JPH04305104A - Electrostatic capacity type length-measuring equipment - Google Patents

Abstract

PURPOSE:To enable cost to be reduced, at the same time stability and temperature characteristics of a circuit to be improved, and a thickness dimension of a detection portion to be reduced by eliminating a need for an electronic circuit for converting a proportional constant and then displaying a displacement using a direct-measurement rectangular waveform voltage. CONSTITUTION:A flat-plate shaped movable core electrode 15 is inserted and placed between opposing flat-plate shaped measurement electrodes 10 and 11, a flat-plate shaped fixed core electrode 14 is provided at this movable core electrode 15, and at the same time a measurement capacitor is formed by the movable core electrode 15 and the measurement electrodes 10 and 11. When a capacitance changes since the movable core electrode 15 enters the measurement capacitor through a spindle 25, an amount of mechanical displacement is detected by allowing a change in a measurement rectangular waveform voltage E3 with an electronic device so that the feedback voltage Em which is induced at both core electrodes is equal to 0 to be measured using a voltmeter, etc.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention relates to a length measuring device that converts mechanical displacement into an electrical signal as a change in capacitance.
The present invention relates to a length measuring device in which the relationship between displacement and capacitance is linear and is not affected by fluctuations in the permittivity of a dielectric between electrodes.

0002

2. Description of the Related Art A conventional capacitive length measuring device of this type has a structure as shown in FIG. Figure 1
0, the main parts of this length measuring device include a cylindrical reference electrode 1 and a measuring electrode 2, a cylindrical common core electrode 3 arranged concentrically within the electrodes 1 and 2, and an electrode. 1 and a cylindrical screen 4 that moves along the center between the core electrode 3 and the core electrode 3.

A reference square wave voltage Vr and a measurement square wave voltage Vm are applied to the electrodes 1 and 2, respectively. These voltages Vr and Vm have the same frequency and a phase difference of 180° (opposite phase).
The voltage Vr is a square wave voltage, and the voltage Vr is constant and the voltage Vm is variable.

In the detection section of the length measuring device having such a configuration, a measurement capacitor Cm (capacitance cm) is formed between the electrode 1 and the core electrode 3, and a capacitance cm is formed between the electrode 2 and the core electrode 3. A reference capacitor Cr (capacitance cr) is formed.

In this length measuring device, when the screen 4 is displaced and the capacitance cm of the measuring capacitor Cm changes, the electronic device changes the measuring square wave voltage Vm so that the AC voltage induced in the core electrode 3 becomes zero. be done. That is, this applies a reference square wave voltage V to the measurement capacitor Cm.
A current generated in the core electrode 3 by applying r;
By applying the measurement square wave voltage Vm to the reference capacitor Cr, the measurement square wave voltage Vm is changed so that the sum with the current generated in the core electrode 3 becomes zero. From this relationship, a relational expression as shown in Equation 1 is established.

[0006]

[Math 1]

Here, in Equation 1, the voltages Vm and Vr have different signs because their phase difference is 180°, and Vr=-
When expressed as Vr', it becomes Equation 2.

[0008]

[Math 2]

In equation 2, the proportionality constant Vr'/cr is positive, and the relationship between the capacitance cm of the measuring capacitor Cm and the measured square wave voltage Vm is that as the capacitance cm increases, the measured square wave voltage Vm also increases, and the capacitance cm When Vm decreases, the measured square wave voltage Vm also decreases.

In FIG. 10, the screen 4 is moved so as to be inserted into the electrode 1 (moved to the right in the figure, in the X-axis direction).
If the displacement X is positive, then the measurement capacitor Cm
The capacitance cm is expressed by equation 3.

[0011]

[Math 3]

Here, co represents the capacitance of the measurement capacitor Cm when the screen 4 is at the reference position (X=0), and a is a proportionality constant. Number 2 above
From Equation 3, the measured square wave voltage Vm can be expressed as a linear expression of the displacement X as shown in Equation 4.

[0013]

[Math 4]

As shown in equation 4, the proportionality constant -Vr'aco
/cr is always a negative value, and as a result, as shown in FIG. 11, when the displacement X increases, the measured square wave voltage Vm decreases,
As the displacement X decreases, the measured square wave voltage Vm will increase.

