JPH0452502A - Capacitance type device for measuring length - Google Patents

Abstract

PURPOSE:To display displacement with a rectangular wave voltage used directly, by forming a measuring capacitor between a measuring ring electrode and a measuring core electrode and by forming a correcting capacity and a reference capacitor between a correcting ring electrode and a reference core electrode. CONSTITUTION:When a spindle 15 moves and thereby a measuring core electrode 12 is displaced rightward, capacitance C1 of a capacitor C1 changes. Concurrently, a measuring rectangular wave voltage E3 is made variable so that a feedback voltage Em induced by the electrode 12 and a reference core electrode 13 be zero. In order to make the total of an induced current zero, accordingly, it is necessary to induce the current in the direction of canceling the sum of the current induced by the capacitor C1 and a correcting capacitor C2 by increasing the voltage E3 impressed on a reference capacitor C3, and the voltage E3 is increased by an electronic device. In this way, the voltage E3 has a proportional relationship of increasing from zero gradually in accordance with the displacement of the electrode 12.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a length measuring device that converts mechanical displacement into an electrical signal as a change in capacitance. This relates to a length measuring instrument in which the relationship is linear and the constant of proportionality is positive.

<Prior Art> A conventional capacitive length measuring device of this type has a structure as shown in FIG.

As shown in the figure, the main parts of this length measuring device include a cylindrical reference electrode 1, a measuring electrode 2, a cylindrical common core electrode 3 disposed concentrically within the electrode 1.2, Electrode] - and core electric f! 3 and a cylindrical screen 4 that is movable along the central axis.

A reference square-wave voltage V and a measuring square-wave voltage V,n are applied to these electrodes 1.2, respectively. This voltage Vr, V
ffl is a square wave voltage with the same frequency and a phase difference of 180 degrees (opposite phase), voltage vr is constant, and voltage V is variable.

In the detection section of the length measuring device having such a configuration, a measurement capacitor C7 (capacitance cm) is formed between the electrode 1 and the core electrode 3, and a reference capacitor C7 is formed between the electrode 2 and the core electrode 3. , (capacitance cr) is formed.

In this length measuring device, when the screen 4 is displaced and the capacitance C of the measuring capacitor C changes, the electronic device measures the square wave voltage so that the AC voltage induced in the core electrode 3 becomes zero.

is changed. That is, this is the current generated in the core electrode 3 by applying the reference square wave voltage Vr to the measurement capacitors C,,l, and the current generated in the core electrode 3 by applying the measurement square wave voltage V, to the reference capacitor Cr. The purpose of this is to change the measured square wave voltage Vm so that the sum of the current and the measured current becomes zero.

From this relationship, the following relational expression is established.

cm Vr 10 cr Vm = 0 ■m-' r Cm / Cr...(1
) Here, in equation 1), the voltages V, , = V have different signs because their phase difference is 180 degrees, and VrVr''
Expressed as, Vm - Vr' Cm / Cr =
・(2) becomes.

In this equation (2), the proportionality constant V%/Cr is positive, and the relationship between the capacitance C□ of the measuring capacitor C1, and the measured square wave voltage V1 is as follows: When the capacitance C, increases, the voltage Vm also increases; When c, decreases, voltage V,a also decreases.

In Fig. 6, if the displacement X when the screen 4 is moved so as to be inserted into the electric current 1 (moves to the right in the figure) is positive, then the capacitance C of the measurement capacitors C, , l
, , is expressed by the following formula.

C,=co (1aX) =-ac(,X+c,)-(3) where C
6 represents the capacitance of the measurement capacitor C1 when the screen 4 is at the reference position (X=0),
a is a positive proportionality constant.

From the above equations (2) and (3), the measured square wave voltage V can be expressed as a linear equation of the displacement X as follows.

Vm = (Vr'acOX/cr) +
(Vr'co/Cr) ・
・(4) As shown in equation (4), the proportionality constants −V, +
ac O/cr always takes a negative value, and as a result, as shown in FIG. 7, as the displacement X increases, the measured square wave voltage vffl decreases, and as the displacement X decreases, the voltage ■. will increase.

