JPH03167422A - Capacitance type length measuring device - Google Patents

Abstract

PURPOSE:To perform highly accurate measurement by switching a voltage with an electronic device so that a feedback voltage which is induced in a common-core electrode becomes zero when the capacitances of first and second measuring capacitors are changed by the displacement of a screen. CONSTITUTION:Measuring capacitors C1 and C2 are formed between ring electrodes 9 and 10 and a common core electrode 12 through the window of a screen 13. A reference capacitor C3 is formed between a ring electrode 11 and the electrode 12. Reference rectangular wave voltages E1 and E2 and measuring rectangular wave voltage E3 are applied on the electrodes 9 - 11, respectively. The voltage E3 is made variable with an electronic device so that a feedback voltage Em which is induced in the electrode 12 with the capacitors C1 - C3 becomes zero. In this constitution, even if the central axis between the electrodes 9 - 11 and the electrode 12 is slightly deviated by shocks and the like, the voltage E3 is hardly affected. Since the screen 13 is moved along the central axis between the electrodes 9 - 11 and the electrode 12 and the capacitances C1 and C2 are changed, the movement of the screen is not affected even if backlash in the radial direction is generated in a spindle 15.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a capacitance type length measuring device that converts an amount of mechanical displacement into an electrical signal as a change in capacitance.
In particular, it relates to a length measuring device that is not affected by variations in the permittivity of a dielectric between electrodes.

<Prior Art> As a conventional capacitance type length measuring device of this kind, there is one having a detection section as shown in FIG.

The detecting section of this length measuring device consists of a ring electrode 1.2 which is arranged adjacently through an insulating sheet 5, and a spindle which is arranged concentrically within this ring electrode 1.2 and supported by a bearing 8. A cylindrical common core wire is attached to the outer periphery of 7 with an insulating material 6 in between. 3, and a lead wire 4 for taking out the current induced in this common core electrode 3.

Ring electrode 1.2 and common core electrode 3 in this length measuring device
Capacitors C1 and C are formed between them, respectively.
The dielectric materials of the capacitors C1, , C, are made of the same material (air).

Also, the phase difference of 180 at the same frequency is applied to the electrodes 1.2 and 1.2.
Constant sinusoidal voltages V1 and Vr, which are in opposite phases and have the same peak value, are applied, respectively.

In this length measuring device, when the spindle 7 moves and the common core electrode 3 moves, a current i2 is generated in the common core electrode 3, and the capacitance of the capacitor C8Cr is changed to c. , c, the following relationship holds true.

C 11 V s + C r Vr ” a 1 m
Here, a is a positive proportionality constant and V, -V, so the current i generated in the common core electrode 3 is 1m = Vr (Cr Cs ), /a... (1
〉

In FIG. 6, X indicates the displacement of the spindle 7, that is, the common core electrode 3.6Here, this spindle 7 is the ring electrode 4F! 1. Direction of insertion into 2 (right direction in the diagram)
The displacement X toward C. is positive, the displacement X in the direction of extraction (to the left in the figure) is negative; The displacement X is set to zero when the capacitance C. , Cr is the capacitance Co, then the capacitance c. , c, and the displacement X are as follows.

c. =1εb. X+cg ・− − (2) c,=ε
b, X10c. )...(3) This ε is the capacitor C
1. Permittivity of dielectric material of C, b. , b, is a positive proportionality constant.

Next, this formula (2). Substituting (3) into equation (1), i@ = V , ε(b.+b,)X・−・(4)
Therefore, if the charge rate ε is constant, the current i. ．． will be directly proportional to the displacement X. Therefore, this current i. The amount of displacement X can be obtained by converting with an electronic device,
In the conventional E11 length machine, the displacement amount X is determined as described above.
It was displayed in search of.

<Problems to be Solved by the Invention> In the conventional example described above, the flow i. ．． The length is measured by detecting the capacitor C. The condition is that the dielectric constant ε of the dielectric material in , C, is constant.

