circuit construction becomes simple, and large and expensive high withstand voltage parts such as a high voltage generating transformer and a high withstand voltage for rectification. The diode, high withstand voltage capacitor for rectification, and high withstand voltage transformer for DC / DC converter become unnecessary. Therefore, the surface potential control device according to the present invention can be configured with a simple circuit using a small and inexpensive low withstand voltage component, for example, a surface mount type component with a withstand voltage of about several tens of V. The device becomes smaller, lighter and cheaper.

The surface potential control device according to the present invention is
Since the capacitance between the potential detection electrode and the object to be measured can be vibrated with a large amplitude, the detection sensitivity is increased and the S / N ratio is increased.

[0024]

1 is a diagram schematically showing the structure of an image forming apparatus using a surface potential control device according to the present invention. FIG. 2 is a partially enlarged view of FIG. The image forming apparatus according to the present invention is, for example, a copying machine, a laser beam printer, a facsimile, or the like.

1 and 2, the image forming apparatus according to the present embodiment is a PPC (Plain Paper Cop).
y) A copying machine according to the method, including the surface potential control device according to the present invention. The measured object 40 is, for example, a photosensitive drum. The surface of the measured object 40 is the measured surface S, and the surface potential of the measured object 40 is Vs.

The surface potential control device 10 according to this embodiment is
The surface potential detection sensor 1, the temperature detection sensor Th1, the signal processing unit 20, and the charging device 81 are included.

The surface potential detecting sensor 1 is a potential detecting electrode 1
1, the distance detection electrode 12, and the first shield case 13
And a second shield case 14 and an insulator 400. The first shield case 13 includes a first detection window 15. The second shield case 14 has a second detection window 16
including.

The potential detecting electrode 11 is an electrode capacitively coupled to the surface S to be measured, and is arranged so as to face the surface S to be measured so as to measure the surface potential Vs of the surface S to be measured in a non-contact state. There is. The potential detection electrode 11 is housed inside the first shield case 13 and provided corresponding to the first detection window 15.

The distance detection electrode 12 is an electrode capacitively coupled to the surface S to be measured, and is arranged so as to face the surface S to be measured so as to measure the distance to the surface S to be measured in a non-contact state. .
The distance detection electrode 12 is housed inside the second shield case 14 and provided corresponding to the second detection window 16.

The first shield case 13 and the second shield case 14 are electrically insulated from each other and mechanically coupled by an insulator 400.

The potential detecting electrode 11 is connected to the surface S to be measured.
And the potential Vs of the surface S to be measured S corresponding to the distance between
And a potential distance signal s1 including a potential component corresponding to. The distance detection electrode 12 outputs a distance signal s2 corresponding to the distance to the surface S to be measured.

The temperature detection sensor Th1 is, for example, a thermistor, and is arranged so as to face the surface S to be measured. The temperature detection sensor Th1 outputs a temperature signal tmp1 corresponding to the temperature of the surface S to be measured.

The signal processing unit 20 receives the potential distance signal s1 and the distance signal s2, removes the distance component from the potential distance signal s1 using the distance signal s2, and corresponds to the potential Vs of the surface S to be measured. Generate a potential signal. Also, the temperature signal t
mp1 is input. Then, the potential signal and the temperature signal t
The control signal c1 corresponding to mp1 is input to the charging device 81. The signal processing unit 20 may be, for example, partly or entirely configured by a computer, or may be a passive circuit element,
It may be configured by a dedicated circuit using an active circuit element.

The charging device 81 receives the input control signal c1.
Is a device that applies an amount of electricity corresponding to the measured surface S to the measured surface S, and includes a charger 811 and a high voltage generator 812. Charger 81
Reference numeral 1 is, for example, a corotron having a structure in which a tungsten wire having a diameter of 50 to 100 μm is shielded by a metal such as Al, and a scotron having a structure in which a bias voltage is applied to grid electrodes arranged in a mesh shape. High voltage generator 81
2 is, for example, a PWM control high-voltage power supply or the like.

The high voltage generator 812 operates with a pulse width according to the control signal c1 and outputs a high voltage according to the control signal c1. The charger 812 is arranged so as to face the surface S to be measured, and gives an electric quantity corresponding to the high voltage output from the high voltage generator 812 to the surface S to be measured by corona discharge.

The exposure device 821 irradiates the surface S to be measured with light, and removes electric charges from the portion other than the image portion of the surface S to be measured.
As a result, a so-called electrostatic latent image is formed in which an electric charge remains in the image area. This electrostatic latent image is an invisible image.

The developing unit 822 attaches colored particles (hereinafter, referred to as toner) charged with a polarity opposite to the charge of the image portion to the electrostatic latent image to form a toner image. The toner image is a visible image.

The transfer device 824 applies a toner image to the recording paper 823.
Are superposed on each other, a charge having a polarity opposite to that of the toner is applied from the back side of the recording paper 823, and the toner image is transferred to the recording paper 823 by electrostatic force. The recording paper 823 is sent in the F1 direction. The fixing device 825 applies heat and pressure to the recording paper 823. As a result, the toner image is fixed on the recording paper 823 as a permanent image.

The static eliminator 826 irradiates light to remove the charged electric charge remaining on the surface S to be measured. The cleaner 827 removes the toner remaining on the surface S to be measured.

The surface potential control device according to this embodiment corresponds to the distance component from the potential detecting electrode 11 corresponding to the distance between the potential detecting electrode 11 and the surface S to be measured and the potential Vs of the surface S to be measured. The potential distance signal s1 including the potential component is output. The distance detection electrode 12 outputs a distance signal s2 corresponding to the distance between the distance detection electrode 12 and the surface S to be measured.