In this way, if the direction in which the screen 4 is inserted into the electrode 1 is positive, the relationship between the displacement X and the increase or decrease in the measured square wave voltage vm is reversed, and the displacement X and the voltage Although there is, there is no proportional relationship.

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 X and the measured square wave voltage V, as described above, this voltage V. When measuring with a voltmeter etc. and displaying the displacement
, , will need to be further transformed. Therefore, this conversion requires electronic circuits such as highly accurate arithmetic circuits.

<Problems to be Solved by the Invention> As mentioned above, in the conventional capacitive length measuring device, an electronic circuit is used to actually display the displacement X using the measured square wave voltage V. It is necessary. 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.

In addition, the measurement reference point of conventional capacitive length measuring instruments can only be adjusted using an electronic device.If multiple length measuring devices are configured using the same electronic device, the measurement reference point can be adjusted using the same electronic device. It was necessary to match the detection section of each length measuring device.

The present invention makes it possible to display displacement directly using a square wave voltage without using the conversion electronic circuit in the conventional example, and also makes it possible to adjust the measurement reference point within the detection unit,
The object of the present invention is to provide a capacitance type length measuring device that reduces costs and improves temperature characteristics and stability.

<Means for Solving the Problems> The capacitive length measuring device of the present invention includes a cylindrical measuring ring electrode, a cylindrical correction ring electrode and a reference ring electrode arranged on the same center line, and a measuring ring. A roughly cylindrical measuring core electrode that moves along its central axis inside the electrode and whose outer periphery is shielded by a shield ring at the part that does not form a capacitor between it and the measuring ring electrode, and a correction ring electrode and a reference ring electrode. a cylindrical reference core electrode arranged concentrically with the measurement core electrode and electrically connected to the measurement core electrode, a measurement capacitor C1 is formed between the measurement ring electrode and the measurement core electrode, and a correction ring electrode A correction capacitor C2 and a reference capacitor C3 are formed between the reference ring electrode and the reference core electrode, respectively.

A reference square wave voltage E1, a supplementary square wave voltage E2, and a measurement square wave voltage Em are applied to the measurement ring electrode, correction ring electrode, and reference ring electrode, respectively. This complementary square wave voltage E2 is set to have the same frequency and opposite phase as the reference square wave voltage E1, and the measurement square wave voltage E3 is also set to have the same frequency and opposite phase as the reference square wave voltage E1. ing.

In addition, in this length measuring instrument, by adjusting either or both of the supplementary square wave voltage E2 and the capacitance C2 of the correction capacitor C2, the capacitance c0 of the measurement capacitor C1 when the displacement X of the measurement core electrode is zero can be adjusted. The product C01Eml of the reference square wave voltage E1 and the product C2E21 of the capacitance C2 of the correction capacitor C2 and the complementary square wave voltage E2 are set to be equal.

Furthermore, the electronics provide a constant DC voltage and a variable measurement voltage so that when the capacitance C1 of the measurement capacitor C1 changes due to the displacement of the measurement core electrode, the feedback voltage Effl induced in the measurement core electrode and the reference core electrode becomes zero. D.C.
Voltage E. By switching alternately between the measured square wave voltages E3 is varied.

This electronic device includes a transient suppressor that removes transients in the feedback voltage E, a demodulator that demodulates its output signal, and a demodulator that modulates the amplitude of the demodulated signal until it becomes zero when it is not zero. Measured DC voltage E that varies as a function of polarity. It is equipped with a differential integrator that outputs .

<Operation> In the capacitance type length measuring device of the present invention, the measurement square wave voltage E3 is changed so that the feedback voltage Em induced in the measurement core electrode and the reference core electrode becomes zero.

That is, in order to make the feedback voltage Em zero, the measurement capacitor C
1. The measurement square wave voltage E3 is varied so that the sum of the currents induced in the measurement core electrode and the reference core electrode, respectively, becomes zero by the correction capacitor C2 and the reference capacitor C3.