In this way, the displacement X of the screen 4 is determined by the electrode 1
If the direction of insertion is positive, the relationship between increase and decrease in the displacement X and the measured square wave voltage Vm will be reversed, and although the displacement become.

Generally, a spindle is directly connected to the screen 4, and the direction in which the spindle is pushed in, that is, the direction in which the screen 4 is inserted into the electrode 1, is indicated as a positive value.

Therefore, in the relationship between the displacement It is necessary to further transform the measured square wave voltage Vm so that its proportionality constant is positive while maintaining a linear relationship with X. For this reason, electronic circuits such as highly accurate arithmetic circuits were required for conversion.

[0018]

[Problems to be Solved by the Invention] As mentioned above, in the conventional capacitive length measuring device, it is necessary to use an electronic circuit to display the displacement X using the actual measured square wave voltage Vm. It is. The addition of such an electronic circuit not only leads to an increase in cost, but also causes problems in that it becomes a factor that deteriorates the stability and temperature characteristics of the circuit.

[0019] Furthermore, adjustment of the measurement reference point in conventional capacitance type length measuring instruments can only be performed using an electronic device.
When a plurality of length measuring instruments are configured using the same electronic device, it is necessary to reset the measurement reference point for each detection section of each length measuring instrument.

Furthermore, in the detection section of the conventional capacitive length measuring device, the reference electrode 1, the measuring electrode 2, and the screen 4 are each cylindrical, and the core electrode 3 is cylindrical. Although the width dimension (Y-axis direction) is generous, there is a problem in that it cannot be used in cases where the front and rear thickness dimensions (Z-axis direction) need to be small.

The present invention has been made to solve the above-mentioned problems, and makes it possible to display displacement using a directly measured square wave voltage without the need for an electronic circuit for proportional constant conversion, and at the same time, it reduces costs. The object of the present invention is to obtain a capacitance type length measuring device which is designed to reduce the size of the device, improve circuit stability and temperature characteristics, and reduce the thickness of the detection section.

[0022]

[Means for Solving the Problems] A capacitance type length measuring device according to the present invention transmits mechanical displacement to a pair of flat measuring electrodes facing each other in parallel to which a reference square wave voltage is applied. a flat movable core electrode whose one end side is fixed to the spindle via an insulating member so as to be line symmetrical to the axis of the spindle, and which moves parallel to the measurement electrodes to form a measurement capacitor with the measurement electrodes; and a flat plate-shaped fixed core electrode electrically connected to one end side of the movable core electrode and in which a feedback voltage is induced together with the movable core electrode, and forming a correction capacitor by opposing the fixed core electrode, and a flat correction electrode to which a complementary square wave voltage of opposite phase is applied at the same frequency as the reference square wave voltage and facing the fixed core electrode to form a reference capacitor, and the reference square wave voltage A planar reference electrode is applied with a measurement square wave voltage of opposite phase at the same frequency as , and when the movable core electrode enters the measurement capacitor through the spindle and its capacitance changes, the movable core electrode and an electronic device for varying the measured square wave voltage so that the feedback voltage induced in the fixed core electrode is zero.

[0023]

[Operation] In the capacitance type length measuring device of this invention, the movable core electrode moves so as to enter into the measurement capacitor, and when the capacitance of the measurement capacitor changes, it is guided to the movable core electrode and the fixed core electrode by the electronic device. The measured square wave voltage is varied such that the feedback voltage is zero,
The amount of mechanical displacement is detected by measuring this changing measurement square wave voltage with a voltmeter or the like.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing a schematic configuration of an embodiment of the present invention, FIG. 2 is a front view, and FIG. 3 is a cross-sectional view taken along the line B-B in FIG.
In the figure, 10 and 11 are a pair of flat measurement electrodes facing each other in parallel, 12 is a flat correction electrode, 13 is a flat reference electrode, and 14 is a flat fixed core electrode. A correction electrode 12 and a reference electrode 13 are provided in parallel on one surface of the electrode 14. 15 is the measurement electrode 10
, 11 in parallel, the measuring electrodes 10, 11
One end of the movable core electrode 15 is electrically connected to the fixed core electrode 14 via a conductive member 28 and a spring 29. A measurement capacitor is formed between the measurement electrode 11 and the movable core electrode 15, a correction capacitor is formed between the correction electrode 12 and the fixed core electrode 14, and a correction capacitor is formed between the reference electrode 13 and the fixed core electrode. A reference capacitor is formed between the reference capacitor 14 and the reference capacitor 14. A spindle 25 is fixed to one end of the movable core electrode 15 through an insulating member 19 so that its center axis coincides with the movable core electrode 15, and is electrically grounded.The spindle 25 is slidably supported by a bearing 20. There is. 17,1
8 is a capacitance adjustment screw provided on the correction electrode 12 and the reference electrode 13; 5 is a guide rod attached to the spindle 25; 6 is a guide member having a guide groove 16 for guiding the sliding movement of the guide rod 5; 7; 8 is a measuring electrode 10,
The insulating members 9 and 26 are insulating parts attached above and below the fixed core electrode 14, the correction electrode 12, and the reference electrode 13.