The signal processing unit 20 includes the surface potential detecting sensor 1
Then, the potential distance signal s1 and the distance signal s2 are input.
The signal processing unit 20 uses the distance signal s2 to remove the distance component from the potential distance signal s1 and generate a potential signal corresponding to the potential Vs of the surface S to be measured.

Therefore, even if the distance between the potential detection electrode 11 and the surface S to be measured changes, the distance signal s2 is used to remove the distance component from the potential distance signal s1 to obtain the potential of the surface S to be measured. Since the potential signal corresponding to Vs can be generated, the potential Vs of the surface S to be measured can be accurately detected without having distance dependency.

The surface potential control device according to the present invention is
Since the control signal c1 corresponding to the potential signal is input to the charging device 81, the charging device 81 can be controlled based on the potential Vs of the surface S to be measured. Therefore, the measured surface S
Even when the surrounding environment changes and the potential Vs of the surface S to be measured fluctuates, appropriate feedback control can be applied to maintain the potential Vs of the surface S to be measured at a predetermined value. Then, by keeping the potential Vs of the surface S to be measured at a predetermined value, the image quality of the copying machine can be stabilized.

The surface potential control device according to the present invention is
Since the potential Vs of the measured surface S can be accurately detected, appropriate feedback control can be applied to keep the potential Vs of the measured surface S at a predetermined value.

Further, the surface potential control device according to the present invention is
The charging device 8 receives the control signal c1 corresponding to the temperature signal tmp1.
Since 1 is input, the charging device 81 can be controlled based on the temperature of the surface S to be measured. Therefore, even when the environment around the surface S to be measured changes and the temperature of the surface S to be measured changes, appropriate feedback control is added to maintain the potential Vs of the surface S to be measured at a predetermined value. be able to.

Moreover, according to the above construction, since it is not necessary to feed back a high voltage, the circuit construction becomes simple and large and expensive high withstand voltage parts such as a high voltage generating transformer and a high withstand voltage for rectification. The diode, high withstand voltage capacitor for rectification, and high withstand voltage transformer for DC / DC converter become unnecessary. Therefore, the surface potential control device according to the present embodiment can be configured with a simple circuit using a small and inexpensive low withstand voltage component, for example, a surface mount type component with a withstand voltage of about several tens of V. The control device becomes smaller, lighter and cheaper.

Further, since the surface potential control device according to this embodiment can vibrate the capacitance between the potential detection electrode 11 and the surface S to be measured with a large amplitude, the detection sensitivity is increased and the S / N ratio is increased. The ratio becomes large.

Further, the surface potential control device according to the present embodiment mechanically includes the first shield case 13 in which the potential detection electrode 11 is housed and the second shield case 14 in which the distance detection electrode 12 is housed. Therefore, the relative distance between the distance detection electrode 12 and the surface S to be measured is determined by the potential detection electrode 11
And the surface S to be measured change at the same time. Therefore, the distance signal s2 obtained by the distance detection electrode 12 and the distance component of the potential distance signal s1 obtained by the potential detection electrode 11 show the same distance. Therefore, the distance component of the potential distance signal s1 can be removed by the distance signal s2, and the potential Vs of the surface S to be measured can be accurately detected without having distance dependency.

Further, the surface potential control device according to the present invention is
First shield case 13 and second shield case 14
Since and are electrically insulated, the first shield case 13 and the second shield case 14 can be grounded to different potentials. Therefore, mutual interference between the potential detection electrode 11 housed in the first shield case 13 and the distance detection electrode 12 housed in the second shield case 14 is avoided, and the potential Vs of the surface S to be measured is accurately measured. Can be detected.

The surface potential control device according to the present invention is
Since the potential detection electrode 11 is stored in the first shield case 13 and the distance detection electrode 12 is stored in the second shield case 14, the potential detection electrode 11 and the distance detection electrode 12 are less susceptible to noise. , The S / N ratio becomes large.

Further, in the surface potential control device according to the present embodiment, the first shield case 13 and the second shield case 14 may be made of metal flat plates, or they are fine enough to prevent high frequency radio waves from entering. You may comprise with a metal mesh. Further, the potential detection electrode 11 and the distance detection electrode 12
The shape is arbitrary, and various modes such as a plate shape, a linear shape, a circular shape, and a rectangular shape can be adopted. Furthermore, the potential detection electrode 11
Also, the structure of the distance detection electrode 12 is not particularly limited as long as it satisfies predetermined required characteristics.
For example, the potential detection electrode 11 may be of a chopper type, or may be of a type that changes the coupling capacitance by an electronic circuit method. Further, the measured surface S is generally the surface of the photosensitive drum, but it may be the surface of a charged insulating film or the like. When measuring the electric potential of the charged insulating film, it can be used in a contact state. Also,
A signal corresponding to the humidity around the surface S to be measured or the like may be input to the signal processing unit 20 to perform control based on information such as the humidity. In addition, the surface potential detection sensor 1 and the signal processing unit 20
May be separately configured, or part or all of the signal processing unit 20 may be provided inside the surface potential detection sensor 1.

FIG. 3 is a block diagram more specifically showing a part of the structure of the surface potential control device shown in FIG. 1, and FIG. 4 is a more specific view of a part of the structure of the surface potential control device shown in FIG. 5 is a circuit diagram more specifically showing a part of the structure of the surface potential control device shown in FIG.

In FIG. 3 and FIG. 4, the signal processing unit 20 is
The analog processing unit 202, the switching unit 203, the A / D converter 204, the digital processing unit 205, and the D / A converter 2
08 and.

The analog processing unit 202 is a passive circuit element,
It consists of a dedicated circuit configured using active circuit elements. The digital processing unit 205 includes, for example, a computer,
Digitally processes the input signal.