In the present invention, since the reference square wave voltage E1 and the complementary square wave voltage E2 applied to the measurement capacitor C1 and the correction capacitor C2 are voltages with opposite phases, the currents induced thereby cancel each other out. .

Furthermore, when the displacement X is zero, the current value induced by the measurement capacitor C1 and the correction capacitor C2, that is, Co
lE+l and c2|E2| are set to be equal.

Under the second condition, when the displacement X is zero, the currents induced by the measurement capacitor C1 and the correction capacitor C2 are equal, so their sum becomes zero.

Therefore, in order to make the current induced by the reference capacitor C3 zero, ie C3E3 =O, the measured square wave voltage E9 becomes zero.

Also, the measurement core electrode is displaced and the part where the shield ring is provided comes out of the measurement ring electrode and the part where the shield ring is not provided enters the measurement ring electrode, increasing the capacitance C1 of the measurement capacitor C1. Then,
Since the reference square wave voltage E1 is constant, the induced current increases, and since the current induced by the correction capacitor C2 is constant, the sum of the currents increases.

Therefore, in order to make the sum of induced currents zero, the measurement square wave voltage E3 applied to the reference capacitor C3 is increased to induce a current in a direction that cancels the sum of the induced currents by the measurement capacitor C and the correction capacitor C2. This voltage E3 is increased by the electronics.

As described above, the length measuring device according to the present invention has a proportional relationship in which the measurement square wave voltage Em gradually increases from zero according to the displacement of the measurement core electrode.

The electronic device according to the invention also includes a transient suppressor to eliminate transients occurring in the feedback voltage Em at switching points of the square wave voltage.

<Example> The present invention will be described in detail below 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.

9, 10, and 11 are a measuring ring electrode, a correction ring electrode, and a reference ring electrode, each having a cylindrical shape. The correction ring electrode 10 and the reference ring electrode 11 are arranged so that their centers are located on the same center line, and in this embodiment, the measurement ring electrode 9 is also arranged so that its center almost coincides with the other ring electrode. It is located in

Reference numeral 12 denotes a substantially cylindrical measurement core electrode, which has a mounting hole 12a formed along the central axis from the negative end surface thereof, and a protrusion 2b provided on the other end surface side.

A spindle 15 supported by a bearing 16 is inserted into the mounting hole 12a of the measurement core electrode 12 via a cylindrical insulator 14, and is integrally attached thereto.
This movement of the spindle 15 causes the center axis of the measurement core electrode 12 to move on the center axis of the measurement ring electrode 9.

Further, in this embodiment, a small diameter portion 12C is provided approximately in the center from the end where the protrusion 12b of the measurement core electrode 12 is provided, and a shield is provided on the outer periphery of the small diameter portion 12C via a ring-shaped insulator 41. A link 20 is attached.

13 is a cylindrical reference core electrode, and a correction ring electrode 1
The electrodes 10 and 11 are arranged and fixed along the central axes of the reference ring electrodes 10 and 11 so as to pass through them.

The reference core electrode 13 and the measurement core electrode 12 are electrically connected to each other via a flexible object such as a spring 44 so as not to hinder the movement of the measurement core electrode 12.

Seat between the measurement ring electrode 9 and the measurement core electrode 11ii12
A measurement capacitor CI is formed between the core ring 20 and the portion not covered by the core ring 20, and a correction capacitor C2 and a reference capacitor C8 are formed between the correction ring electrode 10 and the reference ring electrode 11 and the reference core electrode 13, respectively. be done. These measurement capacitor C1, correction capacitor C2
and the capacitances of the reference capacitor C3 are C1, C2 and C8, respectively, and the capacitance c1 is caused by the displacement of the measuring core electrode 12 to the opposite measuring ring electrode 9.
When the area of the portion of the measurement core electrode 12 not covered by the shield ring 20 changes, the reference ring electrode 1
1 are applied with a reference square wave voltage E1, a supplementary square wave voltage E2, and a measurement square wave voltage E3, respectively. This reference square wave voltage E] is always constant, and the complementary square wave voltage E2 has the same frequency as this voltage E1, and is set to an opposite phase voltage with a phase difference of 180 degrees. is always kept constant. The measurement square wave voltage E3, like the voltage E2, has the same frequency and opposite phase as the voltage Em, and is varied by an electronic device to be described later. The measurement square wave voltage E3 is varied by an electronic device so that the feedback voltage E induced in the measurement core electrode 12 and the reference core electrode 13 by the three capacitors 01 to C3 becomes zero.

