JPH0763803A - Non-contact type surface potentiometer - Google Patents

Abstract

PURPOSE:To contrive to make an easier access to a sample to be detected and a miniaturization of a sensor element and the apparatus by eliminating effect due to a mechanical positional deviation in a non-contact type surface potentiometer to measure a surface potential of a photosensitive body or the like while miniaturizing a sensor probe. CONSTITUTION:A sensor element 11 is made up of a Pockels crystal, a polarizer, a wavelength plate and an analyzer, a detection electrode 13 is provided as arranged facing a sample 1 to be detected while an insulation layer 21 is provided between the detection electrode 13 and a crystal of the sensor element 11 and the detection electrode 13 is connected in series to an electrode 12a of the insulation layer 21 and an electrode 12b of the sensor element 11. Then, a surface potential of the sample 1 to be detected is determined with a signal processing section 15 from the intensity of light passing through the ockels crystal in the sensor element 1.

Description

Detailed Description of the Invention

[0001]

This invention relates to a PPC (plain pape)
r copier), FAX (facsimile), and the like, and relates to a non-contact surface potential type for measuring the surface potential of a photoconductor or the like in a non-contact manner.

[0002]

2. Description of the Related Art FIG. 9 is a block diagram showing a conventional surface potential type measuring principle in which the surface potential is measured in a non-contact manner. In the figure, 1 is a sample to be detected such as a photoconductor of a copying machine, which is charged to + (positive) by a power source 2.

Reference numeral 3 is a case of the sensor section, which is a small window 4 for measurement.
Is provided, and a pair of tuning fork type vibrators 5 are arranged inside the small window 4. Reference numeral 6 is a detection electrode arranged inside the small window 4.

FIG. 10 schematically shows the structure of the sensor section. The pair of vibrators 5 are integrally formed with a tuning fork 8 to which a piezoelectric element (piezoelectric ceramics) 7 is adhered, and an alternating voltage is applied to the piezoelectric element 7 from a drive circuit 9. The output of the detection electrode 6 is amplified by the preamplifier 10 and input to a signal processing circuit (not shown).

In the case of measuring the surface potential of the sample 1 to be detected in the surface electrometer as described above, Case 3 is used.
The small window 4 is set toward the surface of the sample to be detected 1. At this time, if there is electric charge on the surface of the sample to be detected 1 due to corona discharge or the like, electric force lines A as shown by the broken line in FIG. This line of electric force A is
Although it reaches the detection electrode 6 through the small window 4 of the case 3,
Here, the distance between the sample to be detected 1 and the detection electrode 6 is fixed to a constant value, the electric force line A is choppered by some method, and the time of the electric force line A reaching the detection electrode 6 having the area S is determined. The surface potential of the sample to be detected 1 can be known by inputting the amount of dynamic change into the gate of the FET incorporated in the signal processing circuit and detecting the amount.

That is, as one method of the chopper of the above-described electric flux line A, the AC method is used in the example of FIG.
Attach the piezoelectric element 7 to the tuning fork 8 with stable frequency,
AC voltage is applied to the piezoelectric element 7 to move the vibrator 5 to the arrow B
In this way, the lines of electric force A are chopped. At this time, when the sample 1 to be detected and the detection electrode 6 in the electrostatic field are regarded as a flat plate capacitor with an electrode space r containing an air layer having _a dielectric constant ε _a , the electrostatic capacitance C and the charge Q of this capacitor are When the applied voltage (potential of the sample to be detected 1) is V, C = ε _a S / r and Q = CV.

From the relation of the above equation, the change in the leakage current I of the capacitor due to the chopping of the electric force line A is obtained, and this is detected as the AC signal voltage. This current I is

[0008]

[Equation 1]

It is represented by At this time, if C = constant,

[0010]

[Equation 2]

[0011] Then, this is amplified as an AC signal voltage by the preamplifier 10 to relatively determine the surface potential of the sample 1 to be detected.