In FIG. 4, the analog processing unit 202 is
The potential detection unit 21 and the distance detection unit 24 are included. The potential detection unit 21 includes an impedance conversion circuit 211, a first amplifier 212, a first rectifying / smoothing circuit 213, a first level shift circuit 214, a modulation signal generating circuit 215, and
And a mechanical chopper 216. Distance detector 24
Includes a signal generator 221, a non-inverting amplifier circuit 222, a second amplifier 223, a second rectifying / smoothing circuit 224, a subtracting circuit 225, and a second level shift circuit 226.

The signal generator 221 shown in FIG. 5 includes an operational amplifier A1, resistors R1 and R2, and a signal source VG. One end of the signal source VG has a first reference potential GND1 which is a ground potential.
Grounded to. The operational amplifier A1 has a non-inverting input terminal grounded. The inverting input terminal of operational amplifier A1 is
It is connected to the other end of the signal source VG via the resistor R1 and is also connected to the output terminal via the resistor R2. The output terminal of the operational amplifier A1 becomes the output terminal of the signal generator 221.

The non-inverting amplifier circuit 222 includes an operational amplifier A2
And a resistor R3. The inverting input terminal of the operational amplifier A2 is connected to the distance detection electrode 12, and the resistance R3
Is connected to the output terminal via. The non-inverting input terminal of the operational amplifier A2 is connected to the output terminal of the signal generator 221. The output terminal of the operational amplifier A2 becomes the output terminal of the non-inverting amplifier circuit 222.

An impedance conversion circuit 211, a first amplifier 212, a first rectifying / smoothing circuit 213, a first level shift circuit 214, a modulation signal generating circuit 215, a signal generator 221, which are electronic components constituting the circuit, Inversion amplifier circuit 222, second amplifier 223, second rectifying and smoothing circuit 2
24, subtraction circuit 225, second level shift circuit 226
Are mounted on one side of the circuit board 19.

Then, the impedance conversion circuit 211,
The first amplifier 212, the first rectifying and smoothing circuit 213, the first
Level shift circuit 214, modulation signal generation circuit 215,
The signal generator 221, the second rectifying and smoothing circuit 224, the subtraction circuit 225, and the second level shift circuit 226 are housed in the first shield case 13, and the non-inverting amplifier circuit 222,
The second amplifier 223 is housed in the second shield case 14.

In the present embodiment, the surface S to be measured is connected to the DC high voltage power supply V _DC, and the surface potential Vs of the surface S to be measured is
For example, from 0 V to −1 with respect to the first reference potential GND1.
Change up to 000V.

The distance between the potential detection electrode 11 and the surface S to be measured is L1 and its electrostatic capacitance is C1. The distance L2 between the distance detection electrode 12 and the surface S to be measured is set to the same value as the distance L1, and the capacitance thereof is C2.

6 and 7 are operation waveform diagrams of the surface potential control device 10 shown in FIG. Hereinafter, the operation of the surface potential control device 10 will be described with reference to FIGS. 3, 4, 6, and 7. First, the electrostatic capacitance C2 of the surface potential control device 10
Is C2 = ε ₀ * S2 / L2, where ε ₀ is the permittivity and S2 is the effective area. Since only air exists between the distance detection electrode 12 and the surface S to be measured, the permittivity ε ₀ is constant and the effective area S2 is also constant. Therefore, the capacitance C
2 depends only on the change of the distance L2, and the capacitance C2 is
It is proportional to the reciprocal of the distance L2. Since the capacitance C2 changes depending on the change in the distance L2, the signal output from the distance detection electrode 12 becomes the distance signal s2 corresponding to the distance L2 with the surface S to be measured.

The signal generator 221 inverts and amplifies the signal input from the signal source VG by the operational amplifier A1, and outputs the signal s2.
1 is output. The signal s21 is shown in FIG. Signal s
21 is an AC signal with a constant cycle and amplitude, for example,
It can be a sine wave with a frequency of 10 kHz.

The non-inverting amplifier circuit 222 includes the signal generator 22.
The signal s21 input from 1 is amplified and output. When the frequency of the signal s21 is f, the impedance Xc between the distance detection electrode 12 and the surface S to be measured is Xc = 1 / (2πf * C2), and the amplification factor of the non-inverting amplifier circuit 222 is (Xc + R
3) / Xc. The voltage Vout output from the output terminal of the non-inverting amplifier circuit 222 can be expressed as Vout = {(Xc + R3) / Xc} * Vm when the amplitude of the signal s21 is Vm.

Since the amplitude Vm and frequency f of the signal s21 are constant, Vout = {(Xc + R3) / Xc} * Vm = (1 + R3 / Xc) * Vm = (1 + R3 * 2πf * C2) * Vm = (1 + R3 *) 2πf * ε ₀ * S2 / L2) * Vm, and the voltage Vout becomes an AC signal that changes depending only on the change in the distance L2.

The second amplifier 223, the second rectifying / smoothing circuit 224, the subtracting circuit 225, and the second shield case 14
Is grounded to the second reference potential GND2 having the same potential as the signal s21. The second amplifier 223 AC-amplifies the AC signal input from the non-inverting amplifier circuit 222 to generate a signal s2.
2 is output. The signal s22 is shown in FIG.

The second rectifying / smoothing circuit 224 outputs the signal s22.
Is rectified and smoothed to output a signal s23. The signal s23 is shown in FIG. Since the second rectifying / smoothing circuit 224 is grounded to the second reference potential GND2, it rectifies and smoothes the signal s22 with the second reference potential GND2 as a reference.

The subtraction circuit 225 outputs the signals s23 to s
21 is subtracted and output. The signal output from the subtraction circuit 225 is a DC signal.

The second level shift circuit 226 adjusts the level of the signal input from the subtraction circuit 225 and outputs the signal Vb to the switch 203. The signal Vb is shown in FIG.
Shown in.

