JP3025649B2 - Capacitance measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type measuring device for measuring a physical quantity of an object to be measured which is located between opposed electrodes for applying an AC voltage at a predetermined interval.

[0002]

Conventionally, an object to be measured such as an insulator, a semiconductor such as a silicon wafer, or a conductor is inserted into a predetermined position between opposed electrodes, and the thickness of the object to be measured, for example, is increased. There is provided a capacitance-type measuring device for measuring the thickness of an object to be measured by utilizing the fact that the capacitance between the electrodes changes according to the change in the thickness.

In general, stray capacitance always exists between adjacent conductors. Therefore, even in the above-mentioned capacitance type measuring device, when the object to be measured is a semiconductor or a conductor, the stray capacitance is constantly generated between the object to be measured and a surrounding object (such as the ground or a transport device). Will exist. However, when a potential difference occurs between the measured object and the surrounding object, a current flows through a stray capacitance existing between the measured object and the surrounding object (a so-called leakage current flows). The correlation between the current and the inter-electrode capacitance determined by the thickness of the object to be measured changes, resulting in a problem that the measurement accuracy is reduced.

In order to solve this problem, an object to be measured and surrounding objects such as a transport device are grounded,
By making the measured object and the surrounding object equipotential,
The current was prevented from flowing through the stray capacitance, and the measurement accuracy was prevented from lowering.

As an apparatus utilizing such a capacitance type measuring apparatus, there is an overlap detecting apparatus used in a semiconductor manufacturing process, for example. This overlap detection device takes out a plurality of stacked silicon wafers as an object to be measured one by one with a picking device such as a suction pad and measures the thickness of the taken out silicon wafers. Are detected as to whether or not they have been taken out.

However, such an overlap detection device has a problem that it is difficult to sufficiently ground the silicon wafer because the silicon wafer moves in a continuous process. For this reason, the silicon wafer and the surrounding object cannot be made to have the same potential, and the measurement accuracy is reduced, leading to a reduction in productivity.

[0007] On the other hand, even when it is difficult to sufficiently ground the moving object, the thickness of the object can be measured without deteriorating the measurement accuracy. This is disclosed in Japanese Patent Publication No. 61-55043. In this device, alternating voltages having phases opposite to each other are applied to a pair of electrodes facing each other, and an object to be measured is inserted at a midpoint between the electrodes having a potential of 0 volt. Thereby, the potential of the object to be measured is kept at 0 volt, that is, the object to be measured and the surrounding object are set at the same potential, thereby preventing a current from flowing through the stray capacitance and preventing a decrease in measurement accuracy. ing.

However, in practice, in a production line in which an object to be measured moves in a continuous process such as a semiconductor manufacturing process, when the object to be measured is transported by a general transport device such as a suction pad, It is conceivable that the object to be measured is inserted while being shifted from the midpoint between the electrodes. In such a case, the potential of the object to be measured is not maintained at 0 volts, so that a potential difference occurs between the object to be measured and the surrounding object, and a current flows through the stray capacitance, which eventually lowers the measurement accuracy. become.

For this reason, when the above-mentioned capacitance type measuring device is applied to an actual production line, the object to be measured can be accurately inserted into a predetermined position between the electrodes. There is a problem in that an accurate transfer device is required, and in particular, when extremely high measurement accuracy is required, such as in semiconductor manufacturing, the entire system becomes more expensive.

The present invention has been made in view of the above circumstances, and has as its object to measure the physical quantity of an object to be measured without reducing the measurement accuracy while making the entire system inexpensive. It is an object of the present invention to provide a capacitance type measuring device capable of performing the above-mentioned.

[0011]

According to the present invention, there is provided a capacitance type measuring apparatus comprising: a first AC voltage applying electrode and a second AC voltage applying electrode facing each other at a predetermined interval; And an AC voltage applying means for applying AC voltages having opposite phases to each other, and a measuring object made of a conductor between the first AC voltage applying electrode and the second AC voltage applying electrode. The object is inserted by the transport device, and the object corresponding to the capacitance between the first AC voltage applying electrode and the second AC voltage applying electrode that changes according to the physical quantity of the object to be measured. For measuring the physical quantity of the object to be measured based on the AC current flowing through the first AC voltage applying electrode or the second AC voltage applying electrode,
A first AC current measuring means for measuring an AC current flowing through the first AC voltage applying electrode; a second AC current measuring means for measuring an AC current flowing through the second AC voltage applying electrode; An applied voltage control means for adjusting an applied voltage to the first and second AC voltage applying electrodes by the AC voltage applying means so that currents detected by the first and second AC current measuring means are substantially the same; The feature is that it is configured to be provided with.

According to the capacitance type measuring device having the above-mentioned structure,
The AC voltage applying means applies AC voltages having phases opposite to each other to the first and second AC voltage applying electrodes, and the object to be measured is placed between the first and second AC voltage applying electrodes.
When inserted by the carrier device, a first capacitor component and a second capacitor component are respectively provided between the first AC voltage applying electrode and the object to be measured and between the second AC voltage applying electrode and the object to be measured. Two capacitor components are formed.

At this time, the AC current flowing through the first capacitor component is measured by the first AC current measuring means, and the AC current flowing through the second capacitor component is measured by the second AC current measuring means. . Then, the applied voltage is adjusted by the applied voltage control means so that the currents detected by the first and second AC current measuring means are substantially the same, and the physical quantity of the object to be measured is measured.

Therefore, a state in which the AC current flowing through the first capacitor component and the AC current flowing through the second capacitor component are substantially the same, that is, the stray capacitance existing between the object to be measured and the surrounding object The physical quantity of the object to be measured can be measured in a state where the AC current hardly flows (leakage current hardly flows).

At this time, as described above, since the AC current hardly flows through the stray capacitance, the measurement accuracy does not decrease, and the object to be measured is such that the object to be measured is between the electrodes for applying the AC voltage. Since it is not necessary to make the position inserted into the device with high precision, the whole system can be made inexpensive accordingly.

Further, the capacitance type measuring apparatus of the present invention is provided by disposing a first AC voltage applying electrode and a second AC voltage applying electrode opposed to each other at a predetermined interval, and inverting the two electrodes. A transfer device for applying an AC voltage applying unit for applying an AC voltage serving as a phase, and transporting an object to be measured made of a conductor between the first AC voltage applying electrode and the second AC voltage applying electrode; And the first AC voltage corresponding to the capacitance between the first AC voltage applying electrode and the second AC voltage applying electrode, which varies according to the physical quantity of the object to be measured. It is intended to measure a physical quantity of the object to be measured based on an AC current flowing through the voltage application electrode or the second AC voltage application electrode, and is provided between the first and second AC voltage application electrodes. Predetermined distance from the object to be measured A potential detection electrode set to a predetermined reference potential in an opposed state so as to exist, AC current measurement means for measuring an AC current flowing through the potential detection electrode, and a current detected by the AC current measurement means being substantially zero. The first and second AC voltage applying means so that
And an applied voltage control means for adjusting an applied voltage to the AC voltage applying electrode.

According to the capacitance type measuring device having the above configuration,
The AC voltage applying means applies AC voltages having phases opposite to each other to the first and second AC voltage applying electrodes, and the object to be measured is placed between the first and second AC voltage applying electrodes.
When inserted by the transport device, between the first AC voltage applying electrode and the object to be measured, between the second AC voltage applying electrode and the object to be measured, and between the potential detecting electrode and the object to be measured. A first capacitor component, a second capacitor component, and a third capacitor component are formed between the first capacitor component, the second capacitor component, and the third capacitor component, respectively.

At this time, the third AC current measuring means
The AC current flowing through the capacitor component is measured. Then, the applied voltage is adjusted by the applied voltage control means so that the current detected by the AC current measuring means becomes substantially zero, and the physical quantity of the measured object is measured.

Therefore, by making the reference potential of the potential detecting electrode equal to the potential of the surrounding object, the AC current flowing through the third capacitor component is substantially zero, and thus the first capacitor component is turned off.
And the AC current flowing through the second capacitor component is substantially the same, that is, the AC current almost flows through the stray capacitance existing between the object to be measured and the surrounding object. The physical quantity of the object to be measured can be measured in a state where there is no (leakage current hardly flows).

At this time, as described above, since the AC current hardly flows through the stray capacitance, the measurement accuracy does not decrease, and the object to be measured is the one between the electrodes for applying the AC voltage. Since it is not necessary to make the position inserted into the device with high precision, the whole system can be made inexpensive accordingly.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment according to the present invention will be described below with reference to FIGS. First, FIG. 2 schematically shows a state when the object to be measured is measured. The base 1 provided as a part of the measuring device has a substantially U-shape. An AC voltage application electrode serving as a first and a second AC voltage application electrode is applied to the lower arm portion 1a and the upper arm portion 1b. Electrodes 2 and 3 are provided so as to face each other at a predetermined interval. Around the AC voltage applying electrodes 2 and 3, the AC voltage applying electrodes 2 and
Guard electrodes 2a, 3a are provided to prevent the lines of electric force generated at the respective ends of 3 from being bent.

The surface of each of the electrodes 2, 2a, 3 and 3a is covered with a thin insulating film for protecting the electrodes, but as long as the dielectric constant of the dielectric existing between the electrodes does not change. This prevents a measurement error from occurring.

The metal plate 4 as an object to be measured is transported by a transport device (not shown) in a state where the metal plate 4 is attracted to a suction pad 5a also made of an insulator, which is provided at a tip end of a suction rod 5 made of an insulator. 2, between the AC voltage applying electrodes 2 and 3 and between the guard electrodes 2a and 3a in the direction of arrow A in FIG.

FIG. 1 schematically shows an electric block configuration.
In the above, the AC voltage applying device 6 as an AC voltage applying means generates a sine wave AC voltage of a predetermined frequency,
The AC voltage is applied to the AC voltage applying electrodes 2 and 3 via AC current measuring devices 7 and 8 as first and second AC current measuring means, respectively. The AC current measuring devices 7 and 8 are provided with AC voltage applying electrodes 2 and 3 respectively.
Measure the alternating current flowing through.

The AC voltage measuring device 9 is connected to the AC voltage applying electrodes 2 and 3 and measures a potential difference between the AC voltage applying electrodes 2 and 3 from the AC voltage applying device 6. , Together with the output terminal of the AC current measuring device 7 and the input terminal of the arithmetic unit 10. The output terminal of the arithmetic unit 10 is connected to the input terminal of the control device 11 including the applied voltage control means, and the arithmetic unit 10 measures the measurement value supplied from the AC voltage measurement device 9 and the AC current measurement. The measurement value given from the measuring device 7 is calculated, and the calculated value is given to the control device 11.

Each output terminal of the AC current measuring devices 7 and 8 is connected to an input terminal of a computing unit 12.
Is connected to the input terminal of the control device 11. The computing unit 12 computes the measurement value given from the AC current measuring devices 7 and 8 and supplies the computed value to the control device 11.

The output terminal of the control device 11 is connected to the input terminal of the AC voltage application device 6, and the control device 11 applies the AC voltage application signal so that the calculation result calculated by the calculator 12 is within a predetermined allowable range. The AC voltage output from the device 6 is controlled. That is, the AC voltage applying device 6
Controls the AC voltage applied to the AC voltage applying electrodes 2 and 3 based on the control from the control device 11. The control device 11 calculates the thickness of the metal plate 4 based on the calculation result given from the calculator 10.

FIG. 3 shows the electrical block configuration shown in FIG. 1 in detail. First, the AC voltage applying device 6
AC power supply 13, variable amplifier circuit 14, changeover switch 15,
It comprises inverting amplifier circuits 16, 17 and operational amplifiers 18, 19, which are connected as shown below.

