JPH04225102A - Capacitance type length measuring machine - Google Patents

Abstract

PURPOSE:To suppress the increase in cost and to make it possible to extend the measur ing range accurately by dividing a measuring electrode into two parts in response to a plurality of measuring ring electrodes, and also dividing a correcting ring electrode and a reference electrode. CONSTITUTION:A plurality of every two pieces of switching points are provided at an interval which is about one half of an interval (p) within measuring ring electrodes A1-An that are aligned at the constant interval (p). When electrode parts B1 and B2 of a movable measuring core electrode B reach the switching points, the set of a specified reference square-wave voltage V1, a correcting square-wave voltage V2 having the same frequency and the negative phase with respect to V1 and measuring square- wave voltage V3 is selectively switched and applied on the electrodes A1-An, correcting ring electrodes E1-En and reference ring electrodes F1-Fn, respectively. A measuring square wave voltage V3 is changed and measured so that the voltage Vm which is induced by core electrodes B, D1 and D2 respectively facing the electrodes A1-An, E1-En and F1-Fn becomes zero. In this way, the displacement can be accurately measured before and after the switching point. Therefore, the measuring range can be made to extend accurately, and the accuracy is not affected by the fluctuation of the dielectric constant between the electrodes.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] This invention relates to a length measuring device that converts mechanical displacement into an electrical signal as a change in capacitance. This invention relates to a length measuring device that is not affected by variations in the permittivity of a dielectric.

0002

2. Description of the Related Art A conventional capacitive length measuring device of this type has a general structure as shown in FIG. That is, the detection section of this length measuring device is composed of capacitors Cm and Cr, where the capacitor Cm is composed of a cylindrical measuring ring electrode 1 and a cylindrical measuring core electrode 2, and the capacitor Cr is composed of a cylindrical adjusting ring. It consists of an electrode 5 and a cylindrical adjustment core electrode 3. This measurement core electrode 2 and adjustment core electrode 3
are electrically connected by a flexible cable 4 or the like, and the measurement ring electrode 1, adjustment core electrode 3, and adjustment ring electrode 5 are fixed. Capacitors Cm and Cr having such a configuration have the same dielectric material (air), and AC voltages Vm and Vr are applied to ring electrodes 1 and 5, respectively. The voltages Vm and Vr are set to be sinusoidal voltages with the same frequency and a phase difference of 180 degrees (opposite phase).

[0003] In the above detection section, a current i that satisfies the following relational expression is applied to the measurement core electrode 2 and adjustment core electrode 3.
m occurs. Note that the capacitances of the capacitors Cm and Cr are respectively Cm and Cr. CmVm+CrVr=aim From this, im=(CmVm+CrVr)/a...(1). Here a is a positive proportionality constant.

X in FIG. 7 indicates the displacement of the measurement core electrode 2, and the displacement in the direction in which the measurement core electrode 2 is pushed into the measurement ring electrode 1 (rightward in the figure) is defined as positive, and X= 0
If the capacitance Cm at the position (the position when the tip of the measurement core electrode 2 is located at S in the figure) is C0, then
The relationship between capacitance Cm and displacement X is as follows. Cm= εb .

[0005] Point S in the figure is the starting point at which the displacement
is adjusted to satisfy the following equation. CrVr+C0Vm=0 From this, capacitance C0 can be expressed as follows. C0=-CrVr/Vm...(3) Here, by substituting equations (2) and (3) into equation (1), im
=εbVmX/a...(4) From this equation (4), if the dielectric constant ε and voltage Vm are constant, the current im is directly proportional to the displacement The amount of displacement can be measured.

[0006]

[Problem to be solved by the invention] In the above conventional example,
If the measurement range is a long stroke of several tens of mm or more, 1μ
In order to ensure accuracy on the order of m or 0.1 μm or more over the entire measurement range, geometrical tolerances such as cylindricity and surface roughness must be extremely small over the entire length of the measurement core electrode and measurement ring electrode; That is, it is necessary to keep processing errors to an extremely small level. Of course, this immediately leads to an increase in costs,
There was a problem in that the precision of the processing machine itself that processes electrodes and the like had to be limited.

Furthermore, since the dielectric constant of air differs depending on temperature, humidity, and density, even if the displacement X is the same, the current im will have a different value if the temperature, humidity, and air density (atmospheric pressure) of the measurement environment are different. For this reason, accurate measurements require constant calibration in accordance with the measurement environment.

Furthermore, the current im varies with a constant b determined by the geometric dimensions of the electrodes of the capacitor Cm. Therefore, in order to connect different detectors to a common electronic device without calibration and obtain correct measurement values, the inner diameter of the measuring ring electrode and the outer diameter of the measuring core electrode must be exactly the same for each detector. However, this is very difficult, so we have no choice but to calibrate the electronic device to match the detector, and it is not possible to directly connect another detector to the electronic device without calibrating the electronic device. Another problem was that it was not possible to measure accurately.

It is an object of the present invention to extend the measurement range with high accuracy without causing an increase in processing costs and without being limited by the precision of processing machines, and to reduce the dielectric constant of the dielectric between the electrodes. It is an object of the present invention to provide a length measuring device which is not affected by variations in the length of the object and is equipped with a compatible detecting section.

0010

[Means for Solving the Problems] The capacitance type length measuring device of the present invention has a plurality of cylindrical measuring ring electrodes A1 to An arranged in parallel on the same center line at a constant interval P, and a plurality of cylindrical measuring ring electrodes A1 to An arranged at a constant interval A measurement core electrode B having first and second core electrode parts B1 and B2 and movable on the center line within the plurality of measurement ring electrodes A1 to An, and a measurement core electrode B electrically connected to the measurement core electrode B. and one fixed correction core electrode D1
and a measurement ring electrode A1 provided concentrically around its outer circumference.
-A number of correction ring electrodes E1 to En corresponding to the number of An, one reference core electrode D2 that is electrically connected to and fixed to the correction core electrode D1, and a measurement electrode provided concentrically on the outer periphery thereof. The reference ring electrodes F1 to Fn are provided in a number corresponding to the number of ring electrodes A1 to An.

[0011] In this length measuring device, a plurality of switching points a1 to an, two of which are preset in each measuring ring electrode, are arranged at equal pitches T corresponding to approximately half the length of the above-mentioned interval P. It is set up.