That is, the conventional capacitor C. , C, is air, and the measurement environment, such as temperature, humidity, etc. When the density (atmospheric pressure) changes, the dielectric constant also changes, and the value of the current i for the same displacement X changes.

For this reason, when making precise measurements, it has been necessary to calibrate it in accordance with the measurement environment.

Also, the proportionality constant b. in equations (2>, (3), (4))
br are respectively capacitors C. ．． , C, is a constant determined by the inner diameter dimensions of the ring electrodes vf11, 2, the outer diameter dimension of the common core electrode 3, and the spacing thereof.

Therefore, the inner diameter of the ring electrodes 1 and 2 and the common core electrode f
If the outer diameter of fi3 is not made strictly the same, the same change 1 [
It is not possible to obtain the same current iffi for X.

However, this is extremely difficult, and therefore, in order to connect a plurality of detection units to the same electronic device, it is necessary to calibrate the electronic device in accordance with each detection unit.

Furthermore, if a detection unit is attached to each channel of a two-channel electronic device and a sum-difference calculation is performed, it is necessary to calibrate each channel according to each detection unit as described above. There was also the problem that accurate measurements would not be possible if the detection unit was sometimes connected to a channel that was not tuned to the one that was tuned.

The present invention is based on temperature. It is an object of the present invention to provide a capacitance type length measuring device that is not affected by changes in the measurement environment such as humidity and atmospheric pressure, and has a detection section that can be connected to an electronic device without being calibrated. .

<Means for Solving the Problems> The capacitive length measuring instrument of the present invention includes first and second cylindrical ring electrodes arranged on the same center line and adjacent to each other in an insulated state. a cylindrical third ring electrode arranged on the same center line as these, a cylindrical common core electrode arranged concentrically with these, the first and second ring electrodes, and a common core electrode. a screen having a window movable along the central axis between the first and second ring electrodes and the common core electrode through the window of the screen; first and second measurement capacitors C1, respectively; A reference capacitor C3 is formed between the third ring electrode and the common core electrode.

A first reference square wave voltage E and a second reference square wave voltage E2 having the same frequency and opposite phase are applied to the first and second ring electrodes, respectively.

Further, a measurement square wave voltage E3 having the same frequency and phase as the first or second reference square wave voltage is applied to the third ring electrode.

Also, the first and second reference square wave voltages Em, E2 are equal to the capacitance c10 of the first measurement capacitor CI and the first reference square wave voltage E! when the displacement X of the screen is zero. product C
IOE l, the capacitance C20 of the second measurement capacitor C2 and f? of the second reference square wave voltage E2. jczoE
It is set so that the sum with 2 becomes zero.

Furthermore, the measuring square wave voltage E3 is such that when the capacitances c10, C20 of the first and second measuring capacitors C1, C2 change due to the displacement of the screen, the feedback voltage E1 induced on the common core electrode becomes zero. It is varied by switching alternately between a constant DC voltage and a variable measured DC voltage Eo by means of an electronic device.

Effect> In the capacitive length measuring device of the present invention, the measurement square wave voltage E3 is varied so that the feedback voltage Etn induced in the common core electrode becomes zero.

That is, the feedback voltages E, . , to zero, the first and second
Measuring capacitor C. , C2 and reference capacitor C3 respectively vary the measured square wave voltage E3 so as to make the sum of the currents induced in the common core electrode zero.

In the present invention, first and second measurement capacitors C1,
Since the first and second reference square wave voltages E1 and E2 respectively applied to C2 are voltages with opposite phases, the currents induced thereby cancel each other out.Furthermore, when the displacement X is zero, , the currents c + oE 1 and C2[IE2 induced by the capacitors C1 and C2 are set to be equal.

Under this condition, when the displacement X is zero, the currents induced by the first and second measurement capacitors C1, C2 are equal and their sum is zero. Therefore, in order to make the current induced by reference capacitor C3 zero, i.e. C3E
Since 3=O, the measured square wave voltage E3 becomes zero.