That is, the output terminal of the AC power supply 13 is connected to the A terminal of the changeover switch 15 via the inverting amplifier circuit 16 and to the B terminal of the changeover switch 15 via the variable amplifier circuit 14. . The C terminal of the switch 15 is connected to the non-inverting input terminal of the operational amplifier 18, and the D terminal of the switch 15 is connected to the non-inverting input terminal of the operational amplifier 19 via the inverting amplifier 17.

The output terminals of the operational amplifiers 18 and 19 are connected to their own inverting input terminals via negative feedback resistors 20 and 21, respectively. These inverting input terminals are connected to the AC voltage applying electrodes 2 and 3 respectively. (In FIG. 3, the electrodes 2 and 3 for applying an AC voltage are indicated by two-dot chain lines).

The changeover switch 15 switches the connection state between the terminals under the control of a microcomputer 22 (to be referred to as a microcomputer hereinafter), which will be described later. Thus, the first state in which the A terminal and the D terminal are connected, and the B terminal and the C terminal are connected, and the A terminal and the C terminal are connected, and the B terminal and the D terminal are connected. It is configured to switch between a connected second state.

The variable amplifier circuit 14 amplifies the amplitude value of the input AC voltage to a value set under the control of the microcomputer 22, and inverts the phase thereof and outputs the inverted voltage. Details will be described later.

The inverting amplification circuit 16 inverts the phase of the input AC voltage and outputs the inverted AC voltage. As described above, the inverting amplifier circuit 16 is provided in consideration of the fact that the phase of the AC voltage is inverted in the variable amplifier circuit 14. A terminal and a B terminal are provided.

The inverting amplifier circuit 17, like the inverting amplifier circuit 16, is configured to invert the phase of the input AC voltage and output the inverted AC voltage. The inverting amplifier circuit 17 is provided so that AC voltages having phases opposite to each other are applied from the AC power supply 13 to the AC voltage applying electrodes 2 and 3.

The AC current measuring device 7 is provided with the operational amplifier 1
8, negative feedback resistor 20, buffer 23 and subtraction circuit 24
And are connected as shown below. That is, the C terminal of the changeover switch 15 is also connected to the input terminal of the buffer 23, and the output terminals of the operational amplifier 18 and the buffer 23 are connected to the subtraction circuit 24.
Is connected to the input terminal of

In this case, the operational amplifier 18 and the negative feedback resistor 20 constitute a current-voltage conversion circuit. When no AC current flows through the negative feedback resistor 20, the output terminal and the non-inverting input terminal of the operational amplifier 18 are not connected. Has the same potential as its own inverting input terminal. When an AC current flows through the negative feedback resistor 20, the operational amplifier 18 outputs an AC voltage applied to the AC voltage applying electrode 2 and an AC current flowing through the negative feedback resistor 20 (AC current flowing through the AC voltage applying electrode 2). An AC voltage obtained by adding the converted AC voltage to the AC voltage is output.

At this time, since only the AC voltage applied to the AC voltage applying electrode 2 is output from the buffer 23, the AC voltage applied from the operational amplifier 18 is subtracted from the AC voltage applied from the operational amplifier 18 by the subtraction circuit 24. By subtracting the voltage, an AC voltage corresponding to the AC current flowing from the subtraction circuit 24 to the AC voltage applying electrode 2 is output.

Similarly, the AC current measuring device 8 includes the operational amplifier 19, the negative feedback resistor 21, the buffer 25, and the subtraction circuit 26, and is connected as shown below. That is, the output terminal of the inverting amplifier 17 is also connected to the input terminal of the buffer 25, and the output terminals of the operational amplifier 19 and the buffer 25 are connected to the input terminal of the subtraction circuit 26.

Also in this case, the subtraction circuit 26 subtracts the AC voltage supplied from the buffer 25 from the AC voltage supplied from the operational amplifier 19 in the same manner as the AC current measuring device 7 described above. An AC voltage corresponding to an AC current flowing from the AC voltage application electrode 3 to the AC voltage application electrode 3 is output.

The AC voltage measuring device 9 comprises a subtraction circuit 27. Specifically, C of the changeover switch 15
Terminal and the output terminal of the inverting amplifier circuit 17
7, that is, the AC voltage applied to the AC voltage application electrodes 2 and 3 is supplied to the subtraction circuit 27. The subtraction circuit 27 subtracts the AC voltage applied from the output terminal of the inverting amplifier circuit 17 from the AC voltage applied from the C terminal of the changeover switch 15, thereby obtaining an AC voltage applied to the AC voltage application electrode 2 from the AC voltage applied to the AC voltage application electrode 2. The AC voltage applied to the AC voltage applying electrode 3 is subtracted, and the result of the subtraction is supplied to a C terminal of a changeover switch 28 described later.

The arithmetic unit 12 comprises an adder circuit 29. Specifically, the output terminals of the subtraction circuits 24 and 26 are connected to the input terminals of the addition circuit 29, that is, the AC voltage corresponding to the AC current flowing through the AC voltage application electrodes 2 and 3 is added. A circuit 29 is provided. The adding circuit 29 adds the AC voltage supplied from the subtracting circuit 24 and the AC voltage supplied from the subtracting circuit 26. The adding AC voltage inverts the phase of the AC voltage obtained by -90 °. The signal is supplied to the A terminal of the changeover switch 28 via the phase shift circuit 30.

The output terminal of the subtraction circuit 24 is -90.
° It is also connected to the B terminal of the changeover switch 28 via the phase shift circuit 31. These -90 ° phase shift circuits 30, 31
In a capacitor component formed when the metal plate 4 is inserted between the AC voltage applying electrodes 2 and 3, the phase of the AC current output from the capacitor component is 90 ° smaller than the phase of the AC voltage. It is provided in consideration of the advance, and outputs the input AC voltage with the phase delayed by 90 °.

The arithmetic unit 10 includes the changeover switch 28, the multiplying circuit 32, a low-pass filter (LPF) 33, an A / D
The converter 34 and the microcomputer 22 are configured as follows. As described above, the changeover switch 2
AC voltages output from the adder circuit 29 and the subtractor circuits 24 and 27 are respectively supplied to the A, B, and C terminals of 8, and the D terminal is connected to the input terminal of the multiplication circuit 32.

The changeover switch 28 changes the connection state between the terminals under the control of the microcomputer 22. Specifically, as shown in FIG. 5, only the A terminal and the D terminal are connected. The state is switched between a first state in which the terminals are connected, a second state in which only the terminals B and D are connected, and a third state in which only the terminals C and D are connected. .

An AC voltage output from the AC power supply 13 is supplied to the multiplying circuit 32 via the inverting amplifier circuit 16. When the changeover switch 28 is in the first state, the AC voltage is supplied from the adding circuit 29. The amplitude of the AC voltage
It multiplies the amplitude value of the AC voltage supplied from the AC power supply 13 and outputs the multiplication result to the low-pass filter 33 and the A / A
The signal is supplied to the microcomputer 22 via the D converter 34.

The multiplying circuit 32 includes a changeover switch 28
Are in the first, second and third states, the amplitude value of the AC voltage output from the addition circuit 29 and the amplitude value of the AC voltage output from the subtraction circuits 24 and 27 are multiplied by the amplitude value of the AC voltage supplied from the AC power supply 13. Thereafter, the signal is supplied to the microcomputer 22 via the low-pass filter 33 and the A / D converter 34.

The low-pass filter 33 removes high-frequency components from the AC voltage supplied from the multiplication circuit 32,
The DC component is provided to an A / D converter 34, and the A / D converter 34 includes a low-pass filter 33.
Is converted into a digital signal and output to the microcomputer 22.

The control device 11 includes the microcomputer 22, the variable amplifier circuit 14, the changeover switch 15, and the changeover switch 2
8. The variable amplifier circuit 14, the changeover switch 15 and the changeover switch 28 are controlled by the microcomputer 22 through control lines 14a, 15a and 28a, respectively.

FIG. 6 shows the internal configuration of the variable amplifier circuit 14 described above. The basic configuration is a well-known R /
A 2R ladder resistor network 14b is used, and a plurality of resistors 14c set to a resistance value R and a plurality of resistors 14d set to a resistance value 2R are connected in a ladder shape.
Of the common connection points of the resistors 14c and 14d, R / 2
The common connection point serving as the output terminal of the R ladder resistor network 14b is connected to the non-inverting input terminal of the operational amplifier 14e.

The output terminal of the operational amplifier 14e is connected to its own inverting input terminal and to the inverting input terminal of the operational amplifier 14g via a resistor 14f.
The non-inverting input terminal of the operational amplifier 14g is grounded, and the output terminal is connected to its own inverting input terminal via a negative feedback resistor 14h. That is, the operational amplifier 14
g, the resistor 14f, and the negative feedback resistor 14h constitute an inverting amplifier circuit. As described above, the variable amplifying circuit 14 inverts the phase of the input AC voltage and outputs the inverted AC voltage. ing.

A movable contact of a change-over switch 14i provided corresponding to each terminal is connected to each terminal of each resistor 14d which is an input terminal of the R / 2R ladder resistance network 14b. . One fixed contact of each changeover switch 14i is connected to the AC power supply 13, and the other fixed contact is grounded. The switching operation of each switch 14i is performed under the control of the microcomputer 22 through the control line 14a.

As described above, the variable amplifier circuit 14
Each changeover switch 14 is controlled based on the control from the microcomputer 22.
i is switched, and the amplitude value of the AC voltage supplied from the AC power supply 13 is amplified and output to a predetermined value. In this case, assuming that the voltage amplification factor of the variable amplifier circuit 14 is a, the voltage amplification factor a is set to 0 <a ≦ 1.

Next, the operation of the first embodiment will be described with reference to FIGS. As shown in FIG. 3, the AC voltage output from the AC power supply 13 is v0, the AC voltage output from the C terminal of the changeover switch 15, that is, the AC voltage applied to the AC voltage applying electrode 2 is v1.
The AC voltage output from the inverting amplifier circuit 17, that is, the AC voltage applied to the AC voltage applying electrode 3 is represented by v2
The AC voltage output from the subtraction circuit 24 is v3, the AC voltage output from the subtraction circuit 26 is v4,
The AC voltage output from the V5, -90 ° phase shift circuit 30
, The AC voltage output from the inverting amplifier circuit 16 is denoted by v7, and the amplitude value of each AC voltage vn is denoted by Vn (n is 0 to 7). Further, it is assumed that peripheral objects such as a transport device that transports the metal plate 4 are sufficiently grounded, and the potential of the peripheral objects is maintained at 0 volt.

Now, the AC voltage applying device 6 causes the AC voltage applying electrodes 2 and 3 to apply the AC voltage v1 having opposite phases to each other.
, V2. In this state, when the metal plate 4 is transported by the transport device and inserted between the electrodes 2 and 3 for applying an AC voltage, the metal plate 4 is electrically conductive.
As shown in FIG. 3, electric lines of force are generated between the AC voltage applying electrode 2 and the metal plate 4 and between the AC voltage applying electrode 3 and the metal plate 4 to form a capacitor component. become. Also, lines of electric force are generated between the guard electrode 2a and the metal plate 4 and between the guard electrode 3a and the metal plate 4, respectively, so that a capacitor component is formed (in FIG. 7, the electric force). The lines are indicated by broken lines E).

At this time, the capacitor component that contributes to the actual measurement is a capacitor component formed between the AC voltage applying electrodes 2 and 3 and the metal plate 4, and the lines of electric force generated in the capacitor component are , Guard electrodes 2a, 3a
Since lines of electric force are also generated between the electrode and the metal plate 4, there is no bending at each end of the AC voltage applying electrodes 2, 3, thereby preventing a measurement error from occurring. ing.