The capacitances of the measurement capacitor, correction capacitor and reference capacitor are c1, respectively.
c2, c3. When the spindle 25 is pushed in, the movable core electrode 15 is configured to move into the measurement capacitor. This movable core electrode 15 moves together with the spindle 25 to measure the capacitance c of the measuring capacitor.
1 changes, the feedback voltage E induced in the movable core electrode 15 and the fixed core electrode 14 by the electronic device described later
The measured square wave voltage E3 is varied such that m becomes zero. Note that the direction in which the movable core electrode 15 enters into the measurement capacitor is taken as positive.

The measurement capacitor, correction capacitor, and reference capacitor are made of the same dielectric material (air), and the measurement electrode 11, correction electrode 12, and reference electrode 13 have a reference square wave voltage E1 and a complementary square wave voltage E2, respectively.
and measurement square wave voltage E3 are applied. The reference square wave voltage E1 and the complementary square wave voltage E2 are set to square wave voltages with the same frequency and a phase difference of 180° (opposite phase), and the reference square wave voltage E1 and the measurement square wave voltage E3 have the same frequency. is set to an opposite phase square wave voltage. Further, the reference square wave voltage E1 and the supplementary square wave voltage E2 are constant voltages that do not change, and the measurement square wave voltage E3 is a voltage that is varied by an electronic device to be described later.

Further, if the capacitance c1 when the displacement X of the spindle 25 is zero is c0, then c0|E1|=
Either or both of the complementary square wave voltage E2 and the capacitance c2 can be adjusted in advance so that the relationship c2|E2| holds true.

Next, it will be explained that the change in the displacement X and the measurement square wave voltage E3 in the capacitive length measuring device is linear and proportional. If the spindle 25 moves, thereby displacing the movable core electrode 15 into the measuring capacitor, this capacitance c1 will also change. At the same time, the electronic device operates to change the measured square wave voltage E3 so that the feedback voltage Em induced in the movable core electrode 15 and the fixed core electrode 14 becomes zero. i.e. measurement capacitor, correction capacitor,
The currents induced in the movable core electrode 15 and the fixed core electrode 14 by the reference capacitor, respectively, are i1, i2,
When i3, the measured square wave voltage E is set so as to satisfy Equation 5.
3 is changed.

[0029]

[Math 5]

This number 5 can be expressed as shown in number 6.

[0031]

[Math 6]

Therefore, the measured square wave voltage E3 can be expressed as shown in Equation 7.

[0033]

[Math 7]

Measurement square wave voltage E3 and reference square wave voltage E1
is a square wave voltage of opposite phase, and the measured square wave voltage E3
Since the complementary square wave voltage E2 is a square wave voltage of the same phase, if E1'=-E1 is replaced and Equation 7 is rewritten, the measured square wave voltage E3 becomes as shown in Equation 8.

[0035]

[Math. 8]

On the other hand, when the spindle 25 moves to the right in FIG. 1 and displacement X is expressed with the direction in which the movable core electrode 15 comes out of the measurement capacitor as positive, the capacitance of the measurement capacitor when X=0 is expressed as c0. Then, the capacitance c1 can be expressed by Equation 9.