[0012] According to the present invention, when the tip b1 or b2 of one of the core electrodes B1 or B2 of the measurement core electrodes B reaches each of the switching points a1 to an, the , a constant reference square wave voltage V1, a complementary square wave voltage V2 with the same frequency and opposite phase as the reference square wave voltage V1, and a measurement square wave voltage V3 with the same frequency and opposite phase as the reference square wave voltage V1 are corrected with the measurement ring electrodes A1 to An, respectively. Ring electrode E1-E
power is supplied to the reference ring electrodes F1 to Fn, and the combination of this power supply is selectively performed.

Further, the capacitances CE1 to CE of the correction capacitors CE1 to CEn formed by the complementary square wave voltage V2, the correction ring electrodes E1 to En and the correction core electrode D1
By adjusting either one or both of n, the tip b1 or b
Measurement capacitor C at the time when 2 reaches the switching point a1 to an
Product C01|V1|~C0n| of capacitance C01~C0n of E1~CEn and absolute value of reference square wave voltage V1
V1| is the product of the capacitances CE1~CEn and the absolute value of the complementary square wave voltage V2 CE1|V2|~CEn|V2
It is set to be equal to |.

Here, due to the displacement of the measurement core electrode B, the capacitance C of the measurement capacitors CA1 to CAn formed by the measurement ring electrodes A1 to An and the measurement core electrode B changes.
When A1 to CAn change, the feedback voltage V induced in the measurement core electrode B, the correction core electrode D1 and the reference core electrode D2
The measured square wave voltage V3 is varied by means of an electronic device by alternating between a constant DC voltage and a variable measured DC voltage V0 such that m is zero.

Further, the electronic device in this length measuring device includes a transient suppressor that removes the transient state of the feedback voltage Vm, a demodulator that demodulates the output signal, and a demodulator that demodulates the output signal of the feedback voltage Vm. and a differential integrator that outputs a measured DC voltage V0 that varies as a function of the amplitude and polarity of that signal until .

[0016]

[Operation] In FIG. 1, the tip b1 of the first core electrode B1
For the measurement when is displaced from the starting point a1 (switching point) to the next switching point a2, the first measurement ring electrode A1, the first correction ring electrode E1, and the first reference ring electrode F1 are set to a certain standard, respectively. A complementary square wave voltage V2 having the same frequency and opposite phase as the square wave voltage V1 and a measuring square wave voltage V3 having the same frequency and opposite phase as the voltage V1 are applied. As a result, each ring electrode A1, E1, F1 and each core electrode B (
Currents iA1, iE1, and iF1 are induced in each core electrode B, D1, and D2 by the action of capacitors CA1, CE1, and CF1 formed between the core electrodes B1), D1, and D2, respectively.

[0017] As the spindle moves and the measurement core electrode integrally attached to the spindle moves, the capacitance CA1 of the capacitor CA1 will change. The electronic device is now activated to connect each core electrode B, D1, D.
The measured square wave voltage V3 is changed so that the voltage Vm induced in the voltage Vm becomes zero. That is, the currents iA1, iE1, iF
1, the voltage V3 is varied so as to satisfy the following equation. iA1+iE1+iF1=0 (5) Here, if the capacitances of capacitors CA1, CE1, and CF1 are CA1, CE1, and CF1, respectively, equation (5) can be expressed as follows. CA1V1+CE1V2+CF1V3=0 Therefore, the measured square wave voltage V3 is as follows. V3=-(CA1V1+CE1V2)/CF1...(
6) Since voltages V3 and V1 are square wave voltages with opposite phases, and voltages V3 and V2 are square wave voltages with the same phase, V1'
When equation (6) is rewritten by replacing = -V1, the measured square wave voltage V3 becomes as shown in the following equation. V3=(CA1V1'-CE1V2)/CF1...(
7)

On the other hand, if the direction in which the spindle is pushed in (the direction in which the measurement core electrode B enters the measurement ring electrode A1) is set as the positive displacement X1, and the capacitance of the capacitor CA1 when X1=0 is C01, then the capacitance is CA1 can be expressed by the following formula. CA1=C01(1+k1X1)...(8) where k
1 is a positive constant determined by the inner diameter of the first measurement ring electrode A1 forming the capacitor CA1, the outer diameter of the measurement core electrode B, and the quotient C01/εr obtained by dividing the capacitance C01 by the dielectric constant εr of the dielectric of the capacitor CA1. be. this(
Substituting equation (8) into equation (7), the measured square wave voltage V3 is:
V3=(k1C01V1'X1/CF1)+(C0
1V1'-CE1V2)/CF1...(9), α1=k1C01V1'/CF1,β1=(C01
V1'-CE1V2)/CF1 (10), then equation (9) is transformed as follows. V3=α1X1+β1…(11)

In the present invention, CE1|V2|=C0
The complementary square wave voltage V2 or capacitance CE1 is adjusted so that 1 |V1|, which is CE1V2=
C01V1' can be replaced with (10)
When substituted into the equation, β=0. Therefore, the measured square wave voltage V3 can be expressed by the following equation. V3=α1X1=k1C01V1'X1/CF1...(1
2) Since this proportionality constant α1 is a positive value, the relationship between voltage V3 and displacement X1 is that when displacement X1 increases, voltage V3 increases in direct proportion to displacement X1, and when displacement X1 decreases, voltage V3 increases. decreases in direct proportion to the displacement X1, and further increases the displacement
When 1 is zero, voltage V3 is also zero. Therefore, the amount of displacement X can be obtained by measuring this voltage V3.

Note that, as shown in equation (9), the voltage V3 is C
The capacitors CA1 and C
If E1 and CF1 are made of the same dielectric material, they will not be affected by the dielectric constant at all.

In addition, in the case of CE1|V2|≠C01|V1|, β1 is a non-zero constant, so the voltage V3 increases by β1, and the displayed value of the measured length is apparently X1=0.
The point moves to the minus side by β1/α1. Therefore, it is necessary to set the relationship CE1|V2|=C01|V1|, and for this reason, the capacitance CE
1 and voltage V2, or both are adjusted.