In this case, the measuring system can be represented by an equivalent circuit shown in FIG. That is, it is assumed that the metal plate 4 is located at the midpoint P between the AC voltage applying electrodes 2 and 3, and a capacitor component formed between the metal plate 4 and the AC voltage applying electrode 2 is formed. Is C1, the capacitance of a capacitor component formed between the metal plate 4 and the AC voltage applying electrode 3 is C2, and the stray capacitance existing between the metal plate 4 and the surrounding object is Cs. , The AC current flowing through the capacitance C1 is denoted by i1, and the AC current flowing through the capacitance C2 is denoted by i2.

The capacitances C1 and C2 are determined by setting the area of the AC voltage applying electrodes 2 and 3 to S,
The distance between the electrode 3 and the metal plate 4 is d1,
Assuming that the distance between the metal plate 4 and the metal plate 4 is d2 and the dielectric constant of air is ε, the following equation is obtained.

[0058]

(Equation 1)

When the angular frequency of the alternating current is ω, since the alternating voltages v 1 and v 2 are applied to the alternating voltage applying electrodes 2 and 3, respectively, the alternating current i 1 flowing through the alternating voltage applying electrodes 2 and 3 is applied. , I2 are represented by the following equations.

[0060]

(Equation 2)

Here, ω = 2πf, f is an alternating current frequency. At this time, the phases of the AC currents i1 and i2 are ahead of the phases of the AC voltages v1 and v2 by 90 degrees.

Here, it is assumed that the metal plate 4 is inserted between the electrodes 2 and 3 for applying the AC voltage when the metal plate 4 is inserted between the electrodes 2 and 3 for applying the AC voltage.
As described above, the AC voltages v1 and v2 having opposite phases are applied to the AC voltage application electrodes 2 and 3, respectively. Therefore, if the amplitude values V1 and V2 are equal, the AC voltage application electrodes The potential at the midpoint between the points 2 and 3 is 0 volt. Therefore, the potential of the metal plate 4 inserted at the midpoint between the AC voltage applying electrodes 2 and 3 is maintained at 0 volt, and is kept equal to the potential of the surrounding object (0 volt).
No leakage current flows through the stray capacitance Cs existing between the capacitor and the surrounding object. At this time, the alternating currents i1, i
2 have the following relationship.

[0063]

(Equation 3)

Therefore, from the above equations (3) to (5),
The following equation holds.

[0065]

(Equation 4)

At this time, the following equation is derived from the above equations (1) to (6).

[0067]

(Equation 5)

In the above equation (7), L is the distance between the AC voltage applying electrodes 2 and 3, and dc is the thickness of the metal plate 4. From the above equation (7), the thickness dc of the metal plate 4 is calculated.
Can be expressed by the following equation.

[0069]

(Equation 6)

Therefore, according to the above equation (8), the distance L between the AC voltage applying electrodes 2 and 3, the dielectric constant ε of air, the angular frequency ω, and the area S of the AC voltage applying electrodes 2 and 3 are constant. In this case, it is understood that the thickness dc of the metal plate 4 can be obtained by calculating the value of (V1 -V2) / I1.

In practice, when the metal plate 4 is inserted between the AC voltage applying electrodes 2 and 3, if the accuracy of the transfer device is not high, the AC voltage applying electrodes 2
It is conceivable that it is inserted at a position deviated from the midpoint between the three. However, if the above equation (5) holds for the alternating currents i1 and i2 flowing through the AC voltage applying electrodes 2 and 3, respectively, the thickness dc of the metal plate 4 can be obtained as described above.

Even if the potential of the surrounding object is not kept at 0 volt, if the above equation (5) holds for the alternating currents i1 and i2, the metal plate 4 and the surrounding object have the same potential. Therefore, even if the potential of the surrounding object is not maintained at 0 volt, the thickness dc of the metal plate 4
It can be seen that is required.

Hereinafter, a procedure for obtaining the thickness dc of the metal plate 4 by the microcomputer 22 will be specifically described. First, equation (8) will be described. The amplitude values V3 and V4 of the AC voltages v3 and v4 output from the subtraction circuits 24 and 26 are calculated by setting the resistance values of the negative feedback resistors 20 and 21 to R1.
Then, it is expressed by the following equation.

[0074]

(Equation 7)

In this case, as described above, the alternating current i1
, I2 are 90 degrees faster than the phases of the AC voltages v1, v2.
Therefore, the phase of each of the AC voltages v3 and v4 is ahead of the phase of the AC voltages v1 and v2 by 90 degrees. The amplitude value V5 of the AC voltage v5 output from the addition circuit 29 is expressed by the following equation since the phase is inverted in the addition circuit 29.

[0076]

(Equation 8)

Therefore, the above equation (8) can be expressed by the following equation using the equation (9).

[0078]

(Equation 9)

This equation (12) is an equation derived as an equation used in calculating the thickness dc of the metal plate 4 in the processing of the flowchart shown below.

Next, the control of the microcomputer 22 will be described with reference to FIG.
This will be described with reference to the flowchart shown in FIG. In FIG. 9, | Va | and ΔVa are parameters in the control program of the microcomputer 22, and | Va |
1 and v2, the absolute value of the amplitude value of the AC voltage whose amplitude value is made variable by the variable amplifier circuit 14 in accordance with the state of the changeover switch 15. Vmax is the maximum amplitude value of the AC voltage amplified and output by the variable amplifier circuit 14. In this case, as described above, the voltage amplification factor a is 0 <a.
Since ≤1, V0 is obtained. Also, the AC voltage vn
The absolute value of the amplitude value Vn is represented as | Vn | (n is 0 to 7).

When the metal plate 4 is inserted between the AC voltage applying electrodes 2 and 3, as described above,
Since there is a case where the electrode is inserted at the middle point between the AC voltage application electrodes 2 and 3 and a case where the electrode is inserted shifted from the middle point, each case will be described.

(1) The metal plate 4 is an electrode 2 for applying an AC voltage,
FIG. 7 shows a state in which the metal plate 4 is inserted at the midpoint between the electrodes 2 and 3 for applying an AC voltage. First, when the measurement is started, the microcomputer 22 initializes a control program in step S1. Specifically, the counter set in the control program is cleared.

Next, in step S2, the microcomputer 22 switches the changeover switch 15 to the first state, that is, connects the A terminal and the D terminal of the changeover switch 15 and connects the B terminal and the C terminal. . As a result, the microcomputer 22 controls the AC voltage v1 in the subsequent processing, that is, | V1 | of the AC voltage v1.
Is changed. At this time, |
V2.vertline. Becomes equal to | V0.vertline. Of the AC voltage v0 output from the AC power supply 13.

The microcomputer 22 determines in step S3
The voltage amplification factor a of the variable amplifier circuit 14 is set to 1 and | Va
Is | Va | = Vmax (= V0). That is, at this time, the alternating voltage v1 and the alternating voltage v2 have opposite phases, and | V1 | and | V2 | have the same relationship. Next, the microcomputer 22
In step S4, Vmax is substituted for ΔVa, and ΔVa = Vmax (= V0).

Then, in step S5, the microcomputer 22 switches the changeover switch 28 to the first state, that is, connects the A terminal and the D terminal of the changeover switch 28,
The amplitude value V6 of the AC voltage v6 is calculated. Then, the microcomputer 22 determines in step S6 that the calculated AC voltage v
| V6 | is calculated from the amplitude value V6 of FIG. 6, and it is determined whether or not | V6 | is within a predetermined allowable range previously stored in the control program.

In this case, since the metal plate 4 is inserted at the midpoint between the AC voltage applying electrodes 2 and 3, the potential of the metal plate 4 is maintained at 0 volt as described above, (0 volts). Therefore, the above equation (5) holds, and from the above equation (11), | V
5 | is 0 volt. Here, the AC voltage v5 and the AC voltage v6 have a phase difference of only 90 °, and | V
Since 5 | is equal to | V6 |, | V6 | is 0 volts. Therefore, the microcomputer 22 determines in step S6
Is determined to be "YES", the process proceeds to step S7.

In practice, it is very difficult to reduce the potential of the metal plate 4 to 0 volt.
In the control program, if the potential of the metal plate 4 is extremely small, that is, if | V6 | is within a predetermined allowable range, the process proceeds to step S7.

The microcomputer 22 that has proceeded to step S7
The changeover switch 28 is switched to the second state, that is, the B terminal and the D terminal of the changeover switch 28 are connected, and the amplitude value V3 of the AC voltage v3 is calculated. Next, the microcomputer 22
Switches the changeover switch 28 to the third state in step S8, that is, connects the C terminal and the D terminal of the changeover switch 28, and sets the AC voltage v1 in the subtraction circuit 27.
Is subtracted from the amplitude value V2 of the AC voltage v2 from the amplitude value V1 of the above equation (V1-V2).

Then, the microcomputer 22 calculates (V1−V2) / V3 in step S9, and
At 0, the distance L between the AC voltage applying electrodes 2 and 3, the dielectric constant ε of air, the angular frequency ω, the AC voltage applying electrodes 2 and 3
Since the area S and the resistance R1 of the negative feedback resistors 20 and 21 are known, the thickness dc of the metal plate 4 is calculated from the above equation (12).

Next, the microcomputer 22 proceeds to step S11.
In, a routine to output and display the calculation result is performed,
In step S12, it is determined whether the next measurement is performed. When the microcomputer 22 determines that the next measurement is to be performed, the process returns to step S1, and when the microcomputer 22 determines that the next measurement is not performed, the process ends.

(2) The metal plate 4 is an electrode 2 for applying an AC voltage,
FIG. 11 shows a case where the metal plate 4 is inserted shifted from the middle point between the AC voltage applying electrodes 2 and 3, unlike the state of (1). The description will be made with reference to the output waveform diagram shown in FIG. still,
In FIG. 11, (a) to (f) show output waveforms of AC voltages v1 to v6, respectively. In FIG. 11, the amplitude values V1, V3, V5
And V6 are shown changed in each cycle, but in practice this is not the case. For the AC voltages v1 and v2, the maximum value of the amplitude value is + V0 and the minimum value is -V
The amplitudes of the AC voltages v3 to v6 are expressed as relative values.

(A) When the metal plate 4 is inserted to the side of the electrode 2 for applying an alternating voltage The state in which the metal plate 4 is inserted to the side of the electrode 2 for applying an alternating voltage is shown in FIG. . The microcomputer 22 executes the steps S1 to S5 described in the above (1), so that at the time t0, the AC voltage v1 in the cycle T1,
| V1 | and | V2 | of v2 are made equal (FIG. 11).
Medium, (a), (b)).

Now, in a state where the metal plate 4 is inserted to be biased toward the AC voltage applying electrode 2, the distance d 1 between the AC voltage applying electrode 2 and the metal plate 4 and the AC voltage applying electrode 3 The relationship with the distance d2 to the metal plate 4 is d1 <d2. At this time, the relationship between the capacitances C1 and C2 described above becomes C1> C2 from the above equations (1) and (2), and | I1 | of the alternating current i1 and |
From the above equations (3) and (4), the relation with | I2 | is | I1 |> | I2 |. At this time, the relationship between | V3 | and | V4 | of the AC voltages v3 and v4 corresponding to the AC currents i1 and i2 is given by | V3 |> | V4 | according to the above equations (9) and (10). (See (c) and (d) in the figure).

Therefore, according to the above equation (11), | of the AC voltage v5 obtained by adding the AC voltage v3 and the AC voltage v4 is |
V5 | greatly fluctuates from 0 volts (see (e) in the figure). As a result, | V6 | of the AC voltage v6 whose phase is delayed by 90 ° from the AC voltage v5 also changes from 0 volt. This greatly fluctuates (see (f) in the figure). When | V6 | of the AC voltage v6 exceeds the predetermined allowable range, the microcomputer 22 determines "NO" in step S6, and shifts to step S13.