Also, the screen is displaced and its window moves, and the first and second measurement capacitors C1 and C2 formed through this window are
When one of the capacitances Cl, c2 decreases and the other increases, the absolute value of the sum of the currents induced by them increases. Therefore, in order to make the sum of the induced currents zero, the measurement square wave voltage E, applied to the reference capacitor C3 is increased to the first and second measurement capacitors C1. It is necessary to induce a current in a direction that cancels the sum of the induced currents by C2, and this voltage E3 is increased by the electronics.

In this manner, the length measuring device according to the present invention has a proportional relationship in which the measured square wave voltage E3 gradually increases from zero in accordance with the displacement of the screen.

In particular, the measured square wave voltage E3 in the present invention is determined as a capacitance ratio as described later, so it is not affected by changes in the dielectric material, and the first to third ring electrodes and the common core electrode are not movable. Their positional relationship remains unchanged, and by simply adjusting the capacitance c3 of the reference capacitor C3, it is possible to obtain the same measured square wave voltage E3 for the same displacement. By adjusting in this way, there is no need to calibrate errors even if a plurality of detection units are connected to the same electronic device.

Example Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a schematic explanatory diagram showing the structure of a detection section of an rIp capacitance type length measuring device according to an embodiment of the present invention.

9, 10, and 11 are cylindrical first to third ring electrodes. The first to third ring electrodes 9 to 11 are arranged so that their centers are located on the same center line.

Further, the first and second ring electrodes 9 and 10 are arranged adjacent to each other with a ring-shaped insulator 14 in between.

■2 is a cylindrical common core electrode, and these electric currents fl9 to 1 are arranged along the central axis of the first to third ring electrodes 9 to 1.
1 is inserted therethrough.

13 is a screen, which is integrally attached to the spindle 15 supported by a bearing 16.

As shown in the cross-sectional views of FIGS. 2(a) and 2(0), this screen 13 has a cylindrical shape, and a window 13a is provided on its outer peripheral wall.

Further, this screen 13 is displaced along the center line between the first and second ring electrodes i9, 10 and the common core electrode 12 as the spindle 15 is displaced.

The first and second ring electrodes 9 and 10 and the common core electrode 1
2 are connected through the window 13a of the screen 13 to the first and second measurement capacitors CI. C2 is formed, and the third ring electric 8i! 11 and common core electric f! A reference capacitor C3 is formed between the reference capacitor C3 and the reference capacitor C3. These first and second measurement capacitors C1, C2 and reference capacitor C3
The capacitances of are CI + C 2 and c
3, and the capacitance Cl, C2 is screen 1
3, the first and second ring wires W9.10 and the common core wire 'If!' face each other through the window 13a. It can be varied by changing the area of 12.

Note that the dielectric materials in the capacitors C and C3 in this embodiment are all air.

Further, first and second reference square wave voltages E1 and E2 and measurement square wave voltage E3 are applied to the first to third ring electrodes 9 to 11, respectively.

This first reference square wave voltage E1 is always constant, and the second reference square wave voltage E1 is always constant.
The reference square wave voltage E2 has the same frequency as the voltage E, and is set to a voltage of opposite phase with a phase difference of 180 degrees, which is also always kept constant.

The measurement square wave voltage E3 is a voltage having the same frequency and the same phase as the voltage E or E2, and in this embodiment, it is in the same phase as the voltage E1. Note that this voltage E3 is connected to the capacitor Cl
The feedback voltage E induced in the common core electrode 12 by ~C3
It is varied by an electronic device, which will be described later, so that 7 becomes zero.

Furthermore, if the capacitances Cl and C2 are respectively ClO+c20 when the change X of the screen l3 is zero, then
The voltage E1 is adjusted so that c10EI +C20E2 =O.
Or E2 is adjusted in advance.

Next, the relationship between the displacement X in the detection section of the capacitive length measuring device of this embodiment and the measured square wave voltage E3 will be explained using a mathematical formula.

When the spindle 15 moves and the screen 13 is displaced rightward in FIG. 1, the capacitor C. , C2, the capacitance Cl, C2 changes.