[0037]

[Math. 9]

Here, b is the distance between the measurement electrode 11 and the movable core electrode 15 forming the measurement capacitor, and the distance between the measurement electrode 11 and the movable core electrode 15.
, is a positive constant determined by the geometric dimensions such as the width of the movable core electrode 15 and the quotient c0 /ε obtained by dividing the capacitance c0 by the dielectric constant ε of the dielectric between the electrodes.

By substituting equation 9 into equation 8, the measured square wave voltage E3 can be expressed as equation 10.

[0040]

[Math. 10]

[0041] Then, coE1'b/c3 of several 10 is α
If (c0 E1'-c2E2)/c3 is replaced by β, Equation 10 is transformed into Equation 11.

[0042]

[Math. 11]

In this embodiment, c2|E2|
=c0 |E1|, which can be replaced with c2E2=c0 E1', so when this is substituted into equation 11, β=0. Therefore, the measured square wave voltage E3 can be expressed as Equation 12.

[0044]

[Math. 12]

Since this proportionality constant α is a positive value, the relationship between the measured square wave voltage E3 and the displacement X is as shown in FIG. 4, as shown in FIG. When the displacement X increases and the displacement X decreases, the measured square wave voltage E3 decreases in direct proportion to the displacement X, and when the displacement X is zero, the measured square wave voltage E3 also becomes zero. In addition, as shown in Equation 10, the measured square wave voltage E3 is c0 /c3,
Since the capacitance ratio is determined by the capacitance ratio c2/c3, if the measurement capacitor, correction capacitor, and reference capacitor are made of the same dielectric material, they will not be affected by the dielectric constant at all. Also, c2 | E2 | ≠
In the case of c0|E1|, β is a non-zero constant, so the measured square wave voltage E3 increases by β, and the displayed value of the measured length appears to be that the point at X=0 is only β/α. It will move to the negative side. Therefore, c2|E2|=c0
It is necessary to set the relationship |E1|, but in order to set it in this way, it is necessary to adjust either or both of the capacitance c2 and the complementary square wave voltage E2 as described above. To adjust the capacitance c2, use the adjustment screw 1 attached to the correction electrode 12.
7. Generally, electrical components such as potentiometers with good temperature characteristics are used on the electronic device side to adjust the complementary square wave voltage E2, but since they do not remain unchanged even when the temperature changes, very good temperature characteristics are used. If characteristics are required, the absence of electrical components such as potentiometers is preferred. By providing a correction capacitor in the detection section, it is possible to adjust the zero point of displacement X without using electrical parts such as a potentiometer, and the zero point of displacement It is possible and easy. Note that it is difficult to attach an electrical component such as a potentiometer for changing the supplementary square wave voltage E2 to the detection section side. Further, by providing the adjustment screw 17 on the correction capacitor and the correction capacitor, the measurement origin of any detection unit can be made to coincide with each other.

The capacitance c3 of the reference capacitor is adjusted by the adjustment screw 18. By adjusting the capacitance c3 of each detector, α can be set to the same value, and different detectors can be connected to a common electronic device without recalibration.

The measurement capacitor is calibrated with the measurement electrodes 10, 11 and the movable core electrode 15 arranged in parallel. The movable core electrode 15 moves in parallel. Furthermore, the movable core electrode 15 has its central axis connected to the spindle 25.
The spindle 25 is fixed to one end side of the spindle 25 via an insulating member 19 so as to substantially coincide with the central axis of the spindle 25.
When the movable core electrode 15 is pushed in, the movable core electrode 15 also moves on the central axis of the spindle 25. Therefore, when the guide rod 5 is slid along the guide groove 16, the spindle 25 rotates very slightly due to the gap between the guide groove 16 and the guide rod 5, and as the spindle 25 rotates, the movable core electrode Even if 15 rotates, the variation in the proportionality constant b shown in Equation 12 becomes extremely small, and has almost no effect on the measured square wave voltage E3.