[0012]

However, in the above-mentioned conventional non-contact type surface electrometer, when the position of the detection electrode or the position of the chopper deviates from the small window through which the lines of electric force pass, the output is generated. There is a problem in that the level changes from a predetermined value and the surface potential cannot be measured accurately.

Further, since it has a small window, when it is actually incorporated into a machine for use, for example, toner or the like enters the case and adversely affects the piezoelectric tuning fork, resulting in leakage or deterioration of sensitivity. There were problems such as.

The present invention has been made by paying attention to the above-mentioned problems, it is possible to measure the surface potential accurately, a dustproof structure is possible, and it is possible to prevent the occurrence of leakage due to toner and the like. An object of the present invention is to provide a non-contact type surface electrometer capable of downsizing the sensor probe, easily cleaning the sensor probe, and downsizing the sensor element part and the device.

[0015]

The non-contact surface electrometer of the present invention comprises a sensor element using a Pockels crystal in which the refractive index of light changes according to an applied voltage, and a sensor element facing the surface of a sample to be detected. A sensing electrode to be arranged is provided, an insulating layer is provided between the sensor element and the sensing electrode, and the sensing electrode, the electrode of this insulating layer, and the electrode of the sensor element are connected in series, and the Pockels of the sensor element is provided. A signal processing unit for detecting the surface potential of the sample to be detected from the intensity of light passing through the crystal is provided.

Further, a polarization beam splitter for separating the light emitted from the crystal of the sensor element into transmitted light and reflected light is provided, and a divider for canceling the intensity change of the incident light is built in the signal processing unit. It was done.

[0017]

In the non-contact type surface electrometer of the present invention, since the optical sensor is used, the measurement can be performed without being affected by the mechanical positional relationship, and the dustproof structure can be obtained.

Further, since the sensor probe having only the detection electrode and the other portion can be separated, the sensor probe can be downsized and the sensor probe can be easily cleaned.

Furthermore, since the insulating layer is provided between the detection electrode and the sensor element, the voltage applied to the sensor element increases, and the sensor element and the device can be made compact.

[0020]

1 is a diagram showing a schematic configuration of a non-contact type surface electrometer according to an embodiment of the present invention. In the figure, 1 is a sample to be measured whose surface potential is to be measured, 11 is a sensor element using a Pockels crystal in which the bending rate of light changes according to an applied voltage, and one side is provided with an insulating layer 21. Electrode 1
2a is provided, and the electrode 12b is directly provided in parallel on the other side.

Reference numeral 13 denotes a detection electrode which is arranged so as to face the surface of the sample 1 to be detected. The detection electrode 13 and the sensor element 11 are provided.
The insulating layer 21 is interposed between the detecting electrode 13, the electrode 12a of the insulating layer 21, and the electrode 12b of the sensor element 11 connected in series. The end of the detection electrode 13 is electrically connected to one electrode 12a through the lead wire 14, and the other electrode 12b is grounded. A signal processing unit 15 detects the surface potential of the sample 1 to be detected from the intensity of light that has passed through the Pockels crystal in the sensor element 11.

The detection electrode 13 is formed of, for example, a metal plate of copper, brass, aluminum or the like, and the lead wire 14 is connected to the end thereof. And this detection electrode 13
Are arranged in parallel with the sample to be detected 1 with a distance d1, and a voltage corresponding to the surface potential of the sample to be detected 1 is detected by the detection electrode 13.
The intensity of the emitted light that is applied to the sensor element 11 via the insulating layer 21 and that has passed through the sensor element 11 changes according to the applied voltage. Therefore, the signal processing unit 15 can obtain the surface potential of the sample to be detected 1 from the intensity of the emitted light.

FIG. 2 is a diagram showing an equivalent circuit of the sensor section having the above structure. As shown in the figure, the capacitance C1 of the air layer between the sample to be detected 1 and the detection electrode 13 and the insulating layer 2
It is a series circuit of the capacitor capacitance C2 of 1 and the capacitor capacitance C3 of the sensor element 11.