The second level shift circuit 226 may be constructed by using a non-inverting amplifier circuit whose gain can be adjusted by using a variable resistor. In some cases, it can be omitted.

On the other hand, the first shield case 13 is grounded to the first reference potential GND1 which is the ground potential. The modulation signal generation circuit 215 of the potential detection unit 21 outputs a signal having a constant frequency, for example, a 700 Hz signal. The mechanical chopper 216 is inserted between the measured surface S and the potential detection electrode 11 at the frequency of the signal input from the modulation signal generation circuit 215. When the mechanical chopper 216 is inserted, the dielectric constant between the surface S to be measured and the potential detection electrode 11 changes by Δε ₀ , and the capacitance C1 changes by ΔC1.

The charge ΔQ generated in the potential detecting electrode 11 is
When the effective area is S1 and the potential difference between the surface S to be measured and the potential detection electrode 11 is V1, ΔQ = (Δε ₀ S1 / L1) * V1 = ΔC1 * V1 can be expressed. Therefore, the modulation current i induced in the potential detection electrode 11 can be expressed as i = ΔQ / Δt = (Δε ₀ S1 / L1) * V1 / Δt = ΔC1 * V1 / Δt. The modulation current i includes a distance component L1 corresponding to the distance between the potential detection electrode 11 and the surface S to be measured, and a potential component V1 corresponding to the potential of the surface to be measured. Then, the potential detection electrode 11 outputs the modulation current i as the potential distance signal s1.

The impedance conversion circuit 211 converts the potential distance signal s1 input from the potential detection electrode 11 into a voltage signal, and at the same time, converts the high impedance into a low impedance and outputs it as a signal that is easy to handle.

The first amplifier 212 AC-amplifies the signal input from the impedance conversion circuit 211 and outputs the signal s.
11 is output. The signal s11 is shown in FIG. The signal s11 is a substantially sine wave signal having the same frequency as the signal output from the modulation signal generation circuit 215, for example, 700 Hz.

The first rectifying / smoothing circuit 213 outputs the signal s11.
Is converted into a DC signal, and a signal obtained by multiplying the component corresponding to the potential Vs of the surface S to be measured by the component proportional to the displacement signal is output.

The first level shift circuit 214 adjusts the DC level of the signal input from the first rectifying / smoothing circuit 213 and outputs the potential displacement signal Va to the switch 203. The potential displacement signal Va is shown in FIG. 7 (b).

The first level shift circuit 214 can be constructed by using a non-inverting amplifier circuit similar to the second level shift circuit 226. In some cases, it can be omitted.

The temperature detection sensor Th1 outputs a temperature signal tmp1 corresponding to the temperature of the surface S to be measured to the switch 203. The switch 203 includes switching means sw1, sw2, sw3.
Of the electric potential displacement signal Va via the switching means sw1.
The signal Vb is input to the A / D converter 204, the signal Vb is input to the A / D converter 204 via the switching means sw2, and the switching means sw3 is input.
The temperature signal tmp1 is input to the A / D converter 204 via.

FIG. 8 is a flowchart showing the digital processing. The processing operation in the digital processing unit 205 will be described below with reference to FIGS. 3 and 8.

In the initial setting, R of the digital processing unit 205 is set.
The reference voltage Vref is stored in the OM. This reference voltage V
ref is the same value as the signal output from the level shift circuit 226 when the distance detection electrode 12 is at the reference position. The switching means sw1, sw2, sw3 are turned off.
Then, the following processing is repeated at a predetermined time interval, for example, 20 ms.

First, the switching means sw1 is turned on, the analog potential displacement signal Va is input to the A / D converter 204, and the digital potential displacement signal Va is input to the digital processing section 20.
5 RAM to store.

Next, the switching means sw1 is turned off and the switching means sw2 is turned on to input the analog signal Vb to the A / D converter 204 and store the digital signal Vb in the RAM of the digital processing section 205.

Next, the switching means sw2 is turned off and the switching means sw3 is turned on to set the analog temperature signal tmp1 to A.
Input to the A / D converter 204, and the digital temperature signal tmp
1 is stored in the RAM of the digital processing unit 205. Then, the switching means sw3 is turned off.

In the digital processing section 205, the signal V
b is divided by the reference voltage Vref signal to generate the displacement signal Vc. This displacement signal Vc becomes a signal corresponding to the displacement from the reference position.

From the potential displacement signal Va to the displacement signal V
c is divided to generate a potential signal. This potential signal is
The signal corresponds to the surface potential Vs of the surface S to be measured.

Then, the control signal c1 corresponding to the potential signal and the temperature signal tmp1 is generated. D / A converter 208
Is the digital control signal c1 and the analog control signal c1
And is output to the charging device 81.

Next, the surface potential control device 10 and the surface to be measured S
A method for removing and outputting the distance component corresponding to the distance L1 between the potential detection electrode 11 and the surface S to be measured when the distance between and changes will be described. FIG. 9 shows the relationship between the surface potential Vs of the measured surface S and the signal Vb, and FIG. 10 shows the relationship between the surface potential Vs of the measured surface S and the potential displacement signal Va.

As shown in FIGS. 9 and 10, the signal Vb does not depend on the surface potential Vs but on the distance L2. The potential displacement signal Va is proportional to the surface potential Vs and the distance L1
Depends on.

In the present embodiment, the distance L1 between the surface S to be measured and the potential detection electrode 11 is the same as the distance L2 between the surface S to be measured and the distance detection electrode 12, so the distance L1 (= L
When 2) changes, the electrostatic capacitances C1 and C2 change by the same ratio. Therefore, the signal V when the distance L1 changes
The change amount of b is proportional to the change amount of the potential displacement signal Va.