The microcomputer 22 that has proceeded to step S13
Determines whether the AC voltage v6 and the AC voltage v7 are in phase or out of phase. Specifically, in the multiplication circuit 32, the amplitude value V6 of the AC voltage v6 and the amplitude value V7 of the AC voltage v7 are multiplied, and when the multiplication result is positive, A
Since a positive voltage is supplied from the / D converter 34, it is determined that the phases are the same, and when the multiplication result is negative, the A / D
Since a negative voltage is applied from converter 34, it can be determined that the phases are opposite.

Here, the AC voltage v5 output from the adding circuit 29 is obtained by adding the AC voltage (v3 + v4).
Are reversed, the phase becomes opposite to the AC voltage v3 under the condition that the metal plate 4 is biased toward the AC voltage applying electrode 2 side. Therefore, the AC voltage v6 whose phase is delayed by 90 ° with respect to the AC voltage v5 has an opposite phase to the AC voltage v1 whose phase is delayed by 90 ° with respect to the AC voltage v3.

At this time, the AC voltage v1 and the AC voltage v7 have the same phase with respect to the AC voltage v0 because both phases are inverted. As a result, the AC voltage v6 and the AC voltage v7 have opposite phases. When the output of the A / D converter 34 becomes negative, the microcomputer 22 can determine that the metal plate 4 is biased toward the AC voltage applying electrode 2 side. After making the determination, the process proceeds to step S15.

The microcomputer 22 that has proceeded to step S15
In order to reduce the AC voltage v1 applied to the AC voltage applying electrode 2 at the time t1, ΔVa becomes ΔVa / 2
(= Vmax / 2 = V0 / 2), and step S16
, The switching operation of the changeover switch 14i of the variable amplifier circuit 14 is performed so that | Va |
Substitute a). As a result, the microcomputer 22 sets the period T2
The amplitude value V1 of the AC voltage v1 at V1 is V0 / 2.

Accordingly, the amplitude value V1 of the AC voltage v1 applied to the AC voltage applying electrode 2 is reduced, so that the amplitude value I1 of the AC current i1 flowing through the AC voltage applying electrode 2 is also changed. The amplitude values V3, V5, V6 of the AC voltages v3, v5, v6 also change. In step S17, the microcomputer 22 increments a counter of the control program.

Then, the microcomputer 22 proceeds to step S18.
, The amplitude value V6 of the AC voltage v6 is calculated again,
In step S19, | V6 of the calculated amplitude value V6
It is determined whether or not | is within a predetermined allowable range. At this time, if | V6 | is within a predetermined allowable range, the microcomputer 2
In No. 2, it can be determined that the metal plate 4 and the surrounding object are kept at substantially the same potential, and that the alternating current hardly flows through the stray capacitance Cs, and it is determined as “YES” in the step S19. Then, the microcomputer 22 calculates the thickness dc of the metal plate 4 by executing steps S7 to S12 (executes the process described in the above (1)).

On the other hand, if | V6 | of the input amplitude value V6 exceeds the predetermined allowable range, the microcomputer 22 determines that there is still a potential difference between the metal plate 4 and the surrounding object, and the floating capacitance Cs It is determined that an alternating current is flowing through step S2.
Move to 0. Microcomputer 22 shifted to step S20
Determines whether the count value of the control program exceeds a predetermined value, and if it is within the predetermined value, the process proceeds to step S21. Then, in step S21, the microcomputer 22 determines again whether the AC voltage v6 and the AC voltage v7 have the same phase or the opposite phase.

Here, if the AC voltage v6 and the AC voltage v7 are in opposite phases, the microcomputer 22 determines that the amplitude value V1 of the AC voltage v1 must be further reduced below V0 / 2, and in step S21 , "NO",
The process returns to step S15.

On the other hand, when the AC voltage v6 and the AC voltage v7 change from the opposite phase to the same phase, the microcomputer 2
2 judges that the amplitude value V1 of the AC voltage v1 must be raised above V0 / 2, and in step S21,
If "YES" is determined, the process proceeds to step S22. still,
In this case, the case where the process proceeds to step S22 will be described.

Microcomputer 22 shifted to step S22
Is that at time t2, ΔVa becomes ΔVa / 2 (= Vmax / 4
= V0 / 4), and the process proceeds to step S23 to perform a switching operation of the changeover switch 14i of the variable amplifying circuit 14, and |
(| Va | + ΔVa) is substituted for Va |. Thereby, the microcomputer 22 sets the amplitude value V1 of the AC voltage v1 in the cycle T3 to (3/4) V0. Then, the microcomputer 22 executes steps S17 to S19 again to determine whether or not | V6 | of the AC voltage v6 is within a predetermined allowable range.

In FIG. 11, as a specific example,
The microcomputer 22 calculates the amplitude value V1 of the AC voltage v1 at time t.
At (3), (5/8) V0 is set, and at time t4,
(11/16) V0, and at time t5, (21 /
32) V0 is set, and at time t6, | V6 | of the AC voltage v6 in the cycle T6 is determined to be within a predetermined allowable range, and the thickness dc of the metal plate 4 is calculated. Actually, the amplitude value V4 of the AC voltage v4 also changes in each cycle, but FIG. 11 shows only the phase relationship, and the amplitude value V4 is constant.

If the microcomputer 22 determines in step S20 that the count value of the control program has exceeded a predetermined value, it performs an error processing routine in step S24 and returns to step S1.

(A) When the metal plate 4 is inserted with a bias toward the AC voltage applying electrode 3 When the metal plate 4 is inserted with a bias toward the AC voltage applying electrode 3, at time t 0, Since the AC voltage v6 and the AC voltage v7 have the same phase, the microcomputer 22 determines "YES" in step S13, and proceeds to step S14. Then, in step S14, the microcomputer 22 switches the changeover switch 15 from the first state to the second state, that is, connects the A terminal and the C terminal of the changeover switch 15 and connects the B terminal and the D terminal. The connection controls the AC voltage v2, that is,
In the subsequent processing, the state where | V2 | of the AC voltage v2 is changed. At this time, | V1 |
Is constant at | V0 |. Thereafter, the same processing as the above (A) is executed.

As described above, the microcomputer 22 outputs the AC voltage v
6 and the AC voltage v7 are in phase with each other, and based on the determination result, the AC voltage v1 or the AC voltage v2 is set so that | V6 | of the AC voltage v6 falls within a predetermined allowable range. Control, and finally, when | V6 | of the AC voltage v6 is within a predetermined allowable range, the processing described in the above (1) is executed to calculate the thickness dc of the metal plate 4. ing.

In the above embodiment, the case where the object to be measured is the metal plate 4, that is, the case where the object to be measured is a conductor, has been described. However, the object to be measured is an insulator or a semiconductor. The case where the object to be measured is an insulator or a semiconductor will be described below.

First, the case where the object to be measured is an insulator will be described. In this case, the measurement system can be represented by an equivalent circuit shown in FIG. Assuming that the capacitance of the insulator is Ci, the thickness of the insulator is di, and the dielectric constant of the insulator is εx, the capacitance Ci of the insulator is expressed by the following equation.

[0111]

(Equation 10)

At this time, the left side of the above equation (7) can be expressed by the following equation from the above equations (1), (2) and (13).

[0113]

[Equation 11]

The distance L between the AC voltage applying electrodes 2 and 3 is expressed by the following equation.

[0115]

(Equation 12)

Accordingly, the above equation (14) is represented by the following equation.

[0117]

(Equation 13)

Therefore, the formula for calculating the thickness di of the insulator can be expressed by the following formula.

[0119]

[Equation 14]

Next, a case where the object to be measured is a semiconductor will be described. In this case, the measurement system can be represented by an equivalent circuit shown in FIG. In FIG. 13, a portion indicated by a broken line W is a semiconductor. At this time, the thickness of the semiconductor is d
Assuming that s and the resistivity in the thickness direction of the semiconductor are ρx, the resistance Rx in the thickness direction of the semiconductor is expressed by the following equation.

[0121]

(Equation 15)

At this time, when no current flows through the resistance Ry in the plane direction of the semiconductor and the stray capacitance Cs, the left side of the above-mentioned equation (7) is obtained by the above-mentioned equations (1), (2) and (1).
From 8), it can be expressed by the following equation.

[0123]

(Equation 16)

The distance L between the AC voltage applying electrodes 2 and 3 is represented by the following equation.

[0125]

[Equation 17]

Thus, the above equation (19) is represented by the following equation.

[0127]

(Equation 18)

Therefore, the equation for calculating the thickness ds of the semiconductor can be expressed by the following equation.

[0129]

[Equation 19]

That is, when the object to be measured is a conductor, an insulator, and a semiconductor, the equation (8) for calculating the thickness dc of the conductor and the equation (17) for calculating the thickness di of the insulator, respectively. And the formula (2) for calculating the thickness ds of the semiconductor
It can be seen that 2) is represented by the following equation.

[0131]

(Equation 20)

In the above equation (23), d is the thickness of the object to be measured, and Z is a coefficient. Here, the coefficient Z is
The case where the object to be measured is a conductor, an insulator, and a semiconductor is shown as follows.

[0133]

(Equation 21)

From the above equations (24) and (26), whether the object to be measured is a conductor or a semiconductor is as follows.
This is based on the value of ε × ω × ρx, and is specifically determined by whether or not the following equation is satisfied.

[0135]

(Equation 22)

That is, for the resistivity ρx,

(Equation 23) Holds, the object to be measured is a conductor, and conversely, if the above equation (28) does not hold, the object to be measured can be regarded as a semiconductor. As described above, in the present invention, it can be seen that the thickness of the object to be measured can be measured not only for the conductor but also for an insulator or a semiconductor.

As described above, according to the first embodiment, the AC voltage applying device 6 applies the AC voltages v 1 and v 2 having opposite phases to the AC voltage applying electrodes 2 and 3, The measuring devices 7 and 8 measure the AC currents i1 and i2 flowing through the AC voltage applying electrodes 2 and 3, respectively. Then, the control device 11 controls the | V6 | of the AC voltage v6 to fall within a predetermined allowable range, that is, the | V3 | of the AC voltage v3 corresponding to the AC current i1.
And v2 of AC voltage v4 corresponding to AC current i2 are controlled so that AC voltages v1 and v2 are substantially the same. When | V6 | is within a predetermined allowable range, | V3 | of the voltage v3 and | V4 of the AC voltage v4
When | is substantially the same, the thickness dc of the metal plate 4 is calculated.

Therefore, | I1 | of the AC current i1 flowing through the capacitance C1 and the AC current i2 flowing through the capacitance C2
Is approximately equal to | I2 |, that is, stray capacitance Cs
The thickness dc of the metal plate 4 can be measured in a state where almost no AC current flows (no leakage current flows).

In this case, since the AC current hardly flows through the stray capacitance Cs, the measurement accuracy does not decrease, and the metal plate 4 is inserted between the AC voltage applying electrodes 2 and 3 as a transfer device. Since it is not necessary to make the position to be set with high precision, the entire system can be made inexpensive accordingly.

The predetermined allowable range for measuring accuracy is as follows:
Since it can be set variably by the microcomputer 22,
When high precision measurement is required, the predetermined tolerance is set small, while high precision measurement is not required.
For example, when it is desired to shorten the processing time required for the measurement, it is possible to flexibly cope with the purpose of use, for example, by setting a predetermined allowable range large. Furthermore, the object to be measured is
Even in the case of an insulator or a semiconductor instead of a conductor, their thickness can be measured.

Next, a second embodiment of the present invention corresponding to claim 2 will be described with reference to FIGS.
The same portions as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. Hereinafter, different portions will be described.

In FIG. 14, upper arm 41 of base 41
a is provided with an AC voltage applying electrode 3 and a guard electrode 3a, and the lower arm 41b is provided with an AC voltage applying electrode 2 and a guard electrode 2a together with a potential detecting electrode 42. A guard electrode 42a is provided around the periphery. The surfaces of the electrodes 42 and 42a are also covered with a thin insulating film to protect the electrodes. However, unless the dielectric constant of the dielectric existing between the electrodes changes, the measurement error is reduced. It does not happen.