On the other hand, in the measurement from the switching point a2 to the next switching point a3, since there is a seam between the first measurement ring electrode A1 and the second measurement ring electrode A2 during this period, these measurement ring electrodes A1, Instead of measuring from the capacitance formed between A2 and the first core electrode part B1, a fourth measuring ring electrode A4 and the second core electrode part B2 is formed between the fourth measurement ring electrode A4 and the second core electrode part B2, which is not affected by the seam. Measured from the capacity. That is,
Fourth measurement ring electrode A4 and fourth correction ring electrode E4
Then, the state is switched to apply the reference square wave voltage V1, complementary square wave voltage V2, and measurement square wave voltage V3 to the fourth reference ring electrode F4, respectively. For this reason, each ring electrode A4,
E4, F4 and each core electrode B (B2), D facing them
1 and D2, capacitors CA4, CE4,
CF4 is formed.

Here, when the tip b1 of the first core electrode part B1 of the measurement core electrode B moves from the switching point a2, the tip b2 of the second core electrode part B2 moves from the switching point a7 accordingly. , the capacitance CA4 of the capacitor CA4 changes. At this time, similarly to the measurement of the switching points a1 and a2, the electronic device is activated to change the voltage V3 so that the voltage Vm becomes zero. That is, capacitor CA4,
Each core electrode B, D1, D2 due to the action of CE4 and CF4
Assuming that the currents flowing in are iA4, iE4, and iF4, the voltage V3 is changed so as to satisfy the following equation. iA4+iE4+iF4=0 (13) Here, if the capacitances of capacitors CA4, CE4, and CF4 are CA4, CE4, and CF4, respectively, then equation (13) can be expressed as follows. CA4V1+CE4V2+CF4V3=0 Therefore, the measured square wave voltage V3 is as follows. V3=-(CA4V1+CE4V2)/CF4...(
14) Here, if V1'=-V1 is replaced as described above, the voltage V3 becomes as shown in the following equation. V3=(CA4V1'-CE4V2)/CF4...(
15)

Further, the direction in which the spindle is pushed in and the measurement core electrode B enters after the switching point a2 (a7) is set as positive, and the displacement from the switching point a2 (a7) at this time is expressed as X2, and X2= If the capacitance of capacitor CA4 at 0 is C04, capacitance CA4 can be expressed by the following equation. CA4 = C04 (1 + k2 It is a positive constant determined by the quotient C04/εr divided by the rate εr. Substituting this equation (16) into equation (15), the voltage V3
is, V3=(k2C04V1'X2/CF4)+(
C04V1'-CE4V2)/CF4...(17), α2=k2C04V1'/CF4,β2=(C04
V1'-CE4V2)/CF4 (18), the equation (17) is transformed as follows. V3=α2X2+β2…(19)

In the present invention, CE4|V2|=C0
The complementary square wave voltage V2 or capacitance CE4 is adjusted so that 4|V1|, which is CE4V2=
C04V1' can be replaced with (17)
When substituted into the equation, β2=0. Therefore, the measured square wave voltage V3 can be expressed by the following equation. V3=α2X2=k2C04V1'X2/CF4...(2
0) Since this proportionality constant α2 is a positive value, the relationship between voltage V3 and displacement X2 is that when displacement X2 increases, voltage V3 increases in direct proportion to displacement X2, and when displacement X2 decreases, voltage V3 increases. decreases in direct proportion to the displacement X2, and further increases the displacement
When V2 is zero, voltage V3 is also zero. Therefore, by measuring this voltage V3, switching points a2 to a3 (a7 to
The amount of displacement a8) can be obtained.

Hereinafter, when the tip b1 of the first core electrode part B1 reaches the switching point, by selectively combining the power supply to the measurement ring electrode, correction ring electrode, and reference ring electrode in sequence, an extremely long Stroke measurement becomes possible. In addition, in each measurement, the voltage V3 is C04/
Since the capacitors CA4, CE4, CF4, etc. are composed of capacitance ratios such as CF4 and CE4/CF4, if they are composed of the same dielectric material, they will not be affected by the dielectric constant at all. Also, in each measurement, CE4|V2|=C04|V1
It is necessary to set the relationship as shown by |, and for this reason, adjustment is performed in a manner similar to adjusting one or both of the capacitance CE4 and the voltage V2.

Furthermore, the electronic device according to the invention includes a transient suppressor to eliminate transients occurring in the feedback voltage Vm at switching points of the square wave voltage.

[0028]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings. FIG. 1 is a schematic explanatory diagram showing the structure of a detection section of a capacitive length measuring device according to an embodiment of the present invention. A1 to A6 are cylindrical first to sixth measurement ring electrodes. This first
The centers of the -sixth measurement ring electrodes are located on the same center line, and they are arranged at regular intervals P. 1
3 is an insulating member provided to electrically insulate each of the first to sixth measurement ring electrodes A1 to A6, and is interposed between each of the first to sixth measurement ring electrodes. .

B is a measuring core electrode movable on the center line within the measuring ring electrodes A1 to A6. This measurement core electrode B
is composed of a first core electrode part B1 and a second core electrode part B2. These first and second core electrode parts B1,
B2 has large diameter portions B1-1, B2-1 and small diameter portions B1-2, B2-2 protruding from one end surface thereof, and recesses B1-3, B2 on the other end surface of each large diameter portion. -3 is provided. A spindle 6 is inserted and fixed in the recess B1-3 via a cylindrical insulating member 7, and the recess B
2-3, the small diameter portion B1-2 of the first core electrode portion B1 is inserted and fixed. As a result, the spindle 6 and the first and second core electrodes B1 and B2 are integrated and electrically conductive, and their outer peripheral surfaces and the measurement ring electrodes A1 to A6
and the inner circumferential surface thereof are arranged at a predetermined interval.