Therefore, when the distances L1 = x1 and x2, the potential displacement signals Va = Va (x1) and Va (x
2) and signals Vb = Vb (x1) and Vb (x2), Va (x1) / Va (x2) = Vb (x1) / Vb (x
2) can be expressed as Here, if x1 is defined as the reference position and Vb (x1) is defined as the reference voltage (Vref), then Va (x1) = Va (x2) / (Vb (x2) / Vref) = Va (x2) / Vc .

In the surface potential control device 10, the distance L
When 1 is at x2 which is displaced from the reference position (x1), V
a (x2) and Vb (x2) are detected. Therefore,
By substituting Va (x2) and Vb (x2) into the above equation, the potential Vs of the surface S to be measured can be accurately detected without having distance dependency.

As described above, the signal processing unit 20 of the surface potential control device 10 changes the potential displacement signal Va to the displacement signal Vc = Vb.
By dividing / Vref, the component corresponding to the distance L1 between the potential detection electrode 11 and the surface S to be measured can be removed, and a potential signal corresponding to the surface potential Vs of the surface S to be measured can be generated. it can.

FIG. 11 shows the detection result of the surface potential Vs. In FIG. 11, the reference position (x1) is 3 mm, and the distance L is
It is a figure which shows the detection result of the surface electric potential Vs when 1 changes from the reference position. In FIG. 11, the potential signal detected by the surface potential control device 10 according to the present embodiment is shown by a solid line, and the result detected by the conventional high voltage feedback type potential detection device is shown by a dashed line.

As shown in FIG. 11, the surface potential control device 10 according to the present invention allows the potential Vs of the surface S to be measured even when the distance L1 between the surface S to be measured and the potential detection electrode 11 changes. Can be accurately detected without having distance dependency.

Further, in the surface potential control device according to the present embodiment, part of the signal processing unit 20 includes the digital processing unit 205, so that the number of passive circuit elements and active circuit elements can be reduced accordingly. Therefore, the surface potential control device can be downsized and the cost can be reduced.

In particular, when the digital processing unit 205 is configured by using the RAM and ROM built in the copying machine, the laser beam printer, the facsimile, etc., the size and cost can be greatly reduced. You can

Further, since the surface potential control device according to this embodiment includes the digital processing unit 205, the setting of the surface potential control device can be changed only by rewriting the RAM of the digital processing unit 205. It is possible to configure a surface potential control device having properties.

Further, the surface potential control device according to the present embodiment has the potential detection electrode 1 which is a portion having a high impedance.
1, impedance conversion circuit 211, first amplifier 21
2 is housed in the first shield case 13, the distance detection electrode 12, which is a high impedance portion, the non-inverting amplifier circuit 222, and the second amplifier 223 are housed in the second shield case 14, and the first shield case 13 is grounded to the first reference potential GND1 and the second shield case 14 is grounded to the second reference potential GND2. For this reason, the portion with high impedance is less likely to be affected by noise, and the S / N ratio is increased.

Further, in the surface potential control device according to the present embodiment, electronic components are mounted only on one surface of the circuit board 19 and a circuit pattern is formed. Therefore, the circuit board 19
When arranging the first shield case 13 and the second shield case 14 on each other, it is not necessary to insulate the first shield case 13 and the second shield case 14 from the other surface of the circuit board 19. Therefore, manufacturing becomes easy.

Further, in the surface potential control device according to the present invention, the first rectifying / smoothing circuit 213, the first level shift circuit 214, the modulation signal generating circuit 215, the signal generator 221, and the second portion, which are low impedance parts, are provided. Rectifying and smoothing circuit 224, subtraction circuit 225, second level shift circuit 2
26 may not be housed in the first shield case 13 and may be provided outside the first shield case 13 and the second shield case 14.

In the surface potential control device according to the present invention, the distance L2 between the distance detecting electrode 12 and the surface S to be measured is
The value may be different from the distance L1 between the potential detection electrode 11 and the surface S to be measured. However, as shown in the embodiment, when these distances have the same value, signal processing becomes easy.

FIG. 12 is a block diagram showing another embodiment of the surface potential control device according to the present invention. In FIG. 12, the same components as those shown in FIG. 4 are designated by the same reference numerals.

The analog processing section 202 of the surface potential control device shown in FIG. 12 includes a potential detecting section 31 and a distance detecting section 24. The potential detecting unit 31 includes the impedance conversion circuit 2
11, the first amplifier 212, and the first rectifying and smoothing circuit 2
13, a first level shift circuit 214, a modulation signal generation circuit 215, a stationary electrode 317, and an impedance generator 318. The surface S to be measured and the potential detection electrode 11 are opposed to each other via the stationary electrode 317, and the impedance generator 318 and the stationary electrode 31 that constitute the electrostatic capacitance C1.
7 is housed in the first shield case 13.
The stationary electrode 317 can be made of a conductive material, for example, a metal material.

One end of the impedance generator 318 is electrically connected to the stationary electrode 317, and the other end is electrically connected to the first shield case 13.

The modulation signal generation circuit 215 outputs a signal having a constant frequency, for example, a 700 Hz signal.

The impedance generator 318 periodically changes the impedance of the stationary electrode 317 at the frequency of the signal input from the modulation signal generation circuit 215. The impedance of the stationary electrode 317 has, for example, a frequency of 7
It changes to a sine wave of 00 Hz.

When the impedance of the stationary electrode 317 changes, the electrostatic capacitance C1 changes, and the potential detecting electrode 11 outputs the potential distance signal s1. This operation is basically the same as the operation of the surface potential control device described with reference to FIGS. 1 to 11.