As in the first embodiment, the metal plate 4 is transported by the transport device while being sucked by the suction pad 5a made of an insulator.
14, it is inserted from the direction of arrow B, and at this time, it faces the potential detection electrode 42 at a predetermined interval.

FIG. 1 schematically showing an electric block configuration.
In 5, the AC voltage applying device 43 generates a sine wave AC voltage of a predetermined frequency, applies the AC voltage to the AC voltage applying electrode 3, and outputs the AC voltage to the AC current measuring device 7.
Is applied to the AC voltage applying electrode 2 via the. The AC current measuring device 7 measures an AC current flowing through the AC voltage applying electrode 2.

The AC voltage measuring device 9 is connected to the AC voltage applying electrodes 2 and 3 and measures the AC voltage applied from the AC voltage applying device 43 to the AC voltage applying electrodes 2 and 3. The terminal is connected to the input terminal of the calculator 44 together with the output terminal of the AC current measuring device 7. Arithmetic unit 4
4 is connected to the input terminal of the control device 45, and the calculator 44 calculates the measurement value given from the AC voltage measurement device 9 and the measurement value given from the AC current measurement device 7, The calculated value is given to the control device 45.

An alternating current measuring device 46 as an alternating current measuring means is connected to the potential detecting electrode 42. The AC current measuring device 46 measures an AC current flowing through the potential detecting electrode 42, and supplies the measurement result to the control device 45. The output terminal of the control device 45 is connected to the input terminal of the AC voltage application device 43, and the control device 45 controls the AC voltage application device so that the measurement result measured by the AC current measurement device 46 falls within a predetermined allowable range. 43 is controlled. That is, the AC voltage applying device 43
Controls the AC voltage applied to the AC voltage applying electrode 3 based on the control from the control device 45. Also,
The control device 45 calculates the thickness of the metal plate 4 based on the calculation result calculated by the calculator 44.

FIG. 16 shows the electrical block configuration shown in FIG. 15 in detail. First, the AC voltage applying device 4
3 is an AC power supply 13, a variable amplifier circuit 47, a buffer 48
And an operational amplifier 18, which are connected as shown below. That is, the output terminal of the AC power supply 13 is connected to the non-inverting input terminal of the operational amplifier 18 and is connected to the AC voltage applying electrode 3 via the variable amplifier circuit 47 and the buffer 48.

The variable amplifying circuit 47 has the same internal configuration as that of the variable amplifying circuit 14 described in the first embodiment shown in FIG. 6, but has a different voltage amplification factor.
Specifically, assuming that the voltage amplification factor is b, 0 <b <k, and
k is set to a constant sufficiently larger than 1.

The output terminal of the operational amplifier 18 is connected to its own inverting input terminal via a negative feedback resistor 20, and the inverting input terminal is connected to the AC voltage applying electrode 2.
It is connected to the.

The AC current measuring device 7 includes an operational amplifier 18, a negative feedback resistor 20, a buffer 23, and a subtraction circuit 24, as in the first embodiment. The output terminal of the subtraction circuit 24 is a -90 ° phase shift circuit. Changeover switch 28 through 31
B terminal.

The AC voltage measuring device 9 comprises a subtraction circuit 27. Specifically, the output terminal of the AC power supply 13 and the output terminal of the buffer 48 are connected to the input terminal of the subtraction circuit 27, so that the AC voltage applied to the AC voltage application electrodes 2, 3 is reduced. It is provided to a subtraction circuit 27. The subtraction circuit 27 includes the AC power supply 1
From the AC voltage supplied from the output terminal of
8 is subtracted from the AC voltage applied to the AC voltage applying electrode 2,
The AC voltage applied to the AC voltage applying electrode 3 is subtracted,
The result of the subtraction is provided to the C terminal of the changeover switch 28.

The AC current measuring device 46 includes an inverting amplifier circuit 49.
It is composed of The inverting amplifier circuit 49 is connected to the potential detection electrode 42 (in FIG. 16, the potential detection electrode is indicated by a two-dot chain line), and converts the AC voltage given from the potential detection electrode 42 into its phase. Is inverted and output to the -90 ° phase shift circuit 50. Further, the potential detecting electrode 42 is virtually grounded, so that its potential is maintained at 0 volt.

The -90 ° phase shift circuit 50 is provided for a capacitor component formed between the metal plate 4 and the potential detection electrode 42 when the metal plate 4 is inserted between the AC voltage application electrodes 2 and 3. The phase of the alternating current output from the capacitor component is provided in consideration of the fact that the phase advances by 90 ° from the phase of the alternating voltage.

As in the first embodiment, the arithmetic unit 44 includes a changeover switch 28, a multiplying circuit 32, a low-pass filter 33,
The A / D converter 34 and the microcomputer 51 are configured as follows. That is, the changeover switch 2
The AC voltage output from the inverting amplifier circuit 49 and the subtraction circuits 24 and 27 is applied to the A, B, and C terminals of 8, respectively, and the D terminal is connected to the input terminal of the multiplication circuit 32. . The changeover switch 28 is connected to the microcomputer 5
Under the control from 1, the connection state between the terminals is switched as shown in FIG.

The control device 45 comprises the microcomputer 51, the variable amplifier circuit 47 and the changeover switch. Note that the variable amplifier circuit 47 and the changeover switch 28
Each of them is controlled by the microcomputer 51 through the control line 47a and the control line 28a.

Next, the operation of the second embodiment will be described with reference to FIG.
21 will be described with reference to FIG. As shown in FIG. 16, the AC voltage output from the AC power supply 13, that is, the AC voltage applied to the AC voltage applying electrode 2 is represented by v8
, The AC voltage output from the buffer 48,
The AC voltage applied to the AC voltage applying electrode 3 is v9, the AC voltage output from the subtraction circuit 24 is v10, the AC voltage output from the inverting amplifier 49 is v11, and the AC voltage output from the -90 ° phase shift circuit 50 is v11. And the amplitude value of each AC voltage vn is represented as Vn (n is 8 to 12). Also,
A surrounding object such as a transport device is sufficiently grounded, and the potential of the surrounding object is maintained at 0 volt.

In the second embodiment, the equation for calculating the thickness dc of the metal plate 4 is the same as the AC voltages v1, v in the first embodiment.
2 and v3 are AC voltages v8, v9 and v
Since this corresponds to 10, the above equation (12) can be expressed by the following equation.

[0158]

(Equation 24)

Now, the AC voltage applying device 43
AC voltages v8 and v9 having opposite phases to each other are applied to the AC voltage applying electrodes 2 and 3. In this state, when the metal plate 4 is transported by the transport device and inserted between the electrodes 2 and 3 for applying an AC voltage, since the metal plate 4 is conductive, FIG.
As shown in FIG. 3, electric force is applied between the AC voltage applying electrode 2 and the metal plate 4, between the AC voltage applying electrode 3 and the metal plate 4, and between the potential detecting electrode 42 and the metal plate 4, respectively. A line is generated and a capacitor component is formed.

Further, between the guard electrode 2a and the metal plate 4,
Between the guard electrode 3a and the metal plate 4 and the guard electrode 42
17a and the metal plate 4 generate lines of electric force, respectively, to form a capacitor component (FIG. 17).
In the figure, the lines of electric force are indicated by broken lines F). Also in this case, since the lines of electric force generated in the respective capacitor components are provided with the guard electrodes 2a, 3a and 42a around the AC voltage applying electrodes 2, 3 and 42, respectively. , 3 and 42 are not bent at each end, so that measurement errors do not occur.

In this case, the measuring system can be represented by an equivalent circuit shown in FIG. That is, it is assumed that the metal plate 4 is located at the midpoint Q between the AC voltage application electrodes 2 and 3 and is opposed to the potential detection electrode 42. The capacitance of the capacitor component formed between the AC voltage applying electrode 2 and C1 is the capacitance of the capacitor component formed between the metal plate 4 and the AC voltage applying electrode 3. 4 and potential detection electrode 4
And the capacitance of the capacitor component formed between
, The stray capacitance existing between the metal plate 4 and the surrounding object is represented by Cs
The AC current flowing through the capacitance C1 is denoted by i1, the AC current flowing through the capacitance C2 is denoted by i2, and the AC current flowing through the capacitance C3 is denoted by i3.

In the second embodiment, | I1 | of the AC current i1 flowing through the AC voltage applying electrode 2 and the AC current i2 flowing through the AC voltage applying electrode 3 as described in the first embodiment are used. Is different from that in which the metal plate 4 and the surrounding object are made substantially equipotential by controlling such that | I2 | Specifically, the metal plate 4 and the surrounding object are made substantially equipotential by controlling | I3 | of the alternating current i3 flowing through the potential detecting electrode 42 to an extremely small value.

In the first embodiment, one of the AC voltages v 1 and v 2 applied to the AC voltage applying electrodes 2 and 3 is controlled in accordance with the position where the metal plate 4 is inserted. On the other hand, in the second embodiment, | V8 | of the AC voltage v8 applied to the AC voltage applying electrode 2 is kept constant, and the AC voltage v9 applied to the AC voltage applying electrode 3 is controlled. .

Hereinafter, the procedure for obtaining the thickness dc of the metal plate 4 by the microcomputer 51 from the above equation (29) will be described with reference to the flowchart shown in FIG. In FIG. 19, ΔVb is a parameter in the control program of the microcomputer 51. The absolute value of the amplitude value Vn of the AC voltage vn is | Vn | (n is 8 to 12).
It is expressed as

(1) When the metal plate 4 is the electrode 2 for applying an AC voltage,
FIG. 17 shows a state in which the metal plate 4 is inserted at the midpoint between the electrodes 2 and 3 for applying the AC voltage. First, when measurement is started, the microcomputer 51 initializes a control program in step T1. Specifically, the counter set in the control program is cleared.

Next, in step T2, the microcomputer 51 sets the value of the voltage amplification factor b of the variable amplifier circuit 47 to 1, and sets | V9 | of the AC voltage v9 to | V9 | = | V8 |. That is, at this time, the alternating voltage v8 and the alternating voltage v9 are in opposite phases and | V8 | and | V9 | have the same relationship. Next, in step T3, the microcomputer 51 substitutes | V8 | for ΔVb, and sets ΔVb = | V8 |.

Then, in step T4, the microcomputer 51 switches the changeover switch 28 to the first state, that is, connects the A terminal and the D terminal of the changeover switch 28,
An amplitude value V12 of the AC voltage v12 is calculated. Then, the microcomputer 51 determines in step T5 that the calculated AC voltage v
| V12 | is calculated from the twelve amplitude values V12, and it is determined whether or not | V12 | is within a predetermined allowable range stored in advance in the control program.

In this case, since the metal plate 4 is inserted at the midpoint between the AC voltage applying electrodes 2 and 3, the potential of the metal plate 4 is maintained at 0 volt as described above, (0 volts). Therefore, since | V12 | of the AC voltage v12 corresponding to the AC current i3 is 0 volt, the microcomputer 51 determines “YES” in step T5 and shifts to step T6.

In the second embodiment as well, since it is actually very difficult to reduce the potential of the metal plate 4 to 0 volt, the control program of the microcomputer 51 sets || If I3 | is an extremely small value, that is, if | V12 | of the AC voltage v12 is within a predetermined allowable range, the process proceeds to step T6.

The microcomputer 51 that has proceeded to step T6
The changeover switch 28 is switched to the second state, that is, the B terminal and the D terminal of the changeover switch 28 are connected, and the amplitude value V10 of the AC voltage v10 is calculated. Next, the microcomputer 51
Switches the changeover switch 28 to the third state in step T7, that is, connects the C terminal and the D terminal of the changeover switch 28, and subtracts the amplitude value V9 of the AC voltage v9 from the amplitude value V8 of the AC voltage v8. Subtracted result (V8-V9
) Is calculated.

