JP2002098504A - Capacitance type gap sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for signal processing of a capacitance type gap sensor capable of accurately carrying out the measurement of gap even in the case that the potential of a body to be measured is in float condition for the ground. SOLUTION: The capacitance type gap sensor includes a first detecting electrode e1 that is disposed at an objective surface 2a approximately parallel to, distant from, and opposing to a conductive surface to be measured 1a, and forms the electrostatic capacity in the space with the surface to be measured 1a, a second detecting electrode e2 that is insulated from and concentric to the first detecting electrode e1, and forms the electrostatic capacity in the space with the surface to be measured 1a, and detects a measured amplitude information corresponding to the combined capacity between the first/second detecting electrodes e1, e2 and the surface to be measured 1a that varies in accordance with a gap d between the surface to be measured 1a and the objective surface 2a. When the measurement of the surface to be measured 1a is carried out using the method for signal processing of the capacitance type gap sensor, the objective surface 2a is moved back and forth for a determined distance in an approximately normal direction to the surface to be measured 1a. Then, two values output from the first/second detecting electrodes e1, e2 detecting before and after moving back and forth are memorized, and the output value corresponding to the gap d is determined from the measured amplitude information using a transferring algorithm based on the two memorized values.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type displacement sensor and, more particularly, to a signal processing method for a capacitance type gap sensor for measuring a distance between an object to be measured and the sensor.

[0002]

2. Description of the Related Art As is well known, in a capacitance type gap sensor, for example, as shown in FIG. 1, first and second surfaces provided on a measurement surface 1a of a measurement object 1 and an object surface 2a of a measurement head 2 are provided. by measuring the electrostatic capacitance generated between the second detection electrode e _1, e _2, an object to be measured 1 and the first, the distance between the second detection electrode e _1, e ₂ (hereinafter, the gap d Name)
Is measured. That is, the conductive object 1 shown in FIG. 1 is positioned on the ground member 3 whose potential is kept at GND via the object support 4 and is separated in a direction substantially perpendicular to the surface 1a to be measured. A guard electrode e is provided on the opposed object surface 2a.
₃ first detection electrodes mutual concentric manner insulated shield e ₁ and the second detection electrode e ₂ is provided with.

[0003] The first detection electrode e ₁ and the second detection electrode e ₂ of the same capacitive gap sensor are denoted by the same reference numerals.
5 ", a counter voltage signal of an AC bridge 7 to which an AC power supply 6 of the processing circuit 5 is applied is input to a differential means 8, and an output signal of the differential means 8 is amplitude-extracted. voltage amplitude signal is input to the means 9 are extracted, linear processing is the. Figure 2 is an object to be measured 1 and the first with the same voltage amplitude signal linearization means 10, second detection electrode e _1, e ₂ e ₁ , E ₂
And an equivalent circuit of an AC bridge 7 composed of capacitors C _α , C _β , and C _{γ. The} capacitance generated between the first detection electrode e ₁ and the DUT 1 is “C ₁ ”, and the second detection is Electrode e ₂
- When "C _2" electrostatic capacitance generated between the measured sample _1, "C 1" combined capacitance C ₀ of the "C _2" is changed in accordance with the gap d. Further, the stray capacitance generated in the detection electrode e ₁ is shown as "C _S" in FIG.

At this time, a combined capacitance C ₀ generated on the detection electrode is obtained.
Is that the potential of the DUT 1 is GND, so that C ₂ is
The bypass is performed as shown in the inside, and C ₀ = C _S + C ₁ ...

FIG. 3 shows the signals S ₁ , S ₂ ,
The relationship between S ₃ , S ₄ , S ₅ and the gap d is shown. An AC signal having a frequency f ₁ is applied to the AC bridge 7, and the combined capacitance C ₀
And the signal S ₁ output by the partial pressure of the capacitor C _α

(Equation 1) (When the potential of the DUT 1 is GND) Expression (2) (where A ₁ , B ₁ , and D ₁ are constants, A ₁ > 0) and the partial pressure of the capacitor C _β and the capacitor C _γ Output signal S ₂

(Equation 2) Equation (3) (where E is a constant, d ₀ is the gap at the midpoint of the measurement range) is a signal S ₃ which is obtained by taking the difference between

(Equation 3) (In the case where the potential of the DUT 1 is GND) The following amplitude information S _{4 of} Expression (4) is extracted.