FIG. 13 is an exploded perspective view showing a more specific embodiment of the surface potential control device shown in FIG. 2, and FIG. 14 is FIG.
FIG. 15 is a cross-sectional view of the surface potential control device shown in FIG. 15, and FIG. 15 is a perspective view showing the structure of part of the surface potential control device shown in FIG. 13 more specifically.

13 and 14, the signal processing section 20
Are provided inside the surface potential detection sensor 1. The surface potential detection sensor 1 includes a potential detection electrode 11, a distance detection electrode 12, a first shield case 13, a second shield case 14, a circuit board 19, and an insulator 400. The signal processing unit 20 includes an electronic component (not shown) forming a circuit and a mechanical chopper 216 shown in FIG. The mechanical chopper 216 includes piezoelectric elements 217 and 218 attached to two legs arranged to face each other to form a tuning fork portion.

The first shield case 13 is composed of a first upper lid 131 and a first lower lid 132 each made of a flat metal plate, and has a first detection window 15 and a first notch 17. Including. The second shield case 14 is composed of a second upper lid 141 and a second lower lid 142 made of a metal flat plate, and includes a second detection window 16 and a second notch 18. The circuit board 19 is a single board. The circuit board 19 includes a first board portion 191, a second board portion 192, and a connecting portion 1.
And 93, the connecting portion 193 connects the first substrate portion 191 and the second substrate portion 192.

The first detection window 15 is formed on the side surface 134 of the first shield case 13, and the second detection window 16 is
It is formed on the side surface 144 of the second shield case 14, and the first detection window 15 and the second detection window 16 are formed on the same surface side. The potential detection electrode 11 has a first detection window 15
And the distance detection electrode 12 is provided corresponding to the second detection window 16. The mechanical chopper 216 is provided between the potential detection electrode 11 and the first detection window 15.

The first shield case 13 and the second shield case 14 are arranged so that the side surface 133 of the first shield case 13 and the side surface 143 of the second shield case 14 face each other with the insulator 400 in between. It is located in.
The first notch 17 is provided on the side of the side surface 133 farther from the side surface 134. The second notch 18 is the side surface 1.
It is provided on the side farther from the side surface 144 in 43.

The circuit board 19 is provided with electronic components constituting a circuit and has a circuit pattern formed on only one surface thereof. The circuit board 19 is provided so as to straddle the first notch 17 and the second notch 18, and the first board portion 191 is arranged on the opening surface of the first lower lid 132. The second substrate portion 192 is arranged on the opening surface of the second lower lid 142. The connecting portion 193 is arranged corresponding to the first cutout 17 and the second cutout 18.

The first shield case 13 is overlapped so that the opening surface of the first upper lid 131 and the opening surface of the first lower lid 132 face each other. Second shield case 14
Are overlapped so that the opening surface of the second upper lid 141 and the opening surface of the second lower lid 142 face each other. The potential detection electrode 11, the mechanical chopper 216, and the first substrate unit 19
1 is housed inside the first shield case 13, and the distance detection electrode 12 and the second substrate portion 192 are housed inside the second shield case 14.

In the surface potential control device according to this embodiment, the circuit board 19 holds the space between the first shield case 13 and the second shield case 14, so that they are electrically insulated from each other. It can be mechanically coupled.

Further, in the surface potential control device according to this embodiment, since the insulator 400 is provided between the side surface 133 and the side surface 143, when the circuit board 19 bends due to the stress applied from the outside. But the first shield case 13
And the second shield case 14 do not come into contact with each other,
The insulation between the two can be reliably maintained.

Since the surface potential control device according to this embodiment is provided with the notches 17 and 18, the first shield case 13 and the second shield case 14 can be easily positioned on the circuit board 19. can do.

Further, in the surface potential control device according to the present embodiment, since the notches 17 and 18 are provided at the portions far from the detection windows 15 and 16, the influence of noise is reduced and the S / N ratio is reduced. growing.

Further, in the surface potential control device according to this embodiment, the notches 17 and 18 can be made smaller by making the connecting portion 193 of the circuit board 19 smaller. For this reason, it becomes difficult for radio waves to enter through the notches 17 and 18, so that it is less susceptible to noise and the S / N ratio increases.

Further, in the surface potential control device according to the present embodiment, since the electronic components forming the circuit are mounted on the same circuit board, the work of mounting the electronic components on the circuit board becomes easy.

Further, in the surface potential control device according to the present embodiment, since the electronic components constituting the circuit are mounted on the same circuit board, wiring by the circuit pattern becomes possible,
There is no need to use connectors or wires. Therefore, the number of parts can be reduced, and the cost can be reduced. Further, since it is not necessary to use a connector or a wire, noise generated from the line can be reduced and the S / N ratio becomes large.

Further, as shown in the embodiment, it is preferable that the distance between the potential detecting electrode 11 and the distance detecting electrode 12 is small. When the distance between the potential detection electrode 11 and the distance detection electrode 12 is small, the relative distance between the potential detection electrode 11 and the surface S to be measured and the relative distance between the distance detection electrode 12 and the surface S to be measured. Since the difference between and is small, the detection accuracy is high.

FIG. 16 is an enlarged partial cross-sectional view showing still another embodiment of the surface potential control device according to the present invention, which is an enlarged view of the distance detection electrode and the second shield case.
In FIG. 16, the same components as those shown in FIGS. 1 to 15 are designated by the same reference numerals.

The surface potential control device shown in FIG.
In addition to the configuration shown in FIG. 15, a dielectric 510 is included. The dielectric 510 is provided so as to close the second detection window 16 from the inside and the outside of the second shield case 14. The distance detection electrode 12 is formed on the surface of the dielectric 510 and is integrated with the dielectric 510. The dielectric 510 may be organic, inorganic, or composite.