In step T8, the microcomputer 51 calculates (V8−V9) / V10, and in step T9
, The distance L between the AC voltage applying electrodes 2 and 3, the dielectric constant ε of air, the angular frequency ω, the area S of the AC voltage applying electrodes 2 and 3, and the resistance value R1 of the negative feedback resistors 20 and 21 are known. Therefore, the thickness dc of the metal plate 4 is calculated from the above equation (29).

Next, the microcomputer 51 determines in step T10
In, a routine to output and display the calculation result is performed,
In step T11, it is determined whether the next measurement is to be performed. When the microcomputer 51 determines that the next measurement is to be performed, the process returns to step T1, and when the microcomputer 51 determines that the next measurement is not performed, the process ends.

(2) The metal plate 4 serves as the AC voltage applying electrode 2,
FIG. 21 shows a case where the metal plate 4 is inserted shifted from the middle point between the AC voltage applying electrodes 2 and 3, unlike the state of (1). The description will be made with reference to the output waveform diagram shown. still,
In FIG. 21, (a) to (e) show output waveforms of AC voltages v8 to v12, respectively. In FIG. 21, the amplitude values V9 to V12 are changed for each period for the sake of a brief description, but this is not a limitation. For the AC voltages v8 and v9, the maximum value of the amplitude value is represented as + V0 and the minimum value thereof is represented as -V0. For the AC voltages v10 to v12, the magnitude of the amplitude value is represented as a relative value. .

(A) When the Metal Plate 4 is Inserted Unevenly toward the AC Voltage Applying Electrode 3 FIG. 20 shows a state in which the metal plate 4 is inserted unevenly toward the AC voltage applying electrode 3. . The microcomputer 51 executes Steps T1 to T4, and at time t0, | V8 |, | V9 | of the AC voltages v8, v9 in the cycle T1.
(See (a) and (b) in FIG. 21).

Now, in the state where the metal plate 4 is inserted to the side of the AC voltage applying electrode 3 sideward, the AC voltage v12 output from the -90 ° phase shift circuit 50 is changed to the AC voltage described in the first embodiment. v6, the | V12 of the AC voltage v12
| Greatly varies from 0 volt (FIG. 21).
Middle, see (e)). If | V12 | of the AC voltage v12 exceeds the predetermined allowable range, the microcomputer 22 determines “NO” in step T5, and proceeds to step T1.
The process moves to 2.

Microcomputer 51 which has proceeded to step T12
Determines whether the AC voltage v12 and the AC voltage v8 are in phase or out of phase. Specifically, in the multiplication circuit 32, the amplitude value V12 of the AC voltage v12 and the amplitude value V8 of the AC voltage v8 are multiplied, and when the multiplication result is positive, A /
Since the positive voltage is supplied from the D converter 34, it is determined that the phases are the same, and when the multiplication result is negative, the negative voltage is supplied from the A / D converter 34, so that the phases can be determined to be opposite.

Here, since the phase of the AC voltage v11 output from the inverting amplifier circuit 49 is inverted in the inverting amplifier circuit 49, the metal plate 4 is biased toward the AC voltage applying electrode 3 side. Under the condition, it has the same phase as the AC voltage v10. Therefore, the phase becomes 90 with respect to the AC voltage v11.
The AC voltage v12 delayed by .degree. Has the same phase as the AC voltage v8 whose phase is delayed by 90.degree. With respect to the AC voltage v10. Therefore, the microcomputer 51 can determine that the metal plate 4 is biased toward the AC voltage applying electrode 3 side, and determine “YES” in step T12, and shift to step T13.

Microcomputer 51 which has proceeded to step T13
In order to reduce the AC voltage v9 applied to the AC voltage applying electrode 3 at time t1, ΔVb is changed to ΔVb / 2
(= V8 / 2), and in step T14, by switching the changeover switch of the variable amplifier circuit 47, (| V9 | -.DELTA.Vb) is substituted for | V9 |. Thereby, the microcomputer 51 determines that the AC voltage v
The amplitude value V9 of 9 is V8 / 2.

Therefore, the amplitude value V9 of the AC voltage v9 applied to the AC voltage applying electrode 3 is reduced, so that the amplitude value I2 of the AC current i2 flowing through the AC voltage applying electrode 3 is also changed. The amplitude values V10, V11, V12 of the AC voltages v10, v11, v12 also change. In step T17, the microcomputer 51 increments the counter of the control program. Then, in step T18, the microcomputer 51 determines whether or not the count value of the control program has exceeded a predetermined value. If the count value is within the predetermined value, the process returns to step T4.

The microcomputer 51 returning to step T4 calculates the amplitude value V12 of the AC voltage v12 again, and returns to step T5.
, It is determined whether or not | V12 | of the calculated amplitude value V12 is within a predetermined allowable range. At this time, if | V12 | is within a predetermined allowable range, the microcomputer 51
And the surrounding objects are maintained at substantially the same potential, and it can be determined that an alternating current hardly flows through the stray capacitance Cs, and "YES" is determined in the step T5. And
The microcomputer 51 executes steps T6 to T11 to calculate the thickness dc of the metal plate 4 (executes the process described in (1) above).

On the other hand, if | V12 | of the input amplitude value V12 exceeds the predetermined allowable range, the microcomputer 51 determines that there is still a potential difference between the metal plate 4 and the surrounding object, and the floating capacitance Cs It is determined that an alternating current is flowing through step T1.
Then, it is determined again whether the AC voltage v12 and the AC voltage v8 have the same phase or the opposite phase.

Here, if the AC voltage v12 and the AC voltage v8 have the same phase, the microcomputer 51 determines that the amplitude value V9 of the AC voltage v9 must be further reduced below V8 / 2. , "YES", and the process returns to step T13.

On the other hand, when the AC voltage v12 and the AC voltage v8 change from the same phase to the opposite phase, the microcomputer 5
1 judges that the amplitude value V9 of the AC voltage v9 must be raised above V8 / 2, and in step T12,
If "NO" is determined, the process shifts to step T15. Note that, in this case, the case where the process proceeds to step T15 will be described.

Microcomputer 51 which has proceeded to step T15
Is that at time t2, ΔVb becomes ΔVb / 2 (= V8 / 4).
And the process proceeds to step T16, where the variable amplifying circuit 4
7 is changed over to | V9 | (| V9 |
+ ΔVb). Thereby, the microcomputer 51
The amplitude value V9 of the AC voltage v9 in the cycle T3 is represented by (3 /
4) V8. Then, the microcomputer 51 executes Steps T17 to T18 and T4 to T5 again, so that the AC voltage v12
It is determined whether or not | V12 | is within a predetermined allowable range.

In FIG. 21, as a specific example,
The microcomputer 51 calculates the amplitude value V9 of the AC voltage v9 at time t.
At (3), (5/8) V8, and at time t4,
(11/16) V8, and at time t5, (21 /
32) V8 is set, and at time t6, | V12 | of the AC voltage v12 in the cycle T6 is determined to be within a predetermined allowable range, and the thickness dc of the metal plate 4 is calculated.

When the microcomputer 51 determines in step T18 that the count value of the control program has exceeded a predetermined value, it performs an error processing routine in step T19, and returns to step T1. I have. In this case, finally, | V9 | of the AC voltage v9 becomes smaller than | V8 | of the AC voltage v8.

(A) When the metal plate 4 is inserted to be biased toward the AC voltage applying electrode 2 When the metal plate 4 is inserted to be biased toward the AC voltage applying electrode 2, at time t 0, Since the AC voltage v12 and the AC voltage v8 have opposite phases, the first step T
It is determined “NO” in the process of No. 12, and thereafter, the same process as the above (A) is executed. In this case, finally, | V9 | of AC voltage v9 becomes | V of AC voltage v8.
V8 |.

As described above, the microcomputer 51 outputs the AC voltage v
12 and whether or not the AC voltage v8 has the same phase. Based on the result of the determination, the AC voltage v9 is controlled so that | V12 | of the AC voltage v12 falls within a predetermined allowable range. When | V12 | of the AC voltage v12 is within a predetermined allowable range, the processing described in the above (1) is executed to calculate the thickness dc of the metal plate 4.

As described above, according to the second embodiment, AC voltages v8 and v9 having opposite phases to each other are applied to the AC voltage applying electrodes 2 and 3 by the AC voltage applying device 43. 46, the AC current i3 flowing through the potential detecting electrode 42 is measured. Then, the control device 11 controls the AC voltage v12 so that | V12 | of the AC voltage v12 corresponding to the AC current i3 falls within a predetermined allowable range.
9 is controlled, and when | V12 | is within a predetermined allowable range, the thickness dc of the metal plate 4 is calculated.

Therefore, the state where | I3 | of the alternating current i3 is extremely small, that is, | I1 | of the alternating current i1 flowing through the capacitance C1 and | I2 | of the alternating current i2 flowing through the capacitance C2, Are substantially equal, that is, the thickness dc of the metal plate 4 can be measured in a state where an AC current hardly flows through the stray capacitance Cs (no leakage current flows).

In this case, since the AC current hardly flows through the stray capacitance Cs, the measurement accuracy does not decrease, and the metal plate 4 is inserted between the AC voltage applying electrodes 2 and 3 as a transfer device. Since it is not necessary to make the position to be set with high precision, the entire system can be made inexpensive accordingly.

The predetermined allowable range for measuring accuracy is as follows:
Since it can be variably set by the microcomputer 51,
When high precision measurement is required, the predetermined tolerance is set small, while high precision measurement is not required.
For example, when it is desired to reduce the processing time required for the measurement, it is possible to flexibly cope with the purpose, for example, by setting a predetermined allowable range large.

In the second embodiment, since the object to be measured functions as an electrode of a capacitor component formed between the object and the potential detecting electrode 42, an insulator is applied to the object to be measured. Although it is not possible to apply a semiconductor, its thickness can be measured.

Next, a third embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. The same portions as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. Hereinafter, different portions will be described. In the third embodiment, unlike the first embodiment in which the control of the AC voltage applied to the AC voltage application electrodes 2 and 3 is performed by software under the control of the microcomputer 22, the third embodiment is performed by hardware. In particular, the configuration of the AC voltage applying device 6 is different.

That is, the AC voltage applying device 6 comprises an AC power supply 13, an inverting amplifier circuit 61, operational amplifiers 18 and 19, a light control variable resistor 62, a multiplying circuit 63, a low-pass filter 64, and an integrating circuit 65. They are connected as shown below.

The output terminal of the AC power supply 13 is connected to the operational amplifier 1
8 and to the non-inverting input terminal of the operational amplifier 19 via the photoconductive cell 66 in the light control variable resistor 62 and the inverting amplifier circuit 61. The photoconductive cell 66 includes a light control variable resistor 62
The resistance value changes according to the amount of light emitted from the light emitting diode 67. The resistance value decreases when the light amount of the light emitting diode 67 is large, and the resistance value increases when the light amount is small.

The output terminal of the AC power supply 13 is connected to one input terminal of the multiplication circuit 63, and the other input terminal of the multiplication circuit 63 is connected to the output terminal of the + 90 ° phase shift circuit 68. The multiplying circuit 63 calculates the amplitude value of the AC voltage supplied from the AC power
The output terminal is multiplied by the amplitude value of the AC voltage supplied through the phase shift circuit 68, and the output terminal thereof is connected to the light emitting diode 6 through the low-pass filter 64 and the integration circuit 65.
7 is connected to the cathode terminal.

Low-pass filter 64 and integrating circuit 65
Removes the high-frequency component of the applied AC voltage and supplies the DC component to the light-emitting diode 67. In this case, a negative voltage is applied to the cathode terminal of the light emitting diode 67, and the anode terminal of the light emitting diode 67 is grounded.