[0006]

(Equation 4) (When the potential of the DUT 1 is GND) Expression (5) If the amplitude information S ₄ is a signal S ₅ linearized so as to be linear with respect to the change of the gap d, the gap d
Can be detected.

(Equation 5) (When the potential of the DUT 1 is GND) Equation (6) (where L is a function for linearizing S ₄ and A ₃ is a constant)

[0007]

By the way, in the conventional capacitance type gap sensor, the value of the gap d is known by the above-described signal processing method. When measuring the gap d between the detection electrodes e ₁ and e ₂ , for example, when the object support 4 is a non-conductive material, the potential of the object 1 floats from GND, and FIG. As shown in the figure, the stray capacitance C _W between GND and the DUT 1
Will occur.

FIG. 5 shows an equivalent circuit of the AC bridge 7 in this case. Since the stray capacitance C _W is generated in parallel with the electrostatic capacitance C ₂ generated between the detection electrode e ₂ and the DUT 1, each capacitor is connected. The combined capacitance C ₀ that forms the AC bridge 7 together with C _α , C _β , and C _γ is a combined capacitance of the stray capacitance C _S , the electrostatic capacitances C ₁ , C _2, and the stray capacitance C _W , and is expressed by the following equation.

(Equation 6) (Equation (7)) In this case, if the stray capacitance C _W is sufficiently large (C _W → ∞), since the equation (7) becomes C ₀ = C _S + C ₁ , the potential of the DUT ₁ becomes This is equivalent to the case of GND.

However, when the potential of the DUT 1 is floating as shown in FIG. 4, the signal S ₁ is a composite capacitance C ₀ to be detected.
Are different from each other, the potential of the DUT 1 is G as shown in the following equation.
It differs from the case of ND.

(Equation 7) (When the potential of the DUT 1 is floating) Expression (8) (where A ₂ ≠ A ₁ , B ₂ ≠ B ₁ , D ₂ ≠ D ₁ , A ₂ ,
B ₂ and D ₂ are constants, A ₂ > 0)

[0010] As a result, the signal S ₅ in the case where the potential of the object to be measured 1 is floating from the GND, as shown in FIG. 6, the potential of the object to be measured 1 is a different state from that of GND.
Here, the signal S ₂ is the same as when the potential of the DUT 1 is GND,

(Equation 8) It is.

The signal S ₃ is

(Equation 9) (In the case where the potential of the DUT 1 is floating) Since the equation (9) is used, the amplitude information S ₄ and S _{5 obtained} are

(Equation 10) (When the electric potential of the DUT 1 is floating) ... Expression (10) S ₅ = L (S ₄ ) (When the electric potential of the DUT 1 is floating) ... Expression (11) (However, L is expressed as a function used in equation (6).

Here, when the equations (10) and (5) are compared, A ₁ ≠ A ₂ , B ₁ ≠ B ₂ , and D ₁ ≠ D _2, so that S ₅ = L using the amplitude information S ₄ as it is. Even if the linearization conversion of (S ₄ ) is performed, the amplitude information S ₅ does not become linearized corresponding to the gap d. Therefore, in the signal processing method of the conventional capacitance type gap sensor, when the potential of the DUT 1 is floating from GND, accurate gap measurement cannot be performed due to the electrical state of the DUT 1. There is.

An object of the present invention is to provide an accurate gap measurement even when the potential of an object to be measured is in a floating state from GND in view of the above-described problem of the signal processing method of the conventional capacitive gap sensor. To obtain a signal processing method for a capacitance type gap sensor and a capacitance type gap sensor capable of performing the following.