2], either or both of the complementary square wave voltage E2 and the capacitance c2 are 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.

The spindle 15 moves, which causes the measurement core electrode 12 to
When is displaced to the right in FIG. 1, the capacitance C1 of the capacitor C1 changes. At the same time, an electronic device, which will be described later, operates to connect the measuring core electrode 12 and the reference core electrode f! 1
The measured square wave voltage Em is varied so that the feedback voltage Em induced in the voltage 3 becomes zero.

That is, the currents induced in the measurement core electrode 12 and the reference core electrode 13 by the capacitors C1 to C3 are respectively il and i.
2, i3, the measured square wave voltage E9 is varied so as to satisfy the following equation.

il +i2 +i3 =O...(5>Capacitor 0
Since the capacitances of 1 to C3 are C1 to cg, respectively, and the voltages applied to the measurement ring electrode 9, correction ring electrode 10, and reference ring electrode 11 are E1 to E3, respectively, equation (5) is as follows. It can be expressed as

CI El +c2 E2 +C3El =0 Therefore,
The measured square wave voltage E3 can be expressed as follows.

E3= (clEl +C2E2)/C3...(
6) Voltages E3 and El are square wave voltages with opposite phases, and voltage E3
and E2 are in-phase square wave voltages, so E1'=-
When Equation (6) is rewritten by replacing E1 with El, the measured square wave voltage E3 becomes as shown in the following equation.

El = (c+Et'C2E2)/C3-(
7) Meanwhile, the spindle 15 moves to the right in FIG.
Measurement core electric 8i! If the direction in which the portion not covered by the shield ring 20 of No. 12 enters the measurement ring electrode 9 is set as positive, and the capacitance of the measurement capacitor C1 at X-0 is C6, then the capacitance C] is expressed by the following formula. be able to.

CI = CO (1 + bX) - (8) where b is the measuring ring electrode 9 forming the measuring capacitor C1
, the outer diameter of the measurement core electrode 12, and a positive constant.

Substituting this equation (8) into equation (7), the measured square wave voltage E
m is El = (b CQ E1'X/C3) + (C
o EIC2E2)/C3...(9) It can be expressed as α-bc,)E+'/c3, β-(coElo-C2E2)/c3...(
1o), equation (9) is transformed as follows.

E3=αX+β (11) In this embodiment, it is set so that C21E2 1=c0 1E, which is C2E2-c. It can be replaced with E1', and by substituting this into equation (10), β=0
becomes. Therefore, the measured square wave voltage E3 can be expressed by the following equation.

E3 = aX = cr, E1'bX/c3 --- (1
2> Since this proportionality constant α is a positive value, the relationship between voltage Em and displacement When the displacement X decreases, the voltage E3 decreases in direct proportion to the displacement X, and when the displacement X is zero, the voltage E3 also becomes zero.

In addition, as shown in equation (9), the voltage E3 is Co/C3, C
Since the capacitance ratio is 2/C9, if the capacitors C1 to C3 are made of the same dielectric material, they will not be affected by the dielectric constant at all.

In addition, in the case of c2|E2|≠Co lEt l, β is a non-zero constant, so the voltage E3 increases by β, and the displayed value of the measured length appears to be at the point above where X=0 is β. /α will move to the negative side.

Therefore, it is necessary to set the relationship C21E2 1=c0 1EI l, but to set it in this way, it is necessary to adjust one or both of capacitance c2 and voltage E2 as described above. Rough adjustment is made with the large adjustment screw 42, and then fine adjustment is made with the adjustment screw 43 with a small diameter.