Output terminals of the subtraction circuits 24 and 27 are connected to input terminals of absolute value circuits 69 and 70, respectively, and output terminals of the absolute value circuits 69 and 70 are connected to a division circuit 71. The absolute value circuits 69 and 70 are respectively provided with the subtraction circuit 2
The absolute value of the amplitude value is calculated from the AC voltage given from the power supply circuits 4 and 27, and the calculated absolute value is provided to the division circuit 71.

The dividing circuit 71 divides the absolute value given from the absolute value circuit 70 by the absolute value given from the absolute value circuit 69, and gives the result of the division to a microcomputer (not shown).

As in the first embodiment, the AC current measuring device 7 includes an operational amplifier 18, a negative feedback resistor 20, a buffer 2
3 and a subtraction circuit 24, and an AC current measuring device 8
Is composed of an operational amplifier 19, a negative feedback resistor 21, a buffer 25, and a subtraction circuit 26. The AC voltage measuring device 9 includes a subtraction circuit 27, and the computing device 12 includes the adding circuit 29. The arithmetic unit 10 includes absolute value circuits 69 and 70 and a division circuit 71, and the control device 11 includes a light control variable resistor 62, a multiplication circuit 63,
It comprises a low-pass filter 64, an integration circuit 65 and a microcomputer.

Next, the operation of the third embodiment will be described. As shown in FIG. 22, the AC voltage output from the AC power supply 13, that is, the AC voltage applied to the AC voltage applying electrode 2 is represented by v13, and the AC voltage output from the inverting amplifier circuit 61, that is, AC The AC voltage applied to the voltage application electrode 3 is v14, the AC voltage output from the subtraction circuit 24 is v15, and the AC voltage output from the subtraction circuit 26 is v14.
16. The AC voltage output from the adding circuit 29 is represented by v17, +9
The AC voltage output from the 0 ° phase shift circuit 68 is v18,
The amplitude value of each AC voltage vn is expressed as Vn, and the absolute value of the amplitude value Vn is expressed as | Vn | (n is 13 to 18). Further, it is assumed that peripheral objects such as a transport device that transports the metal plate 4 are sufficiently grounded, and the potential of the peripheral objects is maintained at 0 volt.

In the third embodiment, the expression for calculating the thickness dc of the metal plate 4 in the microcomputer is the AC voltages v1, v2 and v3 of the expression (12) described in the first embodiment.
Correspond to the AC voltages v13, v14 and v15, respectively,
Since the amplitude value of each AC voltage is given as an absolute value by the absolute value circuits 69 and 70 and the division circuit 71, it can be expressed by the following equation.

[0204]

(Equation 25)

(1) The metal plate 4 is the electrode 2 for applying the AC voltage,
In the case where the metal plate 4 is inserted at the midpoint between the three, the thickness dc of the metal plate 4 is calculated as follows. That is, the AC voltage v15 is supplied from the subtraction circuit 24 to the absolute value circuit 69, and | V15 |
To the dividing circuit 71. A subtraction result (V13−V14) obtained by subtracting the amplitude value V14 of the AC voltage v14 from the amplitude value V13 of the AC voltage v13 is output from the subtraction circuit 27 to the absolute value circuit 7.
0, and | (V13−V14) | is supplied from the absolute value circuit 70 to the division circuit 71.

Then, in the division circuit 71, | (V13
−V14) | / | V15 | is calculated, and the calculation result | (V13−
V14) | / | V15 | is given to the microcomputer, and the microcomputer calculates the thickness dc of the metal plate 4 from the above equation (30).

(2) The metal plate 4 serves as the AC voltage applying electrode 2,
(A) When the metal plate 4 is inserted with a bias toward the AC voltage applying electrode 2 side. In this case, the AC voltage v18 output from the + 90 ° phase shift circuit 68 is Since the AC voltage v17 output from the adder circuit 29 is advanced by 90 ° in the + 90 ° phase shift circuit 68, the AC voltage v17 has the same phase as the AC voltage v13. Accordingly, the outputs of the multiplying circuit 63 and the low-pass filter 64 become positive, and the output of the integrating circuit 65 becomes negative. Accordingly, a larger negative voltage is applied to the cathode terminal of the light emitting diode 67.

As a result, the alternating current flowing in the forward direction of the light emitting diode 67 of the light control variable resistor 62 increases, and the light amount of the light emitting diode 67 increases. Accordingly, the resistance value of photoconductive cell 66 decreases, and amplitude value V14 of AC voltage v14 increases. And finally, the integration circuit 6
5 is held constant, and the amplitude value V14 of the AC voltage v14 is
Does not increase and when the state of equilibrium is reached, the processing described in the above (1) is executed, and the thickness dc of the metal plate 4 is increased.
Is calculated.

(A) When the metal plate 4 is inserted with a bias toward the AC voltage applying electrode 3 In this case, the AC voltage v18 is opposite to the case (A).
Has an opposite phase to the AC voltage v13. Therefore, the outputs of the multiplying circuit 63 and the low-pass filter 64 become negative, and the output of the integrating circuit 65 becomes positive. Accordingly, the negative voltage applied to the cathode terminal of the light emitting diode 67 approaches 0 volt. .

Thus, the alternating current flowing in the forward direction of the light emitting diode 67 of the light control variable resistor 62 decreases, and the light amount of the light emitting diode 67 decreases. Accordingly, the resistance value of the photoconductive cell 66 increases, and the amplitude value V14 of the AC voltage v14 decreases. And finally,
When the output of the integrating circuit 65 is kept constant and the amplitude value V14 of the AC voltage v14 does not decrease and becomes in an equilibrium state, the processing described in the above (1) is executed and the thickness dc of the metal plate 4 is increased. Is calculated.

As described above, according to the third embodiment, the AC voltage applying device 6 applies the AC voltages v13 and v14 having opposite phases to the AC voltage applying electrodes 2 and 3, respectively. The AC voltage v14 is controlled by the switch 62 so that | V15 | of the AC voltage v15 is substantially equal to | V16 | of the AC voltage v16, and | V15 | of the AC voltage v15 and | V16 | Are approximately equal, the thickness d of the metal plate 4
It was configured so that c could be calculated.

Therefore, as in the first embodiment, | I1 | of the alternating current i1 flowing through the capacitance C1 and the capacitance C1
2 where | I2 | of the alternating current i2 flowing through
That is, the thickness d of the metal plate 4 is kept in a state where almost no AC current flows through the stray capacitance Cs (no leakage current flows).
c can be measured.

In this case, since the AC current hardly flows through the stray capacitance Cs, the measurement accuracy does not decrease, and the metal plate 4 is inserted between the AC voltage applying electrodes 2 and 3 as a transfer device. Since it is not necessary to make the position to be set with high precision, the entire system can be made inexpensive accordingly.

Further, since the control of the AC voltage applied to the AC voltage applying electrode 3 is performed by hardware using the light control variable resistor 62, the processing of the microcomputer can be reduced correspondingly. it can. Further, even if the object to be measured is not a conductor, but an insulator or a semiconductor,
Their thickness can be measured.

Next, a fourth embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. The same parts as those in the second embodiment are denoted by the same reference numerals, and description thereof will be omitted. Hereinafter, different parts will be described. In the fourth embodiment, the electrode 3 for applying an AC voltage is used.
Unlike the second embodiment in which the control of the AC voltage applied to the microcomputer is performed by software under the control of the microcomputer 51, the control is performed by hardware similarly to the third embodiment. In particular, the configuration of the AC voltage applying device 43 is different.

That is, the AC voltage applying device 43 includes an AC power supply 13, an inverting amplifier circuit 81, an operational amplifier 18, a light control variable resistor 82, a multiplying circuit 83, and a low-pass filter 84.
And an integrating circuit 85, which are connected as shown below.

The output terminal of the AC power supply 13 is connected to the operational amplifier 1
8 is connected to the AC voltage applying electrode 3 via the photoconductive cell 86 in the light control variable resistor 82 and the inverting amplifier circuit 81.
Like the photoconductive cell 66 described in the third embodiment, the photoconductive cell 86 changes its resistance value according to the amount of light emitted from the light emitting diode 87 in the light control variable resistor 82. When the amount of light from the light emitting diode 87 is large, the resistance value is small, and when the amount of light is small, the resistance value is large.

The output terminal of AC power supply 13 is connected to one input terminal of multiplication circuit 83, and the other input terminal of multiplication circuit 83 is connected to the output terminal of -90 ° phase shift circuit 88. . The multiplication circuit 83 calculates the amplitude value of the AC voltage supplied from the AC power supply 13 and the potential detection electrode 42
It multiplies the amplitude value of the AC voltage supplied through the inverting amplifier circuits 49 and 89 and the -90 ° phase shift circuit 88, and its output terminal is provided through the low-pass filter 84 and the integrating circuit 85. Is connected to the cathode terminal.

[0219] Low-pass filter 84 and integrating circuit 85
Removes the high-frequency component of the applied AC voltage and supplies the DC component to the light emitting diode 87.
Also in this case, a negative voltage is applied to the cathode terminal of the light emitting diode 87, and the anode terminal of the light emitting diode 87 is grounded.

Output terminals of the subtraction circuits 24 and 27 are connected to input terminals of absolute value circuits 90 and 91, respectively, and output terminals of the absolute value circuits 90 and 91 are connected to a division circuit 92. The absolute value circuits 90 and 91 are respectively similar to the absolute value circuits 69 and 70 described in the third embodiment.
The absolute value of the amplitude value is calculated from the AC voltage supplied from the power supply circuits 4 and 27, and the calculated absolute value is supplied to the division circuit 92.

The dividing circuit 92 divides the absolute value given from the absolute value circuit 91 by the absolute value given from the absolute value circuit 90, and gives the result of the division to a microcomputer (not shown).

As in the second embodiment, the AC current measuring device 7 includes an operational amplifier 18, a negative feedback resistor 20, a buffer 2
And an AC current measuring device 4
6 includes an inverting amplifier circuit 49. The AC voltage measuring device 9 includes a subtraction circuit 27. The arithmetic unit 44 includes absolute value circuits 90 and 91 and a division circuit 92, and the control unit 45 includes a light control variable resistor 82, a multiplication circuit 83, a low-pass filter 84, an integration circuit 85, and a microcomputer. .

Next, the operation of the fourth embodiment will be described. As shown in FIG. 23, the AC voltage output from the AC power supply 13, that is, the AC voltage applied to the AC voltage applying electrode 2 is represented by v 19, the voltage output from the inverting amplifier circuit 81, that is, the AC voltage The AC voltage applied to the application electrode 3 is v20, the AC voltage output from the subtraction circuit 24 is v21, and the AC voltage output from the inverting amplifier circuit 49 is v20.
22, the AC voltage output from the inverting amplifier circuit 89 is represented by v23,
The AC voltage output from the -90 ° phase shift circuit 88 is denoted by v24, the amplitude value of each AC voltage vn is Vn, and the absolute value of Vn is |
Vn | (n is 19 to 24). Further, surrounding objects such as a transfer device for transferring the metal plate 4 are sufficiently grounded, and the potentials of the surrounding objects are maintained at 0 volt.

In the fourth embodiment, the equation for calculating the thickness dc of the metal plate 4 in the microcomputer is the AC voltages v8, v9 and v10 of the equation (29) described in the second embodiment.
Correspond to the AC voltages v19, v20 and v21, respectively.
Since the amplitude values of these AC voltages are given as absolute values by the absolute value circuits 90 and 91 and the division circuit 92, they can be expressed by the following equations.

[0225]

(Equation 26)

(1) When the metal plate 4 is the electrode 2 for applying an AC voltage,
In the case where the metal plate 4 is inserted at the midpoint between the three, the thickness dc of the metal plate 4 is calculated as follows. That is, the AC voltage v21 is supplied from the subtraction circuit 24 to the absolute value circuit 90, and | V21 |
To the dividing circuit 92. A subtraction result (V19-V20) obtained by subtracting the amplitude value V20 of the AC voltage v20 from the amplitude value V19 of the AC voltage v19 is output from the subtraction circuit 27 to the absolute value circuit 9.
1 and | (V19−V20) | is supplied from the absolute value circuit 91 to the division circuit 92.