At the same time, an electronic device to be described later operates to vary the measured square wave voltage E3 so that the feedback voltage Em induced in the common core electrode 12 becomes zero. That is, capacitor C1~
Assuming that the currents induced in the common core electrodes 12 by C3 are 11+12+13, the measured square wave voltage E3 is varied so as to satisfy the following equation.

i1 +i2 +i3 =O... <5) The capacitances of the capacitors C1 to C3 are Cl to C3, respectively, and the first to third ring voltages tf! Since the voltages applied to 9 to 11 are El to E3, respectively, equation (5) can be expressed as follows.

Cl Em +c2 E2 +c3 E3 =0 Therefore, the measured square wave voltage E3 can be expressed as follows.

E3 = (CI El +C2 E2)/C3(
6> On the other hand, when the spindle 15 moves to the right in FIG. 1 and the direction in which the screen 13 moves accordingly is expressed as a positive displacement X, the capacitor C1 when X=O
, C2 is c10+C20, so the capacitance CI+c2 can be expressed by the following equation.

C+-c+o(1 bl X) ... (7) C2
=C2o(1+b2X)... (8) Here b
1 and b2 are positive proportionality constants determined by the inner diameters of the first and second ring electrodes 9.10 and the outer diameter of the common core electrode 12, respectively.

Substituting these equations (7) and (8) into equation (6>), the measured square wave voltage E3 is as follows: E3 = (C+oE+ +C20E2 (b+
clOE1b2C20E2 )X)/C3...
It can be expressed as (9).

When X=O in advance, C I+)E 1 + C 20E
Since it is set so that 2 = Q, under this condition, equation (9>) becomes the following equation.

E3 “clOEI (bl +b2) X/C3
(10) From equation (10), voltage E3 is proportional to displacement X, and its proportionality constant α is α=c10EI (bl +b2) X/C3(1
1) becomes.

As shown in equation (10), the voltage E3 is expressed as a capacitance ratio such as C+o/c3, so if the capacitors CI to C3 are horizontally connected with the same dielectric material, the influence of the change in dielectric constant can be avoided. I won't receive it at all.

Further, in this embodiment, when the capacitance 63 of the capacitor C3 is adjusted, the proportionality constant α changes.

That is, by simply adjusting this capacitance C3, it is possible to make the proportionality constant α equal to the same value, and it is possible to connect different detection units to a common electronic device without calibration.

To adjust the capacitance C3, first make a rough adjustment using the adjusting screw 18 with a large diameter, and then make a fine adjustment using the adjusting screw 19 with a small diameter.

In addition, the capacitors Cl to C3 in this embodiment are cylindrical first to third ring capacitors vi!, respectively. 9~l1 and the cylindrical common core electric f! 12, and the first to third ring electrodes 9 to 11 and the common core electrode 12.
are fixed so that their central axes coincide.

Therefore, even if the central axes of the ring electrode and the core electrode are slightly shifted due to an impact, etc., the fluctuations in b1 and b2, which constitute the proportionality constant in equation (11), will be extremely small.
There is almost no effect on voltage E3.

Furthermore, in this embodiment, the screen 13 is connected to the ring electrodes 9 to 11 and the common core electrode f! The capacitances CI and C2 change only when the screen 13 moves along the central axis of the screen 12, and even if play in the radial direction occurs in the spindle 15, such movement of the screen 13 in the radial direction will almost always change the capacitance. It does not affect C1 and C2.

In this regard, in conventional devices, the spacing between the common core electrode and the ring electrode changes due to the play of the spindle in the radial direction, which has a great effect on the capacitance.

Also, basically in this detection section, the common core electrode 12
The feedback voltage Em induced in the excitation square wave voltage E1~
It is necessary to prevent the voltages E1 to E3 from influencing each other, and it is also necessary to prevent the voltages E1 to E3 from influencing each other.

Therefore, in this embodiment, the wires connecting the electronic device and the detection section for guiding the voltages E1 to E1 and Em are connected to the shields 21 to 24.
It is shielded by

In particular, the line leading the feedback voltage Em is required to be completely shielded, but it is also possible to simplify the shielding by the following method.