[0014]

SUMMARY OF THE INVENTION According to the present invention, there is provided, in accordance with the present invention, a method comprising: A first detection electrode that forms a capacitance, and a second detection electrode that is concentrically located in an insulated state with respect to the first detection electrode and forms a capacitance between the surface to be measured, A capacitance type for detecting measurement amplitude information corresponding to a combined capacitance between the first and second detection electrodes and the measured surface, which varies according to a gap between the measured surface and the object surface. In the gap sensor, when measuring the surface to be measured, the object surface is reciprocated by a predetermined distance in a direction substantially perpendicular to the surface to be measured, and the first and second detection electrodes obtained before and after this reciprocal displacement are moved. A conversion algorithm that stores two output values and uses these two stored values It is accomplished by the signal processing method of the capacitance type gap sensor for determining the more output value corresponding to the gap from the measured amplitude information.

Further, according to the present invention, the object is to form an electrostatic capacitance between the conductive film and a surface to be measured which is provided on a substantially parallel object surface opposed to the surface to be measured. A first detection electrode, and a second detection electrode concentrically positioned in an insulated state with respect to the first detection electrode and forming a capacitance between the first detection electrode and the surface to be measured; And a capacitance type gap sensor that detects measurement amplitude information corresponding to a combined capacitance between the first and second detection electrodes and the measurement target surface, which changes according to a gap between the object surface and the first detection electrode,
When measuring the surface to be measured, a moving means for reciprocating the object surface by a predetermined distance in a direction substantially perpendicular to the surface to be measured, and first and second detection electrodes obtained before and after the reciprocal displacement. This is also achieved by a capacitance type gap sensor including storage means for storing two output values, and calculation means for obtaining an output value corresponding to the gap from the measured amplitude information by a conversion algorithm using these two stored values. Is done.

In the following description of a preferred embodiment of the present invention, 1) the moving means moves a guide mechanism whose displacement distance is predetermined mechanically, and moves the object plane along the guide mechanism. A configuration including a piezoelectric actuator, a displacement actuator such as an electromagnetic solenoid, or manual means will be described.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 7 shows a capacitance type gap sensor according to the present invention, in which a conductive measuring object 1 is positioned via a measuring object support 4 on a ground member 3 whose electric potential is kept at a GND state. guard electrode e ₃ first detection electrodes mutual concentric manner insulated shielded with e ₁ and the second detection electrode e ₂ is provided on the objective surface 2a which is spaced apart opposed to a substantially perpendicular direction of the measurement surface 1a This is the same as in the case of the conventional capacitance gap sensor described above.

The capacitance type gap sensor according to the present invention is characterized by a guide mechanism provided on the sensor support 8, and the objective surface 2a and the measured surface 1 facing the conductive measured surface 1a.
When measuring the gap d, which is the distance between
The objective surface 2a can reciprocate a known predetermined distance Δd in the direction opposite to the surface to be measured 1a.

That is, the conductive object 1 shown in FIG. 7 is held by the object support 4 on the ground member 3 at the potential GND, and the object surface 2
Although the measuring head 2 which is opposed to the distance a is supported by the sensor support 11, in the case of the present invention, the sensor support 1
1 includes a flange 2b of the measuring head 2 and the surface 1a to be measured.
The guide groove 12 is formed to guide in a direction substantially perpendicular to the guide groove 12.

That is, upper and lower stopper surfaces 13U, 1 which receive the flange 2b of the measuring head 2 are provided above and below the guide groove 12.
3D is formed, and a displacement actuator 14 for reciprocating the measurement head 2 along the guide groove 12 is interposed between the upper surface of the measurement head 2 and the opposing surface of the sensor support 11, and the displacement actuator 14 The gap is changed in the measuring head 2 by a known predetermined distance Δd.
As the displacement actuator 14 to be used, for example, a moving means such as a piezoelectric element (PZT) or an electromagnetic solenoid can be used. For the reciprocation, a manual moving means such as a precision feed means may be used. it can.

In the case of the present invention, the first detection electrode e ₁
And the signal from the second detection electrode e ₂ is supplied to a processing circuit 5 including an AC bridge, a differential means, and an amplitude extracting means, and a voltage amplitude signal is extracted by the processing circuit 5, as in the prior art. The extracted voltage amplitude signal is output to arithmetic means 15 supplied by a CPU or the like. The calculating means 15 is connected via a data bus to a storing means 16 capable of temporarily storing a voltage amplitude signal before and after the movement of the measuring head 2, and the calculating means 1
5, the voltage amplitude signal of the measuring head 2 before and after the movement read and converted is converted by a predetermined algorithm,
Linear processing is performed at 0.