Next, the measurement principle of the above-mentioned non-contact type surface electrometer will be described in detail. FIG. 3 is a diagram showing the measurement principle, and the surface of the sample 1 to be detected is charged positively or negatively (here, positive) by the power supply 2. Also, a sensor element 11 mainly composed of Pockels crystal 11
Is the applied voltage (surface potential of the sample to be detected 1) as described above.
The refractive index (transmittance) of light changes in accordance with. This sensor element 11 is composed of a uniaxial crystal LiTaO ₃ crystal of a trigonal system, a polarizer, a wave plate, and an analyzer. When a voltage is applied, the refraction of light is caused according to the applied voltage. The rate changes linearly, and the intensity of the emitted light passing through the rate has a property of depending on the applied voltage.

Further, in FIG. 2, reference numeral 16 is a light receiving portion having a PIN-photodiode (PIN-PD) for receiving the light passing through the inside of the sensor element 11, and 17 is an amplifier for amplifying the output of the light receiving portion 16. The amplified signal is input to a signal processing circuit (including a computing unit) 18, and the signal processing circuit 18 detects the surface potential of the sample 1 to be detected from the intensity of light from the sensor element 11.

FIG. 4 is a diagram showing the measurement operation by the surface electrometer of FIG. The positional relationship between the sensor element 11 and the sample to be detected 1 is as shown in FIG. 4 (a). The sensor element 11 is placed in an electrostatic field, light is made incident through the polarizer from its end face, and emitted light is emitted. To measure the intensity of.

At this time, the incident light is first converted into linearly polarized light through the polarizer, passes through the inside of the crystal having the length L in the sensor element 11, and is converted into elliptically polarized light. FIG. 4B shows the state, and the Z axis (C axis) of the XZ plane.
When linearly polarized light with a wavelength of 45 ° is incident on
This linearly polarized light is converted into elliptically polarized light when passing through the inside of the crystal due to the difference in the bending ratios n _x and n _{y in} the X and Y directions, n _x = _ny and _nz .

Here, actually, in order to reduce the size of the sensor probe, it has been proposed to provide a detection electrode 13 as shown in FIG. The detection electrode 13 is arranged so as to face the surface of the sample to be detected 1, and one end thereof is connected to the electrode 12 a by a lead wire 14. FIG. 6 shows an equivalent circuit thereof.

The above-mentioned air layer between the sample 1 to be detected and the sensor element 11 can be regarded as a series connection between them if the capacitor capacity is C1 and the capacitor capacity of the sensor element 11 is C2. Each potential difference V shown in (b)
The relationship between 1 and V3 is as follows, where d1 is the distance between the sample to be detected 1 and the electrode surface on the opposite side of the sensor element 11, and d is the crystal thickness.

[0030]

[Equation 3]

It is represented by

However, ε is the relative dielectric constant of the crystal.

The total voltage V is V = V1 + V3 (2)

That is, the sample to be detected 1 and the electrode 12b are
When the surface potential of the sample 1 to be detected changes while the distance d1 between the sensor element 11 and the electrode 12a, 12b changes, the light of the sensor element 11 having the optical path length L changes in accordance with the potential. The intensity of the emitted light when passing through the inside changes.
Therefore, if the intensity of the light emitted from the sensor element 11 is detected and the detected voltage is obtained, the values of d1 and L are known, and the surface potential of the sample 1 to be detected can be known.

However, in the above case, the voltage range to be detected is limited. That is, since the LiTaO ₃ crystal of the sensor element 11 has a large relative permittivity ε and ε = 43 (theoretical value), the crystal thickness is 0.5 at a detection distance d1 = 2 mm.
mm, the voltage applied between the crystals (between the electrodes 12a and 12b) is 0.38 V at 50 V and 1.
It becomes 52V. Therefore, under this circumstance, the optical path length L of the crystal becomes large and it is difficult to reduce the size.