FIG. 5 is a block diagram showing the circuit configuration of an electronic device that applies voltage to the detection section, and FIG. 6 is a time chart showing the phase relationship of the output voltage. In the figure, 30 is an oscillator that outputs a reference square wave voltage Eosc.
This oscillator 30 may be either a crystal type or a CR type, but in the case of a crystal type, the frequency is generally high, so a frequency divider is used to obtain the desired frequency. DC voltage Er
and ground level is the output voltage of the oscillator 30 Eosc
The reference square wave voltage E1 shown in FIG. 6 is obtained by switching with an electronic switch 31 controlled by
and ground level is the output voltage of the oscillator 30 Eosc
The supplementary square wave voltage E2 shown in FIG. 6 is obtained by switching with an electronic switch 32 controlled by .

E4 shown in FIG. 6 is the feedback voltage Em or E
m' is an AC voltage amplified by the input amplifier 33, and this AC voltage E4 is generated every half period (t1) of the square wave voltage Eosc.
1, t12, t13, t21, t22, t23...) by the demodulator 34 and input to the differential integrator 35. If the demodulated signal differs from zero, the differential integrator 35
The output DC voltage E0 of varies as a function of the amplitude and polarity of the demodulated voltage until the input to the differential integrator 35 reaches zero.

The measured square wave voltage E3 is the output voltage Eo between the output DC voltage E0 and a constant voltage (ground level in FIG. 5).
It is obtained by switching the electronic switch 36 at sc. Therefore, like the output DC voltage E0, the measured square wave voltage E3 also changes until the input to the differential integrator 35 reaches zero. The measured square wave voltage E3 thus obtained is directly proportional to the displacement of the movable core electrode 15, as described above.

Also, transients appear in the output DC voltage E0 due to undesired coupling and time delays, which occur at the switching points (sides) of the square wave and decay after a certain time. This transient condition reduces the stability of the output DC voltage E0, reduces the stability of the measured square wave voltage E3, and reduces the stability of the length measurement instrument's indication. For this reason,
For length measuring instruments that require very high stability, consideration must be given to eliminating the effects of transient conditions. This transient state is caused by the input amplifier 33
This can be removed by providing a transient suppressor between the demodulator 34 and the demodulator 34, and a highly stable measured square wave voltage E3 can be obtained.

FIG. 7 is a block diagram showing a case where a transient suppressor is provided in an electronic device that applies a voltage to a detection section, and FIG. 8 is a time chart showing the phase relationship of the output voltage. The reference square wave voltage E1 is connected between the DC voltage Er and the ground level by the output voltage Eosc, the time delay circuit 37 and the frequency 1.
The switching can be performed by an electronic switch 31 controlled by a frequency divider circuit 38 which divides the frequency by /2. Complementary square wave voltage E
2 is the output voltage E between the DC voltage -Er and the ground level.
osc, an electronic switch 32 controlled by a time delay circuit 37 and a frequency divider circuit 38 that divides the frequency by 1/2.
It is obtained by

In the simplest case, the transient suppressor 39 is an electronic switch, which controls the output voltage E, which is the clock signal of the oscillator 30.
The part that is not in a transient state (t01~
t02, t11-t12, t21-t22,...) are allowed to pass. This transient-free signal is input to the demodulator 34, and every cycle of the output voltage Eosc (t0, t2,
t4,... and t1, t3, t5...) and input to the differential integrator 35. When the demodulated signal differs from zero, the output DC voltage E0 of the differential integrator 35 varies as a function of the amplitude and polarity of the demodulated voltage until the input to the differential integrator 35 reaches zero.

The measured square wave voltage E3 is a voltage between the output DC voltage E0 and a constant voltage (ground level in FIG. 7).
sc, an electronic switch 36 controlled by a time delay circuit 37 and a frequency divider circuit 38 that divides the frequency by 1/2.
It is obtained by Therefore, like the output DC voltage E0, the measured square wave voltage E3 also changes until the input to the differential integrator 35 reaches zero. The measured square wave voltage E3 thus obtained is proportional to the displacement of the movable core electrode 15 and is completely unaffected by transients of the alternating current voltage E4.