In the surface potential control device according to this embodiment, since the dielectric 510 blocks the second detection window 16, the inside of the second shield case 14 can be protected from dust and humidity.

Further, in the surface potential control device according to this embodiment, the dielectric 51 is provided between the distance detection electrode 12 and the surface S to be measured.
0 is provided. Therefore, the dielectric constant between the distance detection electrode 12 and the surface S to be measured is increased, and the detection accuracy is improved.

Further, in the surface potential control device according to the present embodiment, since the distance detection electrode 12 is formed on the surface of the dielectric 510 provided in the second detection window 16, the distance detection electrode 12 can be attached. It will be easier.

Further, in the surface potential control device according to the present embodiment, since the distance detection electrode 12 is formed on the surface of the dielectric 510 provided in the second detection window 16, the mounting accuracy of the distance detection electrode 12 is high. Is less likely to occur, and the detection accuracy is improved.

FIG. 17 is an enlarged partial sectional view showing still another embodiment of the surface potential control device according to the present invention, which is an enlarged view of the distance detection electrode and the second shield case.
In FIG. 17, the same components as those shown in FIG. 16 are designated by the same reference numerals.

The surface potential control device shown in FIG.
A dielectric 520 is included instead of the dielectric 510 shown in FIG. The dielectric 520 is provided so as to close the detection window 16 from the inside of the second shield case 14. Then, the distance detection electrode 12 is formed on the surface of the dielectric 520, and the dielectric 52
It is integrated with 0.

The surface potential control device according to this embodiment is shown in FIG.
Since it has the same configuration as the surface potential control device shown in FIG. 6, it is possible to obtain the same operational effect.

FIG. 18 is an exploded perspective view showing still another embodiment of the surface potential control device according to the present invention. FIG. 19 is a sectional view of the surface potential control device shown in FIG.

18 and 19, FIGS.
The same reference numerals are attached to the same components as those shown in FIG. The surface potential control device shown in FIGS. 18 and 19 includes an insulating substrate 60, a screw 70, and a metal member 80 in addition to the configuration shown in FIGS. FIG.
In FIG. 1, the first upper lid 131 is omitted for convenience of illustration.

The insulating substrate 60 is a highly rigid substrate,
An emboss 61 is formed on one surface. First lower lid 1
32, a hole corresponding to the emboss 61 is formed in the second lower lid 142. A hole corresponding to the screw 70 is formed in the circuit board 19.

In the surface potential control device according to this embodiment, the first lower lid 13 is formed so that the holes formed in the first lower lid 132 and the second lower lid 142 correspond to the emboss 61.
The second and second lower lids 142 are mounted on the insulating substrate 60 and fixed with an adhesive or the like. The circuit board 19 is embossed 6
Screw 7 mounted on 1 and fitted in emboss 61
It is fixed at 0.

The mechanical chopper 216 has a metal member 8
Fixed to the first lower lid 132 via the
It is electrically connected to 32. Then, the first lower lid 132
The first upper lid 131 and the second upper lid 141 are superposed on the second lower lid 142.

In the surface potential control device according to the present embodiment, the circuit board 19 is mounted on the first lower lid 132 and the second lower lid 142 via the emboss 61, so that the circuit board 19 is mounted.
It is possible to form a circuit pattern by mounting electronic components that form a circuit on both surfaces of.

Further, in the surface potential control device according to this embodiment, since the insulating substrate 60 has rigidity, the surface potential control device does not bend even when external stress is applied.

[0139]

As described above, according to the present invention, the following effects can be obtained. (A) It is possible to provide a surface potential control device that can accurately detect the potential of the measured object even when the distance to the measured object changes. (B) It is possible to provide a surface potential control device that can detect the potential of a measured object with high sensitivity. (C) Appropriate feedback control can be added to maintain the potential of the measured object at a predetermined value. (D) It is possible to provide a surface potential control device having a simple circuit configuration. (E) It is possible to provide a small and lightweight surface potential control device. (F) It is possible to provide an inexpensive surface potential control device that does not use high voltage components.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a configuration of an image forming apparatus using a surface potential control device according to the present invention.

FIG. 2 is a partially enlarged view of FIG.

FIG. 3 is a block diagram more specifically showing a partial configuration of the surface potential control device shown in FIG. 1.

FIG. 4 is a block diagram more specifically showing a partial configuration of the surface potential control device shown in FIG.

5 is a circuit diagram more specifically showing a partial configuration of the surface potential control device shown in FIG.

FIG. 6 is a diagram showing operation waveforms of the surface potential control device according to the present invention.

FIG. 7 is another diagram showing operation waveforms of the surface potential control device according to the present invention.

FIG. 8 is a flowchart showing digital processing.

FIG. 9 is a surface potential Vs of the surface potential control device according to the present invention.
It is a figure which shows the relationship between V and signal Vb.

FIG. 10 is a surface potential V of the surface potential control device according to the present invention.
It is a figure which shows the relationship between s and the electric potential displacement signal Va.

FIG. 11 is a surface potential V of the surface potential control device according to the present invention.
It is a figure which shows the detection result of s.

FIG. 12 is a block diagram showing another embodiment of the surface potential control device according to the present invention.

13 is an exploded perspective view showing a more specific example of the surface potential control device shown in FIG.

14 is a cross-sectional view of the surface potential control device shown in FIG.

FIG. 15 is a perspective view showing the structure of a part of the surface potential control device shown in FIG. 13 more specifically.

FIG. 16 is a partial cross-sectional enlarged view showing still another embodiment of the surface potential control device according to the present invention.

FIG. 17 is an enlarged partial sectional view showing still another embodiment of the surface potential control device according to the present invention.

FIG. 18 is an exploded perspective view showing still another embodiment of the surface potential control device according to the present invention.

FIG. 19 is a cross-sectional view of the surface potential control device shown in FIG.