That is, as shown in FIG. 3, the input side of the impedance transformer 26 and one side of the discharge resistor 27 are connected to the common core electrode 12 in the detection section, and the f side of the discharge resistor 27 is grounded. At the same time, the output side of the impedance transformer 26 is connected to an electronic device. Thereby, the impedance between the impedance transformer 26 provided in the detection section and the electronic device can be reduced, and the shield can be simplified.

Therefore, if high sensitivity and high precision are not required, it becomes possible to shield the wires leading the voltages E+, E2, E3, and EY' all at once, instead of one by one.

However, high sensitivity. If high precision is required, it is desirable to shield each wire individually.

In addition, by making the first to third ring electrodes 9 to 11 and the common core electrode 12 of the same material, the thermal expansion of the parts becomes the same, preventing unbalance of the capacitor due to temperature changes, and improving the detection part. Temperature performance can be improved.

FIG. 4 is a diagram showing the circuit configuration of an electronic device that applies a voltage to the detection section, and FIG. 5 is a time chart showing the phase relationship of the output voltage.

30 is an oscillator that outputs a square wave voltage Eosc as a reference. This oscillator 30 may be either a crystal type or a CR type, and in the case of a crystal type, a frequency divider may be used to obtain a desired frequency.

31 and 32 are electronic switches, the electronic switch 31 switches between the DC voltage E and the ground level in response to the voltage E OSC and outputs it as a first standard, quasi-square wave voltage E1; Voltage E between DC voltage -E, and ground level. 5c, it is switched and output as the second reference square wave voltage E2.

33 is an input amplifier that inputs the feedback voltage Effi;
34 inputs the output voltage E4 and outputs the voltage E. S. every half cycle (tII, j 12+ t13... and t2
1. 35 is a differential integrator that inputs the demodulated voltage, and 36 is a differential integrator that inputs the demodulated voltage, and 36 is a voltage E between the output DC voltage Eo and the ground level.
. It is an electronic switch that switches in response to sc and outputs the measured square wave voltage E3.

In the above electronic device, the voltages Em and E2 are square wave voltages having the same frequency and opposite phases because DC voltages of different polarities are intermittently output from the electronic switches 31 and 32 at the same timing.

Further, the voltage E3 is intermittently applied to the electronic switch 36 at the timing of the DC voltage Eo from the differential integrator 35 and the voltage EOSC.
It is synthesized by outputting from.

This DC voltage E. is synthesized as follows.

First, the feedback voltage E, is amplified by the input amplifier 33, and the amplified voltage E4 is demodulated every half period by the demodulator 34. Furthermore, if the demodulated voltage is not zero, the DC voltage Eo output by the differential integrator 35 will vary as a function of the amplitude and polarity of the demodulated voltage until the demodulated voltage reaches zero.

As a result, voltage E3 is DC voltage E. together with differential integrator 3
5 until the input voltage reaches zero.

As a result, the voltage E satisfies the relationship of equation (10), is directly proportional to the displacement X, and has a positive proportionality constant.

According to this embodiment, the measured square wave voltage E3 proportional to the displacement of the spindle is expressed as a ratio of capacitances, so if the dielectric materials of the 3g capacitors 01 to C3 are the same, the dielectric constant is not affected at all.

Therefore, it is not affected by changes in the measurement environment and can perform highly accurate measurements without calibration or correction due to changes in dielectric constant.

Furthermore, since the central axes of the three ring electrodes and the common core electrode in the present invention are aligned and fixed, the influence of their positional deviations on the measured square wave voltage E3 can be almost eliminated. , it is possible to provide a detection unit having substantially constant characteristics.

Furthermore, since the characteristics of the plurality of detection sections can be made uniform simply by adjusting the reference capacitor C3, the plurality of detection sections can be connected to a common electronic device without recalibration.

Furthermore, the positions of the three ring electrodes and the common core electrode are fixed, and the screen integrated into the spindle moves between them in the direction of the central axis, so even if radial play occurs in the spindle, it will not be affected. , there is almost no effect on the positional relationship between the ring electrode and the common core electrode or the position in the central axis direction of the screen window, and there is no drop in accuracy due to such backlash.