Basically, it is necessary that the feedback voltage Em induced in the fixed core electrode 14 and the movable core electrode 15 is not affected by the excitation square wave voltages E1, E2, E3, and the excitation square wave voltage Em is It is also necessary to prevent the wave voltages E1, E2, and E3 from influencing each other. Therefore, the lines 21, 22, 23, and 24 connecting the detection section and the electronic device are shielded. When a correction capacitor and a reference capacitor are arranged in the detection section, the shielding of the line 24 to which the feedback voltage Em is guided can be simplified by connecting the fixed core electrode 14 to the input side of the impedance transformer 26 and the discharge resistor, as shown in FIG. The other side of the discharge resistor 27 is grounded, and the output side of the impedance transformer 26 is connected to the input amplifier 33 of the electronic device. This makes it possible to reduce the impedance between the impedance transformer 26 and the input amplifier 33, simplify shielding, and reduce the excitation square wave voltage E when high sensitivity and precision are not required.
1, E2, E3, Em' lines 21, 22, 23
, 24 can be shielded together. but,
E1, E2, E3 when high precision and high sensitivity are required.
, Em' can be further stabilized by using shields for each of the wires 21, 22, 23, and 24 to which they are guided. Note that by making the measurement electrodes 10 and 11, the correction electrode 12, the reference electrode 13, the movable core electrode 15, and the fixed core electrode 14 made of the same material, it is possible to improve the temperature performance of the detection section.

[0056]

As described above, according to the present invention, when the movable core electrode moves into the measurement capacitor by the spindle and the capacitance of the measurement capacitor changes, the feedback induced in the movable core electrode and the fixed core electrode. The measuring square wave voltage is changed by an electronic device so that the voltage becomes zero, and the mechanical displacement is detected by measuring this changing measuring square wave voltage with a voltmeter, so the proportional It is possible to display displacement using a directly measured square wave voltage without the need for an electronic circuit for constant conversion, and it also reduces costs, improves circuit stability and temperature characteristics, and improves the thickness of the detection part. This has the effect of making it smaller.

[Brief explanation of drawings]

FIG. 1 is a sectional view taken along the line A-A in FIG. 2, showing an embodiment of a detection section of a capacitive length measuring device according to the present invention.

FIG. 2 is a front view showing an embodiment of the detection section of the capacitive length measuring device.

FIG. 3 is a sectional view taken along line BB in FIG. 2;

FIG. 4 is a characteristic diagram showing the relationship between measured square wave voltage and displacement according to the present invention.

FIG. 5 is a block diagram showing an example of an electronic device for a capacitive length measuring device according to the present invention.

FIG. 6 is a time chart showing the phase relationship in FIG. 5;

FIG. 7 is a block configuration diagram showing another example of an electronic device for a capacitive length measuring device according to the present invention.

8 is a time chart showing the phase relationship in FIG. 7. FIG.

FIG. 9 is a circuit diagram in which an impedance transformer and a discharge resistor are attached to the detection section.

FIG. 10 is a cross-sectional view showing an example of a detection section of a conventional capacitive length measuring device.

FIG. 11 is a characteristic diagram showing the relationship between the measured square wave voltage and displacement of the detection unit in FIG. 10;

[Explanation of symbols]

10, 11 Measuring electrode 12 Correction electrode 13 Reference electrode 14 Fixed core electrode 15　Movable core electrode 25 Spindle

Claims (1)

[Claims] Claim 1: A reference square wave voltage is applied to flat measurement electrodes that face each other in parallel, and a spindle that transmits mechanical displacement, through an insulating member, one end of which is symmetrical to the axis of the spindle. a flat movable core electrode whose sides are fixed, which is inserted between the measurement electrodes and moves parallel to the measurement electrodes to form a measurement capacitor with the measurement electrodes;
A flat plate-shaped fixed core electrode is electrically connected to one end side of the movable core electrode and in which a feedback voltage is induced together with the movable core electrode, and a correction capacitor is formed by opposing the fixed core electrode, and the above-mentioned A flat correction electrode to which a complementary square wave voltage of opposite phase is applied at the same frequency as the reference square wave voltage and facing the fixed core electrode forms a reference capacitor, and has the same frequency as the reference square wave voltage. a plate-like reference electrode to which a measurement square wave voltage of opposite phase is applied at a frequency, and the movable core electrode enters into the measurement capacitor through the spindle and changes its capacitance, and the movable core electrode and the fixed an electronic device that varies the measured square wave voltage so that the feedback voltage induced in the core electrode becomes zero; A capacitive length measuring instrument characterized by a linear relationship between the amount of displacement and capacitance, and a proportionality constant of which is a positive value.