Additionally, when adjusting the voltage E2, electrical components such as potentiometers with good temperature characteristics are generally used on the electronic device side, but if even stricter temperature characteristics are required, such electrical components are used. It is preferable not to use . In this case as well, in this embodiment, by adjusting the correction capacitor C2, it is possible to adjust the point of X=0 without adjusting the voltage E2 using electrical components. or,
By providing this correction capacitor C2 and its adjustment screws 42 and 43, even when a plurality of detection sections are used simultaneously, it is possible to make all the measurement origins coincide.

Furthermore, the capacitance c3 of the reference capacitor C3 in this embodiment is adjusted by roughly adjusting with the large adjusting screw 18 and then finely adjusting with the small adjusting screw 19.

Therefore, the capacitance c3 in the plurality of detection sections can be adjusted to the same value, and it is possible to connect the plurality of detection sections to the same electronic device.

Furthermore, the measurement capacitor C1 in this embodiment is a cylindrical measurement ring capacitor 8i! 9 and the cylindrical measuring core electric [! Further, this measuring core electrode 12 moves along the central axis of the measuring ring electrode 9 together with the spindle 15, and movement in directions other than this moving direction is restricted. Further, the correction capacitor C2 and the reference capacitor C9 are each composed of a cylindrical correction ring electrode 10, a reference ring electrode 11, and a cylindrical reference core electrode 13. The central axes of the reference core electrode 13 are also fixed so as to coincide with each other.

Therefore, even if the distance between the central axes changes slightly due to an impact, etc., the change in b, which constitutes the proportionality constant in equation (12), is extremely small and has almost no effect on the voltage E3. .

Also, basically in this detection section, the measurement core electrode 12
and a return electrode E1. guided to the reference core electrode 13. It is necessary to prevent the voltages Em from being influenced by the square wave voltages E1 to E3 for excitation, and it is also necessary to prevent the voltages Em to E3 from influencing each other.

Therefore, in this embodiment, the voltages E1 to Em, E.

Shield the wire connecting the detection unit and the electronic device to guide the
1 to 24 are shielded.

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

That is, as shown in FIG. 3, 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 13, and the other side of the discharge resistor 27 is grounded. 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 E1, E2, E3, and Effi' 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.

In addition, by making the measurement ring electrode 9, correction ring electrode 10, reference ring electrode 11, measurement core electrode 12, and reference core electrode 13 made of the same material, the thermal expansion of the parts is the same, and the unbalance of the capacitor due to temperature changes is prevented. It is possible to prevent this, and it is possible to improve the temperature performance of the detection section.

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 reference square wave voltage E osc. 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 is a time delay circuit that delays the square wave voltage F-osc for a certain period of time, and 32 is a frequency divider circuit that divides the frequency of the output signal into 1/2.

33 and 34 are electronic switches, and the electronic switch 33 connects the frequency dividing circuit 32 between the DC voltage Er and the ground level.
The electronic switch 34 switches between the DC voltage -Er and the ground level in response to a signal from the frequency divider circuit 32 and outputs it as a reference square wave voltage E1, and the electronic switch 34 also switches between the DC voltage -Er and the ground level in response to a signal from the frequency divider circuit 32 to output the reference square wave voltage E1. It is output as a square wave voltage E2.

35 is an input amplifier that inputs the feedback voltage Em.

36 is a transient suppressor for removing the transient state generated in the voltage signal E4 outputted from the input amplifier 35, and in this embodiment, the square wave voltage signal E os from the oscillator 30 is removed.
It is composed of an electronic switch that connects and disconnects the voltage signal E4 in response to the voltage signal E4.

A synchronous demodulator 37 inputs the voltage signal E4 from which the transient state has been removed, demodulates the signal from the frequency divider 32 every cycle, and outputs the demodulated signal.

38 inputs the demodulated voltage signal to generate a DC voltage signal.

It is a differential integrator that outputs .

39 is a DC voltage signal. This is an electronic switch that switches between the voltage E3 and the ground level in response to a signal from the frequency divider 32, and outputs the measured square wave voltage E3.

In the above electronic device, the voltages E7 and E2 are DC voltages of different polarities that are intermittently outputted from the electronic switches 33 and 34 at the same timing, so that the voltages E7 and E2 become square wave voltages having the same frequency and opposite phases.