Further, the impedance transformer and the discharge line can be shielded together within the detection section.

Further, ring electrodes 9 to 9 forming capacitors CI to C3
By making the materials of the common core electrode 11 and the common core electrode 12 the same, it is possible to improve the temperature performance of the detector.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the horizontal construction of the detection part of a capacitance type length measuring device according to an embodiment of the present invention, and Fig. 2 (a) and (b) are central longitudinal sections of the screen shown in Fig. 1. Fig. 3 is a diagram showing a state in which an impedance transformer and a discharge resistor are attached to the detection unit shown in Fig. 1, and Fig. 4 is a capacitance according to an embodiment of the present invention. Figure 5 is a time chart showing the voltage phase relationship in Figure 4. Figure 6 is a diagram showing the structure of the detection section of a conventional capacitive length meter. 9 ・ 1 0 ・ 1 1 ・ 1 2 ・ 1 3 ・ 1 4 ・ 1 5 ・ 2 1 , 3 0 ・ 3 1 , ・First ring electrode, ・Second ring electrode, ・Third ring electrode. , ・Common core electrode, ・Screen, ・Insulator, ・Spindle, 22, 23.24・ ・Oscillator, 32.36...Electronic switch, ・Shield, 3 3 34 3 5 CI C2 C3 CI Em E2 E3 Em C2 input amplifier, demodulator, differential integrator, first measurement capacitor, second measurement capacitor, reference capacitor, C3...capacitance, first reference square wave voltage, second reference square wave voltage, measurement square wave voltage , Feedback voltage. Fig. 2 (A) A0 Fig. 2 (0) Fig. 5 Fig. 6

Claims (3)

[Claims] (1) Cylindrical first and second ring electrodes arranged on the same center line and adjacent to each other in an insulated state, and a cylindrical ring electrode arranged on the same center line as the first and second ring electrodes. A third ring electrode, a cylindrical common core electrode arranged concentrically within the first to third ring electrodes, and a cylindrical common core electrode having a cylindrical shape with a window provided on its outer periphery;
an electrically grounded screen movable along their central axes between the ring electrode and the common core electrode, the first and second ring electrodes and the common core electrode being connected to each other through a window in the screen; a reference capacitor C_3 is formed between the third ring electrode and the common core electrode, and a first reference square capacitor C_3 is formed between the third ring electrode and the common core electrode. Wave voltage E_
1 is applied to the second ring electrode, and a second reference square wave voltage E_1 having the same frequency and opposite phase as the first reference square wave voltage E_1 is applied to the second ring electrode.
_2 is applied to the third ring electrode, and the first or second
Measured square wave voltage E with the same frequency and in phase as the reference square wave voltage
_3 is applied and the displacement X of the screen is zero, the capacitance c_1_0 of the first measurement capacitor C_1 when the displacement X is zero and the first reference square wave voltage E_1.
c_1_0E_1, the capacitance c_2_0 when the displacement of the second measuring capacitor C_2 is zero, and the second measuring capacitor C_2.
The first and second reference voltages E_1 and E_2 are set such that the sum of the product c_2_0E_2 of the reference square wave voltage E_2 is zero.
and the capacitance C_ of the first and second measurement capacitors C_1 and C_2 is determined by the displacement of the screen.
1. Measure square wave by switching alternately between a constant DC voltage and a variable measured DC voltage E_0 by means of an electronic device such that when C_2 changes, the feedback voltage E_m induced in the common core electrode becomes zero. A capacitive length measuring device characterized in that voltage E_3 is variable. (2) The input side of the impedance transformer and one side of the discharge resistor are connected to the common core electrode, the output side of the impedance transformer is connected to the electronic device, and the other side of the discharge resistor is grounded. The capacitance type length measuring device according to claim 1. (3) The capacitive length measuring device according to claim 1 or 2, wherein the first to third ring electrodes and the common core electrode are made of the same material.