Further, the optical path length L and the applied voltage V between the crystals are
_{As for} the relation of _z , if the phase difference is δ,

[0037]

[Equation 4]

[0038]

Where λ = measurement wavelength n _e = refractive index of extraordinary light n _o = refractive index of ordinary light γ ₃₃ , γ ₁₃ = electro-optical constant At this time, in order to convert the above linearly polarized light to elliptically polarized light , it is necessary to determine L and V _z so that the phase difference occurs to π / 4~π / 2. Then, the crystal thickness d = 0.
When 5 mm and the detection distance d1 = 2 mm, the voltage V _z applied to the crystal is obtained by the equations (1) and (2). As a result,
As described above, it becomes about 0.38V at 50V. Under this circumstance, the size of the crystal becomes large, and it is difficult to detect the change in light intensity.

Therefore, in this embodiment, as shown in FIG.
An insulating layer 21 is provided between the sensor element 11 and the detection electrode 13 to reduce the synthetic capacitor capacity and increase the voltage applied to the crystal. Therefore, the voltage drop of the air layer becomes small, and if the charge amount is Q, as shown in the equivalent circuit of FIG.

[0041]

[Equation 5]

It becomes

Where ε ₀ = vacuum permittivity ε ₁ = air layer permittivity ε ₂ = insulating layer permittivity ε ₃ = crystal permittivity S 1, S 2, S ₃ = electrode area of each capacitor

[0044]

[Equation 6]

Now, the detected potential of PPC, FAX, etc. is V =
When it is set to 50 to 1000 V and V ₃ = ₃ Vmin at 50 V, the relative permittivity ε ₁ = 1, ε ₂ = 2, ε ₃ = 32.7.
(LiTaO ₃ crystal), detection and measurement distance d1 = 2 mm, insulating layer thickness d2 = 0.1 mm, crystal thickness d3 = 0.5 mm, and measurement wavelength λ _P = 670 mm, the optical path length L of the crystal is (3 ) From the equation, when the phase difference δ = π / 2, L = 11.68
mm.

Under this condition, S2 = S3 = 11 × 2 mm
^In the case of ² , the detection electrode area S1 = 240 mm ² . At this time, the voltage V3 applied to the crystal is V = 50V, V3 = 3V, V = 200V, V3 = 12V, V = 1000V, V3 = 60V.

Therefore, until now, the optical path length of the crystal L≈5
7.50 mm (without dielectric constant) was 11.6
It becomes 8 mm, and V3 becomes 0.38V → 3V 1.52V → 12V 12V → 60V, respectively.

As described above, by interposing the insulating layer 21 on the crystal of the sensor element 11, the voltage applied to the crystal is increased, and the optical path length of the crystal and the detection electrode area can be reduced. Therefore, the sensor element 11 and the device can be downsized, and the configuration as a simple measuring instrument or a measuring instrument is easy.

Although the insulating layer 21 is bonded on the crystal in the above example, the same effect can be obtained by bonding the insulating layer 21 on the detection electrode 13 as can be seen from the equivalent circuit of FIG.

Further, as shown in FIG. 7, the sensor probe 19 having only the detection electrode 13 and the main body 20 including the optical system (sensor element 11) and the signal processing unit 15 are separated and connected by the lead wire 14. An optical surface electrometer can be realized.

Therefore, there is no influence of mechanical displacement as in the conventional case, the surface potential can be easily and accurately measured, a dustproof structure is possible, and the occurrence of leakage due to toner or the like can be prevented. it can.

Furthermore, since the sensor probe 19 having only the detection electrode 13 and the main body 20 including other optical system and signal processing system can be separated as described above, the sensor probe 19 should be brought close to the surface of the sample 1 to be detected. It is possible to reduce the size of the sensor probe 19, and
Cleaning of the sensor probe 19 is also easy.

From the principle diagram of FIG. 5, the intensity I of the emitted light is

[0054]

[Equation 7]

[0055] is represented by, I also changes if the change is I _O. That is, it is necessary to achieve the stability of the incident light intensity I _O is incident so as not to change optical constant voltage source, it is necessary to consider the constant current.

Therefore, as shown in FIG.
Light passing through the crystal L of the sensor element 11 and the wave plate 24 is split into transmitted light (P wave) and reflected light (S wave) by the PBS (polarizing beam splitter) 25, and the intensity of the light is divided. Take the ratio of. In this way, the fluctuation of the incident light I _O can be ignored.