In the division circuit 92, | (V19
−V20) | / | V21 | is calculated, and the calculation result | (V19−
V20) | / | V21 | is given to the microcomputer, and the microcomputer calculates the thickness dc of the metal plate 4 by the above equation (31).

(2) The metal plate 4 serves as the AC voltage applying electrode 2,
(A) When the metal plate 4 is inserted with a bias toward the AC voltage applying electrode 2 side, in this case, the AC voltage v24 output from the -90 ° phase shift circuit 88 Is the AC voltage v output from the inverting amplifier circuit 49.
22 is inverted in phase by the inverting amplifier 89, and the AC voltage v23 output from the inverting amplifier 89 is −90 °
Since the phase is delayed by 90 ° in the phase shift circuit 88, it becomes the same phase as the AC voltage v19. Accordingly, the outputs of the multiplying circuit 83 and the low-pass filter 84 become positive, and the output of the integrating circuit 85 becomes negative. Accordingly, a larger negative voltage is applied to the cathode terminal of the light emitting diode 87.

Thus, the alternating current flowing in the forward direction of the light emitting diode 87 of the light control variable resistor 82 increases, and the light amount of the light emitting diode 87 increases. Accordingly, the resistance value of the photoconductive cell 86 decreases, and the amplitude value V20 of the AC voltage v20 increases. And finally, the integration circuit 8
5 is held constant, and the amplitude value V20 of the AC voltage v20 is maintained.
Does not increase and when the state of equilibrium is reached, the processing described in the above (1) is executed, and the thickness dc of the metal plate 4 is increased.
Is calculated.

(A) When the metal plate 4 is inserted with a bias toward the AC voltage applying electrode 3 side. In this case, the AC voltage v24
Has the opposite phase to the AC voltage v19. Therefore, the output of the multiplying circuit 83 and the output of the low-pass filter 84 become negative, the output of the integrating circuit 85 becomes positive, and accordingly, the negative voltage applied to the cathode terminal of the light emitting diode 87 approaches 0 volt. .

As a result, the AC current flowing in the forward direction of the light emitting diode 87 of the light control variable resistor 82 decreases, and the light amount of the light emitting diode 87 decreases. Accordingly, the resistance value of the photoconductive cell 86 increases, and the amplitude value V20 of the AC voltage v20 decreases. And finally,
When the output of the integration circuit 85 is held constant and the amplitude value V20 of the AC voltage v20 does not decrease and the balance becomes an equilibrium state, the processing described in the above (1) is executed and the thickness dc of the metal plate 4 is increased. Is calculated.

As described above, according to the fourth embodiment, the AC voltage applying device 43 applies AC voltages v19 and v20 having opposite phases to the AC voltage applying electrodes 2 and 3, respectively. 82 controls the AC voltage v20 so that | V24 | of the AC voltage v24 becomes an extremely small value. When | V24 | of the AC voltage v24 is an extremely small value, the thickness dc of the metal plate 4 is reduced. Was calculated.

Therefore, as in the second embodiment, the state where | I3 | of the alternating current i3 is an extremely small value, that is, | I1 | of the alternating current i1 flowing to the capacitance C1, and flows to the capacitance C2. In a state where | I2 | of the AC current i2 is substantially equal, that is, in a state where the AC current hardly flows through the stray capacitance Cs (no leak current flows), the metal plate 4
Can be measured.

In this case, almost no AC current flows through the stray capacitance Cs, so that the measurement accuracy does not decrease.
As the transfer device, the metal plate 4 is composed of the electrode 2 for applying an AC voltage,
Since it is not necessary to make the position inserted between 3 with high accuracy,
Accordingly, the entire system can be made inexpensive.

Further, since the control of the AC voltage applied to the AC voltage applying electrode 3 is performed by hardware using the light control variable resistor 82, the processing of the microcomputer can be reduced accordingly. it can. Furthermore, the object to be measured is
Even in the case of a semiconductor instead of a conductor, their thickness can be measured.

Next, a fifth embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. The same parts as those in the second and fourth embodiments are denoted by the same reference numerals, and description thereof will be omitted. Hereinafter, different parts will be described. In the fifth embodiment, the base 1
The shape of No. 01 is different from the second and fourth embodiments, and the metal plate 4 is inserted from the direction of arrow C in FIG. According to the fifth embodiment, the same effects as those of the second and fourth embodiments can be obtained, and the length of the metal plate 4 in the longitudinal direction is sufficiently large with respect to the longitudinal direction of the base 101. Can be measured at the central portion of the metal plate 4.

The present invention is not limited to the above embodiment, but can be modified or expanded as follows.
The present invention may be applied to a detection device that detects minute objects such as paper and dust attached to an object to be measured. Although a sine wave is used as the alternating current, a square wave, a triangular wave, or the like may be used. In the third and fourth embodiments, as a means for controlling the AC voltage, a photocoupler may be used instead of the light control variable resistors 62 and 82. Further, another means may be used as long as it controls the AC voltage applied to the AC voltage applying electrode 3 according to the potential of the metal plate 4.

[0238]

As apparent from the above description, according to the capacitance type measuring apparatus of the first aspect, when the object to be measured is located between the electrodes for applying the AC voltage, the first AC current measurement is performed. Means for measuring an AC current flowing through a first capacitor component formed between the first AC voltage applying electrode and the object to be measured, and a second AC current measuring means for measuring a second AC voltage An AC current flowing through a second capacitor component formed between the application electrode and the object to be measured is measured, and the applied voltage control means makes the detection currents of the first and second AC current measurement means substantially the same. The applied voltage is adjusted so that the physical quantity of the object to be measured is measured.

Therefore, the state in which the alternating current flowing through the first capacitor component and the alternating current flowing through the second capacitor component are substantially the same, that is, the stray capacitance existing between the object to be measured and the surrounding object The physical quantity of the object to be measured can be measured in a state where almost no AC current flows.

At this time, since almost no AC current flows through the stray capacitance, the measurement accuracy does not decrease.
Since the position where the object to be measured is inserted between the AC voltage applying electrodes does not need to be accurately set, the entire system can be made inexpensive accordingly.

According to the capacitance type measuring device of the present invention, when the object to be measured is located between the electrodes for applying the AC voltage, the AC current measuring means connects the electrode for potential detection to the object to be measured. The alternating current flowing through the capacitor component formed between the two is measured, and the applied voltage is adjusted by the applied voltage control means so that the current detected by the alternating current measuring means becomes substantially zero, and the physical quantity of the object to be measured is measured. It was configured to be.

Therefore, by setting the reference potential of the potential detecting electrode to be equal to the potential of the surrounding object, it is possible to prevent the stray capacitance existing between the object to be measured and the surrounding object from flowing in a state where AC current hardly flows. The physical quantity of the measurement object can be measured.

At this time, since almost no AC current flows through the stray capacitance, the measurement accuracy does not decrease.
Since the position where the object to be measured is inserted between the AC voltage applying electrodes does not need to be accurately set, the entire system can be made inexpensive accordingly.

[Brief description of the drawings]

FIG. 1 is an electrical block diagram showing a first embodiment of the present invention.

FIG. 2 is a perspective view showing a state in which a metal plate is inserted between electrodes for applying an AC voltage.

FIG. 3 is an electrical block diagram showing details of FIG. 1;

FIG. 4 is a diagram showing a connection state of a changeover switch (part 1);

FIG. 5 is a diagram showing a connection state of a changeover switch (part 2).

FIG. 6 is a circuit diagram showing an internal configuration of a variable amplifier circuit.

FIG. 7 is a side view showing a state where a metal plate is inserted at a midpoint between electrodes for applying an AC voltage.

FIG. 8 is an equivalent circuit diagram showing a measurement system.

FIG. 9 is a flowchart showing control of a microcomputer.

FIG. 10 is a side view showing a state where a metal plate is inserted so as to be shifted from a middle point between electrodes for applying an AC voltage.

FIG. 11 is a waveform chart showing an output state of each AC voltage.

FIG. 12 is a diagram corresponding to FIG. 8 when an object to be measured is an insulator;

FIG. 13 is a diagram corresponding to FIG. 8 when the object to be measured is a semiconductor.

FIG. 14 is a view corresponding to FIG. 2, showing a second embodiment of the present invention.

FIG. 15 is a diagram corresponding to FIG. 1;

FIG. 16 is a diagram corresponding to FIG. 3;

FIG. 17 is a diagram corresponding to FIG. 7;

FIG. 18 is a diagram corresponding to FIG. 8;

FIG. 19 is a diagram corresponding to FIG. 9;

FIG. 20 is a diagram corresponding to FIG. 10;

FIG. 21 is a diagram corresponding to FIG. 11;

FIG. 22 is a view corresponding to FIG. 3, showing a third embodiment of the present invention.

FIG. 23 is a view corresponding to FIG. 3, showing a fourth embodiment of the present invention.

FIG. 24 is a view corresponding to FIG. 2, showing a fifth embodiment of the present invention.

[Explanation of symbols]

In the drawing, 2 is a first AC voltage applying electrode, 3 is a second AC voltage applying electrode, 4 is a metal plate (measurement target), 6 is an AC voltage applying device (AC voltage applying means), 7 Is an AC current measuring device (first AC current measuring device), 8 is an AC current measuring device (second AC current measuring device), 11 is a control device (applied voltage control device), 42 is a potential detecting electrode, 45 Denotes a control device (applied voltage control means), and 46 denotes an AC current measuring device (AC current measuring means).

Claims (2)

(57) [Claims] 1. An AC voltage applying electrode and a second AC voltage applying electrode facing each other at a predetermined interval, and an AC voltage applying means for applying AC voltages having opposite phases to both electrodes. Means for inserting an object to be measured made of a conductive material between the first electrode for applying an AC voltage and the second electrode for applying an AC voltage by a transport device, and a physical quantity of the object to be measured The first AC voltage applying electrode or the second AC voltage corresponding to the capacitance between the first AC voltage applying electrode and the second AC voltage applying electrode, which varies according to In a capacitance type measuring device for measuring a physical quantity of an object to be measured based on an AC current flowing through an application electrode, a first AC current measurement for measuring an AC current flowing through the first AC voltage application electrode Means, the second AC voltage A second AC current measuring means for measuring an AC current flowing through the additional electrode; and the first and second AC voltage applying means so that currents detected by the first and second AC current measuring means are substantially the same. An electrostatic capacitance type measuring apparatus comprising: an applied voltage control means for adjusting an applied voltage to a second AC voltage applying electrode. 2. An AC voltage applying electrode and a second AC voltage applying electrode facing each other at a predetermined interval, and an AC voltage applying means for applying AC voltages of opposite phases to both electrodes. Means for inserting an object to be measured made of a conductive material between the first electrode for applying an AC voltage and the second electrode for applying an AC voltage by a transport device, and a physical quantity of the object to be measured The first AC voltage applying electrode or the second AC voltage corresponding to the capacitance between the first AC voltage applying electrode and the second AC voltage applying electrode, which varies according to In a capacitance type measuring device for measuring a physical quantity of the object to be measured based on an alternating current flowing through an application electrode, the object to be measured positioned between the first and second AC voltage application electrodes, Facing each other with a predetermined interval A potential detection electrode set to a predetermined reference potential in the state, AC current measuring means for measuring an AC current flowing through the potential detection electrode, and an AC current measuring means for detecting the AC current by the AC current measuring means to be substantially zero. An electrostatic capacitance type measuring apparatus comprising: an applied voltage control means for adjusting an applied voltage to the first and second AC voltage applying electrodes by the AC voltage applying means.