[Explanation of symbols] 10 Surface potential control device 1 Surface potential detection sensor Th1 temperature detection sensor 20 Signal processing unit 11 Potential detection electrode 12 Distance detection electrode 13 First shield case 14 Second shield case 400 insulator 40 Object to be measured s1 potential distance signal s2 distance signal

Claims (9)

[Claims] 1. A surface potential control device including a charging device, a surface potential detection sensor, and a signal processing unit, wherein the charging device applies a quantity of electricity corresponding to an input control signal to an object to be measured. A device, wherein the surface potential detection sensor includes a potential detection electrode and a distance detection electrode, the potential detection electrode is an electrode capacitively coupled to the object to be measured, and corresponds to a distance to the object to be measured. Distance component to
A potential distance signal including a potential component corresponding to the potential of the measured object is output, and the distance detection electrode is an electrode capacitively coupled to the measured object, and a distance corresponding to the distance to the measured object. Outputs a signal, the signal processing unit, the potential distance signal and the distance signal is input, using the distance signal, removes the distance component from the potential distance signal, to the potential of the measured object. A surface potential control device that generates a corresponding potential signal and inputs a control signal corresponding to the potential signal to the charging device. 2. The surface potential control device according to claim 1, wherein the charging device includes a charger and a high voltage generator, and the high voltage generator has a high voltage according to the control signal. The high voltage is input to the charger, and the surface potential control device applies an amount of electricity corresponding to the high voltage to the object to be measured. 3. The surface potential control device according to claim 1, wherein the signal processing unit includes a digital processing unit, and the digital processing unit digitally processes an input signal. Control device. 4. The surface potential control device according to claim 3, wherein the signal processing unit further includes an analog processing unit, and the analog processing unit includes a potential detection unit and a distance detection unit. Including, the potential detection unit performs analog processing of the potential distance signal and outputs, the distance detection unit performs analog processing of the distance signal and outputs, and the digital processing unit outputs from the distance detection unit. The signal that is generated by dividing the signal obtained by the reference voltage signal to generate a displacement signal corresponding to the displacement from the reference position, and the signal output from the potential detection unit is divided by the displacement signal to generate the potential signal. Electric potential control device. 5. The surface potential control device according to claim 4, wherein the potential detection unit multiplies a component corresponding to the potential of the measured object by a component proportional to the displacement signal. Outputting a potential displacement signal, the distance detection unit, a signal generator, a non-inverting amplifier circuit,
A second amplifier, a second rectifying and smoothing circuit, a subtracting circuit,
A second level shift circuit, the signal generator outputs a signal having a constant frequency, and the non-inverting amplifier circuit converts the signal input from the signal generator with an amplification factor based on the distance signal. Amplify and output, the second amplifier AC-amplifies and outputs the signal input from the non-inverting amplifier circuit, and the second rectifying and smoothing circuit outputs the signal input from the second amplifier. And subtracting the signal input from the signal generator from the signal input from the second rectifying and smoothing circuit, and outputting the subtraction circuit. Adjusting the level of the signal input from the subtraction circuit and outputting the adjusted signal, the digital processing unit dividing the signal input from the second level shift circuit by a reference voltage signal to generate the displacement signal. Surface potential control device Place 6. The surface potential control device according to claim 5, wherein the potential detection unit includes an impedance conversion circuit, a first amplifier, a first rectifying / smoothing circuit, and a first level shift circuit. A circuit, a modulation signal generation circuit, and a mechanical chopper, the modulation signal generation circuit outputs a signal of a constant frequency, the mechanical chopper, at the frequency of the signal input from the modulation signal generation circuit, The capacitance between the device under test and the potential detection electrode is changed, the impedance conversion circuit converts the potential distance signal into a voltage signal and outputs the voltage signal, and the first amplifier converts the impedance conversion signal. A signal input from the circuit is AC-amplified and output, and the first rectifying / smoothing circuit converts the AC signal input from the first amplifier into a DC signal and outputs the DC signal. The level shift circuit, the first by adjusting the DC level of the input signal from the rectifying and smoothing circuit, the surface potential control device for outputting a potential displacement signal. 7. The surface potential control device according to claim 5, wherein the potential detection unit includes an impedance conversion circuit, a first amplifier, a first rectifying / smoothing circuit, and a first level shift circuit. A circuit, a modulation signal generation circuit, a shield case, a stationary electrode, and an impedance generator, the shield case includes a detection window, the potential detection electrode, the impedance conversion circuit, and the first An amplifier, the first rectifying / smoothing circuit, the first level shift circuit, the modulation signal generating circuit, the impedance generator and the stationary electrode are covered, and the detection window is the stationary electrode. And the measurement object, the stationary electrode is disposed between the measurement object and the potential detection electrode, the modulation signal generation circuit outputs a signal of a constant frequency, The impedance generator changes the impedance of the stationary electrode at the frequency of the signal input from the modulation signal generation circuit, the impedance conversion circuit converts the potential distance signal into a voltage signal and outputs the voltage signal, The first amplifier AC-amplifies and outputs the signal input from the impedance conversion circuit, and the first rectifying / smoothing circuit converts the AC signal input from the first amplifier into a DC signal. The surface potential control device that outputs the potential displacement signal, wherein the first level shift circuit adjusts the DC level of the signal input from the first rectifying and smoothing circuit and outputs the potential displacement signal. 8. The surface potential control device according to claim 1, wherein the distance between the potential detection electrode and the object to be measured, and the distance detection electrode and the object to be measured. The surface potential control device having the same distance. 9. An image forming apparatus including a surface potential control device and an object to be measured, wherein the surface potential control device is the device described in any one of claims 1 to 8. Is an image forming apparatus that is a photosensitive drum.