In this case, the PIN-photodiode 16
There are two a and 16b, and the signal passing through the amplifier 17 is processed by adding a division circuit to the signal processing unit 15. Further, with such a configuration, the drive circuit of the light source 22 becomes simple.

[0058]

As described above, according to the present invention, the optical sensor element is used, the detection electrode is provided, and the insulating layer is provided between the sensor electrode and the sensor electrode.
There is no effect due to mechanical displacement, and there is an effect that the surface potential can be easily and accurately measured and a dustproof structure can be obtained.

Further, since the sensor probe having only the detection electrode and the main body including other optical system and signal processing system can be separated, the sensor probe can be downsized and the sensor probe can be easily cleaned. effective.

Further, by providing the insulating layer on the sensor element, the voltage drop in the air layer is reduced, and therefore the voltage applied to the sensor element is increased, and the sensor element and the device can be miniaturized. effective.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of the sensor unit of FIG.

FIG. 3 is a block diagram showing the measurement principle of the electrometer of FIG.

FIG. 4 is an explanatory diagram showing a measurement operation of the electrometer of FIG.

FIG. 5 is a configuration diagram when a detection electrode is provided.

6 is an equivalent circuit diagram of the sensor unit of FIG.

7 is a block diagram showing the overall configuration of the electrometer of FIG.

FIG. 8 is an explanatory diagram when a polarization beam splitter is used.

FIG. 9 is a configuration diagram showing a conventional example.

FIG. 10 is a perspective view showing the structure of the sensor unit of FIG.

[Explanation of symbols]

 1 sample to be detected 11 sensor element 12a, 12b electrode 13 detection electrode 15 signal processing unit 25 PBS (polarizing beam splitter)

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[Procedure amendment]

[Submission date] October 22, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Title of invention

[Correction method] Change

[Correction content]

[Title of the Invention] non-contact type surface potential meter

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0001

[Correction method] Change

[Correction content]

[0001]

This invention relates to a PPC (plain pape)
r copier), it relates noncontact surface voltmeter for measuring a surface potential of a photosensitive member used in the FAX (Facsimile) etc. in a non-contact manner.

[Procedure amendment 4]

[Document name to be amended] Statement

[Name of item to be corrected] 0002

[Correction method] Change

[Correction content]

[0002]

2. Description of the Related Art FIG. 9 is a block diagram showing the measurement principle of a conventional surface potential meter which measures the surface potential in a non-contact manner. In the figure, 1 is a sample to be detected such as a photoconductor of a copying machine, which is charged to + (positive) by a power source 2.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0044

[Correction method] Change

[Correction content]

[0044]

[Equation 6]

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0046

[Correction method] Change

[Correction content]

Under this condition, S2 = S3 = 11 × 2 mm
^In the case of ² , the detection electrode area S1 = 232 mm ² . At this time, the voltage V3 applied to the crystal is V = 50V, V3 = 3V, V = 200V, V3 = 12V, V = 1000V, V3 = 60V.

[Procedure Amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0047

[Correction method] Change

[Correction content]

Therefore, until now, the optical path length of the crystal L≈5
7.50mm had become (no dielectric) is, 11.6
It becomes 8 mm, and V3 becomes 0.38V → 3V 1.52V → 12V 12V → 60V, respectively.

Claims (2)

[Claims] 1. A sensor element using a Pockels crystal in which the refractive index of light changes according to an applied voltage, and a detection electrode arranged facing the surface of a sample to be detected. An insulating layer is provided between and, the sensing electrode, the electrode of this insulating layer, and the electrode of the sensor element are connected in series,
A non-contact type surface potential type comprising a signal processing unit for detecting the surface potential of the sample to be detected from the intensity of light that has passed through the Pockels crystal of the sensor element. 2. A polarization beam splitter for separating the light emitted from the crystal of the sensor element into transmitted light and reflected light, and a divider for canceling the intensity change of the incident light is built in the signal processing unit. The non-contact type surface potential type according to claim 1, wherein