Next, the processing in the calculating means 15 will be described in detail. FIG. 8 shows the measured amplitude information S when the stray capacitance C _W described in the description of FIG. 4 is changed to three different values. The characteristic curve of ₄ -gap d is shown. As understood from the figure, the electrical state of the object to be measured 1 (the value of the stray capacitance C _W), the relationship between the measured amplitude information S ₄ and the gap d is understood to be a different characteristics.

FIG. 9 shows an unknown initial gap amount d _S.
Is added to the measured amplitude information S ₄ (d _S ) and the gap variation Δd known from the state according to the present embodiment, and the measured amplitude information S ₄ when the gap is d _S + Δd.
6 is a graph showing a relationship with (d _S + Δd) and plotting the initial gap amount d _S within a range of possible values. As understood from FIG. 9, the three curves do not intersect each other, that is, the amplitude information S ₄
The characteristic curve passing through the points plotted on FIG. 9 from the two values of (d _S ) and the amplitude information S ₄ (d _S + Δd) after the movement is as follows:
It turns out that there is only one. This is, even when the characteristics of the amplitude information S ₄ and the gap d is unknown, by obtaining the two values using the present embodiment, which means it is possible to identify its characteristics.

Next, a specific procedure for obtaining the gap d using the amplitude information S ₄ (d _S ) and the moved amplitude information S ₄ (d _S + Δd) will be described. The amplitude information S ₄ (d _S ) measured from the equivalent circuit shown in FIG. 5 can be expressed by the following equation (12).

[Equation 11] ... Equation (12)

Similarly, the measured amplitude information S ₄ after the movement is obtained.
(D _S + Δd) can be expressed by the following equation (13).

(Equation 12) (Equation (13)) where C _α , C _β , and C _γ are known capacitances of the capacitors constituting the bridge, the dielectric constant of vacuum is ε ₀ , and the intervening between the electrode and the DUT 1 the dielectric constant of the material (usually air) to the epsilon _gamma. At this time, the area of the first detection electrode e ₁ is A ₁ , and the second detection electrode e 1
The _second area and A _2, represents a stray capacitance between the first detection electrode e ₁ and the second detection electrode e ₂ in C _S. V ₀ is the amplitude of the AC voltage applied to the AC bridge 7.

The unknowns in the above equations (12) and (13) are two, “C _W ” and “d _S ”, and the amplitude information S
₄ (d _S ) and the moved amplitude information S ₄ (d _S + Δd) are values actually measured by the capacitance type gap sensor of the present invention. Therefore, as shown in the following equation, if “d _S ” is eliminated from Equations (12) and (13), “C _W ” is determined by the measured values S ₄ (d _S ) and S ₄ (d _S + Δd). It is obtained as a derived function G.

(Equation 13) ... Expression (14)

From the above results, the amplitude information S ₄ before and after the movement measured by using the guide mechanism of the present embodiment.
(D _s ) and amplitude information S ₄ (d _s + Δd) are given by equation (14).
Is substituted into S ₄ (d _S ) without identifying “d _S ”.
And S ₄ (d _S + Δd) as a function
"Can be obtained. Thus, if the measurement amplitude information obtained during the measurement of the gap d S ₄ and _{(d), S 4 (d} ) in the previous equation (12)" C _W d _S "To" d ", S ₄ (d _S ) and S ₄
S ₄ as a function of (d _S + Δd) and gap d can be determined.

[Equation 14] ... Equation (15)

That is, as understood from the equation (15),
Using S ₄ (d _S ) and S ₄ (d _S + Δd) and other parameters obtained separately, the gap d can be derived as a function of the amplitude information S ₄ as follows.

(Equation 15) Expression (16) Here, the function F represents a relationship for linearizing “S ₄ ”.