Reference numeral 9 denotes a shield ring, which is externally attached to the small diameter portion B1-2 between the first and second core electrode portions B1 and B2 via an insulating member 8 which is cylindrical and has a flange at its end. and grounded. Reference numeral 11 denotes a shield ring attached to the outer periphery of the small diameter portion B2-2, which does not constitute a capacitor, of the second core electrode portion B2 via a cylindrical insulating member 10 having a flange at the end. Note that this shield ring 11 is also grounded. D1 is a correction core electrode that is electrically connected to and fixed to the measurement core electrode B by a coil spring 12 or the like. E1 to E6 are cylindrical correction ring electrodes, which are arranged concentrically so that their inner peripheral surfaces and the outer peripheral surface of the correction core electrode D1 are spaced apart from each other by a predetermined distance. D2 is a reference core electrode electrically connected to the correction core electrode D1 and fixed at a predetermined interval. F1 to F6 are cylindrical reference ring electrodes, which are arranged concentrically so that their inner peripheral surfaces and the outer peripheral surface of the reference core electrode D2 are spaced at a predetermined distance.

Next, the operation and function of the capacitance type length measuring device having the above structure will be explained with reference to FIGS. 1 and 2(a) to 2(g). First, in this capacitance type length measuring device, as described later, the measurement ring electrodes A1 to A6, the correction ring electrodes E1 to E6, and the reference ring electrodes F1 to F6 are used.
The switching points for the power supply are set at positions a1 to a12 in FIG. 2. The switching points a1 to a12 in this embodiment are set at equal intervals with a pitch T, and this interval T is approximately half the length of the interval P in which the measurement ring electrodes A1 to A6 shown in FIG. 1 are provided. Preferably, the measurement ring electrodes are set accurately, and it is further preferable that two measurement ring electrodes are set at a time. The positions of each of these switching points a1 to a12 are 10n
By actually accurately displacing the measuring core electrode B using a high-precision measuring device capable of measuring on the order of m or a block gauge, and storing the measured square wave voltage V3 at that time in an electronic device, etc. Set in advance.

Furthermore, the interval L0 between the first core electrode part B1 and the second core electrode part B2 is sufficiently larger than the variable inter-electrode interval P, and furthermore, the distance L0 between the first and second core electrode parts B1 and B2 is sufficiently larger than the variable inter-electrode interval P. The distance L between the tips b1 and b2 is set to be exactly an integral multiple of the switching point interval T (in the embodiment, L=5T).

[0033] In the detection section set as above,
As shown in FIG. 2(a), with the tip b1 of the first core electrode part B1 inserted up to the starting point a1, which is the switching point near the opening in the first measurement ring electrode A1, A constant reference square wave voltage V1 is applied to the measurement ring electrode A1, and at the same time, a complementary square wave voltage V2 of the same frequency and opposite phase as the reference square wave voltage V1 is applied to the first correction ring electrode E1, and The first reference ring electrode F1 has a reference square wave voltage V
A measurement square wave voltage V3 of the same frequency and opposite phase as 1 is applied. Also, at this time, other measurement ring electrodes A2 to A6, other correction ring electrodes E2 to E6, and other reference ring electrodes F2 to F6
Both are electrically grounded. Thereby, a capacitor CA1 is formed between the first measurement ring electrode A1 and the first core electrode part B1, a capacitor CE1 is formed between the first correction ring electrode E1 and the correction core electrode D1,
Further, a capacitor CF1 is formed between the first reference ring electrode F1 and the reference core electrode D2.

Here, the measurement core electrode B, the correction core electrode D
The measured square wave voltage V3 is varied by the electronic device such that the AC voltage Vm induced in the reference core electrode D2 and the reference core electrode D2 becomes zero. Further, the adjustment screws 41 and 42 of the first correction ring electrode E1 are adjusted so that the measured square wave voltage V3 becomes zero.
The capacitance CE1 of the capacitor CE1 is adjusted by . The capacitance CE1 is first roughly adjusted using the large adjustment screw 41, and then finely adjusted using the small adjustment screw 42. If compatibility of the detection part is not required, the complementary square wave voltage V2 may be adjusted, but electrical components such as potentiometers with good temperature characteristics are generally used on the electronic device side to adjust this voltage V2. However, this does not mean that there is no change at all even when the temperature changes, so if good temperature characteristics are strictly required, it is preferable not to use electrical parts such as potentiometers. By setting as above,
Point a1 becomes the starting point of measurement.

Next, in the process of displacing the measurement core electrode B from the state shown in FIG. 2(a) to just before the state shown in FIG. 2(b), that is, in the measurement from the starting point a1 to the second switching point a2, a square wave voltage V1 on the first measurement ring electrode A1, the first correction ring electrode E1 and the first reference ring electrode F1;
V2 and V3 are applied respectively, and the measurement core electrode B
The capacitance CA1 of the capacitor CA1 changes with the displacement of the capacitor CA1. Here, the voltage V3 is changed by the electronic device so that the AC voltage Vm induced in the core electrodes B, D1, and D2 becomes zero, and a measurement square wave voltage V3 is obtained that changes in proportion to the displacement of the measurement core electrode B. be able to.

Thereafter, as shown in FIG. 2(b), when the tip b1 of the first core electrode portion B1 reaches the switching point a2, the second
The tip b2 of the core electrode part B2 is the fourth measuring ring electrode A.
4 reaches switching point a7. In this state, a constant reference square wave voltage V1 is applied switched from measurement ring electrode A1 to measurement ring electrode A4, and to the remaining measurement ring electrodes A2, A3, A5, including the first measurement ring electrode A1,
A6 is electrically grounded.

At this time, a complementary square wave voltage V2 having the same frequency and opposite phase as the reference square wave voltage V1 is switched and applied from the first correction ring electrode E1 to the fourth correction ring electrode E4. The remaining correction ring electrodes E2, E3, E5, and E6, including the correction ring electrode E1, are electrically grounded.

Furthermore, at this time, the measurement square wave voltage V3 having the same frequency and the opposite phase as the reference square wave voltage V1 is switched and applied from the first reference ring electrode F1 to the fourth reference ring electrode F4. The remaining reference ring electrodes F2, F3, F5, and F6, including one reference ring electrode F1, are electrically grounded.

In this case, the capacitor CA formed between the fourth measurement ring electrode A4 and the second core electrode part B2
4, a capacitor CE4 formed between the fourth correction ring electrode E4 and the correction core electrode D1, and a capacitor CF4 formed between the fourth reference ring electrode F4 and the reference core electrode D2. AC to core electrodes B, D1, D2
A voltage Vm is induced and the electronic device changes the voltage V3 so that this voltage Vm becomes zero. Furthermore, a fourth correction ring electrode E is connected so that this measured square wave voltage V3 becomes zero.
The capacitance CE4 of the capacitor CE4 is adjusted using the adjustment screws 47 and 48 shown in FIG. Note that if compatibility of the detection section is not required, the measurement square wave voltage V3 may be made zero by adjusting the complementary square wave voltage V2.

In the process of displacing the measurement core electrode B from the state shown in FIG. 2(B) to just before the state shown in FIG. 2(C), the fourth measurement ring electrode A4, the fourth correction ring electrode Voltages V1, V2, and V3 are applied to E4 and the fourth reference ring electrode F4, respectively, and the capacitor CA4 is varied by the displacement of the tip b2 of the second core electrode part B2 from the switching point a7. , D1, and D2 become zero, and a voltage V3 proportional to the displacement of the measurement core electrode B can be obtained in the same way as in the measurement operation described above.

Thereafter, as shown in FIG. 2(c), when the tip b2 of the second core electrode part B2 reaches the switching point a8, the first
The tip b1 of the core electrode portion B1 reaches the switching point a3. In this state, a constant measurement square wave voltage V1 is applied switching from electrode A4 to electrode A2, and the remaining electrodes A1, A3, A5, A6, including electrode A4, are grounded. Also, at this time, the complementary square wave voltage V2 is applied by switching from the electrode E4 to the electrode E2, and the electrodes E1, E3, E5, including this electrode E4,
E6 is grounded. Furthermore, the measured square wave voltage V3 is applied to the electrode F4.
The voltage is applied by switching from to electrode F2, and the voltage is applied to electrodes F4, F1,
F3, F5, and F6 are electrically grounded.

In this case, the capacitor CA formed between the second measurement ring electrode A2 and the first core electrode part B1
2, a capacitor CE2 formed between the second correction ring electrode E2 and the correction core electrode D1, and a capacitor CF2 formed between the second reference ring electrode F2 and the reference core electrode D2. The voltage V3 is varied by the electronic device so that the voltage induced in B, D1, and D2 becomes zero, and the adjustment screws 43 and 44 adjust the capacitor CE2 or adjust the complementary square wave voltage V2 in the same way as the measurement operation described above. to make the measured square wave voltage V3 zero.

In the process of displacing the measurement core electrode B from the state shown in FIG. 2(c) to just before the state shown in FIG.
1, V2, and V3 are applied to the first core electrode part B.
The capacitor CA2 is varied by the displacement of the tip b1 from the switching point a3, and the voltage V is changed by an electronic device so that the AC voltage Vm induced in the core electrodes B, D1, and D2 becomes zero.
3 can be varied to obtain a voltage V3 proportional to the displacement.

Similarly, in the state shown in FIG. 2(d),
The tip b2 of the second core electrode part B2 reaches the switching point a9,
At this time, a voltage V1 is applied to the electrode A5 to form a capacitor CA5 between it and the second core electrode part B2, and a voltage V2 is applied to the electrode E5 to form a capacitor CE5 between it and the correction core electrode D1. Furthermore, voltage V3 is applied to electrode F5, and capacitor CF5 is connected between reference core electrode D2.
At this time, the voltage V3 is increased by an electronic device so that the voltage Vm induced in the core electrodes B, D1, and D2 becomes zero.
is varied, and the capacitor C is adjusted by adjusting screws 49 and 50.
The measured square wave voltage V3 is made zero by adjusting E5 or adjusting the complementary square wave voltage V2. From Figure 2(d) to Figure 2
Immediately before the state shown in (e), electrodes A5, E5, F5
Voltages V1, V2, and V3 are applied to these, respectively, and a voltage V3 proportional to the displacement can be obtained.

Further, in the state shown in FIG. 2(e), the tip b1 of the first core electrode portion B1 reaches the switching point a5, and the electrode A3
A voltage V1 is applied to the electrode E3 to form a capacitor CA3 between it and the first core electrode B1, and a voltage V2 is applied to the electrode E3 to form a capacitor CE3 between it and the correction core electrode D1. A voltage V3 is applied to F3 to form a capacitor CF3 between it and the reference core electrode D2. At this time, the voltage V3 is varied by the electronic device so that the voltage Vm induced in the core electrodes B, D1, and D2 becomes zero, and the capacitor CE3 is adjusted by the adjusting screws 45 and 46, or the complementary square wave voltage V2 is adjusted. The measured square wave voltage V3 is made zero. From FIG. 2(e) to immediately before the state shown in FIG. 2(f), voltages V1 and V2 are applied to electrodes A3, E3, and F3.
, V3 are respectively applied, and a voltage V3 proportional to the displacement can be obtained.

In the state shown in FIG. 2(F), the tip b2 of the second core electrode part B2 reaches the switching point a11, and the voltage V1 is applied to the electrode A6, causing a voltage difference between it and the second core electrode part B2. A voltage V2 is applied to the electrode E6 to form a capacitor CE6 between it and the correction core electrode D1, and a voltage V3 is applied to the electrode F6 to form a capacitor CF6 between it and the reference core electrode D2. form. At this time, the voltage V3 is varied by an electronic device so that the voltage Vm induced in the core electrodes B, D1, and D2 becomes zero, and by adjusting the capacitor CE6 with the adjusting screws 51 and 52 or adjusting the complementary square wave voltage V2. Set the measurement square wave voltage V3 to zero. From FIG. 2(F) to immediately before the state shown in FIG. 2(G), voltages V1, V2, and V are applied to electrodes A6, E6, and F6.
3 is applied to each, and a voltage V3 proportional to the displacement can be obtained.

In the state shown in FIG. 2(g), the tip b1 of the first core electrode part B1 reaches the switching point a7, and the voltage V1 is applied to the electrode A4 again, causing a gap between it and the first core electrode part B1. A voltage V2 is applied to the electrode E4 to form a capacitor CE4 between it and the correction core electrode D1, and a voltage V3 is applied to the electrode F4 to form a capacitor CF4 between it and the reference core electrode D2. form. and,
In the diagram of FIG. 2(g), the tip b1 of the first core electrode part B1
In the process of changing from the switching point a7 to just before the switching point a8, voltages V1, V2, and V3 are applied to the electrodes A4, E4, and F4, respectively, and a voltage V3 proportional to the displacement can be obtained.

In addition, in FIG. 2(A), the first core electrode portion B1
The measurement until the tip b1 reaches the switching point a1 is the capacitor CA formed by the electrode A3 and the second core electrode part B2.
3, a capacitor CE3 formed by the electrode E3 and the correction core electrode D1, and a capacitor CF3 formed by the electrode F3 and the reference core electrode D2.

Table 1 shows the "combinations of power feeding" in the above operation.

[0050]

As mentioned above, the detection section in this embodiment is
The combination of power supply to the measurement ring electrode, correction ring electrode, and reference ring electrode is selectively switched according to each switching point position, and the measurement square wave is applied so that the voltage induced on the core electrodes B, D1, and D2 becomes zero. The voltage is changed and this measurement square wave voltage is measured. Therefore, this switching point a
By precisely setting the positions of 1 to a12, it is possible to precisely measure the displacement before and after this switching point, and as a result, the measurement range can be precisely extended, and the dielectric constant of the dielectric between the electrodes can be accurately measured. It is not affected by fluctuations in

Further, the amount of displacement measured by this detection section is displayed, for example, as follows. When the measurement core electrode B is displaced in the direction of entering the measurement ring electrode,
A value γ corresponding to the moving distance of the tip b1 of the first core electrode part B1 is displayed, and when the tip b1 reaches the switching point a2, the length corresponding to the switching point pitch T is determined from the value stored in the electronic device. It is counted up by one count. This first
The tip b1 of the core electrode part B1 changes from the switching point a2 to the switching point a.
In the process of moving to just before 3 [FIGS. 2(b) to 2(c)], a value 1+γ, which is the value γ corresponding to the moving distance at that time and one count up to the previous switching point a2, is displayed. Furthermore, in the process of the tip b1 moving from the switching point a3 to the switching point a4 [Fig. 2 (c) to (d)], the value γ corresponding to the moving distance at that time is added by one count up to the previous switching point a2. A value 1+1+γ is displayed, which is the sum of two counts, including one count up to the switching point a3. Similarly, when the tip b1 reaches each switching point, the count is added one count at a time and displayed.

Conversely, when the measurement core electrode B is displaced in the direction of coming out of the variable electrode, contrary to the above-mentioned movement of the measurement core electrode B toward the inside of the measurement ring electrode, when each switching point is reached, 1 The counted down values are added and displayed.

Further, in this embodiment, an example was explained in which the number of measurement ring electrodes, correction ring electrodes, and reference ring electrodes was up to six, but the number is not limited to this, of course, and the number can be arbitrary. This can be set to .

Furthermore, if the diameter accuracy and length accuracy of the measurement ring electrodes A1 to A6 and the core electrode portions B1 and B2 of the measurement core electrode B are very good, the correction ring electrode and the reference ring electrode are each It may be composed of two rings.

Furthermore, in the embodiment shown in FIG. 1, the measurement capacitor, correction capacitor, and reference capacitor are installed in the detection section, but the correction capacitor and reference capacitor may be placed in the electronic device as shown in FIG. .

Furthermore, it is also possible to integrate the core electrodes D1 and D2 and omit the conducting wire between the core electrodes.

[0058] Also, the capacitors CA1 to CA1 in this embodiment
CA6 is composed of cylindrical measurement ring electrodes A1 to A6 and cylindrical core electrode parts B1 and B2, and furthermore, the central axes of the measurement ring electrodes A1 to A6 and the central axis of the measurement core electrode B almost coincide. In addition, the measurement core electrode B is attached to the insulating member 7 so that its center axis almost coincides with the center axis of the spindle.
It is fixed to the spindle 6 via. This results in
When the spindle 6 is pushed and moved, the measurement core electrode B also moves coaxially with the central axis of the spindle. Therefore, even if the central axes of the measuring ring electrode and the measuring core electrode slightly move due to an impact or the like, and the distance between the central axes changes slightly, the proportionality constants of equations (12) and (20) described above will not change. The fluctuations in k1 and k2 that make up the voltage are extremely small, and the voltage V
3 has almost no effect.

Furthermore, the center axes of the correction ring electrodes E1 to E6 and the correction core electrode D1, and the center axes of the reference ring electrodes F1 to F6 and the reference core electrode D2 are fixed and substantially coincident. Therefore, even if the distance between the center axes of each electrode changes slightly (12
) and (20), the fluctuations in the proportionality constants k1 and k2 are very small, and in this case as well, there is almost no effect on the voltage V3.

On the other hand, the small diameter portion B1-2 of the measurement core electrode B,
The outer periphery of B2-2 is covered with shield rings 9 and 11 via insulating members 8 and 10, and by electrically grounding these shield rings 9 and 11, the portion of measurement core electrode B that does not constitute a capacitor is The shield is ensured.

[0061] Basically, in this detection section, the feedback voltage Vm induced in the core electrode is the square wave voltage V for excitation.
1, V2, and V3, and it is also necessary to prevent voltages V1, V2, and V3 from influencing each other. Therefore, in this embodiment, the voltage V1
The wires connecting the detection unit and the electronic device for guiding ~V3 and Vm are shielded by shields 21 to 24. In particular, it is required that the line leading the feedback voltage Vm be completely shielded, but it is also possible to simplify the shielding by the following method.

That is, as shown in FIG. 4, in the detection section, the input side of the impedance transformer 26 and one side of the discharge resistor 27 are connected to the reference core electrode D2, and the other side of the discharge resistor 27 is connected to the ground. At the same time, the output side of the impedance transformer 26 is connected to an input amplifier with a low input impedance, such as a current-voltage conversion circuit in an electronic device. Thereby, the impedance between the impedance transformer 26 provided in the detection section and the input amplifier in the electronic device can be reduced, and the shield can be simplified. For this reason, when high sensitivity and high precision are not required, it becomes possible to shield the wires leading the voltages V1, V2, V3, and Vm' all at once instead of one by one. However, if high sensitivity and precision are required, it is desirable to shield each wire one by one.

[0063] Also, each ring electrode A1 to A6, E1 to E6
, F1 to F6 and each core electrode B, D1, and D2 are made of the same material, so that the thermal expansion of the parts is the same, preventing capacitor imbalance due to temperature changes, and improving the temperature performance of the detection unit. be able to.

Furthermore, by using a ball retainer in the spindle bearing to keep it in a preloaded state, the play of the spindle can be reduced to zero, and the influence of the play of the spindle can be eliminated.

FIG. 5 is a diagram showing the circuit configuration of an electronic device that applies a voltage to the detection section, and FIG. 6 is a time chart showing the phase relationship of the output voltage. 30 is an oscillator that outputs a square wave voltage VOSC as a reference. This oscillator 3
0 may be either a crystal type or a CR type, and in the case of a crystal type, a frequency divider can be used to obtain a desired frequency.

31 is a time delay circuit that delays the square wave voltage VOSC by a certain period of time, and 32 is a time delay circuit that delays the output signal by 1/2.
This is a frequency divider circuit that divides the frequency.

33 and 34 are electronic switches, and the electronic switch 33 switches between the DC voltage Vr and the ground level in response to a signal from the frequency divider circuit 32 and outputs it as a reference square wave voltage V1. The switch 34 also connects the frequency dividing circuit 32 between the DC voltage -Vr and the ground level.
It switches in response to a signal from and outputs it as a complementary square wave voltage V2.

35 is an input amplifier to which the feedback voltage Vm is input.

Reference numeral 36 denotes a transient suppressor for removing a transient state generated in the voltage signal V4 outputted from the input amplifier 35. In this embodiment, the voltage signal V4 is removed in response to the square wave voltage signal VOSC from the oscillator 30. It consists of an electronic switch that connects and disconnects the

37 is the voltage signal V from which the transient state has been removed.
This is a synchronous demodulator that inputs a signal from the frequency divider circuit 32 and demodulates the signal from the frequency divider circuit 32 for each period.

38 inputs the demodulated voltage signal and converts it to DC
This is a differential integrator that outputs a voltage signal V0.

Reference numeral 39 is an electronic switch that switches between the DC voltage signal V0 and the ground level in response to a signal from the frequency divider circuit 32 and outputs it as a measurement square wave voltage V3.

In the above electronic device, the voltages V1 and V2 are square wave voltages having the same frequency and opposite phases because DC voltages of different polarities are intermittently output from the electronic switches 33 and 34 at the same timing.

Further, the voltage V3 is the DC voltage from the differential integrator 38.
The voltage V0 is synthesized by being intermittently outputted from the electronic switch 39 at the timing of the voltage signal from the frequency dividing circuit 32.

Furthermore, the DC voltage V0 is synthesized as follows. First, the feedback voltage Vm is amplified by the input amplifier 35 and applied to the transient suppressor 36 as a voltage E4. In this voltage signal V4, a transient state that occurs in the feedback voltage Vm occurs at the switching points (t00, t10, t20, . . . ) of the square wave. This transient state attenuates and becomes stable after a certain period of time, and in this example, t00 in FIG.
This occurs between t01 and t01, between t10 and t11, between t20 and t21, and so on. The transient suppressor 36 which receives this voltage signal V4 connects and disconnects the input voltage signal V4 every half cycle of the voltage VOSC and outputs the same. The electronic switches 33, 34, and 39 in this embodiment are set to switch states in response to a signal obtained by delaying the voltage VOSC by a predetermined time. Therefore, the generation timing of the square wave voltages V1, V2, and V3 output from these electronic switches and the voltage VOS
The timing of occurrence with C is shifted by the amount of delay as described above. Therefore, if the setting is made so that the transient state of the voltage signal V4 is within the range of this generation timing shift, the transient suppressor 36 can be turned off only while the transient state is occurring in the voltage signal V4. , thereby making it possible to remove the transient state of the voltage signal V4.

The voltage signal V4 from which the transient state has been removed in this way is demodulated every cycle by the demodulator 37. Furthermore, if the demodulated voltage is not zero, the DC voltage V0 output by the differential integrator 38 is varied as a function of the amplitude and polarity of the demodulated voltage until the demodulated voltage reaches zero. As a result, voltage V3 changes together with DC voltage V0 until the input voltage of differential integrator 38 reaches zero. As a result, the voltage V3 satisfies the relationships of the above-mentioned equations (12) and (20), is proportional to the displacement X, and has a positive proportionality constant.

[0077]

[Effects of the Invention] According to the present invention, the measurement range is not covered by one measurement ring electrode, but by a plurality of measurement ring electrodes, and the measurement core electrode is also divided into two accordingly. Furthermore, since the correction ring electrode and the reference ring electrode are also divided so as to correspond to the measurement ring electrode, the respective errors can be reduced for each divided range. Therefore, it is no longer necessary to apply continuous geometric tolerances over the entire length of the measurement range as in the past, so processing costs can be significantly reduced compared to the past, and the limitations of the processing machine are not excessive. It disappears.

Furthermore, since the switching point is provided within the measurement range, measurement errors occurring before the switching point are not accumulated in subsequent measurement values, and accuracy can be improved.

Furthermore, according to the present invention, there is no need to consider geometrical tolerances over the entire length of the measurement range, so the gap between the measuring ring electrode and the core electrode can be made smaller than in the conventional case. It is possible to increase the capacitance change of the variable capacitor per unit measurement length while maintaining the same geometrical tolerance and measurement accuracy as that of the conventional method, and the sensitivity and stability of measurement can be improved accordingly.

Furthermore, since the reference capacitor and the correction capacitor are each provided with adjustment screws for capacitance adjustment, different detection sections can be connected to a common electronic device without calibrating the measurement origin or the like.

Furthermore, since the measured square wave voltage V3 is composed of a ratio of capacitances, by making the dielectric of all capacitors the same, it is not affected by the dielectric constant at all, and is not affected by changes in the dielectric constant. This eliminates the need for calibration or correction.

Furthermore, since the center axes of the measurement ring electrode and the measurement core electrode are almost the same, and the center axes of the correction ring electrode and the correction core electrode, and the reference ring electrode and the reference core electrode are also almost the same, the center axes of the measurement ring electrode and the measurement core electrode are almost the same. Even if the distance between them changes slightly, the effect on the measured voltage can be made very small.

Furthermore, by using a ball retainer in the spindle bearing to keep it in a preloaded state, the backlash of the spindle can be reduced to zero, and the backlash of the spindle can be eliminated.

Furthermore, by providing an impedance transformer and a discharge resistor in the detection section, if high sensitivity and high precision are not required, the lines leading to voltages V1, V2, V3, and Vm' can be shielded all together. I can do it. In particular, when high sensitivity and high precision are required, more stability can be achieved by also using individual shields.

Furthermore, capacitors CA1 to CA6, CE
By using the same material for the ring electrode and the core electrode that constitute 1 to CE6 and CF1 to CF6, it is possible to improve the temperature performance of the detection section.

Furthermore, by providing a transient suppressor in the electronic device, the voltages V0 and V3 can be synthesized from signals without a transient state, thereby further improving the stability of the length measuring device.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the structure of a detection section of a capacitive length measuring device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a displacement measurement state by the detection section shown in FIG. 1;

FIG. 3 is a diagram showing a partially modified example of the detection unit shown in FIG. 1;

FIG. 4 is a circuit diagram showing an impedance transformer attached to the detection section shown in FIG. 1.

FIG. 5 is a diagram showing the configuration of an electronic device of a capacitive length measuring device according to an embodiment of the present invention.

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

FIG. 7 is a diagram showing the structure of a detection section of a conventional capacitive length measuring device.

[Explanation of symbols]

A1-An Measuring ring electrode B Measuring core electrodes B1, B2 First and second core electrode parts D1 Correction core electrode D2 Reference core electrodes E1-En Correction ring electrodes F1-Fn Reference ring electrode 6 Spindles 8, 10 Insulating member 9 , 11 Shield ring 12 Spring 21-24 Shield 26 Impedance transformer 27 Discharge resistor 30 Oscillator 33, 34, 36, 39 Electronic switch 35 Input amplifier 37 Demodulator 38 Differential integrator 41-52, 61-72 Adjustment screw V1 Reference square wave voltage V2 Complementary square wave voltage V3 Measurement square wave voltage Vm Feedback voltage

Claims (6)

[Claims] Claim 1: A plurality of cylindrical measurement ring electrodes (A
1, A2, ...An, n is a positive integer), and first and second core electrode parts (B1, B2) with a constant interval,
A measuring core electrode (B) movable on the center line within the plurality of measuring ring electrodes (A1, A2,...An), and one fixed measuring core electrode electrically connected to the measuring core electrode (B). A correction core electrode (D1) and this correction core electrode (D
1) The measurement ring electrode (
A number of correction ring electrodes (E1, E2, ...En, n is a positive integer) corresponding to the number of electrodes (A1, A2, ... An) are electrically connected to the correction core electrode (D1) and are fixed. one reference core electrode (D2), and a number of reference ring electrodes corresponding to the number of measurement ring electrodes (A1, A2,...An) provided concentrically around the outer periphery of this reference core electrode (D2). (F1, F2,...Fn, n is a positive integer), and at a position within each of the measurement ring electrodes at an equal pitch (T) corresponding to approximately half the length of the interval (P). A plurality of switching points (a1, a2,
...an, n is a positive integer), and the measurement core electrode (B
) of one of the core electrode parts (B1 or B2) (
b1 or b2) is the plurality of switching points (a1, a2,...
When each of the reference square wave voltages (A1, A2, ...An) is reached, a constant reference square wave voltage (V1) is applied to the measurement ring electrodes (A1, A2, ...An) corresponding to the switching point position, and the reference square wave voltage The correction ring electrodes (E1, E
2,...En) and the reference ring electrodes (F1, F2,...Fn) to which a measuring square wave voltage (V3) of the same frequency and opposite phase as the reference square wave voltage (V1) is applied. is selectively performed, and the correction capacitors (CE1, C
E2,...CEn) capacitance (CE1, CE2,
...CEn), the capacitance (C01, C02, ...C0n) of the measurement capacitor (CE1, CE2, ...CEn) at the time when the switching point (a1, a2, ...an) is reached. ) and the absolute value (|V1|) of the reference square wave voltage (V1) (C01|V
1|, C02|V1|,...C0n|V1|) is the product (CE1|V2|) of the capacitance (CE1, CE2,...CEn) and the absolute value (|V2|) of the complementary square wave voltage (V2).
, CE2|V2|,...CEn|V2|) and removes the transient state of the feedback voltage (Vm); a demodulator that demodulates the output signal; said measuring core electrode (B) by means of an electronic device comprising a differential integrator that outputs a measured DC voltage (V0) which varies as a function of the amplitude and polarity of its signal until this signal becomes zero when it is not zero. The displacement of the measuring capacitors (CA1, CA2,...CAn) formed by the measuring ring electrodes (A1, A2,...An) and the measuring core electrode (B)
) changes, the measurement core electrode (B) and the correction core electrode (D1) change.
and the feedback voltage (Vm) induced in the reference core electrode (D2)
) is zero. Capacitive length measuring device. 2. Selectively the reference square wave voltage (V1)
, the measuring ring electrodes (A1, A2) to which the complementary square wave voltage (V2) and the measuring square wave voltage (V3) are applied.
,...An), the correction ring electrodes (E1, E2,...En
) and the remaining other measurement ring electrodes except one of each of the reference ring electrodes (F1, F2,...Fn);
2. The capacitive length measuring device according to claim 1, wherein the correction ring electrode and the reference ring electrode are grounded. 3. The plurality of correction ring electrodes (E1, E
2,...En) and reference ring electrodes (F1, F2,...Fn
3. The capacitance type length measuring device according to claim 1, wherein each electrode of the capacitance type length measuring device is provided with a capacitance adjusting means. 4. An input side of an impedance transformer and one side of a discharge resistor are connected to the reference core electrode or a correction core electrode, an output side of the impedance transformer is connected to the electronic device, and the other side of the discharge resistor is connected to the reference core electrode or the correction core electrode. 4. The capacitance type length measuring instrument according to claim 1, wherein the capacitance type length measuring instrument is grounded on one side. 5. The measurement ring electrode, the correction ring electrode, the reference ring electrode, the measurement core electrode, the correction core electrode, and the reference core electrode are made of the same material, according to any one of claims 1, 2, 3, and 4. capacitive length measuring device. 6. The capacitance type length measuring device according to claim 1, wherein a ball retainer is used in the bearing of the spindle to maintain a preloaded state.