Further, the voltage E3 is synthesized by outputting the DC voltage Eo from the differential integrator 38 intermittently from the electronic switch 39 at the timing of the voltage signal from the frequency divider 32.

Furthermore, the DC voltage E. is synthesized as follows.

First, the feedback voltage Em, , is amplified by the input amplifier 35 and applied to the transient suppressor 36 as a voltage signal E4.

In this voltage signal E4, the transient state occurring in the feedback voltage Effl has a square wave switching point (too, t + o, t2
Occurs at ゜・). This transient state attenuates and becomes stable after a certain period of time, and in this embodiment, the transient state is
It has occurred for 21 days...

The transient suppressor 36 that receives this voltage signal E4 connects and disconnects the input voltage signal E4 every half period of the voltage E osc and outputs it. Electronic switch 33.34 in this example
．． 39 is set to switch states in response to a signal obtained by delaying the voltage E osc by a predetermined time. Therefore, the square wave voltage E1 output from these electronic switches
, E2, E3 and the voltage E osc are shifted by the amount of delay as described above.

Therefore, if settings are made so that the transient state of the voltage signal E4 falls within the range of this generation timing shift, the voltage signal E4
The transient suppressor 36 can be turned off only while a transient condition is occurring in the voltage signal E4, thereby eliminating the transient condition in the voltage signal E4.

The voltage signal E4 from which the transient state has been removed in this manner is demodulated every cycle by the demodulator 37.

Additionally, the DC voltage E output by the differential integrator 38 as a function of the amplitude and polarity of the demodulated voltage if the demodulated voltage is not zero until this demodulated voltage reaches zero. is changed.

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

As a result, the voltage E3 satisfies the relationship of equation (9), is directly proportional to the displacement X, and has a positive proportionality constant.

<Effects of the Invention> According to the present invention, the displacement amount X of the measurement core electrode is directly proportional to the displacement X, assuming that the direction in which the portion of the measurement core electrode not covered by the shield ring enters the measurement ring is positive. It can be detected from the measured square wave voltage E3 where the proportionality constant becomes positive.

Therefore, electronic circuits such as arithmetic circuits as in conventional examples are not required, and the influence of such electronic circuits on stability and temperature characteristics can be eliminated, improving stability and temperature characteristics, and further improving stability and temperature characteristics. It is also possible to reduce costs.

In addition, by providing a correction capacitor and an adjustment screw for adjusting its capacitance, it is possible to adjust the zero point of the detection section without using electrical components such as potentiometers, which reduces the impact on the stability of electrical components and temperature characteristics. The influence can be eliminated, and stability and temperature performance can be improved.

In particular, since the zero point can be adjusted on the detecting section side without moving the detecting section, when used attached to machinery, it is possible to eliminate the need for a fine movement zero point adjusting device that is generally provided on the machine side. Therefore, it is particularly effective when switching and using a large number of detection units in one electronic device.

Furthermore, by providing adjustment screws for capacitance adjustment on the reference capacitor and the correction capacitor, it is possible to connect different detection units to a common electronic device without calibrating the measurement origin or the like.

Furthermore, since the measured square wave voltage E3 is composed of a capacitance ratio, all capacitors are made of the same dielectric material, so that it is not affected by the dielectric constant at all.

Furthermore, because the center axes of the measurement ring electrode and measurement core electrode are aligned, and the center axes of the correction ring electrode, reference ring electrode, and reference core electrode are also aligned, even if the distance between the center axes changes slightly, , the influence on the measured voltage can be made very small.

Furthermore, by using a ball retainer in the spindle bearing and keeping 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.

Furthermore, by providing an impedance transformer and a discharge resistor in the detection section, when high sensitivity and high precision are not required, the lines leading to the voltages E1 to Em+Em' can be shielded together.

Moreover, the measurement ring electrode 9 that constitutes the capacitors C1 to C9
By using the same material for the correction ring electrode 10, the reference ring electrode 11, the measurement core electrode 12, and the reference core electrode 13, it is possible to improve the temperature performance of the detection section.

Additionally, by providing a transient suppressor within the electronic device, voltage E can be reduced from a signal without transients. , E3 can be synthesized, 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 instrument according to an embodiment of the present invention, and FIG. 2 shows the relationship between the displacement X of the measuring core electrode and the measuring square wave voltage E3 shown in FIG. FIG. 3 is a circuit diagram showing the impedance transformer attached to the detection unit shown in FIG. 1, and FIG. FIG. 5 is a time chart showing the voltage phase relationship in FIG. 4. FIG. 6 is a diagram showing the structure of the detection section of a conventional capacitive length measuring device. Reference square wave voltage V in the length measuring device shown in Figure 6
, and the displacement X of the screen. 9...Measurement ring electrode, 10...Correction ring electrode, 11...Reference ring electrode, 12...Measurement core electrode, 13...-Reference core electrode, 15...Spindle, 16... Bearing, 18.19.42.43...Adjustment screw, 20, 21, 26, 27, 30, 33, 37, 38, IE transport/shield ring, 22.23.24...Shield, spring,・Impedance transformer, ・Discharge resistor, ・Oscillator, 34.36.39...Electronic switch, ・Input amplifier, ・Demodulator, ・Differential integrator, ・Reference square wave voltage, Complementary square wave voltage, ・Measurement square wave voltage, ・Feedback voltage, ・Measurement capacitor, ・Correction capacitor, Reference capacitor. Figure Makoto i

Claims (4)

[Claims] (1) A cylindrical measurement ring electrode, a cylindrical correction ring electrode and a reference ring electrode arranged on the same center line,
a substantially cylindrical measurement core electrode that is movable within the measurement ring electrode along its central axis and whose outer periphery is shielded by a shield ring at a portion that does not constitute a capacitor between it and the measurement ring electrode; and the correction ring electrode. and a cylindrical reference core electrode arranged concentrically within the reference ring electrode and electrically connected to the measurement core electrode,
A measurement capacitor C_1 is formed between the measurement ring electrode and the measurement core electrode, a correction capacitor C_2 and a reference capacitor C_3 are respectively formed between the correction ring electrode and the reference ring electrode and the reference core electrode, A reference square wave voltage E_1 is applied to the electrode, a complementary square wave voltage E_2 having the same frequency and an opposite phase as the reference square wave voltage E_1 is applied to the correction ring electrode, and a reference square wave voltage E_1 is applied to the reference ring electrode. When a measurement square wave voltage E_3 having the same frequency and opposite phase is applied and the displacement X of the measurement core electrode is zero, the capacitance c_0 and the reference square wave voltage E when the displacement of the measurement capacitor C_1 is zero are
The product c_0|E_1| with the absolute value of _1, the capacitance c_2 of the correction capacitor C_2, and the complementary square wave voltage E_
a transient suppressor that removes a transient state of the feedback voltage E_m induced in the measurement core electrode and the reference core electrode, and demodulates its output signal. and a differential integrator that outputs a measured DC voltage E_0 which varies as a function of the amplitude and polarity of the demodulated signal until this signal becomes zero when the demodulated signal is not zero. , a constant DC voltage and a variable measurement DC voltage E such that when the capacitance c_1 of the measurement capacitor C_1 changes due to the displacement of the measurement core electrode, the feedback voltage E_m becomes zero.
A capacitance type length measuring device characterized in that a measurement square wave voltage E_3 is varied by alternately switching between E_0 and E_0. (2) An impedance transformer whose input side is connected to the reference core electrode and whose output side is connected to the electronic device, and a discharge resistor whose one side is connected to the reference core electrode and whose other side is grounded are provided. 2. The capacitance type length measuring device according to claim 1. (3) The capacitive length measuring instrument according to claim 1 or 2, wherein the measuring ring electrode, the correction ring electrode, the reference ring electrode, the measuring core electrode, and the reference core electrode are made of the same material. (4) The capacitance type length measuring instrument according to any one of claims 1 to 3, wherein a ball retainer is used in a bearing of the spindle attached to the reference core electrode to create a preloaded state.