As described above, if two pieces of measured amplitude information S ₄ (d _S ) and moved amplitude information S ₄ (d _S + Δd) are obtained for the DUT 1 in the measurement state in advance. , the gap d is the use of measurements S ₄ at this time equation (16)
Thus, accurate gap measurement can be performed regardless of the electrical state of the DUT 1.

[0030]

As is apparent from the above description, according to the present invention, there is an effect that the gap can be measured accurately regardless of the electrical state of the DUT 1.

[Brief description of the drawings]

FIG. 1 is an enlarged view of a main part of a conventional capacitance type gap sensor and a signal processing circuit diagram.

FIG. 2 is an equivalent circuit diagram of an AC bridge of the capacitance type gap sensor.

FIG. 3 shows signals S _{1 to} S ₅ of the capacitance type gap sensor.
FIG. 4 is a characteristic curve diagram showing a relationship between the distance d and a gap d.

FIG. 4 is an explanatory diagram of the same capacitance type gap sensor when there is a stray capacitance.

FIG. 5 is an equivalent circuit diagram corresponding to FIG. 2 of the same capacitance type gap sensor when there is a stray capacitance.

FIG. 6 is a graph corresponding to FIG. 3 when there is a stray capacitance.

FIG. 7 is an enlarged view of a main part and a signal processing circuit diagram of the capacitance type gap sensor according to the present invention.

FIG. 8 is a signal S ₄ -gap diagram of the same capacitance type gap sensor when C _W changes.

[9] S ₄ when changing the gap d _S (d _S +
△ d) a -S ₄ (d _S) schematic.

[Explanation of symbols]

_CS floating capacitance d gap e ₁ first detection electrode e ₂ second detection electrode e ₃ guard electrode 1 object to be measured 1a object to be measured 2 measuring head 2a object surface 2b flange 3 ground member 4 object to be measured 5 processing circuit 7 AC bridge 8 Differential means 9 Amplitude extraction means 10 Linearization means 11 Sensor support 12 Guide groove 13U, 13D Upper and lower stopper surface 14 Displacement actuator 15 Calculation means 16 Storage means

Claims (3)

[Claims] A first detection electrode provided on a substantially parallel object surface which is spaced apart from and opposed to a conductive measurement surface to form a capacitance between the first measurement electrode and the measurement surface; A second detection electrode that is concentrically positioned in a state insulated from the detection electrode and forms a capacitance between the measurement surface and the measurement surface, and a gap between the measurement surface and the object surface is provided. A capacitance type gap sensor that detects measurement amplitude information corresponding to a combined capacitance between the first and second detection electrodes and the surface to be measured, the gap being changed in response to the measurement; The objective surface is reciprocated a predetermined distance in a direction substantially perpendicular to the surface, and two output values of the first and second detection electrodes obtained before and after the reciprocal displacement are stored, and the two stored values are stored. From the measured amplitude information to the gap by a conversion algorithm using Capacitive gap signal processing method of a sensor and obtains the the output value. 2. A first detection electrode provided on a substantially parallel objective surface spaced apart from and opposed to a conductive measurement surface to form a capacitance between the first detection electrode and the first measurement electrode. A second detection electrode that is concentrically positioned in a state insulated from the detection electrode and forms a capacitance between the measurement surface and the measurement surface, and a gap between the measurement surface and the object surface is provided. A capacitance type gap sensor that detects measurement amplitude information corresponding to a combined capacitance between the first and second detection electrodes and the surface to be measured, the gap being changed in response to the measurement; Moving means for reciprocating the object plane by a predetermined distance in a direction substantially perpendicular to the plane; storage means for storing two output values of the first and second detection electrodes obtained before and after the reciprocal displacement; , Said measurement by a conversion algorithm using these two stored values Capacitive gap sensor, characterized in that the width information comprises calculating means for calculating an output value corresponding to the gap. 3. The moving means includes a guide mechanism having a mechanically predetermined displacement distance, a displacement actuator such as a piezoelectric element, an electromagnetic solenoid, or a manual means for moving the objective surface along the guide mechanism. The capacitance type gap sensor according to claim 2, comprising: